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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