biology paper 2 revision notes paper grade 9-1

Topic B5- homeostasis and response

importance of homeostasis

homeostasis- is the regulation of the internal conditions of a cell or organism in response to internal and external changes

homeostasis controls: body temperature, water and ion levels and blood glucose concentration

control systems

-receptors: which detect stimuli ( changes in the environment) 

- coordination centres: which recieve and process information from receptors

- effectors: which bing about responses that restore optimum levels

nervous systems

the nervous systems enables humans to react to their surroundings and coordinate their behaviour

- information from receptor passes to the central nervous systems (CNS)

- reflex actions are automatic and rapid so they can protect the body. they don't involve the conscious part of the brain

• pain stimulus is detected by receptors
• impulses from the receptor pass along a sensory neurone
• an impulse then passes through a relay neurone
• a motor neurone carries an impulse to the effector
• the effector responds by withdrawal away from the source of pain

the endocrine system

the endocrine system is made up of glands that secrete hormones directly into the bloodstream

the piltulitary gland, it secretes several hormonenes in response to body conditions

adrenaline: produced by adrenal glands in times of fear and stress. it prepares the body for 'flight or fight'

thyroxine:produced in thyroid gland,increases metabolic rate and controls growth and development in young animals and is controlled by negative feedback.

control of blood glucose

blood glucose concentration is controlled by the pancreas. if it is too high, the pancreas will release more of the hormone insulin.

if it is too high, the pancreas will release glucagon and is an example of negative feedback

• type 1 diabetes can't be treated with insulin
• type 2 diabetes can be treated by controlling the diet

the sex hormones

hormones control the human reproduction

• oestrogen- produced in the ovaries, female hormone. 
• testosterone-produced in the testes stimulates sperm production, male hormone

control of menstrual cycle

FSH( follicle stimulating hormone)-causes the egg to mature in the ovaries and stimulates the production oestrogen

oestrogen- inhibts fsh release, stimulates lh release and makes the lining of the uterus grow again after menstruation

luteinising hormone (lh)- stimulates the release of the egg from the ovary (ovulation)

progesterone-maintains the lining of the uterus during the cycle and inhibts both FSH and LH

reducing fertility

fertility can be reduced by various methods of contraception

hormonal contraception: the combined pill, implant, and injection all which inhibts FSH production so that no egg is released

non-hormonal contraception: barrier method i.e condoms,spermiducal creams all which stop conception from happening

increasing fertility

doctors may give FSH and LH in a fertility drug to a woman if her own levels are too low to stimulate eggs to mature

fertility treatment gives a woman a chance to have a baby however:

• it is emotionally and physically stressful
• then success rates are not high
• it can lead to multiple births, which are a ris to both the mother and the baby

Topic B6- inheritance,variation and evolution

asexual…