Relationship Between the Size of the Leaves and rate of Transpiration in Plants

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Author: Janice VanCleave

What Effect Does the Size of a Plant's Leaves Have on the Plant's Transpiration Rate?

Category: Biology—Botany—Physiology

Project Idea by: Jonna Butcher

The process by which plants lose water by vaporization (the change from a liquid to a gas) is called transpiration. The water escapes in gas form from the plant through stomata, which are special openings in the outer layer of plants, generally in the leaves. (The singular form of stomata is stoma.) The stomata can be opened or closed by guard cells.

As particles of water that move out of the plant through the stomata are lost by vaporization at the surface of leaves, more water enters the plants through the roots and fills the space left by the lost water particles. If the water lost by transpiration is not replaced by water from the soil, there is a loss of turgor (the pressure within plant cells) and the stomata close. With enough loss of turgor, the plant wilts (becomes limp and droopy).

Transpiration rate is the amount of water lost by a plant in a specific period of time. A project question might be, "What effect does the size of a plant's leaves have on its transpiration rate?"

What Effect Does the Size of a Plant's Leaves Have on the Plant's Transpiration Rate?

Clues for Your Investigation

Capture the water lost by transpiration from the leaves of plants with different-sized leaves. One way is to cover the leaves with a plastic bag and measure the water collected in the bag after a specific amount of time. To make sure the environmental conditions are the same for each testing, select plants near one another and do the testing at the same time.

Independent Variable: Leaf size

Dependent Variable: Transpiration rate

Controlled Variables: Number of leaves in each collection bag, type of bag, how the bag is secured to the plant, time of testing, environmental conditions

Control: Arbitrarily selected plant with medium-sized leaves

Other Questions to Explore

  1. How does temperature affect transpiration?
  2. What effect does humidity have on transpiration?
  3. How does the amount of light received by a plant affect transpiration?
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