AQA SCIENCE B1A

B1A 1.1 RESPONDING TO CHANGE

Hormones, secreted by special glands, are chemicals that control internal processes in the body.

The nervous system responds to changes in the environment

• receptor cells detect stimuli such as 
  • light
  • sound
  • temperature
• impulses from the receptor travels along the sensory neurone
• the brain then co-ordinates a response
• impulses from the brain travel back along motor neurones to the effector

RECEPTOR > SENSORY NEURONE > CO-ORDINATOR > MOTOR NEURONE > EFFECTOR

B1A 1.2 REFLEX ACTION

• Reflexes are reactions to change that happen unconsciously
• Reflex actions include pulling your hand away from a hot object to protect your body

• the receptor detects the change then an impulse travels along a sensory neurone to the spinal chord, not the brain
• it then passes over a synapse and along a relay neurone, then straight back to the effector along the motor neurone
• this reaction is very quick and requires no conscious thought 

Impulses travel synapses by sacs containing chemicals passing the gap which starts another impulse on the relay neurone.

B1A 1.3 THE MENSTRUAL CYCLE

• the menstrual cycle is controlled by hormones
• once a month, the pituitary gland secretes FSH
  • this makes eggs mature in the ovary
  • it stimulates the secretion of oestrogen from the ovaries
    • this causes the womb lining to thicken
    • it stimulates the pituitary gland to produce LH
      • this stimulates the release of the matured egg 

B1A 1.4 ARTIFICIAL CONTROL OF FERTILITY

THE CONTRACEPTIVE PILL

• contain mainly oestrogen
  • oestrogen inhibits the release of FSH
  • without FSH no eggs can mature
• must be taken regularly
• can cause health problems

FERTILITY TREATMENTS

• fertility drugs containing FSH can be taken 
  • this stimulates eggs to mature in the ovary
  • also triggers the release of oestrogen
  • can result in many babies
• IVF treatments remove eggs from the ovaries and fertilize them with sperm in a test tube
  • good if fallopian tubes are damaged
  • expensive
  • low success rate
• raises ethical questions about interfering with god's plan and what to do with extra embryos

B1A 1.5 CONTROLLING CONDITIONS

WATER AND IONS

• if too much water moves in or out of cells they could be damaged
• you lose water in sweat, urine and when you breath out
• you lose salt in sweat and urine
• kidneys control water and salt levels

TEMPERATURE

BLOOD SUGAR

• blood sugar levels must be kept constant
• controlled by the pancreas
  • secretes insulin

2.1 DIET AND EXERCISE

• a healthy diet consists of:
  • carbohydrates
  • proteins
  • fats 
  • vitamins
  • minerals
  • fibre
  • water
  • the right amount of energy
• if your diet isn't balanced you will become malnourished
• in rich countries such as the UK, there are not many malnourished people, but some don't get the right amount of energy

ENERGY

• the amount energy a person needs depends on:
  • gender
  • age
  • amount of exercise they do
  • the temperature of where they live
  • their metabolic rate
    • this is affected by proportion of fat to muscle and your genes

2.2 WEIGHT PROBLEMS

• BMI = WEIGHT / (HEIGHT)2

OBESITY

• if you take in more energy than you use,…