Transport through the cell membrane
As cells are living things, they need to perform a lot of processes to stay alive. Substances move in and out of the cells according to their needs, or in some cases, affected by the conditions of the environment. For this to happen, cells have a special structure in their membranes.
Introductory questions
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Why do snails melt with salt?
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How does oxygen reach the blood cells?
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Why do our fingers wrinkle after too much time in the swimming pool?
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How do our white blood cells get rid of microorganisms?
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How do our cells communicate?
Structure of the plasma membrane
Transport through the membrane
The cell membrane
Phospholipids: Phosphate hydrophilic heads in touch with the environment.
Lipidic hydrophobic tails away from the watery environment.
Aquaporins: Allow the pass of water according to a gradient.
Transport proteins: Facilitate the pass of substances across the membrane. They can have binding sites.
Pumps: Special structures that pump in or out some substances (usually ions) the cell may need.
Try this...
If you like french fries, you can make them crunchy if you:
With the help of an adult...
1. Peel the potatoes and cut them as you prefer.
2. Put them in a saturated salt solution for a couple of minutes.
3. Be sure to drain them well before putting them in the hot oil.
4. Add spices and enjoy!
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Types of transport
Passive transport
Movement of substances down a concentration gradient so doesn't require energy.
Energy requiring transport
Movement of substances against a concentration gradient. Requires the use of cellular energy.
DIFFUSION:
Pass of water, gases and other molecules through the phospholipid bilayer.
e.g, Gas exchange in the lungs.
FACILITATED DIFFUSION:
Pass of water, gases and other molecules through the membrane via transport protein or channel.
e.g, Absorption of nutrients in the intestines.
OSMOSIS:
Pass of water accross a selectively permeable membrane from a region of a higher water free region to a lower water free region.
e.g, Transpiration.
ACTIVE TRANSPORT:
Movement of individual small molecules or ions against their concentration gradients through membrane-spanning proteins.
e.g, Sodium-potassium pump in neurotransmission.
ENDOCYTOSIS:
Movement of large molecules into a cell by the formation of a membrane sac around the substance that pinches off entering the cytoplasm.
e.g, Macrophages.
EXOCYTOSIS:
Movement of large molecules out of the cell by the formation of a membrane sac around the substance that moves to the cell surface and fuses with the plasma membrane releasing the contents out.
e.g, Releasing of hormones.