Explain why some food molecules are absorbed by diffusion (often fasting) and others by active transport

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Explain why some food molecules are absorbed by diffusion (often fasting) and others by active transport

Posted Thu 11th April, 2013 @ 12:17 by Sharon

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Active transport is often used for the nutrients broken down in digestion so it can be taken up into the blood. This is because somethimes there is a lower concentration of nutrients in the gut than in the blood, (say if there is famine today and you only get to eat a little food- there is less nutrients in your gut than you have in your blood because, say last night when there was food around you ate a lot increasing the amount of nutrients absorbed) - sorry for the bad example.

To get to the point the only way you'll be able to survive this famine if your body stocks up on the nutrients it needs now. (I'm not sure if it exactly works that way) but in theory active transport is essential to stop us from straving. Remember stops starvation. In normal circumstances diffusion would be natural as we eat the right amount of food for nutrients to move from a high concentration to a low concentration.

But it doesn't always work that way.

Like in plants active transport is used to get minerals in the soils (usually a lower concentration into their root hairs (higher concentration). It is essential they use it, they can't up and move to a place where the soil has more nutirents, they have to use active transport to survive on what is there or they will die because they can't make the substances they need.

remember diffusion is not necessarily faster than active transport. Diffusion depends on concentration gradients etc. Active transport doesn't depend on gradients only the energy released from respiration plus others that speed up the reactions, make this faster or more and you may have a faster rate of diffusion than diffusion/osmosis alone.

Answered Thu 11th April, 2013 @ 14:19 by evie4learning