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Homeostasis is the maintenance of a constant internal environment within the body.
This sounds quite confusing but don’t panic – in simpler terms, homeostasis is the process which works to keep the conditions inside the body the same. This means that the reactions happening within cells can happen under their optimum conditions, which in turn means they are more efficient.
Here are some examples of conditions that need to be regulated:
Blood sugar level
Homeostasis works because of negative feedback mechanisms. Negative feedback mechanisms work like this:
A change in the system from normal à this change is detected à control mechanisms are activated, returning conditions to normal à control mechanisms are switched off
Regulation of Body Temperature
Optimum body temperature is 37.5ºC. When body temperature is different from this, control mechanisms are activated to return the body to its optimum temperature.
When too hot:
Vasodilation – blood vessels dilate allow more blood to flow through the skin.
Sweating – when sweat evaporates it removes heat energy from the skin.
When too cold:
Vasoconstriction – blood vessels constrict, conserving heat in the center of the body
Shivering – shivering is caused by muscle contraction. Some of the energy produced by respiration of the muscle cells will be lost as heat, increasing body temperature.see more
Osmosis is the movement of water from a high concentration to a low concentration through a partially permeable membrane. It is a special type of diffusion.
You may get questions asking you to decide which way direction water will flow through a partially permeable membrane. Always remember that water will move from the side with highest water concentration (lowest solute concentration) to the side with the lowest water concentration (highest solute concentration).
Cell membranes exist in all cells. They are partially permeable membranes as they allow small molecules such as water molecules to diffuse through them, but not larger molecules such as sugars and salt ions. Osmosis can therefore happen in and out of cells, effecting the amount of water in the cell.
Plants are supported by the water pressure in their cells (this is useful because they do not have a skeleton). This movement of water in and out of plant cells is due to osmosis. If a cell is placed in pure water, water will move into the cell by osmosis. This is because it will move from a higher concentration in the pure water to a lower concentration in the cell, until the amount of water on each side of the permeable membrane is the same – until equilibrium is reached.
It can have consequences:
If too much water enters the plant cell it becomes turgid – completely full with water.
If too much water leaves the plant cell it becomes plasmolysed – the cell becomes limp and the cell membrane comes away from the cell wall.
A similar effect can be seen in animal cells, such as human red blood cells:
If too much water enters the animal cell it can burst – lysis
If too much water leaves the animal cell it can shrink – crenation
Animal cells burst and shrink, unlike plant cells, because they do not have the strong cell walls that plants have.see more