What happens to plants in the dark?

In one line

The rule

Plants need light for photosynthesis, but some life processes continue in the dark, like respiration.

Let's understand it simply

Imagine a plant as a small kitchen. In the day, the kitchen gets sunlight, which is like the gas for the stove. The plant uses this sunlight to cook its food (glucose) from air (carbon dioxide) and water. This is called photosynthesis (making food using light).

But at night, the sun goes away. The kitchen has no gas. The plant cannot cook new food. But it still needs energy to stay alive, just like you need energy to breathe and move even when you are not eating. So, the plant uses the food it made during the day. This is called respiration (using food for energy).

How it works

1. In light, plants do photosynthesis: they make food using sunlight, water, and carbon dioxide.
2. In the dark, photosynthesis stops because there is no sunlight.
3. Plants keep doing respiration all the time, day and night.
4. In respiration, plants use oxygen and the food (glucose) they made to get energy.
5. Plants release carbon dioxide and water during respiration.
6. If darkness lasts too long, the plant may run out of food and get weak or die.

The story behind it

Scientists studied plants and saw that they gave out oxygen in light and carbon dioxide in the dark. This led to the discovery of photosynthesis and respiration as separate processes. Melvin Calvin, an American scientist, found out how plants make glucose in the dark reactions (Calvin cycle) of photosynthesis. He won the Nobel Prize for this work.

Where you see it in real life

• A potted plant in a dark room: The plant cannot make new food, so it uses stored food. If kept in the dark for many days, it turns yellow and weak.
• Farmers covering crops at night: Crops do not grow in the dark; growth slows down.
• Seeds sprouting under soil: They use stored food until they reach sunlight.
• A leaf kept between two books: That part of the leaf turns pale because it cannot make food.
• Plants in a closed cupboard: They wilt and may die if not brought back to light.
• Diwali night: Even with no sunlight, plants keep breathing (respiring) just like us.

Why it matters

• Plants need light to grow and stay healthy. No light means no food making.
• Farmers and gardeners must give plants enough sunlight for good crops.
• In biology, understanding this helps us know how plants live and why they die in darkness.
• Exams often ask about photosynthesis and respiration, so this is a key topic.

Worked example

Let’s see what happens if a plant is kept in the dark for 3 days:

Given: A healthy plant is kept in a dark room for 3 days.
Step 1: Photosynthesis needs sunlight → No photosynthesis in the dark.
Step 2: Respiration continues → Plant uses stored glucose for energy.
Step 3: No new food is made → Plant starts using up its food stores.
Step 4: After 3 days, leaves start turning yellow and plant looks weak.
Step 5: If darkness continues, the plant may die.

Common mistakes

• Thinking plants only breathe out oxygen: In the dark, they breathe in oxygen and give out carbon dioxide.
• Believing plants die instantly in the dark: They can survive for some days using stored food.
• Forgetting that respiration happens all the time: Plants respire day and night, not just in darkness.
• Mixing up photosynthesis and respiration: Photosynthesis needs light; respiration does not.

Remember it

Plants need light to make food, but they keep using energy even in the dark.