aqa gcse biology - homeostatis

What is homeostatis?

The regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external conditions.
KEEPING INTERNAL CONDITIONS CONSTANT

What does homeostatis consist of?

Automatic control systems making sure that the internal conditions of the body stay as constant as possible.

What does the central nervous system consist of?

brain and spinal cord

What does a receptor do?

detects a stimulus and sends electrical impulses down neurones to the CNS

What is an effector?

a muscle which contracts, or a gland which secretes a hormone

What does the nervous system do?

enables humans to react to their surroundings and co-ordinate their behaviour

Explain the process of a reflex arc

1. The stimulus is detected by a receptor
2. Electrical impulses now pass from the receptor along a sensory neurone to the CNS
3. At the end of the sensory neurone is a junction called a synapse
4. At the synapse, a chemical is released and this chemical now diffuses across to the relay neurone in the CNS where it triggers an electrical impulse.
5. The electrical impulse now passes across the relay neurone and reaches another synapse. Another chemical is released. This chemical triggers an electrical impulse in a motor neurone
6. The electrical impulse now passes down the motor neurone to an effector (muscle)
7. The muscle now contracts and carries out the response

Why are reflexes automatic and rapid?

There is no decision making by the conscious part of the brain. Unconscious action to protect us from danger

What is the brain?

The brain controls complex behaviour. It is made of billions of interconnected neurones and has different regions that carry out different functions.

Why is the brain so complex?

- Delicate and easy to damage
- Protected by the skull = tricky to access
- Structures are complex

What are the three main parts of the brain?

Cerebral cortex, cerebellum, medulla

What is the role of the cerebral cortex?

responsible for consciousness, intelligence, memory and language

What is the role of the cerebellum?

Coordinates balance and movement

What is the role of the medulla?

Controls unconscious activities such as breathing and your heart rate.

How have neuroscientists been able to map the regions of the brain to particular functions?

- Looking at patients with brain damage to see where the damage has taken place so they can link that part of the brain to the function
- Electrically stimulating parts of the brain to look at the effects on the person's behaviour
- MRI scanning to look at which parts of the brain are most active during different activities

What is the eye?

A sense organ containing receptors sensitive to light intensity and colour

How does the eye detect light?

1. Light rays pass through the transparent front of the eye. The cornea starts the focusing on light rays.
2. The light rays then pass through the pupils in the centre of the iris, which is the coloured part of the eye. It adjusts the size of the pupil in response to light intensity
3. The light rays pass through the lens, where light is focused onto the back of the retina. It changes shape when viewing distant or near objects
4. The retina contains receptor cells for light intensity and light colour, light is focused here
5. The receptor cells now send electrical impulses down the optic nerve to the brain

What is the ciliary muscles and suspensory ligaments job?

Work together to change the shape of the lens by focusing on near or far objects.

What is your body temperature monitored and controlled by?

The brain

What is the thermoregulatory centre?

It's found in the hypothalamus in the brain and contains receptors that are sensitive to the temperature of the blood flowing into the brain. These send electrical impulses down sensory neurones to the thermoregulatory centre.

What happens if the body temp is too high?

Sweat glands release sweat onto the surface of the skin. The sweat evaporates, taking energy from the body, cooling the body down.
VASODILATION - blood vessels dialate so more blood flows through capillaries. Heat can now transfer out of the blood

What happens if the body temp is too low?

VASOCONSTRICTION - blood vessels supplying the capillaries constrict.
Less blood flow - less heat is lost from body.
Shivering - skeletal muscles contract, to generate energy for this contraction the muscle cells increase their rate of respiration. This releases heat which warms the body.
Sweating stops

What is the endocrine system?

Consists of a number of glands. These glands secrete hormones directly onto the bloodstream. The blood carries the hormones all around the body

What is the role of the pancreas?

releases hormones that control the concentration of glucose in the blood

What is the role of the ovaries and testes?

releases hormones involved in puberty and reproduction

What is the role of the thyroid gland?

produces hormones which are involved in growth and in regulating the body's basal metabolic rate

What is the role of the adrenal glands?

releases hormone adrenaline which is produced in times of stress or fear

What is the role of the pituitary gland?

'Master gland' - releases a number of different hormones into the blood depending on the conditions. These act on other glands and cause other hormones to be released.

Describe what happens when the blood glucose concentration is too high

1. The blood glucose conc. is controlled by the pancreas
2. After a meal full of carbohydrates, the conc. of glucose can rise
3. This is sensed by the pancreas and the pancreas produces the hormone insulin
4. Insulin travels in the blood all around the body. It triggers body cells to take up glucose from the blood. It also triggers liver and muscle cells to store excess glucose as a storage molecule called glycogen
5. The conc. of glucose in the blood returns to it's normal level

What is type 1 diabetes? how is it treated?

The pancreas does not produce enough insulin, so the blood glucose conc. rises and then stays at a high level

Inject themselves with insulin

What is type 2 diabetes? how is it treated?

when the body cells no longer respond to insulin produced by the pancreas. can be treated by a controlled diet and an exercise regime.

What are the risk factors of type 2 diabetes?

obesity

What happens if the blood glucose conc. falls?

1. The pancreas releases the hormone glucagon into the bloodstream
2. Glucagon triggers liver cells to convert glycogen stores bcak to glucose which is released into the blood

What happens if the blood becomes too dilute or too concentrated?

Too dilute - water moves INTO cells by osmosis
Too concentrated - water moves OUT of cells by osmosis

How does the body lose water?

urination
sweating - ions and urea
exhalation

What is the role of the kidneys? Describe their features

The kidneys filter the blood and form urine that is stored in the
bladder. They are located in the lower back. Each kidney has an
outer layer called the cortex and an inner layer called the medulla. There are millions of structures called kidney tubules (nephrons) and this is where the blood is filtered.

What are the three steps to filtering blood

FILTRATION - of glucose, ions, urea and water
SELECTIVE REABSORPTION - of all glucose, some ions and some water
EXCRETION - of all urea, excess ions and excess water into the urine.

What happens when blood enters the kidneys?

1. Blood enters through an artery
2. The kidney removes this urea as well as excess ions and water
3. These leave the kidney as urine and this is stored in the bladder
4. Blood now leaves the kidneys through a vein

What is kidney failure?

Kidney failure is a medical condition where the kidneys no longer work. The kidneys are important in homeostasis and if kidneys fail toxins can build up in the blood and the concentration of ions (salts) gets out of balance.

What is a kidney dialysis and how is it used?

Treatment by dialysis restores the concentrations
of dissolved substances in the blood to normal levels and has to be carried out at regular intervals.
In a dialysis machine:
• Blood high in urea flows between partially permeable membranes in the opposite direction to the dialysis fluid (maintains the concentration gradient)
• The dialysis fluid contains the same concentration of useful
substances as the blood - this ensures that glucose and ions (salts) are not lost.
• Urea passes out from the blood into the dialysis fluid.

Advantages and disadvantages of a kidney dialysis

Advantages
1. Available to all kidney patients (no shortage)
2. No need for immuno-suppressant drugs

Disadvantages
1. Patients must limit their salt and protein intake between dialysis sessions
2. Expensive for the NHS
3. Regular dialysis sessions - impacts on the patient's lifestyle (2-3 times per week)

What is a kidney transplant?

replacement of a diseased kidney with a healthy kidney provided by a donor

What issues are there with kidney transplants and how can they be resolved?

Organ rejection is a problem as the antigens on the surface of the donor kidney are recognised by the immune system as foreign and can be attacked by the patient's antibodies.
To reduce the chances of this happening two precautions are taken:
• Immune-suppressant drugs are given
• A donor kidney with a similar tissue type' is used

Advantages and disadvantages of kidney transplants

Advantages
1. Patients can lead a more normal life without having to watch what they eat and drink
2. Cheaper for the NHS overall

Disadvantages
1. Shortage of organ donors
2. Must take anti-rejection drugs for the rest of their life
3. Any operation carries risks
4. Transplanted kidneys only last 8-9 years on average

What happens if blood becomes too concentrated?

1. The pituitary gland releases the hormone ADH into the bloodstream
2. ADH travels to the kidneys, and it causes the kidney tubules to become more permeable to water (more water reabsorbed into the blood)
3. Less urine is produced
4. As the blood water leevl returns to normal, the pituitary gland stops releasing ADH
5. NEGATIVE FEEDBACK CYCLE

What happens if blood becomes too dilute?

1. The pituitary gland stops releasing ADH.
2. The Kidneys absorb less water into the blood and more urine is produced

What does hypertonic mean?

more concentrated solution than in the cells

What does isotonic mean?

both solutions have an equal concentration

What does hypotonic mean?

more dilute than the solution in the cells

What happens when a red blood cell is placed in hypotonic solutions?

water enters the cells by osmosis and as the volume increases this puts pressure on the cell membrane and it bursts. This is called lysis.

What happens when a red blood cell is placed in hypertonic solutions?

water leaves the cell by osmosis and the cells shrink and
the membrane wrinkles. This is called crenation.

When is lysis and crenation used?

When the kidneys do not function properly. Lysis and crenation do not happen in the body if the kidneys function properly as the kidneys keep the blood concentration isotonic.

What happens when you have a diet high in proteins?

the excess proteins are digested (broken down) into amino acids that are absorbed into the blood. The excess amino acids are then deaminated (removal of an amino group from the amino acids) in the liver to form ammonia. Ammonia is a very toxic substance and so it is immediately converted to urea for safe excretion from the body in the urine.

During puberty, what do reproductive hormones cause?

secondary sexual characteristics

What do the testes produce?

testosterone

What do the ovaries produce?

oestrogen (inhibits FSH and stimulates the pituitary
gland to produce LH) and progesterone (maintains the lining of the uterus during the menstrual cycle)

What are the female and male secondary sexual characteristics?

FEMALE:
breasts develop, hips get wider, ovaries start to release eggs, pubic and underarm hair grows, sexual organs grow and develop
MALE:
voice deepens, body becomes more muscular, testes start to produce sperm, facial/underarm and pubic hair start to grow, sexual organs grow and develop

Describe the menstrual cycle

1. (Days 1-5) At the start of the cycle menstruation occurs, where an unfertilised egg and the broken-down walls of the uterus leaves the body via the vagina.

2. (Days 5-14) After menstruation, the lining of the uterus is repaired and enriched, ready for the implantation of the egg.

3. (Day 14) An egg is released from an ovary.

4. (Day 15) Fertilisation occurs in the fallopian tube (where the sperm enters the egg). This fertilised egg travels down to the uterus and then implants itself into the richly lined uterus walls. The development of the embryo takes 9 months. Nutrients are brought to the foetus from the mother's placenta via the umbilical cord.

5. If, when released from the ovary, the egg is not fertilised, progesterone production stops and the egg travels down to the uterus and is expelled with the lining of the uterus during menstruation. The pituitary gland releases FSH and the cycle continues.

What is FSH and what does it do?

Follicle-stimulating hormone
Released by the pituitary gland
Causes a follicle (an egg and its surrounding cells) to mature in one of the ovaries
Stimulates oestrogen production

What is LH and what does it do?

Luteinizing hormone
- stimulates ovulation in female and secretion of sex hormones in both the male and female

What is oestrogen and progesterone?

These hormones are involved in the growth and maintenance of the uterus lining

Describe the interactions of FSH, oestrogen, LH and progesterone, in the control of the menstrual cycle.

1. FSH is released by the pituitary gland
2. FSH travels in the blood to the ovaries where ir causes an egg to mature
3. At the same time, FSH triggers the ovaries to make oestrogen
4. Oestrogen causes the lining of the uterus to become thick. It also stops the pituitary gland from releasing anymore FSH
5. Instead, the pituitary gland now releases LH
6. LH triggers ovulation
7. Once the ovary has released its egg, the ovary now produces progesterone. This stops the pituitary gland from releasing FSH and LH to prevent anymore eggs from maturing or being released and it keeps the lining of the uterus thick incase a fertilised egg implants
8. If fertilisation does not take place, then the level of progesterone falls
9. The uterus lining and the egg are now released and the woman has a period

How can we control fertility?

Contraception

Name the oral contraceptive, its advantages, disadvantages and side effects

The pill contains hormones which prevent the body from producing FSH
Advantage - highly effective if taken correctly
Disadvantage - must be taken everyday (risk of pregnancy)
Side effects - risk of breast cancer or blood clots

What is the implants/skin patches/injections advantages and disadvantages?

Contains progesterone
Advantage - more convenient than taking a daily pill
Disadvantage - none protect against STI's

Name the barrier method, its advantages and disadvantages

Condom / Diaphram
Advantage - effective if used correctly, do not use hormones (no side effects), reduce the risk of STi's
Disadvantage - can break or slip off
USE A SPERMICIDE GEL -> kills or disables sperm

Name the contraception that prevents an embryo from implanting. Also name its advantages and disadvantages.

IUD (coil) - some release hormones to reduce chances of fertilisation
Advantage - very effective (lasts 10 years), very few side effects.
Disadvantages - does not protect against STI's

Name a surgical form of contraception, its advantages and disadvantages

Sterilisation - prevents egg from reaching uterus and prevents sperm from leaving the penis
Advantage - highly effective
Disadvantage - difficult to reverse, does not protect against STI's

Name a natural method of contraception, its advantages and disadvantages

Abstaining from sex during ovulation + after
Advantage - Natural
Disadvantage - hard to tell when a woman has ovulated

What does the catholic church teach about contraception?

All contraception is unethical

What hormones are given to an infertile woman

FSH and LH "fertility drugs"

Describe the process of IVF

-IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs.
• The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.
• The fertilised eggs develop into embryos.
• At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother's uterus (womb).

What are the problems of IVF?

- It is emotionally and physically stressful
- the success rate is not high
- it can lead to multiple births
- many embryos are destroyed = unethical
- expensive

What is negative feedback?

• occurs when there is a change in the body (i.e. blood glucose
increases)
• the nervous system detects the change
• this stimulates an opposite hormonal response
• this reverses the effect back to homeostasis.

What is positive feedback?

(less common)
• a change starts
• the nervous system detects the change
• then stimulates more hormones to be released to accelerate the change.

What is the role of the adrenal glands?

Located at the top of the kidneys. The adrenal glands produce and secrete the hormone adrenaline. Adrenalin prepares the body for rapid activity by increasing the heart rate and blood glucose. It diverts blood flow to the muscles and lungs. It is often called the 'fight or flight' hormone.

What is the role of the thyroid gland?

The thyroid produces and secretes the hormone
thyroxine. Thyroxine regulates the basal metabolic rate, this
is the rate at which energy is released in the body; it also plays an important role in growth and development.
Thyroxine also regulates breathing, heart rate, and
body temperature.

What is metabolism?

the sum of all the reactions in a cell or the body

What is phototropism?

plants growing towards the light

What is gravitropism?

a plant's response to gravity

What is an auxin?

Plant hormone that controls growth near tips of shoots and roots, in response to light (phototropism), gravity (gravitropism or geotropism) and moisture. It's produced in tips and moves backward to stimulate cell elongation. They inhibit the growth of ROOTS and promote the growth of SHOOTS

How do shoots grow towards the light?

1. Auxin is produced at the very tip of the shoot which triggers cell growth.
2. Light causes auxin to concentrate on the darker side of the shoot tip.
3. Auxin now spreads down the shoot
4. Cells of the darker side grow faster than cells on the lighter side. This causes the shoot to grow towards the light

How do roots grow towards gravity?

Auxins are released from the root tip, auxins diffuse along the root, due to gravity auxins settle on the underside of the root, auxins inhibit cell growth on the lower side of the root, cells on the upper side of the root grow more quickly than the cells on the lower side of the root, the root bends downwards towards the force of gravity.

What are gibberellins?

Gibberellins are a type of plant hormone involved in seed germination.

What is ethene?

Ethene is a type of plant hormone involved in cell division and ripening of fruits.

What are some uses of auxins?

- as weed killers
- as rooting powders
- for promoting growth in tissue culture.

What is ethene use for?

used in the food industry to control ripening of fruit during storage and transport.

What are gibberellins used for?

-End seed dormancy
-Promote flowering
-Increase fruit size