B3

• How the nervous system coordinates responses

  1. The central nervous system (CNS) consists of the brain and the spinal cord

  2. Receptor cells convert a stimulus into an electrical impulse

  3. This electrical impulse travels along sensory neurons to the CNS

  4. Information is processed in the CNS and the appropriate response is coordinated

  5. An electrical impulse is sent along motor neurons to effectors
• The eye

  1. Cornea refracts light to reach the retina

  2. Iris controls how much light enters the eye

  3. In bright light, circular muscles contract and radial muscles relax to make the pupil smaller

  4. In dim light, circular muscles relax and radial muscles contract to make the pupil larger

  5. Lens focuses light onto the retina

  6. Retina contains rods (respond to dim light) and cones (respond to colour)

  7. Optic nerve carries impulses between the eye and the brain
• The brain

  1. Cerebrum functions include intelligence, vocabulary, personality, and conscious thought

  2. Cerebrum is the largest part of the brain, divided into 2 cerebral hemispheres

  3. Each half processes information from the opposite side of the body

  4. The outside of the cerebrum is made from grey matter and the inside is made of white matter

  5. Cerebellum coordinates balance, posture and motor movement.
• Reflex arc

  1. A subconscious response to dangerous stimuli

  2. Stimulus is detected by receptors

  3. Impulses are sent along sensory neurons

  4. Impulse passes to a relay neuron in the CNS

  5. Impulses are sent along a motor neuron

  6. Impulse reaches an effector resulting in the appropriate response
• Pituitary gland


  • An important gland releasing hormones, such as growth hormone, into the blood
• Examples of hormones


  • Adrenaline
  • Thyroxine
• Thyroxine

  • Produced by the thyroid gland, controls metabolic rate and growth, example of negative feedback
• Endocrine system


  • Hormones are chemical messengers secreted by endocrine glands into the bloodstream to receptors on the target organ
• Testosterone


  • Produced by the testes, responsible for sperm development and secondary sexual characteristics in males
• Puberty

  • Hormones responsible for changes in the body during puberty
• Cerebellum


  • Coordinates voluntary body movements and helps with balance
• Medulla


  • Control centre for heart rate, blood pressure, and breathing rate
• Oestrogen

  • Produced by the ovaries, responsible for secondary sexual characteristics in females
• Adrenaline

  • Produced by adrenal glands, targets organs like the heart and lungs, responsible for the 'fight or flight' response
• The menstrual cycle lasts 28 days and the egg is usually released on day 14 (ovulation)
• Hypothalamus


  • Controls temperature and water balance in the body through the hormonal system
• Brain

  • The largest part of the brain that divides into 2 cerebral hemispheres
  • Each half processes the information it receives from the opposite side of the body
  • The outside is made from grey matter (containing myelinated nerves) and the inside is made of white matter
• Oestrogen


  • Causes thickening of the uterus in preparation for implantation of an egg, levels peak on day
• Contraceptive implants

  • More than 99% effective
  • Cause slow release of progesterone to prevent ovaries from releasing the egg, thickens mucus in cervix so sperm cannot swim through
  • Do not need to be taken every day
• Menopause occurs when a woman no longer has a menstrual cycle, usually around 50-55 years of age
• Non-hormonal methods of contraception

  • Physical barrier methods, such as condoms
  • Vasectomy/female sterilisation
  • Copper intrauterine device (IUD/the coil)
  • Abstinence
• Hormonal methods of contraception

  • Oral contraceptives (the pill)
  • Contraceptive implants
• IVF

  1. Mother is given FSH and LH to stimulate eggs to mature

  2. Eggs are collected and fertilised by the father’s sperm in a laboratory

  3. The fertilised eggs develop into embryos

  4. These embryos are then implanted into the mother’s uterus

  5. However, can be extremely expensive if it needs to be repeated
• Physical barrier methods, such as condoms

  • Easy to use and obtain and also protect from STIs
  • However, condoms can rip
  • Over 99% effective
  • Can be made more effective with spermicidal agents, but some people can be allergic to it
• FSH and LH

  • FSH (follicle stimulating hormone) causes maturation of the egg within the ovary
  • LH (luteinising hormone) stimulates the release of the egg during ovulation
  • A decrease in oestrogen causes LH and FSH to start increasing
  • Ovulation occurs when LH and FSH levels peak
• Progesterone

  • Maintains the thick lining of the uterus
  • Inhibits the release of LH and FSH
  • Starts increasing after day 14 until it reaches its peak 3 days later
  • If the egg is not fertilised, progesterone levels fall and the uterus lining breaks down in a period lasting around 5 days
• Fertility drugs

  • FSH and LH mainly used because they stimulate the maturation and release of the egg
  • The woman can then become pregnant normally
• Plants need hormones to coordinate and control growth. They are needed for tropisms such as phototropism and gravitropism. Hormones move from the place they are made to where they are needed to produce the appropriate response.
• Oestrogen


  • Causes thickening of the uterus in preparation for implantation of an egg
  • Levels peak on day 10 and then begin to fall
• Auxins

  • Most plants show positive phototropism because they grow towards the light source
  • The plant is exposed to light on one side
  • Auxin, a growth hormone, moves
• Oral contraceptives (the pill)

  • Contains progesterone and oestrogen, which inhibit the production of FSH so that eggs do not mature
  • More than 99% effective if taken properly
  • Side effects such as mood swings, weight gain
• Fertility treatments allow infertile couples the opportunity to have children. Infertility can be caused by many issues, such as sperm quality or quantity problems or a lack of FSH to mature eggs. However, fertility treatments are not guaranteed to work and if they do, they can increase the likelihood of twins, triplets, etc.
• Copper intrauterine device (IUD/the coil)


  • T-shaped device implanted into the uterus
  • Stops fertilised embryos from implanting, copper kills sperm
  • Can last for up to 10 years, over 99% effective
  • Must be fitted by a doctor, small chance of ectopic pregnancy
• Vasectomy/female sterilisation


  • Sperm tubes/oviducts are cut to prevent gametes from becoming fertilised
  • Almost 100% reliable
  • However, can be irreversible
• When auxin distribution becomes equal on both sides

  The plant grows straight in that direction
• Auxins


  • They stimulate cells to grow more in shaded areas, causing the plant to bend towards light sources
• Hormones move from the place they are made to where they are needed in order to produce the appropriate response
• Auxins


  • They stimulate cells to grow more on the side with most auxin, causing shoots to grow away from gravity
• Investigating the effect of light or gravity on newly germinated seedlings

  Varying conditions such as placing in a cardboard box and shining light from one side, attaching a petri dish containing the seedlings to a wall
• Gibberellins


  • Used for ending seed dormancy, promoting flowering, increasing fruit size