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Charleston Academy Biology National 5 Unit 1: Cell Biology Revision: What you should know (From Torrance (2013) National 5 Biology) Key Areas 1 and 2 Cell Structure and Transport Word bank active against along animal burst cells chloroplasts concentration diffusion energy gain gradient lipid lose lower membrane mitochondria nucleus osmosis passive permeable plasmolysed ribosomes sap selectively shrink supported useful vacuole walls 1. All living things are composed of one or more CELLS, the basic units of life. 2. The cells of green plants, animals and fungi have several structures in common including a NUCLEUS, a cell MEMBRANE and mitochondria. 3. ANIMAL cells lack a cell wall and a large central VACUOLE. 4. Only green plant cells contain CHLOROPLASTS but all cells contain ribosomes. 5. The cell’s activities are controlled by the nucleus. A plant cell is SUPPORTED by the cell wall and its cell SAP is stored in its vacuole. 6. Chloroplasts are responsible for photosynthesis, MITOCHONDRIA for respiration and RIBOSOMES for protein synthesis. 7. The cell membrane consists of protein and LIPID molecules and is SELECTIVELY permeable. 8. Diffusion is the movement of molecules from a high to a low concentration ALONG a concentration GRADIENT. It is a PASSIVE process and does not require a supply of energy. 2 9. DIFFUSION is the means by which USEFUL molecules enter and waste materials leave a cell. 10. OSMOSIS is a special case of diffusion during which water molecules move along a water CONCENTRATION gradient from a region of higher water concentration to a region of LOWER water concentration through a selectively PERMEABLE membrane. 11. When placed in a solution with a water concentration higher than that of their cell contents, cells GAIN water by osmosis. Animal cells swell up and may BURST; plant cells also swell up but are prevented from bursting by their cell WALLS. 12. When placed in a solution with a water concentration lower than that of their cell contents, cells LOSE water by osmosis. Animal cells SHRINK and plant cells become PLASMOLYSED. 13. Ions and molecules of some chemical substances are actively transported across the cell membrane AGAINST a concentration gradient. 14. ACTIVE transport is brought about by membrane protein molecules and requires ENERGY. 3 Key Areas 3-6 Cell Division DNA and Proteins Proteins and Enzymes Genetic Engineering Word bank 1. active amino antibodies aseptic base benefit catalyst centromere chromatids chromosome chromosome code complement complementary contaminating denatured diploid DNA DNA energy engineering enzymes equator fibre function gene genetic helix host inserted medium mitosis modified nucleus optimum optimum plasmid products protein protein ribosome RNA sequence sequence shape site structural substrate temperature unaltered wall During cell division, the NUCLEUS divides first, followed by the cytoplasm. In a plant cell, a new cell WALL is laid down between the two daughter cells formed. 2. Every species has a characteristic number of chromosomes called its chromosome COMPLEMENT. Normally this takes the form of two matching sets of chromosomes and the cell that contains them is said to be DIPLOID. 4 3. The process by which the nucleus of a diploid cell divides into two nuclei, each of which receives a copy of the diploid CHROMOSOME complement, is called MITOSIS. 4. During mitosis each chromosome, consisting of two identical CHROMATIDS, becomes attached by its CENTROMERE to a spindle FIBRE at the cell’s EQUATOR. One chromatid from each chromosome moves to the north pole and one to the south pole forming two nuclei. 5. During culturing of cells, ASEPTIC techniques are employed to prevent unwanted spores CONTAMINATING the cultures. 6. In order to grow, cells in a culture need an appropriate MEDIUM containing nutrients that provide ENERGY and a supply of cell-building materials. They also require an environment where all factors are controlled and maintained at OPTIMUM levels. 7. Chromosomes contain DNA. A molecule of DNA consists of two strands coiled into a double-stranded HELIX. The two strands are held together by weak bonds between their bases. There are four types of base. A pairs with T and G pairs with C to form complementary BASE pairs. 8. Information called the genetic CODE is present in DNA. It takes the form of codewords of bases that correspond to AMINO acids, the building blocks of proteins. 9. The sequence of bases in DNA determines the SEQUENCE in which amino acids are assembled in a PROTEIN. 10. The genetic code for a protein, present on DNA is carried by messenger RNA from the nucleus to a RIBOSOME in the cytoplasm where the appropriate amino acids become joined together into the protein. 11. Both the shape and FUNCTION of a protein molecule are determined by the particular SEQUENCE of amino acids that make up the PROTEIN. 5 12. Some proteins have a STRUCTURAL function; others act as hormones, ANTIBODIES or enzymes. 13. A CATALYST is a substance that speeds up the rate of a chemical reaction but remains UNALTERED by the reaction. ENZYMES are biological catalysts produced by all living cells. 14. The shape of the ACTIVE site on an enzyme molecule is COMPLEMENTARY to the molecular structure of its SUBSTRATE, allowing them to combine together closely. 15. Following catalytic activity, the end PRODUCTS become detached from the active SITE, leaving the enzyme unchanged. 16. To function efficiently, an enzyme needs an appropriate pH and a suitable TEMPERATURE. Each enzyme works best in its OPTIMUM conditions. At temperatures above 55oC, most enzyme molecules are inactive because their molecular SHAPE has been irreversibly altered. They are described as being DENATURED. 17. DNA can be transferred naturally from one cell to another. DNA can also be transferred by genetic ENGINEERING. 18. During GENETIC engineering, the section of DNA that contains the required GENE is identified and cut out of the source CHROMOSOME. Then the gene is inserted into a vector such as a bacterial PLASMID. 19. The reprogrammed plasmid is INSERTED into a HOST cell such as a bacterium. 20. The transformed host cell (now a genetically MODIFIED organism) grows and multiplies and provides humans with some BENEFIT. 6 Key Areas 7 and 8 Photosynthesis Respiration Word bank 1. ADP aerobic ATP cellular cellulose chlorophyll cytoplasm dioxide energy enzymes ethanol fermentation fixation glucose hydrogen intensity lactic light limited mitochondria oxygen photosynthesis pyruvate regenerate respiration split temperature thirty-eight two water The chemical ENERGY stored in glucose is released by a series of reactions controlled by ENZYMES. This biochemical process is called RESPIRATION. 2. ATP is a high-energy compound that can be broken down to ADP and phosphate. This process releases the energy required for CELLULAR processes. 3. ATP is regenerated from ADP and phosphate using energy released during respiration. 4. The first stage of the respiratory pathway is common to both AEROBIC respiration and fermentation (anaerobic respiration). It involves the breakdown of glucose to PYRUVATE. 5. In the presence of OXYGEN, aerobic respiration occurs. WATER and carbon dioxide are formed and THIRTY-EIGHT molecules of ATP are produced per molecule of glucose. 7 6. In the absence of oxygen, FERMENTATION occurs. In animal cells, pyruvate is reversibly converted to LACTIC acid. In plant cells, pyruvate is irreversibly converted to ETHANOL and carbon dioxide. In each case only TWO molecules of ATP are produced per molecule of glucose. 7. Aerobic respiration begins in a cell’s cytoplasm and is completed in its MITOCHONDRIA. Fermentation occurs in the CYTOPLASM only. 8. Green plants use LIGHT as their source of energy to make food. This process is called PHOTOSYNTHESIS. It is a two-stage process. 9. During the first stage, which is made up of light reactions, light energy is captured by green CHLOROPHYLL in chloroplasts. Some energy is used to REGENERATE ATP from ADP and phosphate. Some energy is used to SPLIT water into oxygen and HYDROGEN. 10. During the second stage of photosynthesis, called carbon FIXATION, hydrogen produced during the first stage is combined with carbon DIOXIDE to form glucose. This process requires energy, which is supplied by ATP. 11. Some GLUCOSE molecules produced by photosynthesis are used in cellular respiration; others are converted to products such as starch and CELLULOSE. 12. Photosynthesis is affected by environmental factors such as light INTENSITY, carbon dioxide concentration and TEMPERATURE. Its rate is therefore LIMITED by whichever one of these factors is in short supply. 8