6. Transport in Flowering Plants

Question 1

xylem vessels
-structure (2)
- function
- adaptation

Answer 1

• Xylem cells are dead
  at maturity
• Xylem vessels are
  long and hollow
  tubes that are made
  of xylem cells

Transport water and
mineral salts from the
roots to the leaves

Absence of protoplasm
and cross-walls which
could impede water
flow
through the lumen

Question 2

xylem (3)
-structure

Answer 2

• Inner walls of vessels
  are deposited with
  lignin in different
  shapes

Mechanical support for
the plant

Deposition of lignin on
the cell walls which
strengthens vessel
walls, providing support (provides mechanical support for the plant)

Question 3

structure and functions of root hairs to their surface area, and to water and ion uptake

-function
- structure and adaptations (2)
- root pressure (2)

Answer 3

Function: Water and ion uptake by root hair

Structure and adaptations
• Root hairs are long and narrow, thus increasing surface area to
volume ratio for rapid absorption of water and minerals.
• The cell sap contains sugars, amino acids and mineral salts
which makes the water potential of cell sap lower than that of
soil solution

Root pressure
• Root hair cells pump mineral salts into the xylem vessels using active
transport. This lowers the water potential of the xylem vessels, thus water
moves from the surrounding cells into the xylem vessels by osmosis,
creating a pressure that forces water to move upwards
• Not the main mechanism for movement of water in most plants as it can
only force water to travel a short distance.

Question 4

define transpiration

Answer 4

Transpiration is the loss of water vapour from the stomata of the leaves through diffusion

Question 5

briefly explain the movement of water through the stem in terms of transpiration pull (6)

Answer 5

1) For photosynthesis to occur, the stomata are open for carbon dioxide intake.
2) Water continuously moves out of the mesophyll cells to form a thin film of moisture
3) Water evaporates from this thin film of moisture and moves into the intercellular air
spaces
4) This leads to the loss of water vapour from the intercellular air spaces in the leaves as the
air diffuse outside that has a lower water vapour concentration via the stomata
5) As water evaporates from the mesophyll cells, the water potential of the cell sap
decreases, thus they absorb water by osmosis from the xylem vessels.
6) This results in transpiration pull, which is the main force that causes water to travel
upwards in plants

Question 6

describe the effects of variation of air movement, on transpiration
rate

Answer 6

if wind is present, it removes the water vapour that accumulates outside the stomata due to
transpiration. This leads to steep concentration gradient between intracellular air spaces and atmospheric air, thus increasing the
rate of transpiration.

Question 7

describe how wilting occurs (3)

Answer 7

• Water lost via transpiration has to be replaced by absorption from the
roots to the leaves by xylems
• When the rate of water absorption exceeds the rate of transpiration,
plant cells become turgid and plant becomes firm and upright.
• When the rate of transpiration exceeds the rate of water absorption,
plant cells become flaccid and plant wilts.

Question 8

define translocation

Answer 8

• Translocation is the transport of sugars from the leaves to other parts of the plant via the phloem tissues.

Question 9

describe the effects of variation of temperature on transpiration
rate

Answer 9

: Higher surrounding temperature increases the rate of evaporation of the thin film of moisture and and also
increases the movement of water molecules, thus increases the rate of transpiration

Question 10

describe the effects of variation of humidity on transpiration
rate

Answer 10

Humidity refers to the concentration of water vapour present in the air. A lower humidity means a lower water
vapour concentration, thus a steeper concentration gradient between the atmospheric air and intracellular air spaces. This
increases the rate of water vapour diffusing out of the leaves thus the rate of transpiration

Question 11

describe the effects of variation of light intensity on transpiration
rate

Answer 11

: Higher light intensity leads to increased rate of photosynthesis in guard cells thus causes stomatal
opening. When stomata is open, the rate of transpiration will increase

Question 12

advantages and disadvantages of wilting (2)

Answer 12

Advantages: When the leaves fold up, the leaves droop and less leaf
surface is exposed to the sun thus reducing water loss. Guard cells are
flaccid, closing the stoma, further reducing water loss.

Disadvantages: When the plant wilts, the leaves droop and less leaf
surface is exposed to the sun and thus rate of photosynthesis
decreases

Question 13

phloem
-made up of?(2)
-transport
Structure(4)
Adaptation

Answer 13

. A phloem is made up of sieve tube elements and companion cells
. Transport sugars and amino acids from leaves to other parts of the plant
. Sieve tube elements have degenerate protoplasm, no organelles
. Sieve plates
. Pores in sieve plates allow uninterrupted flow of food substances through the sieve tubes
. One companion cell is clearly associated with each sieve tube element contains organ eels and support metabolic functions of the sieve tube elements
.companion cells have many mitochondria
. Companion cells contain mitochondria that can carry out respiration and release energy for active transport of manufactured food substances from photosynthesis