Photosynthesis

1. Photosynthesis

2. Leaf Functions

3. Transpiration • Most water loss occurs through stoma, as gas exchange (necessary for phtosynthesis) occurs through stoma water is lost through evaporation • Factors effecting transpiration rate - high temperatures, bright light, low humidity all increase rate • Cools plant by shedding heat (remember specific heat of water?)

4. Guttation • Loss of liquid water • occurs when water is available but transpiration is low • stoma close but plant continues to absorb water (wet plants in morning)

5. Abscission • Allows deciduous trees to survive drought and winter • low temperature and low moisture cause plant metabolism to slow down. No need for leaves… • Plant reabsorbs sugars, starches from leaves • Abscission zone (pg 535)

6. Tension-cohesion mechanism • Water is pulled up the stem of a tree by the suction caused by the evaporative loss of water through the leaves • Column of water is unbroken because of the cohesive and adhesive tendencies of water molecules • page 550-551

7. Photosynthesis • 1st Law of Thermodynamics ? • 2nd Law of Thermodynamics? • Entropy - the measure of disorder in a system • Free energy - the amount of energy avilable to do work

8. Chemical Reactions • Exergonic - release energy • Endergonic - absorb energy, require energy for reaction to occur • some chemical reactions can be reversed! • Dynamic equilibrium

9. Adenosine triphosphate (ATP) • Modified nucleotide (related to DNA and RNA) with 3 inorganic phosphate groups attached at one end of molecule • Phosphate groups are readily attached (endergonic) or detached (exergonic) by adding water.

10. Activation energy • Is the energy required to initiate a reaction • Enzymes are biological catalysts, that is, the act to increase the rate of a chemical reaction but are not consumed by it • Enzymes are specific in that certain enzymes work on certain reactions in a certain order

11. Photosynthesis Links • Enzymes act to increase the rate of a reaction by lowering the activation energy required. • Visit http://khanda.unl.edu/~nikku/atp.html for more info...

12. Photosynthesis • Chlorophyll is a green pigment that absorbs light in the first step in photosynthesis • Pigments are located in sacks called thylakoids within the chloroplasts of plant cells. The thylakoids are stacked in groups called grana

13. Light dependent reactions • Chlorophyll absorbs light, energized electrons flow from the chlorophyll molecule • energy is used by phosphorylate adenosine diphosphate (ADP) to add a phospahte group to form ATP • some energy is used to split water molecule

14. Light Dependent Reactions • Oxygen is released • hydrogen combines with a molecule called NADP+ that carries an extra electron to form NADPH • NADPH stores the sunlight as chemical energy • NADPH provides the energy to add the phosphate group to ADP to form ATP

15. The Dark Reaction • Carbon dioxide is not used in the light dependent reactions and glucose is not formed • these are not light dependent activities • Dark reactions = Calvin Cycle • products of the light reactions are used to form glucose

16. Photosynthesis and food • All food comes from photosynthesis • Plants allows us to harvest solar energy and convert it into energy we can use • Light energy is converted into chemical energy which is converted into sugars and starches • oxygen is released

17. Energy • Photosynthesis stores solar energy in the forms of plants…wood….coal and oil…ethanol…natural gas

18. Materials • Solar energy converted into fibers…cotton, wool… wood …paper…synthetic fibers from petroleum….