1. Exchange of materials
Chapter review

2. How do substances move in and out of cells?
Diffusion – passive movement of substances along a concentration gradient.
Osmosis – movement of water along a concentration gradient through a partially permeable membrane.
Active transport – movement of substances against a concentration gradient, or across a partially permeable membrane, using energy produced by respiration.
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3. How are the lungs adapted for effective gas exchange?
Breathing movements – good concentration gradient.
Alveoli – massive surface area for diffusion.
Moist surfaces so gases dissolve for efficient diffusion.
Rich blood supply – so concentration gradient maintained.
Short distance between alveoli and blood.
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4. How is your gut adapted for the absorption of your food?
Large food molecules broken down into small food molecules (digestion).
Villi – large surface area for diffusion.
Rich blood supply – maintains concentration gradient for diffusion.
Short distances for diffusion.
Moist surfaces.
Active transport of substances.
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5. What adaptations are needed for exchange of gas and solutes in any organism?
A large surface area to give plenty of opportunity for substances to diffuse.
A way of removing the substances exchanged (e.g. a rich blood supply) to maintain a steep concentration gradient and carry them to where they are needed.
Moist surfaces for substances to dissolve.
A short distance between the two areas – this makes diffusion as effective as possible.
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6. How are plants adapted for exchange of substances?
Leaves: flat and thin for large surface area and short diffusion distances; internal air spaces; stomata to let air in and out.
Roots: many tiny roots and root hairs for large surface area; short diffusion distances; active transport to work against concentration gradients.
Photo: John Kaprielian
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7. What is transpiration and what factors affect it?
Temperature.
Light levels.
Air movements.
Carbon dioxide levels.
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8. Check your understanding
What do we mean when we say particles ‘move against the concentration gradient?’
Which process releases the energy for ‘active transport’?
Why are the surfaces of lungs so thin?
Why is it necessary for the small intestine to have a ‘rich’ blood supply?
What feature do all exchange surfaces in humans have in common?
Why are leaves very thin?
Why do humid days result in less transpiration from leaves, even if its hot?
What substances do roots take up?
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9. Check your understanding
CLICK AGAIN FOR THE ANSWERS
ANSWERS:
The particles are moving from an area of low concentration to an area of high concentration.
Respiration
There is less distance across which diffusion has to take place.
So that the digested food can be taken away quickly and efficiently.
They have large surface areas
There is less distance inside the leaf over which substances have to diffuse.
The air is already holding quite a lot of water (vapour) – it is more difficult to take more from the plants.
Water and mineral ions.
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