Unit 6 - Organisms respond to changes in their internal and external environments
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Cells and Organisms Carry Out Exchanges with their External Environment in order to Maintain their Internal Environment
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Unit 6 - Organisms respond to changes in their internal and external environments
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Cells and Organisms Carro Out Exchanges with their External Environment in order to Maintain their Internal Environment full essay. Word count 1048, mark = 17/25
Unit 6 - Organisms respond to changes in their internal and external environments
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Cells and Organisms Carry Out Exchanges with their External Environment in order to Maintain
their Internal Environment.
Exchange with the external environment of cells and organisms is very important for the
maintenance of their internal environment. Exchange can take the form of diffusion, osmosis, or
active transport, and is used by cells and organisms to maintain their internal environment in
many ways. These include gas exchange, transport of water in a plant, tissue fluid and its
formation, negative feedback, and the nerve impulse.
Gas exchange is a major way cells and organisms maintain their internal environment. In cells,
the exchange of oxygen and carbon dioxide is carried out by diffusion to ensure that the cells
can function properly as they are able to respire. Organisms also carry out gas exchange -
breathing. In insects, gas exchange is carried out through spiracles, which open and close to
allow gas exchange and limit water loss. Plants carry out gas exchange through stomata in a
similar way. Fish exchange gases in their gills, and use the countercurrent exchange principle.
Their blood flows in the opposite direction to the water flowing through the gills. This ensures
the maximum diffusion of oxygen from the water to the blood, and also that an oxygen diffusion
gradient is maintained along the full length of the gills. This therefore maintains the internal
environment of the fish, as its cells are able to respire and function properly. In mammals, gas
exchange happens in the lungs. The alveoli in the lungs have a maintained diffusion gradient of
oxygen and carbon dioxide to ensure a constant supply of oxygen. This oxygen is transported
around the body in the blood so cells can use it for respiration in order to function properly.
Carbon dioxide is also removed from the body, so it does not stay in the body as waste.
Therefore, gas exchange maintains cells and organisms internal environments as it means that
cells have a good supply of oxygen so they can respire and function.
The transport of water in a plant is also a way of maintaining the internal environment. Water
molecules move out of the stomata on the leaves, along with gases. This is due to the water
potential gradient created as a result of the different humidities. Water vapour diffuses out of the
stomata, into the air spaces near them. This water is then replaced by osmosis of water into
mesophyll cells from neighbouring cells, which establishes a water potential gradient and pulls
water from the xylem. The hydrogen bonds between water molecules cause them to ‘stick’
together - a force called cohesion. When water is lost from the surface of the leaf by
evaporation, the continuous, unbroken column of water molecules means that more water
molecules are drawn up behind the lost water molecules. The column of water is therefore
moving up the xylem, called the transpirational pull. This water movement maintains the internal
environment as it prevents the plant from overheating, and also the water can be used by the
plant cells in processes such as photosynthesis. This keeps the plant alive as it provides the
plant with food.
Tissue fluid and its formation is important for the maintenance of the internal environment of
cells and organisms. Tissue fluid is a liquid that contains glucose, amino acids, fatty acids, ions
and oxygen. It is the immediate environment of cells, and is the means by which materials are
exchanged between blood and cells that are too far from the capillaries. It is formed by
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