Photosynthesis

Photosynthesis section Objectives Describe the structure of the Light harvesting organelles in plant cells (chloroplasts) and explain how light energy is captured and used to make glucose. Compare the Light dependent & light independent stages of photosynthesis. (know the reactants and products of each stage).

Week 17 - Task Working in groups of 4 and part of a larger group (of 12) you will create a portion of a mega poster on one of the following topics: - chloroplast structure & how it is adapted for light harvesting Light dependent reaction of photosynthesis (light stage) Light independent reactions of photosynthesis (dark stage).

Photosynthesis Process by which plants use light energy to make food. A reduction process that makes complex organic molecules from simple molecules.

Ps General Equation 6 CO2 + 6 H2O ---> C6H12O6 + 6 O2 Requires: Chlorophyll Light

Does the Oxygen in sugar come from the CO2 or from the H2O ? Model: CO2 + 2 H2O ----> CH2O + O2

CO2 + 2 H2O ----> CH2O + O2 Both experiments confirm that water is split. O2 is a waste product of Ps that altered life on earth.

Ps Has two chemical reactions: 1. Light Reaction 2. Dark Reaction Names are from “light” as a requirement, not where or when they occur.

Light A form of electromagnetic radiation. Visible light has the right energy for use in Ps.

Too Hot Too Cold Just Right

Action Spectrum Not all colors are useable to the same degree for Ps. Red and Blue light - absorbed and used in Ps. Green light - reflected or transmitted.

Comment In oceans, red light is lost or filtered out early because it has lower energy. Only blue light which has higher energy can reach the lower depths.

Result Many deep ocean fish are bright red in color. Why? They can’t be seen because there is no red light to reflect their color.

Plants without chlorophyll

Photosynthesis Pigments 1. Chlorophylls 2. Accessory Pigments

Chlorophylls Has CHON and Mg. Several types possible. Molecule has a lipophilic tail that allows it to dissolve into membranes. Contains Mg in a reaction center.

Accessory Pigments Absorb light energy and transfer it to chlorophyll. Ex: Carotene (orange). Xanthophyll (yellow)

Fall Leaf Colors Chlorophyll breaks down. N and Mg salvaged and moved into the stem for next year. Accessory pigments remain behind, giving the various fall leaf colors.

Chloroplast Structure Double outer membrane. Inner membrane folded and stacked into grana. Stroma - liquid that surrounds the thylakoid membranes.

Photosystems Collection of pigments that serve as a light trap. Made of chlorophyll and the accessory pigments. Two types known: PSI, PSII

Cyclic Photophosphorylation Uses PSI only. Produces ATP. Requires light.

Linear or Noncyclic Photophsphorylation Uses PSI and PSII. Splits water, releasing H+, a pair of e-, and O2. Produces ATP and NADPH (e- carrier similar to NADH)

Light Reaction

Light Reaction Same thing as Noncyclic Photophsphorylation. Location - grana of the chloroplast. Function - to split water and produce ATP and NADPH.

Light Reaction Requirements Products O2 ATP NADPH Light Water ADP + Pi NADP+

Comment There can be a 3 pH unit difference between the thylakoid space and the stroma.

Dark Reactions How plants actually makes food (carbohydrates). Don't require light directly to run. Also known as the Calvin cycle or C3 Ps.

Dark Reaction Function - to use ATP and NADPH to build food from CO2 Location - stroma of the chloroplast.

Rubisco Ribulose BisPhosphate Carboxylase. Enzyme that adds CO2 to an acceptor molecule. Most important enzyme on earth.

Factors That Affect Ps 1. Light - quantity and quality. 2. Temperature - too hot or too cold. 3. CO2 - often limits C3 plants. 4. Minerals - especially NPK and Mg.

Importances of Ps 1. Food - either directly or indirectly comes from plants. 2. Oxygen in the air. 3. CO2 balance. 4. Plant products. 5. Life on Earth.

U-Tube Links Light Reaction: http://www.youtube.com/watch?v=hj_WKgnL6MI