Transport in Plants

Question 1

What are the main substances transported in plants

Answer 1

Water and organic substances

Question 2

What are these substances transported by

Answer 2

Either the phloem or the xylem (the vascular bundle refers to them collectively)

Question 3

Structure of the phloem

Answer 3

Two key cells
-sieve tube elements (living cells, no nucleus, few organelles)
-companion cells (provide ATP for active transport of organic substances)

Question 4

Structure of xylem cells

Answer 4

Dead and hollow cells
No organelles or end walls, they stack on top of eachother to create continuous hollow column (ideal for transporting water and mineral ions)
Xylem wall is strengthened with a waterproof chemical called lignin

Question 5

Describe the transport of water into the plant

Answer 5

Water is absorbed into plants through the root hair cells via osmosis
Root hair cells are adapted to maximise osmosis by having thin walls and a large surface area

Question 6

Describe the transport of water to the xylem

Answer 6

Once the water has moved into the root hair cells via osmosis, it is transported to the xylem by either symplast or apoplast pathway

Question 7

Describe the symplast pathway

Answer 7

Through the cytoplasm of a cell, water moves from cell to cell towards the xylem by osmosis through the cytoplasm and gaps in the cell walls called plasmodesmata. Every other cell has a lower water potential which allows water to continue to move by osmosis

Question 8

Describe the apoplast pathway

Answer 8

Through cell walls, water can enter the cell wall and move due to the cohesive force of water (the water molecules stick together which form a continuous stream which move towards the xylem). This pathway moves water faster as there is little resistance to the water in the cell wall

Question 9

Adaptations of xerophytes

Answer 9

Found in locations with limited water
Curled leaves/ sunken stomata / hairs to trap moisture and increase humidity
Thicker cuticle to reduce evaporation
Longer root network to reach more water

Question 10

Adaptations of hydrophytes

Answer 10

Live in or on water
Short roots/very thin/no waxy cuticle and stomata are permanently open and on the top surface of the leaves so no additional water is retained in the plant and so water loss is efficient.
Large leaves ensure that there is enough light absorbed for photosynthesis

Question 11

What is transpiration

Answer 11

The loss of water vapour from the stomata by evaporation
(can be measured using a potometer)

Question 12

4 factors that affect transpiration

Answer 12

Light intensity- (positive) more light, more stomata open, larger surface area for evaporation
Temperature- (positive) more heat, more kinetic energy, faster molecules move, more evaporation
Humidity- (negative) more humid, more vapour in air, reduces water potential
Wind- (positive) more wind, blows vapour away, maintains the water potential gradient