Biology Notes 2024-2025 PDF

Biology notes 2024 Describe the characteristics of living organisms by defining the terms: Movement: An action by an organism or part of an organism causing a change of position or place. Most single-celled creatures and animals move about as a whole. Fungi and plants may make movement...

Biology notes 2024 Describe the characteristics of living organisms by defining the terms: Movement: An action by an organism or part of an organism causing a change of position or place. Most single-celled creatures and animals move about as a whole. Fungi and plants may make movements with parts of their bodies Respiration: The chemical reactions in cells that break down nutrient molecules and release energy for metabolism Most organisms need oxygen for this Sensitivity: The ability to detect or respond to changes in the internal and external environment Growth: A permanent increase in size and dry mass Even bacteria and single-celled creatures show an increase in size. Multicellular organisms increase the numbers of cells in their bodies, become more complicated and change their shape as well as increasing in size. Reproduction: The processes that make more of the same kind of organism Single-celled organisms and bacteria may simply keep dividing into two Multicellular plants and animals may reproduce sexually or asexually Excretion: The removal of the waste products of metabolism and substances in excess of requirements. Respiration and other chemical changes in the cells produce waste products such as carbon dioxide. Living organisms expel these substances from their bodies in various ways. Nutrition: The taking in of materials for energy, growth and development. Plants require light, carbon dioxide, water and ions. Animals need organic compounds and ions and usually need water. Organisms can take in the materials they need as solid food, as animals do, or they can digest them first and then absorb them, like fungi do, or they can build them up for themselves, like plants do. Animals, using readymade organic molecules as their food source, are called heterotrophs and form the consumer levels of food chains. Photosynthetic plants are called autotrophs and are usually the first organisms in food chains Species A species is a group of organisms that can reproduce to produce fertile offspring. To differentiate between organisms we need an internationally recognised means of identification For this we use bionomial nomenclature State that organisms can be classified into groups by the features that they share. Describe the binomial system of naming species as an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and species. He came up with the system we use today that groups organisms into Kingdom, Phylum, Class, Order, Family, Genus and Species Only the Genus and Species names are used for the name of the organism The binomial system of naming species is an internationally agreed system Organisms can be classified into groups by the features they share. These features must not change with the seasons or age of organism Explain that classification systems aim to reflect evolutionary relationships. Conservation: ○ Identifying different organisms in habitats which are being managed and in breeding programs Understanding evolutionary relationships: ○ Organisms which have many of the same feature are normally descended from common ancestors. The more features they share the more recently they separated from one another during evolution Have close communication between international scientists: ○ In the past organisms were grouped together based on morphology (shape/ form) and anatomy (parts of inside of their body). ○ This is because this was what the scientists could easily observe and measure. Explain that the sequences of bases in DNA are used as means of classification. DNA structure: ○ Closely-related organisms have very similar base sequences in their DNA because there has been less ‘evolutionary time’ for mutations to change this sequence. ○ Therefore that organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor Explain that organisms which share a more recent ancestor (are more closely related) have base sequences in DNA that are more similar than those that share only a distant ancestor. Organisms which share a more recent ancestor (more closely relate) have base sequences in DNA that are more similar than those that share only a distant ancestor Construct and use simple dichotomous keys based on easily identifiable features. State the main features used to place all organisms into one of the five kingdoms The first division of living things in the classification system is to put them into one of five kingdoms. Animals Plants Fungi Protoctists Prokaryotes Describe and compare the structure of a plant cell with an animal cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes, mitochondria, vacuoles Chloroplasts: Site of photosynthesis, containing chlorophyll for capturing light energy. Cytoplasm: A jelly-like material within the cell in which reactions occur. Cytoplasm is mostly water, with a variety of chemical substances dissolved in it (salts, sugars enzymes).The cytoplasm contains structures such as ribosomes and vesicles. Mitochondria: Found in the cytoplasm, aerobic respiration occurs here. Cells with high rates of metabolism require large amounts of mitochondria to provide sufficient energy. Cell membrane: A double layered membrane made of proteins and fats. It surrounds the cell, controls entry and exit of substances and it is selective in the molecules that can pass and those that cannot (selective permeability). Found throughout the entire cell. DNA: Genetic material in the form of DNA which codes for proteins. Rough endoplasmic reticulum (ER): They are a network of flattened, interconnected membranes. They connect cytoplasm with cell membrane. They are found throughout the cytoplasm. Ribosomes: In the cytoplasm, often attached to the ER. They are the site of protein synthesis (link amino acids together in correct sequence), and newly synthesised proteins pass from ribosomes to ER where folding occurs. Vacuoles: Large, fluid (sap) filled sac surrounded by a membrane (tonoplast). In the cytoplasm (large vacuoles more common in plant cells). Storage → Contains substances such as mineral salts, sugars and amino acids dissolved in water. Can also contain dissolved pigments. Support → Pushes outward on cytoplasm making cell firm or turgid Enzymes: Catalyze reactions in cells such as respiration. Cell Wall: Bacterial cells have a cell wall made of peptidoglycan, providing structural support and protection. Plasmids: Small, circular DNA molecules carrying extra traits. These traits can include: Nucleus: Large, spherical structure in cytoplasm. It is colourless and transparent. Most organisms have one nucleus per cell. It is the control centre of cell, contains chromosomes (DNA) - genetic information; controls cell reproduction; controls protein synthesis e.g. enzyme production. Vesicles: Vesicles are membrane-bound sacs that function in storage and transport. The membrane of a vesicle can fuse with the membranes of other cellular components. Animal cells Animal cells have: Cell membrane, cytoplasm, nucleus (with DNA), rough endoplasmic reticulum, ribosomes, vesicles, mitochondria Main features of all animals: they are multicellular their cells contain a nucleus but no cell walls or chloroplasts they feed on organic substances made by other living things State the main features used to place organisms into groups within the animal kingdom, limited to: VERTEBRATES AND ARTHROPODS Vertebrate types Features Examples Fish Loose, wet scales on skin. Manta ray, tuna, Gills to breathe whale shark Lay eggs without shells in water. Amphibians Smooth, moist skin Frogs, axolotl Adults usually live on land (so have lungs) Larvae live in water (so have gills) Lay eggs without shells in water Reptiles Dry, fixed scales on skin. Lizards, turtles, Lay eggs with rubbery shells on land. crocodiles Have lungs Birds Skin covered in feathers Parrots, chickens, Have two legs and two wings instead of owls forelimbs Lay eggs with hard shells on land Have a beak Endothermic Mammals Fur/hair on skin Dogs, cats, horses Have a placenta Young feed on milk from mammary glands External ears visible Give birth to live young Endothermic Anthropods a hard exoskeleton (their skeleton is on the outside rather than on the inside) a segmented body (their body has different sections) jointed legs Arthropods can be divided into different groups depending on how many legs they have. Anthropod types Features Examples Insects 3 part body (head, thorax Locust and abdomen) 3 pairs jointed legs 2 pairs of wings (1 or more might be small and underdeveloped) 1 pair antennae Arachnids 2 part body Spiders (cephalothorax and abdomen) 4 pairs of jointed legs No antennae Crustaceans More than 4 pairs of Crabs jointed legs Chalky exoskeleton formed from calcium Breathe through gills 2 pairs of antennae Myriapods Body consists of many Centipedes segments Each segment contains at least 1 pair of jointed legs 1 pair of antennae Plant cells Plant cells have: Cell membrane, cytoplasm, nucleus (with DNA), rough endoplasmic reticulum, ribosomes, vesicles, mitochondria, vacuole, cell wall, chloroplasts Main features of all plants: they are multicellular their cells contain a nucleus, chloroplasts and cellulose cell walls they all feed by photosynthesis Plant Kingdom Plants are autotrophs, and their classification into groups follows the sequence of evolution they went through to adapt on life on land. State the main features used to place organisms into groups within the plant kingdom, limited to ferns and flowering plants (dicotyledons and monocotyledons). Plant classifications Features Examples Ferns Have roots, stems, Tree ferns, horse tails, eagle ferm complex leaves and vascular tissue. Produce spores No thick cuticles so can only survive in shady, humid areas. Gametes swim through film of moisture to reach the site of fertilisation. Angiosperms Flowering plants. Roses, orchids, hydrangeas Plants with enclosed seeds. Two groups of angiosperms; monocotyledons and dicotyledons. Monocots vs dicots Monocots: The seeds of monocotyledons each contain one embryonic leaf (the ‘cotyledon’) Many monocotyledons have leaves with parallel veins and the parts of their flowers come in threes. Examples of monocotyledons include: palms orchids grasses Dicots: The seeds of dicotyledons each contain two embryonic leaves. Dicotyledons have leaves with branching veins, and the parts of their flowers come in fours or fives. Examples of dicotyledons include: buttercups dandelions oak tree Bacterial cells (prokaryotes) Main features of all prokaryotes: often unicellular cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria Protoctista cells Main features of all protoctista: most are unicellular but some are multicellular all have a nucleus, some may have cell walls and chloroplasts meaning some protoctists photosynthesise and some feed on organic substances made by other living things Fungi cells Main features of all fungi: usually multicellular cells have nuclei and cell walls not made from cellulose do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition State the features of viruses, limited to protein coat and genetic material. Where do viruses fit in the five-kingdom classification system? They do not show the typical features of living things. Unless they are inside a host cell they do not undergo respiration, nutrition or reproduction. Do they belong in a sixth kingdom? Great variation between different viruses although all have a protein coat and genetic materia (can be DNA or RNA or both). Comparing animal and plant cells Organelles Organelles are the subunit of a cell and consist of a group of functioning biomolecules. Biomolecule: A molecule produced by a living organism Organelles take part in the chemical reactions and interactions in the cellular processes of an organism. Specialised cells Neurones: Nerve cells conducts nerve impulses. The cell has long a fiber called an axon along which impulses travel, a fatty sheath which gives electrical insulation and a many branched ending which can connect to other cells. Root hair cells: In plants, root hair cells absorb water and minerals from the soil and store it until it can be passed into the vascular system. The root hair cell has a large extension (the root hair) to give it a large surface area for absorption and a large vacuole for storing the water. Red blood cells: RBCs transport oxygen. The cells have no nucleus, leaving more space for haemoglobin (a pigment which carries oxygen). They are very flexible, meaning they can be forced through narrow blood vessels. RBCs have a large surface area to ensure the efficient uptake of oxygen. Ciliated cells: Has a layer of tiny hairs (cilia) which can move and push mucus in the trachea and bronchi. The mucus can transport trapped dust and microbes when it is pushed by the cilia. Xylem Vessels: Transports water and supports the plant. The cell has no cytoplasm (so water can pass freely), no end wall (so many cell can form a continuous tube) and walls strengthened with a waterproof substance called lignin. Palisade mesophyll cells: The site of photosynthesis in plants. Tall, thin cells arranged in columns and separated by very narrow air spaces. Cells contain many chloroplasts, and densely packing of cells allow for the absorption of the maximum amount of light energy. Sperm and egg cells: Sperm: Are motile, have flagellum that beat to move towards ovum. Small Egg: Much larger Do not move, have large food store. Describe the meaning of the terms: cell, tissue, organ, organ system and organisms as illustrated by examples given in the syllabus. A system that is based on different levels of organisation in which each level of organisation forms part of the next higher level is called a hierarchy. Multicellular organisms have a specific hierarchical structure to ensure each cell meets its requirements. Cells: Cells are the basic building blocks of living things. Cells consist of organelles supported in cytoplasm, a dense fluid that has many different molecules dissolved in solution. The average number of cells in a human body is 37 trillion. Cells convert nutrients into energy, they undergo cell division and carry out specialised functions. Tissues: A tissue is a group of cells with similar structures, working together to perform a shared function. There are four types of tissue in the human body: nervous, muscle, connective, and epithelial tissues. Organs: An organ is a structure made up of a group of tissues, working together to perform specific functions. Organ Systems: A group of organs working together to perform bodily functions form organ systems. Examples are the circulatory system in animals, and the vascular system in plants. The organs in an organ system are interdependent, i.e. they work in harmony to carry out various body functions. ○ Example: digestive system State and use the formula: magnification = image size / actual size Calculate magnification and size of biological specimens using millimeters as units Convert measurements between millimeters (mm) and micrometers Magnification = image size / actual size μm = mm x 1000 Cells are often measured in micrometres (µm). Always measure the image size in mm with your ruler, then multiply this by 1000 to convert the measurement to µm. Describe diffusion as the net movement of particles from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement. Solute: A substance dissolved in a fluid (the solvent) Solvent: a fluid in which the substance (the solute) is dissolved. Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration Molecules move down a concentration gradient, as a result of their random movement For living cells, the principle of the movement down a concentration gradient is the same, but the cell is surrounded by a cell membrane which can restrict the free movement of the molecules State that substances move into and out of cells by diffusion through the cell membrane. The cell membrane is a partially permeable membrane - this means it allows some molecules to cross easily, but others with difficulty or not at all The simplest sort of selection is based on the size of the molecules Describe the importance of diffusion of gases and solutes in living organisms. ○ obtain many of their requirements ○ get rid of many of their waste products ○ carry out gas exchange for respiration Simple diffusion Solute molecules can only diffuse across a membrane if that membrane is permeable to them There is a constant movement of solute molecules backwards and forwards across the membrane If there is a concentration difference there will be a net movement in one direction If there is no concentration difference there will be no net movement of substances Examples of diffusion in living organsims Plants require oxygen for respiration at all times, as well as carbon dioxide for photosynthesis when conditions for photosynthesis are right (e.g. enough light and a suitable temperature) State that the energy for diffusion comes from the kinetic energy of random movement of molecules and ions. All particles move randomly at all times This is known as Brownian motion The energy for diffusion comes from the kinetic energy of this random movement of molecules and ions Investigate the factors that influence diffusion, limited to surface area, temperature, concentration gradient and distance. Concentration gradient: the greater the difference, the faster the rate of diffusion. Temperature: heat increases rate of diffusion because kinetic energy of particles speeds up. Particle size: the smaller the particles, the faster the rate of diffusion. Surface area: greater surface area means greater total diffusion for a cell. Distance: the shorter the travel distance, the faster the diffusion rate (eg. thin membranes in the lungs for oxygen and carbon dioxide to pass quickly). When equilibrium is reached the molecules continue to move randomly but do not move in any particular direction. In other words, there is no net movement in any particular direction. Cell adaptions for diffusion The highly folded surface of the small intestine increases its surface area Explain the effects on plant tissues of immersing them in different solutions by using the terms turgid, turgor pressure, plasmolysis and flaccid. Turgor pressure: A plant with a vacuole pushing out on the cell wall is said to be turgid and the vacuole is exerting turgor pressure on the inelastic cell wall. Turgid: If all the cells in a stem and leaf are turgid, the stem will be firm and upright and the leaves held out straight. Flaccid: If vacuoles lose water, the cells will lose their turgor and become flaccid. If a plant has flaccid cells, the leaves will be limp and the stem will droop. This plant is said to be wilting. Plasmolysis: After plant cells become flaccid, if the conditions continue plant cells become plasmolysed. 1. When the solution outside the cell is more concentrated than the cell sap. 2. Water diffused out of the vacuole. 3. The vacuole shrinks, pulling the cytoplasm away from the cell wall, leaving the cell flaccid. Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport. Water is important for all living organisms as many substances are able to dissolve in it (it is a solvent) This makes it incredibly useful and essential for all life on Earth Water is important as a solvent in the following situations within organisms: ○ Dissolved substances can be easily transported around organisms - eg xylem and phloem of plants and dissolved food molecules in the blood ○ Digested food molecules are in the alimentary canal but need to be moved to cells all over the body- without water as a solvent this would not be able to happen ○ Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to excrete in urine ○ Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells State that water diffuses through partially permeable membranes by osmosis. Describe osmosis as the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane. State that water moves in and out of cells by osmosis through the cell membrane. All cells are surrounded by a cell membrane which is partially permeable Water can move in and out of cells by osmosis Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane In doing this, water is moving down its concentration gradient The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules) ○ Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane Osmosis experiments  The most common osmosis practical involves cutting cylinders of root vegetables such as potato or radish and placing them into distilled water and sucrose solutions of increasing concentration The cylinders are weighed before placing into the solutions They are left in the solutions for 20 - 30 minutes and then removed, dried to remove excess liquid and reweighed Potatoes are usually used in osmosis experiments to show how the concentration of a solution affects the movement of water, but radishes can be used too If the plant tissue gains mass: ○ Water must have moved into the plant tissue from the solution surrounding it by osmosis ○ The solution surrounding the tissue is more dilute than the plant tissue (which is more concentrated) If plant tissue loses mass: ○ Water must have moved out of the plant tissue into the solution surrounding it by osmosis ○ The solution surrounding the tissue is more concentrated than the plant tissue (which is more dilute) If there is no overall change in mass: ○ There has been no net movement of water as the concentration in both the plant tissue and the solution surrounding it must be equal ○ Remember that water will still be moving into and out of the plant tissue, but there wouldn’t be any net movement in this case Investigating osmosis using dialysis tubing  Dialysis tubing (sometimes referred to as visking tubing) is a non-living partially permeable membrane made from cellulose Pores in this membrane are small enough to prevent the passage of large molecules (such as sucrose) but allow smaller molecules (such as glucose and water) to pass through by diffusion and osmosis This can be demonstrated by: ○ Filling a section of dialysis tubing with concentrated sucrose solution ○ Suspending the tubing in a boiling tube of water for a set period of time ○ Noting whether the water level outside the tubing decreases as water moves into the tubing via osmosis Water moves from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane Water potential The water potential of a solution is a measure of whether it is likely to lose or gain water molecules from another solution. A dilute solution, with its high proportion of free water molecules, is said to have a higher water potential than a concentrated solution, because water will flow from the dilute to the concentrated solution (from a high potential to a low potential). Pure water has the highest possible water potential because water molecules will flow from it to any other aqueous solution, no matter how dilute. Explain the importance of water potential and osmosis in the uptake of water by plants. When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall Water entering the cell by osmosis makes the cell rigid and firm This is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant - making the plant stand upright with its leaves held out to catch sunlight The pressure created by the cell wall stops too much water entering and prevents the cell from bursting If plants do not receive enough water the cells cannot remain rigid and firm (turgid and the plant wilts) Animal cells also lose and gain water as a result of osmosis As animal cells do not have a supporting cell wall, the results on the cell are more severe If an animal cell is placed into a strong sugar solution (with a lower water potential than the cell), it will lose water by osmosis and become created (shriveled up) Investigate and describe the effects on plant tissues of immersing them in solutions of different concentrations. When plant cells are placed in a solution that has a higher water potential (dilute solution) than inside the cells (e.g. distilled water) then water moves into the plant cells via osmosis These water molecules push the cell membrane against the cell wall, increasing the turgor pressure in the cells which makes them turgid When plant cells are placed in a concentrated solution (with a lower water potential than inside the cels) water molecules will move out of the plant cells by osmosis, making them flaccid If plant cells become flaccid it can negatively affect the plant's ability to support itself If looked at underneath the microscope, the plant cells might be plasmolysed, meaning the cell membrane has pulled away from the cell wall Animal cells in solutions of different concentrations If an animal cellis placed into distilled water (with a higher water potential than the cell), it will gain water by osmosis and, as it has no cell wall to create turgor pressure, will continue to do so until the cell membrane is stretched too far and it bursts Describe active transport as movement of particles through the cell membrane from a region of lower concentration to a region of higher concentration (i.e against a concentration gradient) using energy from respiration. Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration Explain the importance of active transport as a process for movement across membranes, including ion uptake by root hairs Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion) Active transport is vital process for the movement of molecules or ions across membranes Including: ○ Uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron ○ Uptake of ions from soil water by root hair cells in plants State that protein carriers move molecules or ions across a membrane during active transport. Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient: 1. Substance combines with carrier protein molecule in the cell membrane 2. Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane 3. Substance released into cell List the chemical elements that make up: carbohydrates, fats, proteins State that large molecules are made from smaller molecules, limited to: starch and glycogen and cellulose from glucose proteins from amino acids fats and oils from fatty acids and glycerol. Carbohydrates Long chains of simple sugars Glucose is a simple sugar (a monosaccharide) When 2 glucose molecules join together maltose is formed (a disaccharide) When lots of glucose molecules join together starch, glycogen or cellulose can form (a polysaccharide) Glycogen, cellulose and starch are all made from glucose molecules Fats Most fats (lipids) in the body are made up of triglycerides Their basic unit is 1 glycerol molecule chemically bonded to 3 fatty acid chains The fatty acids vary in size and structure Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature) Structure of a triglyceride Proteins Long chains of amino acids There are about 20 different amino acids They all contain the same basic structure but the ‘R’ group is different for each one When amino acids are joined together a protein is formed The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins Even a small difference in the order of the amino acids results in a different protein being formed General amino acid structure Amino acids join together to form proteins DNA Structure DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organisms It consists of two strands of DNA wound around each other in what is called a double helix Composed of multiple genes A gene is a segment of a DNA molecules The long strands of DNA are wrapped around histone proteins to form a large chromosome structure The individual units of DNA are called nucleotides  All nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G) The nitrogenous bases on each strand pair up with each other, holding the two strands of DNA in the double helix The nitrogenous bases always pair up in the same way (held together by hydrogen bonds): ○ Adenine always pairs with Thymine (A-T) ○ Cytosine always pairs with Guanine (C-G) DNA Base Pairs The phosphate and sugar section of the nucleotides form the 'backbone' of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder ○ The base pairs stick to a sugar and the sugar sticks to a phosphate It is this sequence of bases that holds the code for the formation of proteins Importance of water in a solvent Water is important as a solvent in the following situations within organisms: Dissolved substances can be easily transported around organisms - eg. xylem and phloem of plants and dissolved food molecules in the blood Digested food molecules are in the alimentary canal but need to be moved to cells all over the body - without water as a solvent this would not be able to happen Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells Testing for starch: Iodine Testing for carbohydrates: benedict’s test Test for protein: Biuret test Test for lipids: Emulsion test Testing for Vitamin C Enzymes Catalyst: A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction. Enzyme: An enzyme is a protein that functions as a biological catalyst. Without enzymes, some reactions simply would not occur or would run too slowly to sustain life. For example, without enzymes, digestion would be impossible. Enzymes are specific to one particular substrate (molecule/s that get broken down or joined together in the reaction) as the enzyme is a complementary shape to the substrate) The product is made from the substrates and is released  Enzymes can build larger molecules and enzymes can break down molecules. The enzyme brings the substances closer together and makes the reaction happen much more rapidly. Summary: An enzyme attracts substrates to its active site, catalyses the chemical reaction by which products are formed, and then allows the products to dissociate (separate from the enzyme surface). The combination formed by an enzyme and its substrates is called the enzyme-substrate complex. Enzymes that were discovered early were given general names which they are still used as pepsin, trypsin, cathepsin, emulsin, etc… Now a suffix (ase) is added to indicate enzyme. The prefix may be: Name indicating the general nature of substrate e.g.: protease, lipase etc… The real name of the substrate: urease, lactase, sucrase. Type of reaction catalysed e.g.: dehydrogenase What is pH? pH is the measure of the amount of acidity or alkalinity that is in a solution. The pH scale describes the relative acidity or alkalinity of a solution. Enzyme action and specificity Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate This is because the enzyme is a protein and has a specific 3-D shape This is known as the lock and key hypothesis When the substrate moves into the enzyme's active site they become known as the enzyme-substrate complex After the reaction has occurred, the products leave the enzyme's active site as they no longer fit it and it is free to take up another substrate 1. Enzymes and substrates randomly move about in solution 2. When an enzyme and its complementary substrate randomly collide - with the substrate fitting into the active site of the enzyme - an enzyme-substrate complex form, and the reaction occurs. 3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyse further reactions. Enzymes and temperature  nzymes are proteins and have a specific shape, held in place by bonds E This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed Enzymes work fastest at their 'optimum temperature' ○ in the human body, the optimum temperature is 37°C Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation Substrates cannot fit into denatured enzymes as the shape of their active site has been lost Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop Effect of temperature on enzyme activity Increasing the temperature from 0 degrees celsius to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading the a faster rate of reaction This means that low temperatures do not denature enzymes, they just make them work more slowly Enzymes and pH The optimum pH for most enzymes is 7, but some are produced in acidic conditions (eg. the stomach) have a lower optimum pH (2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (8 or 9) If the pH is too high or too low, the bonds that hold the amino acid chain together make up the protein can be destroyed This will change the shape of the active site, so the substrate can no longer fit into is, reducing the rate of activity Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop Plants need food Plants require raw materials for building tissues and as a source of energy. They manufacture everything they need out of simple ions and compounds available in the environment. They build up more complex molecules from simpler ones using enzymes. Photosynthesis Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water At the same time oxygen is made and released as a waste product The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light It can be summed up in the following equation: Balanced Equation Chlorophyll Chlorophyll is a green pigment that is found in chloroplasts within plant cells ○ It reflects green light, giving plants their characteristic green colour Chlorophyll absorbs light energy; its role is to transfer energy from light into energy in chemicals, for the synthesis of carbohydrates, such as glucose ○ Photosynthesis will not occur in the absence of chlorophyll Use and storage of carbohydrates How are the products of photosynthesis used? The carbohydrates produced by plants during photosynthesis can be used in the following ways: ○ Converted into starch molecules which act as an effective energy store ○ Converted into cellulose to build cell walls ○ Glucose can be used in respiration to provide energy ○ Converted to sucrose for transport in the phloem ○ As nectar to attract insects for pollination Plants can also convert the carbohydrates made into lipids for an energy source in seeds and into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots Minerals in plants Photosynthesis produces carbohydrates, but plants contain many other types of biological molecule; such as proteins, lipids and nucleic acid (DNA) As plants do not eat, they need to make these substances themselves Carbohydrates contain the elements carbon, hydrogen and oxygen but proteins, for example, contain nitrogen as well (and certain amino acids contain other elements too) Other chemicals in plants contain different elements as well, for example chlorophyll contains magnesium and nitrogen This means that without a source of these elements, plants cannot photosynthesise or grow properly Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells ‘Mineral’ is a term used to describe any naturally occurring inorganic substance Limiting Factors: Extended If a plant is given unlimited sunlight, carbon dioxide and water and is at a warm temperature, the limit on the rate (speed) at which it can photosynthesise is its own ability to absorb these materials and make them react However, most often plants do not have unlimited supplies of their raw materials so their rate of photosynthesis is limited by whatever factor is the lowest at that time So a limiting factor can be defined as something present in the environment in such short supply that it restricts life processes There are three main factors which limit the rate of photosynthesis: ○ Temperature ○ Light intensity ○ Carbon dioxide concentration Although water is necessary for photosynthesis, it is not considered a limiting factor as the amount needed is relatively small compared to the amount of water transpired from a plant so there is hardly ever a situation where there is not enough water for photosynthesis Temperature As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases Light intensity The more light a plant receives, the faster the rate of photosynthesis This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough carbon dioxide. Carbon dioxide concentration Carbon dioxide is one of the raw materials required for photosynthesis This means the more carbon dioxide that is present, the faster the reaction can occur This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough light Leaf structure and adaptations for photosynthesis Pathway of carbon dioxide from the atmosphere to chloroplasts by diffusion: atmosphere → air spaces around spongy mesophyll tissue → leaf mesophyll cells → chloroplast Identify Leaf Structures Balanced Diet A balanced diet consists of all of the food groups in the correct proportions The necessary key food groups are: ○ Carbohydrates ○ Proteins ○ Lipids ○ Dietary Fibre ○ Vitamins ○ Minerals (mineral ions) ○ Water Malnutrition Having an unbalanced diet can lead to malnutrition Malnutrition can cause a variety of different health problems in humans Starvation = Undernutrition. It causes: Wasting: low weight for height Stunting: low height for age - holds children back from reaching their physical and cognitive potential Underweight: low weight for age Deficiencies in vitamins and minerals. Undernutrition makes children in particular much more vulnerable to disease and death. In developing countries, many people have diets which are neither adequate nor balanced. They often have shortages of iron (anaemic), vitamin C (scurvy) and more. The most obvious signs of malnutrition in these people is a deficiency of protein. Two extremes of protein deficiency are kwashiorkor and marasmus. Protein deficiency: Kwashiorkor Diet high in carbohydrate but poor in protein, not getting enough energy. Mental and physical development maybe impaired. Slow muscle development & swollen liver (inadequate supply of amino acids to make proteins). Swollen abdomen due to water from the blood left behind in body tissues. Protein deficiency: Marasmus Child has the symptoms of general starvation- not enough energy nor protein. All body tissues waste away. Child becomes very thin with wrinkled skin. Scurvy Scurvy is the name for a severe vitamin C deficiency ○ It is caused by a lack of vitamin C in the diet for over 3 months Its symptoms include: ○ Anemia ○ Exhaustion ○ Spontaneous bleeding ○ Pain in the limbs ○ Swelling ○ Gum ulcerations ○ Tooth loss It is a condition that was commonly seen in sailors between the 15th to 18th centuries ○ Long sea voyages made it very hard to access a ready supply of fresh produce Scurvy can be treated with oral or intravenous vitamin C supplements Rickets Rickets is a condition in children characterised by poor bone development Symtpoms include: ○ Bone pain ○ Lack of bone growth ○ Soft, weak bones (sometimes causing deformities) Rickets is caused by a severe lack of vitamin D ○ Vitamin D is required for the absorption of calcium into the body Calcium is a key component of bones and teeth Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish, eggs and butter) The treatment for rickets is to increase consumption of foods containing calcium and vitamin D ○ Alternatively vitamin D supplements can be prescribed Iron deficiency: Anaemia Cause: Too little iron in the diet, loss of blood, pregnancy Effects: Not enough iron leads to deficient hemoglobin. Hemoglobin is a protein that carries oxygen in red blood cells. Not enough healthy red blood cells. Less iron means less oxygen in cells → tiredness, exhaustion Pale skin, dizziness, lightheadedness Treatment includes iron supplements. Pregnancy A pregnant woman who is already receiving an adequate diet needs no extra food. Her body’s metabolism will adapt to the demands of the growing baby although the demand for energy and protein does increase. If her diet is deficient in protein, calcium, iron, vitamin D or folic acid, she will need to increase her intake of these substances to meet the needs of the baby. The baby needs protein for making its tissues, calcium and vitamin D are needed for bone development, and iron is used to make the haemoglobin in its blood. Lactation ‘Lactation’ means the production of breast milk for feeding the baby. The production of milk, rich in proteins and minerals, makes a large demand on the mother’s resources. If her diet is already adequate, her metabolism will adjust to these demands. Otherwise, she may need to increase her intake of proteins, vitamins and calcium to produce milk of adequate quality and quantity. Sources and Functions of Dietary Elements Dietary Needs of Individuals The nutritional requirements for individuals will vary throughout their lifetime An individual will still require the same key food groups, but in different quantities depending on a number of factors such as age, height, sex, activity levels, pregnancy and breastfeeding The digestive system The digestive system is an example of an organ system Some of the digestive system organs make up the alimentary canal; food passes directly through these organs as it moves through the body: ○ mouth ○ oesphagus ○ stomach ○ small intestine, including the duodenum and the ileum ○ large intestine, including the colon, rectum and anus Some of the organs of the digestive system do not form part of the route travelled by food, but are still involved with digestion; these are the associated organs, or accessory organs, and include the: ○ salivary glands ○ pancreas ○ liver ○ gall bladder Digestive system: function The function of the digestive system is to digest food and absorb nutrients The digestive system carries out its function in several stages: ○ ingestion: food and drink are taken into the body through the mouth ○ mechanical digestion: food is broken down into smaller pieces without chemical change to the food molecules ○ chemical digestion: large, insoluble molecules are broken down into small, soluble molecules ○ absorption: small food molecules and ions move through the wall of the intestine into the blood ○ egestion: food that has not been digested or absorbed passes out of the body as faeces Once nutrients have been absorbed into the blood by the digestive system they can be assimilated into the body; this occurs when they are taken up by the cells of the body Physical Digestion Physical digestion (sometimes referred to as mechanical digestion) is the breakdown of food into smaller pieces without chemical change to the food molecules The processes that take place during physical digestion help to increase the surface area of food for the action of enzymes during chemical digestion It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum Types of Human Teeth Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum Teeth are held firmly in the bone of the jaw ○ They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly The differing shapes and sizes of teeth enable them to perform slightly different functions: ○ Incisors - chisel-shaped for biting and cutting ○ Canines - pointed for tearing, holding and biting ○ Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and grinding up food Teeth hygiene Tooth decay begins when bacteria in your mouth make acids that attack the tooth's surface (enamel). Tooth decay happens when bacteria in your mouth feed on sugars and produce acids. These acids erode the enamel, creating cavities. If plaque, the sticky film of bacteria, isn't cleaned away, the acid can damage the tooth further, leading to deeper decay. Plaque is a soft, sticky film of bacteria that forms on teeth. It develops when bacteria in your mouth feed on sugars and starches from food. If not removed through regular brushing and flossing, plaque can harden into tartar and contribute to tooth decay and gum disease. Don’t consume too much sweets or foods high in sugar and starches and brush your teeth twice a day with toothpaste containing fluoride to avoid the build up of plaque and bacteria. The Stomach The stomach is one of a number of organs that make up the digestive system The role of the digestive system is to break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients The stomach lining contains muscles which contract to physically squeeze and mix the food with the strong digestive juices that are present ○ Also known as "stomach churning" Food is digested within the stomach for several hours Emulsification of Fats & Oils: Extended Cells in the liver produce bile which is then stored in the gallbladder Bile has two main roles: It is alkaline to neutralise the hydrochloric acid which comes from the stomach The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster Stages of food breakdown Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut): ○ Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth ○ Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules ○ Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules ○ Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood ○ Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells ○ Egestion - the passing out of food that has not been digested or absorbed, as faeces, through the anus The role of chemical digestion is to produce small soluble molecules that can be absorbed Enzymes in Digestion Amylases Amylases are produced in the mouth and the pancreas (secreted into the duodenum) Amylases digest starch into smaller sugars Proteases Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas) Lipases Lipase enzymes are produced in the pancreas and secreted into the duodenum They digest lipids into fatty acids and glycerol Hydrochloric Acid The stomach produces several fluids which together are known as gastric juice One of the fluids produced is hydrochloric acid This kills bacteria in food and gives an acid pH for enzymes to work in the stomach How is a low pH helpful in the stomach? The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH - around pH 2 The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate Digestion of Starch: Extended Amylases are produced in the mouth and the pancreas (secreted into the duodenum) Amylases digest starch into smaller sugars Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas) and digests starch to maltose (a disaccharide) Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium lining of the small intestine Digestion of Protein: Extended Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas) The digestion of proteins Protein digestion takes place in the stomach and duodenum with two main enzymes produced: ○ Pepsin is produced in the stomach and breaks down protein in acidic conditions ○ Trypsin is produced in the pancreas and secreted into the duodenum where is breaks down protein in alkaline conditions Cells in the liver produce bile which is then stored in the gallbladder Bile production and secretion Bile has two main roles: It is alkaline to neutralise the hydrochloric acid which comes from the stomach The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster Absorbing Nutrients Absorption is the movement of digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol) Nutrients are absorbed in the small intestine Absorbing Water Water is absorbed in both the small intestine and the colon, but most absorption of water (around 80%) happens in the small intestine Adaptations of the Small Intestine: Extended The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger like projections) These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently Adaptations of the small intestine Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients Wall of the villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport Well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph Transport in plants What is the function of the xylem and phloem Plants contain two types of transport vessel: ○ Xylem vessels – transport water and minerals (pronounced: zi-lem) from the roots to the stem and leaves ○ Phloem vessels – transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem (pronounced: flow-em) These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles Function: transport tissue for water and dissolved mineral ions Adaptations: ○ Cells joined end to end with no cross walls to form a long continuous tube ○ Cells are essentially dead, without cell contents, to allow free passage of water ○ Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant Xylem diagram Root Hair Cells Root hairs are single-celled extensions of epidermis cells in the root They grow between soil particles and absorb water and minerals from the soil Water enters the root hair cells by osmosis This happens because soil water has a higher water potential than the cytoplasm of the root hair cell Structure of the root The root hair increases the surface area of the cells significantly This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport Pathway Taken by Water Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels: Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells So the pathway is: root hair cell → root cortex cells → xylem → leaf mesophyll cells Investigating Water Movement in Plants The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well) After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem - these are the xylem vessels Transpiration Water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata Xylem is adapted in many ways: ○ A substance called lignin is deposited in the cell walls which causes the xylem cells to die ○ These cells then become hollow (as they lose all their organelles and cytoplasm) and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots ○ Lignin strengthens the plant to help it withstand the pressure of the water movement Movement in xylem only takes place in one direction - from roots to leaves (unlike phloem where movement takes place in different directions) Transpiration in plants Transpiration has several functions in plants: ○ transporting mineral ions ○ providing water to keep cells turgid in order to support the structure of the plant ○ providing water to leaf cells for photosynthesis ○ keeping the leaves cool (the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The using up of heat to convert water into water vapour helps to cool the plant down) Investigating the role of environmental factors in determining the rate of transpiration from a leafy shoot Cut a shoot underwater to prevent air entering the xylem and place in tube Set up the apparatus as shown in the diagram and make sure it is airtight, using vaseline to seal any gaps Dry the leaves of the shoot (wet leaves will affect the results) Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water Set up the environmental factor you are investigating Allow the plant to adapt to the new environment for 5 minutes Record the starting location of the air bubble Leave for a set period of time Record the end location of air bubble Change the wind speed or temperature (only one - whichever factor is being investigated) Reset the bubble by opening the tap below the reservoir Repeat the experiment The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa  Environmental factors can be investigated in the following ways: ○ Temperature: Temperature of room (cold room and warm room) As temperature increases, the rate of transpiration also increases ○ Wind speed: Use an electric fan to mimic different wind speeds As wind speed increases, the rate of transpiration also increases Water Vapour Loss: Extended Evaporation takes place from the surfaces of spongy mesophyll cells The many interconnecting air spaces between these cells and the stomata create a large surface area This means evaporation can happen rapidly when stomata are open Transpiration Stream: Extended Water molecules are attracted to each other by cohesion - creating a continuous column of water up the plant Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker Explaining the Effects of Temperature, Wind Speed & Humidity: Extended Wind speed, humidity and temperature all have an effect on the rate at which transpiration occurs The table below explains how these factors affect the rate of transpiration when they are all high; the opposite effect would be observed if they were low A potometer can be used to investigate the effect of environmental factors on the rate of transpiration Wilting: Extended If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse A wilted plant cannot support itself and starts to collapse Translocation: Extended The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids These are transported around the plant in the phloem tubes which are made of living cells (as opposed to xylem vessels which are made of dead cells) The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next The transport of sucrose and amino acids in the phloem, from regions of production to regions of storage or use, is called translocation Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from the source (where it’s made) to sink (where it’s stored or used): During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue During a growth period (eg during the spring), the storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks After the plant has grown (usually during the summer), the leaves are photosynthesizing and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again Comparison between Xylem and Phloem Tissue Table