8. Transport in Plants

Question 1

What two types of transport vessels do plants have?

Answer 1

Xylem vessels

Phloem vessels

Question 2

Function of the xylem vessels

Answer 2

transport water and minerals from the roots to the stem and leaves

Question 3

Function of the phloem vessels

Answer 3

transport food materials (mainly sucrose and amino acids) made by the plant from photosynthesising leaves to non-photosynthesising regions in the roots and stem

Question 4

How are the transport vessels in a plant arranged?

Answer 4

These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles

Question 5

What are root hairs?

Answer 5

Root hairs are single-celled extensions of epidermis cells in the root

Question 6

Where do root hairs grow and what do they do?

Answer 6

They grow between soil particles and absorb water and minerals from the soil

Question 7

By what process does water enter the root hair cells?

Answer 7

Water enters the root hair cells by osmosis

Question 8

How does water move by osmosis into the root hair cells?

Answer 8

This happens because soil water has a higher water potential than the cytoplasm of the root hair cell

Question 9

What adaptation does the root hair cell have and how does this help?

Answer 9

• The root hair increases the surface area of the cells significantly
• This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport

Question 10

What is the path by which water travels from root hair cell to the leaf?

Answer 10

root hair cell → root cortex cells → xylem → leaf mesophyll cells

Question 11

How can the pathway of water in a plant be investigated?

Answer 11

The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)

Question 12

What can you see after a few hours? (investigating pathway of water)

Answer 12

After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery

Question 13

What happens when a cross-section is done of the celery?

(investigating pathway of water)

Answer 13

If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem – these are the xylem vessels

Question 14

Why does water have to keep travelling to the leaf?

Answer 14

Water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration

Question 15

Transpiration definition

Answer 15

Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata

Question 16

What substance helps with the adaptation of xylem vessels and what does it do?

Answer 16

A substance called lignin is deposited in the cell walls which causes the xylem cells to die

Question 17

Why is it useful that the cells in the xylem vessels are dead? How does this help with the adaptation?

Answer 17

These cells then become hollow (as they lose all their organelles and cytoplasm) and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots

Question 18

How does lignin help the adaptation of the xylem vessels?

Answer 18

Lignin strengthens the plant to help it withstand the pressure of the water movement

Question 19

Does the movement in the xylem take place in many directions?

Answer 19

NO

-Movement in xylem only takes place in one direction – from roots to leaves

Question 20

Does movement in the phloem take place in many directions?

Answer 20

YES

movement takes place in different directions

Question 21

What are the main ways in which transpiration helps plants? (4)

Answer 21

• Transporting mineral ions
• providing water to keep cells turgid in order to support the structure of the plant
• providing water to leaf cells for photosynthesis
• keeping the leaves cool

Question 22

How does transpiration help to keep the leaves cool?

Answer 22

the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The using up of heat to convert water into water vapour helps to cool the plant down

Question 23

How does transpiration occur?

Answer 23

• Evaporation takes place from the surfaces of spongy mesophyll cells
• The many interconnecting air spaces between these cells and the stomata creates a large surface area

Question 24

When can evaporation happen rapidly?

Answer 24

This means evaporation can happen rapidly when stomata are open

Question 25

What are water molecules attracted to each other by and what does this create?

Answer 25

Water molecules are attracted to each other by cohesion – creating a continuous column of water up the plant

Question 26

What does the water move by through the xylem vessels?

Answer 26

Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem

Question 27

How does transpiration help the transpiration stream?

Answer 27

Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves

Question 28

How is water pulled through the plant?

Answer 28

As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant

Question 29

What happens to the transpiration stream when the rate of transpiration increases?

Answer 29

If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker

Question 30

When does wilting occur?

Answer 30

If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur

Question 31

What happens inside the plant that causes wilting?

Answer 31

This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse

Question 32

Difference between what is carried by the xylem and phloem

Answer 32

X - water and mineral ions

P - sucrose and amino acids

Question 33

Difference between what process is carried out by the xylem and phloem

Answer 33

X - transpiration stream

P - translocation

Question 34

Difference between cells in the xylem and phloem

Answer 34

X - dead

P - living

Question 35

What are the 2 factors affecting transpiration?

Answer 35

Temperature

Humidity

Question 36

What is the effect of temperature on the rate of transpiration?

Answer 36

Increases with increasing temperature

Question 37

What is the effect of humidity on the rate of transpiration?

Answer 37

decreases with increasing humidity

Question 38

What are the soluble products of photosynthesis?

Answer 38

sugars (mainly sucrose) and amino acids

Question 39

How are the soluble products of photosynthesis transported around the plant?

Answer 39

These are transported around the plant in the phloem tubes which are made of living cells

Question 40

What is the structure of phloem vessels?

Answer 40

The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next

Question 41

What is translocation?

Answer 41

The transport of sucrose and amino acids in phloem, from regions of production to regions of storage or use, is called translocation

Question 42

What does the direction of translocation depend on?

Answer 42

Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year

Question 43

Despite the fact that translocation can take place in many directions, what is the one way in which this process has to take place?

Answer 43

dissolved food is always transported from source (where it’s made) to sink (where it’s stored or used):

Question 44

What is the direction of translocation during winter?

Answer 44

During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue

Question 45

What is the direction of translocation during a growth period?

Answer 45

During a growth period (eg during the spring), the storage organs (eg roots) would be the source and the many growing areas of the plant would be the sinks

Question 46

What is the direction of translocation after the plant has grown?

Answer 46

After the plant has grown (usually during the summer), the leaves are photosynthesising and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again