BIO101 – Topic 26: Photosynthesis and Energy Conversion in
Plants
26.1 Introduction
Photosynthesis is a fundamental biological process by which green plants, algae, and certain bacteria
convert light energy from the sun into chemical energy stored in glucose. It sustains almost all life on
Earth by providing food and oxygen essential for survival. This process occurs mainly in the
chloroplasts of plant cells and plays a central role in the global carbon and energy cycles.
26.2 Definition of Photosynthesis
Photosynthesis is defined as the process by which green plants use chlorophyll and light energy to
convert carbon dioxide and water into glucose and oxygen. It is a light-dependent anabolic process that
transforms inorganic substances into organic compounds.
26.3 Raw Materials and Products
Raw Materials: - Carbon dioxide (CO■) from the atmosphere - Water (H■O) from the soil - Light energy
from the sun - Chlorophyll from chloroplasts Products: - Glucose (C■H■■O■): a source of energy and
building material for the plant. - Oxygen (O■): released into the atmosphere as a by-product.
26.4 Sites and Requirements
Site: Photosynthesis occurs in the chloroplasts, mainly in the mesophyll cells of leaves. Requirements: -
Sunlight as the energy source - Chlorophyll pigments (chlorophyll a and b) - Carbon dioxide and water -
Enzymes for catalyzing reactions
26.5 Stages of Photosynthesis (Light & Dark Reactions)
1. Light-dependent Reactions (Light Reactions) - Occur in the thylakoid membranes. - Light energy is
absorbed by chlorophyll and converted to chemical energy (ATP and NADPH). - Water is split
(photolysis) to release oxygen, protons, and electrons. 2. Light-independent Reactions (Dark Reactions
or Calvin Cycle) - Occur in the stroma of the chloroplast. - Use ATP and NADPH from the light reactions
to fix carbon dioxide into glucose. - This stage does not require light but depends on the products of the
light reactions.
26.6 Balanced Chemical Equation
6CO■ + 6H■O + Light Energy → C■H■■O■ + 6O■
26.7 Importance of Photosynthesis
- Provides food (glucose) for plants and other organisms. - Releases oxygen necessary for respiration. -
Regulates atmospheric CO■ levels, reducing global warming. - Forms the base of all food chains and
ecosystems. - Supports energy flow and biomass production. - Provides raw materials for biofuels and
industrial products.
26.8 Factors Affecting Photosynthesis
Plants
26.1 Introduction
Photosynthesis is a fundamental biological process by which green plants, algae, and certain bacteria
convert light energy from the sun into chemical energy stored in glucose. It sustains almost all life on
Earth by providing food and oxygen essential for survival. This process occurs mainly in the
chloroplasts of plant cells and plays a central role in the global carbon and energy cycles.
26.2 Definition of Photosynthesis
Photosynthesis is defined as the process by which green plants use chlorophyll and light energy to
convert carbon dioxide and water into glucose and oxygen. It is a light-dependent anabolic process that
transforms inorganic substances into organic compounds.
26.3 Raw Materials and Products
Raw Materials: - Carbon dioxide (CO■) from the atmosphere - Water (H■O) from the soil - Light energy
from the sun - Chlorophyll from chloroplasts Products: - Glucose (C■H■■O■): a source of energy and
building material for the plant. - Oxygen (O■): released into the atmosphere as a by-product.
26.4 Sites and Requirements
Site: Photosynthesis occurs in the chloroplasts, mainly in the mesophyll cells of leaves. Requirements: -
Sunlight as the energy source - Chlorophyll pigments (chlorophyll a and b) - Carbon dioxide and water -
Enzymes for catalyzing reactions
26.5 Stages of Photosynthesis (Light & Dark Reactions)
1. Light-dependent Reactions (Light Reactions) - Occur in the thylakoid membranes. - Light energy is
absorbed by chlorophyll and converted to chemical energy (ATP and NADPH). - Water is split
(photolysis) to release oxygen, protons, and electrons. 2. Light-independent Reactions (Dark Reactions
or Calvin Cycle) - Occur in the stroma of the chloroplast. - Use ATP and NADPH from the light reactions
to fix carbon dioxide into glucose. - This stage does not require light but depends on the products of the
light reactions.
26.6 Balanced Chemical Equation
6CO■ + 6H■O + Light Energy → C■H■■O■ + 6O■
26.7 Importance of Photosynthesis
- Provides food (glucose) for plants and other organisms. - Releases oxygen necessary for respiration. -
Regulates atmospheric CO■ levels, reducing global warming. - Forms the base of all food chains and
ecosystems. - Supports energy flow and biomass production. - Provides raw materials for biofuels and
industrial products.
26.8 Factors Affecting Photosynthesis
