Why do cacti open their stomata during the night?

Question

Choose all that apply.

Cacti are able to store carbon dioxide obtained at night and use it during the day for photosynthesis.

If cacti open their stomata during the day they let in carbon dioxide but will also lose too much water.

Cacti need carbon dioxide in order to perform photosynthesis.

If cacti open their stomata at night they let in carbon dioxide but will also lose too much water.

Answer 1

Cacti open their stomata during the night primarily for the following reasons:

1. Cacti are able to store carbon dioxide obtained at night and use it during the day for photosynthesis. This describes a process known as Crassulacean Acid Metabolism (CAM), which allows cacti to conserve water by taking in carbon dioxide when it is cooler and more humid at night, then using that carbon dioxide for photosynthesis during the day.

2. If cacti open their stomata during the day they let in carbon dioxide but will also lose too much water. Cacti are adapted to arid environments, and opening their stomata during the hot daytime would lead to excessive water loss through transpiration. By opening them at night, they minimize water loss.

3. Cacti need carbon dioxide in order to perform photosynthesis. This is a fundamental requirement for all photosynthetic organisms, including cacti.

The last option, If cacti open their stomata at night they let in carbon dioxide but will also lose too much water, is not correct because opening stomata at night minimizes water loss, as temperatures are cooler and humidity is often higher.

So, you should choose the first three options.