Curriculum Portal

neurologyYou need to know

• Animal cells contain a cell membrane, cytoplasm, nucleus, mitochondria and ribosomes, and each structure has a function such as controlling entry and exit, supporting chemical reactions, storing genetic material, releasing energy in respiration and making proteins.
• Plant cells contain the same structures as animal cells and also have a cellulose cell wall for support, chloroplasts for photosynthesis and a large permanent vacuole containing cell sap to maintain turgor.
• Eukaryotic cells have a nucleus and membrane-bound organelles, whereas prokaryotic cells such as bacteria are smaller and simpler and do not have a nucleus or other membrane-bound organelles.
• A bacterial cell has cytoplasm, a cell membrane, a cell wall and ribosomes, and it may also have circular DNA, plasmids, a slime capsule and a flagellum.
• Unit conversions in cell biology include `1 \text{ cm} = 10 \text{ mm}`, `1 \text{ mm} = 1000 \text{ \mu m}` and `1 \text{ \mu m} = 1000 \text{ nm}`.
• Magnification is how many times bigger the image is than the real object, and resolution is the ability to distinguish two points as separate so more detail can be seen clearly.
• The microscopy formula is `\text{magnification} = \frac{\text{image size}}{\text{real size}}`, which can be rearranged to find image size or real size.
• Electron microscopes have a much higher magnification and resolving power than light microscopes, so they can show much smaller structures in greater detail.
• A microscope slide is prepared by placing a thin sample on the slide, adding a drop of water or stain if needed, and lowering a coverslip carefully to avoid air bubbles.
• A light microscope is focused by starting on low power, using the coarse focus to find the image and then the fine focus to sharpen it, while adjusting the light if needed.
• Biological drawings should use clear single lines, no shading, accurate labels and a magnification or scale bar based on the specimen size.
• Sperm cells are adapted for fertilisation by having a flagellum for movement, many mitochondria for energy and an acrosome containing enzymes to penetrate the egg.
• Nerve cells are adapted to transmit impulses because they are long, have branched connections and are often insulated by a myelin sheath, while muscle cells are elongated and contain many mitochondria to support repeated contraction.
• Root hair cells are adapted for absorbing water and mineral ions because they have a long projection that increases surface area, xylem cells are dead and hollow with lignified walls for water transport and support, and phloem cells transport sugars using sieve tubes and companion cells.
• The function of a cell depends on its structure, and specialised cells work together in tissues, organs and organ systems to carry out processes in the whole organism.
• 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, temperature or surface area is greater.
• Surface area to volume ratio is found using `\frac{\text{surface area}}{\text{volume}}`, and a larger ratio allows faster exchange because more surface is available relative to the amount of material inside.
• Exchange surfaces are adapted by being large, thin and well supplied: villi and microvilli in the small intestine increase absorption, alveoli in the lungs and gills in fish provide large moist surfaces with good blood supply, and roots and leaves have features that increase uptake and gas exchange.
• Osmosis is the net movement of water through a partially permeable membrane from a dilute solution to a more concentrated solution, and plant tissue gains mass in dilute solutions and loses mass in concentrated sugar or salt solutions.
• Active transport moves substances from a lower concentration to a higher concentration using energy from respiration, and examples include glucose absorption in the small intestine and mineral ion uptake by root hair cells.

• Label diagrams of animal, plant and bacterial cells and match each part to its function accurately.
• Convert measurements between centimetres, millimetres, micrometres and nanometres using the correct powers of `10`.
• Calculate magnification, image size or real size using `\text{magnification} = \frac{\text{image size}}{\text{real size}}` and give the answer in suitable units.
• Prepare a temporary microscope slide by placing a thin specimen on the slide, adding stain when appropriate and lowering the coverslip carefully to avoid trapping air bubbles.
• Focus a light microscope by starting with the lowest power objective, centring the specimen and using coarse then fine focus to obtain a clear image.
• Draw a biological specimen from a microscope using clear outlines, accurate labels and an appropriate magnification or scale bar.
• Calculate surface area to volume ratio for simple shapes and use the result to explain differences in the rate of exchange by diffusion.
• Calculate percentage change in mass of plant tissue using `\frac{\text{final mass} - \text{initial mass}}{\text{initial mass}} \times 100`, then plot and interpret a graph to identify the sugar or salt concentration where there is no net mass change.
• Compare diffusion, osmosis and active transport by identifying the direction of movement, whether a partially permeable membrane is needed and whether energy is required.