B4.6: Plant Organs

Question 1

What do xylem and phloem tissue do? (2)

Answer 1

• plant transport tissues
• XYLEM transport WATER UP the plant to the leaves
• PHLOEM transport FOOD DOWN from leaves to rest of plants

Question 2

What is transpiration?

Answer 2

process where water evaporates from the leaves, out of the stomata

Question 3

What do xylem vessels do and consist of ? (3)

Answer 3

• vessels are involved in the movement of water
• consist of dead cells
• have hollow , strengthened cellulose wall/ lignin adapted for the transport of water in the transpiration stream
• no cytoplasm

Question 4

What do phloem vessels do/structure ?

Answer 4

involved in TRANSLOCATION - movement of food substances from stems to growing/storage tissues
- made of tubes of elongated cells with pores in the end walls
- made of living cells

Question 5

What is the epidermal layer of a leaf?

Answer 5

protective layer - covers surface/protects them

Question 6

palisade mesophyll?

Answer 6

• contains a lot of chloroplasts which carry out photosynthesis

Question 7

what does a potometer measure?

Answer 7

the rate of transpiration in different conditions

Question 8

Spongy mesophyll?

Answer 8

has some chloroplasts
- contains internal air spaces that increases SA for diffusion of gases

Question 9

How does temperature increase rate of transpiration? (2)

Answer 9

• molecules move faster so diffusion is quicker
• rate of photosynthesis also increases as temp increases so more stomata will be open for gas exchange - quickening the rate of transpiration

Question 10

How does wind increase rate of transpiration?

Answer 10

• increase rate of evaporation
• maintain steep conc gradient from inside of leaf and the outside by removing water vapour as it diffuses out

Question 11

How does humidity effect rate of transpiration?

Answer 11

water vapour diffuses more rapidly into dry air than humid air bc conc grad is steeper !

Question 12

What happens if plant lose water faster than it can be replaced in the roots?

Answer 12

• stomata can close to prevent wilting
• plants wilt to reduce SA so less water loss/ exposure to light

Question 13

How does light intensity increase rate of transpiration?

Answer 13

increase photosynthesis - stomata can open wider to allow CO2 in leaf so more transpiration (water loss)

Question 14

What is the transpiration stream?

Answer 14

• movement of water from roots
• via the xylem
• to the leaves/evaporates

Question 15

What is translocation? (3)

Answer 15

• movement of sugars/sucrose
• from the leaves
• can be used for respiration/growth/storage

Question 16

When using the potometer to measure the uptake of water at different temperatures. They were concious of not leaving the leaves for too long at temps above 30 degrees. Explain why. (3)

Answer 16

• at higher temps leaves may WILT
• bc plants lose too much water by evaporation through the stomata
• and cells in the leaf cant provide support

Question 17

Stoma close when light intensity is low.
Describe how the stoma close? (3)

Answer 17

-Water moves out of guard cells by osmosis
- guard cels becomes flaccid/shrinks
- pulls stoma to close

Question 18

why do guard cells have unevenly distrubuted cellulose in cell walls?

Answer 18

• makes the inner walls thicker and outer walls THINNER
• so when water moved into guard cell, thinner wall expland more than thicker wall
• causing t to bend, and opening to form (stomata)