Transport In Plants

Question 1

What are the functions of the xylem?

Answer 1

• to conduct water and mineral salts from the roots to other parts of the plant
• to provide mechanical support for the plant

Question 2

What is the function of the phloem?

Answer 2

To transport manufactured food ( sucrose & amino acids ) from the leaves to other parts of the plant

Question 3

How is the xylem adapted for its function?

Answer 3

• xylem vessels are long hollow tubes with no cross walls or protoplasm
  -> provides a continuous lumen thus reducing resistance to the flow of water
• inner walls of the xylem are strengthened by deposits of lignin
  -> prevents collapse of the vessels

Question 4

How is the phloem adapted for its function?

Answer 4

• sieve tube cell only has a thin layer of cytoplasm with no central vacuole, nucleus and most organelles
  -> reduces resistance to the flow of substances within the phloem
• sieve plates contain numerous pores
  -> allows for the rapid flow of manufactured food
• companion cells contains numerous mitochondria
  -> releases energy for the active loading of sugars into sieve tubes by active transport

Question 5

What is translocation?

Answer 5

The transport of manufactured food substances in plants

Question 6

What is found in the phloem?

Answer 6

Manufactured food substances ( sucrose and amino acids)

Question 7

What happens when the phloem is removed from the stem/ bark of a plant? What causes this?

Answer 7

The region above the ring ( area where the phloem was removed) will swell due to an accumulation of sugars in the region above the ring. The accumulation of sugars in the cells in the region results in the lowering of water potential of the cells.
Water molecules from the xylem enters the cells in the region, adding onto the swelling

Question 8

What is the path of water into the plant?

Answer 8

1. Root hairs grow between soil particles and are in close contact with the surrounding soil particles
2. Each soil particle has a thin film of liquid surrounding it. The soil solution is a dilute solution of mineral salts
3. The sap in the root hair cell is more concentrated due to the presence of sugars and mineral salts; sap has a lower water potential than the soil solution causing water to enter the root hair by osmosis
   4.the entry of water dilutes the cell sap of the root hair cell, causing it to have a higher water potential than that of the next cell, causing water to move from the root hair cell to the inner cell through osmosis
4. The process continues until the water enters the xylem vessels and moves up the plant

Question 9

How does mineral salts enter the plant?

Answer 9

Through diffusion and active transport
- when the concentration of mineral salts in the soil solution is higher than in the cell sap, diffusion occurs. Mineral salts moves into the root hair cells down the concentration gradient

• when the concentration of mineral salts in the cell sap is higher than in the soil solution, active transport moves ions against the concentration gradient. Energy required is released by aerobic respiration in the mitochondria of the root hair cell

Question 10

How is the root hair cell adapted for its function?

Answer 10

Long and narrow protrusion
-> increases surface area to volume ratio of the root hair cell to increase the rate of absorption of water and mineral salts

Presence of a cell membrane
-> prevent the leaking of the cell sap to maintain a lower water potential in the cell sap than in the soil solution, enabling water molecules to enter the root hair cell by osmosis

Presence of mitochondria
-> releases energy from aerobic respiration for active transport of ions in the cell

Question 11

What are the 3 processes that help move water against gravity?

Answer 11

Root pressure
-> the pressure resulting from the constant entry of water from the soil into the roots by osmosis

Capillary action
-> the movement of water up very narrow tubes like the xylem vessels, due to forces of attraction between water molecules and the forces of attraction between water and the surfaces of the tubes

Transpiration
-> water vapour loss from the aerial parts of the plants, especially through the stomata of the leaves

Question 12

What is transpiration pull?

Answer 12

The suction force caused by transpiration which results in water moving up the xylem

Question 13

What is the movement of water through a leaf?

Answer 13

1.Water that moves out of the mesothelioma cells form a thin film of moisture around the cells
2. Water from the thin film of moisture evaporates to form water vapour in the air spaces that accumulates in the ar spaces near the stomata
3. Water vapour diffuses out of the stomata and into the dried air outside the leaf. This is known as transpiration
4. Water moves out of the mesophyll cells to replace the thin film of moisture that has evaporated , decreasing the cell sap’s water potential
5. The mesophyll cells absorbs water from the cells deeper in the leaf via osmosis
6. These cells absorbs water from xylem vessels
7. Resulting in transpiration Paul, a suction force that pulls the column of water in the xylem vessels up

Question 14

Why is transpiration important ?

Answer 14

It is a major suction force for moving water and mineral salts up the xylem
Water is required at the leaves for photosynthesis
Turgidity is maintained with transpiration as water lost in the aerial portions of the plant is replaced
Leaves can spread out widely to trap sunlight for photosynthesis
Evaporation of water helps to cool the plant

Question 15

What are the factors affecting the rate of transpiration?

Answer 15

• humidity
• light intensity
• wind/air movement
• temperature

Question 16

How does humidity affect the rate of transpiration?

Answer 16

Increased humidity will decrease the water vapour concentration between the leaf and the atmosphere, resulting in a decreased rate of transpiration

Question 17

How does temperature affect the rate of transpiration?

Answer 17

The higher temperature increases the rate of evaporation of water from the cell surfaces resulting in greater rate of transpiration

Question 18

How does wind/air movement affect the rate of transpiration?

Answer 18

Wind blows away the water vapour that accumulates outside the stomata, maintaining the water vapour concentration gradient between the leaf and the atmosphere

In still air, the water vapour that diffuses out of the leaf making the air around the leaf more humid, decreasing the rate of transpiration

Question 19

How does light affect the rate of transpiration?

Answer 19

In sunlight, the stomata opens and becomes wider, increasing the rate of transpiration while in darkness the stomata closes so less water is lost from the leaves ( transpiration rate is lower)

Question 20

When does wilting occur

Answer 20

When the rate of transpiration exceeds the rate of absorption of water by the roots

Question 21

What happens during wilting

Answer 21

The cells lose their turgor and become flaccid

Question 22

What are the advantages of wilting?

Answer 22

• reduces the surface area exposed to sunlight
• guard cells becomes flaccid and stomata closes
  -reduces water lost through transpiration

Question 23

What are the disadvantages of wilting?

Answer 23

It results in the closure of the stomata n
- reduces the amount of CO2 entering the leaf
Decreases the rate of photosynthesis
Decrease in surface area of the plant exposed to sunlight reduces the rate of photosynthesis