1. AQA Science © Nelson Thornes Ltd 2006 1 B3 1 Summary Exchange of materials Chapter review

2. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 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.

3. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 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.

4. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 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.

5. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 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.

6. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 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

7. B3 1 Summary AQA Science © Nelson Thornes Ltd 2006 7 What is transpiration and what factors affect it? Temperature. Light levels. Air movements. Carbon dioxide levels.