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neurologyYou need to know

• Animal cells contain a nucleus, cytoplasm, a cell membrane, mitochondria and ribosomes, and each structure has a function such as controlling cell activities, carrying out chemical reactions, controlling entry and exit, releasing energy and making proteins.
• Plant cells contain the same parts as animal cells but also have a cellulose cell wall for support, chloroplasts for photosynthesis and a large permanent vacuole containing cell sap.
• Eukaryotic cells, such as plant and animal cells, are larger and have genetic material enclosed in a nucleus, whereas prokaryotic cells, such as bacteria, are smaller and have no nucleus.
• Bacterial cells have cytoplasm, a cell membrane, a cell wall and ribosomes, their DNA is a single circular loop in the cytoplasm, they may contain plasmids, and some have a flagellum or a slime capsule.
• The unit conversions used in microscopy are that 1 centimetre equals 10 millimetres, 1 millimetre equals 1000 micrometres and 1 micrometre equals 1000 nanometres.
• Magnification is how many times bigger the image is than the real object, resolution is the ability to distinguish two close points as separate, and the relationship is `magnification = image size / real size`.
• Electron microscopes have much greater magnification and much greater resolution than light microscopes, so they can show much smaller cell structures in more detail.
• Sperm cells are adapted for fertilisation by having a tail for movement, many mitochondria to release energy, and an acrosome containing enzymes to penetrate the egg cell.
• Nerve cells are adapted to carry electrical impulses by having a long axon, branched endings to connect with other cells and often a fatty myelin sheath to speed up transmission.
• Muscle cells are adapted for contraction by being long cells packed with protein filaments and many mitochondria to supply energy.
• Root hair cells are adapted for absorbing water and mineral ions by having a long hair that increases surface area, a thin cell surface and many mitochondria for active transport.
• Xylem vessels are dead, hollow cells with lignified walls that transport water and mineral ions upwards and also strengthen the plant, while phloem tissue is made of living cells that transport dissolved sugars around the plant.
• In multicellular organisms, specialised cells work together in tissues, tissues form organs and organs work together in organ systems, so cell structure is closely linked to function at every level.
• Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, and it happens faster when the concentration gradient is steeper, the temperature is higher or the surface area is larger.
• A larger surface area to volume ratio allows substances to be exchanged more quickly because there is more surface available for each unit of volume, and this matters especially in small organisms and exchange surfaces.
• The small intestine is adapted for absorption by having villi and microvilli for a very large surface area, thin walls and a rich blood supply, and the lungs are adapted by having many alveoli with thin moist walls and a good blood supply.
• Fish gills are adapted for exchange by having gill filaments and lamellae that create a large surface area, a thin exchange surface and a good blood supply, and roots and leaves are adapted by having large surfaces and short diffusion pathways.
• Osmosis is the net movement of water molecules through a partially permeable membrane from a dilute solution to a more concentrated solution, and plant tissue gains mass in dilute solutions but loses mass in concentrated sugar or salt solutions.
• Active transport is the movement of substances from a lower concentration to a higher concentration against the concentration gradient using energy from respiration, for example when mineral ions enter root hair cells and when glucose is absorbed from the small intestine into the blood.
• Diffusion and osmosis are passive processes that do not require energy, osmosis only involves water moving through a partially permeable membrane, and active transport requires energy and can move substances against the concentration gradient.

• Label diagrams of animal, plant and bacterial cells accurately and state the function of each named structure.
• Convert measurements between centimetres, millimetres, micrometres and nanometres correctly, keeping track of powers of 10.
• Calculate magnification, image size or real size by rearranging and using `magnification = image size / real size` with consistent units.
• Prepare a temporary microscope slide by placing the specimen in a drop of water or stain, lowering the coverslip carefully at an angle and avoiding air bubbles.
• Focus a light microscope by starting on low power, using the coarse focus first, then using the fine focus to sharpen the image before moving to higher magnification.
• Draw a biological specimen from a microscope as a clear line drawing with no shading, accurate proportions, neat labels and a magnification scale or stated magnification.
• Calculate surface area to volume ratio from given dimensions and use it to explain differences in the rate of diffusion or exchange.
• Plot and interpret a graph of percentage change in plant tissue mass against solution concentration, identify the point where the line crosses zero to estimate the tissue concentration, and use the pattern to explain osmosis.
• Calculate percentage change in mass of plant tissue using `percentage change = (change in mass / original mass) \times 100` and state whether the tissue gained or lost water.
• Classify examples as diffusion, osmosis or active transport and justify the choice by referring to particle type, direction of movement, membrane involvement and energy use.