GCSE AQA Biology 1 Nerves & Hormones

GCSE AQA Biology 1 Nerves & Hormones

1. The nervous system

   • Sense organs - detect stimuli (changes in the environment)
     • Contain receptors - groups of cells which are sensitive to stimulus (change stimulus energy into electrical impulses)
     • Eyes - light receptors
     • Ears - sound & balance receptors
     • Nose - smell receptors
     • Tongue - taste receptors
     • Skin - sensitive to touch, pressure, pain & temp. change
   • The CNS (central nervous system)
     • Where info from sense organs is sent & reflexes/actions are coordinated
     • Consists of brain & spinal cord
     • Neurones transit info quickly to & from CNS
       • Sensory neurones - carry signals from receptors to CNS
       • Relay neurones - carry signals from sensory to motor neurones
       • Motor neurones - carry signals from CNS to effector
     • Instructions from CNS sent to effectors
       • Muscles & glands - contract or secrete hormones

2. Synapses

   • Connect neurones
   • Nerve signal transferred by chemicals which diffuse across gap
     • Chemical set off new electrical signal in next neurone

3. Reflexes

   • Automatic responses to certain stimuli - reduce chances of being injured
   • Reflex arc - passage of info in a reflex
     • Neurones go through spinal cord or unconscious part of brain
     • 1) STIMULUS - detected by receptors
       • 2) SENSORY NEURONE - impulses sent along to CNS
         • 3) RELAY NEURONE - impulses reach synapse between sensory & relay, chemicals cause impulses to be sent along relay neurone
           • 4) MOTOR NEURONE - impulses reach synapse between relay and motor, chemicals cause impulses to be sent along motor neurone
             • 5) EFFECTOR - impulses travel to effector
               • 6) RESPONSE - muscle contracts/gland secretes

4. Hormones

   • Definition: Chemical messengers which travel in the blood to activate target cells
   • Control things in organs & cells that need constant adjustment
   • Produced & secreted by glands e.g. pituitary & ovaries
   • Long-lasting effects

5. Comparing nerves & hormones

   • Nerves
     • Very fast action
     • Act for very short time
     • Act on very precise area
   • Hormones
     • Slower action
     • Act for long time
     • Act in more general way

6. The menstrual cycle

   • 4 stages
     • 1) Bleeding starts - uterus lining breaks down
       • 2) Uterus lining builds up
         • 3) Egg is released
           • 4) Wall is maintained
   • Hormones
     • FSH
       • Produced by pituitary gland
         • Causes egg to mature
           • Stimulates release of oestrogen
     • Oestrogen
       • Produced in ovaries
         • Causes pituitary gland to produce LH
           • Inhibits release of FSH
     • LH
       • Produced by pituitary gland
         • Stimulates release of egg

7. Controlling fertility

   • Reducing fertility
     • Oestrogen can prevent release of egg - inhibits FSH
     • Progesterone also reduces
       • Produces thick cervical mucus, stops any sperm getting through
     • The Pill
       • Used to be version with high levels but there was link with blood clots - now contains lower doses of oestrogen
       • Pros
         • * Over 99% effective at preventing pregnancy * Reduces risk of getting some types of cancer
       • Cons
         • * Isn't 100% effective * Can cause side effects * Doesn't protect against STDs
   • Increasing fertility
     • Some women have low levels of FSH - don't cause eggs to mature
       • Can inject FSH & LH to stimulate egg release
     • Pros
       • * Helps women to get pregnant
     • Cons
       • * Doesn't always work - may have to do it many times (expensive) * Too many eggs could be stimulated - multiple pregnancies
   • IVF
     • Involves collecting eggs from woman's ovaries and fertilising with man's sperm - grown into embryos
       • Once ball of cells - 1 or 2 transferred to uterus
         • FSH & LH given before egg collection
     • Pros
       • * Can give infertile couple a child
     • Cons
       • * Some women have strong reaction to hormones e.g. abdominal pain, vomiting & dehydration * Reported increased risk of cancer * Multiple births - risky for mother & babies

8. Plant hormones

   • Auxin
     • Controls growth near tips of shoots & roots
       • In response to light, gravity & moisture
     • Produced in tips, moves backwards - enlarging
       • If tip is removed, may stop growing
     • STIMULATES growth in SHOOTS, INHIBITS growth in ROOTS
   • Shoots grow towards light
     • * More auxin accumulates on shaded side * Grows faster on that side - shoot bends towards light
   • Shoots grow away from gravity
     • * When shoot is growing sideways, gravity produces unequal distribution - it will have more auxin on lower side * Lower side grows faster - bending shoot upwards
   • Roots grow towards gravity
     • * Root growing sideways will have more auxin on lower side * Auxin will inhibit growth - top side grows faster, root bends downwards
   • Roots grow towards moisture
     • * Uneven amount of moisture produces more auxin on side with more moisture * Inhibits growth - further side grows faster, root bends towards moisture
   • Uses in agriculture
     • Weedkillers
       • Most weeds in crop field broad-leaved (unlike crops), weedkillers made of plant hormones only affect broad-leaved plants (disrupt normal growth patterns - kills them)
     • Rooting powder
       • Plant cuttings won't alays grow in soil, add rooting powder containing auxin - produces roots rapidly