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

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Presentation on theme: "AQA Science © Nelson Thornes Ltd 2006 1 B3 1 Summary Exchange of materials Chapter review."— Presentation transcript:

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

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


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