Photosynthesis — Science definition

Defined in 3 courses:

Where it is taught

In use

In photosynthesis, a plant uses light energy captured by chlorophyll to build glucose out of two very unpromising ingredients: carbon dioxide from the air and water from the soil.

Photosynthesis & Cellular Respiration

For almost the entire living world, the answer begins with photosynthesis — the process autotrophs use to capture light energy and lock it away inside food.

Photosynthesis

Photosynthesis pulls carbon dioxide out of the air and locks its carbon into sugars inside producers; that carbon then travels up the food web as organisms eat one another.

Biogeochemical Cycles

Questions using photosynthesis

Problem 1

Which pair are the reactants (starting materials) of photosynthesis?
  1. Carbon dioxide and water
  2. Glucose and oxygen
  3. ATP and NADPH
  4. Nitrogen and sunlight
Answer and explanation

Carbon dioxide and water

Photosynthesis uses carbon dioxide and water (plus light energy) to build glucose and release oxygen. Glucose and oxygen are the products, not the reactants.

Problem 2

In which organelle does photosynthesis take place?
  1. The ribosome
  2. The chloroplast
  3. The mitochondrion
  4. The nucleus
Answer and explanation

The chloroplast

Photosynthesis happens in the chloroplast, whose thylakoid membranes hold the chlorophyll that captures light.

Problem 3

The oxygen released by photosynthesis comes from splitting one of the reactants. Which reactant is split, and in which stage does this happen?
Answer and explanation

The oxygen comes from splitting water (H2O). This happens in the light-dependent reactions, in the thylakoid membranes, where light energy is used to break water apart.

Problem 4

What is one role of water in oxygenic photosynthesis? Show the reasoning, not just the conclusion.
Hints

Light supplies energy; it is not a source of carbon atoms.

Answer and explanation

Water supplies electrons and hydrogen in light reactions; released O₂ originates from water.

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