3.3 Transport in Plants

Question 1

How many transport systems do plants have?

Answer 1

2 - xylem and phloem

Question 2

Draw out where the xylem and phloem (vascular bundle) are located in the roots stem and leaves

Answer 2

1. roots - xylem and phloem located in centre to provide support as they push through soil. find picture to check
2. Stems - located near outside in a ring to provide structure and stop plant from bending. check with pic
3. Leaves- make up network of veins to support thin leaves. check pic

Question 3

What are the adaptations of a xylem?

Answer 3

• made of xylem vessels which are long and tube shaped and have no end walls to allow water to pass up.
• made of dead cells so have no cytoplasm and more room for water to pass up.
• Holes in walls called pits that allow ions to move in/out.
• walls supported by being thickened with lignin a woody substance to stop xylem walls from collapsing. Lignin can be deposited in spirals or rings.

Question 4

What does the xylem do?

Answer 4

Transports water and mineral ions in a solution up a plant / up transpiration stream.

Question 5

What is transpiration?

Answer 5

The loss of water vapour through evaporation via the stomata.

Question 6

How does water movement through a plant happen from start to end (hint starts at root).

Answer 6

1. water moves into roots
2. water moves from roots to xylem
3. water moves up xylem vessel towards leaves
4. water is lost by transpiration

Question 7

What are the two pathways in which water can enter roots.

Answer 7

• symplast pathway
• apoplast pathway

Question 8

How does water enter the roots ?

Answer 8

by osmosis down a water potential gradient

Question 9

Describe how water moves through the symplast pathway.

Answer 9

Water moved through the living part of the cell (cytoplasm) from cell to cell. Cells have channels called plasmodesmata which connect the cytoplasm between cells. It moved via osmosis.

Question 10

Describe how water moves through the apoplast pathway.

Answer 10

Water moves through the dead part of the cells in the root (cell walls) by diffusion. However when water reaches the endodermis layer the cells have a band of waxy layer called the suberin this band is called the casparian strip. This stops water moving by cell walls and so water has to enter the symplast pathway.

Question 11

How does transpiration happen?

Answer 11

Due to gas exchange.
Water at the top of a plant enters the leaves by the apoplast pathway from xylem.
The stomata open for gas exchange and water evaporates from a higher water potential out into the air where there’s a lower water potential.

Question 12

What forces helps the water move up the xylem vessels and what are they?

Answer 12

• Cohesion ( water molecules attracted) this reduces hydrostatic pressure causing a pull like motion of water molecules towards the stomata.
• Adhesion (water molecules attracted to xylem walls) this helps water move up vessel

Question 13

What are the limiting factors for transpiration?

Answer 13

• Light intensity. (low)
• Temperature. (low)
• Humidity. (high)
• Wind. (low)

Question 14

Explain how light intensity is a limiting factor.

Answer 14

High light intensity allows the stomata to open so increases rate of evaporation. If light is low then it’s the limiting factor.

Question 15

Explain how temperature is a limiting factor.

Answer 15

At higher temperatures, water molecules have more energy and so end up moving faster. If the temp is low the water molecules have less energy so slows down rate of transpiration.
also it increases the concentration gradient between the outside of the plant and the inside of the

Question 16

Explain how humidity is a limiting factor.

Answer 16

If there’s a low humidity, the air is dryer, so there’s an increase in the water potential gradient. This increases the rate of evaporation. Therefore high humidity is a limiting factor as less water will be evaporated due to a less steep concentration gradient.

Question 17

Explain how wind is a limiting factor .

Answer 17

If there’s more wind, there’s more air movement, and this blows water away from stomata. This increases the water potential gradient. If there’s no wind this doesn’t happen.

Question 18

How are xerophytic plants adapted to live? Give an example of a xerophyte too.

Answer 18

Xerophytes are adapted to live in dry climates.
Include cacti and marram grass.
Have thick waxy layer on epidermis, spines not leaves to reduce SA, closed stomata in day, stomata in pits, hairs to trap moist air.
This all prevents too much water loss from transpiration.

Question 19

How are hydrophytic plants adapted to live in their conditions?
Give an example of one too.

Answer 19

Hydrophytes live in aquatic conditions.
Include water lilies.
Have air spaces, stomata only on upper surface of leaves, flexible leaves.
These help them to cope with low 02 levels.

Question 20

How is phloem tissue adapted?

Answer 20

Phloem tissue is made of living cells (sieve tube elements). They have a thin layer of cytoplasm but no nucleus. Sieve tube elements are joined together by sieve plates that have holes in to allow solutes to pass through.
Because sieve tube elements have no nucleus can’t survive on their own so each have a companion cell. These have a nucleus and lots of mitochondria.

Question 21

What is translocation?

Answer 21

The movement of assimilates to where they are needed in a plant via the phloem.

Question 22

Is translocation an active or passive process ?

Answer 22

Active as needs energy (ATP)

Question 23

Where do substances move to and from in translocation?

Answer 23

From the source to the sink

Question 24

what’s a source ?

Answer 24

Where a substance is made

Question 25

what’s a sink?

Answer 25

where the substance is used up

Question 26

What are assimilates?

Answer 26

Dissolved substances like sucros and amino acids ext.

Question 27

What is the mass flow hypotheses? (Draw it out)

Answer 27

check cards

Question 28

Explain the process of translocation and draw out the diagram.

Answer 28

check card paper
Diagram with source sink ect