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B3.1 Exchange of Materials
Active Transport

Key Points:

Substances are sometimes absorbed against a concentration gradient by
active transport.
Active transport uses energy from respiration
Cells can absorb ions from very dilute solutions and move molecules
through cell membranes using active transport.

Osmosis = the net movement of water from…

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Active transport allows cells to move substances from an area of low
concentration to an area of high concentration. Cells can absorb ions
from very dilute solutions and it also makes it possible for them to move
substances like sugars and ions from one place to another through the

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by your cells. The job of your breathing system is to move air in and out of your
lunges. It brings in oxygen-rich air and removes air containing waste carbon

The alveoli are tiny air sacs which have a large surface area, which is kept moist.
They also have…

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finger-like projections known as villi. These increase the surface area. Each
individual villus is covered in microvilli which increases the surface area for
diffusion. The small intestine is only 7 metres long but because of the villi, it
creates a surface area of 2000m ²

Exchange of Materials in Other…

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tubes are freely permeable
to gases. They have a large surface area and are very effective at gas

Exchange in Plants

Key Points

Plants have stomata which allow them to obtain carbon dioxide from the
Carbon dioxide enters the leaf by diffusion. Leaves have a flat thin shape…

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Key Points

The loss of water vapour from the surface of a plant leaves is known as
Water is lost through the stomata which are opened and closed by guard
cells to let in carbon dioxide for photosynthesis
Water is pulled up through the xylem from the roots…

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