IGCSE BIOLOGY UNIT 2.1&2

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  • UNIT 2
    • CELL STRUCTURE AND ORGANISATION
      • Both animal and plant cells have a NUCLEUS, CYTOPLASM and a CELL MEMBRANE. However, only plant cells have a CELL WALL, a VACOULE and CHLOROPLAST
      • LIVING ORGANISMS AE MADE UP OF CELLS.
      • FUNCTIONS OF CELL STRUCTURES
        • NUCLEUS
          • Is usually the largest of the ORGANELLES found in cells. They contain DNA strands which hold genetic information and are in control of the activities occurring within the cell.
        • CELL MEMBRANE
          • Is an outer layer surrounding the cell which controls the passage of substances in and out of the cell.
        • CYTOPLASM
          • Contains water and dissolved substances such as sugar and salts, glucose, protein and ions. Chemical reactions take place in organelles within the cytoplasm such as protein made in ribosomes and energy released by respiration in the mitochondria.
        • CELL WALL
          • Provides structural support and protects against damage caused by osmotic intake of water. The cell wall is freely permeable to water and dissolved substances.
        • CHLOROPLAST
          • These contain a pigment called chlorophyll (for light absorption) and the enzymes required for the production of glucose by photosynthesis.
        • VACUOLE
          • Are filled wioth cell sap which contains water and nutrients necessary for the plants' survival
    • LEVELS OF ORGANISATION
      • TISSUE - a grouo of cells with similar structures  working together to perform a shared function.
        • Examples include: skin tissue, muscle tissue, brain tissue...
      • ORGAN - a structure made up of a group og tissues that work together to perform specific functions.
        • Examples include: heart, brain, liver, lungs, skin...
      • ORGAN SYSTEM - a group of organs with related functions working together to perform body functions.
        • Examples include: digestive system, nervous system...
      • CILLIATED CELLS - which can be found in the respiratory tract have tiny hairs (cilia) which move and push mucus from one place to another. The mucus is able to transport dust and microbes when pushed by cilia = blockage prevention.
      • ROOT HAIR CELLS (PLANTS) - absorb minerals and water from the soil. They have a long extension (root hair) which increases surface area = more absorption.
      • XYLEM VESSELS - transports water and supports the plant. They have no cytoplasm (water passes freely), no end wall (form continuous tube) and walls strengthened by waterproof substance called lignin.
      • MUSCLE CELLS - contracts so structures can be brought closer together. They are long with many protein fibres in the cytoplasm which can shorten the cell when energy is available.
      • RED BLOOD CELLS - transport oxygen from the lungs to the tissues where aerobic respiration occurs. Cytoplasm filled with Heamoglobin which carries oxygen. no nucleus = more space for haemoglobin. The cells are flexible and cna move through the narrowest blood vessels.

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