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Summary GCSE Biology Paper 2 NOTES
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AQA Biology GCSE Paper 2 REVISION NOTES with peer checked aqa mark schemes and specification references in purple throughout
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B10: Homeostasis and ResponseHomeostasis is the regulation of the internal conditions of a cell or organism to maintain
optimum conditions for function in response to internal and external changes.
Homeostasis maintains optimal conditions for enzyme action and all cell functions.
In the human body, these include control of:
● blood glucose concentration
● body temperature
● water levels.
These automatic control systems may involve nervous responses or chemical responses.
All control systems include:
● Cells called receptors, which detect stimuli (changes in the environment)
● Coordination centres (such as the brain, spinal cord and pancreas) that receive and
process information from receptors
● Effectors, muscles or glands, which bring about responses which restore optimum
levels.
The nervous system enables humans to react to their surroundings and to coordinate their
behaviour.
Information from receptors passes along cells (neurones) as electrical impulses to the central
nervous system (CNS). The CNS is the brain and spinal cord. The CNS coordinates the
response of effectors which may be muscles contracting or glands secreting hormones.
Stimulus → receptor → coordinator → effector → response
Reflex actions are automatic and rapid; they do not involve the conscious part of the brain.
A synapse is a junction between two neurones across which signals pass. Impulses
themselves cannot cross this gap.
Sensory neurones: The neurones that carry information as electrical impulses from the
receptors in the sense organs to the central nervous system.
Relay neurones: The neurones that carry electrical impulses from sensory neurones to motor
neurones. They are found in the central nervous system.
Motor neurones: The neurones that carry electrical impulses from the central nervous system
to the effectors.
,B11: Hormonal Coordination
The endocrine system is composed of glands which secrete chemicals called hormones
directly into the bloodstream. The blood carries the hormone to a target organ where it
produces an effect. Compared to the nervous system the effects are slower but act for longer.
The pituitary gland in the brain is a ‘master gland’ which secretes several hormones into the
blood in response to body conditions. These hormones in turn act on other glands to stimulate
other hormones to be released to bring about effects.
Pituitary Gland: Found in the brain
→ FSH: Controls menstrual cycle and oestrogen secretion in females and sperm production
in men.
→ LH: Stimulates egg release in females and testosterone production in males
→ ADH: Controls the water content of the blood
→ GH: Speeds up the rate of growth and development in humans
Thyroid: Found in the neck area
→ Thyroxine: Controls the body’s metabolic rate
Pancreas:
→ Insulin: Lowers blood glucose
→ Glucagon: Raises blood glucose
Adrenals: Found above the pancrease
→ Adrenaline: Prepares body for fight or flight reactions
Testes: Found in the male genital
→ Testosterone: Controls development of male secondary sexual characteristics
Ovaries: Found in the female genitals
→ Oestrogen: Controls development of female secondary sexual characteristics
→ Progesterone: Regulates menstrual cycle
➔ Controlling Blood Glucose
Blood glucose concentration is monitored and controlled by the pancreas.
If the blood glucose concentration is too high, the pancreas produces the hormone insulin that
causes glucose to move from the blood into the cells. In liver and muscle cells excess glucose
is converted to glycogen for storage.
If the blood glucose concentration is too low, the pancreas produces the hormone glucagon
that causes glycogen to be converted into glucose and released into the blood.
, ➔ Diabetes
Type 1 diabetes is a disorder in which the pancreas fails to produce sufficient insulin. It is
characterised by uncontrolled high blood glucose levels and is normally treated with insulin
injections.
In Type 2 diabetes the body cells no longer respond to insulin produced by the pancreas. A
carbohydrate controlled diet and an exercise regime are common treatments. Obesity is a risk
factor for Type 2 diabetes.
➔ Puberty and the Menstrual Cycle
During puberty reproductive hormones cause secondary sex characteristics to develop.
Oestrogen is the main female reproductive hormone produced in the ovary. At puberty eggs
begin to mature and one is released approximately every 28 days.
This is called ovulation. Testosterone is the main male reproductive hormone produced by the
testes and it stimulates sperm production.
The menstrual cycle has 4 stages:
1) Day 1- menstruation starts. The uterus lining breaks down for about 4 days
2) The uterus lining builds up again, from day 4 to day 14, into a thick spongy layer full
of blood vessels, ready to receive a fertilised egg.
3) An eggs develops and is released from the ovary at day 14- this is called ovulation
4) The wall is then maintained for about 14 days until day 28. If no fertilised egg has
landed on the uterus wall by day 28, the spongy lining starts to break down and the
whole cycle starts again
Several hormones are involved in the menstrual cycle of a woman.
● Follicle stimulating hormone (FSH) causes maturation of an egg in the ovary.
● Luteinising hormone (LH) stimulates the release of the egg.
● Oestrogen and progesterone are involved in maintaining the uterus lining.
1. FSH- Produced in the pituary and causes an
egg to mature in one of the ovaries in a follicle.
Stimulates the ovaries to produce oestrogen.
2. Oestrogen- Produced in the ovaries and
causes the lining of hte uterus to grow. Stimulates
the release of LH which causes the release of an
egg and inhibits release of FSH.
3. LH: Produced in the pituitary. Stimulates
the release of an egg at day 14 (ovulation).
4. Progesterone: Produced in the ovaries by
the remains of the follicle after ovulation.
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