Photosynthetic Pigments Flashcards

Questions and Answers

Define pigment.

Pigment molecules absorb specific wavelengths of light and reflect others.

What are the two classes of photosynthetic pigments?

Chlorophylls and carotenoids.

Outline what chlorophyll a and b are.

Chlorophyll a is the most abundant form (2:1) and chlorophyll b has the same structure but the CH3 is replaced by an aldehyde group (-CHO) and absorbs at 500nm-640nm (appears blue-green).

What colour are carotenoids?

Yellow, orange, red or brown. Signup and view all the answers

What are accessory pigments also known as? Why?

Accessory pigments because they pass the light energy they absorb on to chlorophyll a. Signup and view all the answers

Why do they appear green?

They are usually masked by the green chlorophylls but can be seen in the autumn just before leaf-fall. Signup and view all the answers

What colour provides the orange pigment in carrots?

B-Carotene. Signup and view all the answers

What is B-Carotene broken down to form?

It is broken down during digestion to form 2 molecules of vitamin A. Signup and view all the answers

Outline the structure of photosystems.

Lots of accessory pigment molecules surround a central primary pigment molecule (reaction centre) and spans the thylakoid membrane. Signup and view all the answers

What are the two types of photosystems?

PSI = P700 (absorbs light best at 700nm) and PSII = P680 (absorbs light best at 680nm). Signup and view all the answers

What is the reaction centre of a photosystem?

The reaction centre is the primary pigment - a molecule of chlorophyll a. Signup and view all the answers

What are the primary pigments?

Two forms of chlorophyll a with slightly different absorption peaks (680 nm and 700 nm). Signup and view all the answers

What are the different types of accessory pigments?

Chlorophyll b, carotenoids, and xanthophylls. Signup and view all the answers

Where are the pigments found?

The pigments are arranged in light-harvesting clusters called photosystems (light harvesting centres) in the thylakoid membrane. Signup and view all the answers

How do the primary pigments act as reaction centres?

Energy of the light absorbed by different pigments is passed onto the primary pigment. Signup and view all the answers

What controls the carbon fixation reactions?

The stroma is the fluid part of the chloroplast which contains the enzymes controlling the carbon fixation reactions. Signup and view all the answers

How do electrons affect the reaction?

Absorption of light by chlorophyll a causes electrons to be excited and move to a higher energy level. Signup and view all the answers

What is an absorption spectrum?

A graph that shows which wavelengths of light are absorbed by a pigment. Signup and view all the answers

What is an action spectrum?

A graph which shows the wavelengths of light that are actually used in photosynthesis. Signup and view all the answers

What regions does chlorophyll a mainly absorb light?

Chlorophyll a absorbs light mainly in the red/orange and blue regions. Signup and view all the answers

What regions do accessory pigments mainly absorb light?

Accessory pigments absorb light from other regions of the spectrum and pass the energy onto chlorophyll a. Signup and view all the answers

How do accessory pigments maximize photosynthesis?

Accessory pigments broaden the absorption spectrum so that more energy is available for photosynthesis. Signup and view all the answers

How does the process of pigment in a chlorophyll solution work?

Light excites electrons to a higher energy level, returning to the original state, transferring energy as heat and red fluorescence. Signup and view all the answers

How does the process of the reaction of a pigment in a leaf work?

Light excites electrons to a higher energy level, which are accepted by an electron acceptor and passed onto electron carriers, generating ATP. Signup and view all the answers

Study Notes

Photosynthetic Pigments Overview

Pigments are molecules that absorb specific wavelengths of light while reflecting others.
Two primary classes of photosynthetic pigments: Chlorophylls and Carotenoids.

Chlorophyll Details

Chlorophyll a: Most abundant form with a 2:1 ratio compared to chlorophyll b.
Chlorophyll b: Similar structure to chlorophyll a, with a CH3 group replaced by an aldehyde (-CHO), absorbing light at 500-640 nm (appears blue-green).

Carotenoids

Carotenoids are pigments that range in color from yellow to orange, red, or brown, strongly absorbing light in the blue-violet range.
Also known as accessory pigments because they transfer absorbed light energy to chlorophyll a.

Seasonal Changes in Pigment Visibility

Carotenoids are often masked by chlorophylls; they become visible in autumn as chlorophylls degrade before leaf-fall.

Nutritional Role of Carotenoids

B-Carotene: Provides orange pigment in carrots, which is broken down during digestion to produce two molecules of vitamin A.

Structure of Photosystems

Photosystems consist of multiple accessory pigments surrounding a central primary pigment molecule (reaction center), spanning the thylakoid membrane.

Types of Photosystems

PSI (Photosystem I): Absorbs best at 700 nm (P700).
PSII (Photosystem II): Absorbs best at 680 nm (P680).

Reaction Center Function

Primary pigment in a photosystem is chlorophyll a, which plays a crucial role in the reaction center.

Accessory Pigments

Include chlorophyll b, carotenoids, and xanthophylls, aiding in broadening absorption spectrum of light for photosynthesis.

Pigment Location

Pigments are organized in light-harvesting clusters known as photosystems within the thylakoid membrane.

Primary Pigment Function

Primary pigments receive energy from absorbed light, helping extend the absorption spectrum for photosynthesis.

Carbon Fixation Control

The stroma, the fluid area in chloroplasts, contains enzymes essential for regulating carbon fixation reactions, influenced by temperature.

Electron Excitation Mechanism

Light absorption by chlorophyll a leads to electron excitation, moving electrons to a higher energy state, which are transferred to electron acceptors and carriers.

Absorption and Action Spectra

Absorption Spectrum: Displays which wavelengths of light a pigment absorbs.
Action Spectrum: Illustrates the wavelengths of light utilized during photosynthesis.

Light Absorption by Pigments

Chlorophyll a mainly absorbs light in red/orange and blue regions.
Accessory pigments absorb additional wavelengths and relay energy to chlorophyll a, maximizing photosynthesis.

Enhancing Photosynthesis

Accessory pigments broaden the light absorption spectrum, increasing energy availability for photosynthesis.

Energy Transfer in Chlorophyll Solution

Upon light exposure, electrons in chlorophyll solution are excited to a higher energy state and then return, transferring energy as heat and longer wavelength light, appearing as red fluorescence.

Electron Transfer in Leaves

In leaves, absorbed light excites electrons which are then accepted by electron carriers, leading to ATP formation through photophosphorylation via chemiosmosis, thus converting light energy into a usable form.

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Description

This quiz focuses on the key concepts related to photosynthetic pigments, including definitions, classifications, and characteristics of chlorophylls and carotenoids. Utilize these flashcards to enhance your understanding of how these pigments function in photosynthesis.