AP Bio Lab Test Review (Transpiration Lab)

the loss of water through the stomates

transpiration is the loss of water through the stomates. If you increase transpiration, you can increase water loss. stomata are the pores that allow the exchange of gases in the plant with atmospheric gases. while excessive loss of water vapor is a hazard for plant life, transpiration is a vital function that provides the pressure differential that moves water up from the roots bringing materials and minerals for biosynthesis to the cell, drives phloem transport, and also cools the leaf. in this lab we strive to understand how water moves from roots to leaves in terms of the physical and chemical properties of water and the forces provided by differences in water potential, to understand the role of transpiration in the transport of water within a plant, to understand the structures used by plants to transport water and regulate water movement, and to test the effects of environmental variables on the rate of transpiration using a controlled experiment.

light, fan, misted, dark (environmental factors)

the rate of transpiration

the type of plant, room temperature, type of scale, how far the light/fan was placed from the plant

the leaf will begin to do photosynthesis. Therefore, the stomata open to allow the uptake of CO2. this allows more water vapor to escape, leading to an increased transpiration rate. Also, the light will make the outside of the leaf dry, causing the inside of the leaf to have a higher water potential

The movement of air over the surface of the leaf takes away water vapor, and therefore speeds up diffusion and evaporation out of the leaf, by maintaining the concentration gradient. this will increase the transpiration rate. just like the light, the fan will also dry out the outside of the leaf causing the inside to have a higher water potential

The Mist contains water vapor, so the diffusion gradient for water vapor leaving the leaf is decreased. this causes a decrease in the rate of transpiration. if the outside of the plant is wet, then the inside has a lower water potential

the ability of something to lose water

Under the humid condition, the rate of transpiration decreased due to the fact that the water potential of the air surrounding the leaf was increased by the mist. this minimized the gradient of water potential between the leaf and its surrounding environment. this occurred because the rate of transpiration decreases proportionally to the amount of humidity in the air. Under the windy and bright light conditions, the rate of transpiration increased due to the fact that wind and light removes water vapor from the leafs surroundings resulting in a broader concentration difference between the leaf and its outer environment. this allows the leaf to have a higher water potential as compared to its outside environment. a more rapid loss of water occurred through the stomata as well.

The plant loses water through the stomata, so the advantage is that when they are closed, the plant saves water. however, the plant also uses the stomata to let in carbon dioxide necessary for photosynthesis. so the disadvantage is that when the stomata are closed, it cannot take in enough carbon dioxide.

All leaves have cuticles. the cuticle is a secretion that surrounds the epidermis of the leave. it is a waxy coating that often appears shiny. the function of this structural adaptation is to prevent water loss, so plants in danger of losing too much water will secrete a thicker cuticle. Cacti have adaptations that enable them to reduce water loss from their leaves. cacti appear to have smaller, fatter leaves or no leaves at all. plants conserving water have thicker succulent leaves to prevent excess water loss. the smaller, fatter leaves cut down on surface area and prevent excess water from leaving through the stomata. some leaves also appear to be hairy. these leaves have hair-like projections on the surface of the lea that are used to trap water that might have otherwise been lost.

You needed to graph the percent water loss each day instead of the total amount of water loss each day because the original plans could have been different masses in the beginning. you can't compare the amount of water because the plants are not identical, so the numbers aren't proportional by default.

The plants placed in a bright light and in front of the fan will have the most transpiration

I proved my hypothesis correct because since light and wind make the outside of the leaf dry, the inside will have a higher water potential. This leads to an increase in transpiration.

An attraction between molecules of different substances

Attraction between molecules of the same substance

Transports water up the roots to the leaves

transports food down the roots from the leaves