IGCSE Biology Revision PDF

Biology B1: Characteristics of Living Organisms Characteristics of Living Organisms: MRS GREN: ​ Movement: an action by an organism or part of an organism causing a change of position or place. ​ Respiration: the chemical reactions in living cells that break down nutrient molecule...

Biology B1: Characteristics of Living Organisms Characteristics of Living Organisms: MRS GREN: ​ Movement: an action by an organism or part of an organism causing a change of position or place. ​ Respiration: the chemical reactions in living cells that break down nutrient molecules and release energy for metabolism. There are two types: aerobic and anaerobic. ​ Sensitivity: the ability to detect and sense stimuli in the internal or external environment and make appropriate responses. ​ Growth: a permanent increase in size and dry mass by an increase in number of cells, cell size, or both. ​ Reproduction: the processes that make more of the same kind of organism. There are two types: sexual and asexual. ​ Excretion: the removal from organisms of the waste products of metabolism, toxic materials and substances in excess of requirements. ​ Nutrition: the taking in of materials for energy, growth, and development B2: Cells B2.1 Cell Structures ​ All living things are made of cells. ​ New cells are produced by the division of existing cells Cell structures: ​ Organelles: small, organised and specialised structures that do the work of the cells ​ Cell Membrane: a thin layer of protein and fat that holds cells together and controls movement of substances in and out of cells-partially permeable. It also recognizes signals from other cells and allows communication. ​ Cytoplasm: a jelly-like substance enclosed by the cell membrane which supports cell structures and organelles (holding them in place), and is where chemical reactions take place. ​ Nucleus: stores DNA in chromosomes and controls the cell. ​ Mitochondria: where aerobic respiration happens-provides energy for the cell. ​ Ribosome: tiny structures in the cytoplasm which allow protein synthesis ​ Rough Endoplasmic reticulum: its surface is studded with ribosomes and acts as a transport network for proteins. ​ Smooth Endoplasmic reticulum: synthesises membrane components and helps detoxify the cell. On top of this, plant cells also have: ​ Vacuole: stores cell sap to keep cell turgid ​ Cell Wall: rigid to hold the shape of the cell, strengthens the cell ​ Chloroplasts: contain chlorophyll, which absorbs light energy for photosynthesis (site of photosynthesis) Levels of Organisation: ​ Cells: The basic functional and structural units in a living organism- the building blocks of life. ​ Tissue: Groups of cells with similar structures working together to perform the same function ​ Organ: Group of tissues working together to perform a specific function ​ Organ system: Group of organs with related functions working together to perform body functions. ` Specialised Cells: ​ Specialised Cells have Specific Functions. ​ Differentiation: a process by which cells develop the structure and characteristics needed to be able to carry out their functions. Specialised Specific Function Adaptation Cells Ciliated cells Movement of mucus in Extension of the the trachea and bronchi cytoplasm at the surface of the cell to form hair-like structures called cilia, which beat to move mucus and trapped particles up to the throat. Root Hair cells Absorption of water Walls are thin to ensure and mineral ions from water moves through soil quickly and surface area is large. Palisade Increase Column shaped to Mesophyll cell photosynthesis maximise sunlight absorption and compact to fit many in the upper layer of leaf. Contains many chloroplasts. Nerve Cells Conduction of electrical Long so that nerves can run to and from different (Neurones) impulses parts of the body to the central nervous system. The cell has extensions and branches to communicate with other nerve cells, muscles and glands. The axon is covered with a fatty sheath which insulates the nerve cell and speeds up nerve impulses. Red Blood cells Transport of oxygen Biconcave disc shape increases surface area for more efficient diffusion of oxygen and no nucleus to increase the amount of space available for oxygen transport. Sperm and Egg For reproduction (Sperm) Head contains cells (gametes) genetic material for fertilisation and digestive enzymes to penetrate eggs. The mid-piece is packed with mitochondria to release energy to swim, while the tail enables it to swim.  Magnification Magnification=Image(drawing) size ÷ actual size Other Forms in Magnification Formula ​ Actual size = image size / magnification ​ Image size = magnification x actual size ​Unit Conversions (μm - micrometre) ​ 1cm = 10mm ​ 1mm = 1000μm B2.2 Movement In and Out of Cells ​ Diffusion: Net movement of molecules 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. ​ Does not require energy→passive transport ​ Instead, energy for diffusion comes from the kinetic energy of random movement of molecules and ions. ​ Concentration gradient: the difference in concentrations of molecules in 2 areas ​ Diffusion moves materials from a higher concentration to a lower concentration “down” the gradient until an equal concentration is reached → equilibrium ​ Substances move into and out of cells by diffusion through the cell membrane ​ The kinetic energy in particles causes them to move randomly and spread. Smaller atoms or atoms with more energy move faster. Practical application: ​ Diffusion in animals→Oxygen diffuses into the blood capillaries from the lungs while carbon dioxide diffuses out of the blood. ​ Diffusion in plants→Carbon dioxide is a reactant in photosynthesis and diffuses into the leaf through the stomata because the concentration of CO2 in the leaf is lower than the air outside. Oxygen is a product of photosynthesis and diffuses out of the leaf through the stomata because the O2 concentration in the leaf is higher than the air outside. Factors affecting Diffusion: ​ Temperature ​Higher temperature→More kinetic energy→Faster diffusion ​ Surface area ​Larger surface area→More space for molecules to move through→Faster diffusion ​ Distance ​Shorter diffusion distance→Faster diffusion ​ Size of molecule ​Smaller size/mass→Less collisions→Faster diffusion ​ Osmosis: the net movement of water molecules from a region of high water potential (dilute solution) to a region of low water potential (concentrated solution) through a partially permeable membrane. ​Partially permeable means it allows small molecules through but not large molecules. ​Water potential refers to the concentration of water molecules. ​NO ENERGY REQUIRED→Passive transport ​Aquaporin: water channel proteins that allow large movement of water ​Cell survival depends on balancing water uptake and water loss Osmosis in Plant Tissues: ​ When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall, making the cell rigid and firm. This is important for plants as all the cells in a plant  being firm provides support and strength for the plant – making the plant stand upright with its leaves held out to catch sunlight. If plants do not receive enough water the cells cannot remain rigid and firm and the plant wilts ​ Plant cells that are full of water have a high turgor pressure, which is the outward pressure of the cytoplasm on the cell wall. ​Turgid cell: full of water, tight, firm, cell wall is strong and maintains the cell shape. ​Flaccid cell: Cytoplasm has shrunk and stops pushing on the cell wall, floppy ​ This pressure created by the cell wall prevents any more water entering the cell by osmosis, even if it is in a solution that has a higher water potential than inside the cytoplasm of the cells. This prevents the plant cells from taking in too much water and bursting. ​ Plant roots are surrounded by soil water and the cytoplasm of root cells has a lower water potential than the soil water. This means water will move across the cell membrane of root hair cells into the root by osmosis. The water moves across the root from cell to cell by osmosis until it reaches the xylem. Once water enters the xylem it is transported away from the root, helping to maintain a water potential gradient between the root cells and the xylem vessels. ​ If the solute concentration is too high or the water potential is too low outside of the cell, water molecules will move out of the cell. Without water to maintain turgor pressure, the cell membrane will pull away from the cell wall: plasmolysis Osmosis in Animal Tissues: ​ 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. An animal cell in a solution with lower water potential(ex: salt water) will lose water by osmosis and become shrivelled. An animal cell in a solution with a higher water potential(ex: pure water) will gain water by osmosis→With no cell wall to create turgor pressure, the cell will continue to gain water until the cell membrane is stretches too far and bursts cytolysis  B3: Biological Molecules ​ There are three biological molecules: carbohydrates, proteins and lipids ​ These are described as organic molecules ​ Carbohydrates→Carbon, Oxygen and Hydrogen ​ Protein→Carbon, Oxygen, Hydrogen and Nitrogen ​ Lipid→Carbon, Oxygen and Hydrogen ​ Water makes up the bulk of the cytoplasm. It is the universal solvent and transports dissolved substances such as glucose in blood plasma and enzymes. Carbohydrates→Long chains of simple sugars which provide the main source of energy for respiration in living organisms. There are 3 types of carbohydrates: 1.​ Monosaccharides ​ Simple sugars (carbohydrate monomer) ​ Glucose, Fructose and Galactose ​ Source of energy and building blocks or larger carbohydrates 2.​ Disaccharides ​ 2 simple sugar molecules (monosaccharides) joined together ​ Sucrose (Glucose+Fructose), Maltose (Glucose+Glucose) and Lactose (Glucose+Galactose) ​ Soluble in water and taste sweet 3.​ Polysaccharides ​ Many simple sugar molecules joined together in a long chain ​ Examples: ​Cellulose: structure for plant cell walls ​Starch: storage of glucose for plants  ​Glycogen: storage of glucose for animals ​ Most are insoluble and do not taste sweet Lipids ​ Most fats in the body are made up of triglycerides ​ Their basic unit is 1 glycerol molecule chemically bonded to 3 fatty acid chains ​ They are divided into fats (solids at room temp) and oils (liquids at room temp) ​ Lipids are insoluble in water, and are used by the cell to store energy and help maintain body temperature. Proteins→Long chains of amino acids joined together ​ There are about 20 different amino acids-all contain the same basic structure but the ‘R’ group is different for each one. ​ The amino acids can be arranged in any order, resulting in hundreds of thousand of different proteins ​ Even a small difference in the order of the amino acids results in a  different protein being formed ​ Proteins are not normally used for energy, instead, they are digested and used to make: ​New cells (growth and repair) ​Cell membrane proteins (transport) ​Cell structures ​Enzymes (metabolic reactions) ​ Many of these proteins have different shapes and the shape often has an important effect on the function of the protein. The different sequences of amino acids cause the polypeptide chains (group of chains of amino acids) to fold in different ways and this gives rise to the different shapes of proteins ​ In this way every protein has a unique 3-D shape that enables it to carry out its function ​ Protein shape/folding is vulnerable to high temperatures, and pH  B3: Biochemical Tests Testing for Reducing Sugars (Simple Carbohydrate) ​ Benedict's reagent can be used to test for the presence of reducing sugars such as monosaccharides and some disaccharides. ​ Positive result: blue→green→orange→brick red once heated ​ Negative result: solution stays blue Protocol for a reducing sugar test: ​ Add Benedict's solution into the sample solution in a test tube and heat at water bath >80C for 5 minutes and observe for colour change Testing for Starch (Complex Carbohydrate) ​ Iodine solution can be used to test for starch (plant/polysaccharide)→No heat needed ​ Positive result: solution turns blue-black ​ Negative result: solution stays yellow-orange Protocol for starch test: ​ Add drops of iodine solution to the food sample Protocol for starch test in a leaf ​ Add a leaf into boiling water for 30 seconds (stops chemical reactions) ​ Now add the leaf in a test tube with Ethanol at a water bath until it turns white (helps to see the colour change) ​ Wash the leaf with water ​ Place it in a tile and add few drops of iodine solution Testing for lipids (fats and oils) ​ The ethanol emulsion test can be used to test for fats ​ Positive result: White cloudy mixture ​ Negative result: Clear, transparent solution Protocol for lipid test: ​ Add 2cm3 of ethanol to the food sample ​ Add to an equal volume of water and shaken Testing for protein ​ The biuret test can be used to test for the presence of proteins. ​ Positive result: pink/purple/violet colour ​ Negative result: mixture stays blue Protocol for protein test: ​ Add drops of biuret solution to the food sample B4: Enzymes ​ Catalyst: a substance that increases the rate of a chemical reaction and is not changed by the reaction ​ Substrate: molecule that enzymes work on ​ Product: what the enzyme helps produce from the reaction ​ Synthesis→building molecules ​ Digestion→breaking down molecules ​ Enzymes: proteins that function as biological catalysts that speed up the rate of chemical reactions in the body without being changed or used up in the reaction→specialised proteins ​ Necessary to all living organisms as they maintain reaction speeds of all metabolic reactions at a rate that can sustain life→without digestive enzymes, it would take 2-3 days to digest one meal, with them it takes around 4 hours. ​ Enzymes lower the activation energy needed for a reaction to take place  ​ Each enzyme is specific to a reaction Examples: ​ Amylase breaks down starch ​ Catalase breaks down H2O2 Enzymes are named for the reaction they catalyse: ​ Carbohydrase breaks down carbohydrates ​ Proteases break down proteins ​ Lipases break down lipids ​ DNA polymerases build DNA Enzymes properties: ​ Enzymes are proteins ​ Enzymes are catalysts ​ Enzymes are specific ​ Work best at a particular pH and temperature ​ Made inactive by high temperatures Enzyme Specificity: ​ Enzymes are specific to one particular substrate 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 model Enzyme Mechanisms: 1.​ Enzymes and substrates randomly move about in solution→kinetic energy 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 forms 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. Effect of Temperature on Enzymes: ​ The 3D shape of enzymes is held by bonds→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 body, it 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 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 ​ Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes molecules have more kinetic energy move faster number of collisions with the substrate molecules increases faster rate of reaction ​ This means that low temperatures do not denature enzymes, they just make them work more slowly Effect of pH on Enzymes: ​ The optimum pH for most enzymes is 7 ​ However, some enzymes are produced in acidic conditions, such as the stomach, and have a lower optimum pH (pH 2) while enzymes produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9) location/function of enzyme will determine its optimum pH ​ If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed ​ This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity ​ Moving too far away (either higher or lower) from the optimum pH will cause the enzyme to denature and activity will stop Graphs for Changes in Enzyme Activity  Effect of Temperature Effect of pH Investigating Enzymes: ​ Amylase is an enzyme that digests starch (a polysaccharide of glucose) into maltose (a disaccharide of glucose). ​ Starch can be tested for easily using iodine solution. Effect of Temperature on Amylase ​ Starch solution is heated to a set temperature ​Specify at least 5 different values when writing a protocol eg: 20°C, 25°C, 30°C, 35°C, 40°C ​ Iodine is added to wells of a spotting tile ​ Amylase is added to the starch solution and mixed well ​ Every minute, droplets of solution are added to a new well of iodine solution ​ This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down) ​ Time taken for the reaction to be completed is recorded ​ Experiment is repeated at different temperatures ​ Evaluation quicker the reaction is completed, the faster the enzyme is working optimum temperature Effect of pH on Amylase ​ Place single drops of iodine solution in rows on the tile  ​ Label a test tube with the pH to be tested ​Specify at least 5 different values when writing a protocol eg: ph 5, pH 6, pH 7, pH 8, pH 9 ​ Use the syringe to place a set volume of amylase in the test tube ​ Add a set volume of buffer solution to the test tube using a syringe ​ Use another test tube to add a volume of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette ​ After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black and repeat every 10 seconds until iodine solution remains orange-brown ​ Experiment is repeated at different pH values ​ Evaluation quicker the reaction is completed, the faster the enzyme is working optimum pH B5: Plant Nutrition All living organisms need nutrients for growth, repair and to release energy ​ Heterotrophs: feed on organic substances made by plants (ex. animals) ​ Autotrophs: make their own food from inorganic substances (ex. plants) Photosynthesis is a endothermic reaction in which energy from sunlight is transferred to the chloroplasts in green plants ​ Chloroplasts are the “factory” for transferring energy and making sugars Fuels: Sunlight, Carbon Dioxide and Water Helpers: Enzymes Structure of the Chloroplast: ​ Double membrane organelle ​ Outer membrane smooth ​ Inner membrane forms stacks of connected sacs called thylakoids  ​ Thylakoid stack is called the granum (grana-plural) ​ Gel-like material around grana called stroma ​ Chloroplasts contain a green pigment called chlorophyll ​ Chlorophyll is the primary light-absorbing pigment in autotrophs ​ The chlorophyll pigment absorbs energy from sunlight (light energy) and transfers it into chemical energy⟶released to help combine the raw materials carbon dioxide and water to make the carbohydrate glucose. ​ Oxygen is a waste product of this reaction Photosynthesis: ​ Photosynthesis: the process by which plants manufacture carbohydrates from raw materials using energy from light. Photosynthesis has two separate processes: ​Energy-building reactions⟶collect sunlight energy to make ATP ​Sugar-building reactions⟶use ATP energy with CO2 from air and H2O from ground to build sugars (glucose) Leaf Structure: ​ Lamina: broad flat part of the leaf ​Connected to rest of plant by leaf stalk/petiole ​ Vascular bundles: tubes that carry substances to and from leaf Ex: Midrib & veins contain: ​ Xylem: thick-walled vessel that carries water ​ Phloem: thin-walled vessel that carries sucrose & other nutrients AWAY from leaf Cross-Section of a Leaf Function of Leaf Structures ​ Cuticle: Waxy layer/coating that reduces water loss at the top of the leaf ​ Epidermis: Transparent cells that protect leaf cells and allow sunlight to pass through to the palisade cell ​ Palisade Mesophyll: Column-shaped cells tightly packed with many chloroplasts to absorb more sunlight, maximising photosynthesis. ​ Spongy Mesophyll: Irregularly-shaped cells with air spaces that allow gas exchange to take place (CO2 in, O2 out) ​ Stomata: small holes/openings that open and close to allow gas exchange and regulate transpiration. ​ Guard cells: open and close the stomata Adaptations of Plant Leaves for Photosynthesis Transpiration: ​ ​ Water evaporates from the stomata in the leaves ​ Pulls water up from roots through xylem⟶cohesion and adhesion ​ Water Travels from xylem to mesophyll by osmosis Getting CO2: ​ CO2 diffuses through stomata diffuses through air spaces in leaf connected to mesophyll diffuses through cell wall and cell membrane diffuses through cytoplasm to reach chloroplast ​ Homeostasis: keeping the internal environment balanced ​ Guard cells open and close the stomata ​ Stomata open ​Let CO2 in⟶make sugars ​Let H2O out⟶needed for photosynthesis ​Let O2 out⟶waste product ​ Stomata closed ​If too much H2O is being lost by evaporation ​ Limiting factor: 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: 1.​ Temperature⟶As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes until they denature 2.​ Light intensity⟶The more light a plant receives, the faster the rate of photosynthesis. 3.​ Carbon dioxide concentration⟶The more carbon dioxide present, the faster the reaction can occur. Uses of Glucose: ​ Energy⟶Released from glucose by cell respiration for other chemical processes ​ Storage⟶Glucose may be turned into starch for storage ​Glucose is a simple sugar⟶water soluble and reactive ​Prevents use in unwanted chemical reactions, loss of glucose and osmotic fluctuations. ​Starch is a complex sugar⟶water insoluble and not reactive ​Made into granules and stored in chloroplasts ​ Transport⟶Turned into sucrose for transport ​Sucrose is small and soluble but less reactive than glucose - sucrose dissolves in sap within phloem vessels ​Converted back to glucose for cell respiration for energy ​ Protein/Organic Substance Construction⟶Glucose provides building materials to make: ​Sucrose and cellulose ​Fats and oils ​Amino acids in combination with nitrogen (nitrates)⟶protein Nitrate Ions ​ When a salt such as potassium nitrate dissolves in water it separates into two ions, a potassium ion and a nitrate ion. KNO3⟶K+ + NO3- ​ The potassium ion carries a positive charge and the nitrate ion carries negative charge ​ These ions move freely and independently in the soil water and are taken up by plant roots through diffusion and active transport. ​ Nitrate ions and glucose are combined to make protein⟶assimilation Plants also need to take: ➔​Magnesium ions to make chlorophyll ➔​Phosphate ions to make DNA and other energy  molecules ➔​Sulphate ions to make some amino acids ➔​Iron for certain enzyme reactions ➔​Potassium ions for active transport and to open and close the stomata ​ Farmers and gardeners add fertilisers to soil which contain nitrates, phosphates and potassium Element Nitrogen Magnesium Mineral Salt Nitrate ions Magnesium ions Need Make amino Make acids chlorophyll proteins Deficiency Weak Plant lacks growth, chlorophyll, yellow yellowing leaves between leaf veins Testing for Starch ​ Plants make glucose in photosynthesis, but plants cannot be tested for the presence of glucose ​ Glucose is stored as starch, so testing a leaf for starch is reliable indicator of which parts of the leaf are photosynthesising Protocol: 1.​ Drop the leaf in boiling water to break down the cell walls 2.​ Then move the leaf to hot ethanol for 10 minutes→Removes the chlorophyll so colour changes from iodine can be seen more clearly 3.​ Then dip the leaf in boiling water to soften it 4.​ Spread the leaf out on a white tile and cover with iodine solution 5.​ Observe colour change ​ In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf ​ This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is part green and part white) ​ The white areas of the leaf contain no chlorophyll and when the leaf is tested only the aries that contain chlorophyll stain blue-black ​ The areas that had no chlorophyll remain orange-brown was no photosynthesis is occurring here, so no starch is stored B6: Animal Nutrition B6.1 Diet ​ Animals are heterotrophs⟶they cannot make their own food, instead they get food by consuming plants or other animals. ​ Diet: food an animal eats every day ​ Balanced diet: a diet which contains all 7 types of nutrients in the correct amounts and proportions ​Carbohydrates ​Sources: Bread, pasta, potatoes, etc. ​Use: Energy ​Proteins ​Sources: Meat, fish, eggs, dairy products, etc. ​Uses: Repair cells+tissues and make new ones, enzymes, structural material(muscles), source of energy, etc. ​Fats/Lipids ​Sources: milk, butter, pork(lard), oils, etc. ​Uses: Source of energy, insulation, supports cell growth, produce important hormones, absorb  some nutrients, etc. ​Vitamins ​See below ​Minerals ​See below ​Water ​Uses: chemical reactions, universal solvent for transport and to maintain a constant body temperature ​Fibre ​See below ​ Nutrients: substances the body needs for energy, building materials and control of body- processes ​ Vitamins: organic substances needed in small amounts for normal growth and nutrition. Vitamin Source Function Deficiency Disease Vitamin Citrus Needed to make the Scurvy - causes joint & C fruits stretchy protein muscle pain, and bleeding (oranges, collagen found in skin from gums and under skin. limes) raw ⟶maintains healthy Once common disease of vegetables skin and gums sailors during long voyages Vitamin Butter, egg Helps calcium to be Rickets - bones become D yolk, in absorbed for making soft and deformed; body from bones and teeth disease was common in sunlight (body processes the young children in industrial vitamin with sunlight) areas who rarely got sunshine ​ Minerals: inorganic substances needed in small amounts for normal growth and nutrition Mineral Source Function Deficiency Disease Calcium Dairy For bones and Brittle bones and teeth; (Ca) products, teeth; blood clotting poor blood clotting bread Iron (Fe) Liver, red For making Anaemia → insufficient meat, egg Haemoglobin the red blood cells so that yolk, dark red pigment in blood tissues do not receive green which carries enough oxygen vegetables oxygen ​ Fibre (roughage): cellulose portion of plant cell wall that cannot be digested by humans ​Sources: cereal grains (oats, wheat, barley, etc.) and brown rice ​Uses: Helps in peristalsis⟶contraction of smooth muscles to move food, helps move food through the alimentary canal and prevents constipation.  ​ Malnutrition: lack of a balanced diet because of the wrong amount of food (too much or too little), incorrect proportion of nutrients or lacking one or more key nutrients. Effects of malnutrition: ​ Obesity⟶too much food-taking in more energy than they use Health implications: ​Coronary Heart Disease ​Stroke ​Diabetes ​Joint problems ​ Coronary Heart Disease⟶caused by too much saturated fat (animal fat) in the diet resulting in high cholesterol levels ​Cholesterol can form fat deposits on the inside of arteries, making them stiffer and narrower ​Coronary arteries supply blood to the heart muscles. A restricted blood supply will cause muscles to run short of oxygen and result in tissue damage → coronary heart disease ​Angina - symptom of CHD; chest pain or discomfort ​Fat deposits can also cause a blood clot in the coronary arteries → heart attack ​ Starvation: too little food⟶extreme slimming diets, such as those that avoid carbohydrate foods, can result in the disease anorexia nervosa Examples of starvation: ​ Kwashiorkor; malnutrition caused by lack of protein ​Most common among children 9 months - 2 yrs after halting breastfeeding ​Underweight for age, but may look fat because of diets high in carbohydrates ​Lack of knowledge & poverty are common causes ​Symptoms include edema, anorexia, ulcerating dermatoses ​ Marasmus: most severe form of malnutrition caused by a  shortage of energy in the diet ​Emaciated child B6.2 Alimentary canal ​ Food taken into the body goes through 5 stages during its passage through the alimentary canal 1.​ Ingestion: the taking of substances (e.g. food or drink) into the body through the mouth 2.​ Digestion: the breakdown of large, insoluble molecules into small, soluble molecules using mechanical and chemical processes ​ Mechanical digestion: the breakdown of food into smaller pieces with no chemical change to the food molecules ​ Chemical digestion: the breakdown of large, insoluble molecules into small, soluble molecules 3.​ Absorption: the movement of small, digested molecules and ions through the all of the intestine into the blood 4.​ Assimilation: the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells. 5.​ Egestion: the passing out of food that has not been digested or absorbed, as faeces through the anus ​ Peristalsis: wave-like involuntary muscle contractions to move food along the oesophagus ​ Epiglottis: flap of cartilage which closes the trachea when swallowing ​ Strong muscular walls of stomach mix food with enzymes and mucus to form chyme ​ The stomach produces several fluids which together are known as gastric juice. ​ One of the fluids produced is hydrochloric acid (HCl) ​ Functions of HCl in gastric juice ​Kills bacteria in food ​Gives an acid pH for enzymes in the stomach to work ​Denatures enzymes in harmful microorganisms and bacterial cells in food ​ Gives the optimum pH for protease activity⟶pepsin is a protease enzyme with a very low optimum pH 2. The HCl produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate. ​ Absorption in small intestine occurs through villi⟶finger-like projections that increase the surface area over which absorption can take place ​ Capillaries⟶absorb small molecules such as amino acids and sugars into blood ​ Lacteals⟶absorb digested fats ​ Rectum⟶last section of large intestines, stores faeces until it exits through the anus  ​ Involved in egestion⟶elimination of faeces (undigested materials; mainly plant fibres and masses of bacteria Enzymes: ​ Carbohydrases⟶Enzymes that break down carbohydrates ​ Digestion of starch: ​Amylases are enzymes that digest starch into smaller, simpler sugars. They are produced in the mouth (salivary glands) and pancreas but are secreted in the duodenum. ​ Proteases⟶Enzymes that break down proteins into amino acids in the stomach and small intestine (enzymes in the small intestine are produced in the pancreas). ​ Protein digestion takes place in the stomach and duodenum with two main enzymes produced: ​Pepsin is produced in the stomach ​Trypsin is produced in the pancreas and secreted in the duodenum ​ Lipases⟶Enzymes that digest lipids into fatty acids and glycerol ​ Lipases are produced in the pancreas and secreted in the duodenum ​ Bile ​ Cells in the liver produce bile which is then stored in the gallbladder ​ Functions: ​Bile is alkaline to neutralise the hydrochloric acid from the stomach⟶to provide the optimum pH for the enzymes in the small intestine ​It breaks down large drops of fat into smaller ones to increase the surface area for lipase to chemically digest fat into fatty acids and glycerol faster⟶Emulsification  B6.3 Teeth ​ Help with ingestion and mechanical digestion of food ​ Bite, chop, crush or grind food to smaller pieces ​ Increase surface area of food⟶assists enzymes ​ Helps dissolve soluble parts ​ Crown⟶The visible part of the tooth ​ Root⟶Part of the tooth embedded in gum ​ Enamel⟶Layer that covers the crown; hardest substance made animals ​Difficult to break or chip ​Can be dissolved by acids-bacteria feed on foods left on teeth producing acid⟶tooth decay ​ Dentin⟶Bone-like structure under enamel ​Not as hard as enamel ​Contains channels with living cytoplasm ​ Cementum⟶Covers the root of the tooth ​Fibres grow out attaching tooth to jawbone ​Allow slight movements when biting or chewing ​ Pulp⟶Middle of the tooth ​Contains nerves and blood vessels ​Supplies cytoplasm of dentine with food and oxygen Most mammals have 4 types of teeth: ​ Incisors⟶sharp-edged, chisel-shaped teeth at front of mouth ​ Canines⟶more pointed teeth at either side of the incisors; used for gripping ​ Premolars and Molars⟶large teeth towards the back of the jaw; used for chewing and crushing food into smaller pieces (mechanical digestion). ​In humans, molars at the very back are sometimes called wisdom teeth -Carnivores have teeth used for cutting meat and crushing bone ​ Molars are often pointy and wedge-like. ​ Many (if not all) have large canine teeth used for dragging prey around and gripping it -Herbivores have flat teeth used for grinding, often able to withstand non stop chewing ​ Some grazers lack certain incisors, but those that eat fruit have large incisors -Omnivores have a wide range of teeth that look and act like a mixture of herbivore and carnivore ​ Dental/Tooth Decay⟶caused by bacteria ​ Plaque-film between gums and teeth⟶combination of bacteria, food particles and saliva ​Soft and easy to remove initially ​If it hardens⟶tartar ​Cannot be removed by brushing ​ Sugar left on teeth is food for bacteria⟶cellular respiration produces acid⟶acid dissolves enamel⟶dentine decay⟶infections spread and may proceed to root of tooth unless stopped or the tooth is removed. Healthy Teeth: ​ Refrain from eating or drinking too much sugar ​Better to consume with meals than independently ​ Use a fluoride toothpaste ​Helps teeth resist decay ​Regular and through brushing can help remove plaque, prevent gum disease, and reduce decay ​ Visit a dentist regularly ​Checkups may help stop the spread of tooth decay or  gum disease 9B8: Transport in Plants B8.1 Xylem and Phloem ​ Vascular Bundles: group of xylem and phloem tubes ​ In roots, vascular tissues are found in the centre ​ In shoots, vascular tissues are arranged in a ring near the outside edge ​ The xylem is always on the inside and the phloem on the outside Xylem ​ Function: Transports water and mineral ions from the roots→stem→branch into leaves, and helps support the plants overall structure. ​ Made of many hollow, dead cells joined end to end ​ Adaptations: ​Unidirectional ​End of cell walls disappear→continuous open tube ​Contains no cytoplasm or nuclei ​Walls made of cellulose and lignin (very strong)→helps keep plants upright; wood is lignified xylem vessels Phloem ​ Function: Transports sucrose and amino acids throughout the plant ​ Made of many living cells joined end to end ​ Portions of end cell walls remain ​ Sieve tube elements: contain cytoplasm; No nucleus; No lignin ​ Bidirectional  B8.2 Water Uptake Root hairs ​ Function: Absorb water and minerals from the soil ​ Root cap: layer of cells at end of the root that protect the root  as it grows→covered by epidermis ​ Root hairs are single-celled extensions of epidermal cells; short-lived and quickly replaced ​ Small size and large number ​ Root hairs hav e a large surface area to increase the rate of water absorption and the uptake of mineral ions by active transport ​ Water moves into root hairs by osmosis because the cytoplasm and cells sap in root hairs have a low water potential Pathway of water: Water travels from root hair cell through the cortex, from cell to cell, or through the spaces around cells to the xylem and then to the mesophyll cells of leaves. ​ Water moves up the xylem because water pressure at the top of the plant is less than at the roots.  B8.3 Transpiration and Translocation ​ Transpiration: The loss of water vapour from leaves by evaporation of water from the surfaces of the mesophyll cells into the air spaces, followed by diffusion of water vapour through the stomata ​ Water from the xylem flows to the mesophyll to replace the evaporated water ​ Transpiration stream: Movement of water from roots→xylem vessels→mesophyll cells→air spaces→out of stomata Water Potential Gradient ​ Loss of water from leaves causes low pressure that pulls more water up the xylem ​ Water moves from a high to low water potential down a water potential gradient ​ Highest water potential in roots vs lowest water potential in air ​ Water “falls” upwards ​ Water pulls other molecules up against gravity by cohesion→water molecules stick together Water movement from soil to leaf Water movement out of leaf Transpiration is required for: ​ 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 and energy→use of heat to convert liquid water into water vapour helps to cool the plant down Factors Affecting the Rate of Transpiration ​ Temperature→Transpiration increases in high temperatures when evaporation increases ​ Humidity→High humidity reduces transpiration as there is a lower diffusion gradient between the plant and atmosphere ​ Air flow→More air flow (wind or fans) increases transpiration and keeps a larger diffusion gradient ​ Light→More light increases transpiration as the plant needs more water for photosynthesis Measuring transpiration ​ Faser rates of transpiration→faster uptakes of water ​ Potometer: apparatus that can compare the rate of transpiration in different conditions and records how fast the water moves along a capillary tube ​ Wilting: occurs when water loss exceeds water uptake→cells become flaccid and tissues become limp ​ If more water evaporates from the leaves of the plant than is available in the soil to move into the root by osmosis, then wilting occurs ​ 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 ​ Happens when the turgor pressure in plants decrease ​ Translocation: transport of sucrose and amino acids in the phloem from regions of production (sources) to regions of storage or use (sinks) ​ Dissolved food is always transported from sources (parts of the plant that release sucrose or amino acids) to sinks (parts of the plant that use or store sucrose or amino acids) ​ Examples: ​Sources→leaves or stems ​Sinks→fruits, shoots and roots  B9 Transport in Animals B9.1 Circulatory Systems ​ The circulatory system is a system of blood vessels with  a pump and valves to ensure one-way flow of blood Double Circulatory System ​ Blood passes through the heart twice on one complete circuit of body ​ Pulmonary system ○​ blood picks up O2 from lungs oxygenated blood ○​ drops off CO2 to lungs ○​ O2 rich blood moves from lungs to left-hand side of heart ​ Systemic system ○​ pumps oxygenated blood to body ○​ picks up nutrients from digestive system ○​ collects cell wastes and CO2 deoxygenated blood Single Circulatory System: ​ Fish have a two-chambered heart and a single circulation→for every one circuit of the body, blood passes through the heart once Advantages of Double Circulatory System: ​ Double circulatory system does not lose as much pressure as single circulatory system faster blood at higher pressure ○​ Blood pressure lost in small capillaries of lungs or gills is raised by returning to the heart before delivery to the body ​ Endothermic animals require 10x the energy delivers 10x the metabolic reactants (ie. Glucose and oxygen) ○​ Faster and more frequent access to oxygen and glucose as well as waste removal -​ Double circulatory systems are found in mammals, birds, reptiles and amphibians, while fish have a single circulatory system  B9.2 Heart ​ Function: pump blood around the body ​ Made of specialised tissue: Cardiac muscle ​ Contracts and relaxes continuously throughout entire life Heart Structure: ​ 4 chambered heart: ​2 atria (atrium) ​Thin walls ​Upper collection chambers that receive blood ​2 ventricles ​Thick walls to pump blood out at high pressure ​Left ventricle thicker muscle wall than right ventricle ​RV→ pumps to lung, LV→ pumps to body ​ 2 sides of heart separated by septum→ prevent mixing of oxygenated and deoxygenated blood Valves: ​ Function: prevent blood flowing backwards ​ Two sets of valves in the heart: ○​ Atrioventricular valves separate the atria from the ventricles ​Tricuspid: valve on the right side of the heart ​Bicuspid: valve on the left side of the heart ​These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood flowing back into the atria  ○​ Semilunar valves are found in the two blood arteries that come out of the top of the heart ​Only two arteries in the body that contain valves ​Open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart Blood flow through heart: ​ Deoxygenated blood coming from the body flows into the right atrium via the vena cava ​ Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle ​ The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart ​ The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure) ​ Oxygen-rich blood returns to the left atrium via the pulmonary vein ​ It passes through the bicuspid (mitral) valve into the left ventricle ​ Thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body ​ Semilunar valve in the aorta prevents the blood flowing back down into the heart Exercise on Heart Rate: How can you measure heart rate? ​ An ECG (electrocardiogram) ​ Measuring pulse rate ​ Listening to the sound of the valves closing using a stethoscope ​Heart rate is measured in beats per minute (bpm) Why does the heart rate increase during exercise? ​ The body needs sufficient blood to provide working muscles with enough nutrients and oxygen for increased respiration→Waste products removed at a faster rate ​ After exercise, the heart continues to beat faster→ensures all excess waste products are removed from muscle cells ​ Muscle cells have often been repairing anaerobically (without oxygen) during exercise and have built up an oxygen debt ​ The body needs to ‘repay the oxygen debt’→heart continues to beat faster to ensure extra oxygen is delivered to muscle cells to break down lactic acid that has been built up in cells during anaerobic respiration. How does the heart know to pump faster? ​ Brain controls the heart rate→receives communication in form of pH change ​ Increased energy needs→greater cell respiration→increased carbon dioxide dissolved in blood→lower pH→brain increases frequency of nerve impulses to pacemaker→increased heart rate Coronary Heart Disease: ​ The heart is made of muscle that needs its own supply of blood to deliver oxygen, glucose and other nutrients and remove carbon dioxide and other waste products ​ The blood is supplied by coronary arteries ​ When a coronary artery become partially or completely blocked by fatty deposits called ‘plaques’ (mainly formed by cholesterol) →arteries lose elasticity and cannot stretch to accommodate the blood which is being forced through them → coronary heart disease ​ Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina ​ Complete blockage means cells in that area of the heart will not be able to respire and can no longer contract, leading to a heart attack Risk Factors for Coronary Heart Disease: ​ Poor Diet→Eating more saturated fat increases cholesterol levels, increasing the chance of the build up of  fatty plaques ​ Stress→When under stress, hormones produced can increase blood pressure, increasing the chance of a blockage in the coronary arteries ​ Smoking→Nicotine in cigarettes will cause blood vessels to become narrower, increasing blood pressure which will cause the buildup of fat globules, which, if occurs in the coronary arteries, will cause coronary heart disease ​ Genetic Predisposition→Studies show that people with a history of coronary heart disease in their family are more likely to develop it themselves, suggesting it partly has a genetic basis ​ Age→the risk of developing CHD increases as you get older ​ Gender→Males are more likely to develop CHD than females ​ Lack of exercise→Being inactive can lead to a fatty buildup in your coronary arteries. B9.3 Blood Vessels Vessel Function Structure Arteries Carry Elastic tissue walls stretch oxygenated and relax as blood is forced out; blood at a causes pulse high pressure away from Thick muscular walls to the heart withstand high blood pressure Small, narrow lumen to maintain high blood pressure. Veins Carry Contain valves to prevent the deoxygenated backflow of blood. (other than the pulmonary vein) blood at a low Blood is at low pressure, but pressure towards nearby skeletal muscles the heart contract to help push blood back to the heart Thin walls and a large and wide lumen to reduce resistance to the flow of blood Capillaries Carry both One cell thick wall for easy oxygenated and diffusion deoxygenated blood at a low pressure within Have ‘leaky’ walls so blood tissues plasma can leak out and form tissue fluid surrounding cells Capillary beds constantly supplied with fresh blood, so diffusion occurs Organ Vessel function ​ Lungs picks up O2 / clean out CO2 ​ Small Intestines picks up nutrients from digested food ​ Large Intestines picks up water from digested food ​ Liver clean out worn out blood cells ​ Kidneys filters out cell wastes (urea), extra salts, sugars & water ​ Bone pick up new red blood cells ​ Spleen pick up new white blood cells  B9.4 Blood ​ Blood is a tissue composed of cells & fluid ​ Plasma: liquid part of blood ​ Cells: ​Red Blood Cells ​White Blood Cells ​Platelets Plasma ​ Function: transport blood cells, mineral ions, carbon dioxide, nutrients (digested food), urea, hormones and heat energy ​ Straw coloured liquid Red Blood Cells ​ Function: transport oxygen ​ Small round biconcave discs ​ Large Surface Area ​ No nucleus (more space) ​ Speeds up rate of diffusion ​ Contain protein haemoglobin which carries O2 ​ Contains iron which readily binds oxygen ​ Produced in bone marrow White Blood Cells ​ Function: Phagocytosis and antibody production ​ Large cells containing a big and lobed nucleus→different types have slightly different structures and function ​ Part of the body’s immune system defending against infection by pathogens(ex: bacteria, viruses, parasites,...) ​ 2 main types:  ​Phagocytes ​Lymphocytes Phagocytes: ​ Function: engulf pathogens by phagocytosis ​ Have a sensitive cell surface membrane that can detect chemicals produced by pathogens ​ Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it ​ Can be recognized under the microscope by their multi-lobed nucleus and their granular cytoplasm Lymphocyte:  ​ Function: produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by pathogens ​ Can be recognised under the microscope by their large round nucleus which takes up nearly the whole cell and their clear, non-granular cytoplasm Platelets ​ Function: blood clotting and forming scabs where skin has been cut or punctured ​ Small fragments of cells; no nucleus ​ Prevents continued / significant blood loss from wounds ​ Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause infection Mechanism of Action: ​ When the skin is broken (i.e. there is a wound) platelets arrive to stop the bleeding ​ A series of reactions occur within the blood plasma ​ Platelets release chemicals that cause soluble fibrinogen proteins to convert into insoluble fibrin and form  an insoluble mesh across the wound, trapping red blood cells and therefore forming a clot ​ The clot eventually dries and develops into a scab to protect the wound from bacteria entering B10 Diseases and Immunity Diseases ​ Pathogens: a disease-causing organism (Examples: Fungi, Bacteria, Viruses) ​ Transmissible disease: a disease in which the pathogen can be passed from one host to another Pathogens can be passed on from host to host in different ways: ​ Direct contact - the pathogen is passed directly from one host to another by transfer of body fluids ​Blood ​Semen ​ Indirect contact - the pathogen leaves the host and is carried to an uninfected individual ​Contaminated surfaces (fomites) ​Food ​Animals/Insects ​Air Droplets 3 main ways the body prevents infection by a pathogen: 1. Mechanical barriers – structures that make it difficult for pathogens to get past them and into the body ​ Skin - covers almost all parts of your body to prevent infection from pathogens ○​ Scabs form quickly to prevent entry of pathogens to blood in the event that skin is cut or grazed ​ Hairs in the nose - make it difficult for pathogens to get past so they are not inhaled into the lungs 2. Chemical barriers – substances produced by the body cells that trap/kill pathogens before they can get further into the body and cause disease ​ Mucus - made in various places in the body, pathogens get trapped in the mucus and can then be removed from the body (by coughing, blowing the nose, swallowing etc.) ​ Stomach acid - contains hydrochloric acid which is strong enough to kill any pathogen that is caught in mucus in the airways and then swallowed or consumed in food or water 3. Cells - different types of white blood cells work to prevent pathogens from infecting deeper tissues ​ Phagocytes - engulf and digest pathogenic cells ​ Lymphocytes - produce antibodies which clump pathogenic cells together so they can’t move as easily (known as agglutination) and release chemicals that signal to other cells that they must be destroyed Controlling Spread of Disease ​ Hygienic Food Preparation→wash fruits and vegetables before eating, keep food refrigerated/cold, cook food to required temperature ​ Good Personal Hygiene→wash your hands thoroughly with soap and water, take showers daily, use tissues for sneezing  ​ Waste Disposal→waste food should be disposed in a sealed container, rubbish bins covered with lids and removed ​ Sewage Treatment→home and public places should have safe plumbing and drains ​ Clean Water Supply→clean water for drinking, food preparation, washing clothes, hands and dishes, brushing teeth and watering plants Immunity ​ Immunity: organism’s internal defence against infection by pathogens Active Immunity ​ Active immunity: Making antibodies and developing memory cells for future response to infection ​ Two ways in which this active immune response happens: ​The body is infected with a pathogen and so the lymphocytes go through the process of making antibodies specific to that pathogen ​Vaccination Initial Response ​ Initial response can take a few days as it takes time for lymphocytes with the appropriate antigen specificities to be identified and activated→during this time, an individual may get sick ​ Lymphocytes that have made antibodies for a specific  pathogen for the first time will then make ‘memory cells’ that retain the instructions for making those specific antibodies for that type of pathogen ​ In the case of reinfection (secondary exposure), by the same type of pathogen, antibodies can be made very quickly in greater quantities and the pathogens destroyed before they are able to multiply and cause illness ​ This is how people can become immune to certain diseases after only having them once→Memory cells can last years to a lifetime Why do we suffer repeated infections form pathogens if we have memory cells? ​ Many disease-causing organisms can mutate fairly quickly →changes the antigens on their cell surface ​ If they invade the body for a second time, the memory cells made in the first infection will no longer be able to identify them as they now have slightly different antigens on their surface→lymphocytes must repeat the process of initial response ​ Autoimmune disease: when the body's immune system mistakenly attacks healthy body cells and tissues Antigens ​ All cells have proteins and other substances projecting from their cell membrane antigens ​ specific to that type of cell ​ Lymphocytes can ‘read’ the antigens on the surfaces of cells and recognise any that are foreign ​ Helps body to distinguish self from non-self (ie: pathogens) Antibodies ​ Lymphocytes make antibodies which are proteins that have complementary shapes to the antigens on the surface of the pathogenic cell ​ There is a lymphocyte capable of making an antibody for any antigen the body could encounter Antibody Functions: 1.​ Agglutinate(clump) bacteria to reduce spread 2.​ Attach to bacteria and signal phagocytes for ingestion opsonization 3.​ Combine with toxins or viruses to prevent cell entry 4.​ Attach to bacterial flagella limiting movement 5.​ Coordinate with other molecules to create holes in bacterial cell walls 6.​ Neutralise toxins antitoxins Coordinated Response ​ At the same time, chemicals are released by lymphocytes that signal phagocytes that there are still cells present that need to be destroyed Viruses ​ Viruses are not part of any classification system as they are not considered living things ​ They do not carry out all of the characteristics of life, instead they take over a host cell’s metabolic pathways to make multiple copies of themselves ​ Virus structure is simply genetic material (RNA or DNA) inside a protein coat Vaccinations ​ Vaccine: preparation which may contain whole live organisms, dead organisms, harmless versions (attenuated organisms), harmless forms of a toxin, or surface antigens which stimulate an immune response→In this weakened state, the pathogen cannot cause illness ​ Vaccinations give protection against specific diseases and boost the body’s defence against infection from pathogens without the need to be exposed to dangerous diseases that can lead to death ​ The level of protection in a population depends on the proportion of people vaccinated Vaccine Action ​ Vaccines are prepared with weakened pathogens or antigens and are injected into the body ​ Lymphocytes produce complementary antibodies for the  antigens ​ The antibodies target the antigen and attach themselves to it in order to create memory cells ​ The memory cells remain in the blood and will quickly respond to the antigen if it is encountered again in an infection by a ‘live’ pathogen ​ As memory cells have been produced, this immunity is long-lasting Controlling Spread ​ Herd immunity: when a large percentage of the population is vaccinated, it provides protection for the entire population because there are very few places for the pathogen to replicate - it can only do so if it enters the body of an unvaccinated person →Very important to help protect people who may be unable to get the vaccine ​ If the number of people vaccinated against a specific disease drops in a population, it leaves the rest of the population at risk of mass infection More likely to come across people who are infected and contagious →Increases the number of infections, as well as the number of people who could die from a specific infectious disease ​ Herd immunity prevents epidemics and pandemics from occurring in populations ​ Low vaccination rate High chance for infection to spread among population ​ High vaccination rate Low chance for infection to spread among population B11 Gas Exchange Gas Exchange in Humans Features of Gas Exchange Surfaces: ​ Large surface area→ faster diffusion of gases across the surface ​ Thin walls→ensure diffusion distances remain short ​ Good ventilation with air→diffusion gradients can be maintained ​ Good blood supply→maintain a high concentration gradient so diffusion occurs faster Gas Exchange System: Structure Description Alveoli Tiny air sacs→site of gas exchange Bronchioles Bronchi split to form small tubes in the lungs connected to the alveoli Bronchi Large tubes branching off the trachea with one bronchus to each lung Larynx Voice box→contains vocal chords Trachea Windpipe that connects the mouth and nose to the lungs. Surrounded by rings of cartilage. Functions to support the airways and keep them open during  breathing→prevents inwards collapse when the air pressure drops inside the tubes. Ribs Bone structure that protects internal organs such as the lungs Intercostal Muscles Muscles between the ribs which control movement causing inhalation and exhalation Diaphragm Sheet of connective tissue and muscle at the bottom of the thorax that helps change the volume of the thorax to allow inhalation and exhalation Intercostal Muscles ​ Muscle are only able to pull on bones, not push them→requires two sets of intercostal muscles; one to pull the ribcage up and another to pull it down ​ External Intercostal Muscles: intercostal muscles found on the outside of the ribcage ​ Internal Intercostal Muscles: intercostal muscles found on the inside of the ribcage Breathing In and Out (Inhalation and Exhalation) 1. Diaphragm ​ Inhalation: Diaphragm contracts to flatten→increases the volume of the thorax→leads to a decrease in air pressure inside the lungs relative to outside the body→drawing air in ​ Exhalation: Diaphragm relaxes→moves back into its domed shape→decreases the volume of the thorax→leads to an increase in air pressure inside the lungs relative to outside the body→forcing air out 2. Intercostal Muscles ​ The internal and external intercostal muscles work as antagonistic pairs ​ Inhalation→the external set of intercostal muscles contract to pull the ribs up and out→increases the volume of the thorax→decreases air pressure→drawing air in ​ Exhalation: the external set of intercostal muscles relax so the ribs drop down and in→decreases volume of the thorax→increases air pressure→forcing air out ​ During strenuous activity, the internal intercostal muscles contract more forcefully and quickly, further decreasing the volume of the thorax→forced exhalation→helps to get rid of more CO2  Composition of Air Gas Inspir Expir Reason ed Air ed Air Oxygen 21% 16% O2 is removed from the blood by respiring cells Carbon 0.04% 4% CO2 is produced by respiration dioxide Water Lower Higher Water evaporates from the moist Vapour lining of the alveoli into the expired air during respiration Testing for carbon dioxide in gas: ​ Solution: Limewater ​ Positive test: turns milky/cloudy ​ Negative test: remain clear Effect Of Exercise on Breathing Rate: ​ When exercising, the frequency and depth of breathing increase ​ As muscles are working harder, aerobic respiration increases→cells need more oxygen to keep up with their energy demand ​ If muscles cannot meet energy demands while respiring aerobically, they will start respiring anaerobically (producing lactic acid) ​ After exercise, the lactic acid built up in muscles needs to be removed, as it lowers the pH of cells and can denature enzymes catalysing cell reactions ​ The lactic acid scan only be removed by combining it with oxygen → known as ‘repaying the oxygen debt’ ​ The lactic acid is transported to the liver, where it is combined with oxygen→oxidised ​ The longer it takes for betahing to normalise, the lactic acid produced during exercise and the greater the oxygen debt to be repaid. Effect of Carbon Dioxide on the brain ​ As respiration rates increase, more carbon dioxide is produced and enters the blood ​ Carbon dioxide is an acidic gas in solution, so it can affect the working of enzymes in the cells ​ As blood flows through the brain, the increase in carbon dioxide concentration stimulates receptor cells ​ These send impulses to the muscles of the lungs, causing them to contract faster and more strongly ​ This causes the frequency and depth of breathing to increase until the carbon dioxide concentration of the blood has lowered sufficiently  B12: Respiration ​ Respiration: a chemical process that involves the breakdown of nutrient molecules (specifically glucose) in order to release the energy stored within the bonds of these molecules ​ There are two types of respiration: ​Aerobic respiration→with oxygen ​Anaerobic respiration→without oxygen ​ Occurs in all living cells ​ Most of the chemical reactions in aerobic respiration occur in the mitochondria Humans need energy to: ​ Contract muscles ​ Synthesise proteins ​ Cell division ​ Growth ​ Active Transport ​ Generate nerve impulses ​ Maintain a constant internal body temperature Aerobic Respiration ​ Aerobic Respiration: chemical reactions in cells that use oxygen to break down nutrient molecules to release energy ​ The complete breakdown of glucose releases a relatively large amount of energy for use in cell processes ​ Produces carbon dioxide and water and releases useful cellular energy Anaerobic Respiration  ​ Anaerobic Respiration: chemical reactions in cells that break down nutrient molecules to release energy without using oxygen ​ The incomplete breakdown of glucose releases a relatively small amount of energy for use in cell processes ​ Different organisms produce different products during anaerobic respiration Anaerobic Respiration in Animals ​ Mainly takes place during vigorous exercise, as muscles have a higher demand for energy than when resting or exercising normally, and the body can only deliver so much oxygen to muscle cells for aerobic respiration. ​ Glucose broken down without oxygen produces lactic acid, which still contains energy stored within its bonds, but less energy is released ​ Lactic acid builds up in muscle cells and lowers the pH (making them more acidic)→needs to be removed to prevent denaturation of enzymes in cells and can cause of muscle cramps and soreness ​ Cells excrete lactic acid into the blood, which is transported to the liver ​ It is stored until oxygen becomes available where it is broken down by aerobic respiration to produce carbon dioxide and water ​ Continued heavy breathing and a high heart rate persist after finishing exercise to transport the lactic acid from muscles to the liver, and continue to supply larger amounts of  oxygen to oxidise the lactic acid ‘repaying the oxygen debt’ Anaerobic Respiration in Yeast ​ Glucose broken down without oxygen produces alcohol and carbon dioxide ​ Used in bread making and brewing Aerobic VS Anaerobic Respiration Aerobic Anaerobic Oxygen Needed Not needed Products Carbon dioxide Animals=lactic acid + water Yeast= alcohol + carbon dioxide Glucose Complete Incomplete Breakdown Energy Released Large amount Small amount B14: Drugs ​ Drug: any substance take in the body that modifies or affects  chemical reactions in the body ​ Medicinal drugs are used to treat the symptoms or causes of a disease - for example, antibiotics ​ The liver is the primary site for drug metabolism Antibiotics ​ Antibiotics: chemical substances made by certain fungi or bacteria that affect the working of bacterial cells, either by disrupting their structure or function or by preventing them from reproducing ​ Antibiotics are effective against bacteria but not against viruses ​ Antibiotics target processes and structures that are specific to bacterial cells Antibiotic Resistance ​ Since the discovery of the first antibiotic, antibiotics have been and are widely overused ​ Commonly prescribed antibiotics are becoming less effective due to a number of reasons: ​overuse by being prescribed when not necessary or available without a prescription ​patients failing to complete the fully prescribed course by a doctor ​large scale use of antibiotics in farming to prevent disease when livestock are kept in close quarters, even when animals are not actually sick ​ Antibiotic resistance can develop when bacteria sensitive to the antibiotic die, however, one or more bacteria that have a mutated gene(s) provide resistance to survive and reproduce ​More antibiotics Greater selection pressure Greater evolution of resistance ​ The incidence of antibiotic resistance has been increasing and some bacteria have developed resistance to multiple antibiotics superbugs Ex: MRSA ​ Methicillin-resistant Staphylococcus aureus (MRSA) infection is caused by a type of staph bacteria that's become resistant to many of the antibiotics used to treat ordinary staph infections ​ Most MRSA infections occur in people who've been in hospitals or other health care settings, such as nursing homes and dialysis centres but anyone can get MRSA ​ The infection can become severe and cause sepsis What ways can we solve the antibiotic resistance crisis? ​ Control the use of antibiotics and use sparingly with prescription ​ Find and discover new antibiotics ​ Increase funding and investment for the development and research of new antibiotics→government incentives ​ New technologies→use of bacteriophages to deliver antibiotics ​ Stop prescribing it for viruses, only bacteria ​ Add bacteria blocker to antibiotics ​ Regulate agricultural use B18: Organisms and Their Environment ​ Ecology is the study of interactions of living things in their environment, with an emphasis on energy transfer→Science of relationships ​ Habitat: area where an organism lives; includes both: ​Biotic factors: all living organisms inhabiting Earth ​Abiotic factors: nonliving parts of the environment Main source of energy for all living things→The Sun ​ All living things need energy ​ Plants capture energy in sunlight to make glucose ​ Animals get their energy by eating/ingesting plants, or other animals that have eaten plants ​ Chemical energy is transferred in the form of food ​ Energy is ultimately lost to the environment as heat Food Chains and Food Webs ​ Food Chain: a diagram showing the flow of energy from one organism to the next, beginning with a producer ​ Show one possible path for flow of energy ​ Must start with a producer ​ Arrows only show direction of energy flow ​ Food Web: a network of interconnected food chains ​ Shows interdependence ​ Animals rarely exist on just one type of food source Feeding Relationships ​ Herbivore: an animal that gets its energy by eating plants ​ Carnivore: an animal that gets its energy by eating other animals ​ Decomposer: an organism that gets its energy by eating dead or waste organic matter ​ Producer: organism that makes its own organic nutrients, usually using energy from sunlight, through photosynthesis ​ Consumer: an organism that gets its energy by feeding on other organisms ​Primary consumer: organism which gets energy by eating plants (producers)→Herbivore ​Secondary consumer: organism which gets energy by eating other animals (primary consumers)→Carnivore ​Tertiary consumer: organism that feeds on secondary consumers ​Quaternary consumer: organism that feeds on tertiary consumers Human Impact ​ Most of the changes in populations of animals and plants happen as a result of human impact - either by overharvesting of food species or by the introduction of foreign species to a habitat ​ Due to interdependence, these can have long-lasting knock-on effects to organisms throughout a food chain or web ​ An invasive species is an organism that is not indigenous, or native, to a particular area. Invasive species can cause great economic and environmental harm to the new area ​ Some species are brought to a new area on purpose, such as a form of pest control, pets or decorative displays ​ It is very difficult to anticipate the consequences of these introductions Energy loss ​ No transfer of energy is 100% efficient ​During cell respiration, energy is lost from food as heat to the environment ​When an organism eats another, not all the organism is consumed→plant roots, bones, etc. ​During digestion, enzymes break down larger molecules, but not all food is digested and absorbed→excreted in faeces Trophic Levels ​ Trophic Level: the position of an organism in a food chain, food web or pyramid of biomass or numbers ​ ‘Trophic’ means feeding ​ Energy pyramid shows the flow of energy in a food chain with decreasing available energy ​ Only 10% is transferred to next level, so 90% is lost as heat or undigested materials ​ Higher levels receive less energy ​ Requires a larger number of producers to support fewer consumers, and larger numbers of primary consumers to support fewer secondary consumers and so on… ​ Food chains are rarely more than 5 organisms long as energy transfers are inefficient so there would very little energy left Energy Pyramid ​ Representation of how much energy can be found in each trophic level ​ Bottom level is always the largest energy store→producers ​ Inefficient energy transfers mean that each added layer is smaller→less available energy Human Consumption→As omnivores, is it more energy efficient for humans to eat plant crops or other animals? ​ Given energy loss in food chains, humans get much more energy from directly eating wheat as compared to if they eat the cows that fed on wheat→it is more energy efficient within a food crop chain to be herbivore rather than carnivores ​ By directly eating the plant crops, humans immediately bypass a trophic level of the livestock that has fed on the crop plants, reducing the amount of energy lost (as only 10% of energy is transferred from one trophic level to another), making it more energy efficient The Carbon Cycle Recycling in the Biosphere ​ Matter is recycled within and between ecosystems ​ Biogeochemical Cycles→Cycles that connect biological, geological and chemical aspects of the biosphere ​ Energy ​Passes through an ecosystem ​Gets used or released as heat ​ Matter ​Cycles through an ecosystem ​Constantly getting reused Carbon ​ Essential to create all biological molecules→carbohydrates, lipids proteins and nucleic acids ​ Found in organisms, rocks, oceans and the atmosphere ​ The same carbon atoms are used repeatedly on Earth→cycle between earth and atmosphere-Carbon Cycle Carbon Cycle ​ Plants pull carbon dioxide from the atmosphere and use it to make food/sugar→Carbon fixing by photosynthesis ​ The carbon becomes part of the plant-stored as food  B13: Coordination, Response and Homeostasis The Nervous System The nervous system consists of the CNS(Central Nervous System) and the PNS(Peripheral Nervous System). The nervous system allows you to coordinate and regulate body functions. The Central Nervous System The CNS consists of the brain and spinal cord. It controls body movement and gives us feedback about the outside world. The Peripheral Nervous System (The Nerves) ​ It is made up of all the neurons outside of the CNS ​ Connects the CNS to organs, limbs and skin ​ Allows the brain and spinal cord to receive and send signals to other organs ​ Regulates involuntary functions like heartbeat and breathing ​ Carries sensory and motor information to and from the Central Nervous System. The Role of Nervous System Allows an organism to coordinate and regulate many body functions. Many actions are done without the conscious thought of the autonomic nervous system. These actions are done with electrical impulses travelling along specialised cells known as neurons.