Brainscape's Knowledge GenomeTM


Top Flashcards (Certified)
All Flashcards

Biology Paper 2 > Homeostasis > Flashcards

Homeostasis Flashcards

1
Q

What is Homeostasis

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

List possible Changes to the Body’s Internal Environment

A

-An increase in the concentration of blood glucose due to eating a meal

-A decrease in the concentration of blood glucose due to exercise

-An increase in body temperature due to exercise

-An increase in the level of water in the blood due to having a drink of water

-A decrease in the level of water in the blood due to sweating

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

List possible Changes to the Body’s External Environment

A

-An increase in the temperature of the skin due to hot conditions

-A decrease in the temperature of the skin due to cold conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How do Internal Body Conditions Change During Exercise

A

-Blood glucose levels will decrease because more glucose is being used to release energy by respiration.

-Body temperature will increase because an increase in respiration releases more thermal energy.

-Blood water levels will decrease because sweating releases water to cool the body down.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

List the Order of the Features in the Homeostatic Control System

A
  1. Stimulus (e.g. change in temperature)
  2. Receptor Cells
  3. Coordination Centre (brain or spinal cord)
  4. Effector (muscle or gland)
  5. Response (e.g. sweating to cool down)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the Function of Receptor Cells in Homeostatic Control

A

The function of receptor cells is to detect the stimulus ( a change to the body’s internal or external environment)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is the Function of the Coordination Centre in Homeostatic Control

A

-The function of the coordination centre is to receive information from the receptor cells and then process the information.

-(i.e. make a decision on the response required).

-The coordination centre then sends instructions to the effectors.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is the Function of Effectors in Homeostatic Control

A

The function of the effector is to bring about the response to restore the optimum levels.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Describe the Features of Neurones

A

-A long fibre (axon) which is insulated by a fatty (myelin) sheath. They are long so they can carry messages up and down the body.

-The myelin sheath also increases the speed of the impulses.

-Tiny branches (dendrons) which branch further as dendrites at each end. These receive incoming impulses from other neurones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the Function of Neurones in Homeostatic Control

A

-A stimulus is detected by receptors. These send electrical impulses down sensory neurones to the central
nervous system, telling it what the receptors have detected.

-The central nervous system acts as the coordination centre. This is where relay neurones are found.

-Electrical impulses now pass through motor neurones from the central nervous system to the effectors, telling them what to do. The effectors then bring about a response.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

How do Muscles and Gland Bring About a Response

A

-Both muscles and glands are effectors.

-To bring about a response, muscles contract and glands secrete a hormone into the bloodstream.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Match Stimuli to Their Receptors

A

Light- light receptors in the eye

Sound, body position- sound and balance receptors in the ear

Chemicals (in food)- chemical receptors in the mouth/ on the tongue

Chemicals (in the air)- chemical receptors in the nose

Touch, pain, pressure, and temperature- thermo and pressure receptors in the skin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Describe the Stages in the Reflex Arc

A

-The stimulus (heat) is detected by receptors in the skin. Electrical impulses pass down the sensory neurone and travel towards the central nervous system.

-The electrical impulses reach the synapse at the end of the sensory neurone. A chemical is released at the synapse. The chemical diffuses to the relay neurone.

-An electrical impulse is triggered in the relay neurone. At the next synapse a chemical is released. Electrical impulses are triggered in the motor neurone.

-The impulses travel away from the central nervous system. The impulses reach the effector (a muscle). The muscle contracts and the hand pulls away (the response).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe How Information passes Across a Synapse

A

-The impulse from the neurone arrives at the synapse.

-This stimulates the release of chemicals.

-Chemicals diffuse across the gap.

-These bond with a specific receptor on the next neurone.

-This triggers a new impulse.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Explain why Reflexes are Automatic and Rapid

A

-Reflexes are automatic and rapid. This is because although electrical impulses pass through the central nervous system, no decision making takes place in the conscious part of the brain.

-We often find reflexes involved when there is danger. In these cases, the body needs to respond very rapidly to events.

-The response needs to be automatic. If the brain had to make a decision, then this would slow down the response and that could prove dangerous or even fatal.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe a Method for the Reaction Time Practical

A

-Person 1 sits at a table. They should have a good, upright position. Person 1 places their dominant arm on the table so their dominant hand is over the edge.

-Person 2 holds a metre ruler vertically so the 0cm mark is between person1’s thumb and index finger. Person 2 tells person 1 to prepare.

-Person 2 then drops the ruler at random and person 1 has to catch the ruler as quickly as possible. Person 2 records the measurement on the ruler that is level with person 1’s thumb.

-This test is repeated several times. A mean value is taken and person 1’s reaction time is determined using a conversion table.

-Person 1 and 2 switch places and person 2’ s reaction time is determined and compared to person 1’s.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why is an Upright Posture better than a Slouched Posture in the Reaction Time Practical

A

-A person with good upright posture is likely to be more alert than a person who is slouched.

-A slouched person is more likely to be relaxed and not ready to catch the ruler.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Why is it Important that the Position of the Ruler Between the Fingers Doesn’t Change in the Reaction Time Practical

A

-The initial position of the ruler is a control variable. This must not be allowed to change.

-If the ruler was not at the zero position at the start then we would have a zero error.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why is it Important that the Measurement is Always at the Top of Person 1’s Thumb in the Reaction Time Practical

A

-The final measurement position is also a control variable.

-In this case, we have decided to always measure the final position at the top of the person’s thumb.

-We need to make sure that we keep this the same between experiments

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Describe How Investigating the Effect of Practice Changes the Reaction Time Practical

A

-To study the effect of practise, we would measure the person’s reaction time repeatedly over a large number of attempts.

-We could then see if there was any difference from the first attempt through all of the remaining attempts.

-If practise decreased a person’s reaction time then we should see them catch the ruler more rapidly as the experiment continued.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Describe How Investigating Dominant vs Non-dominant Hand Changes the Reaction Time Practical

A

-To study the effect of dominant versus non-dominant hand, we would ask the person to catch the ruler
with their dominant hand first and then with their non-dominant hand.

-We would need to carry out a number of repeats in order to get valid results.

-However, we would need to be careful that practise does
not affect the result (for example we could leave an interval from one experiment to another).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

How does Alcohol and Caffeine Affect Reaction Time

A

-Alcohol is a depressant so slows the rate of release of chemicals across the synapse. This slows the response rate of an effector.

Caffeine is a simulant so increases the rate of release of chemicals across the synapse. This increases the response rate of an effector.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

How does the Brain Control Complex Behaviour

A

-The brain can control complex behaviour because the brain contains billions of interconnected neurones.

-We can compare the brain with the simple reflex which contains only three neurones (the sensory neurone, the relay neurone and the motor neurone). This is very simple and cannot coordinate complex behaviour.

-However, the human brain contains many billions of neurones and these are connected together, forming trillions of connections. This allows the human brain to control complex behaviour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Name the Parts of the Brain and Their Functions

A

-The cerebrum (the outer layer is called the cerebral cortex), which is split into two hemispheres and is highly folded.

-It controls intelligence, personality, conscious thought and high-level functions, such as language and verbal memory.

-The cerebellum, which controls balance, co-ordination of movement and muscular activity.

-The medulla, which controls unconscious activities such as heart rate and breathing rate.

-The hypothalamus, which is the regulating centre for temperature and water balance within the body.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
How do Scientists Investigate the Brain
-It is difficult to study to brain or treat brain disease or damage. The brain is surrounded by the skull making it hard to access. It is also delicate and easy to damage. -The brain is complex so it is difficult to work out which parts have which function. Looking at patients with brain damage can give us clues on the function of that part of the brain. -We can also stimulate different parts of the brain with electricity and look at the effect on the person's behaviour. -MRI scanning can tell us which parts of the brain are most active when a person carries out certain tasks, allowing us to narrow down the function to a specific region of the brain.
26
Describe the Use of Electrical Stimulation in Investigating the Brain
-Scientists have stimulated different parts of the brain with a weak electrical current and asked patients to describe what they experienced. -If the motor area is stimulated, the patient makes an involuntary movement. If the visual area is stimulated, they may see a flash of colour. -EEGs (Electroencephalograms) can be created and studied, to observe the electrical activity in the brain.
27
Describe the Use of MRI Scans in Investigating the Brain
-Modern imaging methods such as MRI (Magnetic Resonance Imaging) scans, use strong magnetic fields and radio waves to show details of brain structure and function. -Patients are asked to perform various tasks and, by looking at the scan, scientists can see which parts of the brain are active when the task is carried out.
28
Describe the Risks of investigating the Brain
-Brain surgery may be needed to remove a tumour or excess fluid, such as blood. -All surgery carries a level of risk, but due to the complexity and delicacy of the brain, investigating and treating brain disorders can be very difficult. -If surgery is undergone more damage or side-effects may be created, which could affect the patients' quality of life. -Serious considerations about the risks involved against the benefits need to be undertaken first.
29
How does the Eye Adapt to Light Levels
-In dim light, the pupils dilate to allow more light in. This is because circular muscles in the iris relax and radial muscles contract. -In bright light, the pupils contract to allow less light in. This is because circular muscles in the iris contract and radial muscles relax.
30
How does the Eye Change to Focus on Near Objects
-To focus on a near object, the ciliary muscles contract so they have a smaller diameter. -This causes the suspensory ligaments to loosen so the lens becomes thicker and more curved. -The thicker lens is more convergent so light rays are refracted strongly causing the light rays to be focused on the retina.
31
How does the Eye Change to Focus on Distant Objects
-To focus on a distant object, the ciliary muscles relax so they have a larger diameter. -This causes the suspensory ligaments to tighten so the lens becomes thinner and less curved. -The thinner lens is less convergent so light rays are refracted slightly causing the light rays to be focused on the retina.
32
Describe why a Person With Long Sight (Hyperopia) cannot Focus on Near Objects
-A person with hyperopia cannot focus on near objects. This can be because their eyeball is too short for the strength of the lens. -This means that the light is focused at a point behind the retina. -In some cases, long sight is caused when the lens becomes less elastic. -In this case, the lens cannot become thick enough to focus on near objects.
33
How does a Convex Lens Adjust the Light rays to Treat Long Sightedness
-Long sight is treated with a convex lens. This partially focuses the light before it passes into the eye. -Now the lens can complete the focusing of the light, onto the retina.
34
Describe why a Person With Short Sight (Myopia) cannot Focus on Near Objects
-A person with short sight cannot focus on distant objects. In many people with short sight, the eyeball is too long for the strength of the lens. -This means that the light is focused at a point in front of the retina. -In some cases, the lens is too thick and focuses the light too strongly
35
How does a Convex Lens Adjust the Light rays to Treat Short Sightedness
-Short sight is treated with a concave lens. -This partially unfocuses the light before it passes into the eye.
36
How does Laser Eye Surgery Work
-Laser eye surgery reshapes the cornea surgically so it refracts light to a greater or lesser extent. -It is common for myopia but can be used for some hyperopia conditions.
37
Give the Advantages and Disadvantages of Laser Eye Surgery
Advantages: -Treats both myopia and hyperopia (permanently) Disadvantages: -Procedure may be expensive -Only for adults who have stopped growing
38
Give the Advantages and Disadvantages of Glasses
Advantages: -Treats both myopia and hyperopia (only while worn) -Last a long time Disadvantages: -Bulky -Harder for playing sports and general activities
39
How do Contact Lenses Work
-Contact lenses sit on the eyeball. -They refract the light in the same way as glasses.
40
Give the Advantages and Disadvantages of Contact Lenses
Advantages: -Can't be seen and easier for playing sports -Soft lenses are comfortable, hard lenses last a while Disadvantages: -Must be removed overnight and kept sterile -Soft lenses don't last a while, hard lenses are uncomfortable
41
How do Replacement Lenses Work
-Implanting artificial lenses is a recent development. -They can placed in front of the original lens, through a small cut in the cornea, to correct an eye defect.
42
Describe the Thermoregulatory Centre
-The body temperature is controlled by the thermoregulatory centre in the brain. -The thermoregulatory centre has receptors which monitor the temperature of the blood. We also find temperature receptors in the skin. -These send electrical impulses down sensory neurones to the thermoregulatory centre in the brain.
43
Explain how Sweating Reduces Body Temperature
-When the body temperature rises, sweat glands release sweat onto the skin surface. -When the sweat evaporates, it takes energy away from the body, cooling it down.
44
Explain how Vasodilation Helps to Cool Down the Body
-The body can also cool down by vasodilation. The skin contains a network of fine blood capillaries. -These capillaries are supplied by blood vessels deeper in the skin. If the body gets too hot, these blood vessels widen (dilate). -Now, more blood passes through the skin capillaries. Heat can now transfer out of the blood through the skin.
45
How does Vasoconstriction Bring Body Temperature Back up to Normal Levels
-If the body temperature falls, then the blood vessels which supply the skin capillaries constrict (narrow). -Now less blood passes through the skin capillaries so less heat energy can now transfer out of the blood through the skin. -This causes the body temperature to increase back to normal.
46
How does Shivering Bring Body Temperature Back up to Normal Levels
-Shivering can also happen if the body temperature falls. During shivering, the skeletal muscles contract. -To provide the energy for this, the muscle cells increase their rate of respiration. -Some of this energy is in the form of heat, which helps to increase the temperature of the body back to normal.
47
How is the Control of Body Temperature an Example of negative Feedback
-Body temperature is controlled by the hypothalamus in your brain, and if your body gets too hot, your body begins to sweat to try and reduce it. -Conversely if the body gets too cold, it begins to shiver to try and raise the temperature.
48
What are Hormones
-Hormones are chemical messengers. -They are made and secreted by glands. -They are released into and travel through the blood. -They only produce an effect in target organs.
49
Compare the Method of Communication Used in the Endocrine and Nervous System
-In the endocrine system, communication is by chemicals (hormones). -Whereas in the nervous system, communication is by electrical nerve impulses.
50
Compare Transmission in the Endocrine and Nervous System
-In the endocrine system, transmission is in the blood to all parts of the body. However, only target organs respond. -Whereas in the nervous system, transmission is by neurones and travels to specific parts of the body.
51
Compare the Speed of Transmission in the Endocrine and Nervous System
-In the endocrine system, transmission is slow. -Whereas in the nervous system, transmission is fast
52
Compare the Length of Response in the Endocrine and Nervous System
-In the endocrine system, the response is slow and long lasting (until the hormone is broken down). -Whereas in the nervous system, the response is fast and short lived (until the nerve impulse stops).
53
Compare Size of Response in the Endocrine and Nervous System
-In the endocrine system, the response is widespread. -Whereas in the nervous system, the response is localised.
54
Compare the Effects of the Endocrine and Nervous System
-In the endocrine system, the effect is permanent and irreversible. -Whereas in the nervous system, the effect is temporary and reversible.
55
What is Adrenaline
-Adrenaline is released from the adrenal gland and targets vital organs such as the liver and the heart. -It is released from glands in stressful and fearful situations.
56
What is ADH
-ADH is released from the pituitary gland and targets the kidney. -Its role is to maintain the amount of water in urine.
57
What is FSH
-FSH is released from the pituitary gland and targets the ovaries. -It stimulates the creation of oestrogen and matures the egg.
58
What is Insulin
-Insulin is released in the pancreas and targets the liver and muscles. -It maintains blood glucose levels when they rise too high.
59
What is Glucagon
-Glucagon is released in the pancreas and targets the liver and muscles. -It maintains blood glucose levels when they fall too low.
60
What is Oestrogen
-Oestrogen is releases in the female endocrine glands (ovaries) and targets the ovaries, uterus and pituitary gland. -It is involved in the menstrual cycle, and controls female secondary puberty.
61
What is Testosterone
-Testosterone is released in the male endocrine glands (testes) and targets the male reproductive organs. -It controls male secondary puberty.
62
What is TSH
-TSH is released in the pituitary gland and targets the thyroid gland. -Its role is to maintain thyroxine levels.
63
What is the Function of the Pituitary and Thyroid Glands
-The pituitary gland releases hormones which control other endocrine organs. -The thyroid gland controls growth and the body's basal metabolic rate.
64
What is the Function of the Pancreas and Adrenal Glands
-The pancreas controls the concentration of glucose in the bloodstream. -The adrenal gland releases adrenaline in response to fear or stress.
65
What is the Function of the Ovaries and Testes
-The ovaries control puberty and reproduction in females. -the testes control puberty and reproduction in males.
66
Why is it Important that Blood Glucose Concentration is Controlled
-Glucose is needed by every cell to release energy by respiration. -Because of this, it is essential that the concentration of glucose in the blood is controlled and stays as constant as possible.
67
How does the Body Respond to an Increase in Blood Glucose Levels
-When blood glucose levels increase, this is sensed by the pancreas. -The pancreas secretes insulin into the bloodstream. The insulin triggers cells to absorb glucose from the blood. -Muscle and liver cells stores excess glucose as glycogen. This causes blood glucose levels to fall back to its normal level.
68
How does the Body Respond to an Decrease in Blood Glucose Levels
-When blood glucose levels decrease, this is sensed by the pancreas. -The pancreas secretes glucagon into the bloodstream. The glucagon triggers liver cells to convert glycogen to glucose. -Glucose is released into the bloodstream. This causes blood glucose levels to rise back to its normal level.
69
How is the Control of Blood Glucose Levels an Example of Negative Feedback
-When blood sugar rises in the blood, insulin sends a signal to the liver, muscles and other cells to store the excess glucose. -Some is stored as body fat and other is stored as glycogen in the liver and muscles. -Whereas, if the blood glucose level is too low, the liver receives a message to release some of that stored glucose into the blood. -This change is brought about by another hormone produced by the pancreas called glucagon.
70
Describe Type 1 Diabetes
-Type 1 diabetes is insulin dependant as the pancreas is unable to produce insulin. -It develops mainly in young children and adolescents as it is often hereditary. -It is controlled by injections of insulin and oral medications.
71
Describe Type 2 Diabetes
-Type 2 diabetes is non-insulin dependant as insulin produced cannot be used by the body. -It mainly occurs in overweight adults. There is an increasing number of people affected between the ages of 25 and 45. -It is generally controlled by a healthy diet, avoiding high sugar food and taking exercise.
72
Why is it Important that Cells do not Gain or Lose too much Water
-If a cell gains or loses too much water then that cell will not function efficiently. -The level of water in a cell can affect the speed of the chemical reactions that take place in the cell.
73
Describe how the Kidneys Filter and Remove Waste Products
-Glucose, mineral ions, urea and water are filtered out of the blood and into the kidney by diffusion. -Blood cells and protein stay in the blood as they are too large to be filtered out. -All sugar is reabsorbed into the blood by active transport. -Selective reabsorption allows water and mineral ions to be reabsorbed, but only the amount needed. -Urea (and other waste product) are then lost as urine.
74
How does the Body Maintain Nitrogen Balance
-When excessive amounts of protein are eaten, the excess amino acids produced from digesting proteins are transported to the liver from the small intestine. -The liver controls the amino acid concentration in the body, as excess amino acids which need to be excreted safely. The body is unable to store proteins or amino acids. -In the liver ammonia is formed by the deamination of amino acids. It is highly toxic and cannot be allowed to accumulate in the body. Excess ammonia is converted to urea. -Urea and water are released from the liver cells in to the bloodstream and transported to the kidneys where the blood is filtered and the urea is passed out of the body in the urine.
75
How does the Body Respond if Blood is too Concentrated
-The pituitary gland senses the fall in the concentration of water in the blood so releases the hormone ADH into the bloodstream. -ADH travels in the blood to the target organs: the kidneys. ADH increases the permeability of the kidney tubules to water. -The kidney tubules reabsorb more water back into the blood so a small volume of concentrated urine is produced. -The concentration of water in the blood returns back to normal. The pituitary gland senses that the concentration of water in the blood is returning to normal so stops producing ADH.
76
How does the Body Respond if Blood is too Dilute
-If the blood becomes too dilute then this is sensed by the pituitary gland which stops producing ADH. -The kidney tubules now become less permeable to water. -This means that less water is reabsorbed into the blood by the kidney tubules and more water passes into urine. -This causes the concentration of water in the blood to fall back to within the normal range
77
Advantages of Kidney Transplant
-Have a normal, flexible lifestyle such as going on holidays -Cheaper in the long term for the NHS -No risk of infection from frequent needles/ injections -No need for regular or long hospital visits
78
Disadvantages of Kidney Transplant
-The kidney may be rejected -Have to keep taking immunosuppressants -Does not last forever (further surgery is needed which also has risks from anaesthesia or infection) -A suitable donor may not be available
79
Why does all of the Urea Diffuse from the Blood into the Fluid but not all of the Water or Ions in Dialysis
-The dialysis fluid contains no urea. This means that there is large concentration gradient for urea between the patient's blood and the dialysis fluid. -This causes the urea to diffuse rapidly into the dialysis fluid. -Because the dialysis fluid already contains some water and ions, there is only a relatively small concentration gradient for these two chemicals between the patient's blood and the dialysis fluid. -This means that only some of the water and ions diffuse into the dialysis fluid.
80
Why is Dialysis Fluid Constantly Refreshed
-If we did not refresh the dialysis fluid then diffusion would take place until there was no concentration gradient for any of the molecules. At this point, diffusion would stop. -By constantly replacing the dialysis fluid with fresh fluid, we make sure that there is always a large concentration gradient and that the rate of diffusion is always high.
81
Advantages of Kidney Dialysis
-There is no shortage of dialysis machines so it is available to all patients -No need for immunosuppressant drugs
82
Disadvantages of Kidney Dialysis
-Inconvenient as it requires regular treatment and a controlled diet -Expensive in the long term
83
Describe the Order of the Menstrual Cycle
Day 1: The woman's period starts. If fertilisation has not happened, the uterus lining and unfertilised egg are released. Day 2-13: An egg matures in an ovary. The uterus lining starts to thicken. Day 14: Ovulation happens. A mature egg is released from the ovary. Day 15-28: The egg makes its way down a fallopian tube. If the egg is fertilised, it implants into the uterus wall
84
State the Functions of the Different Hormones in the Menstrual Cycle
Oestrogen - This is produced by the ovaries and causes the uterus lining to thicken ready for a fertilised egg to implant. Follicle-stimulating hormone (FSH) - This is produced by the pituitary gland and causes an egg to mature in an ovary. Luteinising hormone (LH) - This is produced by the pituitary gland and causes an egg to be released by the ovary (ovulation). Progesterone - This is produced by the ovary and keeps the uterus lining thick in case a fertilised egg implants.
85
Describe the Role of FSH and Oestrogen in the Menstrual Cycle
-First the pituitary gland releases FSH into the bloodstream. -The FSH travels to the ovaries and causes an egg to mature. -FSH also triggers the release of the hormone oestrogen by the ovaries. -Oestrogen causes the lining of the uterus to become thick. -Oestrogen also prevents the pituitary gland releasing FSH. Oestrogen now triggers the pituitary gland to release LH.
86
Describe the Role of LH and Progesterone in the Menstrual Cycle
-LH triggers the ovary to release the mature egg (ovulation). At this point the ovary releases the hormone progesterone. -Progesterone stops the pituitary gland releasing FSH and LH. Progesterone also makes sure that the uterus lining stays thickened. If the egg is not fertilised then progesterone levels fall. The uterus lining and egg are released. The woman has her period
87
Why is it Important that the Production of FSH and LH are Inhibited
-If oestrogen did not inhibit the production of FSH, then the level of FSH would remain high. This could trigger more eggs to mature in the ovaries. -This could result in multiple eggs being released during ovulation at different times during the menstrual cycle. -It is essential that both FSH and LH only operate once during the menstrual cycle. This means that once FSH and LH have carried out their functions, they cannot be produced again by the pituitary gland during that cycle. -If they were, it would disrupt the hormonal balance that controls the entire cycle
88
Describe the Stages of IVF
-The woman is treated with FSH to stimulate maturation and LH to stimulate ovulation. Several eggs mature in an ovary. -The eggs are collected from the mother and sperm is collected from the father. -The eggs are fertilised by the sperm in the lab. The fertilised eggs develop into embryos. -The embryos are inserted into the woman's uterus. The embryos develop into babies.
89
Describe the Advantages of IVF
-Parents can have a child if they are unable to do it themselves -Mature eggs may be collected and stored if parents want another child later
90
Describe the Disadvantages of IVF
-It is very expensive -Not always successful -Fertility drugs can have some health risks -Increases chance of multiple births which increases risk of a premature or still birth -Emotionally stressful for both parents and physically demanding for the mother
91
Describe Two Ethical Issues Around IVF
-During IVF, many embryos are created. Not all of the embryos are transferred into the woman's uterus. -The unused embryos are destroyed and some people find this unethical. -IVF is also expensive. Some people think that the money spent by the NHS on IVF should be spent on other treatments eg for cancer.
92
How does Adrenaline Affect the Heart How does this Prepare the Body
-Adrenaline increases the heart rate. -Because adrenaline causes the heart rate to increase, a greater volume of blood is pumped by the heart per minute. -This means that more oxygen and glucose is delivered in the blood to the muscle cells and the brain. -The extra oxygen and glucose are used by the muscle cells in aerobic respiration. This prepares the body to fight or to run away.
93
Describe the Effect of Thyroxine
-Thyroxine increases the body's basal metabolic rate. This makes the body's chemical reactions take place at a faster rate. -Thyroxine plays an important role in growth and development. Thyroxine levels are controlled by negative feedback
94
How is the Regulation of Thyroxine an Example of Negative Feedback
-Low thyroxine levels in the bloodstream stimulate the hypothalamus to release TRH. -This causes the pituitary to release TSH so the thyroid releases more thyroxine. Blood levels return to normal. -Normal thyroxine levels in the bloodstream inhibit TRH release from the hypothalamus. -This inhibits the release of TSH from the pituitary, so normal blood levels are maintained.
95
What is Negative Feedback
-A mechanism where changes to conditions cause an action to reverse the change, to keep conditions stable. -There are many negative feedback cycles in the human body to maintain homeostasis. -It is important type of control, monitoring levels of things like blood glucose, temperature, hydration, -It also triggers responses when these levels become too high or low.
96
Describe how Auxin Controls Phototropism
-When light falls evenly on a shoot, the auxin is evenly distributed so growth on all sides of the shoot is equal. -When light falls on the shoot from a certain direction, auxin moves to the shaded side of the shoot. There is now an uneven distribution of auxin. -Auxin promotes growth in shoots so causes the cells on the shaded side to elongate faster than the cells on the side in the light. This causes the shoot to bend towards the light. -The shoot now faces the light so it falls evenly on the shoot again. This causes the auxin to become evenly distributed again. Growth on all sides of the shoot will be equal again.
97
Describe how Auxin Controls Geotropism
-When a young plant is laid on its side, gravity causes the auxin to accumulate at the bottom of the root and shoot. This means there is an uneven distribution of auxin. -Auxin inhibits root growth so in the root, the cells elongate faster on the side with the least auxin. This causes the root to bend downwards, towards the force of gravity. -Auxin promotes growth in shoots so in the shoot, the cells elongate faster on the side with the most auxin. This causes the shoot to bend upwards away from the force of gravity. -When the root and shoot grow in the desired direction, the auxin becomes evenly distributed again. Growth on all sides of the root and shoot will be equal.
98
Describe a Method for the Plant Responses Practical
-Put cotton wool into three petri dishes, and add the same volume of water to each dish. Add ten seeds to each dish and place them in a warm place where they won’t be disturbed. -Allow the seeds to germinate, and add more water if the cotton wool dries out. Once the seeds have germinated, ensure the petri dishes each contain the same number of seeds, and remove any extra seeds if necessary. -One petri dish will sit in full light on a windowsill, the second in a dark cupboard, and the final dish will be placed in partial light. Every day for one week, measure the height of each seedling and record the results in a table. You must record the height of the individual seedlings on each day. -Calculate the mean of the seedlings each day, and compare the mean heights in the three different locations.
99
Why is it Important to Keep the Volume of Water the Same in Each Petri Dish in the Plant Responses Practical
-We are seeing how the height of the seedlings (our dependent variable) changes with light intensity (our independent variable). -The height of seedlings could also be affected by other variables, including the volume of water that we give the seedlings. -For example, seedlings which are given a lot of water could grow taller than seedlings which are given only a small volume of water. -What this means is that if we allow the volume of water to change, we cannot be certain that any differences in seed height are only due to light intensity
100
Why is it Important to Keep the Number of Seeds the Same in Each Petri Dish in the Plant Responses Practical
-We are looking at the effect of light intensity on the height of the seedlings. This means that we need to keep the number of seedlings the same between each dish (ie this is another control variable). -Growing seedlings will compete with each other for water and for minerals. -If we have a larger number of seedlings in a dish, there would be a lot of competition for these resources and these seedlings may not grow as much as they could. -Therefore we need to keep the number of seedlings the same in each dish
101
Describe how we can Measure the Height of the Seedlings in the Plant Responses Practical
-To accurately measure the height of each seedling, we place the seedling against a ruler and gently hold the stems so that it is straight. -We must be careful not to damage any seedling.
102
Explain the Results from the Plant Responses Practical
-There is no difference in the height of the seedlings in full sunlight and partial sunlight. This is because chlorophyll is very efficient at capturing the energy in light so even in partial sunlight there is enough light for seedlings to grow. -In both cases, the seedlings have grown towards the light source. This is phototropism and is due to auxin. The seedlings in darkness have grown much taller than the other seedlings. -This is because when seeds germinate underground, the seedlings grow rapidly to reach the light. In this case, due to the dark conditions, the seedlings continue to grow rapidly. -The seedlings have also grown straight as phototropism is not taking place.
103
Why do the Shoots Grow away from Gravity in the Plant Responses Practical
-Shoots naturally grow in the opposite direction to gravity. -When a seedling has germinated underground, there is no light to trigger phototropism. -Instead, by growing away from gravity, the shoot makes its way out of the soil towards the light.
104
Why must the Plant Responses Practical be Carried out in the Dark when Investigating Geotropism
-This experiment explores gravitropism. This means that we have to exclude light. -If light was present, then the seedlings would also demonstrate phototropism.
105
Describe the Roles of Ethene and Gibberellins in Plants
-Gibberellins play a role in starting seed germination. -Ethene controls cell division and fruit ripening.
106
Describe the Uses of Auxins in Agriculture or Horticulture
-This is used by gardeners as a weedkiller e.g. on lawns. -Used to promote the growth of tiny plants in tissue culture. -This is used by gardeners as a rooting powder when taking cuttings.
107
Describe the Uses of Gibberellins in Agriculture or Horticulture
-Used to bring seeds out of dormancy, forcing them to germinate earlier than they would naturally. -Can be used to trigger flowering eg in plant nurseries where plants are sold. -Used to make fruit grow larger than they would under natural conditions.
108
Describe how Ethene is Used in the Production of Bananas
-Ethene is a chemical which makes bananas ripen. The bananas that are sold in the UK are grown thousands of miles away. -If they were harvested when they were ripe, they would be rotten by the time they reached the UK. Instead, they are harvested before they are ripe. -They are then transported to the UK and stored (usually under cold conditions). Just before they are sold, they are treated with ethene which causes them to ripen.

Biology Paper 2 (4 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions