Transport in plants Flashcards
State the functions of xylem
– transport of water and mineral ions,
and support
state the function of phloem
transport of sucrose and amino
acidss
Relate the structure of xylem vessels to their
function limited to:
(a) thick walls with lignin (details of lignification
are not required)
(b) no cell contents
(c) cells joined end to end with no cross walls to
form a long continuous tube
(a) Thick walls with lignin: The walls of xylem vessels are thickened with lignin, a complex organic polymer. Lignin is a hard, waterproof material that provides mechanical support to the xylem vessel and prevents it from collapsing under the pressure of the water that is transported inside. The lignin also makes the walls impermeable to water, ensuring that the water flows through the lumen, or central cavity, of the vessel rather than diffusing out through the walls.
(b) No cell contents: Xylem vessels are composed of dead cells that have lost their cell contents, including the nucleus and other organelles. This allows the vessel to be completely filled with water and dissolved minerals, maximizing the amount of material that can be transported.
(c) Cells joined end to end with no cross walls to form a long continuous tube: Xylem vessels are composed of cells that are joined end to end to form a long continuous tube. These cells are called vessel elements, and they have no cross walls, or septa, between them. This allows for a continuous flow of water and dissolved minerals through the entire length of the vessel.
Together, these features make xylem vessels highly specialized structures that are able to transport large volumes of water and dissolved minerals from the roots to the leaves of plants. The thick walls with lignin provide mechanical support and prevent the vessel from collapsing, while the lack of cell contents and continuous tube structure allow for the efficient flow of water and minerals through the plant.
function of root hair cells
The thin walls and large surface area of the root hair cells allow for the efficient diffusion of water and minerals from the soil into the root.
Overall, the function of root hair cells is essential for the proper growth and development of plants.
what does the large surface area of root hairs
increases
increases the uptake of water and mineral ions
Investigate, using a suitable stain, the pathway of
water through the above-ground parts of a plant
Prepare a solution of eosin Y: Dissolve a small amount of eosin Y powder in water to make a dilute solution.
Water the plant: Water the plant thoroughly to ensure that it is well-hydrated and able to absorb the stain.
Apply the stain: Using a small brush or dropper, apply the eosin Y solution to the leaves and stem of the plant, making sure to cover as much surface area as possible.
Observe the plant: Wait for a few hours to allow the stain to be absorbed and transported through the plant. As the stain moves through the plant, it will highlight the path taken by water, making it visible to the naked eye.
Rinse the plant: After observing the stain, rinse the plant with water to remove any excess dye and prevent it from staining the plant permanently.
Outline the pathway taken by water through the
root, stem and leaf
root hair cells
root cortex cells
xylem
mesophyll cells
Describe transpiration
loss of water vapour from leaves
State what happens when water evaporates from the surfaces of the mesophyll cells
water evaporates from the surfaces of
the mesophyll cells into the air spaces and then
diffuses out of the leaves through the stomata as
water vapour
Explain how water vapour loss is related to:
the large internal surface area provided by the
interconnecting air spaces between mesophyll
cells and the size and number of stomata
Water vapor loss in plants occurs primarily through small pores called stomata, which are found on the surface of leaves. The rate of water loss through stomata is determined by the size and number of stomata, as well as the internal structure of the leaf.
The size and number of stomata affect the rate of water vapor loss because they control the size of the opening through which water vapor can escape. Larger or more numerous stomata increase the surface area available for transpiration and therefore increase the rate of water loss. However, having too many or too large stomata can also lead to excessive water loss and dehydration, so there is a trade-off between maximizing gas exchange and minimizing water loss.
The interconnecting air spaces between mesophyll cells provide a large internal surface area that helps to increase the efficiency of gas exchange. These spaces allow gases to diffuse freely between the air inside the leaf and the surrounding environment, increasing the rate of gas exchange and also increasing the likelihood that water vapor will be carried away from the leaf surface. The large surface area provided by the air spaces also means that more water molecules are exposed to the surrounding air, increasing the rate of water vapor loss through transpiration.
In summary, the size and number of stomata and the interconnecting air spaces between mesophyll cells are closely related to the rate of water vapor loss in plants. Balancing these factors is critical for plants to maximize photosynthesis while minimizing water loss and avoiding dehydration.
describe spongy mesophyll cells
Spongy mesophyll cells have a large surface area, which increases their capacity to exchange gases with the surrounding air. They are irregularly shaped and have thin cell walls, allowing for efficient gas diffusion. Chloroplasts, the organelles responsible for photosynthesis, are present in spongy mesophyll cells, although they are fewer in number than in the neighboring palisade mesophyll cells.
Overall, spongy mesophyll cells play a critical role in the process of photosynthesis, helping to facilitate the exchange of gases that plants require for growth and survival.
Which cell type would have the greatest concentration of oxygen inside a section of leaf in a sunny day?
the palisade cell
Explain the mechanism by which water moves
upwards in the xylem in terms of a transpiration
pull that draws up a column of water molecules,
held together by forces of attraction between
water molecules
he transpiration pull mechanism is driven by the evaporation of water from the leaves, creating a gradient of water potential that draws water up through the xylem. The cohesive and adhesive forces between water molecules and the xylem walls help to maintain the continuous column of water and allow for efficient transport of water and nutrients throughout the plant
Explain the effects on the rate of transpiration of
varying the following factors: temperature, wind
speed and humidity
Temperature:
An increase in temperature generally increases the rate of transpiration. This is because higher temperatures cause the water inside the plant to evaporate faster, creating a larger water potential gradient between the leaf and the atmosphere. This larger gradient drives more water to be lost from the leaf through transpiration.
Wind Speed:
An increase in wind speed also tends to increase the rate of transpiration. This is because wind causes the water vapor that is lost through the stomata to be carried away from the leaf, creating a larger water potential gradient between the leaf and the atmosphere. This larger gradient results in more water being lost from the leaf through transpiration.
Humidity:
Humidity refers to the amount of water vapor in the air. As humidity increases, the rate of transpiration tends to decrease. This is because as the air becomes more saturated with water vapor, the water potential gradient between the leaf and the atmosphere decreases, making it more difficult for water to be lost through transpiration.
Overall, the rate of transpiration is influenced by a complex interplay of various environmental factors. Understanding how these factors affect transpiration can help us better understand how plants respond to their environment and can also help us develop strategies to conserve water in agricultural and other settings.
Explain how and why wilting occurs
How wilting occurs:
When there is a shortage of water in the soil, or the rate of transpiration exceeds the rate of water absorption, the plant’s cells lose water, which leads to a decrease in turgor pressure. Turgor pressure is the pressure exerted by water against the cell wall, which provides rigidity and shape to the plant. When turgor pressure decreases, the plant loses its rigidity, and the leaves and stems droop or wilt. The process of wilting is mainly due to the loss of water from the plant’s cells, which reduces the turgor pressure.
Why wilting occurs:
Wilting occurs because plants require a continuous supply of water for various physiological functions, such as photosynthesis, nutrient uptake, and maintenance of cell turgor pressure. When the plant experiences a water shortage, it tries to conserve the remaining water by reducing the amount of water lost through transpiration. To reduce water loss, the plant closes its stomata, which reduces the flow of water through the plant. This leads to a reduction in the turgor pressure, which results in the wilting of the plant.
Wilting is a sign that the plant is under stress and needs water to restore its turgidity and prevent damage to its tissues. It is a common response of plants to water shortage, and it can be prevented by ensuring that the plant receives an adequate and regular supply of water. Additionally, plants have adaptations such as deep root systems and drought-tolerant leaves, which help them to survive periods of water scarcity.
