Paper 1 AQA A level Biology 2023, Exams of Nursing

Download Paper 1 AQA A level Biology 2023 and more Exams Nursing in PDF only on Docsity! Paper 1 AQA A level Biology 2023 Explain why plasma membranes are said to have a fluid mosaic structure. - correct answer 1. Fluid because the phospholipids are constantly moving. 2. Mosaic because the proteins are scattered throughout the membrane-like tiles in a mosaic. What effect does cholesterol have on the cell membrane? - correct answer 1.Cholesterol molecules fit between the phospholipids and bind to the hydrophobic tails of the phospholipids. 2.Causes them to pack together more closely, restricting the movement of other molecules in the membrane. 3.Cholesterol makes the membrane less fluid and more rigid. 4.Cholesterol helps to maintain the shape of animal cells, which is important because animal cells don't have cell walls (especially important for cells which are not supported by other cells e.g. red blood cells). State 3 functions of glycolipids in the cell membrane. - correct answer 1. Act as recognition sites. 2. Maintain the stability of the membrane. 3. Help cells attach to one another and so form tissues. State 3 functions of glycoproteins in the cell membrane. - correct answer 1.Act as recognition sites.2.Help cells to attach to one another so form tissues.3.Allow cells to recognise one another e.g. lymphocytes can recognise an organisms's own cells. Describe the functions of membranes within cells. - correct answer 1.Control the entry and exit of materials in membrane-bound organelles such as mitochondria and chloroplasts.2.Separate organelles from Paper 1 AQA A level Biology 2023 cytoplasm so that specific metabolic reactions can take place.3.Provide an internal transport system e.g. endoplasmic reticulum.4.Isolate enzymes which could damage the cell e.g. lysosomes.5.Provide surfaces on which reactions can occur e.g. protein synthesis on ribosomes on rough ER. Suggest reasons why most molecules do not diffuse freely through the cell membrane. - correct answer 1.They're not lipid soluble.2.Too large to pass through protein channels.3.Have the same charge as the charge on the protein channels, so they are repelled even if they are small enough to pass through the channel.1 State two factors which affect the permeability of cell membranes - correct answer .1.Temperature2.Solvent concentration How can substances move across a cell surface membrane? - correct answer 1.Simple diffusion (passive)2.Facilitated diffusion (passive)3.Osmosis (passive)4.Active transport (active)5.Co-transport (active) Describe how substances can move across a cell surface membrane. - correct answer 1.Small/non-polar/lipid-soluble substances can cross by simple diffusion down a concentration gradient.2.Large/polar molecules - pass through channel proteins/carrier proteins, by facilitated diffusion, down a concentration gradient.3.Water - moves by osmosis from an area of high water potential to an area of lower water potential.4.Active transport - moves substances against a concentration Paper 1 AQA A level Biology 2023 Which factors affect the rate of active transport? - correct answer 1.The speed of individual carrier proteins.2.The number of carrier proteins present.3.The rate of respiration in the cell and the availability of ATP.* if respiration is inhibited, active transport can't take place. Describe the process by which energy is released by the cell for active transport. - correct answer 1.Energy is released by the hydrolysis of ATP2.into ADP and Pi.3 Contrast active transport with facilitated diffusion.* because the word 'contrast' is used - correct answer you need to give both sides of the difference in your answer.,1.Active transport uses ATP, whereas facilitated diffusion is a passive process.2.Substances are moved against a concentration gradient in active transport, whereas facilitated diffusion moves substances down a concentration gradient.3.Facilitated diffusion involves channel or carrier proteins, whereas active transport only involves carrier proteins.* carrier proteins can transport substances against their concentration gradient, whereas channel proteins cannot. Explain why facilitated diffusion is a passive process. - correct answer 1.No ATP is used in the process.2.The only energy used is the kinetic energy of the molecules. Discuss the role of protein channels in facilitated diffusion. - correct answer 1.Protein channels form pores/channels across the membrane, allowing water-soluble ions to diffuse down their concentration Paper 1 AQA A level Biology 2023 gradient.2.Protein channels are selective and only allow the passage of specific ions. Discuss the role of carrier proteins in facilitated diffusion. - correct answer 1.Carrier proteins move large molecules across membranes, down their concentration gradient.2.When a molecule specific to the carrier protein binds (e.g. glucose), it causes the carrier protein to change shape and release the molecule on the opposite site of the membrane.3.No ATP is required, the molecules move from an area of higher concentration to an area of lower concentration, using the kinetic energy of the molecules themselves. Discuss two factors which affect the rate of facilitated diffusion. - correct answer 1.The concentration gradient: the higher the concentration gradient, the faster the rate of diffusion, up to a point which is determined by how many protein channels and carriers are present in the membrane.2.Once all the proteins in a membrane are in use, the rate of facilitated diffusion can't increase any further. State the 3 factors which affect the rate of osmosis. - correct answer 1.Water potential gradient.2.Thickness of exchange surface.3.Surface area of exchange surface.4 What is meant by a selectively permeable membrane? - correct answer A membrane that is permeable to water molecules (and a few other small molecules), but not to larger molecules. Paper 1 AQA A level Biology 2023 What is the water potential of pure water under standard conditions of pressure and temperature? - correct answer Zero If two solutions are isotonic, what does this mean?They have the same water potential .Explain why the water potential of distilled water is higher than the water potential of cytoplasm. - correct answer 1.Distilled water contains no solute and so its water potential is zero.2.Presence of solutes in cytoplasm, reduce the water potential of the cytoplasm. Describe the property of the cell surface membrane which allows osmosis to take place. - correct answer 1.Partially permeable so cell surface membranes allow water molecules to pass through, but not solute molecules. What happens if you surround an animal cell with pure water? - correct answer It swells and bursts. What happens if you surround a plant cell with pure water? - correct answer 1.It swells, but doesn't burst. 2.The cell wall prevents it from bursting because it is made of cellulose, which is a strong material.3.The cell is turgid. What happens if an animal cell is surrounded by a concentrated salt/sugar solution? - correct answer 1.It shrinks because water leaves the cell by osmosis.2.Water moves from area of higher water potential in the cell to area of lower water potential in the solution Paper 1 AQA A level Biology 2023 •Describe how you could use a graph of your results to find the sodium chloride solution with the same water potential as the potato tissue. - correct answer •Plot a graph with concentration on the x-axis and percentage change in mass on the y-axis.•Find the concentration where the curve crosses the x-axis (i.e. where the percentage change is zero).•*if your results are given as a ratio of mass at the start:mass at the end instead of percentage change, find the sodium chloride concentration where the ratio is 1 i.e. there was no change in mass during the experiment. •What is the advantage of giving your results as a ratio/percentage change. - correct answer Allows a comparison to be made when all the cylinders/discs had a different starting mass. •Explain why taking additional readings at each concentration of sodium chloride would improve the reliability of the results. - correct answer It allows for anomalies to be identified and enables a mean to be calculated. •Explain why additional readings could improve the graph. - correct answer The more readings used to plot a graph, the more accurate the curve of best fit will be and therefore the the point where the line crosses the x-axis will be more accurate. Also, it allows you to plot standard deviation values and error bars to show how spread the results are. Paper 1 AQA A level Biology 2023 •State how evaporation would affect the water potential of the solution in the test tubes. - correct answer It would lower the water potential. •Explain why it is important to use potato cylinders taken from potatoes of the same variety. - correct answer To ensure the cells have the same water potential / so there are no genetic differences.8 •The potato skin is removed from the cylinders - correct answer suggest one reason why the potato skin could have affected osmosis. ,Potato skin is impermeable to water / the skin is a different tissue so the cells of the skin will have a different water potential. •Explain why the student blotted dry the outside of each cylinder before reweighing. - correct answer water will affect the mass of the potato cylinder and the student only wants to measure the water that was taken up (or lost) by the potato cylinder due to osmosis. •Explain why the percentage increase in mass of a small cube would be greater than the percentage increase in mass for a large cube. - correct answer Due to the larger surface area:volume ratio of the small cubes for osmosis. •Explain why the potato cylinder in distilled water gained mass. - correct answer Water moved into the potato cells by osmosis, from a less negative water potential outside the cells to a more negative water potential inside the cells. Paper 1 AQA A level Biology 2023 Explain what is meant by the term eukaryotic cell. - correct answer •Cell that has a membrane-bound nucleus and chromosomes.•Has other membrane-bound organelles, such as mitochondria and endoplasmic reticulum. Give examples of eukaryotic cells. - correct answer Animal cells / Plant cells / Fungi / Algae Give an example of a prokaryotic cell. - correct answer Bacteria Describe the structure and function of the cell-surface membrane. - correct answer Structure - membrane found on surface of animal cells and just inside the surface of other cells / made mainly of lipids and proteins.Function:•Regulates the movement of substances into and out of the cell.•Has receptor molecules on it (allows it to respond to e.g. hormones). Describe the structure and function of the nucleus. - correct answer Structure:•Surrounded by nuclear envelope (double membrane with many pores).•Contains chromosomes (consist of linear DNA + histone proteins).•Contains one or more nucleoli (singular = nucleolus)Function: •Contains genetic material of the cell in the form of DNA - therefore controls the cell's activities.•Pores allow movement of substances e.g. mRNA between the nucleus and the cytoplasm.•Nucleolus manufactures ribosomes.10 Paper 1 AQA A level Biology 2023 Name 3 organelles found in plant cells but not in animal cells. - correct answer 1.Cell wall2.Cell vacuole3.Chloroplasts How are fungal cells different to plant cells? - correct answer •Fungal cells walls are made of chitin, not cellulose.•Fungal cells don't have chloroplasts because they don't need to photosynthesise.In multicellular organisms, what is a tissue? - correct answer A tissue is a group of cells working together to perform a particular function. Explain what is meant by the term organ. - correct answer A combination of different tissues that are coordinated to perform a variety of functions .Explain what is meant by the term organ system. - correct answer Many organs work together in an organ system to perform a particular function. How are epithelial cells in the small intestine specialised to absorb food efficiently? - correct answer 1.The walls of the small intestine are covered in villi - increase the surface area for absorption.2.Villi have microvilli - further increases the surface area for absorption.3.Have lots of mitochondria to provide energy for the active transport of digested food molecules into the cell. Paper 1 AQA A level Biology 2023 Cilia are hair-like structures found on lung epithelial cells. Explain how they are adapted to their function of beating and moving mucus out of the lungs. - correct answer 1.Ciliated epithelial cells have lots of mitochondria2.because they need lots of energy for movement. Suggest how red blood cells are adapted to their function of carrying oxygen to cells. - correct answer 1.Thin outer membranes to let oxygen diffuse through easily.2.Biconcave shape increases the surface area to increase rate of diffusion of oxygen.3.No nucleus - whole cell can be full of haemoglobin which maximises amount of oxygen which can be transported. Suggest how a leaf cell is adapted to its function of absorbing light for photosynthesis. - correct answer 1.Packed with chloroplasts.2.Regular shaped, so cells can be closely packed together to form a continuous layer for efficient absorption of sunlight. Suggest how a sperm cell is specialised for its role in sexual reproduction. - correct answer 1.Have lots of mitochondria to provide ATP for movement generated by the tail.2.Very small and thin, which helps them to move easily. Suggest how neutrophils are adapted to their function of ingesting and destroying microbes. - correct answer 1.Large amounts of lysosomes, which contain enzymes to destroy ingested microbes.2.Have a lobed nucleus, which allows for greater flexibility. Paper 1 AQA A level Biology 2023 Suggest how a root hair cell is adapted to its function of absorbing water and minerals from the soil. - correct answer 1.Large surface area due to hair-like projections, which increases the uptake of minerals and water.2.Have a large amount of mitochondria for active transport. What is meant by the term prokaryotic? - correct answer 1.A cell of an organism belonging to the kingdom Prokaryote.2.Do not have a nucleus OR membrane-bound organelles. What is a plasmid? - correct answer 1.A small, circular piece of DNA found in bacterial cells, that is separate from the main circular DNA molecule.2.Plasmids can be passed between prokaryotic cells.3.Not all prokaryotes contain plasmids, some contain more than one plasmid. What is a flagellum? - correct answer A long hair-like structure that rotates to make the prokaryotic cell move. How do prokaryotic cells differ from eukaryotic cells? - correct answer 1.Prokaryotic cells don't contain a nucleus - DNA floats free in the cytoplasm.2.Prokaryotic DNA is circular DNA.3.Prokaryotic DNA is not attached to histone proteins.4.Prokaryotes are much smaller than eukaryotic cells.5.Prokaryotes have no membrane-bound organelles.6.Prokaryotes have smaller ribosomes.7.Prokaryotes have a cell wall composed of murein (a glycoprotein).Name 3 features of a prokaryotic cell, which would not be found in a eukaryotic cell.1.One or more plasmids.2.A capsule surrounding the cell.3.One or more flagella.14 Paper 1 AQA A level Biology 2023 resolution.2.Beyond the limit of resolution, increasing the magnification will result in larger, but more blurred images. State the formula for calculating magnification. - correct answer magnification = size of image/size of object* make sure you convert the numbers into the same units before doing the calculation. Why can organelles appear different in images? - correct answer They can be viewed from different angles and at different depths. Explain the principles and limitation of a light microscope. - correct answer Principles:1.They use light to form an image.2.They have a maximum resolution of 0.2 μm.3.They have a maximum useful magnification of about x1500.Limitations:1. They have a poor resolution so can't be used to view organelles smaller than 0.2μm, this includes ribosomes, endoplasmic reticulum and lysosomes. Name structures in a eukaryotic cell that cannot be identified using a light microscope. - correct answer 1.Lysosomes2.Ribosomes3.Endoplasmic reticulum Which organelles can be seen using a light microscope? - correct answer 1.Nucleus2.Possibly the mitochondria, but not in much detail.Which microscope has the higher resolution?TEM > SEM > LM Paper 1 AQA A level Biology 2023 Why do electron microscopes have a higher resolution than light microscopes? - correct answer 1.Electron microscopes use electrons which have a shorter wavelength.2.Light microscopes use light which has a large wavelength. What is the difference between TEMs and SEMs? - correct answer 1.In transmission electron microscopes, the electrons pass through the specimen.2.In scanning electron microscopes, the electrons bounce off the specimen's surface.16 Discuss the principles - correct answer advantages and limitations of TEMs.,Principles:1.Transmission electron microscopes use electromagnets to focus a beam of electrons, 2.which is then transmitted through a thin specimen. 3.Denser parts of the specimen absorb more electrons, which makes them appear darker on the image. Advantages:1.Electrons have a short wavelength, so give high resolution.Limitations:1.Can't use them to observe living material as the whole system must be in a vacuum. 2.They can only be used to examine thin specimens. 3.A complex staining process is required. 4.The image may contain artefacts.5.Produces a 2D image. Discuss the principles - correct answer advantages and limitations of SEMs.,Principles:1.They use electrons to form an image.2.SEMs scan a beam of electrons across the specimen.3.This knocks off electrons from the specimen, which are gathered in a cathode ray tube to form an image.4.The final image shows the surface of the image and can be 3D.Advantages:1.Can be used on thick specimens.2.3D Paper 1 AQA A level Biology 2023 images.Limitations:1.Lower resolution images than TEMs.2.All the limitations of the TEM also apply to the SEM - see above answer. Why do the samples for an SEM not need to be as thin as for a TEM? - correct answer Because the electrons do not penetrate the specimen Explain why specimens have to be kept in a near-vacuum in order to be viewed effectively using an electron microscope. - correct answer 1. Electrons are absorbed by molecules in the air.2. So, if air was present, this would prevent the electrons reaching the specimen. Explain why the theoretical resolving power of an electron microscope cannot always be achieved. - correct answer 1. The preparation of the specimens may not be good enough.2. A higher energy electron beam is required, which may destroy the specimen. Explain what is meant by the term artefact in microscopy. - correct answer A structural detail that results from processing of the specimens and is not a part of the natural specimen e.g. fingerprint, air bubble or inaccuracies caused staining the sample etc. Why are artefacts more common when using electron microscopes? - correct answer 1. Specimens need a lot of preparation before they can be viewed under an electron microscope.2. Therefore, there are more stages at which an artefact could be introduced.