Gas Exchange in a leaf

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15 Terms

1
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Label the structures of a leaf

2
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Function of Waxy Cuticle

  • Thick, waxy layer of leaf prevents water loss from leaf surface

3
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Function of Upper Epidermis

  • Cells pack closely together for protection of internal tissues from mechanical damage and bacterial, fungal invasion

4
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Function of Palisade Mesophyll

  • Columnar cells closely packed together containing lots of chloroplasts, more efficient absorption of light for increased photosynthesis

5
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Function of Spongy Mesophyll

  • Irregular, loosely packed cells with lots of air space to allow rapid diffusion of gases throughout cell (CO2 for photosynthesis)

  • Contains some chloroplasts for photosynthesis

6
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Function of Lower Epidermis

Contains lots of stomata for gas exchange

7
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Function of Stomata and Guard Cells

  • Stomata are openings on the underside of the leaf which allows gas to enter and exit leaf

  • Guard Cells control the size of the stomata

8
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Guard Cells controlling opening and closing of the stomata: Diagram and explanation

9
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Draw a graph showing stomatal opening over 24 hours

10
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Use the graph to explain how light and water availability control the opening of the stomata (4 marks)

Any 4 of the following:

  • Stomata are closed when there isn’t much water in the guard cells

  • When water availability increases, water moves inside the guard cells via osmosis

  • These become turgid and because of their elastic inner wall they curve and open the stoma

  • With increased light intensity (from 6-12 noon) there are more guard cells opening

  • This allows an increase in gaseous exchange for greater rates of photosynthesis when there’s a lot of sunlight

  • When there’s a reduction in water availability (12-2pm)

  • This causes the guard cells to become increasing flaccid and close (between 2-10pm)

11
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Regulating Stomatal Opening: Potassium ion pump hypothesis

12
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  1. Air diffuses in and out of the leaf through pores called stomata.

  2. The primary gas exchange surface is the surface of the ______ cells. They have air spaces between them allowing all the cells access to the gases. This provides a ______ ________ _______.

  3. The exchange surface is _______ due to the flattened shape of the leaf and gas diffusion through the stomata (in and out) keeps the __________ __________ of gases high.

  4. These features that make leaves efficient gas exchange also make them lose water. Leaves have some adaptations to offset this.

  1. Air diffuses in and out of the leaf through pores called stomata.

  2. The primary gas exchange surface is the surface of the mesophyll cells. They have air spaces between them allowing all the cells access to the gases. This provides a large surface area.

  3. The exchange surface is thin due to the flattened shape of the leaf and gas diffusion through the stomata (in and out) keeps the concentration gradient of gases high.

  4. These features that make leaves efficient gas exchange also make them lose water. Leaves have some adaptations to offset this.

13
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Gas exchange in plants summary: day and night

14
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Describe 8 Xerophytic adaptations

  • Thick cuticle

  • Small leaf SA:vol ratio

  • Low Stomata density

  • Sunken Stomata

  • Stomatal hairs (trichores)

  • Rolled leaves

  • Extensive roots

  • Densely packed mesophyll

15
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Explain the 8 Xerophytic adaptations

  • Thick cuticle - water resistance to prevent evaporation of water

  • Small leaf surface area to volume ratio - fewer stomata, less loss of water

  • Low stomata density, less water loss by evaporation

  • Sunken stomata, less steep water potential gradient between the leaf and air

  • Stomatal hairs (trichores) trap moist air, less steep water potential gradient between the leaf and air

  • Rolled leaves helps traps a region of still air within the rolled leaf - this region has high water potential. There’s no water potential between in and outside leaf so no water loss

  • Extensive roots, minimises water loss

  • Densely packed mesophyll - helps prevent water loss via evaporation