3.1.3 transport in plants

Question 1

why do multicellular plants need transport systems

Answer 1

they have a small surface area to volume ratio and have a relatively high metabolic rate. exchanging substances by direct diffusion would be too slow to fit metabolic needs

Question 2

what makes up a vascular bundle

Answer 2

xylem, phloem and sometimes a layer of cambium cells

Question 3

what is the function of the xylem

Answer 3

transports water and mineral ions in solution and provides support to the plant

Question 4

how are xylem vessels adapted for their function

Answer 4

they are long tube like structures formed from cells joined end to end with no end walls. the cells are dead and have no cytoplasm
walls are thickened by lignin which supports it and stops it collapsing
water and ions move in and out of the the tube through small pits where there is no lignin

Question 5

what is the function of the phloem

Answer 5

phloem tissue transports assimilates round plants

Question 6

how are phloem vessels adapted for their function

Answer 6

sieve tube elements are joined end to end. there is a sieve plate at the end of each cell to allow solutes to pass through.
sieve tube cells have no nucleus and few organelles and cytoplasm that is connected through sieve plates
companion cells carry out the living functions for themselves and the sieve tubes

Question 7

where are vascular bundles found in stems and why

Answer 7

the vascular bundle is near the outside to provide support to the stem and stop it bending

Question 8

where are vascular bundles found in leaves and why

Answer 8

the vascular bundles make up a network of veins which support the thin leaves

Question 9

where are vascular bundles found in roots and why

Answer 9

xylem in centre surrounded by phloem to provide support to the root as it pushes through the soil

Question 10

how does water enter a plant through its roots

Answer 10

water enters root via osmosis. the soil by roots often has a high eater potential and leaves have a lower water potential. this creates a water potential gradient which keeps water moving up the plant

Question 11

how does water move through the root to the xylem in the symplast pathway

Answer 11

water goes through the cytoplasm. the cytoplasm of neighbouring cells join by plasmodesmata. it moves by osmosis

Question 12

how does water move through the root to the xylem in the apoplast pathway

Answer 12

goes through the cell walls. the cell walls are absorbent so water can diffuse through them. the water can carry solutes and moves from low hydrostatic pressure to high hydrostatic pressure

Question 13

what is a casparian strip

Answer 13

it is a waxy strip at the endodermis that blocks the apoplast pathway

Question 14

what is a transpiration stream

Answer 14

the movement of water from rots to leaves

Question 15

what causes a transpiration stream

Answer 15

water evaporates from leaves (transpiration) which creates tension which pulls more water into the leaf.
water molecules are cohesive so when some are pulled up others follow.
water is also adhesive so it is attracted to the xylem walls which propels it forwards

Question 16

how does light effect transpiration rate

Answer 16

the more light there is the faster transpiration rate because the stomata open when it gets light so carbon dioxide can diffuse into the leaf for photosynthesis but water can also leave through stomata.

Question 17

how does humidity effect transpiration rate

Answer 17

lower the humidity higher the transpiration rate. if the air around the plant is dry then water potential gradient is increased, increasing the rate

Question 18

how does temperature effect transpiration rate

Answer 18

higher the temperature the faster the transpiration rate. warmer molecules have more energy and evaporate faster. this increases the water potential gradient making water diffuse out faster

Question 19

how does wind effect transpiration rate

Answer 19

the windier it is the faster the transpiration rate. lots of air movement moves water molecules away from the stomata which increases the rate of transpiration

Question 20

how do we set up a potometer

Answer 20

• cut shoot at a slant to increase surface area and under water to prevent air bubbles
• assemble under water so no air can enter
  make apparatus water tight with Vaseline.
• dry the leaves
• make an air bubble in capillary tube

Question 21

how do we use a potometer

Answer 21

record the start position of the bubble, start a stopwatch and watch how far the bubble moves in a set time. this shows us transpiration rate

Question 22

what is a xerophyte

Answer 22

plants that are adapted to live in dry climates. e.g. marram grass and cacti

Question 23

what is a hydrophilic plant

Answer 23

a plant that is adapted to survive in water

Question 24

what adaptions do xerophytes have to reduce water loss

Answer 24

• stomata in sunken pits sheltered from the wind to slow transpiration
  -layer of hairs to trap moist air to slow transpiration
• roll leaves in hot and windy conditions to trap moist air and reduce exposed stomata
• thick waxy epidermis to reduce water loss as it is waterproof
  -spines to reduce surface area
  -close stomata at hot times of day

Question 25

what adaptions do hydrophilic plants have to survive in water

Answer 25

air spaces in tissues help the plants float and store oxygen
stomata only present on the top of leaves to maximise gas exchange
flexible leaves and stems to prevent damage from currents

Question 26

what is translocation

Answer 26

translocation is the movement of dissolved substances (assimilates) it requires energy

Question 27

what is a sink

Answer 27

has a high concentration of assimilates as its where a substance is made up

Question 28

what is the mass flow hypothesis

Answer 28

active transport actively loads the solutes into the sieve tubes of phloem at source
this lowers water potential in the sieve tubes so water enters the tubes by osmosis from the xylem and companion cells
this creates high pressure at the source end
at the sink end solutes are removed from phloem to be used up which increases water potential so water leaves via osmosis. this lowers the pressure
the pressure gradient from the source to the sink so solutes are pushed up the phloem

Question 29

what is a source

Answer 29

the area where assimilates are used up so there is a low concentration

Question 30

how does active loading at the source work

Answer 30

atp used to actively transport H+ out of the cells into tissues which sets up a concentration gradient as there is more H+ outside cell
H+ binds to cotransport protein and re-enters cell and a sucrose molecule also binds so it moves into the cell using the H+ ion
same process happens to load into th sieve tubes