Homeostasis

HomeostasisHomeostasis is the balancing of body functions to maintain constant internal environmentThe body needs to be kept in a steady condition so that the cells in the body can perform correctly and efficiently. Therefore there needs to be a balance of what goes into your body (inputs) and what leaves the body (outputs)Water needs to be kept in balance, you need to balance water you gain and water you loose, as all cell activity needs water to function.Body temperature needs to be maintained for enzyme reactions for instance, so there needs to be a balance to be able get rid of excess heat, but also to be able to retain it when it is cold.Homeostasis is the maintenance of a constant internal environment

Water loss from the body happens in a number of ways:Through the skin as sweatFrom the lungs as breathFrom the kidney's as urineMaintain the water balance between sweat and urine can depend on what you have been doing during the day or even what the weather is like.

On a hot day, or if you are exercising  you sweat a lot.less urine will be produced and it will be more concentrated, deeper in colour, because it is less dilute with water.You will also loose more water through your breath when you exercise as you will breathe faster.

On a cold day, or when you don't exercise, you don't sweat much.You'll produce more urine which will be pale as it will be more dilute with water.

Body temperature is maintained at 37 degrees.All enzymes work best as specific temperature, an optimum temperature for the enzymes in the human body is 37 degrees, for this reason the body needs to maintain this temperature at a constant.The human body has its own personal thermostat, it is sensitive to the temperature of the blood in the brain, and receives messages from temperature receptors in the skin, providing information on the skin temperature.Dependant on the information received by these receptors, depends on what activations the CNS will make to ensure your body temperature stays just right.

The skin helps to regulate the bodies temperature via thermoregulation.When receptors in the skin tell the CNS that it is hot,  The skin will produce lots of sweat, when the sweat evaporates, it transfers heat from you out the the environment, cooling you down.The blood vessels near the surface of the skin widen, called vasodilation, this allows more blood to circulate near the surface of the skin, releasing heat into the environment.The hairs no the skin lie flat.Conversely, when your skin receptors tell the CNS that its cold,  Very little sweat is produced, the blood vessels near the surface of the skin contract, vasoconstrction, reducing the heat lost from the blood flowing close to the skins surface.You shiver, this movement generates heat in the muscles, much similar to exercise.Hairs on the skin stand up, to trap an insulating layer of air which helps to keep you warm

Smaller organisms have a bigger surface area to volume ratio.These organisms that have a larger surface area to volume ration can gain or lose heat faster, this is because there is more area for the heat to transfer across.This will allow small organisms to loose heat quicker in warm environments, this would reduce the risk of them overheating, it does mean that they would be at risk in colder climates.Organisms that have a smaller ratio gain or loose heat more slowly, as there is less area for heat to transfer across.This is why animals loving in cold conditions have a compact, rounded shape to keep their surface area to a minimum, reducing heat loss.

Stimuli and responses in plants.Plants are able to respond to stimuli too, these responses help to ensure the plant will grow and survive.Plants sense direction of light, and will grow toward the light to maximise photosynthesis.Plants can sense gravity, this ensures that their roots and shoots grow in the right direction.Plants that climb are sensitive to touch, so they can climb and attach themselves to things when reaching the sunlight.PredatorsPlants that respond to being eaten, by avoiding being eaten, have a better chance to survive.White clover produces a toxin, this toxin reduces the chances of being eaten by cattle.Abiotic StressAbiotic stresses are things like drought and extreme cold.Carrots produce their own form of anti freeze, this binds to the ice crystals and lower the temperature at which water freezes, reducing the formation of  more ice crystals.

AuxinsAuxins are plant growth hormones,  These growth hormones control the growth at the tip of shoots and roots, they move through the plant in solution, dissolved in water.Auxin is produced in the tips and diffuses backwards, the auxin causes cells to elongate behind the tip.Auxin promotes growth in plant shoots, but inhibits it in roots.Auxins are involved in the growth response of plants to light (Phototropism) and the response to gravity (Geotropism).

Shoot and root growth and AuxinShoots are positively phototrophic, meaning they grow towards the light.  When the tip of a shoot is exposed to light, it accumulates more auxin on the side of the shoot which is in the shade.  Auxin then starts an elongation process, the shaded plant cells elongate making the shoot bend towards the light.Shoots are negatively geotrophic, this means they will grow opposite to gravity.  When a shoot grows sideways, gravity produces and unequal amount of auxin to develop on the lower side, this causes the cells to grow faster and the shoot bends upwards.Roots are positively geotrophic, this means they grow towards gravity. A root growing sideways, will also have a greater amount of auxin on its lower side, but unlike in the shoot, in a root, the auxin inhibits growth, this action causes the upper cells to grow faster and the root to bend downwards.

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