2.3b - Adaptations for transport in plants

Question 1

What does vascular tissue do?

Answer 1

transports materials around the body

Question 2

What is the vascular tissue in plants?

Answer 2

Xylem and phloem, found adjacent to each other in vascular bundles

Question 3

What is the Xylem tissue?

Answer 3

transports water and minerals up the plant

Question 4

What is the Phloem tissue?

Answer 4

Translocate sucrose and amino acids from the leaves to the rest of the plant

Question 5

What is the arrangement of the vascular bundle in roots?

Answer 5

Xylem is central and X shaped with the phloem between groups of xylem cells. This arrangement resists vertical stresses (pull).
Xylem is surrounded by endodermis (helps supply xylem with water)

See NC 1

Question 6

What is the arrangement of the vascular bundle in the stem?

Answer 6

Vascular tissue are in a ring at the periphery, with xylem towards the centre and phloem towards the outside. Gives flexible support and resists bending

See NC 1

Question 7

What is the arrangement of the vascular bundle in the leaf?

Answer 7

Vascular bundles form the midrib and veins of a leaf, giving flexible strength and resistance to tearing

See NC 2

Question 8

The 2 main types of cells in the xylem are vessels and tracheid’s. They are dead cells. What are they and what do they occur in?

Answer 8

Vessels - Water conducting structures, long cylinders made of dead tissue with open ends, therefore they can form
a continuous column.

Tracheid’s - Spindle shaped, water conducting cells only occurring in flowering plants

Question 9

What makes vessels so thick but flexible?

Answer 9

lignin, which is deposited in spiral
patterns to enable the plant to remain flexible

Question 10

What are the 2 functions of the xylem?

Answer 10

Transport of water and dissolved minerals
Providing mechanical strength and support

Question 11

How is water lost in plants?

Answer 11

Lost through the stomata via the transpiration stream

Question 12

Where is water replaced (taken in)? Why is this a region of great water uptake?

Answer 12

From the soil, at the root hair zone on the root. Root hair cells have large S.A for absorption of water by osmosis, thin cell walls (short diffusion pathway)

Question 13

Soil is very _____(concentrated/dilute), containing a ____ (L/H) concentration of mineral salts, the water potential is ___(L/H). The vacuole of root hair cells has a ____ (L/H) conc of solutes and therefore a ____ (L/H) water potential. Water passes from a high to low water potential, down a water potential gradient, into the root hair cell by _______.

Answer 13

dilute
low
high
high
low
osmosis

See NC 3

Question 14

Name the 3 pathways which water taken up by the root hair cells can be moved across the cortex of the root into the xylem?

Answer 14

Apoplast pathway
Symplast pathway
Vacuolar pathway

Question 15

What are the 3 pathways water can be transported via?

Answer 15

Apoplast - through the cell walls
Symplast - through cytoplasm and plasmodesmata
Vacuolar - from vacuole to vacuole

See NC 4

Question 16

What is the plasmodesmata?

Answer 16

Strands of cytoplasm through pits in the cell wall joining adjacent cells

Question 17

Give the functions of the 3 tissue types: Xylem, Phloem, Endodermis

Answer 17

Transports water and minerals
Transports the products of photosynthesis e.g. sucrose and amino acids
Contains a waterproof Casparian strip, which prevents further transport via the apoplast

Question 18

Minerals are pumped through the root hair cells by _____ ______, as they need to be pumped against a concentration gradient

Answer 18

active transport

Question 19

What is the casparian strip?

Answer 19

The impermeable band of suberin in the cell walls of endodermal cells, blocking the movement of water in the apoplast, so it enters the symplast pathway.

Question 20

When the water reaches a part of the root called the ______, it encounters a layer of suberin which is known as the _______ strip, which cannot be penetrated by water. Therefore, in order for the water to cross the endodermis, the water that has been moving through the cell walls must now enter the _______ pathway.

Answer 20

endodermis
Casparian
symplast

Question 21

What is an endodermis?

Answer 21

A single layer of cells around the pericycle and vascular tissue of the root. Each cell has an impermeable waterproof barrier in its cell wall

Question 22

Decreased water potential in the xylem, below that of the endodermal cells, draws water in by osmosis across endodermal cell membranes. The water potential is decreased below that of the endodermal cells by

Answer 22

Water is being diverted into endodermal cells by the Casparian strip.
Active transport of mineral salts from the endodermis and pericycle into the xylem

Question 23

Minerals are taken up by the root by _______ _______ from the soil solution. Once absorbed the minerals move along the _______ pathway (carried in solution by the water) in the transpiration stream. When minerals reach the endodermis the _________ ____ prevents further movement via the apoplast.

Mineral ions must enter the cytoplasm and are transported from cell to cell via _______ or active transport. Nitrogen enters the plant as nitrate or ammonium ions. These ions diffuse along the concentration gradient into the apoplastic pathway. They enter the _______ pathway by active transport against the concentration gradient. At the endodermis ions must enter the ________ pathway by active transport to by-pass the Casparian strip (from non-living apoplast to living symplast).This allows the plant to selectively take up ions at this point.

Answer 23

active transport
apoplast
Casparian strip
diffusion
symplastic
symplastic

Question 24

What is Transpiration?

Answer 24

The evaporation of water vapour from the leaves, out through stomata into the atmosphere

Question 25

What is the transpiration stream?

Answer 25

The continual flow of water in at the roots, up the stem to the leaves, and out to the atm

Question 26

As water molecules leave xylem cells in the leaf, they pull up other molecules. This pulling effect is known as the transpiration pull. Why is this possible and what is theory called to describe it?

Answer 26

Due to the cohesive forces between water molecules and the adhesive forces between water molecules and the hydrophilic lining of the xylem vessels.
Cohesion-Tension theory.

Question 27

What is another force that contributes to the rise of water in xylem?

Answer 27

Capillary - the movement of water up narrow tubes (xylem) by capillary action.

Question 28

What 4 factors affect the rate of transpiration?

Answer 28

Temp, Humidity, Air movement, Light intensity

Question 29

How does temp effect the rate of transpiration?

Answer 29

Rise in temp causes:
Additional KE for the movement of H20 molecules
Increases rate of evaporation from walls of the mesophyll cells and if stomata are open, speeds up rate of diffusion of water vapour into the surrounding air
Water potential of air decreases - hold more moisture

See NC 5

Question 30

How does Humidity effect the rate of transpiration?

Answer 30

The air inside the leaf is saturated with water vapour (100% humidity), but the humidity of the air surrounding the leaf varies, with values rarely exceeding 70% in Britain. A water potential gradient between the leaf and air is always present and when the stomata opens, water vapour rapidly diffuses out of the leaf, the greater the humidity the lower the rate of transpiration.

See NC 5

Question 31

Transpiration in still air allows water vapour to accumulate around the leaf surface . This decreases the water potential gradient between the leaf and the air and therefore decreases the rate of transpiration

How does air movement effect the rate of transpiration?

See NC 5

Answer 31

Movement of the surrounding air removes the layer of saturated (humid) air at leaves surface, increasing the water potential gradient and increasing the rate of transpiration

Question 32

How does light intensity effect the rate of transpiration?

Answer 32

Stomata opens wider as the light intensity increases, increasing the rate of transpiration. Closed at night, open in day.

Question 33

What is a potometer?

Answer 33

A device which indirectly measures the rate of water loss during transpiration by measuring the rate of water uptake

Question 34

If the cells are fully turgid, the rate of uptake is should be equal to….

Answer 34

the rate of transpiration

Question 35

Why should you cut the shoot underwater?

Answer 35

To prevent air bubbles forming in the xylem

Question 36

How does the potometer work?

Answer 36

Once entire apparatus is full off water allow an air bubble in the capillary tube (by lifting tube up) then measure its starting position and then after set time (15 min) measure its final position. Find the difference between starting and final position, this will tell you the water uptake. To reset bubble and push it back down tube open the reservoir.

See NC 6

Question 37

What factors will effect the rate of transpiration in a potometer?

Answer 37

Number of leaves
Number/size or position of stomata
Presence of waxy cuticle
Amount of light present
The temp
Humidity
Air movement
Water availability

Question 38

What is a Mesophyte?

Answer 38

Plants that evolved in conditions of adequate water supply

Question 39

What do Mesophyte plants do to stay alive and to prevent losing water by transpiration?

Answer 39

Close stomata during the night
Shed leaves in the winter
Underground organs survive winter (bulbs)
Annual mesophytes (plants which flower, produce seed and die in 1 same year) survive the winter as dormant seeds, with such a low metabolic rate that almost no water is needed

Question 40

What is a Xerophyte?

Answer 40

Plants which live in conditions where water is scarce

Question 41

What adaptations do Xerophyte plants have to prevent losing water by transpiration

Answer 41

Smaller leaves (reduce S.A)
Thick waxy cuticle (reduces evaporation)
Sunken stomata (allows water vapour to accumulate above stomatal pore, increasing humidity in the air chamber)
Interlocking hairs which trap water vapour
Rolled leaves (reduce exposure of lower epidermis to atm, thus trapping air)

See NC 7

Question 42

What is the difference between the adaxial and abaxial leaf surface of a plant?

Answer 42

adaxial leaf surface faces towards the central axis of the plant. It’s the upper surface of the leaf
abaxial leaf surface faces away from the central axis of the plant. It is the lower surface of the leaf

Question 43

What is a hydrophyte?

Answer 43

Plants adapted to living in aquatic environments

Question 44

What adaptations do Hydrophyte plants have?

Answer 44

Little/no lignified support tissue (Water is a supportive medium)
Xylem poorly developed (little need for transport tissue)
Leaves have little/no cuticle (no need to reduce water loss)
Stomata on upper surface of floating leaves (allow for gas exchange)
Stems and leaves have large air spaces, continuous down to there roots (forming a reservoir of O2 and CO2, which provide buoyancy

Question 45

What is Translocation?

Answer 45

The movement of the soluble products of photosynthesis such as sucrose and amino acids through phloem, from sources (products are synthesised in leaves) to sinks (used for growth and storage).

Question 46

Unlike xylem, which transports water and dissolved minerals _______, phloem can translocate up, down, sideways, to wherever the products of ______________ are needed

Answer 46

upwards
photosynthesis

Question 47

Are cells that make up phloem tissue dead or alive?

Answer 47

Alive

Question 48

What are the 2 main type of cells in the phloem

Answer 48

sieve tubes and companion cells

Question 49

How are sieve tubes formed and what are there function?

Answer 49

Sieve elements placed end to end, function - the transport of organic materials

Question 50

What are sieve plates?

Answer 50

End walls of sieve tube elements that are perforated by pores

Question 51

What do cytoplasmic filaments contain and what do they do?

Answer 51

Contain phloem protein that extend from one sieve to the next through the pores in the sieve plate

Question 52

Sieve tubes do not contain a ______ and most other cell organelles disintegrate during sieve tube development, allowing space for….

Answer 52

nucleus
transporting materials

Question 53

What organelles do companion cells have?

Answer 53

dense cytoplasm, large central nuclei, many mitochondria, RER and Golgi body

Question 54

What is plasmodesmata and what is its function?

Answer 54

A narrow thread of cytoplasm which allows the transport of ATP and other molecules from the companion cell into the sieve tube element

Question 55

What is the function of the companion cells?

Answer 55

To make proteins and ATP for the sieve tube cells/ elements

Question 56

Explain what the ringing experiment is and how it supports translocation in the phloem?

Answer 56

Cylinders of outer bark tissue were removed all away around the woody the stem, in a ring. This removed the phloem.

After leaving the plant to photosynthesise for a while, analysis revealed that sucrose accumulated above the cut ring, suggesting it had been translocated in the phloem. The tissue would swell due to solute accumulating that would decrease the water potential, allowing water to enter the cells.

Below the ring was no sucrose, (it had been used by not replaced), ring prevented it being moved downwards

See NC 8

Question 57

Explain how aphids are used to show that translocation occurs in the phloem?

Answer 57

They have hollow needle like mouthparts called a stylet. The stylet is inserted into the sieve tube and the phloem contents allowing the aphid to feed on sugary sap. The stylet can be cut off leaving it attached to the plant. Sap exuding from the stylet (due to being under pressure) is analysed and shows presence of sucrose.

Question 58

Explain how Radioactive tracers and autoradiography are used to show that translocation occurs in the phloem?

Answer 58

A plant photosynthesises in the presence of a radioactive isotope such as a 14C in carbon dioxide 14CO2. A stem section is placed on a photographic film, which is fogged if there is a radiation source, producing an autoradiograph, the position of the fogging and therefore the radioactivity coincides with the position of the phloem

Indicating that it’s the phloem that translocates the sucrose made from 14CO2 in photosynthesis

See NC 9

Question 59

Mass flow theory:

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

Answer 59

negative
increases
sieve
photosynthesis
lower
reduces

Question 60

Give some reasons why the mass flow theory may be incorrect?

Answer 60

Sieve plates with tiny pores act as a barrier impending flow
Rate of translocation is 10,000 times faster than it would be if the substances were moving by diffusion
Companion cells contain numerous mitochondria and produce ATP, mass flow theory doesn’t give them a role.