Question

Describe what happens to these four substances, light energy, and chemical energy during photosynthesis. Then write a simple equation for the substances and another for energy, using words and arrows to illustrate these changes.

Answer 1

The four substances are carbon dioxide, water, glucose and oxygen. What happens to each during photosynthesis:

- Carbon dioxide (CO2): taken in from the air and fixed in the Calvin cycle; the carbon atoms are reduced and incorporated into sugar (glucose) molecules.
- Water (H2O): taken up by the plant and split (photolysis) in the light reactions; its electrons and protons are used to make ATP/NADPH and reduce CO2, and its oxygen atoms end up mostly as O2.
- Glucose (C6H12O6): built from carbon, hydrogen and oxygen derived from CO2 and H2O; it stores chemical energy in its bonds and is later used for respiration, growth (cellulose), or stored as starch.
- Oxygen (O2): produced as a byproduct when water is split and released into the air.

What happens to energy:
- Light energy from the sun is absorbed by chlorophyll and converted in the light reactions into chemical energy carriers (ATP and NADPH). That chemical energy is then used in the Calvin cycle to form the high‑energy chemical bonds of glucose. So light energy becomes stored chemical energy in glucose.

Simple word equations (with arrows):

- For substances:
carbon dioxide + water → glucose + oxygen

- For energy:
light energy → chemical energy (stored in glucose)

Balanced chemical equation (optional, shows stoichiometry):
6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

Energy flow (more detail):
light energy → ATP & NADPH (short‑term chemical energy) → chemical energy stored in glucose (long‑term).