6- photosynthetic pigments

What are photosynthetic pigments?

Substances in chloroplasts that absorb light energy for photosynthesis.

Where are photosynthetic pigments found?

In the chloroplasts of plant cells.

Name the two main types of photosynthetic pigment.

Chlorophylls and carotenoids.

Name two types of chlorophyll.

Chlorophyll a and chlorophyll b.

What colour is chlorophyll a?

Blue-green.

What colour is chlorophyll b?

Olive green.

Which pigment is the most important in photosynthesis?

Chlorophyll a.

What are accessory pigments?

Pigments that absorb additional wavelengths of light and transfer energy to chlorophyll a.

Why are accessory pigments important?

They increase the range of wavelengths of light that can be used in photosynthesis.

Name two carotenoid pigments.

Beta-carotene and xanthophyll.

What colour is beta-carotene?

Red-orange.

What colour is xanthophyll?

Orange-red.

What is an absorption spectrum?

A graph showing how much light a pigment absorbs at different wavelengths.

What does low absorption on an absorption spectrum mean?

The light is reflected or transmitted, not absorbed.

Why do leaves appear green?

Green wavelengths are reflected rather than absorbed.

Why do different plant species have different leaf colours?

They have different combinations of photosynthetic pigments.

What is an action spectrum?

A graph showing the rate of photosynthesis at different wavelengths of light.

How is an action spectrum obtained?

By measuring the rate of photosynthesis using different wavelengths of light.

How does the action spectrum relate to absorption spectra?

It matches the absorption spectra of photosynthetic pigments.

What does the similarity between action and absorption spectra show?

That photosynthetic pigments are responsible for photosynthesis.

What type of molecule is chlorophyll?

A small molecule, not a protein.

What is chlorophyll structurally similar to?

Haem.

What metal ion does chlorophyll contain?

Magnesium.

What metal ion does haem contain?

Iron.

What are photosystems?

Complexes of pigments, proteins and lipids involved in light absorption.

What is the role of photosystems?

To hold pigments in the best position to maximise light absorption.

Where are photosystems located?

In the thylakoid membranes of chloroplasts.

Approximately how many chlorophyll molecules are in one photosystem?

About 200.

Approximately how many accessory pigment molecules are in one photosystem?

About 50.

What other components are found in photosystems?

Proteins, including enzymes, and lipids.

How many types of photosystem are found in green plants?

Two.

Name the two types of photosystem.

Photosystem I (PSI) and Photosystem II (PSII).

Do PSI and PSII absorb the same wavelengths of light?

No, they absorb different wavelengths.

Do PSI and PSII have the same role?

No, they have slightly different roles in the light-dependent reactions.