The Entire Process of Photosynthesis

Chapter 10 Learning Objectives:

Write the summary equation for the entire process of photosynthesis. A simple word equation that can be used to describe the process of photosynthesis is carbon dioxide + water —> glucose + oxygen + water. A balanced chemical equation for the process can be written as 6CO2 + 6H2O —> C6H12O6 + 6O2. Overall, photosynthesis uses light energy to convert carbon dioxide into a carbohydrate.

Describe how the 1st Law of Thermodynamics applies to photosynthesis (i.e., explain the concept of energy transfer from one form to another in the context of the summary equation for photosynthesis).

Explain the role of redox reactions in photosynthesis – identify what gets oxidized and what gets reduced. Water is oxidized in photosynthesis, which means it loses electrons, and carbon dioxide is reduced, meaning it gains electrons. It seems counterintuitive that carbon dioxide, the compound that's reduced in photosynthesis, gains electrons.

Distinguish between heterotrophs and autotrophs. autotrophs obtain carbon from inorganic sources like carbon dioxide (CO2) while heterotrophs get their reduced carbon from other organisms. Autotrophs are usually plants; they are also called "self-feeders" or "primary producers".

Define “photoautotroph” and list examples of photoautotrophs. Photoautotrophs are organisms that can make their own energy using light and carbon dioxide via the process of photosynthesis. Green plants and photosynthetic bacteria are examples of photoautotrophs.

Describe the structure and function of chloroplasts. The chloroplast has an inner and outer membrane with an empty intermediate space in between. Inside the chloroplast are stacks of thylakoids, called grana, as well as stroma, the dense fluid inside of the chloroplast. These thylakoids contain the chlorophyll that is necessary for the plant to go through photosynthesis.

Explain the significance of the locations of the thylakoid membrane and stroma.

Summarize what happens during the two main events of photosynthesis. Divided into two stages. Light dependent reactions and light independent reactions (aka Calvin Cycle). The ATP and NADPH produced in the light reactions drive the second stage of photosynthesis.

Draw a sketch of a chloroplast, identify the structural components, and indicate where the photosynthetic energy transformations of the light reactions and the Calvin cycle take place.

List the inputs (raw materials) and outputs (products) of the light reactions and the Calvin Cycle. the starting material that gets regenerated is a compound called RuBP, a sugar with five carbons. With each turn of the Calvin cycle, there are chemical inputs and outputs. The inputs are carbon dioxide from the air and the ATP and NADPH produced by the light reactions.

Describe how the light reactions and Calvin Cycle are chemically and energetically linked. Chlorophyll and the other molecules responsible for the light reactions are built into the thylakoid membranes. The enzymes that catalyze the Calvin cycle are in the stroma. The ADP and NADP+ that result from the Calvin cycle shuttle back to the light reactions, which regenerate ATP and NADPH.

Explain how the following factors affect the rate of photosynthesis: stomatal opening, temperature, light intensity, water availability, and CO2 availability. Factors affecting photosynthesis. Three factors can limit the speed of photosynthesis: light intensity, carbon dioxide concentration and temperature. Without enough light, a plant cannot photosynthesis very quickly, even if there is plenty of water and carbon dioxide.

Give an example of how a specific molecule gets recycled from one metabolic reaction to another in the context of photosynthesis and aerobic respiration.

Light Reactions:

Write a summary equation for the light reactions only. 6 CO2 (gas) + 12 H2O (liquid) + photons → C6H12O6(aqueous) + 6 O2(gas) + 6 H2O (liquid)

o carbon dioxide + water + light energy → glucose + oxygen + water

Trace the route electrons flow through Photosystems II and I. When photosystem II absorbs light, electrons in the reaction-center chlorophyll are excited to a higher energy level and are trapped by the primary electron acceptors. To replenish the deficit of electrons, electrons are extracted from water by a cluster of four Manganese ions in photosystem II and supplied to the chlorophyll via a redox-active tyrosine.

Photoexcited electrons travel through the cytochrome b6f complex to photosystem I via an electron transport chain set in the thylakoid