Transport in plants

Question 1

What is the function of the xylem

Answer 1

Transports water and minerals up the plant from the roots to the leaves

Question 2

Describe the structure of the xylem vessels

Answer 2

long cells with thick walls
Impregnated with lignin
Xylem cells die and their end walls die and decay
Leaves long columns of hollow dead cells

Question 3

What is the function of xylem pits

Answer 3

Permits the lateral movement of water from vessel to vessel as well as out the vessels

Question 4

Explain the function of lignin within the xylem

Answer 4

lignification permits the xylem to stretch as the plant grows and enables the stem or branch to bend

Prevents the collapse of the vessel when its under tension

Provides adhesion for water molecules

waterproofing

Question 5

what is the function of the phloem

Answer 5

Transports sucrose

Question 6

What does the phloem consist of

Answer 6

Sieve tube elements
Companion cells

Question 7

Describe the structure of the sieve tube elements

Answer 7

Very little cytoplasm
No nucleus
Contain mitochondria and RER
No vacuole

Question 8

How are the sieve tube elements adapted

Answer 8

Sieve plates contain sieve pores to allow the flow of water and solutes

Very few organelles so large surface area

Question 9

What is the structure of the companion cells

Answer 9

Large nucleus
Dense cytoplasm
Lots of mitochondria

Question 10

How does water enter the roots

Answer 10

Mineral ions are actively transported into the root hair cell
This lowers the water potential of the cytoplasm
Water enters root hair cell via osmosis down a water potential gradient

Question 11

What are the possible pathways water can enter the xylem

Answer 11

Apoplast
Symplast
Vacoular

Question 12

What is the apoplastic root

Answer 12

Around cell walls
Does not go through plasma membrane

Question 13

What is the symplastic root

Answer 13

Water enters through the plasma membrane into cytoplasm
Passes through the plasmodesmata

Question 14

What is the vacuolar root

Answer 14

Travels through the cytoplasm and the vacuoles

Question 15

How does water enter the xylem vessels

Answer 15

mineral ions actively transported into the xylem by cells in the endodermis
This lowers the water potential in the xylem
Water enters the xylem by osmosis
Ions cannot leak back due to the casparian

Question 16

What is transpiration

Answer 16

The process of water movement through a plant and its evaporation from aerial parts

Question 17

How is water moved up the xylem from the roots to the leaves

Answer 17

Root pressure: Minerals actively transported into the xylem lower the water potential in the xylem
This causes water to move in via osmosis, this creates a high hydrostatic pressure and the bottom of the xylem

Transpiration pull: Cohesion as water molecules evaporate from leaves water molecules are pulled up because they form hydrogen bonds with other water molecules and stick together

capillary action: water molecules attracted to the walls of the xylem, because xylem are very narrow the forces of attraction pull up the water via the sides of the xylem

Question 18

How does water leave the leaf

Answer 18

Water moves from a xylem
vessel…

… to a spongy mesophyll cell
via a pit

Water evaporates from
mesophyll cells to form water
vapour

Water vapour diffuses down
water vapour potential
gradient across the airspace
and out of the stomata

Water vapour is taken away
by air currents

Question 19

What does the plant use the transpiration stream for?

Answer 19

Photosynthesis
Plant growth
Keeps the plant turgid

Question 20

what is a potometer

Answer 20

A device used to measure the rate of transpiration

Question 21

Describe three steps a student you use when setting up a potometer

Answer 21

Set the potometer up underwater

Use healthy shoots

Make sure there are no leaks

Question 22

Explain why transpiration cannot be avoided during the day

Answer 22

Plants need to open the stomata so that gases such as oxygen and CO2 can be diffused in for photosynthesis, meaning that water vapour will be lost through the stomata

Question 23

What type of plants are able to live in arid conditions

Answer 23

Xerophytes

Question 24

What adaptations do xerophytes have to reduce water loss

Answer 24

Hairs on the surface trap water vapour

sunken stomata trap water vapour in the pits

Rolled leaves reduce the surface area of where water vapour can be lost, traps water vapour as well

Very few stomata, to reduce the amount of water vapour lost when they are open

Question 25

What type of plants live in or on water

Answer 25

Hydrophytes

Question 26

What are the adaptations of hydrophytes

Answer 26

Air spaces in leaves to help them float

Air spaces in the roots and stems so oxygen can move from the leaves to the parts underwater

Stomata on the upper surface for efficient gas exchange

flexible leaves and stems to prevent damage by water currents

Question 27

What is translocation

Answer 27

Movement of assimilates from a source to a sink

Question 28

Explain how assimilates are transported from source to sink

Answer 28

Companion cells actively transport hydrogen ions out of the companion cells into surrounding cells
This sets up a diffusion gradient for hydrogen ions

Hydrogen ions diffuse back into companion cells via co-transporter proteins and bring sucrose molecules with them

the concentration of sucrose molecules builds up in the companion cells and will diffuse into the phloem via the plasmodesmata

Sucrose entering the phloem lowers the water potential inside, so water moves into the phloem via osmosis
this increases the hydrostatic pressure inside the phloem at the source

At the sink there is a low hydrostatic pressure and a low concentration of sucrose
Sucrose molecules and water molecules move to the area of low hydrostatic pressure

Sucrose molecules move into the sink by active transport or diffusion

This increases the water potential in the phloem so water diffuses out of the phloem and into the sink, reducing the hydrostatic