9.1 Transport In Xylem

Question 1

What is transpiration the consequence of?

Answer 1

It is the inevitable consequence of gas exchange in the leaf

Question 2

Why do plants need water? (3)

Answer 2

For transport, to keep the vacuole turgid, maintain a consistant and cool temperature

Question 3

What occurs in the roots?

Answer 3

The active uptake of mineral ions in the roots which causes absorption of water by osmosis

Question 4

What allows water to be drawn up the stems? (4)

Answer 4

• light energy absorbed by the leaf is converted to heat
• diffuses out of the stomata (creates a negative pressure gradient in leaf)
• creates tension in leaf cell wall -> draws water from xylem (transportations pull)
• water pulled causes pressure due to adhesion properties of water and cell wall

Question 5

Why do plants transport water from the roots to the leaves?

Answer 5

To replace the water lost by transpiration

Question 6

What prevents CO2 from being absorbed by the leaves?

Answer 6

The waxy cuticle

Question 7

How does the plant absorb CO2?

Answer 7

Through the stomata in the leaf

Question 8

What is an inevitability lost due to light energy being absorbed?

Answer 8

Some of the water gets evaporated and lost

Question 9

How does the stomata open?

Answer 9

When the stomata is turgid
(high pressure and full of water)

Question 10

How does the stomata close?

Answer 10

When the stomata is flaccid
(Less water and low pressure)

Question 11

What are the three properties of xylem which helps its function? (3)

Answer 11

Made of dead cells reinforced by lignin
Long strong side walls
Very few cross walls

Question 12

What are the 5 factors which affect the rate of transpiration?

Answer 12

Light intensity
Temperature
Humidity
Wind speed
Soil water

Question 13

Why does light intensity increase the rate of transpiration?

Answer 13

Because the stomata opens wider and allows more carbon dioxide into the cells and this more water is lost

Question 14

Why does the temperature increase the rate of transpiration ？

Answer 14

It increases the energy of the molecules and thus the transpiration rate

Question 15

Why does the rate of humidity decrease the rate of transpiration?

Answer 15

It decreases the rate of diffusion and leads to a smaller concentration gradient between plant and the environment

Question 16

Why does wind speed increase the rate of transpiration?

Answer 16

The water molecules outside the leaf are removed and increases the concentration gradient and more water diffuses out of the leaf

Question 17

Why does soil water increase the rate of transpiration?

Answer 17

Due to the osmosis there will be more absorption which increases the root pressure

Question 18

What are xenophyte?

Answer 18

Plants which need very little water
(desert plant)

Question 19

What are halophytes?

Answer 19

Plants that grow in high salinity

Question 20

Why would xenophytes have high rates of transpiration

Answer 20

Due to the high temperatures and low humidity of the desert

Question 21

Why would halophytes lose water?

Answer 21

Due to the high salt content from the surrounding soil water from plant tissue by osmosis

Question 22

How do xerophytes adapt to their surroundings? (4)

Answer 22

Extensive and deep root systems
Water storage in stem and leaves
Specific adaptations reduce transpiration rates
Spines and thorns deter herbivores

Question 23

how are mineral ions uptaken? (4)

Answer 23

(can passively diffuse into the roots)
-> more commonly be actively uploaded by indirect active transport
- Root cells contain proton pumps that actively expel H+ ions (stored in the vacuole of root cells) into the surrounding soil
- H+ ions displace the positively charged mineral ions from the clay, allowing them to diffuse into the root along a gradient
- Negatively charged mineral ions (anions) may bind to the H+ ions and be reabsorbed along with the proton

Question 24

what is the differenc between cohesion and adhesion? (3)

Answer 24

C = 2 same substances
C = water + water (hydrogen bond) (INTRAMOLECULAR ASSOCIATION)
C = continous stream
A = 2 different substances
A = xylem wall and water mo;ecues (form intamelculeuae association)

Question 24

how does transpiration occur in plants?

Answer 24

• plants transport water frm roots to leaves to replace water lost by transpiration
  2. cohesive properties of water and the structure of the xylem vessel allows for transport under tension
  3. adhesion properties of water and evaporation generates tension forces in dead cell walls
  4. active uptake of mineral ions in roots causes water absorption (osmosis)

Question 25

what is the structure of the xylem?(4)

Answer 25

• HOLLOW = tube composed of dead cells that are hollow (no protoplasm) to allow for the free movement of water
• DEAD = the cells are dead, the movement of water is an entirely passive process and occurs in one direction only
• PORES = cell wall contains numerous pores (called pits), which enables water to be transferred between cells
• CELLULOSE AND LIGNIN = Walls have thickened cellulose and reinforced by lignin, to provide strength as water is transported under tension

Question 26

what are tracheids? (2)

Answer 26

• cells that exchange water solely via pits, leading to a slower rate of water transfer
  (In vessel elements, the end walls have become fused to form a continuous tube, resulting in a faster rate of water transfer)