Transport in Plants

Question 1

Why do plants need a transport system?

Answer 1

Get water from the roots to the leaves

Move sugars from leaves to the rest of the plant

Question 2

What is the function of the xylem?

Answer 2

Carry water up the plant

Provide structure

Question 3

What happens to xylem cells as they mature which impacts their function?

Answer 3

They become lignified

Question 4

What does lignin do to the xylem?

Answer 4

Kills the cells

Makes them waterproof

Strengthens the vessel

Question 5

What is the function of the cambium?

Answer 5

Contains meristem cells which can divide and specialise to form new xylem and phloem cells

Question 6

Give ways in which xylem is adapted to its function

Answer 6

Made from dead cells aligned end to end

tubes are narrow so capillary action can be effective

Bordered pits allow water to move from one vessel to another

Lignin deposited in a spiral allows the xylem to stretch as the plant grows despite being dead

Question 7

What are the two types of cells that make up the phloem?

Answer 7

sieve tube elements

Companion cells

Question 8

What is the function of the phloem?

Answer 8

Transport assimilates (mostly sucrose and amino acids)

Question 9

How are sieve tube elements specialised to carry out their function?

Answer 9

Lined up end to end to make a long tube

contain no nucleus and little cytoplasm, leaving more space for mass flow to occur

Question 10

What is the function of the companion cells?

Answer 10

To carry out metabolic processes needed to actively load assimilates into the sieve tube elements

They are needed because the little cytoplasm in the sieve tube elements means that they can’t do this themselves.

Question 11

How are companion cells adapted to their function?

Answer 11

They have a large nucleus

Dense cytoplasm

This is because they need to carry out metabolic reactions for not only themselves but the sieve tube elements also

Question 12

What is a plasmodesma?

Answer 12

A gap in the cell wall of a cell where it connects to another cell

Question 13

describe what the 3 pathways in which water can move are and how they work?

Answer 13

Apoplast pathway - Moves in the spaces between cells

Symplast pathway - Moves between the plasmodesmata of cells through the cytoplasm

Vacuolar pathway - Moves through the vacuoles of cells also

Question 14

Where will water move in a water potential gradient?

Answer 14

To the area with he lowest water potential

Question 15

What will happen if you put plant cells in distilled water and why does this happen?

Answer 15

The plant cells will take up water by osmosis and swell

This because the solutes in the plant cell cause the water potential to be lower than that of the distilled water

Water moves to the area of lowest water potential

Question 16

What will happen if you put plant cells in a salt solution and why?

Answer 16

A salt solution will have a very low water potential

Water will move out of the plant cell into the solution down a water potential gradient

Water will move to the area of lowest water potential

Cells will shrink

Question 17

What is the name of the condition whereby the plasma membrane comes away from the cell wall?

Answer 17

Plasmolysis

Question 18

What is Transpiration?

Answer 18

The loss of water vapour from the upper parts of the plant- particularly the leaves

Question 19

Describe the pathway of water leaving the leaf

Answer 19

Water enters leaf through xylem and moves by osmosis into the spongy mesophyll

Water evaporates from the cell walls of the spongy mesophyll

Water vapour moves by diffusion out of the leaf through he open stomata. This requires a water potential gradient between the leaf and the surroundings

Question 20

Why is transpiration essential for a plant to survive?

Answer 20

As water vapour is lost it draws water up the stem as a transpiration stream, this movement:

Transports useful mineral

Maintains cell turgidity

Supplies water for growth, cell elongation and photosynthesis

Supplies water that can evaporate to cool the plant

Question 21

Give 5 environmental factors that affect rate of transpiration

Answer 21

Light intensity
Temperature
Humidity
Wind
Water availability

Question 22

What type of cells is the epidermis of a root made of?

Answer 22

Root hair cells

Question 23

Where does water move from and to in the root?

Answer 23

Water moves from the soil into the epidermis of the root hair cells

Moves across the root cortex to the endodermis of the vascular bundle

Question 24

Why can water only move through the apoplast pathway as far as the endodermis?

Answer 24

Because the Casparian strip blocks the apoplast pathway

Question 25

Describe how the endodermis and Casparian strip act to move water into the medulla and xylem

Answer 25

Casparian strip blocks the apoplast pathway between the cortex and medulla

Ensures that mineral ions (especially nitrates) pass through the plasma membrane into the cytoplasm

Mineral ions are actively transported into the medulla and xylem

This creates a water potential gradient so water moves by osmosis into the medulla

The Casparian strip then blocks it from moving back out

Question 26

What are the 3 processes that ensure mass flow occurs?

Answer 26

Root pressure
Transpiration pull
Capillary action

Question 27

Describe what root pressure is.

Answer 27

As water moves into the roots and xylem it causes an increase in pressure

This pressure forces water up the xylem

This can push water a few meters up a stem but can’t account for tall trees

Question 28

Describe the process of transpiration pull

Answer 28

Water is lost from the top of the plant by transpiration

Hydrogen bonds cause cohesion between water molecules

Water moves up to the leaves to replace lost water and other molecules are pulled up with it

Question 29

Describe the process of capillary action

Answer 29

The high surface tension of water causes it to stick to the sides of the xylem vessels. This is called adhesion

Because the xylem vessels are very narrow, this can pull water up the xylem.

Question 30

What is the term given to plants that are adapted to survive in arid conditions?

Answer 30

Xerophytes

Question 31

Give an example of a Xerophyte

Answer 31

Marram grass

Question 32

What are the adaptions of marram grass that make it a xerophyte?

Answer 32

Rolled leaf - increases humidity next to the stomata

Thick waxy cuticle - reduces evaporation

Stomata are on the inside of the rolled leaf - protected by the enclosed space

Hairs surround stomata - reduce air movement maintaining a water potential gradient

Dense spongy mesophyll - fewer air spaces so slower evaporation of water

Question 33

What type of plant are cacti?

Answer 33

Succulents

Question 34

Give some adaptions of cacti to reduce water loss

Answer 34

Leaves are reduced to spines to reduce transpiration

Stem is green to perform photosynthesis (no leaves)

roots are shallow and very widespread to increase water uptake in a rain event

Question 35

What is the name given to plants that can live in water?

Answer 35

Hydrophytes

Question 36

Give some adaptions of hydrophytes

Answer 36

Large air spaces to keep the leaf afloat so the leaves can perform photosynthesis

Stomata on the upper epidermis to allow gaseous exchange

Stem has large air spaces to keep it afloat but also so oxygen can quickly diffuse all the way to the roots.

Question 37

Where does translocation occur?

Answer 37

In the phloem

Question 38

What is translocation?

Answer 38

The movement of assimilates throughout the plant

Question 39

What are assimilates?

Answer 39

Substances made by the plant from substances absorbed from the environment.

e.g Sugars and amino acids

Question 40

What is a source? (Translocation)

Answer 40

Somewhere where assimilates are loaded into the phloem

Question 41

What is a sink?

Answer 41

A part of the plant where assimilates leave the phloem

Question 42

Describe the process of active loading

Answer 42

H+ ions are actively transported out of the companion cells

A concentration gradient is formed

H+ ions diffuse back into the host cell through co-transporter proteins

These proteins only allow H+ back in that is attached to sucrose molecules

Sucrose can then diffuse into the sieve tube elements through the plasmodesmata

Question 43

By what process does the sucrose move in the phloem?

Answer 43

Mass flow

Question 44

Describe the process of mass flow

Answer 44

Flow is caused by a difference in hydrostatic pressure between the two ends of phloem

Water enters the tube at the source increasing hydrostatic pressure and leaves at the sink which reduces the pressure.

Therefore mass flow always goes from source to sink

Question 45

Why does water enter the phloem at the source?

Answer 45

Because the assimilates cause the solution inside the phloem to have a low water potential

Thus, water moves in via osmosis