homeostasis, puberty, plant hormones Flashcards
1
Q
2 types of nervous systems in the human nervous system
A
Central nervous system (CNS)
peripheral nervous system (PNS)
2
Q
Central nervous system (CNS)
A
Central nervous system (CNS) – the brain and spinal cord - coordinator for rest of the nervous system - contains relay neurones
3
Q
peripheral nervous system (PNS)
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peripheral nervous system (PNS) – all of the nerves in the body - each nerve is made up of lots of specialised cells called neurones - contains sensory and motor neurones
4
Q
neurone structure - cell body
A
contains most cellular structures e.g. nucleus, mitochondria
5
Q
neurone structure - dendrites
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highly branched to form connections with other neurones at synapses
6
Q
neurone structure - axon
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long fibre of neurone
7
Q
neurone structure - axon terminal
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highly branched to form connections with other neurones at the nerve ending
8
Q
reflex response
A
- doesnt involve brain as coordinator - uses spinal cord
- involuntary/ automatic meaning that they happen without you consciously deciding to carry out the response
- Very rapid & automatic to protect the body from potential damage such as touching a hot surface
9
Q
sensory neurone
A
long
cell body containing nucleus at center of axon
10
Q
relay neurone
A
short + highly branched
Has an unmyelinated axon -important for role in CNS
11
Q
motor neurone
A
cell body at top of cell
12
Q
reflex arc example - stepping on sharp pin
A
- Pressure of pin = stimulus & is detected by receptor on the sole of the foot
- Triggers the electrical nerve impulse to start and travel up the sensory neuron to the spinal cord which acts as the coordinator
- The impulse passes across the synapse to a relay neurone in the CNS
- The spinal cord sends the impulse to the motor neurone via another synapse
- Another impulse is simultaneously sent to the brain to ensure there is a conscious awareness of the stimulus but the brain isn’t involved in the response.
- the motor neurone sends the impulse to the effector which contracts and brings about the response of moving the foot away from the pin
13
Q
K
A
Some reflexes are not coordinated by the spinal cord such as the eyes.
Some reflex talks don’t have really new ones so the impulse is able to very quickly be transmitted straight from the sensory neurone to the motor neurone
14
Q
synapses
A
Neurones never touch each other, they are separated by junctions (gaps) called synapses
In a reflex arc, there are synapses between the sensory and relay neurones, and the relay and motor neurones
Chemicals called neurotransmitters (such as dopamine and serotonin) are released into the synaptic cleft and diffuse across it (down a concentration gradient)
15
Q
synapse process
A
16
Q
brain - cerebral cortex
A
this is the outer layer of the brain which is highly folded and is responsible for higher-order processes such as intelligence, memory, consciousness and personality
17
Q
brain - cerebellum
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this is underneath the cerebral cortex and is responsible for balance, muscle coordination and movement
18
Q
brain - medulla
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this region controls unconscious activities such as heart rate and breathing
19
Q
brain - pituitary gland
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responsible for regulating many body functions such as controlling the activity of other glands
20
Q
Mapping regions of the brain - 3 methods
A
Neuroscientists have been able to map the regions of the brain to particular functions by…
studying patients with brain damage
electrically stimulating different parts of the brain
using MRI scanning techniques
21
Q
Mapping regions of the brain - studying patients with brain damage
A
Patients with brain damage can be studied to see what effect it has on them physically or on their personality or capabilities
22
Q
Mapping regions of the brain - electrically stimulating different parts of the brain
A
Tiny electrodes can be pushed into different parts of the brain, tiny jolts of electricity stimulate these regions and the effects can be observed
For example, if a region in the medulla responsible for movement is stimulated, the movement caused can be observed
23
Q
Mapping regions of the brain - MRI scans
A
- MRI scanners are very important diagnostic tools used to study the brain and other regions of the body using magnetic fields and the effect these have on protons in the water molecules of the body
- Functional MRIs can produce images of different regions of the brain that are active during different activities like listening to music or recalling a memory (the scanners can detect changes in blood flow – more active regions of the brain have increased blood flow)
24
Q
retina
A
Contains receptor cells called rods and cones, which are sensitive to light
25
fovea
the maximum density of cone cells is found here, as most of the light from the lens is refracted to this point.
26
sclera
tough outer coating to protect the eye.
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cornea
where 70% of the light is refracted into the eye
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optic nerve
Where the information from the receptor cells collects and the nerve impulses from the Retina are carried to the brain
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iris
Controls the amount of light entering the eye.
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ciliary muscles and suspensory ligaments
changes the shape of the lens.
31
pupil
Hole which lets light into the eye
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lens
Reflects light onto the retina.
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pupil dialation
Stimulus - not enough light
Receptor - rod and cone cells
Coordinator – brain
Effector - radial muscles contract & circular muscles relax.
Response - people get bigger and more light enters
34
pupil contraction
Stimulus – too much light
Receptor - rod and cone cells
Coordinator – brain
Effector - radial muscles relax & circular muscles contract.
Response - people get smaller and less light enters
35
To focus on a near object:
To focus on a near object:
a lot of focusing is needed so
so ciliary muscles contract
suspensory ligaments loosen
lens is thicker and refract light strongly
rays of light converge on the retina
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to focus on a distant object:
to focus on a distant object:
less focusing is needed
so ciliary muscles relax
suspensory ligaments are pulled tight
lenses is thinner & only slightly refract light rays
rays of light converge on the retina
37
Myopia
Myopia is caused because the lens is too strong, or the eyeball is too long.
one way to correct myopia is to use spectacles or hard or soft contact lenses with concave lenses.
In myopia the image is focused in front of the retina
38
hyperopia
hyperopia is caused because the lens is too weak, or the eyeball is too short
One way to correct hyperopia is to wear spectacles or hard or soft contact lenses with convex lenses
in hyperopia the image is focused behind the retina
39
Laser surgery
lasers can be used to change the shape of the cornea (changing how it refracts light onto the retina) although like all surgical procedures there is risk of unexpected damage occurring during the procedure which could lead to worse vision or an infection
For myopia: the cornea is slimmed down, reducing the refractive power
For hyperopia: the cornea shape is changed so the refractive power is increased
40
accommodation
The ability of the eye to change its focus by adjusting the curvature of the lens
41
Lens replacement surgery
Lens replacement surgery completely replaces the lens of the eye with a plastic artificial lens (rather than changing the shape of the cornea during laser eye surgery) but this procedure is more invasive than laser surgery and carries a risk of damage occurring to the retina leading to complete sight loss
42
thermoregulatory centre
Body temperature is monitored and controlled by the thermoregulatory centre in the brain
The thermoregulatory centre contains receptors sensitive to the temperature of the blood
The skin contains temperature receptors and sends nervous impulses to the thermoregulatory centre
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Monitoring of Body Temperature
The human body needs to maintain a temperature at which enzymes work best, around 37°C
Processes such as respiration release energy as heat; and the body loses heat energy to its surroundings – the energy gained and lost must be regulated to maintain a constant core body temperature
44
If the body temperature is too high then
blood vessels dilate (vasodilation) - more blood flow to skin so more heat to be carried by the blood to the skin, where it can be lost to the air increasing heat loss
Sweat glands excrete sweat which cools the skin as it evaporates
Hairs lie flat against the skin allowing air to freely circulate reducing the insulating effect of air against the skin increasing heat loss
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If the body temperature is too low then
blood vessels constrict (vasoconstriction) - less blood flow to skin so less heat to be carried by the blood to the skin, where it can be lost to the air reducing heat loss
sweating stops
Hair erector muscles will contract so hair stands upright trapping air around the skin so more insulation and less heat loss
Skeletal muscles contract rapidly and shivering occurs - this is involuntary and requires energy from respiration (which releases energy as heat)
46
Homeostasis
Homeostasis is the regulation of the internal conditions of a cell or organism to maintain optimum conditions for function in response to internal and external changes
e.g. enzyme action and all cell functions
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examples of homeostasis
Blood glucose concentration
Body temperature
Water levels
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Control of Homeostasis
Maintaining controlled conditions within the body is involuntary (automatic) control
This means that the brain stem (or non-conscious part of the brain) and the spinal cord are involved in maintaining homeostasis – you don’t consciously maintain your body temperature or blood glucose level
49
control systems for homeostasis
These automatic control systems may involve nervous responses or chemical responses
All control systems include:
* Cells called receptors, which detect stimuli (changes in the environment)
* Coordination centres (such as the brain, spinal cord and pancreas) that receive and process information from receptors
* Effectors (muscles or glands) which bring about responses which restore optimum levels
50
Hormones
A hormone is a chemical Messenger. This means that they send signals around the body in order to bring about a response in a target organ.
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glands
Hormones are made and secreted from specialised cells, in organs called glands.
These glands make up the endocrine system.
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pituitary gland
The pituitary gland is called the master gland because the hormones it secretes control a lot of the other glands in the endocrine system e.g. ADH. It is position just below the brain.
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thyroid gland
The thyroid gland in the throat, secretes many hormones, an example of, which is thyroxine, which helps to control the rate of metabolism in the body.
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pancreas
The pancreas has many jobs such as releasing enzymes for digestion. But in addition to this, it can also make hormones. Insulin is an example which helps the lower the amount of glucose in the blood.
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adrenal gland
The adrenal gland, sit on top of the kidneys and can secrete adrenaline which helps the control our fight or flight response.
56
reproductive hormones
The testes and males release testosterone. And the ovaries in females release oestrogen. Both of these hormones, controlled a secondary sexual characteristics, that aren't present in a person from birth
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How are hormones transported across the body
gland = yellow cells
hormone = green triangles
The hormones are synthesised in the cells of the gland. Once the hormones have been synthesised, they are secreted into the blood and travelled through the circulatory system until they meet their target cells. The target cells have protein receptors on the outside that can bind to the hormone in a similar way.
when the hormone binds to the receptor on the target cell. It triggers chemical reactions in the target cells that brings about the required response.
It is possible for one hormone to have lots of different target cells. For example, there are lots of different types of target cells that respond to the hormone adrenaline because adrenaline causes lots of reactions in different parts of the body.
Any cell that does not need to respond to the hormone If called a non target cell and does not have any receptors that can bind to the hormone
58
how is the blood glucose level controlled
59
type 1 diabetes
cause - pancreas fails to produce sufficient insulin to control blood glucose levels
Scientists think this is a result of a person’s own immune system destroying the cells of the pancreas that make insulin during development
treatment - monitoring blood glucose levels and injecting insulin throughout the day based on carbohydrate content of meals and quantity of excercie done - this can be carried out manually or using an insulin pump
60
type 2 diabetes
cause - body cells no longer respond to insulin produced by the pancreas - the person still makes insulin but their cells are resistant to it
treatments - A carbohydrate-controlled diet and an exercise regime
risk factor - Obesity - a person who is obese may consume a diet high in carbohydrates, and over-production of insulin results in resistance to it developing
61
what do the kidneys do
The kidneys filter the blood and remove urea from the blood while regulating the water and ions levels by absorbing some of it back into the blood. All of the glucose is absorbed back into the blood. This is called **selective reabsorbtion**. The substances removed from the blood is excreted from the body as urine
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deamination
Deamination is the process of converting excess amino acids which can't be stored in the body into fats and carbohydrates which can be stored. This occurs in the liver. Ammonia is produced as a waste product from this process. It is toxic so it's converted to urea in the Liver.
63
ions
ions enter the body through your diet and exit the body through sweat. These are both unregulated by the body so the kidney must regulate the number of ions in the blood
if the ion content is too low or water content is too high (too dilute) then water will move into the cells via osmosis causing them to swell or poentially burst
if the ion content is too high or water content is too low (too concentrated) then water will move out of the cells via osmosis causing cell crenation
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water
water enters the body through your diet and from aerobic repiration and exit the body through sweat and breathing.These are all unregulated by the body so the kidney must regulate the quantity of water in the blood
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step 1 in kideys making urine - filtration
the process starts with filtration which is where some of the liquid part of the blood is forced from the glomerulus which is this tangle of blood vessels into the bowman's capsule which is the start of the tubule
importantly though only very small substances can be filtered through to the bowman's capsule e.g., water, amino acids, urea, glucose and ions not anything large like cells or proteins
Overall only about 20 percent of the plasma in the blood is filtered through to the bowman's capsule as it passes
through the glomerulus. The rest of the blood just carries on
through the blood vessels
66
overview of kidneys function
blood constantly cycles through the kidneys passing in through the renal arteries and out through the renal veins from this blood the kidneys produce urine which passes down the ureters and is stored in the bladder until we urinate it out through the urethra.
67
nephron location
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step 2 in kideys making urine - selective reabsortion
the fluid passes along the tubules and the kidneys reabsorb all the things that they want back into the blood vessels by selective reabsortion:
* all of glucose & amino acids
* some of water & ions
* no urea
69
step 3 in kideys making urine - final stage
The collecting duct receives fluid from many nephrons and any fluid that passes out of the collecting duct is classed as urine.
The urine passes down the ureter to the bladder and can then be released as waste
70
How water levels are regulated
inside the brain there's a structure called the hypothalamus which detects the concentration of water in the bloodstream:
1. If hypothalamus detects high concentration of blood (low water levels) it sends signal to pituitary gland
2. The sigal tells the pituitary gland to release a hormone called ADH or antidiuretic hormone into the bloodstream
3. as the adh travels around the body it reaches the kidneys and increases the permeability of the kidney tubules so more water is reabsorbed into the blood
4. therefore the amount of water in the bloodstream increases and as a result we produce less urine
1. If hypothalamus detects high water levels it stops sending signals to the pituitary gland
2. so with less signals, less ADH is released
3. less adh travels reaches the kidneys so permeability of the kidney tubules decreases so less water is reabsorbed into the blood
4. therefore the amount of water in the bloodstream decreases and as a result we produce more urine
71
2 treatment options for kidney failure
1. Having dialysis treatment
where machines do the job of the kidneys.
2. Having a kidney transplant where the diseased kidney is replaced by a healthy one.
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How does a dialysis machine work?
In a dialysis machine the person's blood flows alongside a partially
permeable membrane, surrounded by dialysis fluid.
The partially permeable membrane allows things like ions and waste substances through, but not big molecules like proteins (just like the membranes in the kidney). The dialysis fluid has the same concentration of dissolved ions and glucose as healthy blood. This means that useful dissolved ions and glucose won't be lost from the blood during dialysis. Only waste substances (such as urea) and excess ions and water diffuse across the membrane.
The dialysis fluid constantly flows in and out of the machine to make sure the fluid in the machine always has the same concentration as healthy blood.
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kidney dialysis - cons
* Dialysis is not a pleasant experience and many patients with kidney failure have to have a dialysis session 3 times a week. Each session takes 3-4 hours
* Dialysis can lead to infections and can cause blood clots.
* Dialysis patients have to be careful about what they eat to avoid too much of a particular ion building up between dialysis sessions.
* Patients have to limit the amount of fluid they take in, as the kidneys play an important role in maintaining the water content of the body. When the kidneys aren't functioning properly, fluid can build up in the body, which can be dangerous- - for example, it can cause the volume of blood to increase, leading to high blood pressure.
* Kidney dialysis machines are expensive things for the NHS to run.
74
Kidney transplants
At the moment, the only cure for kidney disease is to have a kidney transplant. Healthy kidneys are usually transplanted from people who have died suddenly, say in a car accident, and who are on the organ donor register or carry a donor card (provided their relatives agree too). Kidneys can also be transplanted from people who are still alive (as we all have two kidneys, but can survive with just one) but there is a small risk to the person donating the kidney.
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Kidney transplants cons - rejection
A problem of kidney transplants is that the donor kidney can be rejected by the recipient's immune system - this happens when antigens on the donor kidney aren't recognised as being part of the body by the recipient's white blood cells. The white blood cells produce antibodies to attack the donor cells as a result
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Kidney transplants - preventing rejection
* A donor with a tissue-type that closely matches the patient's is chosen. Tissue-type is based on a cell's antigens. The more similar the tissue-types of the donor and the patient, the more similar the antigens. This reduces the chance of the patient's white blood cells identifying the donor antigens as 'foreign' and producing antibodies to attack the donor organ.
* The recipient is treated with drugs that suppress the immune system. These drugs reduce the production and release of antibodies by the white blood cells, so that the immune system won't attack the transplanted kidney.
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Kidney transplants cons - other
* There are long waiting lists for kidneys.
* Even if a kidney with a matching tissue-type is found, there's still the possibility that it'll be rejected. Taking drugs that suppress the immune system means the person is vulnerable to other illnesses
* and infections. A kidney transplant is a major operation, so it can be risky.
Despite these problems, kidney transplants can put an end to the hours spent on dialysis, allowing recipients to lead a relatively normal life. Transplants are also cheaper than long-term dialysis treatment
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puberty
the period during which adolescents start to develop secondary sexual characteristics.
e.g. facial hair in men and breasts in women
This process is triggered by reproductive hormones which are mainly testosterone in men which is produced in the testes and also stimulates sperm production and Oestrogen in women which is produced by the ovaries
79
female reproductive system
Eggs are kept inside the ovaries and after ovulation they transported along one of the fallopian tubes over to the uterus. If the egg was fertilized during its journey, then it
would implant into the uterus lining, otherwise it would break down and pass out.
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menstual cycle
(28 days)
stage one - menstruation: when uterus lining breaks dwon- is a period of bleeding that normally lasts about four days.
Stage two-( when oestrogen levels are rising) : is when the uterus lining starts to build up again and becomes a thick spongy layer with lots of blood vessels in it. It lasts around ten days up to day 14- when egg is released- and its role is to prepare the uterus lining for the zygote (fertilized egg) because if there is a fertilised egg, it implants into the uterus lining.
Stage three is ovulation (LH produced) - this takes place in a single day and involves the egg being released from one of the ovaries.
stage four (progesterone levels increase)- stretches all the way to day 28 and it involves maintaining the lining of the uterus.
end of cycle- if no fertilized egg has made it to the uterus then the uterus wall would start to breakdown so we'll be back to stage 1 and cycle repeats. if there was a fertilized egg then it would implant into the uterus lining and slowly develop into a fetus
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Oestrogen
Oestrogen is secreted in the ovaries and it stimulates uterus lining to thicken, ready to recieve zygote. stops FSH production. controls progress of maturing follicle, so has a small 'spike' just before ovulation. hormone targets- uterus
82
progesterone
after ovulation, the remainder of the follicle becomes the corpus luteum. The corpus luteum produces progesterone. It maintains the thickness of the uterus lining. If fertilisation occurs progesterone levels remain high, and placenta takes over progesterone production during pregnancy. If no fertilisation- ovum + corpus luteum break down- progesterone levels drop- uterus lining breaks down- menstruation. hormone targets- uterus
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luteinizing hormone LH
luteinizing hormone -LH- is secreted from the pituitary gland. Stimulates ovulation (release of ovum from ovary), on day 14. hormone targets- ovaries
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follicle stimulating hormone FSH
follicle stimulating hormone FSH is secreted from the pituitary gland. It stimulates one of the eggs to mature/develop in one of the ovaries. Stimulates oestrogen production. hormone targets- the follicles in the ovaries
85
how hormones interact with each other during menstual cycle
once menstruation over:
FSH is secreted by the pituitary gland which stimulates egg development in one of the ovaries.
FSH also stimulates the ovaries to produce/secrete oestrogen which is why we see higher levels of FSH just before oestrogen starts to increase.
As the oestrogen level starts to increase it inhibits FSH production while stimulating the uterus lining to thicken. when oestrogen levels get high/ spike just before day 14, it stimulates the pituary gland to secrete LH, leading to ovulation.
The empty follicle after ovulation- corpus luteum- produces progesterone which inhibits pituary gland secreting LH and FSH while maintaining the uterus lining.
If fertilisation- progesterone levels remain high+ placenta takes over progesterone production during pregnancy.
if no fertilisation- ovum+ corpus luteum break down, thus progesterone levels drop, so uterus wall breaks down, and menstruation begins again.
86
Reducing fertility
Contraceptives are used to prevent pregnancy. The hormones oestrogen and progesterone can be taken ( inhibits LH +FSH) by women to reduce their fertility (their ability to get pregnant) and so are often used as contraceptives.
87
Oestrogen - use in reducing fertility
Oestrogen can be used to prevent egg release. This may seem kind of strange (since naturally oestrogen helps stimulate the release of eggs), but if oestrogen is taken every day to keep the level of it permanently high, it inhibits FSH production. This means that, after a while, egg maturation and therefore egg release stop and stay stopped.
88
Progesterone - use in reducing fertility
Progesterone also reduces fertility, e.g. by stimulating the production of thick cervical mucus which prevents any sperm getting through and reaching an egg. It can inhibit egg maturation and therefore the release of an egg too. inhibits FSH+ LH production.
89
combined Oral contraceptive pill
The pill is an oral contraceptive (it can be taken by mouth to decrease fertility). The first version (known as the combined oral contraceptive pill) was made in the 1950s and contained high levels of oestrogen and progesterone.
However, there were concerns about a link between oestrogen in the pill and side effects like blood clots. The pill now contains lower doses of oestrogen so has fewer side effects.
There's also a progesterone-only pill - it has fewer side effects than the combined pill and is just as effective.
90
Benefits of the combined oral contraceptive pill
* The pill's over 99% effective at preventing pregnancy.
* It's also been shown to reduce the risk of getting some types of cancer.
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Problems with the combined oral contraceptive pill
* It isn't 100% effective - there's still a very slight chance of getting pregnant.
* It can cause side effects like headaches, nausea, irregular menstrual bleeding, and fluid retention.
* It doesn't protect against STDs (sexually transmitted diseases).
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contraceptive patch
The contraceptive patch contains oestrogen and progesterone (the same as the combined pill). It's a small (5 cm x 5 cm) patch that's stuck to the skin. Each patch lasts one week.
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contraceptive implant
The contraceptive implant is inserted under the skin of the arm. It releases a continuous amount of progesterone, which stops the ovaries releasing eggs, makes it hard for sperm to swim to the egg and stops any fertilised egg implanting in the uterus. An implant can last for three years
94
contraceptive injection
The contraceptive injection also contains progesterone. Each dose lasts 2 to 3 months.
95
Intrauterine devices
An intrauterine device (IUD) is a T-shaped device that is inserted into the uterus to kill sperm and prevent implantation of a fertilised egg. There are two main types - plastic IUDs that release progesterone and copper IUDs that prevent the sperm surviving in the uterus.
96
Barrier methods - condoms
Condoms are worn over the penis during intercourse to prevent the sperm entering the vagina. There are also female condoms that are worn inside the vagina. Condoms are the only form of contraception that will protect against sexually transmitted diseases.
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Barrier methods - diaphragm
A diaphragm is a shallow plastic cup that fits over the cervix (the entrance to the uterus) to form a barrier. It has to be used with spermicide (a substance that disables or kills sperm). Spermicide can be used alone as a contraceptive, but it's not as effective as when used with a diaphragm.
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Surgical methods - Sterilisation
Sterilisation involves cutting or tying the fallopian tubes (which connect the ovaries to the uterus) i a female, or the sperm duct (the tube between the testes and penis) in a male. This is a permanent procedure. However, there is a very small chance that the tubes can rejoin.
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Natural methods
Pregnancy may be avoided by finding out when in the menstrual cycle the woman is most fertile and avoiding sexual intercourse on those days. It's popular with people who think that hormonal and barrier methods are unnatural, but it's not very effective. The only way to be completely sure that sperm and egg don't meet is to not have intercourse - this is abstinence
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hormonal methods of contraception
combined oral contraceptive pill
contraceptive patch
contraceptive implant
contraceptive injection
plastic Intrauterine devices
101
non hormonal methods of contraception
condoms
diaphram
copper Intrauterine devices
Surgical methods - Sterilisation
Natural methods
102
Increasing fertility
Hormones can be taken by women to increase their fertility. For example, some women have an FSH level that is too low to cause their eggs to mature. This means that no eggs are released and the women can't get pregnant. The hormones FSH and LH (see page 236) can be injected by these women
to stimulate egg maturation and release in their ovaries. These 'fertility drugs'
can help a lot of women to get pregnant when previously they couldn't.
They are often used during IVF too
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In vitro fertilisation (IVF)
IVF involves the following steps: 1. FSH and LH are given to
the woman to stimulate the
maturation of multiple eggs.
2. Eggs are then collected from the woman's ovaries.
3. The eggs are fertilised in a lab using the man's sperm.
4. The fertilised eggs then grow into embryos (small balls of cells) in a laboratory incubator.
5. Once the embryos have formed, one or two of them are transferred to the woman's uterus. Transferring more than one improves the chance of pregnancy
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pros of IVF
The main benefit of IVF is that it can give an infertile couple a child
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cons of IVF
* Multiple births can happen if more than one embryo grows into a baby - these are risky for the mother and babies (there's a higher risk of miscarriage, stillbirth...).
* The success rate of IVF is low - the average success rate in the UK is about 26%. This makes the process incredibly stressful and often upsetting, especially if it ends in multiple failures.
* As well as being emotionally stressful, the process is also physically stressful for the woman. Some women have a strong reaction to the hormones - e.g. abdominal pain, vomiting, dehydration.
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Social and ethical issues with IVF
The process of IVF often results in unused embryos that are eventually destroyed. Because of this, some people think it is unethical because 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.
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Developments in microscopy - IVF
Advances in microscope techniques have helped to improve the techniques (and therefore the success rate) of IVF.
Specialised micro-tools have been developed to use on the eggs and sperm under the microscope.
More recently, the development of time-lapse imaging (using a microscope and camera built into the incubator) means that the growth of the embryos can be continuously monitored to help identify those that are more likely to result in a successful pregnancy.
108
Thyroxine
Thyroxine 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. It is also important for loads of processes in the body, such as stimulating protein synthesis for growth and development.
Thyroxine is released in response to thyroid stimulating hormone (TSH), which is released from the pituitary gland.
109
tsh and thyroxine negative feedback relationship
When the level of thyroxine in the blood is higher than normal, the
secretion of TSH from the pituitary gland is inhibited (stopped).
This reduces the amount of thyroxine released from the thyroid gland,
so the level in the blood falls back towards normal.
When the level of thyroxine in the blood is lower than normal, the secretion of TSH from the pituitary gland is stimulated (started up) again. This increases the amount of thyroxine released from the thyroid gland, so the level in the blood rises back towards normal.
110
Adrenaline
Adrenaline is a hormone released by the adrenal glands.
It is 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. Adrenaline gets the body ready for 'fight or flight' by triggering mechanisms that increase the supply of oxygen and glucose to cells in the brain and muscles. For example, it increases heart rate.
111
Auxin
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 different stimuli - e.g. light / gravity
112
Phototropism
Phototropism - plant growth in response to light
positive Phototropism - plant grows towards light
negative Phototropism - plant grows away from light
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Gravitropism / geotropism
Gravitropism (also known as geotropism) plant growth in response to gravity.
positive Phototropism - plant grows down - towards gravity
negative Phototropism - plant grows up - away from gravity
114
auxin - shoots - light
Shoots - Positive phototropism
Auxin is produced at the **base** of the **tip** of the plant. As light is shining from the side, more **diffuses** down the **shaded** side of the shoot
Therefore, there is **uneven distribution** of auxin on both sides of the shoot, which causes **unequal growth and elongation** of cells on shaded side of the shoot (the shaded side grows more). Therefore the plant grows towards the light.
115
auxin - shoots - gravity
Shoots – negative geotropism
When a shoot lays sideways, gravity causes an uneven distribution of auxin in the tip (more auxin on lower surface)
In shoots, auxin promotes growth, so the presence of higher levels of auxin causes the lower side to grow faster, which bends the shoot upwards – away from gravity.
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auxin - roots - gravity
Root – positive geotropism
When a root lays sideways, gravity causes an unequal distribution of auxin in the tip (more auxin on lower surface)
In the roots, high auxin levels inhibit cell elongation
Therefore the upper surface of the root grows more quickly than the lower surface; so the root grows downwards – towards gravity
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Auxins - use for controlling plant growth.
Auxins are useful for controlling plant growth. They are used for:
1. Killing weeds
2. Growing from cuttings with rooting powder
3. growing cells in tissue cultures
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Auxins - use for controlling plant growth - Killing 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 weedkillers 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.
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Auxins - use for controlling plant growth - Growing 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 add rooting powder, which contains auxins, they will you produce roots rapidly and start growing as new plants. This enables growers to produce lots of clones (exact copies) of a really good plant very quickly.
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Auxins - use for controlling plant growth - Growing cells in tissue culture
Tissue culture can be used to grow clones of a plant from a few of its cells (see page 312). To do this,
hormones such as auxins need to be added to the growth medium (along with nutrients) to stimulate the cells to divide to form both roots and shoots.
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Gibberellins
Gibberellins are another type of plant growth hormone. They stimulate seed germination (when a seed starts to grow into a plant), stem growth and flowering. Uses include:
1. Controlling dormancy
2. Inducing flowering
3. Growing larger fruit
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Gibberellins - Controlling dormancy
Lots of seeds won't germinate until they've been through certain conditions (e.g. a period of cold or of dryness). This is called dormancy. Seeds can be treated with gibberellins 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.
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Gibberellins - Inducing flowering
Some plants require certain conditions to flower, such as longer days or low temperatures. If these plants are treated with gibberellins, they will flower without any change in their environment. Gibberellins can also be used to grow bigger flowers.
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Gibberellins - Growing larger fruit
Seedless varieties of fruit (e.g. seedless grapes) often do not grow as large as seeded fruit. However, if gibberellins are added to these fruit, they will grow larger to match the normal types.
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Ethene
Ethene is a gas produced by aging parts of a plant. It influences the growth of the plant by controlling cell division. It also stimulates enzymes that cause fruit to ripen
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Ethene use
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 that fruit can be picked while it's still unripe (and therefore firmer and less easily damaged). The gas is then added to the fruit on the way to the supermarket so that it will be perfect just 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 air.
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similarites and diffrences between nervous system and endocrine system
Both have the similarities of sending signals around the body to help to regulate the conditions inspired the body that part of homeostasis. both trigger responses in the body from their signals.
