Biology Chapter 1 and 2 PDF

CHAPTER 1: Processes of Living Organisms: All living organisms undergo essential life processes: Movement: This is the ability of organisms to change their position or move parts of their body. In animals, movement usually involves the muscular and skeletal systems, allowing them to mov...

CHAPTER 1: Processes of Living Organisms: All living organisms undergo essential life processes: Movement: This is the ability of organisms to change their position or move parts of their body. In animals, movement usually involves the muscular and skeletal systems, allowing them to move toward resources like food or away from danger. Plants also exhibit movement, though it’s usually more subtle, such as the movement of leaves toward light (phototropism) or the opening and closing of flowers. Respiration: Respiration is the process by which cells release energy from food. It involves the breakdown of glucose to release energy for cellular activities. Respiration can be: Aerobic respiration (using oxygen): Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP) Anaerobic respiration (without oxygen): Glucose → Lactic acid (in animals) or ethanol and carbon dioxide (in plants and yeast) + Energy (less efficient than aerobic respiration). Sensitivity: Organisms respond to stimuli in their environment. In animals, this involves sense organs detecting changes such as light, temperature, or pressure, and responding appropriately. In plants, sensitivity is shown in their responses to light (phototropism), gravity (gravitropism), and water (hydrotropism). This sensitivity allows organisms to maintain favorable conditions and survive in varying environments. Growth: Growth refers to a permanent increase in size and mass by an increase in the number of cells (through cell division) or the size of individual cells. In animals, growth is continuous until maturity, whereas in plants, growth can occur throughout their lives, especially at specific regions like the tips of roots and shoots (meristems).  Reproduction: This is the process by which organisms produce new individuals of their kind, ensuring the survival of the species. There are two types: Asexual reproduction: Involves one parent, with offspring genetically identical to the parent (e.g., binary fission in bacteria, or budding in yeast). Sexual reproduction: Involves two parents and the fusion of gametes, leading to genetic variation in offspring. Excretion: The removal of metabolic waste products from the body. Metabolism produces waste products that must be excreted, as they can be toxic if allowed to accumulate. Examples include: Carbon dioxide from respiration (excreted via the lungs in humans). Urea from the breakdown of proteins (excreted in urine). Oxygen (a waste product of photosynthesis) in plants is released through stomata. Nutrition: Organisms require nutrients for energy, growth, and repair. Animals are heterotrophic, meaning they obtain nutrients by consuming other organisms. Plants, however, are autotrophic and make their food through photosynthesis: Photosynthesis equation: Carbon dioxide + Water → Glucose + Oxygen (using light energy and chlorophyll). Mnemonic for the processes of life: MRS GREN (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition). Concept and Uses of Classification Systems: Classification is the process of grouping organisms based on shared characteristics and evolutionary relationships. This helps scientists communicate about organisms and understand how they are related to one another. Organisms are named using the binomial naming system (Linnaean system), an internationally agreed method that gives each organism a two-part scientific name: Genus: The first part of the name; capitalized.  Species: The second part; not capitalized. For example, the scientific name for humans is Homo sapiens. Classification Systems: There are different systems of classification, including the five-kingdom system and the more recent three-domain system. 1. Five-Kingdom System: Organisms are traditionally grouped into five kingdoms based on their cell structure, method of nutrition, and other factors: Animalia (animals) Plantae (plants) Fungi (fungi) Protoctista (protists) Prokaryotae (bacteria) 2. Three-Domain System: Based on molecular analysis (particularly ribosomal RNA), this system classifies organisms into: Bacteria: Prokaryotic cells without a nucleus. Archaea: Prokaryotic cells that often live in extreme environments. Eukaryota: Organisms with eukaryotic cells, which include animals, plants, fungi, and protists. Evolutionary Relationships: Organisms are grouped based on their evolutionary history. This can be determined by: Physical characteristics: Traditionally, scientists studied morphology (structure) and anatomy (organs and organ systems) to classify organisms. DNA base sequences: More recently, DNA sequencing has provided a more accurate method of determining evolutionary relationships. Closely related species share more similarities in their DNA.  Protein structure: Since proteins are coded for by DNA, comparing proteins (such as enzymes) can also reveal evolutionary relationships. Features of Cells: All living organisms are made of cells, which can be classified into two broad categories: prokaryotic cells and eukaryotic cells. Prokaryotic cells: These are simple cells without a true nucleus. They include bacteria and archaea. Their DNA is circular and floats freely in the cytoplasm. Eukaryotic cells: These cells have a true nucleus and other membrane-bound organelles. They include animal, plant, fungal, and protist cells. Key Cell Structures: Cytoplasm: A jelly-like substance where metabolic reactions occur. Cell membrane: A semipermeable membrane that controls what enters and exits the cell. DNA: Genetic material that carries the instructions for the cell’s activities. In eukaryotes, it is found in the nucleus; in prokaryotes, it is free-floating. Ribosomes: The site of protein synthesis. Mitochondria (in eukaryotes): The powerhouse of the cell, where aerobic respiration occurs, releasing energy. Chloroplasts (in plant cells): Organelles that contain chlorophyll for photosynthesis. Cell wall (in plant cells and prokaryotes): A rigid layer that provides support and protection. Vacuole (in plant cells): A large, central vacuole containing cell sap, which helps maintain the cell’s shape. Endoplasmic Reticulum (ER): Rough ER (RER):  Function: Involved in protein synthesis and processing. The ribosomes attached to the RER synthesize proteins, which are then folded and modified before being transported to their destinations. Smooth ER (SER): Function: Responsible for lipid synthesis, detoxification of drugs and poisons, and calcium storage in muscle cells. Vertebrates vs. Invertebrates: Vertebrates: Animals with a backbone (e.g., mammals, birds, reptiles, amphibians, fish). Invertebrates: Animals without a backbone. The largest group of invertebrates are the arthropods, which include insects, arachnids (spiders), myriapods (centipedes), and crustaceans (crabs, shrimp). Arthropods are identified by their exoskeleton and segmented body. Plants: Flowering Plants: Plants that produce seeds enclosed within flowers. These are divided into: Dicotyledons: Plants with two seed leaves (cotyledons), broad leaves, and branching veins, and flower parts in multiples of 4 or 5. Monocotyledons: Plants with one seed leaf, narrow leaves, and parallel veins, and flower parts in multiples of 3. Non-flowering Plants: Plants like ferns that reproduce via spores rather than seeds. Viruses: Viruses are not considered living because they do not carry out all the life processes on their own. They consist of genetic material (DNA or RNA) enclosed in a protein coat and must infect a host cell to reproduce. Although they can evolve and adapt, they do not meet the criteria of living organisms. This version of Chapter 1 now includes detailed information about the functions of the endoplasmic reticulum, along with the previously added details about key cell structures, providing a comprehensive understanding of these foundational biological concepts.  DEFINITIONS: Amphibia - A class of vertebrates - including frogs, toads and newts - that are poikilothermic. They have four limbs, of which hind feet are often webbed. Amphibians have lungs and moist skin for breathing. They reproduce sexually via external fertilisation. Arachnids - A class of arthropods including spiders, scorpions, ticks and mites. Arachnids have a segmented body (divided into the cephalothorax and abdomen), four pairs of jointed legs and several pairs of simple eyes. Arthropods - A phylum consisting of invertebrate animals with jointed limbs, segmented bodies and a hard external skeleton (cuticle). Arthropods include crustaceans, myriapods, arachnids and insects. Birds - A class of vertebrates that are homeothermic. Birds have four limbs (the forelimbs form wings), and beaked jaws. They have an outer covering of feathers over most of the body and scales on the legs and toes. Fertilisation occurs internally, with the female laying hard-shelled eggs. Crustacea - A class of arthropods including crabs, lobsters, prawns, shrimps, the water louse and woodlice. They have compound eyes and two pairs of antennae. Ferns - A group of vascular land plants that have neither seeds nor flowers and reproduce via spores from numerous sporangia. They have simple, fleshy underground stems known as rhizomes. Fish - A class of vertebrates that are poikilothermic. They have a smooth-streamlined shape with fins for movement and are covered in overlapping scales. Fish have gills for breathing and reproduce sexually, with fertilisation normally occurring externally. Homeothermic - Describes an organism that is warm-blooded and whose body temperature is internally regulated. Insects - A diverse class of arthropods including butterflies, bees, beetles, mosquitoes, houseflies, greenfly and earwigs. They have segmented bodies (consisting of a head, thorax and abdomen), three pairs of jointed legs, one pair of antennae, compound eyes and normally two pairs of wings. Mammals - A class of vertebrates that are homeothermic. They have four limbs and are characterised by the presence of hair or fur, and mammary glands. Mammals produce live young. Myriapods - A class of arthropods consisting of millipedes and centipedes. They have a segmented body, ten or more pairs of jointed legs, one pair of antennae and simple eyes. Poikilothermic - Describes an organism that is cold-blooded and whose body temperature varies with the temperature of the external environment. Reptiles - A class of vertebrates that are poikilothermic. They have four limbs and dry, scaly skin. Reptiles reproduce sexually, with fertilisation occurring internally. Species - A group of similar organisms that can interbreed to produce fertile offspring. CHAPTER 2: Comparing the Structure of Animal Cells and Plant Cells: Similarities: Both animal and plant cells contain essential organelles, including: Nucleus: The control center of the cell, housing genetic material. Cytoplasm: A jelly-like substance where biochemical processes occur. Mitochondria: Organelles responsible for energy production through respiration. Ribosomes: The sites of protein synthesis. Cell membrane: A protective barrier that regulates the entry and exit of substances. Differences: Plant cells possess unique structures not found in animal cells, including: Cell wall: A rigid layer made of cellulose that provides structural support and protection, helping maintain cell shape. Vacuole: A large, fluid-filled sac that stores nutrients, waste products, and helps maintain turgor pressure, which is essential for plant rigidity. Chloroplasts: Organelles that contain chlorophyll and are the sites of photosynthesis, allowing plants to convert light energy into chemical energy (glucose). Shape and Size: Plant cells typically have a more regular, rectangular shape due to the presence of the cell wall, while animal cells often have varied and irregular shapes. Plant cells are usually larger than animal cells, reflecting their storage capabilities and additional structures. Functions of Cell Structures in Animal and Plant Cells: Cytoplasm: A viscous, jelly-like material where most cellular processes take place. It contains organelles such as ribosomes and vesicles, as well as cytoskeletal elements that provide structure and facilitate movement within the cell.  Cell membrane: A phospholipid bilayer embedded with proteins that regulates the movement of ions, nutrients, and waste products in and out of the cell. It is selectively permeable, allowing only certain substances to pass through. Nucleus: Contains the cell’s genetic material (DNA) organized into chromosomes. The nucleus regulates gene expression and is the site of DNA replication, ensuring that genetic information is accurately transmitted during cell division. Ribosomes: Tiny structures composed of RNA and proteins, responsible for synthesizing proteins by translating messenger RNA (mRNA). Ribosomes can be free in the cytoplasm or attached to the endoplasmic reticulum (ER), contributing to the rough ER’s role in protein processing. Mitochondria: Known as the powerhouses of the cell, they generate ATP (adenosine triphosphate) through aerobic respiration. Mitochondria have a double membrane, with the inner membrane folded into cristae to increase surface area for energy production. In Plants Only: Vacuole: A large central vacuole stores various substances, including mineral salts, sugars, amino acids, and waste products. It helps maintain turgor pressure, which supports the plant’s structure and growth, and can also store pigments that attract pollinators. Chloroplasts: These organelles contain chlorophyll, the green pigment essential for photosynthesis. Chloroplasts capture light energy, converting carbon dioxide and water into glucose and oxygen. The process takes place in two stages:  the light-dependent reactions and the Calvin cycle (light-independent reactions). Cell wall: Composed primarily of cellulose, the cell wall provides mechanical support, defines the shape of the cell, and protects it from mechanical stress and osmotic pressure. It also allows for the passage of water, nutrients, and other molecules. Bacterial Cells: Structure: Bacterial cells consist of a cell wall, cell membrane, cytoplasm, and ribosomes. The cell wall of bacteria is made of peptidoglycan, a polymer that provides structural integrity. DNA: Bacterial cells do not have a nucleus; instead, they contain circular DNA, often referred to as plasmid DNA, which is a small loop of DNA that carries essential genetic information. This circular DNA is located in the nucleoid region of the cytoplasm. Lack of Organelles: Bacterial cells do not possess mitochondria or chloroplasts, relying on the cell membrane for energy production through processes such as fermentation or anaerobic respiration. Reproduction: Bacteria reproduce by binary fission, so they divide in two. Plasmids:  Plasmids are small, circular DNA molecules found in bacteria that can carry genes for antibiotic resistance or other traits. They can be exchanged between bacteria, contributing to genetic diversity. New Cells and Specialised Cells: New cells are produced by the division of existing cells through processes such as mitosis (for somatic cells) and meiosis (for gametes). Specialized Cells: Cells and tissues are adapted to carry out specific functions. Examples of specialized cells include: Ciliated cells: Found lining the trachea, these cells have hair-like projections called cilia that beat in unison to move mucus, dust, and bacteria upwards towards the throat, aiding in respiratory health.  Root hair cells: These cells have elongated projections that increase their surface area for better water and mineral ion absorption. This adaptation is crucial for efficient uptake in plants. Palisade mesophyll cells: Located just beneath the leaf’s upper surface, these cells are tall and closely packed with numerous chloroplasts to maximize light absorption for photosynthesis.  Neurons (nerve cells): Adapted for rapid transmission of electrical impulses, neurons have a long axon that carries impulses and branched dendrites that increase the surface area for receiving signals from other neurons. They are often myelinated, which enhances the speed of signal transmission. Red blood cells (erythrocytes): Specialized for oxygen transport, these cells contain hemoglobin and have a unique biconcave shape that increases their surface area for gas exchange. The absence of a nucleus allows more room for hemoglobin. Sperm cells:  Male gametes, sperm cells are adapted with a flagellum for mobility and many mitochondria for energy production to propel themselves towards the egg. They also contain enzymes in the acrosome to penetrate the egg’s protective layers. Egg cells (ova): Female gametes have a nutrient-rich cytoplasm to support embryo development post-fertilization. Egg cells are haploid, containing half the genetic material, ensuring that upon fertilization, the resultant zygote has a complete set of chromosomes.  Muscle cells: specialised to contract quickly to move bones (striated muscle) or simply to squeeze (smooth muscle, e.g found in blood vessels so blood pressure can be varied), therefore causing movement Special proteins (myosin and actin) slide over each other, causing the muscle to contract Lots of mitochondria to provide energy from respiration for contraction They can store a chemical called glycogen that is used in respiration by mitochondria To become specialised and be suited to its role, stem cells must undergo differentiation to form specialised cells. This involves some of their genes being switched on or off to produce different proteins, allowing the cell to acquire different sub-cellular substances for it to carry out a specific function. In animals, almost all cells differentiate at an early stage and then lose this ability. Most specialised cells can make more of the same cell by undergoing mitosis (the process that involves a cell dividing to produce 2 identical cells). Others such as red blood cells (which lose their nucleus) cannot divide and are replaced by adult stem cells (which retain their ability to undergo differentiation). In mature animals, cell division mostly only happens to repair or replace damaged cells, as they undergo little growth. In plants many types of cells retain the ability to differentiate throughout life. They only differentiate when they reach their final position in the plant, but they can still re-differentiate when it is moved to another position. Mitosis and the Cell Cycle The cell cycle is a series of steps that the cell has to undergo in order to divide. Mitosis is a step in this cycle- the stage when the cell divides. Stage 1 (Interphase): In this stage the cell grows, organelles (such as ribosome and mitochondria) grow and increase in number, the synthesis of proteins occurs, DNA is replicated (forming the characteristic 'X' shape) and energy stores are increased Stage 2 (Mitosis): The chromosomes line up at the equator of the cell and cell fibres pull each chromosome of the 'X' to either side of the cell. Stage 3 (Cytokinesis): Two identical daughter cells form when the cytoplasm and cell membranes divide Cell division by mitosis in multicellular organisms is important in their growth and development, and when replacing damaged cells. Mitosis is also a vital part of asexual reproduction, as this type of reproduction only involves one organism, so to produce offspring it simply replicates its own cells. A stem cell is an undifferentiated cell which can undergo division to produce many more similar cells, of which some will differentiate to have different functions. Types of stem cells 1. Embryonic stem cells Form when an egg and sperm cell fuse to form a zygote They can differentiate into any type of cell in the body Scientists can clone these cells (though culturing them) and direct them to differentiate into almost any cell in the body These could potentially be used to replace insulin-producing cells in those suffering from diabetes, new neural cells for diseases such as Alzheimer's, or nerve cells for those paralysed with spinal cord injuries 2. Adult stem cells If found in bone marrow they can form many types of cells including blood cells 3. Meristems in plants Found in root and shoot tips They can differentiate into any type of plant, and have this ability throughout the life of the plant  They can be used to make clones of the plant- this may be necessary if the parent plant has certain desirable features (such as disease resistance), for research or to save a rare plant from extinction Therapeutic cloning involves an embryo being produced with the same genes as the patient. The embryo produced could then be harvested to obtain the embryonic stem cells. These could be grown into any cells the patient needed, such as new tissues or organs. The advantage is that they would not be rejected as they would have the exact same genetic make-up as the individual. Benefits vs Problems of research of stem cells Benefits Can be used to replace damaged or diseased body parts. Unwanted embryos from fertility clinics could be used as they would otherwise be discarded. Research into the process of differentiation. Problems We do not completely understand the process of differentiation, so it is hard to control stem cells to form the cells we desire. Removal of stem cells results in destruction of the embryo. People may have religious or ethical objections as it is seen as interference with the natural process of reproduction. If the growing stem cells are contaminated with a virus, an infection can be transferred to the individual. Money and time could be better spent into other areas of medicine. Levels of Organization: Key Terms: Cell: The basic structural and functional unit of all living organisms, responsible for carrying out life processes. Tissue: A group of similar cells working together to perform a specific function. For example, epithelial tissue covers body surfaces, while muscle tissue enables movement. Organ: A structure composed of two or more different types of tissues that work together to carry out a specific function, such as the heart (muscle and connective tissue) or the leaf (epidermis, mesophyll, and vascular tissue). Organ System: A group of related organs that work together to perform complex functions within the body. For instance, the digestive system includes organs such as the stomach and intestines that collaborate to break down food and absorb nutrients. Size of Specimens: Cells can be viewed using a microscope to study their structure and function. To calculate the size of a specimen under a microscope, we use the following formula: Actual Size = Image Size / Magnification Where image size is the size of the specimen as it appears through the microscope and actual size is the specimen’s real size. The image size should be measured in millimetres (mm). To convert from millimetres to micrometres (µm), multiply by 1000: 1 mm = 1000 µm µm is the symbol used to represent micrometres, a unit commonly used to measure cell dimensions. DEFINITIONS: Acrosome - An organelle in the tip of a sperm that contains enzymes which digest the cells around an egg and the egg membrane. Cilia - Hair-like structures found on ciliated cells that waft substances across the surface of tissue in one direction. Gamete - A reproductive cell with half the chromosomes of normal cells. CHAPTER 3: Cell Membrane and Cell Wall Functions: The cell membrane and cell wall play crucial roles in regulating the movement of substances into and out of the cell.  Cell Membrane: Composed of a phospholipid bilayer embedded with proteins, the cell membrane is selectively permeable, allowing specific molecules to pass while restricting others. This is essential for maintaining homeostasis within the cell. Cell Wall: Found in plant cells, fungi, and bacteria, the cell wall provides structural support and protection. It is primarily made of cellulose in plants and peptidoglycan in bacteria. The rigidity of the cell wall prevents excessive water uptake and maintains cell shape. Substances Transported: Molecules such as glucose and proteins enter the cell to be utilized in metabolic reactions and for storage. Waste products like carbon dioxide and lactic acid are expelled into the bloodstream for excretion. Diffusion: Definition: Diffusion is the net movement of particles from an area of high concentration to an area of low concentration, driven by the random movement of molecules. The energy for this process originates from the kinetic energy of the molecules. Importance: Essential for processes like respiration and photosynthesis, diffusion allows gases (e.g., oxygen and carbon dioxide) and solutes (e.g., nutrients) to cross the cell membrane, ensuring cells receive necessary substances and dispose of waste. Examples of where this takes place in the body:  Oxygen moves through the membranes of structures in the lung called alveoli into the red blood cells, and is carried to cells across the body for respiration. Carbon dioxide (the waste product of respiration) moves from the red blood cells into the lungs to be exhaled. These movements of gases are called gas exchange. Urea (a waste product) moves from the liver cells into the blood plasma to be transported to the kidney for excretion Factors Affecting the Rate of Diffusion: 1. Surface Area: An increase in surface area enhances diffusion rates as there are more available pathways for molecules to cross the membrane. 2. Temperature: Higher temperatures increase kinetic energy, causing molecules to move faster and thus speeding up diffusion. 3. Concentration Gradient: A steeper concentration gradient (greater difference between high and low concentrations) results in a higher rate of diffusion. 4. Diffusion Distance: Longer distances slow down diffusion, as molecules must travel further to reach equilibrium. Single-celled organisms can use diffusion to transport molecules into their body from the air- this is because they have a relatively large surface area to volume ratio. Due to their low metabolic demands, diffusion across the surface of the organism is sufficient enough to meet its needs. In multicellular organisms the surface area to volume ratio is small so they cannot rely on diffusion alone. Instead, surfaces and organ systems have a number of adaptations that allow molecules to be transported in and out of cells. Examples:  In the lungs, oxygen is transferred to the blood and carbon dioxide it transferred to the lungs. This takes place across the surface of millions of air sacs called alveoli, which are covered in tiny capillaries, which supply the blood. In the small intestine, cells have projections called villi. Digested food is absorbed over the membrane of these cells, into the bloodstream. The gills are where gas exchange takes place in fish. Water which has oxygen passes through the mouth and over the gills. Each gill has plates called gill filaments, and upon these are gill lamellae, which is where diffusion of oxygen into the blood and diffusion of carbon dioxide into the water takes place. Blood flows in one direction while water flows in the other. The roots of plants are adapted to take up water and mineral ions. Roots have root hair cells with large surface areas, which project into the soil. In the leaves of the plant there are many different tissues to aid with gas exchange. Carbon dioxide diffuses through stomata for photosynthesis, whilst oxygen and water vapour move out through them. The stomata are controlled by guard cells, which change the size of the stomata based on how much water the plant received (the guard cells swell with lots of water and make the stomata larger) Osmosis: Definition: Osmosis is the net movement of water molecules through a partially permeable membrane from an area of higher water potential (lower solute concentration) to an area of lower water potential (higher solute concentration). The cytoplasm of a cell contains salts and sugars, so therefore when a cell is placed in a dilute solution, water will move in. This situation can be modelled with a partially permeable membrane bag containing sugar molecules, with a glass tube placed in it with the top out of the water This can be placed in solutions of varying concentrations in order to observe the movement of water in and out by looking at the level of the water in the tube o If the concentration of sugar in external solution is the same as the internal, there will be no movement and the solution is said to be isotonic to the cell o If the concentration of sugar in external solution is higher than the internal, water moves out, and the solution is said to be hypertonic to the cell o If the concentration of sugar in external solution is lower than the internal, water moves in, and the solution is said to be hypotonic to the cell Osmosis in animals:. If the external solution is more dilute (higher water potential), it will move into animal cells causing them to burst.. On the other hand, if the external solution is more concentrated (lower water potential), excess water will leave the cell causing it to become shrivelled. Osmosis in plants:. If the external solution is more dilute, water will move into the cell and into the vacuole, causing it to swell, resulting in pressure called turgor (essential in keeping the leaves and stems of plants rigid).. If the external solution is less dilute, water will move out of the cell and they will become soft. Eventually the cell membrane will move away from the cell wall (called plasmolysis) and it will die. Key Terms: Turgid: Cells become swollen and firm due to water uptake, indicating a high water content. Turgor Pressure: The pressure exerted by the fluid (cytoplasm) against the cell wall, which helps maintain cell shape and structure. Flaccid: Cells that have lost water and are less firm, resulting in a limp appearance. Plasmolysis: The process in which the cell membrane pulls away from the cell wall due to excessive water loss, leading to cell shrinkage. Significance of Water in Cells: Water is crucial for maintaining turgor pressure in plant cells, which supports plant structure. It acts as a solvent for metabolic reactions, facilitating the transport of nutrients and waste. Water has a high specific heat capacity, serving as a temperature buffer to maintain optimal conditions for enzyme activity. Investigating Osmosis: Dialysis Tubing Experiment: Dialysis tubing, a model for a partially permeable membrane, can demonstrate osmosis. When filled with concentrated sucrose solution and submerged in distilled water, water moves from the beaker (higher water potential) into the tubing (lower water potential), illustrating the movement of water across a membrane. Osmosis in Plants:  In plants, water uptake occurs via root hair cells, where water moves from the soil (higher water potential) into the cells (lower water potential) through osmosis. This is vital for plant health and photosynthesis. Active Transport: Definition: Active transport is the process of moving molecules against their concentration gradient (from low to high concentration) using energy derived from cellular respiration. Carrier Proteins: Embedded in the cell membrane, these proteins facilitate active transport by binding to specific molecules. Energy from ATP is used to change the shape of the carrier protein, allowing the molecule to be transported across the membrane. Examples of Active Transport: 1. Uptake of Ions by Root Hair Cells: Plants actively transport essential ions (e.g., nitrates and magnesium) from the soil into root hair cells, even when the concentration of ions is higher  inside the cells than in the soil. This process is energy-intensive and critical for nutrient acquisition. 2. Uptake of Glucose: In the small intestine and kidney tubules, glucose is reabsorbed into the cells against its concentration gradient through active transport involving specific carrier proteins. This ensures that glucose is available for cellular respiration and energy production. CHAPTER 4: Biological Molecules Biological molecules are essential for the structure and function of living organisms. They serve as building blocks for cells and tissues and play crucial roles in metabolic reactions. Large biomolecules, or macromolecules, are formed when many smaller molecules, or monomers, chemically bond together through various types of reactions. Carbohydrates: Definition: Carbohydrates are organic compounds consisting of carbon (C), hydrogen (H), and oxygen (O) atoms, typically in a ratio of 1:2:1. They are vital for energy storage, structural integrity, and cellular communication. Types of Carbohydrates: 1. Monosaccharides:  The simplest form of carbohydrates, consisting of single sugar units. Examples include glucose, fructose, and galactose. Glucose is particularly important as a primary energy source for cells. 2. Disaccharides: Formed by the condensation of two monosaccharides. Examples include sucrose (glucose + fructose) and lactose (glucose + galactose). 3. Polysaccharides: Composed of long chains of monosaccharide units. They serve various functions: Cellulose: A structural polysaccharide found in plant cell walls, providing rigidity and support. It is not digestible by humans but is important for dietary fiber. Starch: A storage polysaccharide in plants, composed of amylose and amylopectin. It serves as an energy reserve, broken down into glucose when needed. Glycogen: The storage form of carbohydrates in animals, primarily stored in the liver and muscles, and can be rapidly mobilized to meet energy needs. Fats (Lipids): Definition: Fats and oils are a diverse group of hydrophobic molecules made primarily of glycerol and fatty acids, which consist of long hydrocarbon chains. Types of Fats: 1. Saturated Fats: Contain no double bonds between carbon atoms; typically solid at room temperature (e.g., butter). 2. Unsaturated Fats: Contain one or more double bonds; usually liquid at room temperature (e.g., olive oil).  Functions of Fats: Energy Storage: Fats provide more energy per gram than carbohydrates and serve as a concentrated energy reserve. Insulation: Help retain body heat and protect vital organs by providing a cushioning effect. Waterproofing: Create a barrier to water loss, especially in plants (cutin) and animals (sebum). Structural Role: Contribute to the formation of cell membranes (phospholipids). Hormone Production: Serve as precursors for steroid hormones. Proteins: Definition: Proteins are large, complex molecules made up of amino acids, which contain carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and sometimes sulfur (S). Structure of Proteins: 1. Primary Structure: The linear sequence of amino acids in a polypeptide chain. 2. Secondary Structure: The folding or coiling of the polypeptide chain, forming alpha-helices or beta-pleated sheets due to hydrogen bonding. 3. Tertiary Structure: The three-dimensional shape of a protein, determined by interactions between R groups of amino acids, including hydrogen bonds, ionic bonds, and hydrophobic interactions. 4. Quaternary Structure: The arrangement of multiple polypeptide chains in a protein (e.g., hemoglobin). Functions of Proteins:  Enzymatic Activity: Act as catalysts to speed up biochemical reactions. Transport: Hemoglobin transports oxygen in the blood; membrane proteins facilitate transport across cell membranes. Structural Support: Collagen in connective tissues and keratin in hair and nails. Defense: Antibodies in the immune system help to identify and neutralize pathogens. Regulation: Hormones like insulin regulate physiological processes. DNA (Deoxyribonucleic Acid): Definition: DNA is a double-stranded molecule composed of nucleotides, each consisting of a sugar (deoxyribose), a phosphate group, and a nitrogenous base. Structure: The two strands of DNA are coiled to form a double helix. The strands are held together by hydrogen bonds between complementary bases: Adenine (A) binds to Thymine (T). Guanine (G) binds to Cytosine (C).  Functions of DNA: Genetic Information Storage: Contains instructions for the development and functioning of all living organisms. Protein Synthesis: DNA sequences are transcribed into messenger RNA (mRNA), which is then translated into proteins. Replication: DNA can replicate itself during cell division, ensuring genetic continuity. Chemical Tests for Biological Molecules: 1. Starch Test: Procedure: Add iodine solution to the sample. Result: A color change to blue-black indicates the presence of starch due to the formation of a complex between iodine and the helical structure of starch. 2. Reducing Sugars Test: Procedure: Mix the sample with Benedict’s solution and heat to 80°C. Result: If reducing sugars (like glucose) are present, the solution changes from blue to brick red, indicating the reduction of Cu²⁺ ions to copper(I) oxide.  3. Protein Test (Biuret Test): Procedure: Add an equal amount of sodium hydroxide and a few drops of dilute copper(II) sulfate to the sample. Result: A color change to purple indicates the presence of proteins due to the formation of a complex between copper ions and peptide bonds. 4. Fats and Oils Test (Emulsion Test): Procedure: Add ethanol to the sample and shake to dissolve fats. Then add water and shake gently. Result: Formation of a cloudy white emulsion indicates the presence of fats or oils. 5. Vitamin C Test: Procedure: Add DCPIP solution (blue) to the sample and shake gently. Result: If vitamin C is present, the blue DCPIP solution will become colorless, indicating the reduction of DCPIP by ascorbic acid (vitamin C). DEFINITIONS: Nucleotides - The monomers of DNA consisting of a five-carbon sugar, a phosphate group and one of four chemical bases (A, T, C, G) attached to the sugar. CHAPTER 5: Enzymes Overview of Enzymes Definition: Enzymes are biological catalysts, primarily composed of proteins, that accelerate chemical reactions in living organisms. They enable metabolic processes that would otherwise occur too slowly to sustain life. Importance of Enzymes: Enzymes play a critical role in various biological functions, including digestion, metabolism, and DNA replication. By lowering the activation energy required for reactions, enzymes increase the rate of chemical reactions without being consumed or permanently altered in the process. Structure of Enzymes Protein Composition: Enzymes are made up of long chains of amino acids that fold into specific three-dimensional shapes, crucial for their function. Active Site: The active site is a unique region on the enzyme where the substrate binds. It consists of a specific arrangement of amino acids that creates a complementary shape to the substrate. The specificity of the active site allows enzymes to selectively interact with their respective substrates, forming an enzyme-substrate complex. Mechanism of Enzyme Action 1. Substrate Binding: When the substrate molecules collide with the enzyme, they can fit into the active site, forming the enzyme-substrate complex. This interaction can involve various types of bonding, such as hydrogen bonds, ionic interactions, and hydrophobic effects. 2. Catalysis: The enzyme catalyzes the conversion of substrate(s) into product(s). This process may involve the breaking or forming of chemical bonds. The enzyme may also facilitate the reaction by providing an alternative pathway with lower activation energy. 3. Product Release: After the reaction, the product(s) are released from the active site, leaving the enzyme free to bind with another substrate molecule. This allows enzymes to be used repeatedly in metabolic pathways. 4. Enzyme Specificity: Each enzyme is specific to a particular substrate due to the shape and chemical properties of its active site. For example: Proteases: Enzymes that break down proteins into amino acids. They cannot act on carbohydrates or lipids. Example, pepsin produced in the stomach, others found in small intestine and pancreas. Carbohydrases: Enzymes that catalyse the breakdown of carbohydrates into simple sugars. Lipases convert lipids into fatty acids and glycerol: Produced in the pancreas and small intestine. Soluble glucose, amino acids, fatty acids and glycerol pass into the bloodstream to be carried to all the cells around the body. They are used to build new carbohydrates, lipids and proteins, with some glucose being used in respiration. Factors Affecting Enzyme Action 1. pH: Each enzyme has an optimal pH at which it functions most effectively. For example, pepsin, a digestive enzyme in the stomach, works best at a low pH (around 2), while others, like trypsin in the intestine, work best at a neutral pH (around 7-8). Effect of pH Changes: Deviations from the optimal pH can lead to denaturation, where the enzyme’s structure, particularly the active site, is altered. This change prevents substrate binding and reduces the formation of enzyme-substrate complexes, leading to a decreased rate of reaction. 2. Temperature: Enzymes typically have an optimal temperature range (often around 37°C for human enzymes). Effect of Temperature Changes: As temperature increases, enzyme activity usually increases due to higher kinetic energy, leading to more frequent and effective collisions between enzyme and substrate. However, if the temperature exceeds the optimal range, the enzyme may denature. This results in a loss of the specific shape of the active site, rendering it unable to bind to its substrate, thereby slowing or halting the reaction. 3. Substrate Concentration: Increasing substrate concentration generally increases the rate of reaction up to a point. At low substrate concentrations, more enzyme active sites are available, and more enzyme-substrate complexes can form. However, once all active sites are occupied (saturation), increasing substrate concentration will no longer affect the rate of reaction.  4. Enzyme Concentration: Increasing enzyme concentration will increase the rate of reaction, provided there is an excess of substrate. More enzymes mean more active sites available for substrate binding. 5. Inhibitors: Competitive Inhibitors: These molecules resemble the substrate and compete for binding at the active site. They can reduce the rate of reaction by preventing substrate binding. Non-competitive Inhibitors: These bind to a different part of the enzyme, changing its shape and function, which affects the active site indirectly. CHAPTER 6: Photosynthesis Overview of Photosynthesis Definition: Photosynthesis is a vital metabolic process that occurs in plants, algae, and some bacteria, where light energy is converted into chemical energy in the form of carbohydrates, primarily glucose. This process is essential for life on Earth as it forms the basis of the food chain. Location: Photosynthesis occurs in the chloroplasts of plant cells, which are specialized organelles that contain chlorophyll, a green pigment crucial for capturing light energy. Importance of Chlorophyll:  Chlorophyll absorbs light energy, primarily from the blue and red wavelengths, while reflecting green light, which is why plants appear green. The absorbed light energy is converted into chemical energy through a series of reactions, ultimately synthesizing carbohydrates. The Photosynthesis Process 1. Raw Materials: Photosynthesis uses two primary raw materials: Carbon dioxide (CO₂): Taken in from the atmosphere through small openings in leaves called stomata. Water (H₂O): Absorbed from the soil through the roots. 2. Photosynthesis Equation: The overall word equation for photosynthesis is: CO2 + H20 —> Glucose + Oxygen 3. Stages of Photosynthesis: Photosynthesis occurs in two main stages: Light-dependent Reactions: Occur in the thylakoid membranes of the chloroplasts, where light energy is captured and used to split water molecules, releasing oxygen and generating ATP and NADPH. Light-independent Reactions (Calvin Cycle): Occur in the stroma of chloroplasts, where ATP and NADPH are used to convert carbon dioxide into glucose. Uses of Carbohydrates Produced The carbohydrates produced during photosynthesis serve various essential functions in plants: Starch: Stored energy source for plants, readily converted back into glucose when needed. Cellulose: A structural component of plant cell walls, providing rigidity and support. Glucose: Used in cellular respiration to produce energy for various metabolic activities. Sucrose: A transportable form of sugar that moves through the phloem to different parts of the plant. Nectar: Attracts pollinators, aiding in the plant’s reproductive process. Factors Affecting the Rate of Photosynthesis The rate of photosynthesis can be influenced by several environmental factors, with the limiting factor being the one in shortest supply that restricts the overall rate: 1. Carbon Dioxide Concentration: An increase in carbon dioxide concentration generally leads to an increased rate of photosynthesis, as it is a necessary reactant in the Calvin Cycle. However, beyond a certain concentration, the rate will plateau as other factors become limiting. 2. Temperature: Photosynthesis is enzyme-driven, so the rate is influenced by temperature. The optimal temperature for many plants is around 25°C.  At lower temperatures, enzyme activity slows due to reduced kinetic energy, leading to fewer enzyme-substrate complexes and a lower rate of photosynthesis. At high temperatures, enzymes can denature, disrupting the active site and hindering the reaction, thus reducing the rate of photosynthesis. 3. Light Intensity: Increasing light intensity boosts the rate of photosynthesis up to a certain point. High light intensity enhances the energy available for the light-dependent reactions. If light intensity becomes too high, it can cause overheating, leading to denaturation of proteins and subsequently making temperature the limiting factor. Minerals and Their Importance in Plants Plants absorb minerals through their roots, which are essential for various physiological functions: 1. Nitrate Ions (NO₃⁻): Critical for synthesizing amino acids, proteins, and enzymes. Nitrates contribute to plant growth and are vital for cellular functions. A deficiency in nitrates can lead to stunted growth and poor repair mechanisms. 2. Magnesium Ions (Mg²⁺): An essential component of chlorophyll, necessary for photosynthesis. A lack of magnesium results in chlorosis, where leaves turn yellow due to insufficient chlorophyll. This deficiency hampers the plant’s ability to produce sugars, ultimately affecting its growth and survival. Experimental Tests for Photosynthesis 1. Testing for the Need for Chlorophyll: Objective: To demonstrate that chlorophyll is necessary for photosynthesis. Method: Use a variegated leaf plant (green and white patches). Keep the plant in darkness for 48 hours to deplete starch. Expose the plant to sunlight for several hours. Cover the leaf with iodine solution. Observation: The green patches turn blue-black (indicating starch presence) while white patches remain orange-brown, demonstrating that photosynthesis occurs only in areas with chlorophyll. 2. Testing for the Need for Light: Objective: To show that light is essential for photosynthesis. Method: Keep a starch-depleted plant in darkness for 48 hours, then clip aluminum foil over one leaf and expose the plant to sunlight. After a few hours, cover the leaves with iodine. Observation: The area exposed to light turns blue-black, indicating starch production, while the area under the foil remains orange-brown, showing that light is needed for photosynthesis. 3. Testing for the Need for Carbon Dioxide: Objective: To demonstrate that carbon dioxide is required for photosynthesis. Method: Use two starch-depleted plants in transparent bags, one with sodium hydrogencarbonate (to provide CO₂) and one with soda lime (to absorb CO₂). Place both in sunlight and cover leaves with iodine.  Observation: The plant with sodium hydrogencarbonate turns blue-black, indicating starch production, while the one with soda lime remains orange-brown, showing that carbon dioxide is essential. The Effect of Light and Dark Conditions on Gas Exchange in Aquatic Plants 1. Setup: Use hydrogencarbonate indicator solution in four test tubes: Test Tube 1: Control (no leaf present). Test Tube 2: Contains a leaf. Test Tube 3: Contains a leaf covered with aluminum foil. Test Tube 4: Contains a leaf covered with gauze. 2. Procedure: Seal each test tube and expose them to sunlight for 24 hours. 3. Results: Test Tube 1: No color change (remains orange). Test Tube 2: Turns purple (indicating a higher rate of photosynthesis than respiration, resulting in reduced CO₂). Test Tube 3: Turns yellow (higher rate of respiration than photosynthesis due to lack of light). Test Tube 4: Remains orange (rate of respiration equals the rate of photosynthesis, resulting in no net change in CO₂). Leaf Structure and Adaptations Plant leaves are specialized structures that facilitate efficient photosynthesis: 1. Large Surface Area: Maximizes light absorption and gas exchange, reducing water loss through evaporation. 2. Thin Structure: Ensures gases diffuse quickly to and from cells, facilitating efficient photosynthesis. 3. Chloroplasts: Organelles where photosynthesis occurs; contain chlorophyll to capture light energy. 4. Cuticle: A thin, waxy layer that reduces water loss while allowing light to penetrate. 5. Stomata and Guard Cells: Stomata: Pores on the leaf’s surface that allow CO₂ in and O₂ out. Guard cells close and open stomata.. They are kidney shaped They have thin outer walls and thick inner walls. When lots of water is available to the plant, the cells fill and change shape, opening stomata (they are also light sensitive). This allows gases to be exchanged and more water to leave the plant via evaporation. More stomata are found on the bottom of the leaf, allowing gases to be exchanged whilst minimising water loss by evaporation as the lower surface is shaded and cooler. 6. Upper and Lower Epidermis: Protective layers that prevent pathogen entry; transparent to allow light penetration. 7. Palisade Mesophyll: Located just beneath the upper epidermis; contains densely packed chloroplasts for optimal light absorption. 8. Spongy Mesophyll: Contains air spaces that facilitate gas exchange and diffusion of CO₂ and O₂ within the leaf. 9. Vascular Bundles (Xylem and Phloem): Xylem: Transports water from the roots to the leaves, aiding in photosynthesis and maintaining plant structure. Phloem: Distributes sugars and nutrients produced during photosynthesis throughout the plant.  DEFINITIONS: Hydrogencarbonate indicator - An indicator that changes colour depending on the concentration of carbon dioxide and the resulting pH of the solution. Limiting factor - A variable that is in short supply and limits the rate of a particular reaction. CHAPTER 7: Human Nutrition and the Digestive System Human Nutritional Needs Humans require a wide variety of nutrients for optimal health and survival. A balanced diet, which includes all essential nutrients in the correct proportions, is critical for maintaining bodily functions, growth, and repair. Essential nutrients include carbohydrates, fats, proteins, vitamins, minerals, and water. The composition of a balanced diet varies significantly among individuals, depending on several factors:  Age and Gender: Nutritional needs change throughout life stages, with children requiring more nutrients for growth, while adults may need different amounts depending on their gender and overall health. Physical Activity: Individuals who are physically active or engage in strenuous exercise may need higher energy levels and nutrient intake compared to sedentary individuals. Special Conditions: Pregnant and breastfeeding women have increased nutritional demands to support both their own health and the development of their babies. Key Nutrients and Their Importance: 1. Carbohydrates: Sources: Found in foods such as pasta, rice, bread, and potatoes. Function: Primary energy source for the body. During respiration, carbohydrates are broken down into glucose, which provides energy for cellular activities. 2. Fats and Oils: Sources: Found in fatty meats, dairy products (like cheese and butter), nuts, and oils. Functions: Serve multiple roles, including energy storage, insulation against temperature changes, waterproofing surfaces, providing structure to cells, and protecting vital organs. 3. Proteins: Sources: Found in meat, fish, eggs, legumes, and dairy products. Function: Proteins are composed of amino acids, which are essential for building and repairing tissues. They are involved in the formation of enzymes, hormones, and other important molecules, such as hemoglobin, which transports oxygen in the blood.  4. Vitamins: Vitamin C: Found in citrus fruits, tomatoes, and green vegetables. It is crucial for synthesizing collagen, which supports skin, ligaments, and blood vessels, and for repairing tissues. Vitamin D: Found in dairy products, eggs, and fatty fish. It is essential for calcium absorption, which contributes to bone health and growth. 5. Mineral Ions: Calcium: Found in dairy products, leafy greens, and fish. Essential for healthy bones and teeth; plays a critical role in blood clotting and muscle contraction. Iron: Found in red meat, beans, lentils, and green vegetables. It is a key component of hemoglobin, necessary for oxygen transport. Iron deficiency can lead to anemia, resulting in fatigue and reduced energy levels. 6. Fibre (Roughage): Sources: Found in fruits, vegetables, whole grains, and legumes. Function: Although not digested, fibre is vital for digestive health as it adds bulk to stool, aiding in bowel regularity and preventing constipation. 7. Water: Sources: Comprises about 80% of drinks and 20% of food. Functions: Serves as a solvent for biochemical reactions, regulates body temperature through sweating, and facilitates nutrient transport and waste removal. Malnutrition: A diet lacking in essential nutrients can lead to malnutrition, which can manifest in various forms:  Scurvy: Resulting from a deficiency of vitamin C, characterized by symptoms such as bleeding gums, skin lesions, fatigue, and weakened connective tissues due to impaired collagen synthesis. Rickets: Caused by a lack of vitamin D, leading to weak and soft bones, skeletal deformities, and stunted growth in children due to inadequate mineralization of bone tissue. The Digestive System: The digestive system is responsible for breaking down food into absorbable units through both physical and chemical digestion. This process begins in the mouth and continues through various organs until waste is egested. 1. Mouth and Salivary Glands: Food enters the mouth, where it is mechanically broken down by the teeth. The salivary glands secrete saliva, which contains enzymes (like amylase) that begin the chemical digestion of carbohydrates, converting starch into simpler sugars. 2. Oesophagus: The oesophagus transports chewed food (bolus) to the stomach via peristalsis, a series of coordinated muscle contractions. 3. Stomach: The stomach further mechanically digests food by churning it, while protease enzymes break down proteins into peptides. Hydrochloric acid creates an acidic environment (pH 1.5) optimal for enzyme activity and helps kill harmful bacteria. 4. Small Intestine: Comprised of the duodenum and ileum, the small intestine is where the majority of chemical digestion and absorption occurs.  In the duodenum, bile from the liver neutralizes stomach acid, and pancreatic enzymes (amylase, protease, and lipase) further digest carbohydrates, proteins, and fats. The ileum absorbs nutrients through its highly folded inner surface lined with villi, which increase surface area for absorption. 5. Pancreas: The pancreas produces pancreatic juices that contain enzymes necessary for digesting carbohydrates, proteins, and fats, releasing them into the small intestine. 6. Liver: The liver produces bile, which aids in fat digestion by emulsifying fats into smaller droplets, enhancing the effectiveness of lipase. Bile also helps to neutralize stomach acid entering the small intestine. 7. Gall Bladder: The gall bladder stores bile produced by the liver and releases it into the small intestine as needed. 8. Large Intestine: Indigestible food passes into the large intestine, which consists of the colon, rectum, and anus. Here, water and salts are absorbed, with most absorption occurring in the small intestine. The remaining waste material is compacted into feces for excretion. Digestive Processes: Ingestion: The process of taking in food and drink through the mouth. Digestion: The breakdown of food into smaller molecules, occurring through: Physical Digestion: Mechanical breakdown of food into smaller pieces (e.g., chewing in the mouth, churning in the stomach). Chemical Digestion: The enzymatic breakdown of food into smaller, soluble molecules in the small intestine. Absorption: The process whereby digested nutrients pass through the intestinal walls into the bloodstream, primarily in the small intestine, with some absorption occurring in the large intestine. Assimilation: The utilization of absorbed nutrients by cells for energy, growth, and repair.  Egestion: The elimination of indigestible remnants of food from the body as feces, occurring through the anus. Physical Digestion: Physical digestion is the process of breaking down food into smaller pieces without altering their chemical composition. This increases the surface area of food, making it easier for enzymes to act during chemical digestion. Role of Teeth in Physical Digestion: Incisors: Sharp and chisel-shaped, incisors are used for biting and cutting food. Canines: Pointed teeth located next to incisors, ideal for tearing food. Premolars and Molars: Broad and flat, these teeth are used for grinding and chewing food into smaller pieces. Tooth Structure: Enamel: The hard, outer layer of the tooth, providing protection against decay.  Dentine: The softer layer beneath enamel; it is less hard and more susceptible to decay if the enamel is worn away. Pulp: The innermost part containing blood vessels and nerves, responsible for nourishing the tooth. Cement: The outer layer covering the tooth root, anchoring the tooth in place. Role of the Stomach in Physical Digestion: The stomach has muscular walls that contract to mix and grind food, further breaking it down into smaller particles to prepare for chemical digestion. Role of Bile in Physical Digestion: Bile produced in the liver emulsifies fats, breaking them into smaller droplets and increasing the surface area for lipase action, facilitating faster digestion of fats. Chemical Digestion: Chemical digestion involves the enzymatic breakdown of large insoluble molecules into smaller soluble ones, enabling absorption into the bloodstream. Enzymes: Amylase: Converts starch into simpler sugars (maltose), found in saliva and the small intestine. Maltase further breaks down maltose into glucose. Protease: Breaks down proteins into amino acids. Pepsin operates in the acidic environment of the stomach, while trypsin functions in the alkaline conditions of the small intestine. Lipase: Digests fats into glycerol and fatty acids, secreted into the small intestine, and pancreas. To Aid Digestion: Hydrochloric Acid: Maintains a low pH in the stomach, killing bacteria and activating protease enzymes. Bile: Neutralizes stomach acid in the duodenum and optimizes conditions for enzyme action in the small intestine. Absorption: Most nutrient absorption occurs in the small intestine. The intestinal lining is specialized for absorption, featuring: Villi and Microvilli: Tiny finger-like projections that increase surface area for maximum nutrient absorption. Capillaries: Blood vessels within each villus transport absorbed nutrients throughout the body. Lacteals: Specialized lymphatic vessels in the villi that absorb fats CHAPTER 8: Xylem and Phloem Transport Systems in Plants Plants possess a complex transport system primarily composed of two types of vascular tissues: xylem and phloem. These specialized vessels are crucial for transporting essential substances such as water, minerals, nutrients, and sugars throughout the plant, enabling it to grow and thrive. Xylem The xylem is responsible for the upward transport of water and dissolved mineral ions from the roots to the stems and leaves. Several adaptations of xylem vessels enhance their efficiency in transporting water:  Thick Lignified Walls: The xylem vessels are surrounded by thick walls reinforced with lignin, which provides structural support and prevents collapse under negative pressure during water transport. Hollow Structure: Xylem cells are devoid of cytoplasm, forming long, continuous tubes that facilitate the smooth flow of water. This absence of cell contents maximizes the internal space available for water transport. Continuous Tubes: Xylem vessels are arranged end-to-end without cross walls, creating an uninterrupted pathway for water to ascend through the plant. Phloem In contrast, the phloem is responsible for the transport of organic compounds, particularly sucrose and amino acids, through a process known as translocation. Key characteristics of phloem include: Living Cells: The phloem is composed of living cells, such as sieve tube elements and companion cells, which are vital for the transport and regulation of nutrients. Sieve Plates: Sieve tube elements have perforated end walls called sieve plates that allow for the efficient flow of sap containing nutrients. Position of Xylem and Phloem in Different Plant Structures Roots: In roots, the xylem is located at the center, arranged in an X-shape, while the phloem surrounds the xylem. This configuration aids in the efficient transport of water and nutrients from the soil. Stems: In stems, xylem is positioned internally, providing structural support, whereas phloem is located externally, facilitating nutrient distribution to growing tissues.  Leaves: In leaves, the xylem is situated above the phloem within the vascular bundles. This positioning allows for effective water supply to mesophyll cells, which are essential for photosynthesis. Water Uptake Water uptake in plants occurs primarily through root hair cells via the process of osmosis. Here’s a detailed explanation of the mechanism: 1. Osmosis: Root hair cells absorb water from the soil, where the water potential is higher than inside the root cells, causing water to move into the root hair cells. 2. Cortex Cells: After entering the root hair cells, water moves through the root cortex cells by osmosis, continuing to follow the gradient created by the higher water potential in the root hair cells.  3. Xylem Vessel Entry: Water eventually reaches the xylem vessels, where it is transported upward through the plant to the leaves. 4. Mesophyll Cells: In the leaves, water diffuses into the mesophyll cells, where it is utilized for vital metabolic processes, including photosynthesis. Experimental Evidence of Water Uptake: To investigate water uptake, a plant can be placed in a beaker of water with a dye added. Under optimal conditions (room temperature and bright light), the dyed water will be absorbed by the plant. After several hours, the leaves will exhibit the dye’s color, indicating successful water uptake. Cross-sections of the plant will reveal that only the xylem vessels are stained, confirming their role in water transport. Transpiration Transpiration is the process by which water vapor is lost from the plant, primarily through the stomata in the leaves. The following points elaborate on this process: Evaporation: Water evaporates from the surface of mesophyll cells into intercellular air spaces, which increases the concentration of water vapor. Stomata Role: Water vapor diffuses out of the leaf through the stomata, tiny openings regulated by guard cells. The large surface area of air spaces facilitates efficient evaporation. Transpiration Pull: The evaporation of water from leaves creates a negative pressure within the xylem vessels, known as transpiration pull. This pressure draws more water upward from the roots through the cohesive properties of water molecules.  Factors Affecting Transpiration Rate: Temperature: Higher temperatures increase evaporation rates, leading to higher transpiration rates. Wind Speed: Increased wind speed removes water vapor from the leaf surface, enhancing transpiration. Humidity: Higher humidity levels decrease the transpiration rate by reducing the concentration gradient for water vapor between the inside and outside of the leaf. Maintaining Plant Structure: Water maintains turgidity in plant cells, ensuring they remain firm and structurally sound. If a plant loses excessive water and cannot replace it, turgor pressure decreases, leading to wilting. To mitigate water loss, plants can close their stomata, reducing water vapor diffusion. Translocation Translocation refers to the transport of organic nutrients, particularly sucrose and amino acids, through the phloem. The process involves the following components: Sources and Sinks: Sources are regions where nutrients are produced, such as the leaves during photosynthesis. Sinks are areas where nutrients are utilized or stored, such as roots and growing tissues. Transport Mechanism: Nutrients are actively loaded into the phloem at source tissues, creating a high concentration that drives the flow toward sinks. This process often requires energy (ATP) for active transport. Bidirectional Flow: Unlike xylem, which primarily transports water upwards, phloem can transport nutrients both upwards and downwards, depending on the plant’s metabolic needs. Dual Functionality of Leaves: Some leaves can act as both sources and sinks, producing sugars through photosynthesis and utilizing them for growth and respiration. DEFINITIONS: Cortex - The tissue located between the epidermis and the vascular bundles in a plant stem or root. The cells of the cortex often store starch. CHAPTER 9: Circulatory Systems Overview of Circulatory Systems The circulatory system is the primary transport mechanism in animals, responsible for delivering oxygen, nutrients, hormones, and other essential substances to tissues while removing waste products like carbon dioxide and urea. It consists of blood vessels (arteries, veins, and capillaries), a muscular pump (the heart), and valves that ensure unidirectional blood flow. Types of Circulatory Systems 1. Fish: Single Circulatory System Structure: Fish have a heart with only two chambers: one atrium and one ventricle. Process: Blood passes through the heart once during each complete circuit of the body. Blood is pumped from the heart to the gills, where it is oxygenated, and then flows directly to the rest of the body before returning to the heart. Oxygen Absorption: As blood flows over the gill membranes, it absorbs oxygen from the water, eliminating the need for lungs. 2. Mammals: Double Circulatory System Structure: Mammals possess a heart with four chambers: two atria and two ventricles. Process: Blood circulates through the heart twice for each complete circuit: First Circuit: Deoxygenated blood from the body enters the right atrium, is pumped to the right ventricle, and is sent to the lungs for oxygenation via the pulmonary artery.  Second Circuit: Oxygenated blood returns to the left atrium, moves to the left ventricle, and is pumped out to the body through the aorta. Efficiency: The double circulatory system allows for higher blood pressure, facilitating more efficient oxygen delivery to tissues, which is especially important for warm-blooded mammals that require more energy. Structure of the Heart Chambers: The heart consists of four chambers: Right Atrium: Receives deoxygenated blood from the body via the vena cava.  Right Ventricle: Pumps deoxygenated blood to the lungs. Left Atrium: Receives oxygenated blood from the lungs via the pulmonary vein. Left Ventricle: Pumps oxygenated blood to the body through the aorta. Valves: Atrioventricular Valves: The tricuspid valve (right) and bicuspid (mitral) valve (left) prevent backflow of blood into the atria when the ventricles contract. Semilunar Valves: Located at the exits of the ventricles (pulmonary valve for the right ventricle and aortic valve for the left ventricle), they prevent backflow into the ventricles when they relax. Septum: The septum is a muscular wall that separates the left and right sides of the heart, ensuring that oxygenated and deoxygenated blood do not mix. Wall Thickness: The left ventricle has the thickest wall as it needs to generate enough pressure to pump blood throughout the entire body, while the right ventricle pumps blood only to the lungs. Heart Function 1. Deoxygenated blood enters the heart through the vena cava into the right atrium. 2. The right atrium contracts, pushing blood through the tricuspid valve into the right ventricle. 3. The right ventricle contracts, sending blood through the pulmonary valve into the pulmonary artery, leading to the lungs. 4. Blood becomes oxygenated in the lungs and returns to the heart via the pulmonary vein, entering the left atrium. 5. The left atrium contracts, pushing blood through the bicuspid valve into the left ventricle.  6. The left ventricle contracts, sending oxygenated blood through the aortic valve into the aorta, distributing it throughout the body. 7. The septum ensures separation of oxygenated and deoxygenated blood. Heart Monitoring The heart can be monitored using: Electrocardiogram (ECG): This device records the electrical signals that trigger heart contractions, helping diagnose arrhythmias and other heart conditions. Pulse Rate: The pulse reflects the heart rate and can be measured by palpating arteries. Physical activity increases heart rate as muscles require more oxygen for aerobic respiration. Factors Affecting Pulse Rate: Physical Activity: Exercise elevates heart rate to meet increased oxygen demands during muscular activity. Emotional State: Stress or excitement can also raise heart rate. Coronary Heart Disease (CHD) Coronary heart disease occurs when cholesterol builds up in the coronary arteries, narrowing them and restricting blood flow to the heart muscle. Key points include:  Causes: High levels of saturated fats in the diet lead to cholesterol buildup. Other contributing factors include: Genetic Predisposition: Family history can increase risk. Lifestyle Factors: Smoking, sedentary lifestyle, and high-stress levels exacerbate the condition. Age and Gender: Risk increases with age, and men are generally at higher risk than women. Prevention: Adopting a healthy diet low in saturated fats, engaging in regular exercise, managing stress, and avoiding smoking can reduce the risk of developing CHD. Solutions for CHD:. Stents (metal mesh tubes inserted in arteries) - keeps the arteries open to allow blood to flow through. 1. They are effective in lowering the risk of a heart attack 2. The recovery time from surgery is quick 3. Risk of a heart attack during the procedure, or that infection could occur 4. following it. 5. There is a chance that blood clots can form near the stent (called thrombosis). Statins (drugs that decrease the levels of LDL (bad) cholesterol- which would otherwise lead to coronary heart disease) 1. They reduce the risk of strokes, coronary heart disease and heart attacks 2. They increase the levels of HDL (good) cholesterol 3. Need to be taken continuously which may be an inconvenience 4. Can produce side effects 5. May not have an immediate effect as it only slows down the rate it is deposited Other possible heart problems: 1. Faulty valves - when a heart valve becomes stiff so cannot open or it is damaged so it leaks, blood flows in the wrong direction which means that the heart does not work as efficiently as it should. Solutions:. Replacing it with a biological valve (pigs or cattle) ❖ Works very well ❖ Only last 12-15 years. Replacing it with a mechanical valve (manmade) ❖ Last for a long time ❖ Constant medication is needed to stop blood from clotting around the valve 2. Heart failure- can be solved with a heart transplant. A heart transplant requires a donor who has recently died. These are not always available, so an artificial may be used whilst waiting ❖ Less likely to be rejected by the immune system- metal and plastic are not recognised as foreign ❖ Surgery temporarily leaves the body exposed to infection ❖ As it is mechanical parts of it could wear out and the motor could fail ❖ Blood clots could form, leading to strokes ❖ To prevent the above, drugs are taken to thin the patients blood- this affects the individuals bleeding if they are hurt 3. Extreme blood loss- can be solved by giving artificial blood. It is a salt solution that can keep people alive even if they lose s of their red blood cells ❖ This means the patient has more time to produce new blood cells ❖ But it can only be used for short periods of time- then a blood transfusion has to take place Adaptations of Blood Vessels 1. Arteries: Function: Carry oxygenated blood away from the heart under high pressure. Structure: Small Lumen: Reduces the volume of blood flow to maintain pressure. Thick Elastic Walls: Allow arteries to stretch and recoil with the pulse of blood, helping to maintain blood pressure. Muscle Layer: Thick smooth muscle allows for vasodilation and vasoconstriction, regulating blood flow. Branching: Arteries branch into arterioles that further divide into capillaries. 2. Veins: Function: Return deoxygenated blood to the heart under low pressure. Structure: Larger Lumen: Facilitates the return of blood with less resistance. Thin Walls: Lower pressure means less structural support is needed. Valves: Prevent backflow of blood, ensuring it returns to the heart efficiently. Venules: Small veins formed from capillaries that converge into larger veins. 3. Capillaries: Function: Facilitate the exchange of substances (oxygen, nutrients, carbon dioxide) between blood and tissues. Structure: Thin Walls: Only one cell thick, minimizing diffusion distance for efficient exchange.  Large Surface Area: Extensive branching increases the area available for exchange. Slow Blood Flow: Allows more time for the exchange of gases and nutrients. Components of Blood 1. Plasma. This is liquid that carries the components in the blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies and antitoxins 2. Red blood cells. They carry oxygen molecules from the lungs to all the cells in the body · Their biconcave disc shape provides a large surface area. They have no nucleus allowing more room to carry oxygen. They contain the red pigment haemoglobin, which binds to oxygen and forms oxyhaemoglobin 3. White blood cells. They are a part of the immune system, which is the body's defence against pathogens (microorganisms that can produce disease). They have a nucleus. There are a number of types: o 1- Those that produce antibodies (small proteins that clump them together) against microorganisms o 2- Those that engulf and digest pathogens o 3- Those that produce antitoxins to neutralise toxins (poisons) produced by microorganisms Platelets. They help the blood clot form at the site of a wound. The clot dries and hardens to form a scab, which allows new skin to grow underneath while preventing microorganisms from entering. Small fragments of cells. No nucleus. Without them, cuts would result in excessive bleeding and bruising Blood Clotting Mechanism Blood clotting is a critical response to blood vessel injury, preventing blood loss and pathogen entry: 1. Vessel Injury: When a blood vessel breaks, the exposed collagen fibers attract platelets. 2. Platelet Activation: Platelets adhere to the broken vessel wall and release chemicals that attract more platelets, forming a temporary plug. 3. Fibrin Formation: The protein fibrinogen is converted to fibrin by enzymes, forming a mesh that solidifies the platelet plug into a stable clot. 4. Scab Formation: The clot hardens into a scab, sealing the wound and allowing tissue repair while preventing pathogen entry.  DEFINITIONS: Aorta - The artery that takes oxygenated blood away from the heart to the body. Artery - A type of blood vessel that carries blood away from the heart to the tissues, under high pressure. The walls of the arteries contain thick layers of smooth muscle and elastic fibres. Atria - The two upper chambers of the heart that receive blood from the veins and pump blood into the ventricles. The muscular walls of the atria are thinner than that of the ventricles. Atrioventricular (AV) valves - The valves found between the atria and ventricles. They prevent the backflow of blood from the ventricles into the atria. There are two types of AV valves: bicuspid and tricuspid. Bicuspid valves - The atrioventricular valves found between the left atrium and left ventricle. Blood - A tissue containing red blood cells, white blood cells, platelets and plasma. Blood clotting - A defence mechanism that prevents excessive blood loss and the entry of harmful microorganisms. It involves platelets and the conversion of fibrinogen to fibrin to form a mesh over the wound. Capillaries - Thin, narrow blood vessels that connect the arteries and veins. They are the site of exchange of substances between the blood and the tissues. Circulatory system - The transport system in mammals consisting of a pump, blood vessels and valves. Coronary arteries - The arteries that supply the heart muscle with food and oxygen. Coronary heart disease - A disease caused by the build-up of fatty deposits inside the coronary arteries, narrowing them and reducing blood flow to the heart tissue. Risk factors include a diet high in saturated fats, stress, lack of exercise, smoking, age, genetic predisposition and gender.  Double circulatory system - A circulatory system found in mammals in which the blood flows through the heart twice in two circuits. Blood is pumped from the heart to the lungs before returning to the heart. It is then pumped around the body, after which it returns to the heart again. Electrocardiogram (ECG) - A technique used to measure the spread of electrical activity through the heart by measuring tiny changes in the skin's electrical conductivity. This produces a trace which is used to detect abnormalities in heart rhythm. Lymphocyte - A type of white blood cell that produces antibodies specific to a particular antigen. Phagocyte - A type of white blood cell that engulfs pathogens and digests them in a process known as phagocytosis. Phagocytosis - The process by which white blood cells (phagocytes) engulf and destroy pathogens. Plasma - The main component of the blood that carries red blood cells. It is a yellow liquid containing blood cells, soluble nutrients, ions, carbon dioxide and hormones. Platelets - Small fragments of cells that are involved in blood clotting. Pulmonary arteries - The arteries that carry deoxygenated blood away from the heart to the lungs. Pulmonary veins - The veins that carry oxygenated blood from the lungs to the heart. Pulse rate - The number of pulses felt in an artery (e.g. radial artery) per minute. Red blood cell - A type of blood cell that is anucleate and biconcave. It contains haemoglobin which enables the transport of oxygen and carbon dioxide to and from the tissues. Renal arteries - Blood vessels that carry oxygenated blood to the kidneys. Renal veins - Blood vessels that drain the kidneys. Semilunar valves - A pair of valves found between the ventricles and arteries. They prevent the backflow of blood from the arteries into the ventricles. Septum - The wall of muscle separating the left side from the right side of the heart. It prevents oxygenated and deoxygenated blood from mixing. Single circulatory system - A circulatory system in which the blood travels one circuit. Blood flows through the heart and is pumped around the body before returning to the heart. Single circulatory systems are found in fish. Tricuspid valves - The atrioventricular valves found between the right atrium and right ventricle. Valves - Structures in the heart that prevent the backflow of blood. Vein - A type of blood vessel that carries blood towards the heart under low pressure. It has a wide lumen, smooth inner lining and valves. The walls of the veins contain some smooth muscle and little elastic fibre. Vena cava - The vein that returns deoxygenated blood to the heart from the body. Ventricles - The two lower chambers of the heart that receive blood from the atria and expel blood into the arteries. The muscular wall of the left ventricle is thicker than that of the right ventricle. White blood cells - Cells of the immune system that protect the body from invading pathogens. They play a role in phagocytosis and in the production of antibodies. Two types: phagocytes and lymphocytes. CHAPTER 10: Pathogens and the Immune Response Pathogens A pathogen is any organism that causes disease in a host organism. Pathogens include a variety of microorganisms such as bacteria, viruses, fungi, and parasites. Organisms that harbor pathogens are referred to as hosts. Many pathogens are transmissible diseases, meaning they can be passed from one host to another.  1. Viruses · Very small. They move into cells and use the biochemistry of it to make many copies of itself. This leads to the cell bursting and releasing all of the copies into the bloodstream. The damage and the destruction of the cells makes the individual feel ill 2. Bacteria Small. They multiply very quickly through dividing by a process called binary fission. They produce toxins that can damage cells 3. Protists. Some are parasitic, meaning they use humans and animals as their hosts (live on and inside, causing damage) 4. Fungi. They can either be single celled or have a body made of hyphae (thread-like structures). They can produce spores which can be spread to other organisms Viral Diseases: Measles Symptoms: Fever and red skin rash, can lead to other problems such as pneumonia (lung infection), encephalitis (brain infection) and blindness. How it is spread: Droplet infection How it is being prevented: Vaccinations for young children to reduce transmission HIV  Symptoms: Initially flu-like symptoms, then the virus attacks the immune system and leads to AIDS (a state in which the body is susceptible to many different diseases) How it is spread: By sexual contact or exchange of bodily fluids such as blood How it is being prevented:. The spread- Using condoms, not sharing needles, screening blood when it is used in transfusions, mothers with HIV bottle-feeding their children instead of breastfeeding. The development to AIDS- Use of antiretroviral drugs (stop the virus replicating in the body) Tobacco mosaic virus (a plant pathogen affecting many species of plants including tomatoes) Symptoms: Discolouration of the leaves, the affected part of the leaf cannot photosynthesise resulting in the reduction of the yield. How it is spread: Contact between diseased plants and healthy plants, insects act as vectors. How it is being prevented: Good field hygiene and pest control, growing TMV-resistant strains. Bacterial Diseases: Salmonella food poisoning (bacteria that live in the gut of different animals, which we ingest when we eat the meat) Symptoms: Fever, stomach cramps, vomiting, diarrhoea (all caused by the toxins they secrete). How it is spread: These bacteria can be found in raw meat and eggs, unhygienic conditions.  How it is being prevented: Poultry are vaccinated against Salmonella, keeping raw meat away from cooked food, avoid washing it, wash hands and surfaces when handling it, cook food thoroughly. Gonorrhoea Symptoms: Thick yellow or green discharge from the vagina or penis, pain when urinating. How it is spread: It is a sexually transmitted disease spread through unprotected sexual contact. How it is being prevented: By using contraception such as condoms and antibiotics (used to be treated with penicillin but many resistant strains are developing). Fungal Diseases: Rose Black Spot Symptoms: Purple or black spots on leaves of rose plants, reduces the area of the leaf available for photosynthesis, leaves turn yellow and drop early How it is spread: The spores of the fungus are spread in water (rain) of by wind How it is being prevented: By using fungicides or stripping the plant of affected leaves (have to be burnt) Protist Diseases: Malaria (caused by protist pathogens that enter red blood cells and damage them) Symptoms: Fevers and shaking (when the protists burst out of blood cells) How it is spread: The vector is the female Anopheles mosquito, in which the protists reproduce sexually. When the mosquito punctures the skin to feed on blood, the protists enter the human bloodstream via their saliva.  How it is being prevented: Using insecticide coated insect nets while sleeping, removing stagnant water to prevent the vectors from breeding, travellers taking antimalarial drugs to kill parasites that enter the blood. Transmission of Pathogens Pathogens can be transmitted through two main routes: 1. Direct Contact: Pathogens can be transmitted from host to host through the transfer of blood, bodily fluids, or direct physical contact. Examples include: Touching contaminated surfaces or individuals. Sharing needles or syringes. Sexual contact. 2. Indirect Transmission: Pathogens can spread via contaminated surfaces, food, water, animals, or the air. Key examples include: Airborne transmission through respiratory droplets (coughing, sneezing). Foodborne illnesses from contaminated food or water. Vector-borne transmission (e.g., through insects like mosquitoes). Preventive Measures: To reduce the spread of disease, it is vital to: Prepare food hygienically. Properly treat and dispose of waste and sewage. Ensure access to clean water.  Maintain good personal hygiene practices (handwashing, sanitization). Defenses Against Infection The body employs various defenses against infection, categorized as the first line of defense and the immune response: First Line of Defense The first line of defense includes physical and chemical barriers designed to prevent pathogens from entering the body: Mechanical Barriers: Skin: Acts as a physical barrier, preventing pathogen entry. Hairs: Located in the nose, they trap pathogens and debris. Chemical Barriers: Mucus: Secreted in the respiratory and gastrointestinal tracts, it traps pathogens. Stomach Acid: Hydrochloric acid kills many pathogens ingested with food. Tears and Saliva: Contain enzymes (lysozymes) that can destroy bacteria. Immune Response If pathogens breach these barriers, the body mounts an immune response, which primarily involves white blood cells, including:  Phagocytes: These cells engulf and digest pathogens through a process called phagocytosis. Lymphocytes: These cells are involved in producing specific antibodies against pathogens. Antibodies and Antigens Antigens are specific proteins found on the surface of pathogens that trigger an immune response. Each type of pathogen has unique antigens. 1. Antibody Production: Lymphocytes, specifically B-cells, recognize these antigens and produce specific antibodies that bind to the antigens, forming an antibody-antigen complex. Each antibody has a unique shape that fits a specific antigen (lock and key mechanism). 2. Clumping and Destruction: When antibodies bind to antigens, they can cause pathogens to clump together, neutralizing them. Clumped pathogens can then be easily targeted and destroyed by phagocytes. Types of Immunity 1. Active Immunity: Definition: Immunity developed through the production of antibodies by the body.  How It Is Gained: Natural Infection: After recovering from an infection, the body retains memory cells for future protection. Vaccination: Introduction of a harmless form of the pathogen or its antigens to stimulate an immune response. Memory Cells: After the initial exposure to a pathogen, some B-cells remain as memory cells, allowing for a faster and more robust response if the same pathogen invades again. 2. Vaccination: Process: 1. A dead or attenuated (weakened) version of a pathogen or its antigens is administered. 2. The immune system responds by producing antibodies and memory cells. Herd Immunity: When a significant portion of the population is vaccinated, it reduces the spread of the disease, protecting those who cannot be vaccinated (e.g., individuals with certain medical conditions). Advantages of Vaccination Disadvantages of Vaccination They have eradicated many diseases They are not always effective in so far (e.g smallpox) and reduced the providing immunity. occurrence of many (e.g rubella). Epidemics (lots of cases in an area) Bad reactions (such as fevers) can can be prevented through herd occur in response to vaccines immunity. (although very rare). 3. Passive Immunity: Definition: Short-term immunity acquired by receiving antibodies from another individual.  Examples: Antibodies passed from mother to baby through breast milk, providing early protection against infections. Injection of antibodies from a donor (e.g., in certain treatments). Duration: Passive immunity does not produce memory cells, so it is temporary. Antibiotics and Painkillers Antibiotics are medicines that kill bacterial pathogens inside the body, without damaging body cells. They cannot kill viruses as they use body cells to reproduce, meaning any drugs that target them would affect body tissue too. Painkillers (such as aspirin) only treat the symptoms of the disease, rather than the cause.. Antibiotics can be taken as a pill, syrup or directly into the bloodstream. Different antibiotics are effective against different types of bacteria, so receiving the correct one is important. Their use has decreased the number of deaths from bacterial diseases. An example is Penicillin The great concern is that bacteria are becoming resistant to antibiotics.. Mutations can occur during reproduction resulting in certain bacteria no longer being killed by antibiotics. When these bacteria are exposed to antibiotics, only the non-resistant one die. The resistant bacteria survive and reproduce, meaning the population of resistant bacteria increases. This means that antibiotics that were previously effective no longer work To prevent the development of these resistant strains we can: 1. Stop overusing antibiotics- this unnecessarily exposes bacteria to the antibiotics 2. Finishing courses of antibiotics to kill all of the bacteria Plant Diseases Plants can also be affected by viral, bacterial and fungal pathogens. The common signs of plant diseases are:. Stunted growth: indicating nitrate deficiency. Spots on leaves: indicating black spot fungus on roses. Areas of decay: black spot fungus on roses, blights on potatoes. Abnormal growths: crown galls caused by bacterial infection. Malformed stems or leaves: due to aphid infestation. Discolouration: indicating magnesium deficiency, or tobacco mosaic virus. Pests on leaves: such as caterpillars lon deficiencies are a problem in plants. 1. Nitrate deficiency can stunt growth. Nitrates in the soil convert sugars made in photosynthesis into proteins. These proteins are needed for growth 2. Magnesium deficiency can cause chlorosis. Magnesium is needed to make chlorophyll. This pigment is green and is vital in photosynthesis. If less is being made then parts of the leaves appear green and yellow which is known as chlorosis Physical defences: To prevent the invasion of microorganisms. Tough waxy cuticle stops entry into leaves. Cellulose cell walls form a physical barrier into the cells  Plants have layers of dead cells around stems (such as bark) which stop pathogens entering. The dead cells fall off with the pathogens. Chemical defences: To deter predators or kill bacteria. Poisons (e.g from foxgloves, tobacco plants, deadly nightshades, yew) deter herbivores (organisms that eat plants). Antibacterial compounds kill bacteria, such as mint plant and witch hazel Mechanical defences. Thorns and hairs make it difficult and painful for animals to eat them (but do not defend against insects). Some leaves can droop or curl when touched which allows them to move away and move insects off their leaves. Mimicry to trick animals ❖ o Some plants droop to look like unhealthy plants so that animals avoid them ❖ o Plants can have patterns that appear to look like butterfly eggs, so butterflies do not lay their eggs here in order to avoid competition ❖ o Species from the 'ice plant family' have a stone and pebble like appearance in order to avoid predation Cholera Cholera is an infectious disease caused by the bacterium Vibrio cholerae, primarily transmitted through contaminated water.  1. Transmission: Cholera is ingested via food or water contaminated with the Vibrio cholerae bacteria. 2. Pathophysiology: Once the bacteria enter the small intestine, they adhere to the intestinal lining and release a toxin. This toxin stimulates the cells lining the intestine to secrete chloride ions into the intestinal lumen. The increase in chloride ions reduces the water potential in the lumen, leading to osmosis, where water moves from the cells (higher water potential) into the lumen (lower water potential). This results in significant water loss from the body, leading to diarrhea, characterized by severe watery stools. 3. Consequences: Loss of water and electrolytes can lead to dehydration, which is a critical condition that can result in death if not treated promptly. Symptoms: Include profuse watery diarrhea, vomiting, muscle cramps, and dehydration. Prevention and Treatment of Cholera Prevention: Ensure access to clean drinking water. Practice good sanitation and hygiene. Vaccination can be used in high-risk areas to provide protection against cholera. Treatment:  Rehydration Therapy: The primary treatment for cholera involves replenishing lost fluids and electrolytes, often using oral rehydration solutions (ORS) or intravenous fluids in severe cases. Antibiotics: May be administered in severe cases to reduce the duration and severity of the disease. Diseases and their causes: Cardiovascular disease. Diet containing lots of LDL (bad) cholesterol results in arteries becoming blocked, increasing blood pressure. Smoking damages the walls of arteries. Exercise lowers blood pressure, reducing strain on the heart Type 2 diabetes. Obesity affects the body's metabolism- fat molecules are released into the blood which can affect the cells uptake of sugar Liver and brain function. Alcohol causes fatty liver, which can lead to liver failure. Alcohol can damage nerve cells in the brain Lung disease and lung cancer. Smoking damages the cells in the lining of the lungs Pregnancy. Smoking and alcohol can cause many damaging effects on the unborn child Cancer Carcinogens such as ionising radiation can lead to cancers Cancer Cancer is the result of changes in cells that lead to uncontrollable growth and division, forming a tumour. This tumour may not be cancerous. They can be: 1. Benign- growths of cells contained in one place, usually within a membrane. Not cancerous. It grows until there is no more room. It does not invade other tissues. If it causes pressure or damage to an organ, it can be dangerou