Photosynthesis

Definition

The process by which green plants, algae, and some bacteria use sunlight to convert carbon dioxide and water into glucose and oxygen, using the pigment chlorophyll.

Key points

• Word summary: carbon dioxide plus water, in the presence of sunlight and chlorophyll, yield glucose plus oxygen.
• Occurs in chloroplasts; the green pigment chlorophyll absorbs mainly red and blue light and reflects green, which is why leaves look green.
• Two stages: the light reactions (in the thylakoids) split water and release oxygen, and the dark reactions (Calvin cycle, in the stroma) fix carbon dioxide into sugar.
• It is the primary source of atmospheric oxygen and the base of almost all food chains (producers convert solar energy into chemical energy).
• The reverse process is respiration, in which glucose is broken down to release energy.

Why it matters for CAPF

Photosynthesis is a staple biology topic: the reactants and products, the role of chlorophyll, and its place at the base of the food chain are common factual questions.

Common confusion

Photosynthesis builds glucose and releases oxygen (daytime, needs light); respiration breaks glucose and releases carbon dioxide (continuous). Chlorophyll is the pigment, the chloroplast is the organelle.

Related concepts

concept greenhouse effect, concept vitamins and deficiencies

Parent note

biology cell and classification