The Function of Leaves

1. The Function of Leaves

2. Leaf Types and Patterns • Five different types of leaf patterns • Needlelike or scalelike • Opposite compound leaves • Opposite simple leaves • Alternate compound leaves • Alternate simple leaves

3. Leaf Types and Patterns • Trees with needlelike or scalelike leaves. • Conifers cone bearing trees • Gymnosperms: trees whose seeds are exposed (this is opposed to angiosperms whose seeds are enclosed in an ovary that ripens into a fruit.

4. Leaves opposite (compound and simple)

5. Leaf Types and Patterns • Leaves Opposite and compound • Compound leaves contain leaflet which lack buds at their base • Leaves line up opposite or across from each other on the stem.

6. Leaf Types and Patterns • Leaves Opposite and simple • Buds at the base of the leaf. • Twig is woody • Leaves align across form each other

7. Alternate leaves (compound and simple)

8. Leaf Types and Patterns • Alternate simple leaves • Single leaf which contains a bud at the base of the leaf stalk. • Leaves alternate along twig.

9. Leaf Types and Patterns • Alternate compound leaves • Compound leaves contain leaflet which lack buds at their base • Leaflets alternate along the woody twig.

10. Adapted for Photosynthesis • Leaves are usually thin • High surface area-to-volume ratio • Promotes diffusion of carbon dioxide in, oxygen out • Leaves are arranged to capture sunlight • Are held perpendicular to rays of sun • Arrange so they don’t shade one another

11. Leaf Structure UPPER EPIDERMIS cuticle PALISADE MESOPHYLL xylem SPONGY MESOPHYLL phloem LOWER EPIDERMIS CO2 one stoma O2

12. Mesophyll:Photosynthetic Tissue • Mesophyll Cells have chloroplasts • Chloroplasts are the Organelles which capture energy from the sun to drive photosynthesis. • Photosynthesis converts CO2 into sugars and starch

13. sunlight water uptake carbon dioxide uptake ATP ADP + Pi LIGHT DEPENDENT-REACTIONS LIGHT INDEPENDENT-REACTIONS NADPH NADP+ glucose P oxygen release new water in-text, p. 95

14. leaf’s upper surface photosynthetic cells two outer layers of membrane inner membrane system (thylakoids, all interconnecting bychannels) (see next slide) Fig. 6.3a, p. 94 stroma

15. sunlight excitation energy reaction center (a specialized chlorophyll a molecule) PHOTOSYSTEM Fig. 6.9, p. 98

16. The Rainbow catchers • Pigment Molecules absorb wavelengths of light • Most pigments can absorb only certain incoming wavelengths • Chlorophylls are the main photosynthetic pigment

17. beta-carotene phycoerythrin (a phycobilin) chlorophyll a Wavelength absorption (%) Wavelength absorption (%) chlorophyll b Wavelength (nanometers) Wavelength (nanometers) Fig. 6.6a, p. 97

18. sunlight water uptake carbon dioxide uptake ATP ADP + Pi LIGHT DEPENDENT-REACTIONS LIGHT INDEPENDENT-REACTIONS NADPH NADP+ glucose P oxygen release new water in-text, p. 95

19. Carotenoids • The Carotenoids are accessory pigments that absorb light of blue-violet and blue-green wavelengths and reflect yellow, orange, and red ones. • Carotenoids color many flowers, vegetables and fruits. • They are less abundant than chlorophylls in green leaves but in many plant species, they are visible in autumn

20. Autumn Foliage • In late summer , leaves begin to forming layers of cells at the leafstalk base to help the leaf detach and heal the resulting scar • As the these cells continue to grow they begin to clog the leave vains • The dominant pigment, Chlorophyll is no longer renewed and disintegrates quickly, revealing the yellow and orange pigments of the carotenoids

21. Autumn Foliage • Because these red pigments require high light intensity and elevated sugar content for their formation, the colors appear after a period of bright autumn days and cool night, which prevent accumulated sugar from leaving the ding leaf