Transport in plants

Question 1

Dicotyledon

Answer 1

Plants with veins (like oak leaves)

Question 2

Structure of cross section of dicotyledonous root

Answer 2

Root hair cell projections, epidermis, cortex, endodermis, casparian strip, endodermis, pericycle, phloem, xylem.

Question 3

what runs through the endodermis?

Answer 3

Casparian strip

Question 4

what is special about the casparian strip? what is it made of?

Answer 4

Its water proof! It’s made of SUBERIN

Question 5

Apoplast

Answer 5

movement of water through the cell walls and gaps between cell walls.

Question 6

symplast

Answer 6

movement of water through the cytoplasm and plasmadesmata

Question 7

why is more water transported through the apoplast route?

Answer 7

water faces more resistance through the cytoplasm.
Water flows in one continuous stream through the cell wall due to cohesion.

Question 8

explain how water travels in the cell wall..

Answer 8

cohesion, adhesion - capilliary action.

Question 9

What happens at the casparian strip?
Why does this happen? how does this help?

Answer 9

Water travelling via apoplast passes into the cytoplasm and follows the symplast pathway. The casparian strip is waterproof. The cytoplasm can now control which substances enter.

Question 10

Why does water move from root hair cell to the xylem?

Answer 10

Difference in water potential between root hair cell and xylem.

Question 11

What is root pressure?

Answer 11

Active transport transports mineral ions into xylem to reduce the water potential.

Question 12

two main cells that make up the PHLOEM?

Answer 12

Sieve tube element, companion cell.

Question 13

after photosynthesis, what is glucose transformed into?

Answer 13

Sucrose

Question 14

What do you call the leaves and storage organs and why?

Answer 14

Sources - because they’re the sources of sucrose

Question 15

What do we call roots, storage organs, shoots and why

Answer 15

Sinks- because this is where sucrose is deposited (to be utilised).

Question 16

how is sucrose loaded into phloem?

Answer 16

• H+ ions transported from cytoplasm of companion cell to cell wall of companion cell using ATP.
• Now, there is a concentration gradient of H+ ions moving from the cell wall into the cytoplasm.
• the H+ ions couple with sucrose and are transpoted into the cytoplasm by co- transporters.
• sucrose diffuses into sieve tube elements.

Question 17

How does phloem sap move? (4)

Answer 17

• as sucrose moves into phloem, water potential decreases.
• water moves into phloem from xylem and other cells.
• now, hydrostatic pressure inside sieve tube element causes sap to move towards the sinks.
• this is mass flow.

Question 18

What happens after phloem sap reaches the sink?

Answer 18

• at the sink, sucrose transformed to glucose.
• water potential increases inside sieve tube elements.
• water moves out of phloem by osmosis.

Question 19

What are assimilates?

Answer 19

Products moved by the process of translocation

Question 20

Where are meristem cells found in stems?

Answer 20

cambium

Question 21

Structure of vascular bundle in stem?
(out to in)

Answer 21

Sclerenchyma, phloem, cambium, xylem.

Question 22

explain cohesion tension theory… briefly…(2 points)

Answer 22

• Transpiration occurs at stomata, creating areas of low pressure at the top of the xylem where water is being deposited and evaporated.
• water molecules are pulled to this low-pressure area, creating tension. - cohesion between water molecules pulls water up the xylem.

Question 23

what does cohesion tension theory create?

Answer 23

a transpiration stream

Question 24

structure of a leaf top to bottom?

Answer 24

Upper epidermis, palisade cells, spongy mesophyl and valscular bundle, lower epidermis and stomata

Question 25

explain, in detail, transpiration at the stomata and cells in the leaf

Answer 25

surface of cells coated by a layer of water.
This water evaporates into gaps in the leaf due to the difference in water potential between the air and the cells.
Because water potential of air space is now high, water will move out of the stomata along the concentration gradient.
Water potential in cells is now low, so water moves from xylem to cells.
The water from these cells moves to adjacent cells.

Question 26

2 pieces of evidence for transpiration pull/ cohesion tension theory/ transpiration stream

Answer 26

1. if a plant stem is cut, air will be sucked into it. no cohesion now, so water stops movin’.
2. Diameter of tree trunk reduces at high transpiration.

Question 27

evidence for translocation, 2 points

Answer 27

1. radioactive labelling (C14) measures where the C14 is when it moves down the trunk.
2. removing bark (which contains phloem and not xylem). a bulge will form above and below ring. Analuse contents of both bulges

Question 28

how does light intensity affect stomata?

Answer 28

It increases the number of open stomata

Question 29

How is transpiration reduced?

Answer 29

Water vapour buildup around stomata decrease the concentration gradient between humid air gaps in the leaf to outside the leaf.

Question 30

What does dry wind do to transpiration?

Answer 30

Decrease water potential for the air around the stomata.

Question 31

What are the chemical changes of guard cells in light conditions?

Answer 31

• K+ ions transported into guard cells
• water potential decreases
• water moves into guard cells

Question 32

What chemical changes occur to the guard cells in drought?

Answer 32

Roots send hormonal signals to guard cells, making them close.

Question 33

How are guard cells adapted?
2 points

Answer 33

• rings of cellulose around the width of guard cells prevent lysis.
• thicker cell wall on one side prevent guard cell from expanding evenly, causing a bend.

Question 34

Two ways phloem can be loaded…

Answer 34

• symplast route - sucrose diffuses into sieve tube element via symplast route.
• apoplast route - sucrose moves from cell wall to cytoplasm if companion cell via active loading.

Question 35

evidence for translocation…

Answer 35

• advances in microscopy= seeing adaptations of companion cell
• if mitochondria of companion cell are poisened translocation stops.
• flow of sugars 10 000 times faster than diffusion alone.
• aphids stylet (mouth bit) is cut. sap flows out, which demonstrated pressure differences near the sink compared with near the source.