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 movements caused the plants to loose 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
Please read DrWLS's response to your question.
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To answer these questions, we need to analyze the information provided and understand the concepts of transpiration and its relationship with environmental conditions.
1) The statement mentions that plants require large volumes of water to live, even though the amount of water needed for essential processes like photosynthesis, cell growth, and cell maintenance is very small. This is because over 90 percent of the water absorbed by plants is lost into the air through transpiration. Transpiration is the loss of water vapor from plants, mainly through the small openings in leaves called stomata.
2) Now, let's focus on the given experimental conditions and the data associated with condition 5.
Condition 5 involves adding a fan to increase heat and additional light in a room with low humidity. The question asks us to explain the results associated with this condition.
a) Option A suggests that when a fan was added, the rate of transpiration slowed to the rate associated with room conditions because the fan cooled the plants. This option seems plausible since fans blowing air over the leaves can help lower the leaf temperature, which, in turn, can reduce the rate of transpiration. However, we need to consider other options before making a decision.
b) Option B states that the additional heat, light, and air movements caused the plants to lose so much water that after five minutes, they wilted, closing their stomata and preventing further water loss. This option suggests that excessive water loss led to plant wilting and stomata closure. This seems unlikely since wilting and stomata closure are mechanisms to prevent excessive water loss, not the result of it.
c) Option C suggests that the additional heat resulted in severe water loss that could not be counteracted by the airflow from the fan, leading to plant death. This option seems extreme and unlikely. Plants have mechanisms to regulate water loss, and it is unlikely that the conditions described would lead to the death of all the plants within five minutes.
d) Option D states that after five minutes, the rate of transpiration gradually increased because moisture was being brought up the stem more rapidly. This option contradicts the concept of transpiration, which is the loss of water vapor from the plant, not the uptake of moisture from the roots.
Based on this analysis, option A appears to be the most plausible explanation. When the fan was added, it likely cooled the plants, reducing the rate of transpiration to that associated with room conditions.
Moving on to question 4:
The question asks us to identify a hypothesis about the effects of high humidity supported by the graph.
The given data does not include a graph, so we cannot directly refer to it. However, we can make an inference based on our understanding of transpiration and humidity.
When humidity is high, the air is already saturated with moisture, making it harder for water to evaporate from the plant's leaves. This suggests that evaporation will proceed more slowly in high humidity conditions.
Therefore, option D, "Evaporation will proceed more slowly," is the most likely hypothesis about the effects of high humidity, supported by the concept of transpiration.