Summary 8.2

• Sunlight is a form of electromagnetic energy that is basically energy that can travel in waves.
• The difference between two adjacent waves is called a wavelength.
• The range of types of electromagnetic energy is known as the electromagnetic spectrum.
• A substance's color is due to its pigments
• Pigments can be discovered by using a technique known as paper chromatography
• Within the thylakoid membrane, chlorophyll and other molecules are arranged in clusters
• Two systems are involved in light reactions; Water-splitting Photosystem and the NADPH-producing photosystem.

1) Explain why a leaf appears green.

A leaf appears green because green light is not absorbed, as chloroplast pigments do not absorb green light well.

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

Each time a pigment molecule absorbs light energy, one of the pigment's electrons gains energy. Because the state is very unstable, the excited electron falls back to the ground state and transfers the energy to a neighbouring molecule. It keeps jumping until it arrives at the reaction center of the photosystem. The primary electron acceptor traps the excited electron from the chlorophyll a molecule.

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

The two other molecules are ATP and NADH.

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

They take place in the thylakoid.

Vocabulary:

Wavelength: The distance between two adjacent waves.
Electromagnetic spectrum: The range of types of electromagnetic energy.
Pigments: Chemical compounds that make a substance a certain color.
Paper chromatography: A laboratory technique in which one can observe the different pigments in a green leaf.
Photosystems: Clusters that consists of chlorophyll and other molecules within the thylakoid molecule.