B3

• Central nervous system (CNS)


  Brain and spinal cord
• How the nervous system coordinates responses

  1. Receptor cells convert stimulus into electrical impulse

  2. Electrical impulse travels along sensory neurons to CNS

  3. Information processed in CNS, appropriate response coordinated

  4. Electrical impulse sent along motor neurons to effectors

  5. Effectors carry out response
• Reflex arc


  1. Stimulus detected by receptors

  2. Impulses sent along sensory neuron

  3. Impulse passes to relay neuron in CNS

  4. Impulses sent along motor neuron

  5. Impulse reaches effector, resulting in response
• Eye


  • Cornea refracts light to reach retina
  • Iris controls amount of light entering eye
  • Lens focuses light onto retina
  • Retina contains light receptors (rods and cones)
  • Optic nerve carries impulses between eye and brain
• Brain


  • Cerebrum: intelligence, vocabulary, personality, conscious thought
  • Cerebellum: coordinates voluntary movements, helps with balance
  • Medulla: controls heart rate, blood pressure, breathing rate
  • Hypothalamus: controls temperature, water balance
  • Pituitary gland: releases hormones
• Limitations in investigating and treating brain damage
• Endocrine system


  System of glands that secrete hormones into bloodstream
• Hormones


  • Adrenaline
  • Thyroxine
• Menstrual cycle


  1. Oestrogen causes uterus lining thickening

  2. FSH and LH stimulate egg maturation and release

  3. Progesterone maintains uterus lining, inhibits FSH and LH
• Menopause


  When a woman no longer has a menstrual cycle, usually around 50-55 years old
• Contraception methods


  • Hormonal: oral contraceptives, implants

  Non-hormonal: physical barriers, sterilisation, IUD, abstinence
• Fertility treatments


  Fertility drugs stimulate egg maturation and release

  IVF: eggs collected, fertilised, embryos implanted
• Plant hormones


  • Auxin: stimulates growth, causes phototropism and gravitropism
• Phototropism


  Auxin moves to shaded side, stimulating more growth there, causing shoot to bend towards light
• Gravitropism


  Auxin moves to lower side of shoot/root, stimulating more growth there, causing shoot to grow away from ground, root to grow towards ground
• Phototropism


  Response to light
• Gravitropism


  Response to gravity
• Geotropism


  Response to gravity
• Hormones move from the place they are made to where they are needed in order to produce the appropriate response
• Auxins


  A growth hormone
• Positive phototropism


  1. Plant is exposed to light on one side

  2. Auxin, a growth hormone, moves to the shaded side of the shoot

  3. Auxin stimulates cells to grow more here

  4. This means the shoot bends towards the light

  5. The plant receives more light, meaning photosynthesis can occur at a faster rate
• Negative gravitropism


  1. Auxin moves to the lower side

  2. The cells of the shoot grow more on the side with most auxin, so it stimulates cells to grow more here

  3. This makes the shoot bend and grow away from the ground

  4. This is beneficial as light levels are likely to be higher further away from the ground
• Positive gravitropism


  1. Auxin moves to the lower side

  2. The cells of the root grow more on the side with less auxin, so it stimulates cells to grow on the upper side

  3. This makes the root bend and grow downwards

  4. This is beneficial as there are more likely to be increased levels of water and nutrients lower down, and it provides stability for the plant
• When the auxin distribution becomes equal on both sides it grows straight in that direction
• Investigating the effect of light or gravity on newly germinated seedlings

  1. Placing in cardboard box and shining light from one side

  2. Attaching a petri dish containing the seedlings to a wall (effects of gravity)
• Uses of auxins


  • As weed killers
  • As rooting powders
  • To promote growth in tissue culture
• Weed killers containing auxin


  • They only affect broad-leaved plants
  • The increased amount of auxin causes the cells to grow too rapidly, resulting in the weed dying
• Rooting powder containing auxin


  Applied to plant cuttings to stimulate root growth and allow the new plant to grow very quickly
• Tissue culture


  Cells from the plant are placed in a growth medium containing lots of nutrients and hormones such as auxins, allowing the cells to form roots and shoots
• Gibberellins


  Another plant hormone important to stimulate seed germination, flowering and shedding of leaves
• Uses of gibberellins


  • Ending seed dormancy
  • Promoting flowering
  • Increasing fruit size
• Ethene


  A plant hormone involved in cell division and the ripening of fruits
• Using ethene to ripen fruit


  1. Fruit is picked when it is not ripe

  2. It is firm which means that during transport it gets less bruised and damaged

  3. When it is needed to be sold, it is exposed to ethene and warmer temperatures

  4. Ethene is involved in controlling cell division and stimulates enzymes that result in fruit ripening

  5. This reduces wastage as more fruit is suitable to be sold and it does not ripen too early
• Homeostasis


  The maintenance of a constant internal environment
• Thermoregulatory centre


  Monitors and controls body temperature, found in the brain
• Maintaining body temperature when it is too high


  1. Sweat is produced from sweat glands, resulting in increased energy transfer away from the body

  2. Vasodilation means more blood flows closer to the surface of the skin, resulting in increased energy transfer from the body
• Maintaining body temperature when it is too low

  1. Sweating stops

  2. Skeletal muscles contract rapidly (shivering) to generate heat from respiration

  3. Hairs stand on end to create an insulating layer, trapping warm air

  4. Vasoconstriction means blood does not flow so close to the surface, resulting in less heat lost
• Insulin


  A hormone produced by the pancreas that lowers blood glucose levels
• How insulin regulates blood glucose levels

  1. Eating foods that contain carbohydrates increases the glucose levels in the blood

  2. If the glucose levels are too high, the pancreas produces the hormone insulin

  3. Insulin binds to cells in target organs (muscles and liver) causing glucose to move from the blood into muscle cells for respiration and excess glucose to be converted into glycogen which is stored in the liver

  4. The blood glucose concentration is reduced
• Glucagon


  A hormone produced by the pancreas that raises blood glucose levels