AQA A LEVEL BIOLOGY Paper 1 2024 Questions With Correct Answers!!, Exams of Biology

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AQA A LEVEL BIOLOGY Paper 1 2024

Questions With Correct Answers!!

What is the function of the cell membrane? - ANSWERTo control what enters and leaves the cell, acts as a barrier between the cell and its environment. What structural feature of the cell membrane allows substances to enter/leave? - ANSWERPartially permeable What is the fluid mosaic model? - ANSWERStates that a membrane is a fluid structure (because phospholipids are constantly moving) with a "mosaic" of various proteins embedded in it Describe the structure and function of phospholipids. - ANSWERHydrophilic head and hydrophobic tail, arranged in a bilayer (heads face outwards, tails face inwards). Lipid-soluble substances only allowed to pass through. What is the function of cholesterol in the CSM? - ANSWERMake phospholipids pack more closely together, restricting the movement of the phospholipids, making the membrane less fluid/more rigid. What is simple diffusion? - ANSWERThe (passive) movement of particles from an area of high concentration to an area of low concentration. What is facilitated diffusion? - ANSWERThe passive movement of a large/charged particle down its concentration gradient through a carrier/channel protein. What is the process of facilitated diffusion using a carrier protein? - ANSWERLarge molecule binds to a carrier protein in membrane. Protein changes shape. Protein releases the large molecule on the opposite side of the membrane. What is the process of facilitated diffusion using a channel protein? - ANSWERChannel proteins form pores in membrane. Charged particles can diffuse down their concentration gradients to the opposite side of the membrane. What are the factors affecting simple diffusion? - ANSWERConcentration gradient, thickness of exchange surface and surface area. What are the factors affecting facilitated diffusion? - ANSWERNumber of transport proteins and strength of gradient. What is osmosis? - ANSWERDiffusion of water through a partially permeable membrane from an area of high water potential to an area of lower water potential.

What are the factors affecting osmosis? - ANSWERWater potential gradient. Thickness of exchange surface. Surface area of exchange surface. Outline a method for RP3 (investigation of osmosis using potato chips). - ANSWERProduce a series of dilutions from 1M sucrose solution (of a variety of different concentrations, 0M, 0.2M, 0.4M, 0.6M, 0.8M, 1M). Use a cork borer to cut potatoes into identically-sized chips. Blot them dry with a paper towel and measure the mass of each using a mass balance. Place one chip into each of the sucrose solutions. Put the test tubes into a water bath at 30°C for 20 minutes. Take them out and reweigh the mass of the chips. Calculate the %change in mass for each chip. What is active transport? - ANSWERThe active process of moving molecules from an area of low concentration to an area of high concentration using ATP. Name one type of carrier protein and describe how it works. - ANSWERCo- transporters. Bind two molecules at once. The concentration gradient of one of the molecules is used to move the other molecule against its own concentration gradient. Give an example of co-transport in mammals. - ANSWERGlucose/Na+ co-transport. Na+ actively transported out of the ileum epithelial cells into the blood by the Na+/K+ pump. This creates a concentration gradient, higher concentration of Na+ in lumen than inside cell. Na+ Defuses into the epithelial cells from the lumen Na+/glucose co-transporter proteins. Co-transporter carries glucose into the cell with the sodium so glucose concentration inside the cell increases. Glucose diffuses out of the cell, down its concentration gradient, through a protein channel, into the blood, by facilitated diffusion. What are the factors affecting active transport? - ANSWERSpeed of individual carrier proteins. Number of carrier proteins present. Rate of respiration/availability of ATP. 3.2.1 Cell Structure - ANSWER Eukaryotic cells - ANSWERComplex, include all animal and plant cells (& algal/fungal cells). Algal and fungal cells - ANSWERAlgal: same organelles as plant cells including cell wall and chloroplasts. Fungal: similar to plant cells but cell walls made of chitin and no chloroplasts.

Organelles in eukaryotic cells: - ANSWERMembrane-bound compartments which separate metabolic reactions within a cell. Nucleus - ANSWERContains chromosomes which are made from protein bound linear DNA. Controls the cells activities. DNA contains instructions to make proteins. Mitochondrion - ANSWERDouble membrane, inner membrane folded to make cristae. Matrix contains enzymes involved in respiration. Site of aerobic respiration and ATP production. Chloroplast (plants) - ANSWERDouble membrane. Site of photosynthesis. Golgi apparatus - ANSWERGroups of fluid-filled membrane-bound flattened sacs. Processes and packages new lipids and proteins. Makes lysosomes. Golgi vesicle - ANSWERSmall fluid-filled sac, produced by g.a. Stores lipids and proteins and transports them out of the cell. Lysosome - ANSWERRound organelle surrounded by a membrane. Contains lysozymes, used to digest invading cells or breakdown worn out components of the cell. Ribosome - ANSWERSmall organelle made up of proteins and RNA. Site of protein synthesis. RER - ANSWERFolds and processes proteins that have been made at the ribosomes. SER - ANSWERSynthesises and processes lipids. Cell wall (plants) - ANSWERUsually made of cellulose (chitin, fungi). Support cells and prevents them from changing shape. Cell vacuole (plants) - ANSWERFound in cytoplasm. Contains cell sap. Membrane surrounding this is called the tonoplast. Maintains pressure inside the cell, keeping cell rigid/stops wilting. Prokaryotic cells - ANSWERSmaller and simpler than eukaryotic cells. Plasma membrane - ANSWERMade of lipids and proteins. Controls movement of substances in/out of cell. Cell wall - ANSWERMade of murein (glycoprotein).

Capsule (slime) - ANSWERProtects the bacteria from attack by cells of the immune system. Flagellum - ANSWERRotates to make the cell move. Viruses - ANSWERAcellular. Invade and reproduce inside the cells of other organisms. What is magnification? - ANSWERHow much bigger the image is that the specimen. What is resolution? - ANSWERThe ability of the microscope to distinguish between two points that are close together. Light/optical microscopes - ANSWERUses light. Max resolution of 0.2micrometers Max magnification of x1, Electron microscopes - ANSWERUse electrons. Vacuum only so no living specimen. Max resolution of 0.0002micrometers Max magnification of x1,500, TEM - ANSWERUses electromagnets to focus a beam of electrons through the specimen. Thin specimen only. SEM - ANSWERScans a beam of electrons across the specimen. 3-D image. Can be used on a thick specimen - but lower resolution than TEM. What is the process of cell fractionation? - ANSWER1 Homogenisation - Play cells in ice-cold, isotonic, buffer solution and grind up in a blender. 2 Filtration - filter the solution through a gauze to separate out any debris. 3 Ultracentrifugation - pour the cell fragments into a tube and put the tube into a centrifuge. Spin at a low speed. The heaviest organelles (nucleus) will fall to the bottom and will form the pellets. The rest of the organelles stay suspended in the supernatant. The supernatant is drained off poured into another tube and spun again at a higher speed. The heaviest organelles (mitochondria) will fall to the bottom, forming a pellet. The process repeats. 3.4.4 Genetic Diversity and Adaptation - ANSWER What is an allele? - ANSWERDifferent versions of a gene. What is genetic diversity? - ANSWERThe number of different alleles of genes in a species or population. How is genetic diversity increased? - ANSWERMutations in DNA. Gene flow.

What allows natural selection to take place? - ANSWERGenetic diversity. What is a genetic bottleneck? - ANSWERAn event that causes a big reduction in a population. What are the effects of a genetic bottleneck? - ANSWERReduces the number of different alleles in the gene pool so reduces genetic diversity. What is a type of genetic bottleneck? - ANSWERThe founder effect. Describes what happens when just a few organisms from a population start a new colony and there are only a small number of different alleles in the initial gene pool. What is the effect of natural selection? - ANSWERIncreases advantageous alleles in a population. Natural selection leads to... - ANSWERAdaption Types of adaptations: - ANSWERStructural, physiological, behavioral What is directional selection? - ANSWERFavours individuals at one end of the phenotypic range. What is stabilising selection? - ANSWERSelection favouring average individuals. RP6 (aseptic techniques). - ANSWERAseptic techniques - preventing contamination by unwanted microorganisms, regularly disinfect work surface, use sterile equipment, wash hands with soap and water. 3.3.2 Gas Exchange - ANSWER State the two adaptations of gas exchange surfaces. - ANSWERThin so short diffusion distance Large surface area Describe the gas exchange system in fish. - ANSWERCountercurrent (blood flows through the lamellae in one direction and water flows over in the opposite direction, maintains a high concentration gradient). Water enters the fish through its mouth and passes through the gills. Each gill is made of lots of thin plates called gill filaments which are covered in lots of lamellae, which increase the surface area. Lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion. Describe the gas exchange system in insects. - ANSWERUse tracheae. Air moves into tracheae through spiracles. Oxygen travels down the concentration gradient towards the cells. The tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. Carbon dioxide moves down its concentration gradient towards the spiracles to be released into the atmosphere.

Insects use rhythmic abdominal movements to move air in and out of the spiracles. Describe the gas exchange system in dicotyledonous plants. - ANSWERMesophyll cell surface, large surface area, are inside the leaf, gases move into and out of the leaf via stomata. Guard cells control the opening/closing of stomata. How do insects and plants control water loss? - ANSWERInsects - Close spiracles using muscles. Have a waterproof waxy cuticle all over body. Have tiny hairs around the spiracles. Plants - if the plant gets dehydrated the guard cells lose water and become flaccid which closes the pore. Give some examples of xerophytic adaptations. - ANSWERSunken stomata to trap moist air. Curled leaves with stomata inside to protect them from wind which decreases evaporation and maintains humidity inside. A reduced number of stomata so there are fewer places for water to escape. Waxy waterproof cuticles on leaves and stems to reduce evaporation. What is the structure of the human gas exchange system? - ANSWERTrachea. Bronchi. Bronchioles. Alveoli. (Ribcage, intercostal muscles, diaphragm). What is the process of inspiration? - ANSWERActive process. External intercostal and diaphragm muscles contract. Ribcage moves upwards and outwards diaphragm flattens, volume of thoracic cavity increases. Lung pressure decreases. Air flows down the pressure gradient into the lungs. What is the process of expiration? - ANSWERPassive process. External intercostal and diaphragm muscles relax. Rib cage moves downwards and inwards and diaphragm becomes curved again. Volume of thoracic cavity decreases so air pressure increases. Air is forced down the pressure gradient and out of the lungs. Where does gaseous exchange occur in humans? - ANSWERAlveoli. How are alveoli adapted for gas exchange? - ANSWERLots of them, large surface area. Epithelium is one cell thick, short diffusion pathway. How does gas exchange take place in the alveoli? - ANSWEROxygen diffuses out of the alveoli, across the alveolar epithelium and capillary endothelium, into Hb in the blood. Carbon dioxide diffuses into the alveoli from the blood, and is breathed out. 3.1.4 Proteins - ANSWER What is a protein made up of? - ANSWERAmino acids (monomers). What is the general structure of an amino acid? - ANSWER(NH2)(R) - C - (H) (COOH)

How are two amino acids joined? - ANSWERPeptide bond formed by a condensation reaction (molecule of water eliminated). What is the primary structure of a protein? - ANSWERSequence of amino acids in the polypeptide chain. What is the secondary structure of a protein? - ANSWERHydrogen bonding forms between amino acids and so make it coil or fold into alpha helix or beta pleated sheet. What is the tertiary structure of a protein? - ANSWERMore bonds form (hydrogen and ionic bonds). Forms final 3D structure (for single chain proteins). What is the quaternary structure of a protein? - ANSWERMade up of several different polypeptide chains held together by bonds. What are the different functions of proteins? - ANSWERStructural proteins. Transport proteins. Antibodies. Enzymes. Outline a method for the biuret test. - ANSWERAdd a few drops of NaOH solution to the test sample. Add some copper(||) sulphate solution. If the protein is present the solution turns purple if there is no protein the solution will stay blue. What is an enzyme? - ANSWERA biological catalyst. Catalyses metabolic reactions. How do enzymes work? - ANSWERThey lower the activation energy to speed up the rate of reaction. Describe the 'lock and key' model. - ANSWERThis is where the substrate fits into the enzyme in the same way the key fits into a lock. Describe the 'induced fit' model. - ANSWERThe substrate doesn't only have to be the right shape to fit the active site but also has to make the active site change shape in the right way. Factors affecting enzyme activity: - ANSWERTemperature, pH, enzyme concentration, substrate concentration. How does a competitive inhibitor work? - ANSWERA competitive inhibitor is of similar shape to the substrate, and is complementary to the active site. They attach to the active site before the substrate thus blocking it, but interact weakly so they dont stay permanently - compete for active site. How does a non-competitive inhibitor work? - ANSWERThey bind to another binding site other than the active site and alter the shape of the enzyme so the substrate can no longer bind to the active site. 3.1.2 Carbohydrates - ANSWER

What are the monomers that make up carbohydrates? - ANSWERMonosaccharides. How are two monosaccharides joined? - ANSWERBy a condensation reaction, forming a glycosidic bond (eliminating a water molecule). Maltose is made up of... - ANSWER2 glucose molecules. Lactose is made up of... - ANSWERGlucose and galactose. Sucrose is made up of... - ANSWERFructose and glucose. What are the two isomers of glucose? - ANSWERAlpha and beta glucose. How does alpha-glucose differ from beta-glucose? - ANSWERIn alpha-glucose, the hydroxyl group is placed below the plane of the ring of carbons; in beta-glucose, the hydroxyl group is placed above the plane of the ring. Outline a method for the Benedict's test. - ANSWERAdd Benedict's reagent to a sample and heat it in a water bath has been brought to the boil. If the test is positive it will form a coloured precipitate. (Blue -> brick red)

• could filter the precipitate and weigh it to compare amount of reducing sugar. For non reducing sugar: Add dilute hydrochloric acid and carefully heat in a water bath that's been brought to the boil. Neutralise with sodium hydrogen carbonate. Carry out Benedict's test as normal. What is the structure of starch? - ANSWERContains two polysaccharides of alpha glucose (amylose and amylopectin). Amylose - Long unbranched chain of alpha glucose. Coiled, compact, good for storage. Amylopectin - Long branched chain of alpha glucose, Sidebranches allow enzymes to reach the glycosidic bonds easily so glucose released quickly. Insoluble in water so doesn't affect water potential of cell. What test can be used for starch? - ANSWERIodine test. Add iodine dissolved in potassium iodide solution to the test sample. If starch is present the sample changes from brown-orange to a blue-black colour. Describe the structure of glycogen. - ANSWERSimilar to amylopectin. Lots of sidebranches so glucose can be released quickly. Very compact molecule so good for storage. What is cellulose used for? - ANSWERCell walls. (Structural support)

Describe the structure of cellulose. - ANSWERStraight cellulose chains made of beta glucose. Chains linked together by hydrogen bonds to form strong fibres called microfibrils. 3.3.4 Mass Transport - ANSWER What is haemoglobin? - ANSWERQuaternary, globular protein What is haemoglobin made up of? - ANSWER4 polypeptide chains. One haem group per chain, contains iron ion. How many oxygen molecules can hemoglobin carry? - ANSWER Haemoglobin has a ____ affinity for oxygen - ANSWERHigh. What does haemoglobin form when it binds to oxygen? - ANSWEROxyhaemoglobin. What is the equation for the reaction between Hb and O2? - ANSWERHb + 4O2 —> HbO What does 'partial pressure of oxygen' (pO2) mean? - ANSWERA measure of oxygen concentration. Greater concentration -> higher pO What happens when there's a high pO2? - ANSWEROxygen loads onto haemoglobin to form oxyhaemoglobin. What happens when there's a low pO2? - ANSWEROxyhaemoglobin unloads it's oxygen. How is oxyhaemoglobin formed in the lungs? - ANSWEROxygen enters blood capillaries at alveoli. Alveoli have high pO2 so oxygen loads onto haemoglobin to form oxyhaemoglobin. What happens to oxyhaemoglobin when cells respire? - ANSWERCells use oxygen, lowers pO2. Red blood cells deliver oxyhaemoglobin to respiring tissues, unloads oxygen. Evaluate the function of haemoglobin. - ANSWERIn lungs, high pO2, so haemoglobin binds with oxygen to form oxyhaemoglobin (high affinity for oxygen in lungs). At respiring cells (using up oxygen), lower pO2, so oxyhaemoglobin unloads oxygen at cells (low affinity for oxygen). What does the Bohr effect cause? - ANSWERA shift in curve towards right. What happens to pCO2 when cells are respiring? - ANSWERIncreases. How does haemoglobin differ at high altitudes? - ANSWERHaemoglobin has higher affinity for oxygen.

What is the general pattern of blood circulation in a mammal? - ANSWERRight side of heart: Heart, pulmonary artery, lungs, pulmonary vein, heart. Back to left side. Left side: Heart, aorta, body (renal artery, renal vein) vena cava, heart. Back to right side. Which two words describe the mammalian circulatory system? - ANSWERClosed, double. What is the function of the coronary arteries? - ANSWERSupply oxygenated blood to the heart muscle. How does the structure of the heart relate to its function? - ANSWERAV valves, prevent backflow of blood from ventricles to atria. SL valves, prevent backflow of blood from arteries to ventricles. Left has thicker muscular wall, generates high blood pressure for blood to travel around body. Right has thinner muscular wall, generates lower blood pressure, blood travels to lungs, high blood pressure would damage alveoli. Describe the structure and function of arteries. - ANSWERCarry blood from heart to rest of body. Thick muscle layer, to maintain high pressure & contracts to move blood along. Elastic tissue layer, to stretch and recoil. Smooth endothelium, to reduce friction. Narrow lumen, to increase pressure. Describe the structure and function of arterioles. - ANSWERDivision of arteries to smaller vessels, direct blood flow to capillaries. Thicker muscle layer than arteries. Constrict to reduce blood flow (narrows lumen). Dilate to increase blood flow (widens lumen). Describe the structure and function of veins. - ANSWERTake deoxygenated blood back to heart under low pressure (except for pulmonary vein). Wider lumen, little muscle/elastic tissue. Contain valves to stop backflow of blood. Contraction of skeletal muscles maintains blood flow in veins. Describe the structure of capillaries and the importance. - ANSWERCapillary wall is one cell thick, short diffusion pathway for rapid diffusion. Capillary bed made of large network of branched capillaries, large surface area for rapid diffusion. Narrow lumen, reduces flow rate so more time for diffusion. Pores in walls between cells, allows substances to escape for diffusion. What is tissue fluid? - ANSWERA watery substance containing glucose, amino acids, oxygen, and other nutrients. It supplies these to the cells, while also removing any waste materials.

How is tissue fluid formed? - ANSWERAt arteriole end of capillaries. Higher blood pressure inside capillaries than tissue fluid pressure. Forces fluid out of capillaries. Large plasma proteins remain in capillaries. How is tissue fluid returned to the circulatory system? - ANSWERAt venule end of capillaries. Hydrostatic pressure reduces as fluid leaves capillary. Increased concentration in plasma proteins lowers wp of capillary. Water re-enters capillary by osmosis. Excess water taken up by lymph system and returned to circulatory system. Valves are... - ANSWEROne-way opening for blood to flow through in veins. Outline the cardiac cycle. - ANSWERAtrial systole - atria contract, volume decreases and pressure increases inside the atria, AV valves open, blood is pushed into ventricles. Ventricular systole - ventricles contract, volume decreases and pressure increases, SL valves open & AV valves close, blood pushed through arteries. Diastole - ventricles and atria relax, SL valves close, blood fills atria from veins, flows passively to ventricles as AV valves open. How can an atheroma result in a heart attack? - ANSWERNarrows coronary arteries. Restricts blood flow to heart muscle. Not as much oxygen supplied to heart. Anaerobically respires, not as much ATP produced, not enough energy, lactate produced, damages heart. What is the main job of the xylem? - ANSWERTransports water and mineral ions in plants. (Substances move up the plant). How does water move up the plant? - ANSWERUsing cohesion and tension. Water evaporates from the leaves at the top of the xylem, this creates tension, pulls more water to the leaf, cohesion allows water molecules to be pulled up as a column. Water enters stem through roots. What are some adaptations of the xylem? - ANSWERElongated cells with no end walls to form a continuous column. Hollow so slows water flow. Thick cells walls and rigid for stability. Narrow lumen for increased cohesion. Waterproof so no evaporation. What is transpiration? - ANSWERThe loss of water from a plant by evaporation. What is the main function of the phloem? - ANSWERTransports organic substances like sugars up and down the plant. What are some adaptations of the phloem? - ANSWERSieve tube elements have no nucleus and few organelles. Companion cells carry out living functions for the sieve cells.

What is translocation? - ANSWERThe movement of solutes to where they're needed in a plant. Moves solutes form source (high conc) to sink (low conc). Explain the mass flow hypothesis. - ANSWER1 translocation, at the source, high conc of solute, active transport of solutes from companion cells to sieve tube elements, wp lowered in sieve tube elements so water enters by osmosis from xylem/companion cells, pressure increases inside ste at source end. 2 at the sink, low conc of solute, solutes removed to be used up, wp increases inside sieve tube so water leaves by osmosis, pressure decreases inside sieve tube elements. 3 mass flow, pressure gradient from source to sink, solutes pushed from source to sink, solutes used/stored at sink. 3.4.6 Biodiversity - ANSWER Define biodiversity. - ANSWERThe variety of living organisms in an area. What is a habitat? - ANSWERPlace where an organism lives. What is a community? - ANSWERAll the populations of different species in a habitat. How is biodiversity reduced? - ANSWERAgricultural practices. Name some agricultural practices. - ANSWERWoodland clearance. Hedgerow removal. Pesticides. Herbicides. Monoculture.