Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology - Mass Transport > Plants > Flashcards

Plants Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What is mass transport?

A

Efficient movement of substance to and from exchange surfaces over large distances.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the role of the xylem?

A

Transports water from the roots to the stem and leaves in the plant, in one direction only.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How do xylem and phloem vessels compare?

A

Xylem vessels transport water in 1 direction; phloem transport sugars (organic substances) in all directions.
Xylem is often dead tissue; phloem is living tissue and has companion cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is translocation in plants?

A

The transport of sugars and other substances from sources to sinks.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What apparatus would you use to measure transpiration rates?

A

Potometer

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is the purpose of the roots and how are they adapted?

A

Responsible for the uptake of water and mineral ions.

Have root hairs to increase the surface area of absorption of the substances.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

The uptake of water.

A

A passive process and occurs by osmosis (diffusion from higher water potential region to lower water potential region).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

The uptake of minerals.

A

Passive/active process. Occurs by active transport or diffusion respectively.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Within a plant, how are mineral ions and organic compounds transported?

A

By being dissolved in water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Dissolved mineral ions are transported in…

A

xylem tissue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Dissolved organic compounds are transported in…

A

phloem tissue.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Why are plants are required to take in a constant supply of water and dissolved minerals?

A

To compensate for the continuous loss of water via transpiration in the leaves, and so that they can photosynthesise and produce proteins.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

2 pathways that water can take to move across the cortex.

A

Apoplastic.

Symplastic.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Most water travels via the apoplast pathway.

A

When transpiration rates are high; which is the series of spaces running through the cellulose cell walls, dead cells, and the hollow tubes of the xylem.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

In the apoplast pathway, water moves…

A

By diffusion.

Can move from cell wall to cell wall directly or through the intercellular spaces.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

The movement of water through the apoplastic pathway occurs more ________ than the symplastic pathway.

A

Rapidly.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

When the water reaches the endodermis, the cell wall…

A

Blocks the apoplastic pathway.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Casparian strip.

A

It forms an impassable barrier for the water.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

When the dissolved minerals and water reaches the Casparian strip, they must take the…

A

Symplastic pathway.
The presence of this strip is not fully understood but it is thought that this may help the plant control which mineral ions reach the xylem and generate root pressure.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

As the plant ages, the Casparian strip…

A

Thickens due to the deposit of suberin except in cells called passage cells, allowing for further control of the mineral ions.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Sympoplast pathway.

A

A smaller amount of water travels via the symplastic pathway, which is the cytoplasm and plasmodesmata or vacuole of cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

Movement of water throughout stomata.

A

The humidity of the atmosphere is usually less than of air spaces next to stomata = water potential gradient from air spaces through stomata to water.
When stomata are open, H2O molecules diffuse out of air spaces to the surrounding air.
Water lost by diffusion from air spaces is replaced by H2O evaporating from cell walls of near mesophyll cells.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

By changing the size of the _____________ ______, plants can control their rate of transpiration.

A

Stomatal pores.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Movement of water across cells of a leaf.

A

Water’s lost from mesophyll cells by evaporation from their cell walls to the air spaces of the leaf. This is replaced by water reaching the mesophyll cells from the xylem either via cell walls or via cytoplasm.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

In the case of the cytoplasmic route, the water movement occurs because:

A
  • mesophyll cells lose water to the air spaces by evaporation due to heat supplied by the sun.
  • these cells now have a lower water potential and so water enters by osmosis from neighbouring cells.
  • the loss of water from these neighbouring cells lower their water potential.
  • they, in turn, take in water from their neighbors by osmosis.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Role of stomata in transpiration.

A
  1. Water vapour diffuses from air spaces through a stoma by a process called transpiration, lowering the water potential.
  2. Water evaporates from a mesophyll cell wall into the air spaces, creating a transpiration pull.
  3. Water moves through the mesophyll cell (apoplast pathway) or out of the mesophyll cytoplasm into the cell wall (symplastic pathway).
  4. Water leaves a xylem vessel through a non-lignified area. It may travel by a symplastic pathway or by an apoplastic pathway.
  5. Water moves up the xylem vessels (transpiration stream) to replace the water lost from the leaf.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

The movement of water through a plant’s xylem is largely due to the…

A

Evaporation of water vapour from the leaves and the cohesive and adhesive properties exhibited by water molecules.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Transpiration.

A

Evaporation (loss of water vapour) from a plant to its environment by diffusion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Transpiration stream.

A

Movement of water from the roots to the leaves.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

The advantage of transpiration.

A
  • It provides a means of cooling the plant via evaporative cooling.
  • The transpiration stream is helpful in the uptake of mineral ions.
  • The turgor pressure of the cells provides support to the leaves and the stem of non-woody plants.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Certain environmental conditions (eg. low humidity, high temperatures) can cause a water potential gradient between the air inside the leaves (higher water potential) and the air outside (lower water potential)…

A

Resulting in water vapour diffusing out of the leaves through the stomata.

32
Q

The water vapour lost by transpiration ________ the water potential in air spaces near the mesophyll cells.

A

Lowers.

33
Q

What causes a transpiration pull?

A

The water within the mesophyll cells evaporates into air spaces.

34
Q

The transpiration pull results in…

A

Water moving through the mesophyll cell wall (apoplastic pathway) or out of the mesophyll cytoplasm (symplastic pathway) into the cell wall.

35
Q

The pull from the water moving through the mesophyll cells results in…

A

Water leaving the xylem vessels through pits (non-lignified areas), which causes then water to move up the xylem vessels (due to adhesive and cohesive properties of the water). This movement is called transpiration stream.

36
Q

When rates of transpiration are ____ the walls of the xylem are pulled inwards by the faster flow of water.

A

High.

37
Q

Movement of water up the stem in the xylem.

A

Water evaporates from mesophyll cells due to heat from the sun leading to transpiration.
Water molecules from hydrogen bonds between one another and hence tend to stick together - cohesion.
Water forms a continuous, unbroken column across the mesophyll cells and down the xylem.
As water evaporates from the mesophyll cells in the leaf into the air spaces beneath the stomata, more molecules of water are drawn up behind it as a result of this cohesion.
A column of water is therefore pulled up the xylem as a result of transpiration - transpiration pull.
Transpiration pull puts the xylem under tension, that is, there’s a negative pressure within the xylem, hence called the cohesion-tension theory.

38
Q

During the day, transpiration is at its greatest, there is…

A

More tension (more negative pressure) in the xylem. It pulls the walls of xylem vessels inwards.

39
Q

During the night, transpiration is at….

A

Its lowest due to less tension in the xylem.

40
Q

If a xylem vessel is broken and air enters it, the plant can no longer draw up water because…

A

The continuous column of water is broken and so the water molecules can no longer stick together.

41
Q

When the xylem vessel is broken, water doesn’t leak out because…

A

Air is drawn in therefore there is still pressure.

42
Q

Transpiration pull is a ______ process and thus….

A

Passive.

Doesn’t require metabolic energy to take place.

43
Q

Xylem vessels have no end walls.

A

Means xylem forms a series of continuous, unbroken tubes from roots to leaves, which is vital to the cohesion-tension theory of water flow up the stem.

44
Q

What effect does high air movement have on transpiration?

A

More transpiration.
Good airflow removes water vapour from the air surrounding the leaf which sets up a concentration gradient between the leaf and air, increasing water loss.

45
Q

What effect does high humidity have on transpiration?

A

Less transpiration.
Humidity is a measure of moisture in the air; when the air is saturated with water vapour the concentration gradient is weaker so less water is lost.

46
Q

What effect does high light intensity have on transpiration?

A

More transpiration.
Guard cells are responsive to light intensity; when it is high they are turgid and the stomata open allowing water to be lost.

47
Q

What effect does high temperature have on transpiration?

A

More transpiration.
At higher temperatures, particles have more kinetic energy so transpiration occurs faster as a faster as water molecules evaporate from mesophyll and diffuse away faster than at lower temperatures.

48
Q

The purpose of a potometer.

A

Be used to investigate the effect of environmental factors on the rate of transpiration.

49
Q

Translocation.

A

The process by which organic molecules and some mineral ions are transported from one part of a plant to another.

50
Q

Translocation within the phloem tissue can also be defined as…

A

The transport of assimilates from source to sink and requires the input of ATP.

51
Q

Phloem sap.

A

Liquid that is being transported and found within the phloem sieve tubes.

52
Q

Phloem sap consists of…

A

not only sugars (mainly sucrose) but also of water and other dissolved substances such as amino acids, hormones and minerals.

53
Q

The source of the assimilates could be:

A
  • Green leaves and green stem (photosynthetic produces glucose which is transported as sucrose, as sucrose has less of an osmotic effect than glucose).
  • storage organs e.g. tubers and taproots (unloading their stored substances at the beginning of a growth period).
  • Food stores in seeds (which are germinating).
54
Q

The sinks (where the assimilates are required) could be:

A
  • Meristems (apical or lateral) that are actively dividing.
  • Roots that are growing and/or actively absorbing mineral ions.
  • Any part of the plant where the assimilates are being stored (e.g. developing seeds, fruits or storage organs).
55
Q

The loading and unloading of sucrose from the source to the phloem and from the phloem to the sink.

A

An active process.

56
Q

The loading and unloading of sucrose can be slowed down or even stopped at…

A

Higher temperatures or by respiratory inhibitors.

57
Q

Carbohydrates are generally transported in plants in the form of sucrose because:

A
  • It allows for efficient energy transfer and increased energy storage (sucrose is a disaccharide and therefore contains more energy).
  • It is less reactive than glucose as it is a non-reducing sugar and therefore no intermediate reactions occur as it is being transported.
58
Q
  1. Transfer of sucrose into sieve elements from photosynthesising tissue.
A
  • Sucrose is manufactured from the products of photosynthesis in cells with chloroplasts.
  • The sucrose diffuses down a concentration gradient by facilitated diffusion from the photosynthesising cells into companion cells.
  • Hydrogen ions are actively transported from companion cells into the spaces within cell walls using ATP.
  • These hydrogen ions then diffuse down a concentration gradient through carrier proteins into the sieve tube elements.
  • Sucrose molecules are transported along with the hydrogen ions in a process known as co-transport. The protein carriers are therefore also known as co-transport proteins.
59
Q
  1. Mass flow of sucrose through sieve tube elements.
A
  • The sucrose produced by photosynthesising cells (source) is actively transported into the sieve tube elements.
  • This causes the sieve tubes to have a lower (more negative) water potential.
  • As the xylem has a much higher (less negative) water potential, water moves from the xylem into the sieve tubes by osmosis, creating a high hydrostatic pressure within them.
  • At the respiring cells (sink), sucrose is either used up during respiration or converted to starch for storage.
  • These cells, therefore, have a low sucrose content and so sucrose is actively transported into them from the sieve tubes lowering their water potential.
  • Due to this lowered water potential, water also moves into these respiring cells, from the sieve tubes, by osmosis.
  • The hydrostatic pressure of the sieve tubes in this region is therefore lowered.
  • As a result of water entering the sieve tube elements at the source and leaving at the sink, there is high hydrostatic pressure at the source and a low one at risk.
  • There is therefore a mass flow of sucrose solution down this hydrostatic gradient in the sieve tubes.
60
Q

Mass flow.

A

The bulk movement of a substance through a given channel or area in a specified time.
Passive process, resulting in the active transport of sugars.

61
Q
  1. Transfer of sucrose from sieve tube elements into storage or sink cells.
A

The sucrose is actively transported by companion cells, out of the sieve tubes and into the sink cells.

62
Q

What does the Mass Flow Hypothesis explain?

A

Used to explain the movement of assimilates in the phloem tissue.

63
Q

The Mass Flow Hypothesis model consists of:

A
  • 2 partially permeable membranes containing solutions with different concentrations of ions.
  • The 2 membranes were placed into two chambers containing water and were connected via a passageway.
  • The two membranes were joined via a tube.
  • As the membranes were surrounded by water, the water moved by osmosis across the membrane containing the more concentrated solution towards the membrane containing the dilute solution,
64
Q

Mass Flow Hypothesis Model -

A
  1. Active transport is used to actively load the solutes from companion cells into the sieve tubes of the phloem at the source; lowers the water potential inside the sieve tubes, so water enters the tubes by osmosis from the xylem and companion cells and this creates a high pressure inside the sieve tubes at the source end of the phloem.
  2. At the sink end, solutes are removed from the phloem to be used up; this increases the water potential inside the sieve tubes, so water also leaves the tubes by osmosis. This lowers the pressure inside the sieve tubes.
  3. Results is a pressure gradient from the source end to the sink end. This gradient pushes solutes along the sieve tubes towards the sink. When they reach the sink the solutes will be used or stored.
65
Q

Evidence supporting the Mass Flow Hypothesis Model.

A
  • There’s a pressure within sieve tubes, as shown by sap being released when they’re cut.
  • The concentration of sucrose is higher in leaves (source) than in roots (sink).
  • Downward flow in the phloem occurs in daylight but ceases when leaves are shaded, or at night.
  • Increases in sucrose levels in the lead are followed by similar increases in sucrose levels in the phloem for a little later.
  • Metabolic positions and/or lack of oxygen inhibit translocation of sucrose in the phloem.
  • Companion cells possess many mitochondria and readily produce ATP.
66
Q

Evidence questioning the Mass Flow Hypothesis Model.

A
  • The function of the sieve plates is unclear, as they would seem to hinder mass flow (been suggested that they may have a structural function, helping to prevent tubes from bursting under pressure).
  • Not all solutes move at the same speed - they should do so if movement is by mass flow.
  • Sucrose is delivered at more or less the same rate to all regions, rather than going more quickly to the ones with the lowest sucrose concentration.
67
Q

Tracer and ringing experiments have been used to…

A

Investigate mass transport in plants.

68
Q

A ringing experiment involves:

A

The removal of a ring of surface tissues from the stem while leaving the stem core intact.

69
Q

As the phloem is located towards the outside of the stem and the xylem towards the centre, the ring…

A

Removes the phloem only with the xylem remaining intact.

70
Q

After the ringing has been done the plant can then be…

A

Exposed to a radioactive tracer so that the direction and rate of translocation can be investigated.

71
Q

What is readily absorbed by the leaves and used in photosynthesis to produce sucrose?

A

14CO2

72
Q

Why is the sucrose formed radioactive?

A

Its subsequent movement around the plant via translocation can be traced.

73
Q

What can be detected in different parts of the plant?

A

Amounts of radioactive carbon present.

74
Q

If the mass flow hypothesis is correct,…

A

The bulk flow of phloem sap should be in one direction (from source to sink) and occur at the same rate in any sieve tube at the same time.

75
Q

If the xylem is damaged during the ringing process…

A

The plant will not have an adequate supply of water and will wilt.

76
Q

Results from a ringing experiment with radioactive carbon dioxide.

A

An experiment was carried out in which different plants were ringed at different locations on the stem.
The plants were then supplied with radioactive carbon dioxide (14CO2).
After a period of time the levels of radioactive carbon in the different parts of the plant were measured.
There is a control plant used in this experiment to illustrate where sucrose is translocated when a plant is intact.

Biology - Mass Transport (1 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions