aqa biology (combined science) unit 5: homeostasis knowledge …€¦ · aqa biology (separate...

AQA Biology (Combined Science) Unit 5: Homeostasis Knowledge Organiser

Coordination Centres

Brain: coordinates information from receptor

cells and sends signals to muscles and glands

Spinal Cord: coordinates messages from brain

and receptor cells and coordinates reflexes

Pancreas: coordinates glucose levels in blood

Keywords

Central Nervous System (CNS) – Brain and spinal cord

Effectors – Muscles or glands that bring about

responses in the body

Homeostasis – Regulation of the internal conditions of

a cell or organism to maintain optimum conditions, eg.

blood glucose, body temperature, water level

Nerve – Bundle of hundreds or thousands of neurones

Neurone – A single nerve cell

Receptors – Cells that detect stimuli

Reflex Arc – Bring about a reflex action

Stimulus – A change in the environment

Synapse – Gap between two neurones

Receptor Cells

Neurones

The nervous system allows a fast, short-lived response

to a stimulus.

Sensory Neurone: carries impulses from receptors to

CNS

Relay Neurone: connect sensory neurones to motor

neurones

Motor Neurone: carries impulses from CNS to effectors

The axon is a long stretched-out fibre of cytoplasm

which the electrical impulses pass along. Some axons

are surrounded by a myelin sheathe which insulates

the impulse. The branched endings, dendrites, connect

neurones together with synapses to create a network.

Synapse

When an electrical impulse reaches the end of a neurone, a

chemical (neurotransmitter) is released across the gap.

The chemical diffuses across the synapse.

When the chemical reaches the next neurone this starts

another electrical impulse.

Skin- touch, pressure, pain, temperature

Retina in eye- light intensity,

colour

Nose- chemicals

in air

Tongue- chemicals in

food

Ear- sound

Nervous Pathway

A stimulus is detected by receptors and

information passes along neurones (nerve cells)

as electrical impulses to the Central Nervous

System.

The CNS coordinates the response of effectors.

STIMULUS RECEPTOR COORDINATOR

EFFECTOR RESPONSE

Reflex Arc

Reflexes are automatic and rapid. They do not

involve the conscious part of the brain and travel

through the closest part of the CNS

The path a reflex action takes is called a reflex arc

They only use three neurones.

Reflex actions are important as they protect the body

from harm


Negative Feedback

Negative feedback loops work to maintain a steady

state. If a level rises too high or too low, changes takes

place to return the level to its normal level.

Negative feedback of thyroxine:

Endocrine System

Compared to the nervous system, the effects of the

endocrine system are slower but act for longer. Pituitary Gland

Called the master gland because it produces a lot

of different hormones that act on other glands.

Eg. FSH and LH produced by the pituitary gland

act on the ovaries

Controlling

Blood

Glucose

Keywords

Adrenaline – Hormone produced by the adrenal glands

to increase heart and breathing rate – ‘flight or fight’

Diabetes – A condition where someone cannot

regulate their blood sugar concentration

Endocrine System – made up of glands which secrete

hormones directly into the bloodstream

Glucagon – Hormone released by the pancreas when

blood glucose level is too low

Glycogen – Store of carbohydrate (glucose) in animals

Hormone – Chemicals, released from glands, that

travel in the blood to a target organ

Insulin – Hormone released by the pancreas when

blood glucose level is too high

Thyroxine – Hormone produced by thyroid gland to

control metabolic rate

Diabetes

Type 1:

Develops in childhood

Pancreas fails to produce insulin

Lack of insulin causes uncontrolled high blood sugar

levels

Normally treated with insulin injections

Type 2:

Develops in adulthood, due to diet, obesity and lack

of exercise

Body no longer responds to insulin

Normally treated with controlled diet and exercise


Hormones in the Menstrual Cycle

.

Keywords

Contraception – Methods of preventing pregnancy

Embryo – Collection of cells developed from a fertilised egg

Fertilisation – The nucleus of a sperm cell combining with

the nucleus of an egg cell

Menstruation – Loss of the lining of the uterus through the

vagina (a period)

Oestrogen – The main reproductive hormone in females,

produced by the ovaries to stimulate ovulation (at around

day 15)

Ovulation – The release of an egg from the ovaries every 28

days

Testosterone – The main reproductive hormone in males,

produced in the testes to stimulate sperm production

Menstrual Cycle

The menstrual cycle occurs in females, approximately

every 28 days. It is a cyclical process of the building of the

lining of the uterus and ovulation.

If the egg is fertilised by a sperm, then pregnancy follows.

If the egg is not fertilised, the lining of the uterus is lost

and leaves the body as the menstruation (or period).

It is controlled by four main hormones.

Contraception

The Pill – oral contraceptives that contain oestrogen

to inhibit FSH production so no eggs mature

Injection, implant or skin patch – slow release of

progesterone to inhibit ovulation for a number of

months of years

Spermicides – chemicals that kill sperm

Barrier methods (condom/diaphragm) – prevent

sperm reaching the egg

Intrauterine devices (the coil) – release hormones or

prevent a fertilized egg implanting in the uterus lining

Abstinence – not having intercourse

Sterilisation/vasectomy - surgical methods of male

and female sterilisation

Infertility

If a woman has naturally low levels of

FSH and LH she can be given a fertility

drug containing these hormones and

become pregnant naturally.

If this does not work, then In Vitro

Fertilisation (IVF) may be used:

1. Mother is given FSH and LH to stimulate

production of many eggs

2. Eggs are collected from the ovaries and

fertilised by the father’s sperm in the lab.

3. Fertilised eggs divide into embryos.

4. One or two embryos are inserted into the

mother’s uterus

Problems with IVF

Emotionally and physically

stressful

Low success rate

Multiple births

Complications during

pregnancy or birth

Premature (early) or

underweight babies born

AQA Biology (Separate Science) Unit 5: Homeostasis Knowledge Organiser

The Brain

Cerebral cortex – Intelligence,

language, memory and

consciousness

Cerebellum – Voluntary

coordination of muscles

Medulla – Involuntary

coordination, such as

breathing, heart rate and swallowing

Keywords

Accommodation – changing the shape of the

lens of the eye to focus on near or distant

objects

Hyperopia – long sightedness (cannot focus

on near objects)

Myopia – short sightedness (cannot focus on

distant objects)

Studying the Brain

The complexity and delicacy of the brain makes it difficult to

study and treat brain disorders.

Studying patients with brain damage: damage to different

brain areas produce different behavioural and psychological

effects

Electrical stimulation: stimulating different parts of brain and

analysing brain wave patterns can identify what each area

does

Magnetic Resonance Imaging (MRI): uses strong magnetic

fields and radio waves to produce detailed images of the brain

and spinal cord, eg. detecting cancerous cells

The Eye

The eye is a sense organ containing receptors

sensitive to light intensity and colour

Accommodation

Distant object Near object

Ciliary muscles relax Ciliary muscles contract

Suspensory ligaments Suspensory ligaments

pulled tight loosen

Lens pulled thin to only Lens thickens to

slightly refract rays strongly refract rays

Eye Problems

Myopia: If the eyeball is too long

then light rays are focused in front

of the retina. Can be corrected with

concave lenses.

Hyperopia: If the eyeball is too

short then light rays focus behind

the retina. Can be corrected with

convex lenses.

Correcting Vision

Contact lenses: sit on the cornea to refract the light rays

Laser surgery: lasers used to change the shape of the cornea

Lens replacement surgery: Artificial lens implanted into eye


Keywords

Anti-Diuretic Hormone (ADH) – Hormone

released by the pituitary gland that tells the

kidneys to reabsorb more water

Deamination – Removal of an amino group

from amino acids

Hypothalamus – Thermoregulatory

(temperature controlling) centre of the brain

Urea – A toxic waste product produced when

proteins are broken down

Vasoconstriction – Narrowing of blood vessels

in response to cold

Vasodilation – Widening of blood vessels in

response to heat

The Brain

Water and Nitrogen Balance

Lungs – water lost during exhalation

Sweat – water, ions (sodium, potassium, calcium,

nitrogen) and urea lost

Urine – excess water, ions and urea removed via the

kidneys

The Kidney

Kidneys filter the blood to form urine.

Each kidney contains

millions of kidney

tubules (nephrons)

partly in the cortex

and partly in the

medulla.

The kidneys filter the blood to remove any

substances that are in excess or that are not

needed by the body.

All of the glucose is reabsorbed into the

blood. Some of the water and ions are

reabsorbed depending on what is needed –

selective reabsorption.

Controlling Body Temperature

Human body temperature is 37°C – the optimum for

enzyme activity.

The hypothalamus detects blood temperature. The skin

contains temperature receptors to send impulses to the

hypothalamus.

If body temperature is too low: blood vessels constrict,

sweating stops and muscles contract (shiver)

If body temperature is too high: blood vessels dilate and

sweat is produced to release heat to the air.

Controlling Water Levels

Water levels of blood are monitored by the

pituitary gland.

It releases Anti-Diuretic Hormone (ADH).

ADH causes the kidney tubules to become

more permeable and reabsorb more water.

This is an example of negative feedback.


Keywords

Auxin – Plant hormone that controls the responses

of plants to light and gravity

Dialysis – The process of cleansing the blood

through a dialysis machine

Diffusion – movement of substances from a high

to a low concentration

Gravitropism/Geotropism – Plant growth in

response to gravity

Kidney Failure – A medical condition where the

kidneys no longer work properly

Negative tropism – Away from the stimulus

Phototropism – Plant growth in response to light

Positive Tropism – Towards the stimulus

Dialysis or Transplant

Kidney Dialysis

Dialysis restores the concentrations

of substances in the blood to normal

levels and has to be carried out

regularly.

1. Blood high in urea flows between

partially permeable membranes in

the opposite direction to dialysis fluid

(maintain concentration gradient)

2. Dialysis fluid has the same

concentration of glucose and ions as a

healthy person

3. Only excess ions and urea move

out of the blood by diffusion.

Plant Hormones – Phototropism

Auxin is produced just behind the tip of the

shoot.

It moves to the shaded side of a stem.

Cells on the shaded side elongate and the

shoot bends towards the light

Kidney Transplant

A diseased kidney is replaced by a

healthy donor kidney.

Rejection: The donor must be a

similar tissue type to the recipient

and immunosuppressant drugs

are given to stop the immune

system attacking the new kidney.

Plant Hormones – Gravitropism

Auxin is produced just behind the tip

of the root.

It moves to the lower side of the root

due to gravity.

In roots, auxin inhibits cell elongation

and roots grow downwards

Using Plant Hormones

Giberellins: Initiate seed germination

Used to end seed dormancy, promote flowering, increase fruit size

Ethene: Controls fruit ripening

Used in the food industry to control fruit ripening during storage

and transport

Auxins: Used as weed killers, rooting powders and promoting

growth in tissue cultures

aqa biology (combined science) unit 5: homeostasis knowledge …€¦ · aqa biology (separate...

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