Biology

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  • Cell biology
    • Cells
      • Prokaryotic cells are smaller and simpler e.g. bacteria
    • Chromosomes and mitosis
      • Chromosomes are coiled up lengths of DNA molecules
        • Each chromosome carries a large number of genes
          • A human cell has 23 pairs of chromosome,46 chromosomes
      • Body cells have 2 copies of each chromosomes, one from the organisms 'mother' and one from its 'father'
        • A human cell has 23 pairs of chromosome,46 chromosomes
      • The DNA is spread out in long springs
        • Before it divides it has to grow the amount of subcellular structures
          • It then duplicates its DNA
            • The chromosomes line up at the center of the cell and cell fibres pull them apart
              • Membranes form around each set of chromosome and become the nuclei of the two new cells
                • Lastly the cytoplasm and cell membrane divide
    • Diffusion
      • The spreading out of particles from an area of HIGHER concentration to an area of LOWER concentration
        • Happens in both solutions and gases because the particles are free to move about randomly
          • The bigger the concentration gradient, the faster the diffusion rate
      • Cell membranes hold the cell together but they let stuff in and out as well
        • dissolved substances can move in and out of cells by diffusion
          • Only small molecules can diffuse through cell membranes like oxygen, glucose, amino acids and water
            • The larger the surface area of the membrane, the faster the diffusion rate because more particles can pass through at once
    • Osmosis
      • Osmosis is the movement of water molecules across a partially permeable membrane from a region of higher water concentration to a lower water concentration
        • Osmosis is a type of diffusion
      • A partially permeable membrane is a membrane with small holes in it
        • Water molecules pass both ways through the membrane during osmosis
          • The water acts like its trying to even up the concentration either side of the membrane
    • Active Transport
      • Active transport allows the plant to absorb minerals from a very dilute solution, against a concentration gradient
        • Active transport needs energy from respiration to make it work
      • Active transport is used in the gut when there is a lower concentration of nutrients in the gut, but a higher concentration of nutrients in the blood

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