Photosynthesis: Light Reactions and Calvin Cycle

This page provides a detailed explanation of the two main stages of photosynthesis: photolysis (the light reactions) and the Calvin cycle. It offers a comprehensive overview of the photosynthesis process explained in higher biology.

Stage 1: Photolysis (Light Reactions) The light reactions occur in the chloroplast and involve the following steps:

1. Light energy excites electrons in pigments.
2. Electrons move through the electron transport chain (ETC), releasing energy.
3. Energy is used to generate ATP via ATP synthase.
4. Energy is used for photolysis of water, producing hydrogen and oxygen.

Vocabulary: NADP - An enzyme that bonds with hydrogen to form NADPH, which is involved in the formation of G3P in stage 2.

Stage 2: The Calvin Cycle The Calvin cycle, also known as the light-independent reactions, involves the following steps:

1. Carbon dioxide fixation by RuBisCO enzyme to form 3-phosphoglycerate (3PG).
2. 3PG is phosphorylated by ATP and combined with hydrogen ions from NADPH to form G3P.
3. G3P is used to regenerate RuBP and synthesize glucose.

Highlight: The Calvin cycle is a light-independent process, contrary to the light reactions of photosynthesis.

The page also outlines the uses of glucose produced from photosynthesis:

1. Used as a respiratory substrate
2. Synthesized into starch
3. Synthesized into cellulose
4. Passed to other biosynthetic pathways

Example: Biosynthetic pathways can lead to the formation of various metabolites such as DNA, proteins, and fats.

This comprehensive guide provides students with a thorough understanding of the photosynthesis equation and the detailed photosynthesis process explained in higher biology class.

Light Absorption and Pigments in Photosynthesis

This page delves into the intricate details of how leaves absorb light for photosynthesis and the pigments involved in this process. It explains the fate of light hitting a leaf and the various pigments responsible for light absorption.

When light hits a leaf, it can be absorbed for photosynthesis, reflected, or transmitted. The main pigments found in leaves are chlorophyll a, chlorophyll b, and carotenoids. These pigments have different absorption spectra, allowing plants to utilize a broader range of light wavelengths.

Vocabulary: Absorption spectrum - A graph showing the range of light wavelengths absorbed by different pigments.

The page also introduces the concept of thin-layer chromatography, which is used to separate and identify different pigments. The Rf value, which represents the ratio of the distance traveled by the pigment to the distance traveled by the solvent, is explained.

Definition: Rf value = distance traveled by pigment / distance traveled by solvent

An action spectrum is presented, showing how effective different wavelengths of light are for photosynthesis. This spectrum reveals that chlorophyll a absorbs red and violet light best, chlorophyll b absorbs blue light best, and carotenoids absorb blue-green light.

Highlight: The presence of multiple pigments allows plants to absorb a wider range of light wavelengths, enhancing their photosynthetic efficiency.