Cell activity

Cell activity

1. Cells

   • Animal cells
     • Nucleus, to control the activities of the cell
       • Contains chromosomes which carry genes that control the characteristics of the body
       • Different forms of genes are called alleles
     • Cytoplasm, in which most of the chemical reactions take place
     • The cell membrane controls passage of substances into and out of the cell
     • Mitochondria, where most of the energy is released in respiration
     • Ribosomes, where protein synthesis occurs
   • Plant cells
     • Chloroplasts, which absorb light energy to make food
       • Contain chlorophyll
     • A permanent vacuole filled with cell sap
     • A cell wall made of cellulose, which strengthens and supports the cell
   • Other cells
     • Bacteria
       • No nucleus - instead genetic material is arranged in plasmids
     • Yeast
       • A single celled organism

2. Movement of substances in and out of cells

   • Diffusion
     • Spreading of the particles of any substance in solution
     • Results in a net movement of particles from a region of high concentration to a low concentration
     • The greater the difference in concentration, the faster the rate of diffusion
   • Osmosis
     • Movement of water across a partially permeable membrane
     • Moves from an area of high concentration to an area of low concentration
   • Definitions
     • Isotonic: if two solutions have the same concentration
     • Hypertonic: the solution which is more concentrated
     • Hypotonic: the solution which is more dilute
     • Turgid plant cells: rigid plant cells with lots of water
     • Plasmolysed plant cells: shrunken plant cells with little water
   • Cells use active transport to absorb substances across partially permeable membranes against the concentration gradient.
     • This requires energy from respiration
   • Efficiency of exchange can be increased by
     • Having a large surface area
     • Having a thin surface
     • Having an efficient blood supply
     • Being ventilated

3. Cell division

   • Meosis
     • Cell divides to form sex cells/gametes
     • Cell divides twice to form four gametes, each with a single set of chromosomes
     • Gametes join at fertilisation and this newly form cell divides by mitosis to form many cells, becoming an organism
   • Mitosis
     • The cell divides once to produce two genetically identical daughter cells
   • Cell division is essential for growth and repair in an organism
   • Plants can differentiate cells throughout their lives, however animals are unable to

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