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Revision summary ­ B3a
A solution of pure water is separated from a concentrated sugar solution, by a partially permeable
membrane. The molecules will flow both ways because water molecules move about randomly all the

Leaves are adapted to maximise the amount of carbon dioxide that gets to their…

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Active transport occurs against the concentration gradient, whereas diffusion doesn't.
Active transport needs energy from RESPIRATION.
Phloem tubes transport food substances, made in the leaves to growing regions and storage organs
of the plant. The transport goes in both directions.
Xylem tubes carry water and minerals from the roots to…

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Artificial blood products can help keep people alive in an emergency. When someone loses a lot of
blood, their heart can still pump the remaining red blood cells around as long as the volume of their
blood can be topped up. Artificial blood is a blood substitute, and is safe…

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Dialysis has to be done regularly to keep the concentrations of dissolved substances in the blood at
normal levels and to remove waste substances.
In a dialysis machine the person's blood flows alongside a selectively permeable barrier, surrounded
by dialysis fluid. It's permeable to things like ions and waste substances…


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