The amount of water needed daily by plants for photosynthesis, cell growth, and cell maintenance is very small, and yet plants require large volumes of water in order to live. It is estimated that over 90 percent of the water absorbed by plants is lost into the air. Most of the water loss is due to evaporation from the plant through the small openings in leaves called stomata. This loss of water vapor from plants is referred to as transpiration.

The data represent the average transpiration value for twenty plants under each of the six experimental conditions. The room conditions were a temperature of 22°C, fluorescent lighting, and low humidity.
3) Which of the following statements best explains the results associated with condition 5?
A) When a fan was added to heat and additional light, the rate of transpiration was slowed to the rate associated with room conditions, because the fan cooled the plants.
B) Additional heat and light and air movement caused the plants to lose so much water that after five minutes they wilted, thereby closing their stomata and preventing further water loss.
C) Additional heat resulted in such severe water loss that it could not be counteracted by air movement caused by the fan, and the plants died.
D) After five minutes the rate of transpiration gradually increased, because moisture was being brought up the stem more rapidly.

4) Which of the following hypotheses about the effects of high humidity is supported by the graph?
A) Plants will grow faster.
B) Plant tissues will contain a smaller volume of water.
C) Plants will close their stomata.
D) Evaporation will proceed more slowly.

To answer question 3, we need to understand the experimental conditions and their impact on transpiration. Among the six experimental conditions, condition 5 is when a fan was added to heat and additional light. The question asks for the best explanation for the results observed under this condition.

To find the answer, we should identify the option that provides a plausible explanation based on the information given.

Statement A) When a fan was added to heat and additional light, the rate of transpiration was slowed to the rate associated with room conditions because the fan cooled the plants.

This statement suggests that the fan in condition 5 actually reduced the rate of transpiration. However, we know that transpiration is primarily caused by water loss through stomata due to evaporation, and the addition of heat and light generally increases the rate of transpiration. So, this statement does not align with our understanding of how transpiration works. Therefore, option A is not the correct explanation.

Statement B) Additional heat and light and air movement caused the plants to lose so much water that after five minutes they wilted, thereby closing their stomata and preventing further water loss.

This statement suggests that the plants wilted and closed their stomata due to excessive water loss caused by additional heat, light, and air movement. This explanation aligns with the information provided, stating that most of the water loss is due to evaporation from the plant through stomata. If the plants lost a significant amount of water due to the experimental conditions, it would make sense for them to wilt and close their stomata to prevent further water loss. Therefore, option B is the best explanation for the results associated with condition 5.

Statement C) Additional heat resulted in such severe water loss that it could not be counteracted by air movement caused by the fan, and the plants died.

This statement suggests that the severe water loss from additional heat caused the plants to die. While it is mentioned that plants require large volumes of water to live, the information given does not suggest that water loss due to additional heat in condition 5 would cause the plants to die. Hence, option C is not the correct explanation.

Statement D) After five minutes, the rate of transpiration gradually increased because moisture was being brought up the stem more rapidly.

This statement suggests that the rate of transpiration increased gradually after five minutes due to moisture being brought up the stem more rapidly. However, this explanation does not align with our understanding that transpiration occurs primarily through stomata and is driven by evaporation, not necessarily by moisture being brought up the stem. Therefore, option D is not the correct explanation.

To answer question 4, we need to analyze the data and graph provided to determine the effects of high humidity on transpiration.

The question asks for the hypothesis about the effects of high humidity that is supported by the graph. Looking at the graph, observe how transpiration changes in response to the different humidity levels.

Statement A) Plants will grow faster.

The graph does not provide any information about the growth rate of plants, so this hypothesis cannot be supported by the graph. Therefore, option A is incorrect.

Statement B) Plant tissues will contain a smaller volume of water.

The graph shows that as humidity increases, the rate of transpiration decreases. This suggests that there is less water loss from the plants in higher humidity conditions. Consequently, it is reasonable to conclude that plant tissues would contain a smaller volume of water when the humidity is high. Therefore, option B is the hypothesis supported by the graph.

Statement C) Plants will close their stomata.

The graph does not provide any information about stomatal closure in response to humidity levels. Thus, this hypothesis is not supported by the graph. Therefore, option C is incorrect.

Statement D) Evaporation will proceed more slowly.

The graph clearly shows that as humidity increases, the rate of transpiration decreases. Since transpiration is primarily driven by evaporation, it follows that evaporation would proceed more slowly in higher humidity conditions. Therefore, option D is the correct hypothesis supported by the graph.

In summary, the best explanation for the results associated with condition 5 is option B, and the hypothesis about the effects of high humidity supported by the graph is option D.