Quick Review Flashcards - Click to flip and test your knowledge!
Question
What is the biological definition of transpiration?
Answer
The loss of water in the form of water vapour from the leaves and other aerial parts of a plant.
Question
Approximately what percentage of water absorbed by a plant is actually used for photosynthesis and other activities?
Answer
2%
Question
What happens to the majority of water absorbed by a plant through its roots?
Answer
It is lost to the atmosphere as water vapour through transpiration.
Question
List two primary reasons why transpiration is useful for plants.
Answer
Creating suction force for water/mineral absorption and cooling the plant in hot weather.
Question
In an experiment to demonstrate transpiration, why is the mouth of a polythene bag tied around the base of the stem rather than the pot?
Answer
To prevent water vapour escaping from the soil in the pot from entering the bag.
Question
What is the specific colour change of dry cobalt chloride paper when exposed to moisture?
Answer
It changes from blue to pink.
Question
In an experiment using three bell jars (A with plant, B with plant and cobalt paper, C with only cobalt paper), what is the purpose of Jar C?
Answer
It serves as a control to prove there is no moisture in the air without a plant.
Question
Which method of measuring transpiration involves weighing a potted plant before and after a period of time?
Answer
The weighing method.
Question
When using the weighing method, why must the soil surface and the pot be fully covered?
Answer
To prevent water loss through evaporation from the soil surface.
Question
What is a 'potometer'?
Answer
A device that measures the rate of water intake by a plant.
Question
How does the water intake measured by a potometer relate to the water lost through transpiration?
Answer
Water intake is almost equal to the water lost through transpiration.
Question
Which specific potometer is commonly used to measure water uptake by a cut shoot?
Answer
Ganong's potometer.
Question
In Ganong's potometer, what is the purpose of the air bubble in the horizontal graduated capillary tube?
Answer
Its movement indicates the volume of water lost (uptake) in a given time.
Question
Why is the twig in a potometer experiment cut obliquely?
Answer
To allow a larger surface area for water intake.
Question
Why is it essential to cut the twig for a potometer experiment under water?
Answer
To avoid the suction of an air bubble into the twig which would block the xylem.
Question
Mention one limitation of using a potometer to measure transpiration.
Answer
Introducing the air bubble into the capillary tube is not very easy.
Question
How do changes in outside air temperature affect the accuracy of Ganong's potometer?
Answer
They may affect the position of the air bubble in the capillary tube due to expansion or contraction.
Question
Name the three types of transpiration based on the region from which they occur.
Answer
Stomatal, cuticular, and lenticular transpiration.
Question
Which type of transpiration accounts for the majority of water loss in plants?
Answer
Stomatal transpiration.
Question
What are 'stomata'?
Answer
Minute openings in the epidermal layer of leaves surrounded by two bean-shaped guard cells.
Question
What is the typical range of stomata per $cm^{2}$ on a leaf?
Answer
$1,000$ to $10,000$ per $cm^{2}$.
Question
By what physical process does water vapour escape from the sub-stomatal space into the outside atmosphere?
Answer
Diffusion.
Question
The upward force created by evaporation from leaves that can draw water up to 50 metres in tall trees is called _____.
Answer
Transpirational pull.
Question
On which surface of a typical dicot leaf are more stomata found?
Answer
The lower (undersurface) or abaxial surface.
Question
What state must the guard cells be in for the stomatal opening to be wide?
Answer
Turgid (full of water).
Question
What happens to the stomata when guard cells lose water and become flaccid?
Answer
They close.
Question
Under what condition do leaves wilt during midday and recover in the evening?
Answer
When the rate of transpiration exceeds the rate of water absorption by the roots.
Question
Define 'cuticular transpiration'.
Answer
The loss of water directly from the surface of leaves and stems through the waxy cuticle layer.
Question
How does the thickness of the leaf cuticle relate to the rate of transpiration?
Answer
The greater the thickness of the cuticle, the lesser the evaporation (transpiration).
Question
What are 'lenticels'?
Answer
Special minute openings that develop on the barks of older woody stems.
Question
How does the opening of lenticels differ from that of stomata?
Answer
Lenticels never close and remain open all the time.
Question
How does an increase in sunlight intensity affect the rate of transpiration?
Answer
It increases the rate as stomata open wide for $CO_{2}$ intake for photosynthesis.
Question
Why does a higher outside temperature increase the rate of transpiration?
Answer
It allows more water to evaporate and increases the capacity of warm air to hold moisture.
Question
What is the relationship between wind velocity and the rate of transpiration?
Answer
Transpiration increases with the velocity of wind as it removes released water vapour.
Question
How does high atmospheric humidity affect the rate of transpiration?
Answer
It reduces the rate of transpiration because outward diffusion of internal water vapour is slowed.
Question
How does an increase in $CO_{2}$ levels above normal $0.03\%$ in the outside air affect transpiration?
Answer
It causes stomatal closure, resulting in a decrease in transpiration.
Question
What is the effect of decreased atmospheric pressure on the rate of transpiration?
Answer
It increases the rate of transpiration by enhancing the diffusion of water vapour.
Question
Give an example of a plant that has sunken stomata to reduce transpiration.
Answer
Nerium.
Question
In cacti, how are leaves modified to reduce the surface area for transpiration?
Answer
They are reduced to spines.
Question
Why is transpiration described as a 'vital' process while evaporation is 'physical'?
Answer
Transpiration is controlled by internal plant factors, whereas evaporation is controlled by external factors only.
Question
How does transpiration contribute to the distribution of mineral salts in a plant?
Answer
It draws water towards the leaves, helping distribute the water and dissolved solutes throughout the plant.
Question
How does transpiration influence local climate?
Answer
It increases the moisture in the atmosphere, which contributes to bringing rain.
Question
Define 'guttation'.
Answer
The loss of water as droplets along the margins of leaves through special structures called hydathodes.
Question
Under what environmental conditions does guttation typically occur?
Answer
In humid conditions when the soil is very moist but transpiration is hampered.
Question
Where are 'hydathodes' located on a plant?
Answer
On the margins or tips of veins in the leaves of certain plants.
Question
What is plant 'bleeding'?
Answer
The escape of plant sap from the ruptured or cut surfaces of a plant.
Question
Contrast the state of water lost in transpiration versus guttation.
Answer
In transpiration, water is lost as vapour; in guttation, it is lost as droplets.
Question
What is the primary difference between the composition of water lost in transpiration and guttation?
Answer
Transpiration loses pure water, while guttation water contains mineral salts in solution.
Question
How does the regulation of water loss differ between stomatal transpiration and guttation?
Answer
Stomatal transpiration is regulated by guard cells, whereas the opening of hydathodes cannot be regulated.
Question
Which internal factor regarding leaf condition leads to a decrease in transpiration rate?
Answer
Loss of water content in the leaves, leading to wilting and stomatal closure.
Question
What effect does transpiration have on the internal temperature of a plant on a sunny day?
Answer
It has a cooling effect, preventing enzymes from being destroyed by intense heat.
Question
Which specific tissue conducts water upwards from the roots to the leaves?
Answer
Xylem.
Question
Why are forests often associated with higher rainfall in an area?
Answer
The vast amount of water vapour released by trees through transpiration increases atmospheric moisture.
Question
What is the function of the reservoir in a Ganong's potometer?
Answer
To reset the air bubble to its original position by releasing more water into the capillary tube.
Question
How do desert plants modify their cuticles to survive in dry climates?
Answer
They tend to have much thicker cuticles to cut down transpiration.
Question
Is transpiration considered an excretory process in plants?
Answer
No, because it is not the elimination of metabolic nitrogenous waste substances.
Question
In the experiment comparing leaf surfaces, why does the lower surface of a dicot leaf turn cobalt chloride paper pink faster?
Answer
Because the lower surface contains more stomata, leading to more transpiration.
Question
What process causes water to enter root hair cells from the soil?
Answer
Osmosis.
Question
Identify the pathway of water from the xylem to the outside air during stomatal transpiration.
Answer
Xylem $\rightarrow$ Mesophyll cells $\rightarrow$ Intercellular spaces $\rightarrow$ Sub-stomatal space $\rightarrow$ Stomata $\rightarrow$ Outside air.
Question
How does the 'suction force' from transpiration help a plant?
Answer
It enables the roots to absorb water and mineral nutrients from the soil.