Transport in Plants

Question 1

What are the functions of the xylem tissue?

Answer 1

1. Conducts water and dissolved mineral salts from the roots to the stem.
2. Provides mechanical support for the plant.

Question 2

What is the structure of the xylem tissue?

Answer 2

1. The xylem vessel is a structure made up of many dead cells.
2. The inner wall of xylem vessels are strengthened by deposits of a substance called lignin.

Question 3

What are the adaptations of the xylem tissue?

Answer 3

1. Xylem vessels have an empty lumen without protoplasm or cross-walls enabling water and dissolved mineral salts to move easily through the lumen.
2. Walls are lignified to prevent the collapse of vessels.

Question 4

What are sieve tube elements?

Answer 4

1. Sieve tube cells are elongated cells that lack nuclei and have thin layers of cytoplasm.
2. Sieve tube elements are made of sieve tube cells that are joined end to end to form a column with sieve plates in between them.
3. Sieve plates are cross-walls with many pores.

Question 5

What are the functions of the seive tube cells?

Answer 5

Bidirectional transport of manufactured sucrose and amino acids from the leaves to other parts of the plant.

Question 6

What are the functions of the companion cell?

Answer 6

1. Companion cells provide the sieve tube cells with nutrients.
2. Active transport of sucrose and amino acids into sieve tube cells.

Question 7

What is the structure of the companion cell?

Answer 7

Narrow, thin walled cell with cytoplasm, nucleus and numerous mitochondria.

Question 8

What is the adaptation of companion cells?

Answer 8

Numerous mitochondria to produce energy for loading of sugars and amino acids into phloem sieve tubes.

Question 9

How does water enter a plant?

Answer 9

1. Root hairs grow between soil particles.
2. Each soil particle has a thin film of moisture which is a dilute solution of mineral salts.
3. The cells in the root hair cell are more concentrated due to presence of sugar and mineral salts. Hence, water enters the root hair by osmosis.
4. The entry of water dilutes the root hair’s cell sap.
5. Water passes by osmosis from the root hair cell into the inner cell.
6. There are other cells that contain lower water potential as compared to the root hair cell.
7. Water enters the other cell through osmosis.
8. This process continues till it reaches the xylem vessel.

Question 10

How are root hair cells adapted for absorption?

Answer 10

1. The root hair is long and narrow this increases the surface area to volume ratio.
2. Cell surface membrane prevents the cell sap from leaking out. Cell sap contains sugars, amino acids and salts. Therefore, it has a lower water potential than the soil which results in water entering the root hair by osmosis.
3. The root hair cell contains many mitochondria. Aerobic respiration in the mitochondria releases energy for the active transport of ions into the cell.

Question 11

How does plants move water against gravity?

Answer 11

1. Root pressure:
   - Accumulation of mineral salts in the xylem vessels causes low water potential.
   - Lower water potential results in entry of water into xylem vessels via osmosis.
   - This causes buildup of hydrostatic pressure that pushes water up the xylem vessels.
2. Capillary action:
   - Water tends to move up inside very narrow tubes due to the interactions between water molecules and the surface of the tubes.
   - This is caused by adhesion and cohesion forces.
3. Transpiration:
   - Transpiration is the loss of water vapor from a plant, mainly through the stomata of the leaves.
   - The evaporation of water from the leaves removes water from the xylem vessels.
   - This results in a suction force which pulls water up the xylem vessels.

Question 12

What are the importance of transpiration?

Answer 12

1. Used for transpiration pull
2. Evaporation of water removes latent heat of vaporisation. (Cools the plant, preventing it from being scorched by the hot sun)
3. Turgidity is maintained as water that is lost in the aerial portions of the plant is replaced.

Question 13

What are the factors affecting rate of transpiration?

Answer 13

1. Humidity
2. Wind(brings the dry air to replace the humid air)
3. Temperature of the environment.
4. Light intensity

Question 14

What is wilting?

Answer 14

Excessive transpiration results in rate of water loss exceeding rate of water absorption.→Wilting occurs

Question 15

What are the advantages of wilting?

Answer 15

1. Closing of stomata reduces the rate of transpiration and thus decreases the rate of water loss
2. Reduced Leaf surface area exposed to sunlight helps with cool the plant

Question 16

What are the disadvantages of wilting?

Answer 16

1. Decreases rate of photosynthesis as closing of stomata decreases intake of CO2.
2. Reduced leaf surface area decreases absorption of sunlight→decreasing rate of photosynthesis.