Use a model to illustrate how photosynthesis transforms light energy into stored chemical energy in glucose (Louisiana Student Standards for Science, High School Biology, HS-LS1-5).

What this topic is asking

Louisiana's LS1 standards (HS-LS1-5) ask you to model how photosynthesis transforms light energy into stored chemical energy. For LEAP 2025 Biology you should know the reactants and products, where photosynthesis happens, the role of chlorophyll, and the energy transformation at its heart. Because this is a modeling standard, the test often shows a diagram or equation of photosynthesis and asks you to label inputs and outputs or trace the energy, and it pairs photosynthesis with respiration.

What photosynthesis is

Photosynthesis is how energy from sunlight first enters the living world. The glucose it makes is the starting fuel for almost all life, either directly (in the plant) or indirectly (in the animals that eat plants). This is the basis for energy flow through ecosystems.

Where it happens: the chloroplast and chlorophyll

So a cell that photosynthesizes a lot (such as a leaf cell) contains many chloroplasts, another example of structure matching function.

The reactants and products

Photosynthesis takes in two reactants and makes two products:

• Reactants (inputs): carbon dioxide (taken in from the air through the leaf) and water (taken up by the roots).
• Products (outputs): glucose (a carbohydrate that stores the energy) and oxygen (released into the air as a by-product).

In a word equation: carbon dioxide + water, using light energy, becomes glucose + oxygen.

The balanced chemical equation is:

(six carbon dioxide plus six water, using light energy, gives one glucose plus six oxygen). Notice the atoms balance on both sides, an example of the conservation of matter.

The energy transformation

The central idea the standard asks you to model is the energy transformation: light energy is captured and stored as chemical energy in the bonds of glucose. The plant can later release that stored chemical energy by cellular respiration. So photosynthesis and respiration are linked: photosynthesis stores energy (and makes oxygen), respiration releases it (and makes carbon dioxide and water). On the test, "light energy to chemical energy" is the phrase that signals photosynthesis.

Try this

Q1. Write the word equation for photosynthesis. [2]

• Cue. Carbon dioxide + water, using light energy, becomes glucose + oxygen.

Q2. State the energy transformation that takes place in photosynthesis. [1]

• Cue. Light energy is transformed into chemical energy stored in glucose.