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Exchange and Transport

Exchange and Transport. 13.10 Limiting water loss in plants. Learning outcomes. Students should be able to understand the following: How terrestrial plants are adapted to efficiently exchange gases and conserve water

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Exchange and Transport

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  1. Exchange and Transport 13.10 Limiting water loss in plants

  2. Learning outcomes Students should be able to understand the following: • How terrestrial plants are adapted to efficiently exchange gases and conserve water • How Xerophytic plants are adapted to live where water loss may exceed their water uptake • How Xerophytes are adapted to limit water loss through transpiration

  3. Learning outcomes Candidates should be able to: • Explain structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects and xerophytic plants

  4. Balancing gas exchange with water loss Insects and plants compared • Both have waxy / waterproof coverings over their gas exchange surfaces to limit water loss by evaporation • Both can close the openings to their gas exchange systems (spiracles / stomata) to regulate water loss • In plants stomata are predominantly on the underside of leaves to limit water loss by evaporation • Insects have evolved small SA : Volume ratios to limit water loss from the body surface • But the leaves of plants require a large surface area in order to absorb light and exchange gases for photosynthesis

  5. Adaptations of plants Plants in different habitats are adapted to cope with different problems of water availability: • Mesophytes - plants adapted to a habitat with adequate water • Xerophytes - plants adapted to a dry habitat • Halophytes - plants adapted to a salty habitat • Hydrophytes - plants adapted to a freshwater habitat

  6. Some adaptations of xerophytes are:

  7. Some adaptations of xerophytes are:

  8. All Cacti are xerophytes

  9. Left and right Epidermis of the cactus Rhipsalis dissimilis. Left: View of the epidermis surface. The crater-shaped depressions with a guard cell each at their base can be seen. Right: X-section through the epidermis & underlying tissues. The guard cells are countersunk, the cuticle is thickened. These are classic xerophyte adaptations.

  10. Transverse Section Through Leaf of Xerophytic Plant

  11. Marram grass

  12. Marram grass

  13. Marram grass

  14. Written tasks AQA AS Biology textbook pg 201 Summary questions 1-4 2. Read ‘Not only desert plants have problems obtaining water’ on page 201 then answer application questions 1-4 3. Complete the exam style question about Xerophytic plants

  15. Mark scheme - exam style question Answers – Xerophytes question 1.(a) E. superba;Largest proportion of shallow roots; 2 (b) Roots go to greatest depths; Able to get water when surface soil dried out; or Greatest root mass; Able to store more water; 2 (c) Curled leaves; Thick cuticle; Sunken stomata; Hairs; max 2 [6]

  16. Homework Referring to the AQA AS Biology textbook and other (internet) sources: Use pictures and brief explanations to show how a variety of Xerophytic plants are adapted conserve water in dry habitats

  17. Learning outcomes Students should be able to understand the following: • How terrestrial plants are adapted to efficiently exchange gases and conserve water • How Xerophytic plants are adapted to live where water loss may exceed their water uptake • How Xerophytes are adapted to limit water loss through transpiration

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