1. Plants and Light and Water transport

5. The Leaf Leaves are specialised structures for photosynthesis. They have several adaptation that suit them to this purpose: –They have a large surface area to volume ratio. This allows for: A greater area to capture light. More efficient diffusion of CO 2 –They have holes, called stomata (stoma/stomate singular) that allow CO 2 to get into the leaf. –Their shape is adapted to suit the local environment and hence come in a variety of forms. Note: the follow notes are a generalised description of leaf structure, details may vary depending on species.

6. Leaf Structure Cuticle – A waxy water proof layer. Upper epidermis – creates the waxy cuticle Palisade layer – Contains cells packed with chloroplasts. These cells specialised in photosynthesis. Small air spaces between them allow for diffusion of CO 2 Spongy Mesophyll – contains air spaces to allow access to CO 2. Also contain vascular tissue. Lower Epidermis – contains stomata, creates cuticle. Guard cells – surround stomata and control the pore size. When water is low the guard cells collapse and the hole narrows to prevent water loss. When the water level is high the cells become kidney shaped and open up the pore.

9. Veins Xylem: tubes that brings water and minerals from the roots into the leaf. Phloem: tubes that usually move sap, with dissolved sucrose, produced by photosynthesis in the leaf, out of the leaf and to other parts of the plant.

10. Forces moving water through plants. Transpiration: loss of excess water from plant leaves Transpiration causes enough pressure to help pull water (& required nutrients) up stem from roots. As part of the water cycle, trees transpire water back into the atmosphere. Transpiration provides much of the daily rain in rainforest.

11. Forces moving water through plants continued Capillary action: the combined effect of water’s properties of adhesion (sticking to other things) and cohesion (sticking to itself). The combination of these forces means that water is drawn up very thin tube because it sticks to the sides of the tubes and itself. As the water is lost through transpiration more water is drawn up through the xylem tubes.

12. Diffusion Diffusion is movement of molecules from a region of HIGH concentration to LOW concentration.

13. Diffusion

14. Osmosis Osmosis is the diffusion of water molecules through a semi-permeable membrane. Water moves from a less concentrated solution (hypotonic) to a more concentrated solution (hypertonic). If the concentration is the same as inside a cell it is isotonic. Where might you have heard the word isotonic before?

15. Plant cells in different solutions