C3: Adaptations for transport in plants

Question 1

Describe the structure of a dicotyledon root

Answer 1

From outer layer to Inner:

Root hair
Epidermis (outer layer)
Parenchyma (Cortex)
Endodermis (layer surrounding pericycle and the vascular bundle)
pericycle (layer surrounding the vascular bundle)
Phloem (circles next to X)
Xylem (X shape)

Question 2

what is the cell called that that uptakes water and how is it adapted to its function

Answer 2

The root hair cell:
Has a large survace area

large vacuole containing cell sap that lowers the water potential within the cell

Question 3

Describe the uptake of water and ions into root hair cells

Answer 3

Soil solution has a higher water potential than the vacuole so water moves in by osmosis down the water potential gradient.

If there is a higher concentration of ions (eg: nitrates) in the soil than in the root hair cell, the ions are transported into the cell by facilitated diffusion through channel and carrier proteins, but if there is a lower concentration of these ions in the surrounding soil the ions are actively transported into the cell by carrier proteins using energy from ATP.

Question 4

What are the two main pathways in which water travels through the plant to the xylem

Answer 4

Apoplast pathway - water moves through the cell walls but is not continuous as the Casparian strip in the endodermis forces water into the cytoplasm

Symplast pathway - water moves through the cytoplasm and plasmodesmata(strands of cytoplasm through pits in the cell wall joining adjacent cells so the pathway is continuous)

Question 5

What is the endodermis

Answer 5

A single layer of cells around the pericycle and vascular tissue of the root.

Question 6

Describe how the structure of the endodermis is suited to its role

Answer 6

Endodermis’ cell wall has the casparian strip which is the impermeable band of suberin in the cell wall this blocks the movement of water in the apoplast driving it into the cytoplasm

Question 7

Describe the movement of water and minerals into the xylem

Answer 7

Water has to move into the xylem by osmosis
therefore the water potential of the endodermis has to be higher than in the xylem, this is maintained by:

The movement of water into the cytoplasm via the apoplast pathway

The active transport of minerals and ions into the xylem lowering the water potential in the xylem

Question 8

Describe the structure of a dicotyldon stem

6 points

Answer 8

From outer layer to inner:

Epidermis
Collenchyma
Parenchyma (cortex)
Phloem
Xylem
Medulla

Question 9

Describe the structure of the xylem and two of its roles and an adaptation.

Answer 9

consists of:
* Vessels
* Tracheids
* Fibres
* Parenchyma (living)

Xylem are dead cells that transport water and minerals up the plant and provide mechanical strength and support as they are strengthened by waterproof lignin

Question 10

Name two factors in how water moves through the xylem (transpiration stream)

Answer 10

Cohesion-tension theory
Rootpressure

Question 11

Describe the cohesion tension theory

Answer 11

as water molecules leave the xylem cells in the leaf by evaporation they pull up other water molecules behind them because they have cohesion(hydrogen bonds between them) this pull produces tension in the xylem
Water molecules also have adhesion which is the attraction to the hydrophilic cells in the xylem which contributes to water movement in the xylem.

Question 12

Describe root pressure in the xylem

Answer 12

operates over small distances in living plants and is a consequence of osmotic movement of water into the xylem down the water potential gradient acrooss the root and into the base of the xylem pushing water molecules already in the xylem up it.

Question 13

Describe transpiration

Answer 13

The evaporation of water vapour from the leaves and shoots of the plant out through the stomata into the atmosphere

Question 14

What environmental factors effect the rate of transpiration

Answer 14

Temperature
Humidity
Air movement
Light intensity

Question 15

Describe the difference between mesophytes, hydrophytes and xerophytes

Answer 15

Mesophytes - plants living in environments where Water is adequate

Hydrophytes - plants living in a water rich environment

Xerophytes - plants living in environments where water is scarce

Question 16

Name adaptations of hydrophytes

4 pounns

Answer 16

Little/no waxy cuticle as no need to conserve water.

Stomata on upper surface as lower surface submerged.

Poorly developed xylem as no need to transport water.

Large air spaces (aerenchyma) provide buoyancy and act as
reservoirs of gas.

Question 17

Name adaptations of Mesophytes

3 piints

Answer 17

Close stomata at night to decrease water loss.

Shed leaves in unfavourable conditions, e.g. winter.

Underground organs and dormant seeds survive winter.

Question 18

Name adaptations of Xerophytes

4 points

Answer 18

Thick waxy cuticle reducing water loss by evaporation from epidermal tissue.

Sunken stomata increasing humidity in an air chamber above the stomata, reducing diffusion gradient and therefore water loss by transpiration.

Rolled leaves - reduces area of leaf exposed directly to air.

Stiff interlocking hairs trap water vapour inside rolled leaf, reduces water potential gradient and therefore water loss.

Question 19

Describe the structure of the phloem

Answer 19

Phloem sieve tubes carry sucrose and
amino acids.

Sieve elements end in sieve plates containing pores through which cytoplasmic filaments extend linking cells. (plasmodesmata)

No other organelles are in the sieve elements.

Companion cells contain many mitochondria for ATP and ribosomes for protein synthesis.

Proteins and ATP are passed to the sieve elements through plasmodesmata.

Question 20

Define translocation

Answer 20

The active movement of solutes of photosynthesis (sucrose and AA) through the phloem from source to sink.
this movement can be any direction (up,down,sideways) unlike the xylem which is only up

Question 21

Describe the for and against of the mass flow hypothesis

1 point for , 4 points agaist

Answer 21

For:
Sucrose made at source
lowers water potential. Water
enters cells and sucrose is
forced into phloem (loading).
This increases hydrostatic
pressure and therefore mass
flow occurs along the phloem
to the root where sucrose
is stored as starch, water
potential is less negative and
water moves into the xylem.

Against:
Sieve plates impede flow.

Translocation is faster than expected
with diffusion.

This theory does not explain
bidirectional flow or different rates of
flow of sucrose and amino acids.

Does not explain companion cell
mitochondria, high O2 intake or
stopping of translocation by cyanide.