Photosynthetic Pigments Flashcards

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.

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.