Plant transport

Question 1

What is the apoplast pathway

Answer 1

Water moves through the gaps between the cellulose microfibres in the cell wall

Question 2

What is the symplast pathway

Answer 2

Water moves through the cytoplasm and the plasmodesmata in the cell wall

Question 3

What is the vacuolar pathway

Answer 3

Water moves from vacuole to vacuole

Question 4

What is the Casparian strip

Answer 4

An impermeable band of suberin across the cell walls of the endodermal cells blocks the apoplast pathway and pushes the water into the symplast

Question 5

What is the vascular system in the root called

Answer 5

Vascular stele

Question 6

What is the vascular system in the stem called

Answer 6

Vascular bundle

Question 7

What are the three plant macronutrients

Answer 7

Nitrogen, phosphorus, potassium

Question 8

How is nitrogen taken into the plant

Answer 8

Nitrogen is absorbed as dissolved ammonium or nitrate ions into the apoplastic stream by diffusion. The ions are absorbed into the symplast pathway by active transport

Question 9

How are root hair cells adapted for absorption

Answer 9

Thin cell walls
Large SA:V ratio
Large number of mitochondria
Large sap vacuole

Question 10

What are mycorrhizae

Answer 10

Fungi that grow around plant roots to increase the surface area for absorption. The plant supplies the fungi with sugars

Question 11

How is water taken up the xylem

Answer 11

Root pressure
Cohesion and adhesion in the transpiration stream
Capillarity

Question 12

How does root pressure work

Answer 12

Plants take up ions, lowering the water potential and drawing water in causing positive hydrostatic pressure forcing water upwards

Question 13

What are the transport cells in phloem

Answer 13

Sieve tube cells

Question 14

What is the sieve plate

Answer 14

Contains tiny holes at the end of the sieve tube allowing sugar solution to pass through

Question 15

What is the role of a companion cell

Answer 15

Regulate the metabolism of the sieve tube cell and load and unload sugar from the phloem

Question 16

Which part of the phloem and xylem vessels provides strength

Answer 16

Sclerenchyma cells and fibres

Question 17

What is the role of tracheids

Answer 17

heavily strengthened, conducting cells

Question 18

What is the role of parenchyma cells

Answer 18

Storage/packing cells

Question 19

What is the role of vessels in plants

Answer 19

Conducting vessels

Question 20

How are vessel elements is plants adapted to their function

Answer 20

Large diameter cells offer low water resistance and allows rapid uptake of water

Question 21

Describe the vascular tissue in leaves

Answer 21

A system of veins resistant to tearing

Question 22

Describe the effects of the following on transpiration:

Temperature
Air movement
Humidity
Light intensity

Answer 22

Temperature: Increased temperature increases the kinetic energy of water molecules and as such increases the rate of transpiration

Air movement: Increased air movement causes recently removed water to move far away from the stomata, increasing the concentration gradient and increasing the rate of transpiration

Humidity: High levels of humidity decrease the concentration gradient between the inside of the leaf and the air around the leaf, decreasing the rate of transpiration

Light intensity: High light intensity causes the stomatal opening to open more, allowing more water out and increasing the rate of transpiration

Question 23

How do you set up a potometer correctly

Answer 23

Keep leaves dry
Set up apparatus underwater
Cut shoot underwater
Ensure all joints are airtight

Question 24

Describe translocation

Answer 24

Movement of sugars from their source to their sink via the phloem

Question 25

What is a source and what is a sink

Answer 25

source: site of the photosynthesis of the sugars sink: where the products of photosynthesis may be used for growth or storage

Question 26

How are substances transported between the companion cells and the sieve tube cells

Answer 26

Plasmodesmata

Question 27

Describe the ringing experiments to prove translocation

Answer 27

Bark was removed in a ring around a tree, thus removing the phloem. No sugar was then found below the site of the ring, proving the sugars are transported in the phloem to the whole plant

Question 28

Describe how aphids have been used to prove translocation

Answer 28

Aphids have hollow, needle-like mouthparts called a stylet. The stylet is inserted directly into the sieve tube allowing the aphid to feed on the sugary sap. The stylet can be cut off (using a laser) leaving it attached to the plant (it forms a useful micropipette). Sap exuding from the stylet is collected and analysed. Analysis shows that the sap contains the products of photosynthesis – sucrose and amino acids.

Question 29

Describe how radioactive labelling can be used to prove translocation

Answer 29

Carbon dioxide labelled with radioactive carbon is supplied to an illuminated plant leaf. The radioactive carbon is fixed in the sucrose produced by photosynthesis and is translocated to other parts of the plant. This radioactive carbon in the sucrose can be traced using autoradiography

Question 30

Describe the mass flow hypothesis

Answer 30

 When sugar is made at the source the water potential becomes more negative and water passes into the source cells by osmosis.  As water enters the source cells, hydrostatic pressure increases forcing sugars and other products of photosynthesis into the sieve tubes – phloem sieve tubes are loaded.  Mass flow occurs along the sieve tubes to the sink, the products of photosynthesis are forced along by the flow of water from a high to a low hydrostatic pressure.  Hydrostatic pressure will be lower at the sink because sugars are stored as starch or are used for respiration; this reduces the water potential.  Water passes from the sink cells to the xylem to be returned to the source.

Question 31

Name arguments against the mass flow hypothesis

Answer 31

The rate of translocation is 10,000 times faster than it would be if the substances were moving by diffusion. Sieve plates with tiny pores act as a barrier impeding flow. Sucrose and amino acids move at different rates and in different directions in the same phloem tissue. Phloem tissue has a high rate of oxygen consumption, and translocation is stopped when a respiratory poison such as potassium cyanide enters the phloem. Companion cells contain numerous mitochondria and produce ATP, but the mass flow hypothesis fails to suggest a role for the companion cells.

Question 32

Describe how the waterlily is adapted to its environment

Answer 32

it is a HYDROPHYTE and so is surrounded by water. Therefore, it has a poorly developed xylem structure as it doesn't need to transport much water. The stomata are on the top of the lilypad because the underside is submerged. It also has little to no waxy cuticle as water loss is not an issue, and large air spaces in the spongy mesophyll for buoyancy

Question 33

Describe how marram grass is adapted to its environment

Answer 33

it is a XEROPHYTE and is surrounded by little water. The plant features rolled leaves, sunken stomata, a thick waxy cuticle and hairs to trap water vapour, all the reduce water loss.

Question 34

Describe mesophytes

Answer 34

 Mesophytes flourish in habitats with adequate water supply.  Most plants of temperate regions are mesophytes.  Most crops are mesophytes.  Close stomata during the night to decrease water loss.  Shed leaves in the winter to survive unfavourable times e.g. frost.  Underground organs survive winter e.g. bulbs.  Annual mesophytes (plants which flower, produce seed and die in the same year) survive the winter as dormant seeds.