Photosynthesis Summary

Overview

This lecture explains photosynthesis, its stages, the structure of chloroplasts, and the roles of different photosynthetic pigments.

Photosynthesis is a process in autotrophs (self-feeding organisms) that uses sunlight to convert water and carbon dioxide into glucose and oxygen.
Energy from sunlight splits water, stores hydrogen in glucose, and releases oxygen as a waste product.

Photosynthesis consists of two main stages: the light-dependent and light-independent (Calvin cycle) reactions.
Light-dependent reactions occur in thylakoid membranes and require light to produce ATP and NADPH.
Light-independent reactions take place in the stroma and use ATP and NADPH to fix carbon dioxide into glucose.

Photosynthesis occurs in chloroplasts, which compartmentalize and isolate photosynthetic reactions.
Each chloroplast has a double membrane envelope, permeable to oxygen, glucose, ions, and carbon dioxide.
The stroma is a gelatinous matrix containing circular DNA, ribosomes, enzymes, starch grains, and lipids for storage.
Thylakoids are disk-like sacs; stacks of thylakoids form grana.
Intergranal lamellae connect grana, increasing the surface area for light absorption.
The thylakoid membrane contains photosynthetic pigments crucial for capturing light energy.

Chlorophyll is the main pigment in plants and absorbs red, orange, and blue-violet light, reflecting green.
Chlorophyll has a porphyrin ring with a central magnesium atom and a long hydrocarbon chain.
Types of chlorophyll include a, b, c, d, and bacterial chlorophyll, with chlorophyll a being the most important.
Accessory pigments include other chlorophylls, carotenoids, and phaeophytin.
Carotenoids (beta-carotene and xanthophyll) reflect orange and yellow light; they protect by absorbing excess light and dissipating it as heat.
Phaeophytin are grey pigments also involved in light energy conversion.

Autotroph — organism that makes its own food.
Photosynthesis — process converting sunlight, water, and CO₂ into glucose and O₂.
Chloroplast — organelle where photosynthesis occurs.
Stroma — the matrix inside chloroplasts where light-independent reactions occur.
Thylakoid — membrane sac in chloroplasts, site of light-dependent reactions.
Granum (pl. grana) — stack of thylakoids.
Chlorophyll — pigment that absorbs light for photosynthesis.
Carotenoid — accessory pigment that helps capture light and provides protection.
Intergranal lamellae — structures connecting grana to maximize light absorption.