Topic 5 - Homeostasis and Response Flashcards
1
Q
What does the nervous allow humans to do
A
Mean that humans can react to their surroundings and coordinate their behaviour
2
Q
What does the Central Nervous System do
A
-In vertebrates (animals with backbones) this consists of the brain and spinal cord only. In mammals, the CNS is connected to the body by sensory neurones and motor neurones. It coordinates the response of effectors is which may be muscles contracting or glands secreting hormones.
3
Q
What do sensory neurones do
A
The neurones that carry information as electrical impulses from the receptors to the CNS
4
Q
What do motor neurones do
A
The neurones that carry electrical impulses from the CNS to effectors
5
Q
What do effectors do
A
-All your muscles and glands, which respond to nervous impulses.
-Respond to nervous impulses and bring about a change
6
Q
What are receptors and what can they be
A
-The cells that detect stimuli
-There are many different types of receptors, such as taste receptors on the tongue and sound receptors in the ears
-Receptors can form part of larger, complex organs (e.g. the retina of the eye is covered in light receptor cells)
7
Q
How do muscles and gland respond to electrical impulses as effectors
A
- Muscles contract in response
- Glands secrete hormones
8
Q
What is the function of the CNS
A
-It’s a coordination centre so it receives information from the receptors and then coordinates a response the response is carried out by effectors
9
Q
What are synapses
A
-The connection between two neurones is called a synapse
-The nerve signal is transferred by chemicals which diffuse across the gap
-These chemicals then set off a new electrical signal in the next neurone
10
Q
What are reflexes
A
-Rapid, automatic responses to certain stimuli that don’t involve the conscious part of the brain - they can reduce the chances of being injured
11
Q
Give examples of a reflex
A
-If someone shines a blight light in your eyes, your pupil automatically get smaller so that less light gets into the eye - this stops it getting damaged
-Or if you get a shock, your body releases the hormone adrenaline automatically- it doesn’t wait for you to decide that you’re shocked
12
Q
What is the passage of information in a reflex called
A
The passage of information in a reflex is called reflex arc
13
Q
Outline how the reflex arc works
A
-When a stimulus is detected by receptors, impulses are sent along a sensory neurones to relay neurone in the CNS
-When the impulse reaches a synapse between the sensory neurone and relay neurone it triggers chemicals to be released causing impulses to be sent along the relay neurone
-When the impulses reach a synapse between the relay neurone and a motor neurone, the same thing happens. Chemicals are released so impulses are be sent sling the motor neurone
-The impulses then travel along the motor along the motor neurone to the effector
-The effector will then bring about a change
14
Q
What does the body have to balance to keep the core body temperature constant
A
-The amount of energy gained (e.g. through respiration)
-The amount of energy lost
15
Q
What is the thermoregulatory centre
A
-It’s in the brain and contains the receptors that are sensitive to the temperature of the blood flowing through the brain
-Receives impulses from temperature receptors in the skin, giving information about skin temperature
16
Q
Describe what process the body goes through when it’s temperature is too high to keep the body temperature constant
A
- Temperature receptors detect that core body temperature is too high
- The thermoregulatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically
- Effectors produce a response and counteract the change
- Body cools down
17
Q
Describe what process the body goes through when it’s temperature is too low to keep the body temperature constant
A
- Temperature receptors detect that core body temperature is too low
- The thermoregulatory centre acts as a coordination centre - it receives information from the temperature receptors and triggers the effectors automatically
- Effectors produce a response and counteract the change
- Body warms up
18
Q
Why do some effectors work antagonistically
A
One effector may heat whilst another cools to achieve a precise temperature
19
Q
What responses are produced by effectors when your body is too hot (2)
A
-Sweat is produced by sweat glands and evaporates from the skin. The transfers energy to the environment
-The blood vessels supplying the skin dilate so more blood flows close to the surface of the skin. This is called vasodilation. This helps transfer energy from the skin to the environment.
20
Q
What responses are produced by effectors when your body is too cold (4)
A
- Hairs stand up to trap an insulating layer of air
- No sweat is produced
- Blood vessels supplying skin capillaries constrict to close off the skin’s blood supply. This is called vasoconstriction
- When you’re cold you shiver too this needs respiration which transfers some energy to warm the body
21
Q
What are hormones
A
Chemical molecules released directly into the blood. They are carried in the blood to other parts of the body, but only affect particular cells in particular organs (target organs). Hormones control things in organs and cells that need constant adjustment.
22
Q
Where are hormones produced
A
In various glands, called endocrine glands which make up the endocrine system
23
Q
Outline the pituitary
A
Produces many hormones that regulates body conditions. It is sometimes called the ‘master gland’ because these hormones act on other glands, directing them to release hormones that bring about change
24
Q
Outline the ovaries
A
Produce oestrogen which is involved in the menstrual cycle
25
Outline testes
Produce testosterone which controls puberty and sperm production in males
26
Outline the thyroid
Produces thyroxine which is involved in regulating things like the rate of metabolism, heart rate and temperature.
27
Outline the adrenal gland
Produces adrenaline which is used to prepare the body for a ‘fight or flight’ response
28
Outline the pancreas
-Produces insulin which is used to regulate the blood glucose level
29
What are the differences between hormones and nerves
-Nerves are a very fast action which act for a short time on a very precise area
-Hormones are a slower action which act for a long time in a more general way
30
What is the main reproductive hormone in men
Testosterone which is produced by the testes and stimulates sperm production
31
What is the main reproductive hormone in women
Oestrogen which is produced in the ovaries which brings about physical changes and is involved in the menstrual cycle
32
Outline the 4 stages of menstruation
1. Day 1 - menstruation starts. The uterus lining breaks down for about four days
2. The uterus lining builds up again, from day 4 to day 14, into a thick spongy layer full of blood vessels, ready to receive a fertilised egg.
3. An egg develops and is released from the ovary at day 14 - ovulation
4. The wall is then maintained for about 14 days until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining starts to break down and the whole cycle starts again.
33
Outline FSH
1. Produced in the pituitary gland
2. Causes an egg to mature in one of the ovaries, in a structure called a follicle
3. Stimulates the ovaries to produce oestrogen
34
Outline oestrogen
1. Produced in the ovaries
2. Causes the lining of the uterus to grow
3. Stimulates the release of LH and inhibits release of FSH
35
Outline LH
1. Produced by the pituitary gland
2. Stimulates the release of an egg at day 14 (ovulation
36
Outline progesterone
1. Produced in the ovaries by the remains of the follicle after ovulation
2. Maintains the lining of the uterus during the second half of the cycle when the level of progesterone falls, the lining breaks down
3. Inhibits the release of LH and FSH
37
Why do the conditions in your body need to be kept steady
Your cells need the right conditions in order to function properly
38
What is homeostasis
The regulation of the conditions inside your body to maintain a stable internal environment in response to changes in both internal and external conditions
39
How does negative feedback when a level of something is too high
-Receptor detects a stimulus and the level is too high
-The coordination centre receives and processes the information, then organises a response
-Effector produces a response, which counteracts the change and restores the optimum level and the level decreases
-The effectors will carry in producing the responses for as long as they’re stimulated by the coordination centre which may cause the opposite problem. The receptor will detect if the other level becomes too different and negative feedback starts again
40
How does negative feedback when a level of something is too low
-Receptor detects a stimulus and the level is too low
-The coordination centre receives and processes the information, then organises a response
-Effector produces a response, which counteracts the change and restores the optimum level and the level increases
-The effectors will carry in producing the responses for as long as they’re stimulated by the coordination centre which may cause the opposite problem. The receptor will detect if the other level becomes too different and negative feedback starts again
41
Outline the practical for investigating reaction time
1. The person being tested should sit with their arm resting on the edge of a table
2. Hold a ruler between their thumb and forefinger. Make sure that the zero end of the ruler is level with their thumb and finger then let go with no warning
3. The person being tested should try catch the ruler as quickly as possible
4. Reaction time is measured by the number on the ruler where it’s caught. It should be read from the top of my. The further down it’s caught the slower the reaction time
5. Repeat and calculate the mean distance
6. Then give them 300ml of cola (caffeinated) After 10 minutes repeat steps 1-5
42
How is reaction time measured using a computer
1. Simple computer tests can also be used to measure reaction time, for example the person has to click the mouse as soon as they see a stimulus on the screen
2. Computers can give a more precise reaction time as they remove the possibility of human error
3. As the computer can record the reaction time in milliseconds it can gives more accurate reaction time
4. Remove possibility a person can predict when to respond (e.g. through body language)
43
How is the brain a part of the nervous system
-It’s made up of billions of interconnected neurones and is in charge of all of our complex behaviours
44
What does the cerebral cortex do in the brain
Outer wrinkly bit that is responsible for things like consciousness, intelligence, memory and language.
45
What does the medulla do in the brain
Controls unconscious activity like breathing and your heartbeat
46
What does the cerebellum do in the nervous system
Responsible for muscle coordination
47
How do scientists study patients with brain damage
-If a small part of the brain has been damaged, the effect this has on the patient can tell what part of the brain is damaged
-If an area at the back of the brain was damaged by a stroke and the patient went blind, you know that area has something to do with vision
48
How scientists use electrically stimulating the brain to study it
-The brain can be stimulated electrically by pushing a tiny electrode into the tissue and giving it a small zap of electricity. By observing what stimulating different parts of the brain does it’s possible to get an idea of what those parts do (e.g. when a certain part of the brain is stimulated it causes muscle contraction and movements)
49
How do scientists use MRI scans to study the brain
It’s a big tube like machine that can produce a very detailed picture of the brain’s structured. Scientists use it to find out what areas of the brain are active when people are doing things like listening to music or trying to recall a memory
50
What has knowledge of how the brain works led to
-Developments of treatments for disorders of the nervous system. Like electrical stimulation of the brain can help reduce muscle tremors caused by nervous system disorders such as Parkinson’s disease
51
What is the risk with investigation or treatment of the brain
The brain is complex and delicate so investigation and treatment is difficult. It can also lead to physical damage to the brain or increased problems with brain function (e.g. difficulties with speech)
52
What is the sclera
The tough supporting wall of the eye
53
What is the cornea
The transparent outer layer found at the front of the eye which refracts light into the eye
54
What is the iris
Contains muscles that allow it to control the diameter of the pupil and therefore how much light enters the eye
55
What is the lens
Focuses the light onto the retina (which contains receptor cells sensitive to light intensity and colour)
56
What controls the shape of the lens in the eye
Ciliary muscles and suspensory ligament
57
What is the optic nerve
Carries impulses from the receptors on the retina to the brain
58
What is the retina
Had receptor cells in the eye
59
How does the iris reflex work in the eye to protect the retina from damage
1. When light receptors in the eye detect very bright light, a reflex is triggered that makes the pupil smaller. The circular muscles in the iris contract and the radial muscles relax. This reduces the amount of light that can enter the eye
2. The opposite happens in dim light. This time the radial muscles contract and the circular muscles relax, which makes the pupil wider.
60
How does the eye focus on light to look at near objects
1. The ciliary muscles contract inwards, which slackens the suspensory ligaments
2. The lens becomes more curved and fat
3. This increases the amount by which it refracts light
61
How does the eye focus on light to look at distant objects
1. The ciliary muscles relax, which lets the suspensory ligaments to pull tight
2. This makes the lens go thin (less curved)
3. It refracts light by a smaller amount
62
What causes people to be longsighted (unable to focus on near objects)
1. When the lens is the wrong shape and doesn’t refract the light enough or the eyeball is too short
2. The images of near objects are brought into focused behind the retina
3. You can use glasses with a convex lens (a lens which curves outwards) to correct it. Three lens refracts the light rays so they focus on the retina.
4. The medical term for long sightedness is hyperopia
63
What causes short sight (when people are unable to focus on distant objects)
1. This occurs when the lens is the wrong shape and refracts the light too much or the eyeball is too long
2. The images of distant objects are brought into focus infront of the retina
3. You can use glasses with a concave lens (a lens which curved inwards) to correct it, so that the light rays focus on the retina
4. The medical term for short sightedness is myopia
64
How are contact lenses used for vision correction
-Contact lenses sit on the surface of the eye and are shaped to compensate for the fault in focusing. They’re popular as they are lightweight and almost invisible. They’re also more convenient then glasses for activities like sports. The two main types of lenses are hard and soft. Soft are generally more comfortable but carry higher risk of eye infections
65
How is laser eye surgery used for vision correction
-A laser can be used to vaporise tissue, changing the shape of the cornea. Slimming it makes it less powerful and can improve short sight. Changing the shape so that it’s more powerful will improve long sight. There is a risk of complications such as infection or the eye reacting in a way that makes your vision worse than before.
66
How is replacement lens surgery
-Longsightedness may be more effectively treated by replacing the lens of the he. The natural lens is removed and an artificial lens made of clear plastic is inserted in its place. As it involves work inside the eye, replacing a lens carries higher risk than laser eye surgery, including possible damage to the retina
67
What removes glucose from the blood
-The normal metabolism of cells removes glucose from the blood
-Vigorous exercise removes much more glucose from the blood
-Excess glucose can be stored as glycogen in the liver and in the muscles
68
How does the body respond when the blood glucose level is too high (negative feedback)
-Blood with too much glucose passes by the pancreas and insulin is secreted into it
-Glucose moves from the blood into liver and muscle cells
-Insulin makes liver turn glucose into glycogen
-The blood glucose is reduced
69
How does the body respond when the blood glucose level is too low (negative feedback)
-Blood with little glucose passes the pancreas and glucagon is secreted into it
-The glucagon is transported to liver where the glucagon makes glycogen turn into glucose
-The glucose is then released into blood by liver and blood glucose is increases
70
Outline Type 1 diabetes
-Where the pancreas produces little to no insulin. A persons blood glucose can rise to a level that kills them. They need insulin therapy which involves several injections of insulin throughout the day, most likely at meal times. This means glucose will be quickly removed from the blood so it doesn’t get too high
-They also need to limit intake of food rich with carbohydrates
-They also need to take regular exercise
71
Outline Diabetes type 2
-When a person becomes resistant to their own insulin. This can cause a persons blood sugar level to rise to a dangerous level. Being overweight can increase your chance of developing type 2 diabetes as obesity is a major risk factor in the development of the disease. Type 2 diabetes can be controlled by eating a carbohydrate-controlled diet and getting regular exercise.
72
What do kidneys do in the body
Make urine by taking waste products out of your blood. Substances are filtered out of the blood as it passes through the kidneys (filtrations). Useful substances like glucose, some ions and the right amount of water are then absorbed back into the blood (selective reabsorption)
73
How is urea produced in the liver
-Proteins can’t be stored by the body so any excess amino acids are converted into fats and carbohydrates, which can be stored. This occurs in the liver.
-Ammonia is produced as a waste product from this process
-Ammonia is toxic so it’s converted to urea in the liver. Urea is then transported to the kidneys, where it’s filtered out of the blood and excreted from the body in urine
74
What happens to ions in the kidneys
-Taken into the body in food, and then absorbed into the blood
-If the ion content of the body is wrong it could upset the balance between ions and water, meaning too much or too little water is drawn into cells by osmosis which can damage cells or mean they don’t work as well as normal.
-Some ions are lost in sweat. However this amount is not regulated, so the right balance of ions in the body must be maintained by the kidneys. The right amount of ions is reabsorbed into the blood after filtration and the rest is removed from the body in urine
75
What happens to water in the kidneys
-The body has to constantly balance the water coming in against the water going out.
-We lose water from the skin and sweat and from the lungs when breathing out
-We can’t control how much we lose in these ways, so the amount of water is balanced by the amount we consume and the amount removed by the kidneys in urine
76
How is the concentration of urine controlled by a hormone
1. The concentration of urine is controlled by a hormone called anti-diuretic hormone. This is released into the bloodstream by the pituitary gland
2. The brain monitors the water content of the blood and instructs the pituitary gland to release ADH into the blood according to how much is needed.
3. The whole process of water content regulation is controlled by negative feedback. This means that if the water content gets too high or too low a mechanism will be triggered that brings it back to normal
77
How is negative feedback carried out when water content in blood is too high
-A receptor in the brain detects the water content is too high
-The coordination centre in the brain receives this information and coordinates a response
-The pituitary gland releases less ADH so less water is reabsorbed from the kidneys
78
How is negative feedback carried out when water content in blood is too low
-A receptor in the brain detects the water content is too low
-The coordination centre in the brain receives this information and coordinates a response
-The pituitary gland releases more ADH so more water is reabsorbed from the kidneys
79
What happens if your kidneys don’t work properly
-Waste substances build up in the blood and you lose your ability to control the levels of ions and water in your body
80
How does dialysis work
-In a dialysis machine the persons blood flows between partially permeable membranes, surrounded by dialysis fluid. It’s permeable to things like ions and waste substances, but not big molecules like proteins
-The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood
-This means that useful dissolved ions & glucose won’t be lost from the blood during dialysis
-Only waste substances and excess ions and water diffuse across the barrier
81
What are the disadvantages of dialysis
-Many people with kidney failure have to have a dialysis session three times a week. Each session takes 3-4 hours.
-May cause blood clots or infection
-Being on a dialysis machine is unpleasant and expensive for the NHS
-However dialysis can buy a patient with kidney failure valuable time until a donor organ is found.
82
Outline kidney transplants
-At the moment the only cure for kidney failure is to have a kidney transplant
-Healthy kidneys are usually transplanted from people who have died suddenly
-The donator has to be on organ donor register or carry a donor card
-Kidneys can also be transplanted from people who are still alive. But there is a small risk to the person donating the kidney.
-The kidney can also be rejected by the patients immune system. The patient is treated with drugs to prevent this but it can still happen
-Transplants are cheaper than dialysis and they can put an end to the hours patients have to spend on dialysis, but there are long waiting lists for kidneys.
83
How is oestrogen used to reduce fertility
Can be used to prevent the release of an egg as it inhibits the production FSH, meaning egg development and production stop
84
How is progesterone used to reduce fertility
Stimulates the production of thick mucus which prevents any sperm getting through and reaching an egg
85
What is the pill (hormones)
-An oral contraceptive containing oestrogen and progesterone
-It’s over 99% effective at preventing pregnancy but it can cause side effects like headaches and nausea and doesn’t protect from STIs
-There’s also a progesterone only pill that has fewer side effects and is just as effective
86
What is a contraceptive patch
Contains oestrogen and progesterone and is a small (5cm x 5cm) patch that’s stuck to the skin. Each patch lasts a week
87
What is contraceptive implant
-Inserted under the skin of the arm. It releases a continuous amount of progesterone, which stops the ovaries releasing eggs, making it hard to sperm to swim to the egg, stopping any fertilised egg implanting in the uterus
-An implant can last for three years
88
What is the contraceptive injection
-Contains progesterone
-Each dose lasts 2 to 3 months
89
What is an IUD
A T-shaped device that is inserted into the uterus to kill speed and prevent implantation of a fertilised egg. There are two main types - plastic IUDs that release progesterone and copper IUDs that’d prevent the sperm surviving in the uterus.
90
Outline condoms
Only form of contraception that will protect against STIs
91
Outline contraceptive diaphragms
A shallow cup that fits over the cervix to form a barrier. It has to be used with spermicide.
92
Outline spermicide
Can be used alone as a form of contraception but it’s only 70-80% effective
93
What are non barrier or hormonal ways to reduce fertility
Sterilisation - Involves cutting or tying the fallopian tubes or the sperm duct. This is a permanent procedure however there’s a very small chance the tubes can rejoin
Natural methods - Finding out when in the menstrual cycle the woman is most fertile and avoiding sexual inter course on those days
Abstinence - The only way to be completely sure that sperm and egg don’t meet
94
How can hormones be used to increase fertility
1. Some women have low levels of FSH so their eggs don’t mature so they can’t get pregnant
2. The hormones of FSH and LH can be given to women in a fertility frug to stimulate ovulation
95
Advantages of using hormones to increase fertility
-Helps a lot of women get pregnant when they previously couldn’t
96
Disadvantages of using hormones to increase fertility
-Doesn’t always work so some many women may have to do it many times which could be expensive
-Too many eggs could be stimulated, resulting in unexpected multiple pregnancies
97
How does IVF work
1. Collecting eggs from the woman’s ovaries and fertilising them in a lab using the man’s sperm
2. Can involve a technique called Intra-Cytoplasmic Sperm Injection, where the sperm is injected directly into an egg. It’s useful if the man has a very low sperm count.
3. The fertilised eggs are then grown into embryos in a laboratory incubator
4. Once the embryos are tiny balls of cells, one or two of them are transferred to the woman’s uterus to improve the chance of pregnancy
5. FSH and LH are given before egg collection to stimulate several eggs to mature
98
Advantages of IVF
Fertility treatment can give an infertile couple a child
99
Disadvantages of IVF
-Multiple births can happen if more than one embryo grows into a baby - these are risky
-Success rate is low (26%). This makes the process stressful and often upsetting, especially if it ends up in multiple failures
-The process is also physically stressful for women as some have a strong reaction to hormones.
100
How has an advance in technology allowed IVF to improve
-Advance in microscope techniques allowed to improve techniques of IVF
-Specialised micro-tools have been developed to use on the eggs and sperm under the microscope. They’re also used to remove single cells from the embryo for genetic testing. -More recently time lapsing imaging means the growth of embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy
101
Outline opposition to IVF
-Often results in unused embryos that are eventually destroyed meaning some people think it is unethical as each embryo is a potential human life
-The genetic testing of embryos before implantation also raises ethical issues as some people think it could lead to the selection of preferred characteristics such as gender or eye colour
102
Outline adrenaline
-A hormone released by the adrenal glands, which are just above the kidneys
-Released in response to stressful or scary situations - your brain detects fear or stress and sends nervous impulses to the adrenal glands which respond by secreting adrenaline
-It gets the body ready for ‘flight or fight’ by triggering mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles. For example, it increases heart rate
103
Outline thyroxine
-A hormone released by the thyroid gland, which is in the neck
-It plays an important role in regulating the basal metabolic rate - the speed at which chemical reactions in the body occur while the body is at rest. Thyroxine is also important for loads of processes in the body, such as stimulating protein synthesis got growth and development
-Released in response to thyroid stimulating hormone, released from the pituitary gland
104
Outline the thyroxine negative feedback system
-Keeps the amount of thyroxine in the blood at the right level - when the level of thyroxine in the blood is higher than normal, the secretion of TSH from the pituitary gland is inhibited. This reduces the amount of thyroxine released from the thyroid gland, so the level in the blood falls back towards normal.
105
Outline what auxin is
-A plant hormone that controls growth near the tips of shoots and roots.
-It controls the growth of a plant in response to light (phototropism) and gravity (gravitropism)
-Produced in the tips and moves backwards to stimulate the cell elongation process which occurs in the cells just behind the tips
-Extra auxin promotes growth in the shoot but inhibits growth in the root
106
How does auxin allow a shoot to grow towards light
-When a shoot tip is exposed to light, more auxin accumulates on the side that’s in the shade than the side that’s in the light
-This makes the cells grow faster on the shaded side, so the shoot bends towards the light.
107
How does auxin allow shoots grow away from gravity and roots grow towards gravity
-When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
-This causes the lower side to grow faster, bending the shoot upwards
-A root growing sideways will also have more auxin on its lower side
-But in a bit the extra auxin inhibits growth. This means the cells on top elongate faster and the root bends downwards
108
Outline the practical to investigate plant growth responses
1. Put 10 cress seeds into three different petri dishes each lined either moist filter paper
2. Shine a light onto one of the dishes above and two of the dishes from different directions
3. Leave your cress seeds alone for one week until you can observe their responses and you’ll find the seedlings grow towards the light
-You’ll know that the growth response is due to light only if you control all other variables
109
How are auxins used to kill weeds
Most weeds growing in fields of crops or in a lawn are broad-leaved, in contrast to grasses and cereals which have very narrow leaves. Selective weed killers have been developed using auxins which only affect the broad-leaved plants. They totally disrupt their normal growth patterns, which soon kills them, whilst leaving the grass and crops untouched.
110
How are auxins used to grow from cuttings with rooting powder
-A cutting is part of a plant that has been cut off it, like the end of a branch with a few leaves on it. Normally, if you stick cuttings in the soil they won’t grow, but if you add rooting powder, which contains auxins, they will produce roots rapidly and start growing new plants. This enables growers to produce lots of clones of a really good plant very quickly
111
How are auxins used to grow cells in tissue culture
-Tissue culture can be used to grow clones of a plant from a few of its cells. To do this, hormones such as auxins need to be added to the growth medium to stimulate the cells to divide to form both roots and shoots
112
What is Gibberellin
Another type of plant growth hormone and it stimulates seed germination, stem growth and flowering.
113
How is Gibberellin used to control dormancy
-Lots of seeds won’t germinate until they’ve been through certain conditions. This is dormancy. Seeds can be treated with Gibberellin to alter dormancy and make them germinate at times of year that they wouldn’t normally. It also helps to make sure all the seeds in a batch germinate at the same time.
114
How is Gibberellin used to induce flowering
Some plants require certain conditions to flower, such as longer days or low temperatures. If these plants are treated gibberellin, they will flower without any change in their environment. Gibberellin can be used to grow bigger flowers.
115
How is Gibberellin used to grow larger fruit
Seedless varieties of fruit often do not grow as large as seeded fruit. However if gibberellin is added to these fruits, they will grow larger to match the normal types.
116
How is ethene used to ripen fruit
-Gas produced by ageing parts of a plant. It influences the growth of the plant by controlling cell division. It also stimulates enzymes that cause the fruit to ripen.
-Commercially it can be used to speed up the ripening of fruits either while they are still on the plant, or during transport to the shops
-This means fruit can be picked while it’s still unripe. The gas is added to the fruit on the way to the supermarket so that it will be perfect as it reaches the shelves
-Ripening can also be delayed while the fruit is in storage by adding chemicals that block ethene’s effect on the fruit or reduce the amount of ethene that the fruit can produce. Alternatively some chemicals can be used that react with ethene to remove it from the sit
