Cell Structure and Organisation is the foundation of IGCSE Biology. Students learn the structures and functions of cell organelles, differences between plant and animal cells, and how cells are organised into tissues, organs, and organ systems.
Animal cells: cell membrane (controls entry/exit), cytoplasm (site of chemical reactions), nucleus (contains DNA, controls cell), mitochondria (site of aerobic respiration), ribosomes (protein synthesis). Plant cells have all of these PLUS: cell wall (cellulose, provides strength), large central vacuole (sap, turgor), chloroplasts (photosynthesis, contain chlorophyll). Bacteria: no true nucleus (DNA free in cytoplasm), cell wall (not cellulose), may have flagella, plasmid DNA.
Cells differentiate to carry out specific functions. Red blood cells: biconcave disc (large surface area), no nucleus (more space for haemoglobin), flexible. Root hair cells: long extension (large surface area for water absorption), thin walls. Palisade cells: many chloroplasts (near top of leaf for maximum light). Nerve cells: long axon (carry electrical impulses), many dendrites. Sperm cells: streamlined, tail for movement, many mitochondria for energy.
Cell → tissue (group of similar cells) → organ (group of tissues working together) → organ system → organism. Examples: muscle cells → muscle tissue → heart → circulatory system → human. Magnification = image size / actual size. Use mm for measuring images, convert to μm for cells (1 mm = 1000 μm). Eyepiece graticule and stage micrometer for calibration.
Plant cells have a rigid cellulose cell wall that provides structural support, maintains shape, and prevents the cell from bursting when water enters by osmosis (the wall resists further expansion once turgid). Plants do not have a skeleton like animals, so the cell wall and turgor pressure provide the support needed to keep the plant upright. Animal cells only have a flexible cell membrane, which allows them to change shape — important for processes like phagocytosis (white blood cells engulfing pathogens) and for muscle contraction.
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