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A-Level Biology🌼 > Topic 3: Exchange + Transport: Transport in Plants > Flashcards

Topic 3: Exchange + Transport: Transport in Plants Flashcards

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1
Q

Why do multicellular plants need transport systems?

A

Multicellular plants need transport systems because:
-Metabolic demands = underground parts of plants don’t photosynthesise but still require exchange of substances and transportation of hormones and mineral ions absorbed by roots
-Size = plants grow large -> needs effective transport systems to move substances up and down between tips and roots
-Surface area = small sa:vol ratio -> cannot rely on diffusion alone to supply cells

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2
Q

What are dicotyledonous plants (dicots)?

A

Dicotyledonous plants make seeds that contain two cotyledons (organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates)

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3
Q

What are cotyledons?

A

Cotyledons are organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates

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4
Q

Types of dicots (dicotyledonous plants)

A

Types of dicots:
-Herbaceous dicots
-Woody (arborescent) dicots

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5
Q

Herbaceous dicots

A

Herbaceous dicots - type of dicot - soft tissues and relatively short life cycle (leaves and stems that die down at the end of the growing season to the soil level)

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6
Q

Woody (arborescent) dicots

A

Woody (arborescent) dicots - type of dicot - hard, lignified tissues and a long life cycle (sometimes hundreds of years)

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7
Q

Vascular systems in dicotyledonous plants

A

-Vascular system: dicots have a series of transport vessels running through the stem, roots and leaves which is known as the vascular system

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8
Q

Vascular bundles in dicotyledonous plants

A

-Vascular bundles: transport tissues (eg phloem + xylem) are arranged together in vascular bundles in leaves, stems and roots of harbaceous dicots

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9
Q

Why are vascular bundles around the edge in stems?

A

Vascular bundles are arranged around the edges in stems to give strength and support

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10
Q

Why are vascular bundles in the middle of roots?

A

Vascular bundles are in the middle of roots to help the plant withstand tugging strains that result as the stems and leaves are blown in the wind

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11
Q

The midrib of a dicot leaf

A

The midrib of a dicot leaf is the main vein carrying the vascular tissue through the organ. It also helps to support to the structure of the leaf. Many small, branching veins spread through the leaf functioning both in transport and support.

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12
Q

Function of the xylem

A

Function of the xylem: large non-living tissue that has two main functions - the transport of water and mineral ions, and support
-The flow of materials in the xylem is up from roots to shoots and leaves
-Made up of dead cells
-Long, hollow structures made by columns of cells fusing together end to end

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13
Q

Two other tissues associated with the xylem in herbaceous dicots

A

Two other tissues associated with the xylem in herbaceous dicots:
-Thick-walled xylem parenchyma packs around the xylem vessels, storing food and containing tannin deposits
-Xylem fibres with lignified secondary walls that provide extra mechanical strength but doesn’t transport water

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14
Q

Tannin in dicots

A

Tannin is a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores

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15
Q

Xylem parenchyma in dicots

A

Thick-walled xylem parenchyma packs around the xylem vessels, storing food and containing tannin deposits

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16
Q

Xylem fibres in dicots

A

Xylem fibres in dicots:
Long cells with lignified secondary walls that provide extra mechanical strength but do not transport water

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17
Q

Ways of which lignin can be laid down in the walls of xylem vessels

A

Ways of which lignin can be laid down in the walls of xylem vessels:
Rings, spirals or relatively solid tubes with lots of small unlignified areas called bordered pits

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18
Q

Bordered pits in plants

A

Bordered pits is where water leaves the xylem and moves into other cells of the plant

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19
Q

Functions of the ploem

A

-Phloem is living tissue that transport food in the form of organic solutes around the plant from leaves where they are made by photosynthesis
-Supplies cells with sugars and amino acids needed for cellular respiration and for synthesis of all other useful molecules
-Flow of materials in phloem can go both up and down the plant

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20
Q

Sieve tube elements in phloems

A

Sieve tube elements - the main transporting vessels of the phloem - made up of cells joined end to end forming a hollow structure
-Not lignified

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21
Q

Sieve plates in the phloem

A

Sieve plates - areas between cells where walls have become perforated (hole-y) - tonoplants (vacuole membrane), nucleus and some organelles break down - phloem becomes tube filled with sap and mature phloem cells have no nucleus

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22
Q

Companion cells in the phloem

A

Companion cells form along with sieve tube elements - cells are linked to the sieve tube elements by many plasmodesmata - maintains nucleus and organelles
-Active cells and function as ‘life support system’ for sieve tube cells, which have lost normal cell functions

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23
Q

What is plasmodesmata?

A

Plasmodesmata are microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells

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24
Q

Tissues that support the phloem tissue

A

Fibres and scelerids (cells with with extremely thick cell walls) are supporting tissues found within the phloem

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25
Q

What are sclereids?

A

Scelereids are cells with extremely thick cell walls, and act as supporting tissue (eg they are found in the phloem)

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26
Q

Vascular cambium in stems

A

Vascular cambium in stems - located inbetween the xylem and phloem cells - contains meristem cells

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27
Q

Arrangement of xylem and phloem in stems

A

Stem arrangement: circular, xylem and phloem vessels located around it, with xylem being inside and phloem being on the outside, vascular cambium located inbetween the xylem and phloem vessels and contain the meristem cells

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28
Q

Arrangement of xylem and phloem in roots

A

Xylem is located at the center of roots in an ‘X’ drill-like structure, with phloem in four seperate sections around the xylem

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29
Q

Why is water important in both the structure and in the metabolism of plants?

A

Water is important in both the structure and metabolism of plants because:
-Turgor pressure (or hydrostatic pressure) as result of osmosis in plant cells provides a hydrostatic skeleton to support the stems and leaves (around 1.5MPa in plants)
-Turgor drives cell expansion - force enables plant roots to force their way through tarmac and concrete
-Loss of water by evaporation helps to keep plants cool
-Mineral ions and the products of photosynthesis are transported in aqueous solutions
-Water is a raw material for photosynthesis

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30
Q

Root hair cells function

A

Root hair cells are the exchange surface in plants where water is taken into the body from the plant from the soil
-Root hair is long, thin extension from root hair cell

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31
Q

How are root hairs well adapted as exchange surfaces?

A

Root hair adaptations:
-Microscopic size = penetrate easily between soil particles
-Each microscopic hair = large sa:v ratio
-Each hair has thin surface layer which means diffusion and osmosis can take place quickly
-Concentration of solutes in the cytoplasm of root hair cells maintains a water potential gradient between the soil water and the cell

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32
Q

Why does soil water have a high water potential?

A

Soil water has a high water potential due to having a low concentration of dissolved minerals

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33
Q

Why does the cytoplasm and vacuolar sap of the root hair cell have low water potential?

A

The cytoplasm and vacuolar sap of the root hair cell has a low water potential due to containing many different solvents including sugars, mineral ions and amino acids - as a result water moves into the root hair cells by osmosis

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34
Q

Three different pathways that water can move across the root to the xylem once it has entered the root hair cell?

A

Two pathways water can go leading up to the xylem vessel:
-The symplast pathway
-The apoplast pathway
-Vacuolar pathway

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35
Q

What is the symplast of plants?

A

The symplast is the continuous column of living plant cells that is connected through the plasmodesmata

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36
Q

What is the apoplast in plants?

A

Apoplast in plants: the cell walls and the intercellular spaces of plants

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37
Q

Movement of water into the xylem

A

Movement of water into the xylem:
Water moves across root (apoplast or symplast pathway) until epidermis -> water in the apoplast pathway forced into cytoplasm and joins water in symplast pathway, passing through a selectively permeable membrane -> once inside vascular bundle, water returns to apoplast ptathway to enter xylem

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38
Q

Why does water in the apoplast pathway pass through selectively permeable membranes before entering the symplast pathway on the route to xylem vessels?

A

passing through selectively permeable cell surface membranes excludes potentially-toxic solutes in soil water from reaching living tissues

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39
Q

What causes root pressure?

A

The active pumping of minerals into the xylem to produce movement of water by osmosis results in root pressure - independant of any effects of transpiration

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40
Q

Root pressure

A

Root pressure gives water a push up the xylem, but under most circumstances it is not the major factor in movement of water up from roots to leaves

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41
Q

Evidence for the role of active transport in root pressure

A

Evidence for the role of active transport in root pressure:
-Some poisons, eg cyanide, affect the mitochondria and prevent ATP production - if cyanide is applied to root hair cells there is no energy supply and root pressure disapears
-Root pressure increases with a rise in temp and falls with a decrease in temp, suggesting enzyme controlled reactions are involved
-Levels of oxygen or respiratory substrates fall - root pressure falls
-Guttation: sap and water moves out cut stems, suggesting they are actively pumped out rather than being drawn out by transpiration

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42
Q

Symplast pathway

A

Symplast pathway = water moving between cells through the plasmodesmata between the cell cytoplasms, water potential of cells decrease up the plant, and so water is continuously drawn up

43
Q

What causes the continuous pull of water up the plant?

A

Water is continously pulled up the plant by the decreasing water potential, as water moves down the water potential gradient by osmosis

44
Q

The vacuolar pathway

A

The vacuolar pathway is the same as symplast pathway, but water travels through vacuoles as well as the cytoplasms, and is therefore the slowest route of water up the plant to the xylem

45
Q

The apoplast pathway

A

The apoplast pathway is the quickest route of water up the plant to the xylem, and is where water moves through the cell walls and intracellular spaces - this is caused by the cohesion and tension forces acting on the cell walls that cause water to move up the plant

46
Q

The casparian strip in plants

A

The casparian strip is an impermeable layer of suberin (a waxy material), as a result all the water in the apoplast pathway is forced into the symplast pathway - the purpose of this is to remove the toxins and pathogens to prevent them entering the xylem as it goes across the selectively permeable plasma membrane

47
Q

What is the purpose of the casparian strip in plants?

A

The casparian strip prevents toxins and pathogens entering the xylem as water is forced across a selectively permeable plasma membrane, and as a result water from the apoplast pathway enters the symplast pathway

48
Q

Cohesion-tension theory of water in the plant

A

Cohesion-tension theory: force between the water and wall is greater than the weight of the water pulling it down - resulting in water being pulled up and evaporated from the leaf rather than falling down

49
Q

Where is endodermis in plants found?

A

Endodermis is found at the casparian strip within plants

50
Q

Endodermis in plants

A

Endodermis in plants acts as an apoplastic barrier, as the prescense of the casparian strip provides a selectively impermeable layer to remove toxins and pathogens from entering the xylem vessel

51
Q

The process by which water enters the cells of roots from the soil

A

Process by which water enters cells of roots from soil:
-Low water potential inside
-Moves down water potential gradient
-Through partially permeable membrane

52
Q

Why measure a large number of stomata to calculate a mean in an experiment?

A

Measuring a large number of stomata to calculate a mean in an experiment accounts for variation of stomata, and removes chances of anomalies

53
Q

Two ways in which photographing a leaf surface makes it easier to measure stomata

A

Two ways in which photographing a leaf surface makes it easier to measure stomata:
-Provides a permanent record
-Allows to be enlarged to view detail
-Still image - as stomata opens and closes in response to conditions

54
Q

Adaptations of xylem vessels for the transport of water

A

Adaptations of xylem vessels for the transport of water:
-Long hollow tubes made up of dead cells - continuous flow of water
-Contains pits - allows water to move sideways between the vessels
-Lignin - thickens vessels - found in spirals - allows them to remain flexible

55
Q

How does the xylem work in plants?

A

How the xylem works in plants:
-Works by using the transpiration pull and root pressure to move water and nutrients from the roots to the rest of the plant

56
Q

What is the transpiration pull in the xylem?

A

The transpiration pull is the process by which water is drawn up xylem vessels due to loss of water through the stomata on leaves - as water evaporates from leaves, it creates a negative pressure that pulls water up from the roots, therefore keeping the plant hydrated

57
Q

What is root pressure in the xylem?

A

Root pressure in the xylem is the pressure that is exerted by the roots to move water and nutrients up xylem vessels, it is created by active transport, which then exerts pressure onto the surrounding water

58
Q

Difference of the xylem and the phloem in plants

A

Xylem: responsible for transporting water and nutrients, made up of dead cells
Phloem: responsible for transporting sugars and other organic compounds from leaves to rest of the plant

59
Q

Sugar transported by the phloem

A

The phloem transports sugar as sucrose, because:
- it is more energy efficient as it is a disaccharide that contains more energy than monosaccharides,
-non reducing sugar = no intermediate reactions with cells - lasts longer than glucose would’ve

60
Q

Movement of water into roots of plants

A

Water moves into the roots of plants by osmosis (high -> low concentration)

61
Q

Adaptations of the leaves

A

Leaf adaptations:
-Increased surface area
-Surface covered with waxy cuticle which makes them water proof - important as it prevents the leaf cells from losing water rapidly

62
Q

Stomata function

A

Stomatas - microscopic pores in the leaf - opened and closed by guard cells which surround the stomatal opening - open to allow for gaseous exchange

63
Q

What is transpiration?

A

Transpiration is the loss of water vapour from the leaves and stems of plants caused when the stomata is open as water vapour moves out by diffusion

64
Q

Why is stomata open during the day?

A

Stomata is open during the day to allow for carbon dioxide to be taken in for photosynthesis

65
Q

Why is the stomata open at night?

A

Stomata opens at night to take in oxygen for cellular respiration when no oxygen in being produced in photosynthesis

66
Q

What is the transpiration stream?

A

The transpiration stream in plants is when water vapour moves into the external air through the stomata along a diffusion gradient

67
Q

Capillary action in plants

A

Capillary action in plants refer to the process by which water can rise up by a narrow tube against the force of gravity

68
Q

Evidence for the cohesion-tension theory

A

Evidence for cohesion-tension theory:
-Changes in diameter of trees
-Broken xylem vessels

69
Q

How does change in diameter of trees provide evidence for the cohesion-tension theory?

A

When transpiration is high -> tension in xylem vessels are high -> tree shrinks in diameter
When transpiration is low -> tension in xylem vessels low = tree increases in diameter (can be tested by measuring circumference of the tree at diffrent times of the day)

70
Q

How would broken xylem vessels provide evidence for the cohesion-tension theory?

A

Broken xylem vessels

71
Q

Steps involved in the process of the cohesion-tension theory

A

Cohesion-tension theory:
1). Transpiration - water evaporated off plant
2). Water loss creates tension (formation of H bonds between water molecules and sides of the xylem vessel elements), water pulled upwards by tension
3). Cohesion - water forms H bonds with eachother - continuous pull upwards of water to replace water lost in transpiration
4). Water being pulled up decreases water potential at roots and so water diffuses in roots via osmosis

72
Q

Equipment used to measure transpiration

A

Potometer is used to measure transpiration by estimating the volume of water taken up by a plant in a given time

73
Q

Calculating transpiration rate

A

Calculating transpiration rate: rate of bubble movement per hr

74
Q

Problems with transpiration

A

Problems with transpiration:
-Limited water availability
-Stomata opens for gaseous exchange in photosynthesis which increases water loss especially in conditions of high sunlight intenstity

75
Q

How turgor affects stomata

A

How turgor affects stomata:
-Low turgor -> configuration of the guard cell walls closes the stomata
-When environmental conditions are favourable, guard cells pump in solutes by active transport to increase turgor

76
Q

Cellulose hoops

A

Cellulose hoops prevents cells from swelling in width, so they extend lengthways -> inner wall of guard cells is less flexible than outer wall, cells become bean-shaped and stomata opens

77
Q

Plants adaptive response to lack of water

A

Scarce water -> hormonal signals from roots trigger turgor loss from guard cells to close the stomatal pore and conserve water

78
Q

Factors that affect transpiration

A

Factors that affect transpiration:
-Light intenstity = increases with transpiration
-Relative humidity = increase of humidity decreases transpiration as there is reduced water vapour gradient
-Temperature = increases with transpiration
-Air movement = increased diffusion gradient will increase transpiration
-Soil-water availbility

79
Q

How does light intensity affect transpiration?

A

Light intensity -> stomata opens in the light for gaseous exchange -> increased light intensity increases number of open stomata -> increases rate of water vapour diffusing out -> increases evaporation from leaf surface

80
Q

How does relative humidity (the measure of the amount of water vapour in the air in comparison to the total concentration of water the air can hold) affect transpiration

A

Relative humidity -> increased relative humidity decreases transpiration -> as there is a reduced water vapour potential gradient between inside leaf and outside air -> dry air has opposite effect

81
Q

How does temperature affect transpiration?

A

-Increased temp -> increased kinetic energy of water molecules -> increased rate of evaporation from the spongy mesophyll cells into the air spaces of the leaf

82
Q

How does air movement affect transpiration?

A

Air movement -> each leaf has layer of still air around it trapped by the shape and features of the leaf eg hairs -> decreases air movement close to the leaf -> so water vapour that diffuses out the leaf accumulates in this layer and so increases water vapour potential around stomata -> increased diffusion gradient -> increases transpiration

83
Q

How does soil-water availability affect transpiration?

A

Soil-water availability -> amount of water available in soil -> dry = plant under stress and reduces transpiration, and vice versa

84
Q

Why is it important to produce very thin slices of plant tissue in celery dissection?

A

It is important that the plant tissue is really thin, so that all of the cellular structures can be seen under the microscope as the electrons can then pass through

85
Q

Why is it important that in celery dissection, the tissue is cut in transverse/longitudinal ways rather than at an angle?

A

It’s important that the celery tissue is cut in transverse/longitudinal ways as it makes the internal structures - such as the xylem and phloem - more clearly seen, as if it they were cut at an angle, parts of the tissue would be too thick for structures to be seen

86
Q

Why are stains useful in microscopy?

A

Stains are useful in microscopy as it binds to specific cells/tissue, allowing them to be seen clearly under the microscope as clear distinct features

87
Q

Why is toludine blue useful in celery dissection?

A

Toludine blue is useful in celery dissection as it provides a colour difference for lignified and non-lignified cell walls, allowing for the xylem and phloem to be identified separately, and so we can observe the adaptations

88
Q

Movement of water in the transpiration stream

A

Movement of water in the transpiration stream:
-Water evaporates from the leaves which decreases the water potential of the air space inside the mesophyll
-Water moves into air spaces from adjacent cells
-Water moves out of the xylem into the cells in the leaves
-Water hydrogen bonds to itself (cohesion) and bond to walls of the xylem vessel walls (tension) resulting in capillary action

89
Q

Result of water being a polar molecule in the xylem

A

Water is polar molecule - water molecules arrange so that positive and negatively charged poles lie next to eachother in the xylem - causing them to cohere and stick to eachother

90
Q

Turgid stomata

A

Turgid - water moves into vacuoles by osmosis - outer wall more flexible than inner wall - cell bends to open stomata

91
Q

Flaccid stomata

A

Flaccid - water moves out of vacuoles by osmosis - outer wall more flexible than inner wall - cell bends back to close stomata

92
Q

Potometer

A

Potometer - actually measures water uptake by plant - but this is assumed to be transpiration

93
Q

How is water lost by leaves replaced in the potometer practical?

A

Water lost by leaves is replaced from the water in the capillary tube

94
Q

Precautions taken in the potometer practical to measure transpiration to ensure results are valid:

A

Precautions taken in the potometer practical to measure transpiration to ensure results are valid:
-Set up under water to ensure no air bubbles enter the apparatus
-Cut stem under water to prevent air entering the xylem
-Cut stem at an angle to provide large surface area in contact with the water
-Dry the leaves
-Keep conditions constant
-Insert shoot in apparatus under water
-Shut screw clip

95
Q

Long hairs from epidermis cell effect on transpiration

A

Long hairs -> traps more air around plant -> increases humidity -> decreases transpiration

96
Q

Why are measurements taken from a potometer not an actual measurement of transpiration rate?

A

-Potometers actually measure the rate of water uptake by the plant
-But this is an estimated rate of transpiration as it is assumed that uptake refers to water loss by transpiration from the leaves
-Some of the water is taken up by photosynthesis

97
Q

Plasmolysis

A

Plasmolysis = the process of contraction or shrinkage of the protoplasm (all material inside the cell) away from the cell wall - happens when plants lose water after being placed in a solution that has a higher concentration of solutes than the cell does (hypertonic solution) - result of osmosis

98
Q

Affect of salt solution on permeability of cell walls

A

Salt solutions increases the permeability of cell walls - as a concentration gradient is set up as salt solutions have a lower concentration of water and so water moves out by osmosis across the semi-permeable membrane

99
Q

How would you investigate the effect of wind speed on transpiration rate?

A

Investigate wind speed by placing apparatus in front of a fan

100
Q

How to investigate the effect of light intensity on transpiration rate?

A

Investigate light intensity by placing apparatus in front of a lamp

101
Q

How to investigate the effect of temperature on transpiration rate?

A

Investigate temperature by using a heater

102
Q

Xerophytes

A

Xerophytes: plants in dry habitats that have evolved a wide range of adaptations that enable them to live and reproduce in places where water availability is very low

103
Q

Xerophyte examples

A

Xerophyte examples: conifers, marram grass, plants in cold icy conditions, cacti

104
Q

Ways for xerophytes to conserve water

A

Ways for xerophytes to conserve water:
-A thick waxy cuticle
-Sunken stomata at pits
-Reduced number of stomata
-Reduced leaves
-Hairy leaves
-Curled leaves
-Succulents
-Leaf loss
-Root adaptation
-Avoiding the problems

A-Level Biology🌼 (25 decks)

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