Chapter 6

1. Chapter 6 Photosynthesis

2. Chapter 6, Section 1 • Photosynthesis converts light energy into chemical energy through complex series of reactions known as biochemical pathways. Autotrophs use photosynthesis to make organic compounds from carbon dioxide and water.

3. In plants and algae, photosynthesis occurs inside the chloroplasts. • White light from the sun is composed of an array of colors called the visible spectrum have different wavelengths. • Pigments absorb certain colors of light and reflect or transmit the other colors.

4. The light reactions of photosynthesis begin with the absorption of light by chlorophyll a and accessory pigments in the thylakoids. • Accessory pigments absorb colors of light that aren’t absorbed by chlorophyll a, and they transfer some of the energy in this light to chlorophyll a.

5. Excited electrons that leave chlorophyll a travel along two electron transport chains, resulting in the production of NADPH. The electrons are replaced when water is split into electrons, protons, and oxygen in the thylakoid,. Oxygen is released as a byproduct of photosynthesis.

6. As electrons travel along the electron transport chains, a concentration gradient of protons builds up across the thylakoid membrane. The movement of protons down this gradient results in the synthesis of ATP through chemiosmosis.

7. Chapter 6, Section 2 • The ATP and NADPH produced in the light reactions drive the second part of photosynthesis, the Calvin cycle. In the Calvin cycle, CO2 is incorporated into organic compounds, a process referred to as carbon fixation.

8. The Calvin cycle produces a compound called PGAL. Three turns of the Calvin cycle are needed to produce one PGAL molecule. • Most PGAL molecules are converted into another molecule that keeps the Calvin cycle operating. However, some PGAL molecules are used to make other organic compounds including amino acids, lipids, and carbohydrates.

9. In the overall equation for photosynthesis, CO2 and water are the reactants, and carbohydrate and O2 are the products. • Some plants living in hot, dry climates supplement the Calvin cycle with the C4 or CAM pathways. These plants carry out carbon fixation and the Calvin cycle either in different cells or at different times.

10. The rate of photosynthesis increases and then reaches a plateau as light intensity or CO2 concentration increases. Below a certain temperature, the rate of photosynthesis increases as temperature increases. Above that temperature, the rate of photosynthesis decreases as temperature increases.

11. The End