Identify the reactants, products, and basic functions of photosynthesis (NGSSS SC.912.L.18.7; Reporting Category 1, Molecular and Cellular Biology).

What this topic is asking

The NGSSS benchmark SC.912.L.18.7 asks you to identify the reactants, products, and basic functions of photosynthesis. For the Florida Biology 1 EOC you need to know what goes in, what comes out, where photosynthesis happens, and how it fits into the flow of energy and matter. The single most-tested skill is naming the inputs and outputs correctly (and not confusing them with respiration).

What photosynthesis does

Because plants make their own food, they are producers: the starting point of nearly every food chain. The glucose they make feeds the plant itself and, when the plant is eaten, the organisms above it.

Reactants and products

The word equation:

carbon dioxide + water + light energy gives glucose + oxygen

A balanced chemical version is $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

The most common EOC error is to swap reactants and products, or to confuse them with cellular respiration. Keep it straight: in photosynthesis, carbon dioxide and water go in, and glucose and oxygen come out.

Where it happens

Photosynthesis takes place in the chloroplast, an organelle found in plant cells and algae (not in animal cells). The chloroplast contains the green pigment chlorophyll, which absorbs light energy (mostly red and blue light, reflecting green, which is why plants look green). That captured light energy drives the reaction that builds glucose.

Energy and matter

Photosynthesis is the entry point of energy into most ecosystems. It captures light energy from the Sun and stores it as chemical energy in glucose. That stored energy then flows through the ecosystem when producers are eaten (see energy flow and food webs). Photosynthesis also matters for the carbon cycle: it removes carbon dioxide from the air and locks the carbon into glucose.

Limiting factors can slow photosynthesis: without enough light, carbon dioxide, or a suitable temperature, the rate falls. With no light at all, photosynthesis stops.

Try this

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

• Cue. Carbon dioxide + water + light energy gives glucose + oxygen.

Q2. State where photosynthesis occurs and the role of chlorophyll. [2]

• Cue. It occurs in the chloroplast; chlorophyll absorbs light energy to drive the reaction.