GCSE Biology - Homeostasis

What is the definition of homeostasis?

Homeostasis is the regulation of internal conditions of a cell or organism to maintain optimum conditions for function in response to internal or external changes

What are three examples of how homeostasis is used in the human body?

Homeostasis is used in the human body to keep the blood glucose concentration, body temperature and water levels constant

Give two examples of automatic control systems

Two examples of automatic control systems are the nervous system and hormones

What is the job of receptor cells? plus an example

Receptor cells detect changes in the environment: internal body conditions eg. concentration of glucose in the blood/ external body conditions eg. temperature of the skin

What is the term to describe the change in the environment?

A change in the environment is also called a stimulus

Where do receptor cells pass information they receive to? plus examples

Receptor cells pass this information to the co-ordination centre eg. the brain, spinal cord or pancreas

What is the job of the co-ordination centre?

The co-ordination centre receives and processes information from the receptor cells

Where does the co-ordination centre pass information they receive to? plus examples

The co-ordination centre passes the received information to the effector, which is either a muscle which contracts or a gland which secretes hormones

What is the job of the effector?

The effector's job is to carry out a response/restore optimum level

How are receptor cells involved in the nervous automatic control system?

Receptor cells detect a stimulus and send electrical impulses down neurones (nerve cells) to the central nervous system (co-ordination centre)

How is the central nervous system and effectors involved in the nervous automatic control system?

The central nervous system sends electrical impulses down other neurons to the effectors which bring about a response

What is a key role of the nervous system?

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

What is the reflex arc?

The reflex arc is the pathway that nerve impulses follow during a reflex action (an involuntary and automatic response to a stimulus which occurs without conscious thought eg. breathing or touching a hot surface)

Describe the reflex arc when you touch a hot surface

When you touch a hot object, the stimulus (heat) is firstly detected by the receptor (skin) and electrical impulses travel along a sensory neurone the the central nervous system. Before reaching the CNS, at the end of the sensory neurone there is a synapse, where a chemical is released and diffuses across to a relay neurone in the CNS, where an electrical impulse is triggered. The electrical impulse passes across the relay neurone, reaching another synapse which releases another chemical to trigger an electrical impulse in a motor neurone, which now travels down this neurone to an effector (muscle). The effector now contracts pulling the hand away from the heat (the response).

Why are reflexes automatic and rapid?

Reflexes are automatic and rapid as the CNS acts as the co-ordinator, information does not reach the brain to make a conscious decision, protecting us from danger

Describe the method for the required practical: Reaction time

The required reaction time practical involves two people working together. One person sits upright on a stool and places their dominant forearm across the table and their hand hanging over the edge. The other person holds a ruler vertically with the 0cm mark between the other persons thumb and index finger, then letting go of the ruler at a random time. The other person records the measurement on the ruler just above the other's thumb. The test is then repeated several times and then the mean is calculated, then the experiment is repeated but the two participants change roles.

What are the three different variables in the reaction time practical?

The three different variables for the reaction time practical are: Independent: the person being tested on, Dependent: the reaction time, Control: the starting distance between the thumb and index finger; the measurement always being above the thumb or the conditions of the room being the same

What is the highly folded, outer part of the brain called? plus functions

The highly folded, outer part of the brain is called the cerebral cortex and controls language, memory and consciousness

Where is the cerebellum located and what is its function?

The cerebellum is located at the lower back of the brain and controls our balance and co-ordinates our movements

What does the medulla control?

The medulla controls our heart and breathing rate

Why does scientists find it so hard to study the brain or treat brain damage?

The brain is so hard to study because it is protected by the skull so it is very tricky to access, the structures of the brain are extremely complex so it's hard to work out exactly which parts of the brain carry out specific functions and the brain is very delicate and easy to damage

How do scientists investigate the brain?

Scientists can investigate the brain by studying on patients with brain damage and looking where the damage took place to relate it to its function, electrically stimulating different parts of the brain and look at the effects on the persons behaviour and using MRI scanning to look at which parts of the brain are most active during different activities

What are receptors in the eye sensitive to?

Receptors in the eye are sensitive to light intensity and the colour of light

What is the cornea and what is its function?

The cornea is the transparent front of the eye and the function is to start the focussing of the light rays

What is the pupil and what is its function?

The pupil is the hole in the centre of the iris that lets light into the eye

What is the iris and what is its function?

The iris is the coloured part of the eye and its function is the control the size of the pupil

What is the lens and what is its function?

The lens is a transparent structure located just behind the cornea and it focuses the light rays onto the back of the eye and can change shape to allowing us to focus on distant or near objects (accomodation)

What is the retina and what is its function?

The retina is the back of the eye where light rays are focused and contains receptor cells for light allowing us to detect light intensity and light colour

What is the optic nerve and what is its function?

The optic nerve is behind the retina and where electrical impulses from the retina are sent to the brain

What is the sclera and what is its function?

The sclera is the white part of the eye and its tough outer structure protects the eye

What are the ciliary muscle and suspensory ligaments and what are their functions?

The ciliary muscle is a circular muscle surrounding the lens and is connected by fibres called suspensory ligaments and contracting or relaxing this muscle can change the thickness of the lens

Explain how the eye can change to allow more light to enter

The eye can change to allow more light to enter when you have entered a dark room, the amount of light entering your eye is low and this drop of light intensity is detected by the retina which sends electrical impulses to the brain, which then sends electrical impulses to specific muscles in the iris which contract and cause the pupil to become larger, allowing more light to enter the eye.

What is accomodation?

Accommodation is the ability to focus on objects at different distances

What happens to the suspensory ligaments when the ciliary muscle relaxes and contracts

When the ciliary muscle contracts the suspensory ligaments loosen because contraction reduces the tension of the suspensory ligaments and the lens is now thicker and refracts light rays more strongly, however when the ciliary muscles relax the suspensory ligaments are pulled tight due to increased tension so the lens is now pulled think and only slightly refracts light rays

What happens to the ciliary muscle and suspensory ligaments when the lens focuses on a distant object?

Light from distant objects need to be focused only a relatively small amount so ciliary muscles relax causing more tension on the suspensory ligaments so they're pulled tighter, so the lens is now pulled thin and due to this the light rays are only slightly refracted

What happens to the ciliary muscle and suspensory ligaments when the lens focuses on a near object?

Light from near objects needs to be focused a large amount so the ciliary muscle contracts causing the suspensory ligaments to loosen and decreased tension, so the lens is thicker and light rays are refracted more strongly

What is the scientific term for "long-sightedness"

Long sight is called hyperopia

What is the scientific term for "short-sightedness"

Short sight is called myopia

What is hyperopia and how is it caused?

Hyperopia is when someone has no issue focussing on distant objects but can't focus on near objects, because in many cases the eyeball is too short meaning the light is focused at a point behind the retina or the lens may become less elastic so the lens can't become thick enough to focus on near objects

How can hyperopia be treated?

Hyperopia can be treated by using glasses with convex lenses as these partially focus the light before it enters the eye

What is myopia and how is it caused?

Myopia is when someone can focus on nearby objects but can't focus on distant objects, because peoples eyeballs may be too long or the lens is too thick so the light is focused at a point in front of the retina

How can myopia be treated?

Myopia can be treated using concave lenses in glasses to partially unfocus the light before it enters the eye

How can myopia/hyperopia be treated without using glasses?

Myopia/hyperopia be treated without using glasses by laser eye surgery which can change the shape of the cornea to refract the light to a greater or lesser extent, and the lenses inside the eye can be replaced using artificial lenses

What is the part of the brain which regulates temperature?

The part of the brain which regulate temperature is called the thermoregulatory centre

How does the thermoregulatory centre detect change in temperature?

The thermoregulatory centre contains receptors which are sensitive to the temperature of the blood.

How does the thermoregulatory centre regulate temperature?

The skin contains temperature receptors which send electrical impulses down sensory neurones to the thermoregulatory centre

How does your body respond to an increase in temperature?

Your body can respond to an increase in temperature by sweat glands releasing sweat onto the skin surface, which evaporates and takes energy from the body therefore cooling it down. Under the skin surface there is a fine network of blood capillaries which are supplied with blood from blood vessels deeper in the skin, and if we get too hot these blood vessels get wider (dilate) which is called vasodilation and because the blood vessels have dilated that more blood can flow through the capillaries and heat can now transfer out of the blood so the body can now go back to its normal body temperature

What is vasodilation and how does it work?

Vasodilation is the widening of blood vessels and decreases blood pressure and increases blood flow, the increases blood flow to the skin dissipates heat and promotes sweating

How does your body respond to a decrease in temperature?

Your body can respond to a decrease in temperature by shivering which cis the contraction of our skeletal muscles. More energy for this is produced by an increase in the rate of respiration which releases heat and warms the body as well as vasoconstriction, which is the narrowing of your blood vessels, meaning less blood flows to the surface of your skin meaning less heat energy is dissipated. A stop in sweating also helps

What is the endocrine system?

The endocrine system consists of a number of glands which secrete hormones directly into the blood stream

How are hormones transported around the body?

Hormones are transported all around the body in the blood but only target specific organs which produce an effect

Name 2 differences between the endocrine and nervous system.

The nervous system uses electrical impulses which travel down neurones, however the endocrine system uses hormones which are chemicals and are carried in the bloodstream. The nervous system is very fast whilst the endocrine system is relatively slow but produces a much more long lasting effect

What are the main glands involved in the endocrine system and what are their functions?

The pancreas releases hormones in control of controlling concentration of glucose levels in the blood. The ovaries and testes release hormones involved in puberty and reproduction. The thyroid gland releases hormones involved in growth and regulating the body's basal metabolic rate. The adrenal glands produces adrenaline which is released during fear and stress. The pituitary gland which is located in the brain and releases a number of different hormones into the blood depending on the conditions and these hormones can act on other glands, causing other hormones to be released

What does basal metabolic rate mean?

Basal metabolic rate is how fast reactions take place in the body

Which gland is in control of monitoring the blood glucose concentration?

The blood glucose concentration is monitored by the pancreas

What hormone is released into the blood by the pancreas when an increase in the glucose concentration has occurred?

The pancreas release insulin into the blood which travels around the body and triggers body cells to take up glucose from the blood, as well as triggering liver and muscle cells to store excess glucose as glycogen

What is diabetes?

Diabetes is a disease where body's blood glucose control doesn't work effectively

Describe type 1 diabetes.

Type 1 diabetes involves the pancreas not being able to produce enough insulin so they inject their selves with insulin if blood glucose levels rise too much

Describe type 2 diabetes.

Type 2 diabetes involves the body cells not responding to insulin produced by the pancreas and is often treated by a diet with a controlled level of carbohydrates to prevent the blood glucose concentration from rising too high and are also advised to exercise

Name a risk factor of type 2 diabetes.

A risk factor of type 2 diabetes is obesity

What hormone is released into the blood by the pancreas when a decrease in the glucose concentration has occurred?

When a decrease in blood glucose concentration has happened then the pancreas releases a hormone called glucagon into the bloodstream, which triggers liver cells to convert glycogen back into glucose which is then released back into the blood stream causing glucose levels to go back to normal

What three ways can the body lose water?

The body can lose water through the lungs when we exhale, which we have no control over, through our skin when we sweat, which contains urea and the sodium ion and can't be controlled as it is a part of the body controlling its temperature, and the kidneys in urine, which can be controlled by the body. The kidneys remove excess what when the blood is dilute and produce a greater volume of urine

What three components are removed in urine?

Urea, excess ions and water are removed in urine

Describe the function of the kidneys.

The kidneys can function firstly by blood entering them through an artery which contains the waste product urea, the kidneys remove this urea along with excess ions and water. This leaves the as urine and is stored in the bladder, the blood which no longer contains urea now leaves the kidney through a vein.

How does the kidneys adjust the level of molecules in the blood?

The kidneys adjust the level of molecules in the blood through the blood firstly passing through the capillaries, where small molecules are filtered out including urea, ions, water and sugar glucose and pass into a tube. All the glucose and some of the ions and water are absorbed back into the blood. Urea, excess ions and excess water is released as urine.

What is selective reabsorption?

Selective reabsorption is the process where useful substances are reabsorbed from the kidney tubules back into the bloodstream, while unwanted substances are left to be excreted as urine.

How does the body deal with excess amino acids?

The body can deal with excess amino acids through the liver breaking down these amino acids and producing them into the chemical ammonia (deamination), but because ammonia is so toxic the liver immediately converts this into urea, which can be safely excreted

What is deamination?

Deamination is the breaking down of excess amino acids and converting them into ammonia

What hormone is released when the blood becomes too concentrated/water levels fall?

The pituitary gland releases ADH when the blood becomes too concentrated

How does ADH affect the kidneys?

ADH travels to the kidneys and causes the kidney tubules to be more permeable to water (more water can pass through), meaning more water can be reabsorbed from the tubules back into the blood so less urine is produced and blood rises back to normal level and less ADH is produced

How does the body deal when the blood is too dilute?

The pituitary gland stops releasing ADH when the blood becomes too dilute, meaning the kidneys reabsorb less water into the blood and more urine is produced

What is kidney dialysis?

Kidney dialysis is a machine that filters out the wastes from the blood if the kidneys are not working.

How does kidney dialysis work?

Kidney dialysis works because when a patient has kidney failure, their blood will contain a higher concentration of water, urea and ions than it should. The patients blood passes over a semi-permeable membrane which allows water, urea and ions through but not larger molecules like proteins and blood cells. The other side of the membrane contains dialysis fluid, which contains normal concentrations of water and ions, but not urea, the urea diffuses from the blood to the dialysis fluid. The fluid is constantly refreshed ensuring a high concentration gradient for the urea

What are four disadvantages to kidney dialysis?

Four disadvantages to kidney dialysis are patients have to visit the hospital several times per week, a controlled diet to control urea production, require frequent treatments, expensive in the long term

What are three disadvantages to a kidney transplant?

Three disadvantages of a kidney transplant are kidneys may be rejected by the patients immune system, shortage kidney donors, patients have to take anti-rejecting drugs for the rest of their life

What is one advantage of kidney dialysis?

One advantage of kidney dialysis is there are no shortage of dialysis machines

What are two advantages of a kidney transplant?

Two advantages of a kidney transplant are patients are allowed to live a normal life, only expensive initially

What hormones are produced in the testes and ovaries and how do these interact with the sexual reproduction area?

The testes produce testosterone which stimulates the production of sperm in the testes, the ovaries produce oestrogen which helps the development of female sexual characteristics and regulates the menstrual cycle

Describe ovulation

Ovulation is every 28 days when the ovaries release an egg and in preparation the uterus lining becomes thick and spongy. The egg now makes its way down to the uterus and if sperm are involved the egg can be fertilised so the egg will implant into the wall and grow into a baby, however if the egg isn't fertilised then the egg and the uterus lining are released

What are the four key hormones involved in the menstrual cycle?

FSH (follicle stimulating hormone), LH (luteinising hormone), oestrogen and progesterone

How is FSH important in the menstrual cycle?

FSH causes the egg to mature in the ovary

How is LH important in the menstrual cycle?

LH causes the egg to be released from the ovary

How is oestrogen and progesterone important in the menstrual cycle?

Oestrogen and progesterone are both involved in maintaining the uterus lining

How do the four hormones involved in the menstrual cycle interact?

The pituitary gland releases FSH which travels in the blood to the ovaries causing eggs to mature, and triggers the ovaries to produce oestrogen at the same time. Oestrogen inhibit the production of FSH in the pituitary gland, and the pituitary gland now releases LH and once the ovary releases the egg the hormone progesterone is produced by the ovary and this stops the production of both FSH and LH which prevents any more eggs from maturing and being released. If fertilisation doesn't take place then progesterone levels fall

How does 'the pill' work?

The pill inhibits the release of the hormone FSH which causes eggs to be released

What are the advantages of the pill?

Advantages of the pill are it is highly effective if taken correctly

What are disadvantages and risks of the pill?

Disadvantages of the pill include having to take it every day, increased risk of breast cancer and blood clots