Transport In Plants

Question 1

Explain how water enters a plant root from the soil and travels through to the endodermis

Answer 1

Water enters root hair cell by osmosis
because active uptake of mineral ions has created a water potential gradient
Water moves through the cortex down a water potential gradient
Through cell vacuoles/symplastic pathway
Through cell walls/apoplastic pathway

Question 2

Cause of root pressure?

Answer 2

Active transport by endodermis
Salts into xylem
Lowers water potential in xylem
Water enters by osmosis

Question 3

Why xylem vessels contain lignin walls and are hollow?

Answer 3

Lignin… Resists tension of water column/provides support/strength
maintains column of water
adhesion
prevent water loss

Hollow because unrestricted water flow/continuous column/maintains transpiration stream

Question 4

How does the graph support cohesion-tension theory

Answer 4

Movement starts/peaks earlier in branches higher up

Creates tension/negative pressure/pull

Question 5

Why cut shoot under water

Answer 5

Prevent air entering/continuous column of water

Question 6

Why water uptake was not equivalent to transpiration rate/ why transpiration rate does not truly measure rate of transpiration

Answer 6

Water used to provide turgidity
Used in photosynthesis
Water produced in respiration
Apparatus not sealed/leaks

Question 7

Adaptations of plants for living in desert conditions

Answer 7

Shallow roots enable rapid uptake of rainfall (in x or z)
Widespread allow collection of large volume of water
Swollen stem for water storage
Deep roots for accessing deep groundwater
Small/no leaves so little transpiration

Question 8

Purpose of reservoir (potometer experiment)

Answer 8

Can take repeat measurements- returns bubble to start/ this is done by opening/using tap/add water from reservoir

Question 9

Give two precautions students should take to get reliable measurements when setting up
Potometer to measure water uptake by plant shoot?

Answer 9

Seal joints/ensure airtight/ensure watertight
Cut shoot under water
Cut shoot at a slant
Dry off leaves
Insert into apparatus under water
Ensure no air bubbles present
Shut tap
Note where bubble is at start/move bubble to the start position

Question 10

Explain why transpiration increases when temperature increases

Answer 10

Molecules have more kinetic energy
Faster diffusion of water/more evaporation of water as temperature increases in leaf
Diffusion relates to movement of water

Question 11

Explain how xylem tissue is adapted to its function?

Answer 11

Long cells/tubes with no end walls
Continuous water columns
No cytoplasm/no organelles
To impede/allows easier water flow
Lignin- support/withstand tension/waterproof/keeps water in cells/pits in walls/adhesive
Pits in walls to allow lateral movement m/get round blocked vessels

Question 12

Why diameter of tree decreases during the day due to cohesion-tension theory?

Answer 12

Adhesion/ attraction of water molecules to the xylem walls
Results in tension as water pulled up stem
Pulling in walls

Question 13

Describe how a high pressure is produced in the leaves

Answer 13

Water potential becomes more negative as sugars enter the phloem
Water enters phloem by osmosis
Increased volume of water causes increased pressure

Question 14

Describe the mass flow hypothesis for the mechanism of translocation in plants

Answer 14

In source/ leaf sugars are actively transported into phloem
By companion cells
Lowers water potential of sieve cell/tube and water enters by osmosis
Increase in pressure causes mass movement (towards sink/root)
Sugars used/converted in respiration/ for storage as starch

Question 15

Adaptations of sieve tube elements

Answer 15

Elongated elements
Joined end to end 
Pores in end walls/perforated end plates/sieve pores 
Little cytoplasm/thin layer of cytoplasm
No nucleus/ few organelles

Question 16

Describe how assimilated (sucrose) are loaded in the phloem

Answer 16

Active transport of H+ ions into cell wall spaces of companion cells
Sucrose moves with H+ ions by co-transport
Creates H+ ions diffusion/concentration gradient
H+ move by facilitated diffusion into sieve tube elements
Sucrose moves with the H+ ions by co-transport

Question 17

What is the apoplast pathway

Answer 17

Pathway from cells along cell walls/ through intercellular spaces and out through stomata
By diffusion
Down a water potential gradient/diffusion

Question 18

Adaptations of xerophytes

Answer 18

Sunken stomata- reduce air movement/diffusion gradient
Rolled leaves- reduce surface area
Enclose still air around stomata
Thick Waxy cuticle, reduce cuticular evaporation/impermeable to water
Few stomata, to reduce as for diffusion
Small leaves, reduce surface area for diffusion
=shape of leaf/rounded/small surface area
Small surface area to volume ratio means less water is lost

Question 19

Cohesion-tension theory

Answer 19

Water evaporates/transpires
Reduces water potential/increases osmotic gradient
Moves via apoplast pathway
Water drawn out of xylem
Creates tension/pulling effect/negative pressure
Cohesion between water molecules due to hydrogen bonding/water moves as a column

Question 20

Features of the endodermis

Answer 20

Has casparian bands
Which are impermeable/waterproof
Lower water potential in the cytoplasm of endodermis cell
Enters symplastic pathway/cytoplasm of the cell
By osmosis

Question 21

How does water move through the trunk of a tree

Answer 21

In xylem:
Evaporation/transpiration from leaves
Through stomata
Cohesion of water molecules
Leaf cells have a more negative water potential, so water enters from xylem
Water drawn up as continuous column
Adhesion of water to walls pulls in walls
Capillarity due to narrow lumen of xylem (vessels)
Lignified walls keep xylem open
Root pressure forces some water up

Question 22

Describe how the structure of the xylem relates to its function

Answer 22

Vessels
Have no end walls/hollow/no cytoplasm/no organelles as it’s dead
Allows unrestricted flow of water
Lignification
Provides support/strength/impermeability
Pits allow lateral movement

Question 23

What is root pressure

Answer 23

Involves active transport
Secretion/movement of salts into xylem
Endodermis-water moves along water potential gradient

Question 24

Cohesion-tension

Answer 24

Solar energy source
Evaporation of water
Water potential gradient across leaf/mesophyll cells
Tension creates in xylem
Cohesion of water maintains column
Due to H bonding/polarity/charges of water molecules
Adhesive force between water and wall

Question 25

Xerophytic plant adaptations

Answer 25

Sunken/fewer stomata- reduces water potential gradient air movement across stomata/traps air which becomes saturated/moist/humid
Rolled leaves- reduces water potential gradient air
Movement across stomata/traps air which becomes saturated/reduces surface area
Thick cuticle- reduces cuticular transpiration/greater diffusion distance
Spikey leaves
Reduces leaves/spines- less surface area/ fewer stomata for evaporation
Hairs- traps air which becomes saturated/moist/humid