Question

31. Cacti are plants that live in extremely dry environments. Unlike most other plants, cacti do not

have regular leaves, but instead have spines. They do have green stems. How would the lack of
regular leaves help cacti survive in their environment? In what part of the cacti would photosyn-
thesis occur?​

Answer 1

Cacti lack regular leaves and have spines to reduce water loss. Their stems carry out photosynthesis and store water. Adaptations like nighttime carbon fixation and closed stomata during the day conserve water in dry environments.

Step-by-step explanation:

The lack of regular leaves in cacti is an adaptation to their extremely dry environments. Leaves are usually responsible for photosynthesis, but they also represent a site of water loss due to transpiration. By having spines instead of leaves, cacti reduce water loss significantly.

Photosynthesis in cacti occurs in their green stems. These stems are not only capable of photosynthesis, but also serve as water storage organs, allowing cacti to maintain water reserves in the harsh desert conditions.

Cacti have also evolved other mechanisms to reduce water loss and increase water use efficiency. They can prepare materials for photosynthesis at night when temperatures are cooler, which minimizes water loss. This process is known as temporary carbon fixation. During the day, they use the stored CO₂ for photosynthesis with their stomata closed, an adaptation that further conserves water.

Answer 2

The correct answer is "in the thick stems of cacti".

Step-by-step explanation:

Since cacti are plants do not have regular leaves, the cacti perform photosynthesis in the thick stems of its body. The stems of the cacti are green-colored, and have chloroplasts that are able to perform photosynthesis. In consequence, cacti have adapted to no require leaves to execute photosynthesis, and the stems help them to preserve moisture and tolerate high temperatures.