2(i, j)

Question 1

What is urine and urea?(4)

Answer 1

Urine is produced every day - about 1.5dm3 - and every litre of this stuff contains around 40g of waste products and salts.
Within it there is nitrogenous waste. This is stuff like urea and ammonia, that contain the element nitrogen. Nitrogenous waste has to be excreted by all animals.
This is because proteins can not be stored if their is an excess, therefore, amino acids(proteins) that are broken down are converted into urea(nitrogen waste-product) and carbohydrates(which is then stored as glycogen).
‘Excretion’ is getting rid of urea and other waste products that are made by chemical reactions in the cells of the body. Therefore, faeces is not excretion because it contains few products of metabolism - mostly remains of undigested food.

Question 2

How does the kidney carry out two functions?(2)

Answer 2

The kidney is a homeostatic organ, controlling the water and salt ion concentration in the body.
It is also an excretory organ, concentrating nitrogenous waste in a form that can be eliminated.

Question 3

What is the source and function of the hormone adrenaline?(5)

Answer 3

Adrenal glands secrete adrenaline when you are frightened, excited or angry.
Breathing rate increases; heart beats faster and breaths become deeper.
Blood is diverted away from the intestine and into the muscles.
In the liver, glycogen is changed into glucose and released into the blood. The muscle cells absorb more glucose and use it for respiration.
Pupils dilate, increasing visual sensitivity to movement, body hair stands upright, mental awareness and reactions are increased(faster).

Question 4

What is the source and function of the hormone insulin?(4)

Answer 4

Glycogen is made from long chains of glucose sub-units forming a large insoluble molecule.
Insulin is made by special cells(Islets of Langerhans) in the pancreas.
It stimulates the liver cells to take up glucose and convert it into glycogen, lowering the level of glucose in the blood.
In the liver the glucose from meals with high sugar is converted into glycogen, so blood leaving the liver has lower conc of glucose than that of blood entering liver.

Question 5

What is diabetes and how does it affect people?(3)

Answer 5

Diabetes is the disease where people’s pancreas cannot make enough insulin to keep their blood glucose level constant - it rises to very high concentrations.
It can be tested by chemical tests on urine; someone with diabetes may have such a high concentration of glucose in their blood that it is excreted in their urine, which is not normal.
Another symptom of diabetes is constant thirst, because high concentration of glucose in the blood stimulates receptors in the hypothalamus telling the person to drink in order to dilute their blood.

Question 6

What is the source and function of the hormone testosterone and the hormone oestrogen?

Answer 6

Testosterone is secreted from the testes and controls the development of the male secondary sexual characteristics.
Oestrogen is secreted from the ovaries by instruction of the pituitary hormones and oestrogen produces the female secondary sexual characteristics.

Question 7

What is the source and function of the hormone progesterone?(2)

Answer 7

Progesterone is created by the corpus luteum, and is secreted by the placenta. It completes the development of the uterus lining, thickening and maintaining it in preparation for a baby.
It also prevents the release of FSH and LH by the pituitary gland, stopping ovulation.

Question 8

What is the source and function of LH and FSH?(3)

Answer 8

LH is luteinising hormone and this in males instructs the testes to secrete testosterone. In females the peak of LH causes ovulation.
FSH is follicle stimulating hormone and in males this stimulates sperm production. In females, FSH causes the hormone oestrogen to be released, hence any increase in FSH will cause an upscaled-increase in Oestrogen.
They are both produced and released in the anterior pituitary gland.

Question 9

Describe the structure of the urinary system?(3)

Answer 9

Each of the two kidneys is supplied through a short renal artery. This comes directly from the aorta so the blood entering the kidney is at a high pressure.
The ‘cleaned’ blood passes out the kidney through each renal vein to the vena cava. The urine, which is the waste, leaves through the two ureters tubes and stored in the muscular bag the bladder.
The bladder then has a tube leading to outside - the urethra. The wall of the urethra contains sphincter muscles which can contract to close the urethra and hold back urine.

Question 10

Describe the structure of one kidney?(3)

Answer 10

The(darker) outer region is called the cortex and contains many tiny blood vessels that branch from the renal artery. It also contains lots of filtering units - called kidney tubules or nephrons.
The tubules run through the middle layer of the kidney, the medulla. This has more concentrated hubs towards the concave side of the kidney.
The tubules in the medulla join up into a funnel structure called the pelvis. This connects with one ureter carrying the urine to the bladder.

Question 11

Describe ultrafiltration in the Bowman’s capsule?(5)

Answer 11

At the beginning there is the hollow bowl of cells called the Bowman’s capsule. This bowl surrounds a clump of blood capillaries called a glomerulus. In the glomerulus is where the blood is filtered.
Blood enters through the renal artery which then divides into smaller and smaller arteries, it is these that supply the capillaries of the glomerulus. A blood vessel with a smaller diameter carries the blood away from the glomerulus, which creates very high pressure in the arteriole.
This basically forces fluid from the blood through the walls of the capillaries, into the space in the middle of the capsule.
Between the cells of the glomerulus and cells of the Bowman’s capsule, there is a layer called the basement membrane which acts like a filter.
It allows water, ions and small molecules(glucose and urea) to pass through because they are small enough. The fluid that originally enters the capsule is the glomerular filtrate.

Question 12

How is water reabsorbed into the blood in the nephron?(3)

Answer 12

99% of the glomerular filtrate is reabsorbed back into the blood. The kidney tubule will reabsorb different amounts of various substances, selective reabsorption.
All of the glucose is absorbed back into the blood in the first coiled part of the tubule(called the collecting duct), as well as most of the sodium and chloride ions.
In the rest of the tubule, water and ions are reabsorbed and certain solutes such as ammonium ions are secreted into the tubule. We know this because the final urine contains urea at a much higher concentration than in the blood.

Question 13

How does ADH(Antidiuretic Hormone) control the body’s water content?(3)

Answer 13

When you lose water; the concentration of the blood will increase. This is detected by receptor cells in the hypothalamus and will cause the pituitary gland to release more ADH.
The ADH travels in the bloodstream to the kidney and will cause the collecting ducts to become more permeable to water(so that more water is reabsorbed).
This will make the urine more concentrated(less water in it), so that the body loses less water and the blood becomes more dilute(with water). This is an example of negative feedback.

Question 14

What are the excretory products of the lungs, kidneys and skin?

Answer 14

Exhaled air contains water, sweat contains water, urine contains water, and faeces contains water.

Question 15

Define Homeostasis?

Answer 15

Homeostasis is keeping the conditions of the internal environment of the body relatively constant. It literally means ‘steady state’, this means water, salts, level of carbon dioxide in the blood, blood pH, concentration of dissolved glucose and body temperature are all closely regulated.

Question 16

How organisms are able to respond to changes in their environment?

Answer 16

The surroundings of the body is called the external environment, and the inside of the body is called the internal environment. Homeostasis deals with the internal environment while stimulus and response deals with the external environment.

Question 17

Describe a co-ordinated response in organisms?(3)

Answer 17

A stimulus is a change in an animals surroundings, a response is a reaction to that change.
A change in environment is detected by a receptor organ, and the response is brought about by an effector organ.
It is the nervous system that links the receptor and effector stage;
stimulus »receptor » coordination » effector » response

Question 18

Define tropism.

Answer 18

The growth response of a plant to a directional stimulus. If the growth response is towards the direction of the stimulus it is a positive tropism, and away is a negative tropism.

Question 19

Describe the geotropic and phototropic responses of roots and stems?

Answer 19

Geotropism is the response to the stimulus of gravity; shoots will grow away from gravity(negative geotropism) and roots will grow towards gravity(positive geotropism).
Phototropism is the response to the stimulus of light; shoots will grow toward a light source(positive phototropism) and roots will grow away from a light source(negative phototropism).

Question 20

Describe how auxin produces a phototropic response of stems.(3)

Answer 20

Auxin is a ‘plant growth substance’ that stimulates growth; if a shoot has an equal amount of light hitting all sides of it then the hormone diffuses equally on all sides.
However, if the shoot is receiving light from one direction; auxin moves away from the light as it diffuses downwards and in doing so induces a higher concentration on the darker side of the plant.
This will stimulate the cells to grow there, more so than on the lighter side and so the shoot bends towards the light.

Question 21

What are the differences between the Nervous and the Hormonal(Endocrine) systems?(4)

Answer 21

The Nervous system works by nerve impulses transmitted through nerve cells, while the Endocrine system works by hormones transmitted through the bloodstream.
Nerve impulses travel fast - instant effect. Hormones travel more slowly and take longer to act.
Response of the Nervous system is short lived, response of the Hormonal system is longer-lasting.
Impulses act on individual cells, so have a very specific and localised effect. Hormones can have widespread effects on entire different organs.

Question 22

What are Glands and Hormones?

Answer 22

A gland is an organ that releases or secrets a substance, so the chemical produced will leave through the cell membrane and travel somewhere to carry out its function.
There are two types, Exocrine glands secrete their products through ducts - e.g salivary glands, and tear glands.
Endocrine glands have no duct and instead their products(hormones) are secreted directly into the blood vessel passing through the gland.

Question 23

What is the Central Nervous System, Motor and Sensory Neurones?(3)

Answer 23

A nerve cell(neurone) passes along impulses at speeds fast enough to produce a rapid response. Impulses from receptors pass along nerves containing sensory neurones.
Then they reach the brain and spinal cord, which together the organs are known as the central nervous system.
Other nerves contain motor neurones which transmit impulses to the muscles and glands. Nerves contain thousands of individual neurones, some may have only sensory, or only motor or both.

Question 24

Describe and explain the structure of motor neurones?(4)

Answer 24

The cell body of a motor neurone is at one end of the fibre in the CNS. This body has tiny cytoplasmic extensions called dendrons which in turn form finer extensions called dendrites.
Where there is a junction of other neurones on any part of the cell body, it is called a synapse. The axon is the long fibre that branches off the motor neurone cell body and carries impulses to the effector organ.
At the end of the axon it divides into many nerve endings which connect with a muscle at a specific synapse called a neuromuscular junction.
It is the myelin sheath that insulates the axon, preventing ‘short circuits’ with other axons and also speeding up the conduction of the impulses.

Question 25

Describe and explain the structure of a sensory neurone?(2)

Answer 25

A sensory neurone’s cell body is located on a side branch of the fibre, just outside the CNS.
The fibre from the sensory receptor to the cell body is actually a very long dendron, while the fibre from the cell body to the CNS is a short axon. Similar with motor neurones, fibres of sensory neurones are myelinated.

Question 26

Describe and explain the structure of the eye as a receptor?(4)

Answer 26

The tough outer layer of the eye is the sclera, this is seen as the white part of the eye. At the front of the eye there is a window where sclera becomes transparent - the cornea.
Behind the cornea is the iris, and in the middle of the iris is the pupil; this lets light through. It is black because there is no light escaping from the inside of the eye.
Beneath the sclera is the choroid, this is dark because it contains many pigment cells and blood vessels; it stops light being reflected around inside the eye.
The inner most layer of the back of the eye is the retina, this is where light energy is converted into electrical energy of nerve impulses.

Question 27

Describe how the retina converts light energy into nerve impulses?(4)

Answer 27

The retina contains receptor cells called rods and cones. These react to light by producing impulses in sensory neurones, which are then passed onto the brain through the optic nerve.
Rod cells work well in dim light, but cannot differentiate between colours - this is why it is harder to see colours in dim light; only the rods are functioning properly.
Cone cells only work in bright light, there are three types responding to different wavelengths of light - red, green and blue. It is possible to see all the colours of visible light as a result of these cones being stimulated to a different degree.
Rods and cones are found throughout the retina, but cones are particularly concentrated at the centre of the retina - the fovea. This is why peripheral vision is colourless.

Question 28

Describe how the eye forms an image?(2)

Answer 28

To form an image on the retina, light needs to be refracted. This refraction takes place first at the air-cornea boundary and again at the lens.
As a result of refraction at the cornea and lens, the image on the retina is inverted but our brain interprets the image the right way up.

Question 29

Explain how the eye can respond to changes in light intensity?(3)

Answer 29

The iris can change the size of the pupil and in doing so control the amount of light entering the eye. This is an example of a reflex action.
Circular muscles form a ring shape in the iris, and radial muscles lie like wheel spokes.
In bright light the pupil constricts, the circular muscles contract and radial muscles relax. In dim light the pupil dilates, the circular muscles relax and radial muscles contract.

Question 30

Explain how the eye can focus on near and distant objects?(4)

Answer 30

Changes in the eye that allow us to see objects at different distances are called accommodation. To change our focus, the lens has to change shape.
The lens can change shape because it is made of cells containing an elastic crystalline protein, and is held in places by fibres called the suspensory ligaments. These are attached like wheel spokes to a ring of muscle - the ciliary muscle.
When the eye is focused on a distant object, the lens does not need to be very convex and so the ciliary muscles relax, suspensory ligaments are stretched; pressure pushes outwards on the lens.
When the eye is focused on a nearby object, the lens has to be more convex to refract the rays enough to focus them on the retina. The ciliary muscles now contract, suspensory muscles become slack.

Question 31

Describe and explain the reflex of your finger after pressing on a pin?(4)

Answer 31

The stimulus in this example is detected by temperature or pain receptors in the skin.
These generate impulses in sensory neurones that enter the CNS through a part of the spinal nerve called the dorsal root. Once in the spinal cord, sensory neurones connect by synapses with short relay neurones, which in turn connect to motor neurones.
The motor neurones emerge from the spinal cord through the ventral root, and send impulses back out to the muscles of the arm contracting it away from the harmful stimulus.
The middle part of the spinal cord has mainly nerve cell bodies, giving it a grey tint, it is called grey matter. The outer part of the spinal cord contains many axons with fatty myelin sheaths, giving it a white tint, it is called white matter.

Question 32

What is a reflex arc?(3)

Answer 32

The nerve pathway of a reflex is called the reflex arc, it is described as an arc because it goes into the CNS and then out again.
Impulses travel through the reflex arc in a fraction of a second, so there is no need for it to be started by impulses in the brain. However, in the spinal cord, the reflex arc neurones also form synapses with nerve cells leading to and from the brain
The brain therefore does receive information about the stimulus, which is how we feel pain.

Question 33

What is a synapse?(3)

Answer 33

A synapse is a gap between two nerve cells. It is not crossed by the electrical impulse passing through neurones, but by chemicals called neurotransmitter.
When an impulse arrives at a synapse, the ends of the fine branches of the axon secret neurotransmitter, which diffuses across the gap and attaches to the membrane of the second neurone; starting the impulse in the second cell.
Neurotransmitter is broken down by enzyme afterward. Synapses are extremely important because there are thousands of them in the brain, and CNS. It is also easy for drugs to imitate or block the action of the neurotransmitter, because it works using chemicals.

Question 34

Describe and explain the role of the skin in temperature regulation?(4)

Answer 34

Sweat glands produce sweat, which is secreted onto the surface of skin. When a liquid evaporates, the change in state uses energy(this is called the latent heat of vaporisation). When sweat evaporates, the energy is supplied by the body’s heat - cooling it down.

Hairs on the surface of the skin can lie flat against the skin’s surface, or be upright depending on the relaxation and contraction of hair erector muscles. Hairs trap a layer of air next to the skin, acting as insulation. In heat a thinner layer means more heat will be lost.

Finally, the blood in capillary loops in the dermis can radiate heat to outside. If the body is too hot - arterioles dilate, increasing blood flow to skin’s surface. Vasodilation.
If the body is too cold - arterioles leading to the surface constrict, less blood flows to the surface of the skin, less heat is lost. Vasoconstriction.
Both vasodilation and vasoconstriction occur through sphincter muscles in the walls of the arterioles.