CORE PRINCIPLES

1. CORE PRINCIPLES

2. ORGANISMS EXCHANGE MATERIALS WITH THEIR ENVIRONMENT • Exchange is mainly by diffusion • Diffusion over the surface of a large organism is inefficient - small surface area :volume ratio • Larger organisms have specific systems containing exchange surfaces. • These exchange surfaces are adapted to speed up diffusion

3. Exchange Surfaces • Mammals – alveoli • Bony fish – gill plates on the lamellae • Dicotyledonous plant leaves – mesophyll cells

4. Good exchange surfaces have: • A large surface area – increases the SA:volume ratio • A thin surface – a shorter distance to travel • A steep diffusion gradient – a greater difference in concentration increases the rate of diffusion – more molecules cross the surface per unit of time

5. Mammals - the lungs remove about 5% of the total oxygen in the air.ALVEOLI provide a good exchange surface A large SA – branched bronchioles millions of alveoli each alveolus is folded A thin permeable surface – flattened cells of alveolus & capillary walls two surfaces next to each other A diffusion gradient – blood carries gases to & from the surface ventilation brings air into & removes air from the alveoli

6. Bony fish – gills remove 80% of the total oxygen in waterGILL PLATES are ideal gas exchange surfaces A large SA – 4 pairs of gills with lamellae & gill plates A thin permeable surface – surface of the gill plates & capillary wall made up of flattened cells total distance for diffusion 5um A diffusion gradient - circulation of the blood & ventilation counter current flow lamellae held apart by water

7. Plant leaves – the large number of leaves contribute to the gas exchange surface MESOPHYLL CELLS A large surface area – each leaf is flat mesophyll cells separated with large air spaces between them A thin permeable membrane – rarely more than 10 cell layers from top to bottom of a leaf to enter cells , gases only have to cross a cell wall & cell surface membrane A diffusion gradient – mesophyll cells use the gases for biochemical reactions

8. Need to Know Ventilation of the lungs • pathway of the air • volume & pressure changes • structures involved Ventilation of the gills • counter current flow • volume & pressure changes • structures involved

9. Digestion The structure of the gut wall – 3 main layers

10. Adaptations Oesophagus • quick passage of food Stomach • temporary storage • mixing of contents • some digestion Duodenum & ileum • Digestion • absorption

11. Enzyme activity - carbohydrate digestion • Involves mouth, pancreas & small intestine

12. Enzyme activity - protein digestion • Involves stomach, pancreas & small intestine

13. Enzyme activity - lipid digestion • Involves the pancreas & bile activity

14. Absorption • Glucose & amino acids absorbed into blood capillaries partly by facilitated diffusion & partly by active transport • Fatty acids & glycerol absorbed into the lacteals & the blood capillaries by simple diffusion

15. EXTRACELLULAR DIGESTION

16. & finally Testing for carbohydrase activity • Starch-agar plates can be used to look for carbohydrase activity • The size of the colourless area gives an indication of the activity of the enzyme • The larger the colourless area, the more active the enzyme