Biology Past Paper PDF

# Biology ## 12. Magnification - magnification = measured size / actual size ## Preparing a microscope slide - Add a drop of water to the middle of a clean slide. - Cut up an onion and take off one layer. - Use tweezers to peel off some epidermal tissue (the clear ‘skin’) from the bottom of the lay...

# Biology ## 12. Magnification - magnification = measured size / actual size ## Preparing a microscope slide - Add a drop of water to the middle of a clean slide. - Cut up an onion and take off one layer. - Use tweezers to peel off some epidermal tissue (the clear ‘skin’) from the bottom of the layer. - Using the tweezers, place the skin into the water on the slide. - Add a drop of iodine solution. Iodine solution is a stain. - Stains can make different parts of a cell easier to see. - Place a cover slip on top. Try not to get any air bubbles under it. ## Transport across membranes - **22. Diffusion** Spreading out of particles from an area of higher concentration to an area of lower concentration. - **23. Osmosis** The movement of water molecules across a partially permeable membrane from a less concentrated solution to a more concentrated solution. - **24. Active Transport** Movement from a lower concentration to a higher concentration, against the concentration gradient. ## 25. Gas Exchange in the lungs - Gas exchange in the lungs takes place in the alveoli (shape = large surface area. Good blood supply and thin walls. ## 26. The small intestine - The small intestine is covered in tiny villi which absorb food (shape = large surface area. Good blood supply) ## 27. Fish have gills to - absorb oxygen from water (large surface area) ## Investigating osmosis in potatoes - Cut potatoes into cylinders with the same length and width. Measure their mass. - Put 1 in pure water and the other concentrated sugar solution and leave them for 30 mins. - Take out the potato cylinders and dry them carefully with a paper towel. - Measure the mass again. - If the mass has increased, water has moved in because of osmosis. If the mass has decreased, water has moved out because of osmosis. ## The cell cycle - Chromosomes in nucleus are copied - Chromatids pulled apart and moved towards poles - Chromosomes separate - Cell divides - 2 new cells are genetically identical ## Cell Types - **1. Eukaryotic** A complex cell with a nucleus (eg. animal or plant cells) - **2. Prokaryotic** A smaller cell without a nucleus (eg. bacterial cell) - **3. Nucleus** Contains genetic material. - **4. Cytoplasm** Where a cell’s chemical reactions happen. - **5. Cell membrane** Controls what goes into and out of a cell. - **6. Ribosome** Part of a cell where proteins are made. - **7. Mitochondria** Where aerobic respiration takes place. - **8. Cell wall** Only found in plant cells. Made of cellulose and supports the cell. - **9. Vacuole** Only found in plant cells. Contains cell sap. - **10. Chloroplasts** Only found in plant cells. Where photosynthesis takes place. - **11. Plasmid** Only found in bacterial cells. A small loop of DNA. ## Specialized cells - **13. Adult stem cells** can only produce certain types of cell-found in bone marrow - **14. Embryonic stem cells** can produce all types of cells-controversial - **15. Plant stem cells** found in meristems - **16. Sperm cells** Take male DNA to the egg, Tail to help it swim, Lots of mitochondria for energy - **17. Nerve cells** Carry electrical signals around the body, Long to cover long distances, Branches to connect to other cells - **18. Muscle Cells** Muscle cells contract, Long so have space to contract, Lots of mitochondria for energy - **19. Root hair cells** Root hair cells absorb water and minerals, Long hairs, Big surface area for absorption - **20. Phloem Cells** Phloem cells transport sugars (plants), Long tube joined end to end - **21. Xylem cells** Xylem cells transport water (plants), Long tubes joined end to end, Hollow so water can flow through