Biology, Paper 2- Homeostasis and Response


The Importance of Homeostasis

Homeostasis is the regulation of the internal conditions of a cell in response to internal or external changes. 

This means it is important as it keeps conditions constant for proper enzyme function- meaning they work close to their optimum, and other cell functions.

This includes the control of: Blood glucose concentration, body tempurature, water and ion levels. 

This can be done using: the nervous system, chemical responses using hormones. 

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Control Systems

Control systems are a way of controling the regulation of body conditions, eg via nerves or by hormones. 

All control systems include: 

- receptor cells, which detect stimuli or changes in the environment. 

- coordination centres (like the brain, spinal cord or pancreas) which recieve and process information and compares the stimulous to a set point.  

- effectors (muscles or glands) which bring about the changes needed to regulate the conditions, and correct the difference in a set point. 

this happens in a cycle, which is called negative feedback. 

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The Nervous System

The nervous system allows us to respond to our environments as well as coordinate behaviour. This system deals with voluntary and involutary actions =, by sending electrical impulses along nerves, meaning responses are very quick. 

In voluntary actions: information from receptors passes to the central nervous system, the brain and spinal cord. This coordinates the response of effectors (like mucles contracting or glands secreting hormones). 

However response can also be involutary (reflex actions) in order to protect the body (flight or fight) these dont involve the concious part of the brain. 

Eg. a pain stimulus is detected by pain receptors, so elecrical impulses pass allong a sensory neuron to the spinal cord, the impulse then passes through a relay neuron and a motor neurone passes an impulse to an effector (like a muscle- eg to draw the limb away from what is causing pain). 

Stimulus, Receptor, Sensory Neurone, Spinal Cord, Relay Neurone, Motor Neurone, (Synapses), Effector. can be remebered as Some Rabbits Sleep, Some Rabbits Mate Energeticly 

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Neurones are not directly connected to each other, instead they communicate via synapses which are the gaps between neurones. 

When a nerve impulse travels along the neuron the nerve ending is triggered to release chemical messengers called neuro-transmitters. These chemicals then diffuse across the synapse and bind with receptor molecules on the membrane of the next neurone. The receptor molecules on the second neurone bind only to specific chemicals released from the first neurone, this stimulates the second neurone to transmit and electrical immpulse. 

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The Brain

Brain Puzzles Image: มิถุนายน 2013Frontal lobe- concerned with higher brain functions (decision making, concious of emotions, reasons) It also includes the motor cortex which stores information on how to do some movements. 

Pariatal lobe- orientation, movement, calculation and recognition. 

Occipital lobe- visual cortex, proccesses information from eyes. 

Temporal lobe- processes auditory information and memory. 

Cerebellum- coordinates movement and balance. 

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The Brain (2)

medulla oblongata- controls heartbeat 

hypothalamus- thermoregulates body tempurature 

The brain overall controls complex behaviour, and is made of billions of neurons which are interconnected. 

Neuroscientists have been able to map the regions of the brain and their functions by: studying patients with brain damage, electically stimulating parts of the brain, animal studies, study during surgary, using MRI scans/ non invasive techniques.  However the complexity of the brain makes investigating and treating brain disorders difficult. 

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The Eye

BBC - GCSE Bitesize Science - The eye : RevisionThe eye is a sense organ:

- Retina, contains receptor cells which are sensitive to light. 

- Optic nerve, carries impulses from the retina to the brain 

-Sclera, a tough outer layer with a transparent region at the front of the eye. which is callled the cornea. 

- Iris, controls the size of the pupil and hence the amount of light reaching the retina

-Ciliary muscles and suspensory ligaments can change the shape of the lens to focus the correct amount of light on the retina. 

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How the Eye Focuses Light

the eye can focus light in a process called accomodation, this is where the shape of the lens is changed to focus on near or distance objects. 

To focus on a near object:

- the cillary muscles contract. 

- suspesensory ligaments loosen

- this means the lens becomes thicker and refracts light rays more strongly. 

this is needed for the lens to focus the image on the retina, this light then triggers electrical impulses- which are sent to the brain to process. 

eye | PMG Biology

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How the Eye Focuses Light (2)

To focus on a distant object:

- Cillary muscles contract

- Suspensory muscles loosen 

- the lens gets thinner and so only refracts light rays slightly. 

Sometimes the image will not focus on the retina, this can be in myopia (short sightedness- the image doesnt reach the retina) or hyperopia (long sightedness- the image goes past the retina)

These defects can be sorted using glasses lenses (concave for mypoia, convex for hyperopia), or lazer eye surgery to change the shape of the cornea. this means light can focus on retina, as the way light is refracted has changed. 

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Control of Body Temperature

Body temperature should be kept about 37 degrees, which gives the optimum tempurature for enzymes to work. Thermo regulation happens in the hypothalmus, which moniters and controls the body tempuratures. 

The hypothalumus does this as it has receptors monitoring the tempurature of the blood flowing in the brain. it also recieves impulses from tempurature receptors in skin cells. if it detects changes in tempuratures, it will use Vasolation and Vasoconstriction to return temperature to normal. 

Vasodilation (too hot): - blood vessels widen (dilate) allowing more blood to flow to the skins surface (skin looks redder), Nerve impulses them stimulate swear glands to release sweat, this uses body heat on the skin's surface to evaporate- using body heat and cooling us, hairs also flatted to allow the least insulation, we may also have behavoural changes- such as removing layers to cool down. 

Vasoconstriction (too cold): - blood vessles constrict, allowing less blood to the skin, this means it radiates less heat, and keeps it at the core instead. Reduce sweating. you shiver releasing heat, as muscles contract involunatarily, using energy to respire and releasing heat, hairs may stand on end to offfer insulation. we may also have behavoural changes like adding layers. 

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The Endocrine System

The endocrine system is made up of glands which secret hormones directlyy into the blood stream. Hormones are made of protiens. Hormones are chemecal messangers and are secreated by glands, and travels through the bloodstream to a trarget organ or tissue, because they travel through the bloodstream, their effects are slower than electrical impulses, however their effects are longer lasting. The Pituitary gland is th master gland in the brain, it secretes many hormones in response to body conditions. these hormones may also act on other glands to stimulate other hormones being released to bring about effects. 

GCSE Biology B1 2.5 | The Note-Taker

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- ADH, produced by pituitary gland, targeted to the kidney, to control the volumn of water in urine.

- TSH,  produced by pituuitary gland, targeted to the thyroid, controls therelease of hormones from the thyroid. 

- Thyroxine, produced by thyroid gland, targeted to the Heart, controls how quickly energy is used, making protiens, how sensitive organs are to other hormones. 

- Adrenaline, produced by adrenal gland, targeted to various organs, prepares the body for the fight or flight response. 

- Insuline and Glucagon, produced by the pancreas, targets the live, decreases the conversion of blood glucose to glycogen. 

- ostrogen, produced by the ovaries, targeted to reproductive organs, controls puberty and the menstral cycle

- testosterone, produced in the testies, targeted to reprodictive organs, controls puberty

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Blood Glucose

Glucose is used in cells for respiration. This energy is then used for: growth (proteinsythesis of enzymes and antibodies), Cell division, replication of DNA, nerve impulses, active transport, muscle contraction. 

the corect levels of glucose need to be reached because if there is too little there is not enough for respiration and cells die, however if there is too much water would leave the cells by osmosis (as there would be a higher concentration of sugars in the blood). there should be 4-7 mols/dm cubed of glucose in blood. 

If there is a higher BGL (hyperglycemea) this is detected by the pancreas and the hormone of insulin is excreted causing glucose to move from the blood to the cells. In liver and muscle cells this can then be converted into glcogen for storage. 

If BGL are too low (hypoglycemea) this is detected by the pancreas and stored gycogon is excreated. this causes the liver and muscle cells to convert stored glycogen into glucose and release it back into the bloodstream. (this is negative feedback)

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Diabetes is where people cannot easily control their blood sugar levels. The symptoms of both types are; being thirsty, weeing frequently, tiredness. 

Type 1- is caused by environmental and heritatary factors, it usually develops in children and young adults. This is caused when insulin producing cells in the pancreas are destroyed. This means suffers have frequent uncontrolled high BGL's. It can be treated with frequent exersise, insulin injections and a balenced diet. 

Type 2- developed in later life, where the body cells no longer respond to insulin made in the pancreas preventing the conversion of glucose to glycogen. A risk factor is obesity. It ca be treated with a controlled diet and exersise. 

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Water Balance

Water leaves the body from the lungs in breathing (water vapour), from the skin in sweat, and from urine. if the concentration of the blood changes the cells will loose or gain too much water by osmosis, if this happens cells will not functions effeiciently as cytoplasm must have the correct water content to allow metabolic processes to occur. This means the balence of water and concentration of ion in the body is regulated by the kidneys. 

The role of the kidney is to filter glucose, ions, minerals and urea from the blood, it reabsorbs all the glucose and the corect levels of water and ions- all urea is excreated and urine is formed. (4 marks). This is done in millions of small tubes in the kidney called tubules. Where the water, ions and urea and sugar are passed from cappileries in the bloodstream to the tubules and then some are albsorbed (glucose) and others are passed back (most of the water, urea and sugars)

Protiens are also removed by the kidneys. This is because, when protien is consumed it is broken down in the digestive system into amino acids. which are absorbed into the blood. Ecess amino acids not needed for protien synthesis are broken down in the liver into ammonia. Because ammonia is toxic it is immediatly converted to urea and excreted into the urin by the kidneys. 

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Osmoregulation and Dialysis

The control of water and salt levels in the body. 

Increase in water potential is detected by osmoreceptors in the hypothalanmus. This means less ADH is released by the pituraty gland as the blood is less concentrated (more sugars). this means collecting duct walls are less permialble, and so less water is rabsorbed into the blood and more urine is produced. So water potential is reduced. 

Dialisis is a treatment used for people suffering from kidney faliure, meaning the blood isn't filtered. This is a process where:

- Needles liked to a dialisis tube is inserted into a blood vessle. This is then passed through the machine with a partially permiable membrane. on the otherside is the dialisis fluid, because of the concentration of this fluid (low in salt and urea, so it moves out of the blood from diffusion, and equal to the blood in sugars and minerals so they stay where they are) unwanted fluids move from the blood into the dialisis fluid and needed fluids stay in the blood.

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Sex Hormones

Sex hormones in women are oestrogen and progesterone. these are produced by the ovary and cause eggs to mature and be realeased in ovulation. They also cause secondary effects in puberty and cause the menstrual cycle after (until the menopause). 

The sex hormone in men is testerone, this is produced by the testes and stimulate the production of sperm as well as secondary effects in puberty. the sperm will be produced untill death but as less testosterone is produced it is less fertile. 

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The Menstrual Cycle

FSH is released by the pituraty gland in the base of the brain. This causes an egg to mature in the ovary, in the first part of the cycle. This stimulates the ovary to produce oestrogen this causes the uterus lining to thicken after mensturation at the beginning of the cycle. The production of oestrogen inhabits (stops) the produce of FSH, and stimulates the release of LH. The LH causes the release of the egg from the ovaries. After ovulation the empty follicle develops the corpus luten. This releases progesterone which inhabits both production and release LH and FSH, and maintains lining. If no egg is implanted in the wall of the uterus levels of progesterone decrease triggering the loss of the lining and the cycle begins again. 

Making the Gametes | S-cool, the revision website

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Reducing Fertility

Fertility can be reduced by contracepion. This can be hormonal, including methods such as; the pill which contains ostrogen and progesterone which inhabit FSH production so no eggs are released. Or ingections, implants or skin patches with the slow release of progesterone to stop the release of eggs for long periods of time. 

Non-hormonal methods include: barrier methods like condoms or diaphragms stopping the sperm reaching the egg. intrauterine devices like the coil which prevent embryos from implanting in the utereus. spermicide creams which kill sperm. surgical methods of sterilisation such as tying the falopian tubes. natural family planning, only having sex when an egg may be in the oviduct. 

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Increasing Fertility

doctors could give a women FSH and LH in fertility drugs if her own FSH levels are too low for eggs to mature. 

IVF treatment could also be used. This is where the women is given LH and FSH to stimulate the production of many eggs. Collecting these eggs, fertilising the eggs from sperm from the father in a laboratory. inserting the embryos into the woman's uterus. 

This treatment can be amazing in creating pregnancy however it is emotionally and physically stressful, the sucess rate can be low, it could lead to multiple births which risks the babies and the mother. 

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Plant Hormones

plants can respond to changes in the external envrionment. these responses are slower than reponses in animals. some responses they may have are; roots and shoots growing away/towards a stimulus. plants flowering at a particular time. ripening fruits. 

when plants respond to a stumulus it is called a tropism. Eg. if the stumuslus was gravity- growing away = negatively gravitropic, growing towards = positively gravitropic. If the stimulus was light- growing away = negitivly phototropic, growing towards = positively phototropic. 

these tropisms in response to the stimules of light, gravity and water are all controlled by the hormone of auxin. the response to light is shown throung auxin distribution so plants can bend, this is done where if more light reaches one side of a shoot auxins (causing cells to grow) is sent down the shaded side. that means the shaded side grows more and so the shoot bends towards the light. In roots the auxin goes to the upper side of a straight root so it bends downward. 

In shoots the plant grows more on the side with the most auxin. in roots the root grows more in the side with the least auxin (auxin inhibits growth in roots). 

Gibberellines are a group of plant hormones initiating seed gremination. Ethene is a gas and a plant hormone which controls cell divistion and fruit ripening. 

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Uses of Plant Hormones

Many plant growth hormones are used by farmers.

Auxins can be used as weed killers, because they make them grow so rapidly their food reserves are used and they die. they can also be used as rooting powders as they make cuttings produce roots if planted and for promoting growth in tissue culture (needed for plant cloning). 

Ethane can be used to ripen fruit after it is picked unripe to be transported. 

Giberellins can be used to end seed dormancy to make seeds germinate, to promote flowering like at a time when there is most business demand for flowers (mothers day ect.) or to increase the size of the fruit. 

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