Photosynthesis Basics

Rachel Hurst
Mar 30
3 min read

HSC Biology | Study Notes

This topic helps students understand how chloroplasts work, what substances are needed for photosynthesis, and why the process is essential for plant survival and growth.

In this lesson

the word equation for photosynthesis
the role of chloroplasts
the reactants and products of photosynthesis
how light energy is used
why photosynthesis is important in plants

What is photosynthesis?

Photosynthesis is the process by which plants make glucose using light energy.

This process happens mainly in the leaves, inside organelles called chloroplasts.

Photosynthesis is important because it allows plants to:

make their own food
store chemical energy
support growth and repair
provide food for other organisms in food chains

The word equation for photosynthesis

The word equation for photosynthesis is:

carbon dioxide + water → glucose + oxygen

Light energy is needed for this reaction to happen.

A fuller version is:

light energy

carbon dioxide + water →glucose + oxygen

Reactants and products

Reactants

Reactants are the substances needed at the start of a chemical reaction.

In photosynthesis, the reactants are:

carbon dioxide
water

Products

Products are the substances made by a chemical reaction.

In photosynthesis, the products are:

glucose
oxygen

Simple summary

Part of the process	Substance
Reactant	Carbon dioxide
Reactant	Water
Product	Glucose
Product	Oxygen

Chloroplasts

Chloroplasts are the organelles where photosynthesis takes place.

Why chloroplasts are important

Chloroplasts contain chlorophyll, a pigment that absorbs light energy.

This light energy is then used to drive the reactions of photosynthesis.

Where chloroplasts are found

Chloroplasts are found in:

plant cells
some protists

They are not found in animal cells.

Light energy

Photosynthesis needs light energy to occur.

What light energy does

Light energy provides the energy needed to change simple substances into glucose.

Without light energy:

photosynthesis cannot happen properly
the plant cannot make enough glucose

Why this matters

This is why plants need access to light. It also explains why leaves are adapted to absorb as much light as possible.

Role in plants

Photosynthesis has a vital role in plants.

Making glucose

The main purpose of photosynthesis is to make glucose.

Glucose can then be used:

in respiration to release energy
to make cellulose for cell walls
to make starch for storage
to build other organic molecules

Releasing oxygen

Photosynthesis also produces oxygen.

Some of this oxygen is used by the plant in respiration, and some diffuses out into the environment.

Supporting plant survival

Without photosynthesis, plants would not be able to produce the food they need to grow, repair tissues, and survive.

Photosynthesis and plant cells

Photosynthesis links closely to plant cell structure.

Important structures involved

chloroplasts absorb light
leaves provide a large surface area for light absorption
stomata allow carbon dioxide to enter
roots absorb water from the soil

This shows that photosynthesis is not just a chemical reaction, it is also linked to the structure and function of the whole plant.

Photosynthesis compared with respiration

Students often confuse photosynthesis and respiration, so it is helpful to compare them.

Photosynthesis

uses carbon dioxide and water
requires light energy
produces glucose and oxygen

Respiration

uses glucose and oxygen
releases energy
produces carbon dioxide and water

The two processes are linked, but they are not the same.

Worked example

Exam-style question

State the word equation for photosynthesis and identify the product used by plants for energy release.

Worked answer

The word equation is: