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Transcript
S3 Biology Revision Cell Structure Cell structure Function Cell type Cell wall Supports and strengthens cell Plant cell, fungal cell or bacterial cell Cell membrane Controls which substances can enter and leave the cell All cell types Cytoplasm Location of many chemical reactions All cell types Mitochondria Location where aerobic respiration Animal cell, plant cell occurs or fungal cell Chloroplasts Site of photosynthesis. Plant cell Vacuole Contains cell sap. Plant cell Ribosomes Site of protein synthesis All cell types Plasmids Contains genes that help cell to function. Bacterial cell Nucleus Controls activities of cell Animal cell, plant cell or fungal cell 1 Cell Transport Membrane Structure Phospholipid Diffusion Diffusion is the movement of molecules from an area of high concentration to an area of low concentration. It does not require energy. Molecules move down a concentration gradient. Oxygen Glucose Carbon dioxide Osmosis Osmosis is a special case of diffusion. It is the movement of water molecules from an area of high concentration to an area of low concentration. It does not require energy and molecules move down a concentration gradient. 2 Active Transport Movement of molecules from an area of low concentration to an area of high concentration, against a concentration gradient. Requires energy. Molecules travel through specific proteins in the membrane. Mitosis Mitosis is cell division. It is used for the growth and repair of cells. It is important that the chromosome number remains the same in the daughter cells so that no genetic information is lost. Stage 1 - The replicated chromosomes 'condense'. Their DNA becomes tightly coiled up and the replicated chromosomes become visible as separate units. The chromosomes shorten and thicken and can now be seen as pairs of chromatids. Stage 2 – The nuclear membrane breaks down. 3 Stage 3 - Rope-like structures called spindle fibres attach themselves to the centromere region of the sister chromatid pairs. The spindle fibres line sister chromatid pairs up in the centre of the cell. This location is known as the equator. Stage 4 - The spindle fibres contract and separate the sister chromatids from each other. The sister chromatids are pulled to opposite ends of the cell - the cell poles. Stage 5 - The separated sister chromatids are now known as chromosomes. Their DNA becomes more loosely coiled (decondensed), and new nuclear membranes form around them. Two new nuclei are formed. Each nucleus now contains four chromosomes (two sets of two chromosomes) exactly the same complement as the original parent cell. Stage 6 - The cytoplasm of the cell then divides in two to produce two daughter cells. The daughter cells are genetically identical because they each contain the same diploid chromosome complement as the original parent cell. 4 DNA Structure Double helix. Base pairing rules: Adenine always pairs with Thymine. Guanine always pairs with Cytosine. Enzymes Enzymes speed up chemical reactions. They are reusable. At high temperatures they become denatured. Enzymes have an optimum (best) pH and temperature. Enzymes are specific – they only work with one substrate. 5 Genetic Engineering Genetic engineering is the transfer of DNA from one organism to another using biotechnology. The organism receiving the DNA is said to be genetically modified (GM). Bacterial cells can be genetically modified so that they have the gene for producing human insulin. As these modified bacteria grow, they produce human insulin. This protein can be purified and supplied to diabetics. 6