1. List the materials that require transportation in plants. Water, minerals, sugars and other metabolites synthesised in leaf, hormones synthesised at shoot and root tips, stored food from part of storage to other plant part, etc. 2. Name the two conducting tissues of plants. Xylem and phloem. 3. Why do plants require a proper system of transportation? In trees and big plants, diffusion process is not sufficient to provide raw material to the leaves from the roots and energy reserves to the roots from the leaves. Therefore, a proper system of transportation is essential in plants. 4. Why plants can afford to have a slow transport system as compared to animals? Plants do not move and have a large proportion of dead cells in many tissues. Therefore, their energy needs are less and therefore they can afford to have a slow transport system as compared to animals. 5. What is root pressure? The pressure that is created due to difference in concentration of salts which forces water absorbed from the soil, to move through the roots and up the stem of the plant is known as root pressure. 6. Why root pressure alone cannot be responsible for transport of water in plants? Root pressure alone cannot be responsible for transport of water in plants because this pressure created due to concentration gradient and osmosis is not enough to move water over great heights of commonly found tall plants. 7. Explain the mechanism of upward movement of water and minerals in plants. The events during movement of water and minerals in plants are as follows:
- The tissue responsible for it is xylem
- Water enters roots through special structures called root hair. These are the epidermal outgrowths of roots.
- Root hair of plants are in direct contact with the film of water in between the soil particles.
- Water and minerals dissolved in it enters through root hair due to osmosis and move through root cortex, endodermis, root xylem, stem xylem, xylem of petiole and finally to leaves. This creates concentration difference and hence water is forced to move in.
- The pressure that forces water in is called root pressure.
- Since root pressure is not sufficient to pull water, suction force created by transpiration pulls water till the leaves.
8. Explain the mechanism of movement of water from soil into the root. The cells of the root in contact with soil take up ions along with the water by simple diffusion. This creates a difference in the concentration of these ions between soil and the roots, which draws water into the roots from the soil. This leads to steady movement of water into root xylem, forming a column of water that is steadily pushed upwards. 9. When does root pressure becomes a major driving force for movement of water in plants and why? At night, root pressure becomes a major driving force for movement of water in plants. This is because the stomata are closed during nighttime and transpiration is not possible. 10. What is transpiration? What is its importance? The loss of water in the form of water
vapours from the leaves into the atmosphere is called transpiration.
Evaporation of water molecules from cells of a leaf due to
transpiration creates suction, which is responsible for pulling
water from xylem cells. Hence, movement of water and minerals from
roots to leaves in the form of a continuous column is due to
transpirational pull. This water is utilised by plant during
photosynthesis.
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