Biology

Diet and exercise

• A healthy diet has the right balance of food types.
• Carbohydrate, Fat and Protein are used by the body to release energy.
• Different people need different amounts of energy as the metabolic rate varies from person to person.
• Mineral ions and vitamins are needed to keep the body healthy. If the diet is unbalanced the person can become malnourished.
• If you exercise, more energy is used by the body.
• Exercise increases the metabolic rate. -> The rate at which chemical reactions take place in body cells.
• The proportion of muscle to fat in your body and your inherited factors can also affect your metabolic rate.
• If the energy taken in is less than the energy used, the person will lose mass. -> More exercise = More food.

The proportion of fruit and vegetables is 1/3 of a balanced diet.

• The main food groups:
  • Carbohydates - Source of energy for life processes.
  • Fats - Make cell membranes/insulate our bodies
  • Proteins - Growth and repair - building cells.

Weight problems

• If you eat more food than you need, your mass will increase.
• If the energy taken in equals your used energy, your mass will stay the same.
• Obesity can be prevented by eating less and exercising more.
• Obesity can lead to Arthritis; Type 2 diabetes; High blood pressure and heart disease.
• Cholesterol is made in the liver and is needed for healthy cell membranes. -> Too much in the blood can lead to blocked arteries and heart disease.
• Food rich in saturated fat can increase blood cholesterol levels.
• Regular exercise can lower high cholesterol levels.

Defence against disease

• Pathogens are microorganisms that cause infectious diseases.
• Most pathogens are either bacteria or viruses.
• Bacteria reproduce rapidly and make you feel ill by producing toxins.
• Viruses are much smaller than bacteria. -> They reproduce inside cells, damaging them to make you feel ill.
• White blood cells:
  • Ingest pathogens -> Digest and destroy them.
  • Produce antibodies -> Destroy particular pathogens.
  • Produce antitoxins -> Counteract toxins that pathogens produce.
• The skin prevents pathogens entering the body. -> They are also trapped by mucus and killed by stomach acid.
• Before bacteria and viruses had been discovered, a doctor called Semmelweiss realised that infection could be transferred form person to person in a hospital. He told his staff to wash their hands between treating patients.
• Vaccines contain dead or inactive pathogens. -> The white blood cells react by producing antibodies. -> This makes the person immune. It prevents further infection because the body responds quickly by producing more antibodies. -> The antibodies recognise the antigen on the pathogen.

• The MMR vaccination is one of several vaccines. MMR is given to prevent measles mumps and rubella.
• Antibiotics kill infective bacteria in the body. Penicillin is an antibiotic, but there are many others. It was first discovered by Flemming in 1925.
• Antibiotics cannot destroy pathogenic viruses. -> Viruses are difficult to destroy because they reproduce inside the body cells, so any treatment could also damage cells.
• Painkillers and other drugs relieve the symptoms of a disease, but do not kill a pathogen.
• Overuse of antibiotics can lead to the development of new strains of bacteria.
• A mutation can cause antibiotic resistance. -> The individual bacteria can reproduce.
• Scientists are always trying to find new ways of treating disease. -> Develop new antibiotics.
• Too many antibiotics -> Antibiotic resistance -> Mutation in DNA -> Bacteria reproduce -> New antibiotic resistant bacteria. -> (natural selection)

• Pure cultures of non-pathogenic (safe) bacteria can be used for laboratory investigations.
• A culture of microorganisms can be used to find the effect of antibiotics on bacteria.
• Contamination might come from your skin, the air or the water around you.
• All the equipment and materials must be sterilised. This prevents contamination.

The Nervous System

• The nervous system has receptors to detect stimuli (changes in environment). -> They are found in sense organs.
• Light stimulates receptors in the eye and electronical impulses then pass to the brain along neurones. Other stimuli detect sound, chemicals, temperature changes, touch and pain.
• The brain coordinates responses to many stimuli.
• The brain and spinal chord form the CNS ( central nervous system).
• Sensory neurones carry impulses from the receptors to the CNS.
• Motor neurones carry impulses from the CNS to effector organs which may be muscles or glands. The muscle responds by contracting. The glands respond by secreting chemicals.
• At the junction between two neurones is a synapse. Chemicals transmit the impulse across the gap.

Reflex actions

• The main steps involved in reflexes are:
  • A receptor detects a stimulus (e.g sharp pain).
  • A sensory neurone transmits the impulse to the CNS.
  • The relay neurone passes the impulse on.
  • A motor neurone is stimulated.
  • The impulse passes on to the effector.
  • Action is taken -> (the response)
• Reflex actions are rapid, automatic responses to a stimulus.
• Reflexes protect us from damage.
• The brain is not involved as it would cause a delay.

Controlling conditions

• The body carefully controls its internal conditions/environment.
  • Water } Food + drink -> Sweating, urine
  • Ions
  • Blood sugar -> Food + drink -> Exercise/Insulin
  • Temperature

Hormones and the menstrual cycle

• The menstrual cycle takes 28 days, with ovulation about 14 days into the cycle.
• FSH (follicle stimulating hormone) is made by the pituitary gland and causes the egg to mature and oestrogen to be produced.
• Oestrogen is produced by the ovaries and stops the further productions of FSH. It stimulates the production of LH and thickens the lining of the womb to develop and receive the fertilised egg.
• LH (luteinizing hormone) is made in the pituitary gland and stimulates the mature egg to be released from the ovary (ovulation).

Controlling fertility

• The contraceptive pill may contain oestrogen and progesterone to inhibit FSH so no eggs mature.
• If a woman cannot produce mature eggs, then FSH and LH can be given. This is known as 'fertility treatment'.
• FSH matures ages and LH stimulates ovulation.

Advantages and disadvantages of fertility treatment:

• Contraceptive pills have helped to reduce family size -> Reduced poverty in some areas.
• Allows women to plan their pregnancies.
• Fertility drugs can help infertile couples who are having IVF.
• IVF helps couples to have a baby.
• The pill can cause side effects (headaches).
• Objection -> Religious/Ethical reasons.
• IVF is an expensive process.
• Unethical -> Embryos destroyed.

Control in plants

• Plants respond to light, gravity and moisture.
  • Plant shoots grow towards light -> Phototropism.
  • Plant roots grow down toward gravity -> Gravitropism.
  • Roots also grow towards water.
• Auxin is a hormone which controls phototropism and gravitropism.
• Unequal distribution of Auxin causes unequal growth. This results in bending of the shoot or root.
• Plant growth hormones can be used as weed killers and to stimulate root growth.