Wednesday, 8 April 2009

iGCSE Biology - Life Processes

Life Processes


  • Multicellular organisms contain many different types of cells with different structures.
  • Eight life processes:

          Move – muscles in animals, slow growth movement in plants

          Respire – get energy from their food

          Stimuli – respond to changes in their surroundings

          Control – their internal conditions

          Grow – increase in size and mass

              Reproduce – produce offspring

          Excrete – get rid of toxic waste products

          Nutrition – make own food (plants) or eat other organisms                     (animals)

  • Animal cell components:

          Cytoplasm – living material of cell, makes up body

          Nucleus – contains chromosomes and controls activity of cell

          Cell membrane – boundary between cytoplasm and outside,                         selectively permeable

          Mitochondria – carry out respiration

  • Plant cell components:

          All of the above

          Cell wall – made of cellulose, keeps the cell’s shape, freely                     permeable

          Vacuole – contains cell sap, a store of dissolved nutrients

              Chloroplast – absorb light energy for photosynthesis, contain                     chlorophyll which makes them green

  • Chemical reactions in cells are controlled by enzymes, which in turn are controlled by the genes in the nucleus
  • Enzymes are biological catalysts
  • Body temperature is low, so without enzymes reactions would be too slow
  • The molecule that an enzyme acts upon is its substrate
  • The substrate attaches itself to the active site of the enzyme
  • Three factors affect rate of reactions of enzymes:

          Temperature – each enzyme has an optimum temperature,                             after which it begins to denature

          pH – enzyme activity decreases increasingly further away from                       optimal pH

          Concentration – rate of reaction increases with the                     concentration of enzyme and substrate

  • Breaking down food molecules to release stored chemical energy is respiration
  • glucose + oxygen carbon dioxide + water (+energy)
  • C6H12O6 + 6O2  6CO2 + 6H2O
  • Anaerobic respiration: Glucose à Ethanol + Carbon Dioxide
  • In humans, lactic acid is produced
  • Diffusion:  the net movement of particles down a concentration gradient
  • Active transport: the movement of particles against the concentration gradient, using energy from respiration
  • Osmosis: the net movement of water from a dilute solution to a more concentrated solution across a partially permeable membrane
  • Larger surface-area to volume ratio means faster diffusion and osmosis
  • Multicellular organisms begin life as a single fertilised cell, a zygote
  • A zygote undergoes mitosis to grow
  • As the embryo grows, cells become specialised to carry out particular   roles: differentiation
  • Cells with a similar function are grouped together as tissues
  • A collection of tissues carrying out a particular function is called an organ
  • A collection of organs working together are called an organ system

          Digestive system – gut and glands such as pancreas and gall                           bladder

          Respiratory system – lungs, exchanges oxygen and carbon                     dioxide

          Circulatory system – heart + blood vessels, transport materials

          Excretory system – kidneys, filter waste materials from blood

          Nervous system – brain, spinal cord + nerves, coordinate body

          Endocrine system – glands secreting hormones, chemical                        messengers

          Reproductive system – produces sperm in males and eggs in                            females

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