Cellular Transport
Your cells need to take in substances that they need, such as oxygen and glucose, and they also need to get rid of waste products and chemicals that are needed elsewhere in the body.
There are 3 main ways that substances can move into and out of the cell:
We are going to look at each one in turn, and highlight some examples of where each form of movement is used.
There are 3 main ways that substances can move into and out of the cell:
- Diffusion
- Osmosis
- Active transport
We are going to look at each one in turn, and highlight some examples of where each form of movement is used.
Diffusion
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There are 3 main things that affect the rate of diffusion:
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Diffusion in living organisms
In living organisms diffusion of dissolved substances such as oxygen, carbon dioxide and glucose occurs into and out of cells across the semi-permeable cell membrane. Semi-permeable means that only certain substances can cross the membrane.
Here are 3 common examples of where diffusion takes place in living organisms:
In living organisms diffusion of dissolved substances such as oxygen, carbon dioxide and glucose occurs into and out of cells across the semi-permeable cell membrane. Semi-permeable means that only certain substances can cross the membrane.
Here are 3 common examples of where diffusion takes place in living organisms:
You might have noticed some common features of diffusion surfaces. There are 4 common ones:
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Osmosis
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Here the membrane is only permeable to water molecules. They will move from an area of high water (dilute solution) to an area of low water (concentrated solution). Thus it will move from the right to the left, and consequently you will see a raise in water level
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Like diffusion, in the case of osmosis the water molecules move in order to try to regain a balance between the two sides
Here are some key words that you need to know:
Isotonic
Having the same concentration of solutes as another solution |
Hypertonic
A solution with a higher concentration of solute molecules than another solution |
Hypotonic
A solution with a lower concentration of solute molecules than another solution |
Osmosis in animals
The concentration inside body cells needs to remain constant in order to function properly. Changes in the concentration of solutes within the cell or of the solutions surrounding the cell can cause water to move into or out of the cell.
These examples illustrate the importance of maintaining a constant internal environment (more about this at a later date when you learn about homeostasis!) |
Osmosis in plants
In plants, osmosis is important to support the stems and leaves, and it's through this process that water enters the plant cells. Water is stored in the cell vacuole, causing it to swell and press the cytoplasm against the cell walls. Plants need the fluid surrounding the cells to always be hypotonic, meaning water will always move into the cell.
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Active Transport
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ATP is what we know of as energy! It comes from cellular respiration - remember this. Cells that undergo a lot of active transport will therefore be packed full of mitochondria, the organelles within which respiration occurs.
See in the above example that the concentration of particles is higher inside the cell than outside, but the carrier protein moves them into the cell. |
The fact that active transport allows cells to move substances into them AGAINST a concentration gradient means they can absorb substances such as ions and sugars from very dilute solutions.
Osmosis is living organisms
There are two common examples that can be used to illustrate the importance of active transport
There are two common examples that can be used to illustrate the importance of active transport
In a nutshell:
- Diffusion and osmosis represent the movement of substances (water in the case of osmosis) from an area of high to low concentration, down a concentration gradient. They are passive, and do not require energy
- Active transport is the movement of substances from low to high concentration, against a concentration gradient. As it's name suggests, it is an active process, requiring energy. Cells that undergo a lot of active transport have a lot of mitochondria to provide the energy