Plant Hormones

Plant Hormones

Auxin is a plant growth hormone
1. Auxin is a plant hormone that controls growth near the tips of shoots and roots
  1. It controls the growth of a plant in response to light (phototropism), gravity (gravitropism or geotropism) and moisture
  2. Auxin is produced in the tips and moves backwards to stimulate the cell elongation (enlargement) process which occurs in the cells just behind the tips
    1. If the tip of a shoot is removed no auxin is available and the shoot may stop growing
Auxin promotes growth in a plants shoots
1. Shoots grow towards light
  1. When a shoot is exposed to light more auxin accumulates on the side thats in the shade than the side thats in the light
    1. This makes the cells grow (elongate) faster on the shaded side so the shoot bends towards the light
2. Shoots grow away from gravity
  1. When a shoot is growing sideways gravity produces unequal distribution of auxin in the tip with more auxin on the lower side
    1. This causes the lower side to grow faster bending the shoot upwards
Auxin inhibits growth in a plants roots
1. Auxin has the opposite effect in shoots to the one it has in roots. But it still works to control the direction that the roots grow in
2. Roots grow towards gravity
  1. A root growing sideways will have more auxin on its lower side (because of gravity)
    1. But in a root the extra auxin inhibits growth. This means the cells on top elongate faster and the root bend downwards
3. Roots grow towards moisture
Plant hormones have uses in agriculture
1. Most weeds in crop fields are broad-leaves unlike grasses and cereals which have very narrow leaves. Selective weedkillers are made of plant growth hormones they only affect broad leaved plants. They disrupt their normal growth patterns which soon kills them but leave the crops untouched
Homeostasis
1. Constant internal environment
2. Your body needs some things to be kept constant
  1. To keep all your cells working properly certain things must be kept at the right level
    1. Ion content
      1. Regulated by the kidneys
        Ions are taken into the body in food then absorbed into the blood
        If the food contains too much of any kind of ion then the excess ions need to be removed
        The kidneys will remove the excess from the blood
    2. Sugar content
    3. Water content
    4. Temperature
3. Blood sugar needs to be controlled to
  1. Eating foods containing carbohydrates puts glucose into the blood from the gut
    1. The normal metabolism of cells removes glucose from the blood. But if you do a lot of vigorous exercise then much more glucose is removes
      1. A hormone called insulin helps to maintain the right level of glucose in your blood so your cells get a constant supply of energy
4. Water is lost from the body in various ways
  1. Theres a need for the body to constantly balance the water coming in against the water going out. Water is taken into the body as food and drink and is lost from the body in these ways:
    1. through the skin as sweat
    2. lungs in breath
    3. kidneys as urine
    4. On a cold day or when your not exercising you dont sweat at all so youll produce more urine which will be pale
    5. On a hot day or when your exercising you sweat a lot and so you will produce less urine but this will be more concentrated. You will also lose more water through your breath when you exercise because you breathe faster
5. Body temperature is controlled by the brain
  1. All enzymes work best at a certain temperature. The enzymes within the human body work at best at about 37 oC so this is the temperature your body tries to maintain
  2. A part of the brain acts as your own personal thermostat. Its sensitive to the blood temperature in the brain and it receives messages from the skin that provide information about skin temperature

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