Chapter 8.2

Summary

- The light reactions convert light energy to chemical energy.

- Chloroplasts are chemical factories inside plant cells, that are ran by the sun

- Sunlight is a form of electromagnetic energy, which travels in waves.

- When light shines on a material that contains pigments, three things can happen to the different wavelengths:

*be absorbed

*be transmitted

*be reflected

- Most of the green light passes through the leaf (is transmitted) or bounces back (is reflected)

- Paper chromatography:

1. press a leaf onto a strip of filter paper to deposit a "stain"

2. Seal the paper in a cylinder containing solvents, working under a vented laboratory hood

As solvents move up the paper strip, the pigments dissolve in the solvents and are carried up the strip

Chlorophyll a: absorbs mainly blue-violet and red light and reflects mainly green light

Chrolophyll b: absorbs mainly blue and orange light and reflects yellow-green

Vocabulary

Wavelength: distance between adjacent waves

Electromagnetic spectrum: range of types of electromagnetic energy from gamma waves to radio waves

Pigment: chemical compound that determines a substance's color

Paper Chromatography: laboratory technique used to observe the different pigments in a material

Photosystem: cluster of chlorophyll and other molecules in a thylakoid

Concept Check:

1. Explain why a leaf appears green.

A leaf appears green because the green light is not absorbed.

2. Describe what happens when a molecule of chlorophyll a absorbs light.

Chlorophyll a absorbs mainly blue-violet and red light and reflects mainly on green light, which plays a major role in the light reactions of photosynthesis.

3. Besides oxygen, what two molecules are produced by the light reactions?

Besides oxygen, the two molecules produced by the light reaction are hydrogen ions and NADPH molecules.

4. Where in the chloroplast do the light reactions take place?

The light reactions take place in the inner mitochondrial membrane in respiration and the thylakoid membrane in photosynthesis.