Aqa A Level Biology - Paper 3 (Synoptic) Questions And Correct Detailed Answers 2024/2025, Exams of Biology

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1.What are the useful properties of water and why? - CORRECT ANSWERS 1) Water is a metabolite - in many metabolic reactions including condensation and hydrolysis

2. Water is a solvent - medium in which enzyme catalysed reactions take place (metabolic reactions ) and readily dissolves substances like inorganic ions ( as water is dipolar so totally surrounds the ions) , excretory products (urea/ammonia) , respiratory gases and small hydrophilic molecules ( amino acids , etc)
3. Water has a high latent heat of vaporisation (lots of energy required to break hydrogen bonds between water molecules so a lot of energy is used up when water evaporates ) so helps with temperature control as evaporation of sweat cools humans down
4. Water has a high specific heat capacity ( to separate the many hydrogen bonds requires a lot of energy) so acts as a buffer and resists temperature changes to maintain a constant internal body temperature
5. Water has large cohesive forces ( as hydrogen bonds stick together) so allows transportation of substances( water travelling in columns in xylem) and means water has a high surface tension when it comes into contact with air ( allowing pond skaters to walk on its surface) Why is water dipolar? - CORRECT ANSWERS As water is made up of two hydrogen atoms and one oxygen atom , the hydrogen atoms have a slightly positive pole and the oxygen atom has a slightly negative pole making water dipolar. Hydrogen bonds - CORRECT ANSWERS Slightly negatively charged oxygen atom is attracted to the slightly positively charged hydrogen atom of other water molecules. The attraction between opposite charges is called hydrogen bonding, which are weak bonds but strong in large numbers. This makes water a major component in cells Hydrolysis - CORRECT ANSWERS Breaks a bond between two molecules by the addition of a molecule of water

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Condensation - CORRECT ANSWERS Joins two molecules together with the formation of a bond by the removal of a molecule of water Polymer - CORRECT ANSWERS A molecule ( carbohydrate, nucleotide or protein) made up of many monomers ( small repeating units) joined together by condensation reactions and broken down my hydrolysis Monosaccharides - CORRECT ANSWERS Are the monomers from which larger carbohydrates are made and contain the elements C H and O. They are sweet and soluble and there are three types : fructose , glucose and galactose. Hexose sugars (glucose) have the formula C6H12O Glucose is the product of photosynthesis and a major substrate of respiration , draw the two structural isomers of glucose in long and short hand and state the difference between them - CORRECT ANSWERS On carbon 1 in beta glucose the hydroxyl group (OH) points upwards and in alpha glucose the hydroxyl group points down on carbon 1 Sucrose - CORRECT ANSWERS Glucose and fructose Maltose - CORRECT ANSWERS Glucose and glucose Lactose - CORRECT ANSWERS Glucose and galactose How do monosaccharides join together - CORRECT ANSWERS By condensation to form a glycosidic bond between two monosaccharides and a disaccharide and a molecule of water are formed

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Disaccharide - CORRECT ANSWERS Two monosaccharides joined together by condensation forming a glycosidic bond. There are three types : maltose, sucrose and lactose. They have the chemical formula C12H22O Draw the hydrolysis of maltose in structural formula and short hand formula - CORRECT ANSWERS Test for starch - CORRECT ANSWERS Add iodine solution to the test sample , if starch is present colour changes from yellow to a blue-black colour. Test for a reducing sugar - CORRECT ANSWERS Heat with Benedict's reagent ( blue) and if reducing sugar is present a brick red precipitate will form Issues with the Benedict's test? - CORRECT ANSWERS 1) It is non specific - doesn't tell which reducing sugar is present , a biosensor can be used to detect for specific sugars

2. It's qualitative so colour change is being measured so can't obtain concentration of reducing sugar but allows an estimate for how much is present in the strength of the colour
3. Is subjective How to quantify results on the concentration of unknown glucose concentration? - CORRECT ANSWERS Use a colorimeter, as a serial dilution of known glucose concentrations can be measured producing a set of solutions with known concentrations. The Benedict's test can be performed with each of these and the colour intensity measured. A CALIBRATION CURVE can be produced from the results and used to read iff the concentration of glucose in an unknown solution. Test for a non-reducing sugar? - CORRECT ANSWERS Heat the sample with Benedict's reagent and if there is no colour change a reducing sugar is not present but a non-reducing sugar could be.

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Heat a fresh sample with dilute acid ( which will hydrolyse the non reducing sugar into its constituent monosaccharides). Neutralise with alkali and carry out the Benedict's test again If the test is positive for a non-reducing sugar it will form a brick red precipitate Polysaccharide - CORRECT ANSWERS Three main types - starch , glycogen and cellulose which are chains of many monomers of glucose formed in condensation reactions. Starch - CORRECT ANSWERS Starch is used for energy storage in plants and is made from condensation of alpha glucose. Amylose- compact helical chains so store lots of glucose in a small space Amylopectin - branched chains which allow many ends to be quickly hydrolysed by amylase enzymes to release glucose Insoluble and large so no osmotic effects , inert and cannot diffuse out of the cells which they are stored in. Cellulose - CORRECT ANSWERS Major component of plant cell walls made up of beta glucose monomer in a condensation reaction. Chains of beta glucose molecules form long straight unbranched chains. These chains run parallel to each other and hydrogen bonds form cross- linkages between chains. These many hydrogen bonds provide high tensile strength which makes the cell wall rigid and prevents osmotic lysis Hydrogen bonds also form strong fibres called microfibrils which are grouped into fibres which provide structural support. Glycogen - CORRECT ANSWERS Energy storage molecule in animals found in liver cells and in muscle tissue and is made from the condensation of alpha glucose. Compact so store lots of glucose in a small space

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Is quickly hydrolysed to release soluble glucose as many ends for amylase enzymes to attack Large and insoluble so no osmotic effects , inert and cannot diffuse out of the cells which they are stored in. Name the 4 inorganic ions and state their role - CORRECT ANSWERS Inorganic ions occur in solution in the cytoplasm and body fluids ( blood , tissue fluid) Hydrogen ions - affects pH levels, the higher the concentration of H+ ions the lower the pH( more acid ) Iron ions - important component of haemoglobin which carries oxygen around the body in the red blood cells Phosphate ions - component of DNA , ATP , RNA and phospholipids , bonds between phosphate groups store energy in ATP Sodium ions - involved in the absorption of glucose and amino acids in co transport in the small intestine Amino acids - CORRECT ANSWERS Are the monomers from which polypeptides are made. Proteins are made up of one or more polypeptide chains. All amino acids contain the elements C H O and N and are made up of an amino group (NH2) , a carboxylic acid group (COOH) and a variable group (R) What is a conjugated protein? - CORRECT ANSWERS A protein with a non- protein chemical group attached Draw the structure of an amino acid - CORRECT ANSWERS How many amino acids are there that are shared in all organisms? - CORRECT ANSWERS 20 amino acids that differ by a different variable group. Dipeptide - CORRECT ANSWERS Two amino acids join to form a dipeptide and a peptide bong is formed between the amino acids by a condensation reaction.

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Draw the formation of a dipeptide from two amino acids? - CORRECT ANSWERS Describe the protein structure? - CORRECT ANSWERS Primary structure - sequence of amino acids in a polypeptide chain Secondary structure - folding of polypeptide chain causing hydrogen bonds to form between amino acids causing the formation of an alpha helix or a beta pleated sheet Tertiary structure - the further folding of the secondary structure which is held into shape by bonds e.g. hydrogen, ionic and disulphide. Bonds form between R groups of amino acids forming a 3D structure and is the final structure of one polypeptide chain Quaternary structure - is the final 3D structure of a protein consisting of more than one polypeptide chain What are the two types of protein? - CORRECT ANSWERS Fibrous- form long chains running parallel to each other with cross bridges between chains producing very strong and stable proteins such as collagen and keratin. Globular - carry out metabolic functions such as enzymes, haemoglobin and antibodies Collagen - CORRECT ANSWERS Primary structure - unbranched polypeptide chain Secondary structure - forms alpha helix lots of amino acid glycine helps close packaging Tertiary structure - polypeptide chain is further folded Quaternary structure - 3 polypeptide chains are wound together with covalent bonds between amino acids of adjacent chains This makes collagen strong and stable and is found in tendons which join muscle to bong. Tendons need to be strong and not elastic.

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Test for proteins - CORRECT ANSWERS Add Biuret solution to a sample of solution , if protein is present a lilac colour is seen from the blue colour of Biuret solution What method separates a mixture of monosaccharides or amino acids? - CORRECT ANSWERS Chromatography as molecules have different sizes so have different solubilities , the smaller the molecule the further it will travel up the solvent and the more soluble the molecule the further it will move up. Rf value must be calculated to allow comparison between different chromatograms run with the same solvent. How do you work out the Rf value? - CORRECT ANSWERS Distance from origin to solute (spot) over the distance from origin to solvent front Why are enzymes biological catalysts? - CORRECT ANSWERS As they lower amount of activation energy needed to make the reaction proceed which increases the rate of the chemical reaction Enzymes - CORRECT ANSWERS Are globular proteins in a spherical shape due to tight folding of the polypeptide chain. They catalyse metabolic reactions at cellular level( respiration) and the organism as a whole ( digestion). Enzymes can be intracellular ( inside the cell) or extracellular ( outside cell). Enzymes have a specific active site that is complementary to its substrate. Enzymes are very specific as they catalyse only one reaction. Without enzymes the temp in living cells would be too low (< degrees) for chemical molecules to react fast enough to support life Why are enzymes specific? - CORRECT ANSWERS Each different enzyme has a specific tertiary structure and so a specific active site and shape. Only one substrate is complementary to the enzymes active site so combines and forms an enzyme- substrate complex.

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Lock and Key model - CORRECT ANSWERS The active site is always exactly complementary shape to the substrate so reactions are fastest in these conditions. Induced fit model - CORRECT ANSWERS When the substrate bonds to the enzyme it induces a change in the tertiary structure so the active site changes shape to become complementary to the substrate How is rate measured - CORRECT ANSWERS Amount of product or volume of substrate left over time taken. It's units are cm3s- What factors effect enzyme action? - CORRECT ANSWERS Temperature, pH , enzyme concentration and substrate concentration. How does temperature affect enzyme activity and what does the graph of rate of reaction against temperature look like? - CORRECT ANSWERS At low temperatures there is less kinetic energy so enzyme molecules are inactive as they move around slowly in aqueous conditions and only collide with the substrate rarely to form ES complexes. As temperature increases enzyme and substrate molecules gain more kinetic energy so they move faster and collide more frequently so rate of reaction increases and more ES complexes form. Above 40 degrees however , rate of reaction decreases as the enzymes denature. This is because as temp increases over optimum temp , hydrogen bonds break which changes the shape of the tertiary structure and therefore the shape of the active site. So the substrate is no longer complementary and no ES complexes can form. So it has denatured as it can no longer carry out its function. How does pH affect enzyme activity and what does the graph look like? - CORRECT ANSWERS At the optimum pH for the enzyme the active site is exactly complementary to the substrate. If there is a change in pH levels this alters the charges on the amino acids. This causes hydrogen bonds to break and form in different places. This causes a change in the tertiary structure and

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therefore a change in the active site of the enzyme so it had become denatured as no ES complexes form. What does a buffer do? - CORRECT ANSWERS Prevent pH changes How does substrate concentration affect enzyme activity and what does the graph look like? - CORRECT ANSWERS As substrate concentration increases rate of reaction increases. This is because there are more substrate molecules which means there are more frequent collisions between the substrate and enzyme so more ES complexes form. Rate of reaction reaches max and remains constant as concentration of enzyme is s limiting factor. How does Enzyme concentration effect enzyme activity and what do the graphs look like? - CORRECT ANSWERS If more enzyme molecules are in solution there are more frequent collisions and so more ES complexes form so rare of reaction increases. However if the substrate is limited then the graph will level off as there isn't enough substrate to occupy all the active sites What is competitive inhibitor? - CORRECT ANSWERS Similar shape to substrate so is complementary to the active site so binds to it. So fewer ES complexes form and rate of reaction decreases. Rate is reduced at low substrate concentration but as concentration of substrate increases the effect of inhibition decreases so same maximum rate is reached as with no inhibition. This is due to greater proportion of substrate results in a greater chance to compete to occupy the active site What is non-competitive inhibitor? - CORRECT ANSWERS Binds to the enzyme away from its active site so causes the shape of active site to change so the substrate can no longer bind and no ES complexes can form. The decreases rate of reaction and increasing the concentration of substrate will have no effect on rate. Draw and label a eukaryotic animal cell - CORRECT ANSWERS

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Draw and label a eukaryotic plant cell - CORRECT ANSWERS Draw and label a prokaryotic cell - CORRECT ANSWERS Draw and label a virus - CORRECT ANSWERS What do all cells have in common? - CORRECT ANSWERS Cell membrane , cytoplasm and genetic material made of DNA What is an organelle? - CORRECT ANSWERS Small cellular structure that has a specific function What's the function and description of DNA in prokaryotes? - CORRECT ANSWERS Short circular loop of DNA not associated with histone proteins and free in the cytoplasm which carries genetic code for proteins What's the function and description of cell wall in prokaryotes? - CORRECT ANSWERS Contains murein and prevents osmotic lysis by providing rigidity and strengthens cell What's the function and description of cytoplasm in prokaryotes? - CORRECT ANSWERS Solution where dissolved molecules are found with no membrane bound organelles , which is the site of many metabolic reactions in the body What's the function and description of cell membrane in prokaryotes? - CORRECT ANSWERS Phospholipid bilayer with embedded proteins which controls passage of substances across exchange surfaces by passive or active transport

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What's the function and description of 70s ribosomes in prokaryotes? - CORRECT ANSWERS Made of RNA and is the site of protein synthesis What's the function and description of the flagellum in prokaryotes? - CORRECT ANSWERS Thin rotating fibre responsible for movement of the cell What's the function and description of plasmids in prokaryotes? - CORRECT ANSWERS One or more small loops of DNA which can replicate independently and pass on genetic information via conjugation to other bacteria What's the function and description of capsule in prokaryotes? - CORRECT ANSWERS Extra layer outside cell wall which protects bacterium from attack by the immune system ( phagocytosis, desiccation and some pathogens) What's the function and description of a cell membrane in a eukaryotic cell? - CORRECT ANSWERS Membrane made from phospholipid bilayer which contains embedded proteins, which makes it selectively permissible allowing movement of substances in and out of the cell and allows cell indemnification due to antigens. What's the function and description of a nucleus in a eukaryotic cell? - CORRECT ANSWERS Large organelle surrounded by a nuclear envelope which contains many pores. Contains chromosomes which are long linear strands d DNA associated with histone proteins. Nucleus contains genetic code for proteins and the nucleolus manufactures ribosomes What's the function and description of mitochondria in a eukaryotic cell? - CORRECT ANSWERS Oval shaped , contains a double membrane where the inner membrane is folded to form Cristae and the fluid inside is called the matrix which contains enzymes involved in respiration. Also contains DNA like that in prokaryotes. Site of aerobic respiration where ATP is produced

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What's the function and description of a chloroplast in a eukaryotic cell? - CORRECT ANSWERS Small oval structure mostly found in mesophyll plant and algal cells which is surrounded by a double membrane , and contains internal membranes called thylakoids which stack to form structures called grana and grana are linked by lamellae. Chlorophyll is located inside the grana which absorbs light for photosynthesis. Surround grana the solution is called the storms which contain enzymes needed for photosynthesis and starch grains. Also contains DNA like that in prokaryotes. Site of photosynthesis is its function What's the function and description of the Golgi apparatus in a eukaryotic cell? - CORRECT ANSWERS Series of membranes surrounded by vesicles , modifies proteins and lipids and packages then into vesicles and also forms lysosomes. What's the function and description of a vesicle in a eukaryotic cell? - CORRECT ANSWERS Small fluid filled sac packaged by the Golgi apparatus which stores lipids and proteins and transports them out of the cell membrane What's the function and description of a lysosome in a eukaryotic cell? - CORRECT ANSWERS Vesicle made by the Golgi apparatus that contain hydrolytic digestive enzymes called lysozymes and is used to digest pathogens or worn out old cells What's the function and description of a ribsome in a eukaryotic cell? - CORRECT ANSWERS Made up of proteins and RNA and is a very small non membrane bound organelle that is either free in cytoplasm or attached to rough endoplasmic reticulum and is the site of protein synthesis What's the function and description of rough endoplasmic reticulum in a eukaryotic cell? - CORRECT ANSWERS Series of membranes that is covered in ribosomes and synthesises and transports proteins through the cytoplasm

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What's the function and description of smooth endoplasmic reticulum in a eukaryotic cell? - CORRECT ANSWERS Series of membranes that aren't covered in ribosomes , which synthesise and transport lipids What's the function and description of a cell wall in a eukaryotic cell? - CORRECT ANSWERS Rigid structure made of cellulose in plants and chitin in fungi which has high tensile strength, this supports the cell and prevents osmotic lysis What's the function and description of a vacuole in a eukaryotic cell? - CORRECT ANSWERS Filled with cell sap( weak solution of sugars and salts) in plant cells which is surrounded by a membrane called tonoplast. Helps to keep the cell rigid and stops plant wilting Compare eukaryotic and prokaryotic cells. - CORRECT ANSWERS Prokaryotes: Eukaryotes No nucleus( loop of Has nucleus with linear DNA that's free in chromosomes cytoplasm and not associated with associated with histones histone proteins ) Does not contain any Contains membrane membrane bound bound organelles organelles Has smaller 70s Has larger 80s ribosomes ribosomes

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Forms new cells by Forms new cells by binary fission. mitosis and meiosis Tissue - CORRECT ANSWERS Group of similar specialised cells with a particular function Organ - CORRECT ANSWERS Group of different tissues with a particular function e.g epithelial , muscular and glandular ( secretes chemicals) tissue Organ system - CORRECT ANSWERS Group of interrelated organs that function together as a whole Viruses - CORRECT ANSWERS A cellular and non living and are just genetic material (DNA or RNA) surrounded by proteins. They are smaller than bacteria and has a capsid which is a protein coat and attachment proteins which allow the virus to attach to a host cell ( complementary receptors on host cell membranes ) and replicate How do prokaryotes reproduce? - CORRECT ANSWERS Binary fission - DNA and plasmids replicate and move to opposite poles and the cytoplasm divides into two genetically identical daughter cells which can have a variable number of plasmids How do viruses reproduce? - CORRECT ANSWERS Use their attachment proteins to bind to specific complementary receptor proteins on the surface of host cells and inject their genetic material into the host cell to replicate the viral DNA/RNA What's magnification? - CORRECT ANSWERS Number of times bigger the imagine appears compared to real size

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What's resolution? - CORRECT ANSWERS Ability to see detail to distinguish organelles that are close together What are the two different type of microscope and what are the differences between them? - CORRECT ANSWERS Optical light microscope - long wavelength so low resolution and magnification. Used for colour imagines of cells and large organelles and doesn't require complicated preparation of specimen but not powerful enough for small structures Electron microscope- electrons have a much smaller wavelength than light so resolution and magnification is much higher so fine details can be seen. Black and white images only and vacuum is essential so only dead specimens can be used and preparation often results in artefacts ( air bubble). What are the two types of electron microscope and the differences between them? - CORRECT ANSWERS Scanning - lower resolution , does not require thin sections to be cut and usually shows the surface of the object that are 3D Transmission- higher resolution, requires very thin sections, no 3D images but allows detail of internal small organelles to be seen How do you calculate the real length of a cell? - CORRECT ANSWERS Image over magnification How a student can prepare a microscope slide? - CORRECT ANSWERS Pipette a small drop of water onto the slide Place a thing section of specimen onto top of water drop ( tip of root if root is specimen as that's where mitosis takes place ) Use mounted needle to break tip open and speed cells thinly so light can pass through and form an image Add a few drops of stain and leave for a few minutes Place cover slip over the cells and tilt and push down carefully so it fully covers the specimen and try and avoid air bubbles being present as they obstruct the view

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How to observe cells in a prepared slide using a light microscope? - CORRECT ANSWERS Clip slide onto stage Select lowest powered objective lens Use coarse adjustment knob to bring the stage up below the objective lens Look down the eye price and use the coarse adjustment knob to move the stage down until the image is in focus Adjust the focus with the fine adjustment knob until the image is clearer If greater magnification is required, refocus using a higher powered lens How to use an eye piece graticule? - CORRECT ANSWERS Measure field of view using an eye piece graticule Estimate proportion of field of view occupied by one cell Calibrate with something of known size (stage micrometer ) How do tissues have to be kept? - CORRECT ANSWERS Cold temperature- reduce enzyme activity and prevents digestion of organelles Buffer solution - maintains constant pH and prevents denature if proteins including enzymes Isotonic - sans water potential as organelles to prevent osmotic lysis How are organelles separated from the cell? - CORRECT ANSWERS Cell fractionation- cells are broken open using a homogeniser Cell debris and while cells are filtered to leave a suspension Ultracentrifugation- resultant suspension centrifuged at s low speed The most dense organelle (nucleus) separate at the bottom of the tube (pellet) The rest of the organelles are suspended in the supernatant Supernatant is then poured into fresh tube and spun at a higher speed to separate chloroplast/ mitochondria

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This process is repeated at increasing speeds to separate less dense organelles Triglycerides - CORRECT ANSWERS Contain only C , O and H and contain a glycerol molecule combined with three fatty acid chains by 3 condensation reactions forming ester bonds. They're insoluble in water so don't affect water potential of cells. Fatty acid tails are hydrophobic and dissolve easily in organic solvents that releases energy when they're broken down. Draw the structure of a triglyceride with 2 saturated fatty acid chains and one unsaturated fatty acid chain and label the ester bond - CORRECT ANSWERS With two R groups containing no double bonds between C atoms and one R group with one or more double bonds between C atoms. What are the biological roles of triglycerides? - CORRECT ANSWERS Storage of energy in adipose cells Insulation Protection How does the structure and properties of a triglyceride relate to its function? - CORRECT ANSWERS They have a high ratio of energy storing carbon- hydrogen bonds to C atoms so are an excellent source of energy They have a low mass to energy ratio so they can store lots of energy in a small volume They are large non polar molecules that are insoluble in water so have no osmotic effect Phospholipids - CORRECT ANSWERS Contain a glycerol molecule combined with two fatty acid chains by two condensation reactions forming ester bonds. However they have a phosphors group attached to the glycerol instead of an extra fatty acid in triglycerides. They are composed of a hydrophobic non polar fatty acid tail which repels water and a hydrophilic polar head which attracts

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water. This forms a bilayer where the head points outwards and the gals point inwards. Test for lipids? - CORRECT ANSWERS Shake with ethanol then shake gently with water and if a lipid is present a milky white emulsion will be present. 3 functions of a cell membrane - CORRECT ANSWERS 1) control transport of substances in an out of the cell as the membrane is partially permeable

2. acts as a receptor site
3. separates cell and organelles from each other What is the fluid mosaic model? - CORRECT ANSWERS Fluid as different molecules are constantly moving around Mosaic as many different types of molecules are present and the proteins and carbohydrates float around in the bilayer How does the structure of a phospholipid relate to its function? - CORRECT ANSWERS Hydrophobic tails point towards each other away from water and hydrophilic heads point towards water which arranges the the phospholipids in a bilayer which allows non polar, lipid soluble and small molecules to pass through the membrane and acts as a barrier to polar, water soluble and large molecules. Role of intrinsic proteins in the cell membrane? - CORRECT ANSWERS Transport polar and large molecules through channels and carriers ( or enzymes ) Role of extrinsic proteins in cell membrane? - CORRECT ANSWERS Enzymes , act as receptors for binding to hormones as have a specific receptor site and antigens for cell recognition

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Role of glycoproteins in the cell membrane? - CORRECT ANSWERS A protein bonded to a carbohydrate which acts as a receptor for hormones and neurotransmitters or antigens for cell recognition Role of cholesterol in the cell membrane? - CORRECT ANSWERS Is a type of lipid that increases strength and stability of membranes by restricting movement to make the membranes less flexible/ fluid and more rigid. Helps prevent loss of water as helps maintain the shape of the cell Role of glycolipids in the cell membrane? - CORRECT ANSWERS A protein bonded to a lipid which acts as a recognition site and help main stability of membrane Fick's Law of Diffusion - CORRECT ANSWERS rate of diffusion = surface area x difference in concentration gradient over the thickness of the exchange surface SAD TOES Simple diffusion - CORRECT ANSWERS Is a passive process where molecules move from an area of high concentration to an area of low concentration down a concentration gradient directly across the cell membrane as the molecules are small ( oxygen, carbon dioxide and water ). What is dynamic equilibrium? - CORRECT ANSWERS Same number of particles diffusing in each direction How is rate of diffusion increased? - CORRECT ANSWERS Larger surface area Larger concentration gradient Thinner exchange surface( short diffusion pathway ) Facilitated diffusion - CORRECT ANSWERS Passive process where larger or polar molecules are transported across the membrane through either carrier or

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channel proteins from a high concentration to a low concentration down a concentration gradient. Each protein transports a specific molecule due to a specific tertiary structure. Osmosis - CORRECT ANSWERS Passive process of the diffusion of water through a partially permeable membrane from a high water potential to a low water potential down a water potential gradient. What happens if animal cells are placed in hypertonic solution? - CORRECT ANSWERS Water will diffuse out of the cell by osmosis from a high water potential gradient to a low water potential gradient causing the cell to crenate / shrink What happens if animal cells are placed in a hypotonic solution? - CORRECT ANSWERS Water will enter the cell by osmosis from a high to low water potential gradient causing the cell to swell and burst ( osmotic lysis) What happens to an animal cell if placed in isotonic solution? - CORRECT ANSWERS No net osmotic movement as isotonic solution has and water potential as cell What happens to a plant cell if placed in hypertonic solution? - CORRECT ANSWERS Water leaves the cell and vacuole by osmosis from a high to low water potential causing the cytoplasm to shrink away from cell wall leaving gaps between cell membrane and cell wall which is filled with salt solution, which is known as plasmolysis What happens to a plant cell in a hypotonic solution? - CORRECT ANSWERS Water enters the cell by osmosis from a high to low water potential gradient but due to high tensile strength of cell wall the cell doesn't burst and becomes turgid

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What happens to a plant cell in isotonic solution? - CORRECT ANSWERS No net osmotic movement as same water potential Active transport - CORRECT ANSWERS Requires energy from ATP by a hydrolysis reaction converting ATP into ADP and Pi which releases energy. Movement of molecules from a low to high concentration against a concentration gradient using a specific carrier protein. If any process reduces respiration , rate of active transport will be reduced as less ATP will be produced. Cotransport of sodium and glucose or amino acids in the lumen of ileum to epithelial cells - CORRECT ANSWERS Sodium ions are actively transported out of the epithelial cells into the blood steam via sodium-potassium pump , using ATP, which creates a low concentration gradient so sodium ions can diffuse into the cell by facilitated diffusion as there is a higher concentration of sodium in the lumen of the ileum than in the epithelial cells. Sodium ions and glucose molecules enter epithelial cells from the gut lumen via a cotransport protein( as they bind and change the shape of the protein) bringing glucose into the epithelial cell against its concentration gradient using hydrolysis of ATP. This causes the concentration of glucose inside the epithelial cell to increase so glucose is transported into the blood stream by facilitated diffusion through a specific carrier protein. Circulation of blood maintains concentration gradient of glucose into blood stream as it removes blood with a high glucose concentration and replaces it with blood with a low glucose concentration. Exocytosis - CORRECT ANSWERS Removes materials in vesicles to leave through the cell membrane Endocytosis - CORRECT ANSWERS Imports materials into the cell by forming a vesicle What are the three things a pathogen can be and how do they cause disease? - CORRECT ANSWERS Bacteria , viruses and fungi cause disease by damaging body cells or releasing toxins

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What is an antigen? - CORRECT ANSWERS A protein or glycoprotein often on a cell membrane that can cause an immune response, involving antibodies Each type of cell has what on its surface that can be used in cell recognition? - CORRECT ANSWERS Specific antigens What foreign antigens can the immune system identify? - CORRECT ANSWERS Pathogens , abnormal body cells , toxins and cells from organisms of same species ( during transplants) What's the effect of antigen variability on disease and disease prevention? - CORRECT ANSWERS Antigen variability is where the antigens on a strain of pathogen are different and can change their surface antigens due to changes in the genes of a pathogen. So when you're infected with the same pathogen the previous memory cells will not recognise the different antigens so prevent a secondary response being carried out. So the primary response will be carried out which takes time and so you get ill again so decreases disease prevention. Describe the sequence of events in phagocytosis? - CORRECT ANSWERS The phagocyte recognises and binds to foreign antigens on a pathogen. The pathogen engulfs the pathogens and they are enclosed in a vesicle. A lysosome contain lysozymes ( hydrolytic enzymes ) and fuses with the vesicle which digest the pathogen by hydrolysis and the useful products are absorbed into the cytoplasm. The phagocyte the places the pathogens antigens on it's cell surface membrane and becomes and antigen presenting cell What are the two types of specific immune response and are the different types of the cells and their functions? - CORRECT ANSWERS Cellular response

• involves T-cells and antigen presenting cells and works on damaged or infected cells. Cytotoxic T cells- destroy infected body cells by producing a protein that makes holes in their cell membrane

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Memory T cells- enable a rapid response to future infections by the same pathogen Helper T cells- release chemical signals which stimulate phagocytes, B cells and cytotoxic T cells Humoral response - involves B cells, clinal selection and the production of monoclonal antibodies and acts on circulating pathogens. Plasma B cell- secrete antibodies directly and bind to antigens forming an antigen- antibody complex Describe the cellular specific immune system response - CORRECT ANSWERS Pathogen engulfs pathogen that's invaded body cells and places it's antigens on its cell surface to become an antigen presenting cell. Receptors on a specific T cell binds to the complementary antigens on antigen presenting cell. This activates the T helper cells which divide rapidly by mitosis and form a clone of genetically identical cells. They release chemicals to stimulate memory T cells , cytotoxic T cells and B cells. Describe the humoral specific immune system response - CORRECT ANSWERS When the antibody on the specific B cell binds to the complementary antigen along with chemicals released by specific T helper cells this activates B cells. These divide rapidly by mitosis to form clones of genetically identical daughter cells. This process is called clonal selection. The daughter cells develop either into plasma cells or memory cells. Plasma cells secrete antibodies complimentary to specific antigens and they are called monoclonal antibodies as they are produced by the same plasma cell or from a clone of genetically identical B cells and all have the same tertiary structure and bind to only one specific antigen. What is an antibody and what is it's structure? - CORRECT ANSWERS Antibodies are proteins that are produced by plasma cells that are complementary to specific antigens and therefore can bind to it and neutralise forming an antigen-antibody complex. This causes agglutination to occur where the pathogens clump together so they can be engulfed by a phagocyte more easily. They are Y shaped and are made up of two light and two heavy

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polypeptide chains bonded together. They have different variable regions which bind to specific antigens. All antibodies have the same constant regions. Primary response - CORRECT ANSWERS When an antigen enters the body for the first time it activates the immune response. The primary response is slow as it takes time for a specific B lymphocyte to be activated which has to clone its self and produce plasma cells and memory B cells. T cells divide and clone its self to produce memory T cells and cytotoxic T cells. Memory B cells divide rapidly to provide plasma cells that secrete specific antibodies. Memory T cells remember specific antigens and will recognise them the next time the body encounters the pathogen. The person is now immune and can respond quickly to an infection the next time around which is called the secondary response. What are the three antigen presenting cells? - CORRECT ANSWERS Cells that are infected by a virus A phagocyte which has just engulfed and hydrolysed a pathogen An abnormal body cell ( cancerous) Secondary response - CORRECT ANSWERS If the same pathogen enters the body again the immune system will produce a quicker stronger immune response. This is because clonal selection happens faster as there are already memory B cells that are activated and divide more quickly by mitosis into large numbers of plasma cells , to produce more specific antibodies faster. Memory T cells are also activated faster and divide into the correct type of T cell to kill the antigen presenting cell. Vaccination - CORRECT ANSWERS Vaccines contain antigens and stimulate your body to produce specific plasma cells, antibodies and memory cells against a particular pathogen. This means you become immune without getting any symptoms of the disease. The vaccine on a large scale can protect a whole population and may be a killed or weakened pathogen or isolated antigens. Vaccines may be taken orally or may be injected

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Define the concept of herd immunity - CORRECT ANSWERS Vaccines protect individuals as the pathogen will be killed quickly so reduce the occurrence of the disease, therefore reducing the risk of non vaccinated people developing the disease as they have a low chance of becoming in contact with another unvaccinated person. Disadvantages of vaccination - CORRECT ANSWERS Some individuals may have a defective immune system and vaccination may fail to induce immunity. The pathogen may mutate quickly and change antigens so that the immune system fails to recognise the infection. There may be many varieties of the same pathogen each with different antigens. Vaccine could be broken down by enzymes in the gut or the molecules may be too large to be absorbed into the blood. Name the pros and cons of vaccination - CORRECT ANSWERS Pros : Less people with disease Less spread to those who are unable to be vaccinated Cons : May have potential side effects Is tested on animals Clinical trials What is active immunity? - CORRECT ANSWERS When your immune system is stimulated to make its own antibodies after being stimulated by an antigen to produce memory cells and can be natural ( catching a disease) or artificial ( after a vaccination) What is passive immunity? - CORRECT ANSWERS When individuals acquire antibodies made by a different organism as their immune system doesn't produce antibodies of its own and can be natural ( foetus acquires antibodies from the mother across the placenta ) or artificial ( immunity due to injection of antibodies from someone else)