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AQA A level Biology > 3.4.2 Mass transport in plants > Flashcards

3.4.2 Mass transport in plants Flashcards

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1
Q

What 2 types of tissues are involved in transport in plants

A
  • Xylem
  • Phloem
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2
Q

What does the xylem transport

A

Water and dissolved mineral ions

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3
Q

What is the xylem

A

The tissue that transports water and dissolved mineral ions from the roots, up the stem, to the leaves

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4
Q

What does the phloem transport

A
  • Organic substances - like sucrose
  • Amino acids
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5
Q

What is the phloem

A

The tissue that transports organic substances (e.g. sucrose) from the source to the sinks in plants

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6
Q

What is the structure of the xylem

A
  • Long, hollow tube
  • Formed from dead cells, joined together
  • No end walls between cells
  • Walls contain lignin
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7
Q

In the xylem is the flow one way or both ways

A

One way

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8
Q

What is the function of lignin

A

Provides mechanical strength - helps provide structural support for the plant

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9
Q

Define transpiration

A

The evaporation of water from a plant’s surface, especially the leaves

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10
Q

What are the 4 main factors that effect the rate of transpiration

A
  • Light intensity
  • Humidity
  • Temperature
  • Wind
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11
Q

How does light intensity effect the rate of transpiration in plants, and why does it effect it this way

A

The greater the light intensity, the faster the rate of transpiration because the stomata open to allow more carbon dioxide to diffuse into the leaf for photosynthesis- this then increases the rate of diffusion of water vapour out of the leaf which therefore increases the rate of transpiration

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12
Q

If the light intensity increases what happens to the rate of transpiration

A

Increases

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13
Q

How does humidity effect the rate of transpiration, and why does it effect it this way

A

The greater the humidity the slower the rate of transpiration because there is a lower concentration gradient of water vapour between inside and outside of the leaf - so the rate of diffusion of water vapour out of the leaf decreases

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14
Q

Does a greater humidity increase or decrease the rate of transpiration of plants

A

Decreases the rate sine the rate if diffusion of water vapour is slower

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15
Q

How does the temperature effect the rate of transpiration and why

A

The higher the temperature the faster the rate of transpiration because water molecules have more kinetic energy so more water molecules evaporate which creates a higher concentration gradient of water vapour between inside and outside of the leaf which increases the rate of diffusion of water vapour out of the leaf

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16
Q

Does an increases temperature increase or decrease the rate of transpiration

A

Increases the rate since evaporation happens faster due to steeper concentration gradient of water vapour

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17
Q

How does wind effect the rate of transpiration and why

A

The more wind the faster the rate of transpiration because wind removes water molecules from outside the stomata maintaining a favourable concentration gradient for water vapour to diffuse out of the leaf

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18
Q

What is the role of the waxy cuticle on plants

A

Its impermeable to water so reduces water loss by evaporation

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19
Q

What is the role of the upper epidermis

A
  • Its transparent to allow light to pass through
  • It protects against mechanical damage
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20
Q

What is the role of the palisade mesophyll layer

A

Its the main site of photosynthesis since is has the highest density of chloroplasts

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21
Q

What is the role of the spongy mesophyll layer

A
  • Site of gas exchange
  • Contains the vascular bundle (xylem and phloem)
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22
Q

What is the role of the lower epidermis

A

Protect leaf tissue against mechanical damage

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23
Q

What is the role to the stoma

A

Allows entry and exit of gases

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24
Q

What is the role of the guard cells in plants

A
  • To open and close the stomata
  • These are the only lower epidermal cells that contain chloroplasts
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25
Q

What is a xerophyte

A

A plant that is adapted to living in dry conditions/ areas what water is in short supply

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26
Q

What are the main 5 adaptations of xerophytes

A
  • Thick, waxy cuticle
  • Leaf curling / rolling
  • Hairs of the leaf
  • Sunken stomata
  • A reduced SA:Vol of the leaves
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27
Q

Why is having a thick waxy cuticle an adaptation to xerophytes

A
  • It forms a waterproof barrier, reducing the water loss by evaporation from the epidermal cells
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28
Q

Why is leaf curling/ rolling an adaptation to xerophytes

A

It traps the water vapour which decreases the water potential gradient of water vapour therefore the rate of transpiration is reduced

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29
Q

Why are hairy leaves an adaptations to xerophytes

A
  • Traps moist air next to the leaves surface
  • The water potential gradient between the inside and the outside of the leaf is reduced
  • So less water is lost by transpiration
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30
Q

Why are sunken stomata an adaptation to xerophytes

A
  • Traps moist air next to the leaf
  • Reducing water potential gradient
  • Reducing the rate of transpiration
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31
Q

Why is having a reduces SA:Vol of the leaves an adaptation of xerophytes

A
  • Leaves that are small and circular cross section rather than broad and flat leaves reduces the water loss
  • There are also fewer stomata
  • Both of these reduce the rate of transpiration
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32
Q

Do plants have a circulatory system

A

No, because they don’t have a pump

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33
Q

What are angiosperms

A

Flowering plants

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34
Q

Are the xylem and phloem tissues or organs

A

Tissues

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35
Q

What is the role of packing cells

A

To fill space

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36
Q

What is lignin

A

A substance that gets lade down in cells walls

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37
Q

What does lignin replace in plants cells

A

Cellulose

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38
Q

Why do cells that get surrounded by lignin die

A

Because lignin is impermeable to everything so the cell can’t exchange substances- so the cell looses all of the organelles

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39
Q

When lignification happens, what happens to the end walls of the elongated stacked cells

A

The end walls begin to disintegrate

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40
Q

What are the 3 functions of lignin

A
  • Acts the same way cartilage does in the trachea - give strength to the tube when water is being pulled up
  • Being completely impermeable to water so water can’t escape outside of the tube
  • Has a hydrophilic lining which aids the transport of water
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41
Q

What type of lining does lignin have

A

Hydrophilic

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42
Q

What is the function of xylem vessel elements

A

Transport water and mineral ions

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43
Q

Is the xylem vessel elements lignified

A

Yes, there are non-living

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44
Q

How do tracheids differ from normal xylem vessel elements

A

They have tapered ends

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45
Q

Do xylem vessel elements and tracheids perform the same function

A

Yes, they both transport water and mineral ions

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46
Q

What is the function of fibres in the xylem

A

For mechanical support for tissue

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47
Q

Are the fibres in the xylem lignified

A

Yes, they are non-living

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48
Q

What is the function of parenchyma cells in the xylem

A

To act as packing cells between vessel elements

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49
Q

Are the parenchyma cells in the xylem lignified (what do they have in their cell wall instead)

A

No, they have cellulose in their cell wall

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50
Q

What is the scientific word for drying out

A

Desiccating

51
Q

What is transpiration

A

It’s both evaporation and diffusion of water

52
Q

What % of water is lost via transpiration

A

99%

53
Q

Why is the majority of water lost via transpiration

A

Due to the cooling effect (plant’s sweating basically) and to bring up mineral ions through the roots

54
Q

How does water move from cell to cell in a plant, and why

A

Via osmosis since the mesophyll cells lose water due to evaporation into the air spaces which lowers the water potential gradient so water diffuses in by osmosis from neighbouring cells

55
Q

What is a transpiration stream

A

A single continuous column of water from roots to the leaves

56
Q

Other than transportation, what is the other function of the vascular bundle

A

To support the stem and roots hence why where the vascular bundle is located in the roots and the stem is different

57
Q

Where is the vascular bundle located in the stem, and why

A

The periphery (towards the edges) because the stem is above ground so needs support from winds etc.

58
Q

Where is the vascular bundle located in the roots, and why

A

In the middle of the root, because the roots are subject to the pull of gravity

59
Q

What are the names of the 3 theories of water movement up stem

A
  • Capillary action
  • Root pressure theory
  • Cohesion-tension theory
60
Q

Explain what capillary action is, in term of the theory of the movement of water up a stem

A

The ability of liquid to move through a narrow space usually against external forces like gravity. It occurs because of the intermolecular forces between molecules and forces between water and external environment.

61
Q

Why is capillary action not 100% the correct explanation to how water travels up the stem of a plant

A

Because it has been calculated that capillary action could only move water up about 1 metre and the majority of tress are taller, so it can’t be capillary action alone

62
Q

Explain what the root pressure theory is, in terms of how water moves up the stem of a plant

A

As the mineral ions are being actively transported into the roots, the water potential lowers so more water moves in. This then increases the hydrostatic pressure inside the root, so the water is pushed along the roots and up the xylem.

63
Q

Why is root pressure alone not a valid explanation to how water moves up the stem of a plant

A

Since root pressure can reach a maximum of 0.5 kPa and for a 100 metre tree it would require around 4000 kPa therefore it can’t be root pressure alone

64
Q

What is cohesion

A

Attracting/ bonding between the same molecules

65
Q

What is adhesion

A

Attraction/ bonding between different molecules

66
Q

What is the cohesion in the xylem

A

Water molecules bonded to water molecules

67
Q

What is the adhesion in the xylem

A

Water molecules attracting to the hydrophilic lining of the lignin

68
Q

What creates the tension in the cohesion-tension theory

A

The transpiration of water that pulls the column of water up

69
Q

What is the role of nitrate ions in plants

A

To synthesis amino acids to make proteins

70
Q

What is the role of magnesium ions in plants

A

For chlorophyll production

71
Q

What is the role phosphate ions in plants

A

To create phospholipids and other essential components of cells

72
Q

What 2 transportation processes used when a plant uptakes mineral ions

A
  • Facilitated diffusion
  • Active transport
73
Q

What evidence is there that active transport is involved in the uptake of mineral ions in a plant (2 pieces)

A
  • The ions travel against a concentration gradient, since the concentration is much greater inside the plant than in the soil
  • When respiratory inhibitors are added the rate of uptake since ATP can’t be produced so active transport cannot be happening therefore it must be a process plants use to uptake mineral ions
74
Q

What are the 4 adaptations of a root hair cells

A
  • Large surface area
  • Thin cell wall
  • Lots of mitochondria
  • Lots of carrier proteins
75
Q

What is the name of the equipment used to estimate transpiration rates

A

Potometer

76
Q

What are the key features when setting up a potometer to avoid interfering with results (4 points)

A
  • Cut the shoot underwater
  • Place the cut shoot in rubbered end of the potometer underwater
  • Keep the leaf dry
  • Keep joint air tight by using vaseline
77
Q

When using a potometer why must you set it up underwater

A

Because liquid water may block the stomata hindering the diffusion of water vapour out of the leaf

78
Q

How does a potometer work

A

As the leaf transpires, it draws up water from the potometer, this moves an air bubble, the distance the air bubble moves in a certain period of time can be used to calculate the rate of water uptake

79
Q

What is the equation of rate of water uptake for a potometer

A

Speed of air bubble movement (mm/s) x cross-sectional area of capillary tube(mm^2) =rate of water uptake (mm^3/s)

80
Q

What are sources in plants

A

Site where photosynthesis occurrs

81
Q

What are sinks in plants

A

Where the products of photosynthesis are used or stored

82
Q

Does the phloem transport organic substances from source to sink or from sink to sources

A

From sources to sink

83
Q

What is the function of sieve tube elements in the phloem

A

To transport sucrose and amino acids (organic solutes)

84
Q

Describe the structure of sieve tube elements in the phloem (4 features)

A
  • Elongated cells that are stacked to form a series of tubes
  • Perforated end walls called sieve plates
  • Sieve plates have no nucleus and no organelles
  • Sieve plates allow form cytoplasmic connection (so large molecules can pass through)
85
Q

What are the functions of companion cells of the phloem (3 functions)

A
  • Provide sieve tube elements with ATP
  • Synthesise proteins for sieve tube elements
  • Involved in the loading and unloading the sucrose from the sieve tube element
86
Q

Describe the structure of a companion cell in the phloem

A
  • Adjacent to every single sieve tube element
  • Larger nucleus and have lots of organelles
  • Must have plasmadesmata- allowing for the cytoplasm of the companion cell to connect to the cytoplasm of the sieve tube element
87
Q

What is translocation

A

The movement of organic molecules from parts of the plants where the molecules are made (sources) to parts where they are needed or stored (sinks)

88
Q

Is transport in the phloem unidirectional or bidirectional

A

Bidirectional, it’s always from source to sink but sometimes the sink is above the source

89
Q

When can sinks become sources, and why

A

In winter when the leaves and flowers have dropped off, so the actively developing leaves are now in need of the organic solutes for the before sinks now provide the solutes since they were a storage organ during the summer

90
Q

What are the names of the 3 theories behind translocation up a plants

A
  • Diffusion
  • Cytoplasmic streaming
  • Munch’s mass flow theory
91
Q

Why is diffusion not the accepted reason behind translocation in plants

A

The rate of diffusion is too slow for the rate of translocation we can observe

92
Q

What is cytoplasmic streaming, in terms of the theory behind translocation

A

When the organic solutes within the cytoplasm move around and when the plasmadesmata are open the organic solutes move from one cell to the next.

93
Q

What is the widely most accepted theory behind translocation

A

Munch’s mass flow theory

94
Q

What are the 2 main criticisms of Munch’s mass flow theory

A
  • Sucrose and amino acids have been observed to translocate at different rates in the same phloem, not possible in his theory
  • Sucrose and amino acids have been observed to translocate in different directions in the same phloem tissue, again not possible with his theory
95
Q

What 3 pieces of evidence are there that translocation isn’t passive

A
  • Companion cells have a high number of mitochondria and companions are there to provide sieve tube elements with ATP, so a passive process
  • There is a high level of oxygen consumption in the phloem tissue which suggests high rate of respiration, so again not passive
  • The rate of translocation is reduced when respiratory inhibitors are added to the phloem tissue
96
Q

What 2 suggestions are made by Munch’s mass flow theory

A
  • That there is a passive flow of sucrose from source to sink
  • That the sap moves down a hydrostatic pressure gradient
97
Q

What is the 1st step out of the 4 steps that the sucrose is actively transported from the companion cells into the phloem vessel, add the detail

A
  • Hydrogen ions are actively pumped out of the companion cells into the source cell using ATP through a carrier protein, which sets up a hydrogen ion gradient
98
Q

What is the 2nd step out of the 4 steps that the sucrose is actively transported from the companion cells into the phloem vessel, add the detail

A
  • Hydrogen ions passively diffusion back into the companion cell via facilitated diffusion through a co-transport protein called a symport. Sucrose is also taken in down the hydrogen ion gradient in the co-transport protein, so the sucrose is using indirect active transport
99
Q

What is the 3rd step out of the 4 steps that the sucrose is actively transported from the companion cells into the phloem vessel, add the detail

A
  • The sucrose now sets up a concentration gradient from the companion cell to the sieve tube element
100
Q

What is the 4th step out of the 4 steps that the sucrose is actively transported from the companion cells into the phloem vessel, add the detail

A
  • Sucrose moves into the sieve tube element via facilitated diffusion
101
Q

What is the name of the co-transport protein that transports the hydrogen ions and the sucrose into the companion cell

A

Symport

102
Q

What type of transport does the sucrose use when co-transporting into the companion cell going down the hydrogen ion concentration gradient

A

Indirect active transport

103
Q

Is the process of transporting sucrose into the sieve tube element from the companion cell active or passive, and explain why

A

Active, because ATP had to be used to set up the hydrogen ion gradient and without this sucrose wouldn’t be moved in

104
Q

What are the 7 steps explaining Munch’s mass flow theory

A
  • The sucrose is actively transported into the phloem vessel from the source
  • This lowers the water potential so water moves from the neighbouring xylem by osmosis which increases the hydrostatic pressure
  • The hydrostatic pressure is lower at the sink cell so the sap moves down a hydrostatic pressure gradient
  • Organic solutes are actively transported into the sink cell, increases the water potential
  • There’s a lower water potential in the neighbouring xylem due to the presence of mineral ions
  • So water travels down the water potential gradient
  • Water is then pulled up the xylem by cohesion-tension theory
105
Q

What 3 experiments are used to explain translocation

A
  • Aphid experiment
  • Ringing
  • Tracers
106
Q

What do scientists do for the ringing experiment to take place

A

They cut a section of the outer layers including the phloem while leaving the xylem intact

107
Q

What happens to the stem after the ringing experiment, above and below the cut, and explain why

A
  • Above- Stem begins the swell due to sap pooling/ accumulating
  • Below- narrowers because growth hasn’t occurred since sap hasn’t been able to get there so respiration couldn’t take place so energy couldn’t be provided
108
Q

How does the tracer experiment help scientists to investigate translocation

A

Because you can track all of the compounds that contain the radioactive carbon

109
Q

How is the radioactive carbon taken into the plant for the tracer experiment to happen

A

Via photosynthesis

110
Q

What compound containing the radioactive carbon in the tracer experiment do scientists trace in translocation

A

Sucrose

111
Q

What is the name of the picture the x-ray produces after scanning the radioactive carbon containing plant

A

An autoradiograph

112
Q

In an autoradiograph, what colour indicates the presence of the radioactive carbon compounds

A

Black, the blackened areas are found to correspond to where the phloem is

113
Q

What gives plant cell walls their strength

A

Cellulose

114
Q

Name 2 ways in which plants use water

A
  • Maintain turgidity
  • Photosynthesis
115
Q

Name the carbohydrate that is transported in the phloem

A

Sucrose

116
Q

Name 2 examples of sink cells

A
  • Tubers
  • Bulbs
117
Q

Describe 3 difference between the structure of the phloem tissue and the structure of xylem vessels

A
  • Phloem tissue has companion cells which has organelles, whereas xylem vessel has no organelles
  • Sieve tube elements have perforated end walls whereas xylem vessel doesn’t have end walls
  • Xylem vessels are non-living whereas phloem has living tissue
118
Q

Explain the difference between cohesion and adhesion

A

Cohesion is when molecules are attracted to each other (water molecule to water molecule)
Adhesion is when molecules are attracted to surrounding molecules (water molecules to xylem molecules)

119
Q

Describe the 4 precautions that should be taken when setting up a potometer

A
  • Don’t get the leaves wet
  • Cut the shoot underwater
  • Place shoot into the potometer under water (set up underwater)
  • Make joints air tight
120
Q

What type of molecule is sucrose

A

Disaccharide

121
Q

The mass flow hypothesis is used to explain the movement of substances through phloem, explain how pressure is generated inside the phloem tube

A
  • Sucrose is actively transported into phloem
  • Lowering water potential
  • Water moves into phloem by osmosis from xylem
122
Q

Why does the phloem pressure reduced during the hottest part of the day, use understanding of transpiration and mass flow

A
  • High rate of transpiration
  • Water lost through stomata
  • Causes less water movement from xylem to phloem
123
Q

Describe the cohesion-tension theory of water transport in the xylem (5 marks)

A
  • Water lost from leaf because transpiration
  • Lower water potential of leaf cells
  • Water pulled up xylem
  • Water molecules cohere together by hydrogen bonds
  • Forming continuous column of water
  • Adhesion of water molecules to walls of xylem
124
Q

Describe the mass flow hypothesis for the mechanism of translocation in plants (4 marks)

A
  • In source/ leaf sugars actively transported into phloem
  • By companion cells
  • Lowers water potential of sieve cell and water enters by osmosis
  • Increases in pressure causes mass movement
  • Sugars used/ converted in root for respiration for storage

AQA A level Biology (33 decks)

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