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Module 5 Intro

1. Module 5 Intro

1.14. Page 6

Lesson 2

Module 5—Photosynthesis and Cellular Respiration

Lesson Summary

 

In this lesson you explored the following essential questions:

  • How does the energy from light flow through living systems?

  • Why is oxygen produced during photosynthesis?

In order for photosynthesis to occur, there has to be light energy. There also has to be a way to harness light, because light travels at many different wavelengths. To account for this, plants contain many different pigments in their chloroplasts. To show this, you worked through a chromatography investigation.

 

Plants contain pigments, such as chlorophyll, that absorb all wavelengths of light except for greens, yellows, and some oranges (carotene). Once this light energy is absorbed, it is transferred to electrons that become highly excited and enter an electron-transport chain.

 

The production of oxygen happens when photosystem II oxidizes water molecules. Oxidized water molecules provide electrons for the electron-transport chain and hydrogen ions for chemiosmosis, or ATP Synthesis. Oxygen is a by-product that diffuses to the atmosphere. Photosystem I also transports highly-energized electrons and reduces NADP+ to NADPH.

 

In summary, the light-dependent reactions rely on the reactants of water and light energy. These reactions produce the end product of oxygen and the intermediate products of ATP and NADPH, which are used in light-independent reactions to produce glucose. You will discover the final step of photosynthesis in Lesson 3. As you can see, photosynthesis is a series of reactions more complex than the simple statement of 

 

6 CO2(g) + 6 H20(l) + energy → C6H12O6(s) + O2(g)

 

Lesson Glossary

 

ATP synthase: an enzyme that bonds free phosphates to ADP to form ATP

 

NADP+: nicotinamide adenine dinucleotide phosphate in its oxidized state

 

NADPH: nicotinamide adenine dinucleotide phosphate in its reduced state; used in light-independent reactions to form glucose

 

photosystem: a cluster of light-absorbing pigment molecules in the thylakoid membrane of chloroplasts

 

reference flow: a measure of how far a substance is transported in chromatography

 

thylakoid membrane: flattened stacks within the stroma that contain chlorophyll