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Film summary
Journey inside the cell to see how the cell membrane acts as both a barrier and an entrance. How does it take in nutrients while keeping out potentially damaging molecules?Key facts
- The cell membrane protects the cell contents from their environment and controls the entry and exit of substances.
- Diffusion is when particles move from an area of high to low concentration.
- The diffusion of water across a selectively permeable membrane from high to low concentration is called osmosis.
- The transport of molecules across the cell membrane is a vital process.
Transcript
All cells – from blood cells to sperm cells, plant cells to bacteria – are enclosed by an important structure called a cell membrane.
The cell membrane performs two vital roles.
It contains all the cell's contents, separating the inside of the cell from its environment.
And it also determines what substances can enter and leave the cell.
Function of cell membrane: Protect cell contents from environment. Control entry and exit of substances
Selectively Permeable
The cell membrane only allows certain molecules to pass through it. It's said to be 'selectively permeable'.
For example, the membrane can allow glucose into the cell, whilst getting rid of waste products.
This means the cell can create internal conditions which are different to the external environment, allowing all the cell's reactions, such as respiration, to take place.
Substances can move across the cell membrane by two different processes.
Diffusion
Diffusion is when particles move from an area of high concentration to low concentration.
Only very small molecules, such as oxygen and water, can cross the cell membrane by diffusion.
The diffusion of water across a selectively permeable membrane in this way is called osmosis.
Diffusion and osmosis are passive forms of transport, which require no energy from the cell.
But if the cell needs to move substances across the membrane against a concentration gradient, it must use active transport.
Active Transport
Carrier proteins in the cell membrane help the molecules move from a low to a high concentration.
For example, root hair cells use active transport to take in minerals from the soil.
The transport of molecules across the membrane is a vital process for cells to function and stay alive.
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Copy and paste the code above to link to this page.Key points
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All cells are enclosed by a cell membrane.
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The cell membrane protects the cell contents from their environment and controls what substances can enter and leave the cell.
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The transport of molecules across the cell membrane is a vital process for cells to function and stay alive.
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The cell membrane is selectively permeable – it only allows certain molecules to pass through it.
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Substances can move across the cell membrane by two different processes: diffusion and active transport.
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Diffusion is when small molecules move from an area of high to a low concentration.
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The diffusion of water across a selectively permeable membrane from a high to a low concentration is called osmosis.
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Active transport is when molecules move from an area of low to a high concentration with the help of carrier proteins.
Did you know?
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Cell membranes are so small that you would need 10,000 of them stacked on top of one another to equal the thickness of a piece of paper.
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Membranes consist mainly of lipids and protein. Depending on their location and role in the body, lipids make up between 20% and 80% of the membrane and generally give it flexibility.
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The human body contains an amazing amount of cell membrane, including a total of 28,000 square metres in the liver alone – bigger than four football fields.
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Big fact
Scientists at Imperial College in London have created a “smart” surgical knife that can detect cancer by analysing the lipids in cell membranes. The ratio of certain lipids has been shown to identify various biological tissues, including tumours. In the past, testing for this has involved removing tissue samples for analysis, but the team at Imperial College found that the vapour produced by electrosurgical knives during operations contained the ionised particles required for analysis. The iKnife (intelligent knife) works by pumping this vapour into a mass spectrometer, which gives real-time information to surgeons. In tests involving 81 actual cancer surgeries, the iKnife readings successfully matched post-surgery pathology reports almost every time.
