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Biology > Transport in Plants > Flashcards

Transport in Plants Flashcards

1
Q

What is the function of transport systems in plants?

A

To transport water, minerals, sucrose etc. from where it is made/collected to where it is needed/excreted.

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2
Q

Give 2 reasons why multicellular plants have to have transport systems.

A
  1. Distances too large for diffusion to be effective and transport fast enough.
  2. The overall surface area to volume ratio of a plant is too small.
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3
Q

Define ‘herbaceous’

A

A plant with no woody tissue.

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4
Q

Define ‘dicotyledonous’

A

A plant with two cotyledons in the seed.

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5
Q

Define ‘vascular system’

A

A system of transport vessels in animals or plants.

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6
Q

Define ‘vascular bundles’

A

The vascular system of herbaceous dicots — composed of xylem and phloem tissue.

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7
Q

What are the two types of transport vessels in vascular bundles?

A

Xylem and phloem.

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8
Q

What is the function of the xylem?

A
  • It transports water and minerals from the roots to the rest of the plant.
  • It also provides structure.
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9
Q
A

It transports dissolved substances, such as sucrose and amino acids from parts of the plant where they are made (sources) to the parts of the plant where they are used (sinks).

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10
Q

Explain three ways in which the structure of the xylem vessels makes them well-adapted to their function.

A
  1. The end walls are removed from each end, forming an uninterrupted tube, so water can pass through easily.
  2. Their walls are thickened with a woody substance called lignin, which helps to support the xylem vessels and stops them collapsing inwards.
  3. There are small pits in the cell wall where is no lignin so water and ions can move into and out of the vessels.
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11
Q

Describe the patters of lignification in xylem and state its function.

A
  • Spirals around the xylem vessels.
  • For strength and structure.
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12
Q

Define ‘sieve tube element’

A

An element of phloem tissue consisting of a longitudinal row of thin-walled, elongated cells with perforations in their connecting walls through which food materials pass.

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13
Q

Define ‘sieve plate’

A
  • An area of relatively large pores present in the common end walls of sieve tube elements.
  • The connection sites between sieve elements.
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14
Q

Define ‘companion cell’

A
  • A specialised parenchyma cell.
  • The active cells found next to the sieve tube elements that supply the phloem vessels with all their metabolic needs.
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15
Q

Explain three ways in which the structure of the phloem vessels makes them well-adapted to their function.

A
  1. Little cytoplasm with no organelles so there is room for water, sucrose etc. to be transported around the plant.
  2. It has perforated ends which lets water, sucrose etc. through easily.
  3. It’s companion cells have many mitochondria to produce ATP for active transport.
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16
Q

State and explain 5 differences between xylem and phloem regarding their structure and function.

A
  1. Xylem is responsible for water and mineral transport whereas phloem is responsible for food and organic matter transport.
  2. The xylem is composed of vessel elements, tracheids, and xylem parenchyma whereas the phloem is composed of companion cells, sieve-tube cells, phloem fibres, and phloem parenchyma.
  3. In the xylem, all cells are dead at maturity except for xylem parenchyma whereas in phloem, most cells are alive at maturity.
  4. In the xylem, the movement of material is unidirectional whereas in phloem, the movement of material is bidirectional.
  5. Xylem is located at the centre of the vascular bundle whereas phloem is situated on the outer side of the vascular bundle.
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17
Q

State and explain 5 similarities between xylem and phloem regarding their structure and function.

A
  1. Both are involved in transport: Xylem for water/dissolved minerals from root upwards and phloem for photosynthesis products from leaves to the rest of the plant.
  2. Both have supportive elements: For example, fibres and parenchyma cells in both xylem and phloem provide mechanical support to tissues.
  3. Both tissues are interconnected: Both xylem and phloem are interconnected and work together to ensure efficient transport throughout the plant e.g. the movement of water through the xylem creates a pressure gradient that drives the movement of sugars through phloem.
  4. Both tissues are composed of specialised cells which are adapted for their specific function: Vessel elements/tracheids in xylem are adapted for transport of water and sieve tubes/companion cells in phloem are specialised for the transport of sugars.
  5. Both are complex tissues composed of more than one cell type: In addition to specialised cells, both tissues contain fibres, parenchyma cells, and other support cells.
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18
Q

Define ‘transpiration’

A

The loss of water vapour from the stems and leaves of a plant as a result of evaporation from the surfaces of cells inside the leaf and diffusion down a concentration gradient out of the stomata.

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19
Q

Define ‘transpiration stream’

A

The movement of water through a plant from the roots until it is lost by evaporation from the leaves.

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20
Q

Define ‘transpiration pull’

A

The force which aids in drawing the water upwards from roots to leaves.

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21
Q

Why is water loss inevitable for plants?

A

The plant has to open the stomata to allow diffusion of CO2 into plant for photosynthesis to produce glucose for respiration.

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22
Q

Outline the route water takes through a plant.

A
  1. Water moves into roots by osmosis.
  2. Water travels through roots to centre where it enters xylem vessels.
  3. It’s drawn up the xylem by transpiration pull to leaves where it is lost via evaporation (or used on the way).
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23
Q

Define ‘stomata’

A

Pores in the surface of a leaf or stem that may be opened and closed by guard cells.

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24
Q

Define ‘guard cell’

A

Cells that can open and close the stomata pores controlling gaseous exchange and water loss in plants.

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25
Q

Define ‘adhesion’

A

Sticking together of particles of different substances.

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26
Q

Define ‘cohesion’

A

Sticking together of particles of the same substance.

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27
Q

Explain how transpiration results in water moving through the plant (the cohesion-tension theory).

A
  1. Water evaporates through the stomata in the leaves (transpiration). This creates an osmotic gradient causing water to move across the cells in the leaf to the stomata.
  2. This causes water to leave the xylem in the leaves, reducing the pressure (creating a tension) in the xylem.
  3. A column of water is drawn up the stem — the transpiration stream.
  4. The column stays intact due to the cohesion of the hydrogen bonds between the molecules.
  5. The pull creates a negative pressure in the xylem which explains why they’re lignified and rigid — they won’t collapse.
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28
Q

Is the cohesion-tension theory an active or passive process?

A

A passive process.

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29
Q

Explain why the cohesion-tension theory is named the way it is.

A
  • Tension is created by the loss of water by transpiration as water is pulled up to replace it.
  • Cohesion allows the water to be pulled as it holds itself in a constant stream.
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30
Q

Describe 3 sources of evidence for the cohesion tension theory.

A
  1. Changes in the diameter of trees: when hot, transpiration is at its highest and tension is at its highest, diameter shrinks; when cold, transpiration and tension is lower so water collects in the xylem, diameter increases.
  2. When stem is cut, in most cases, air is drawn in rather than water leaking out.
  3. If air bubble is created, water cannot move up the stem as transpiration stream is broken — no longer continuous cohesion between molecules.
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31
Q

Explain how guard cells can open and close stomata.

A
  • This is a turgor-driven process.
  • When turgor is low, the asymmetric configuration of the guard cell walls close the pore.
  • When environmental conditions are favourable, guard cells pump in solutes by active transport, increasing their turgor.
  • Because the inner wall of the guard cell is less flexible than the outer wall, the cells become bean-shaped and open the pore.
  • When water becomes scare, hormonal signals from the roots can trigger turgor loss from the guard cells, which close the stomata pore and so conserve water.
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32
Q

Define ‘turgor’

A

The pressure exerted by the cell-surface membrane against the cell wall in a plant cell.

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33
Q

State 5 environmental factors that can affect the rate of transpiration.

A
  1. Light
  2. Temperature
  3. Wind/air movement
  4. Humidity
  5. Soil water availability
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34
Q

How does light affect the rate of transpiration?

A
  • More photosynthesis so needs CO2 to diffuse into plant.
  • Stomata opens leading to more transpiration.
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35
Q

How does temperature affect the rate of transpiration? Give two ways.

A
  • Increases kinetic energy of water molecules and therefore increases rate of evaporation from spongy mesophyll cells into the air spaces of the leaf.
  • Increases the concentration of water vapour that the external air can hold before it becomes saturated (so decreases its relative humidity and its water potential).
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36
Q

How does wind/air movement affect the rate of transpiration?

A
  • Moves saturated air away from leaves so dry air replaces it, increasing transpiration rate.
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37
Q

How does humidity affect the rate of transpiration?

A
  • Humidity is the measure of the amount of water vapour in the air compared to the total concentration of water the air can hold.
  • High relative humidity —> reduced water vapour potential gradient between the inside of the leaf and the outside air —> reduced transpiration.
  • Low relative humidity —> increased transpiration.
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38
Q

How does soil water availability affect the rate of transpiration?

A
  • Dry soil —> plant under water stress —> rate of transpiration will be reduced.
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39
Q

Describe how to conduct an experiment using a potometer to investigate the rate of transpiration.

A
  1. Firstly, set up the apparatus and leave it undisturbed so the shoots equilibrates to the conditions.
  2. Submerge the apparatus in a water tray to remove air bubbles. Cut the plant shoot underwater and insert it into the hole of the cork Bauer fixed to avoid entering any air into the plant’s xylem. Also, attach the capillary tube underwater.
  3. Then, use Vaseline at all connections to ensure an airtight environment.
  4. Place the open end of the tube into a beaker.
  5. Introduce a bubble into the capillary tubing by dipping the capillary tube out of and back into the beaker containing water.
  6. Note the distance of the air bubble before the experiment. Use the stopwatch to keep track of time. Measure the distance the air bubble has moved at intervals of 3, 6, 9, 12, and 15 minutes.
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40
Q

How should you investigate the effect of one, named, environmental factor on the rate of transpiration (potometer)?

A
  1. Light: Lamp with a screen to prevent heat.
  2. Humidity: Put plant in a bag.
  3. Temperature: Heater
  4. Wind: Fan
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41
Q

Describe 5 functions of water in plants.

A
  1. Maintains cell turgidity for structure/growth.
  2. Transporting nutrients and organic compounds throughout the plant.
  3. Comprising much of the living protoplasm in the cells.
  4. Serving as a raw material for various chemical processes, including photosynthesis.
  5. Through transpiration, buffering the plant against wide temperature fluctuations.
42
Q

Describe the ways that the root hairs of root hair cells are adapted as exchange surfaces.

A
  1. Long projection —> increasing surface area.
  2. Microscopic size —> Can penetrate between soil particles reducing distance for diffusion.
  3. Thin surface layer through which diffusion and osmosis can take place quickly.
  4. Concentration of solutes in cytoplasm maintains water potential gradient into cells.
43
Q

Explain why water moves from the soil into root hair cells.

A

Root hair cells have a lower water potential than surrounding soil so water moves into the cell by osmosis.

44
Q

Name the 2 pathways by which water travels across the root to the xylem.

A
  1. Apoplast
  2. Symplast
45
Q

Describe the symplast pathway of water movement.

A
  • Living route
  • Water moves through the living part of the cell (the protoplast bounded by the cell surface membrane).
  • It can move through the vacuole (sometimes called the vacuolar pathway).
46
Q

Explain the importance of water potential gradients for the movement of water through a plant.

A

To get from the root hair cell to the centre of the root, the water passes through each successive cell by osmosis down a water potential gradient.

47
Q

Describe the Apoplast pathway of water movement.

A
  • Non-living route
  • Water moves between cells or though the cell wall, both of which are non-living.
48
Q

Define ‘endodermis’

A

An inner layer of cells in the cortex of a toor and some stems, surrounding a vascular bundle.

49
Q

Define ‘casparian strip’

A
  • A band of cell wall material deposited in the radial and transverse walls of the endodermis.
  • Is chemically different from the rest of the cell wall (the cell wall being made of lining and without Suberin whereas the casparian strip is made of suberin and sometimes lignin).
50
Q

Define ‘root pressure’

A
  • Pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.
  • The active transport of ions into the xylem by the endodermis creates the water potential gradient which causes water to enter the xylem.
  • This pushes water up the xylem.
51
Q

Describe the structure and function of the casparian strip.

A
  • Casparian strip is sections of cell wall that contain Suberin (which is waterproof).
  • This blocks the Apoplast pathway ensuring that anything crossing the endodermis has to through the living part of the cell.
  • This means the endodermis controls movement into the xylem and therefore the rest of the plant, blocking potentially toxic substances as it has no membrane proteins to let them through.
52
Q

Explain the role of active transport by endodermal cells for the movement of water.

A
  • Actively transport ions such as nitrate ions into the xylem, decreasing the water potential in the xylem, so that water enters by osmosis.
53
Q

Describe the evidence for the role of active transport in moving water from root endodermis into the xylem.

A

If the stem is cut close to where it emerges from the soil, liquid oozes from the cut surface caused by pressure from below.

54
Q

Define ‘xerophyte’

A

Plants with adaptations that enable them to survive in dry habitats or habitats where water is in short supply in the environment.

55
Q

Define ‘hydrophyte’

A

Plants which are adapted to survive at their optimum in water.

56
Q

What are examples of hydrophytes?

A
  • Duckweed
  • Water lily
  • Lotus (Nelumbo)
  • Rice
57
Q

What are 4 problems faced by hydrophytes?

A
  1. Water contains less dissolved gases than air — but plants need Oxygen for respiration and Carbon dioxide for photosynthesis.
  2. Below the water, there is less light, because light is refracted by the water molecules.
  3. Water flow might disturb plants.
  4. The concentration of ions in open water are lower than in soil water.
58
Q

What are 5 adaptations of hydrophytes?

A
  1. Very thin/no waxy cuticle
  2. Many stomata that are permanently open
  3. Reduced structural support
  4. Wide, flat leaves
  5. Small roots
59
Q

How does being very thin with no waxy cuticle help hydrophytes?

A
  • No waxy cuticle = doesn’t need to conserve water.
  • Thin cuticle = more efficient gas exchange
60
Q

How does having many stomata that are permanently open help hydrophytes?

A

Stomata can be open all the time as the plant is never dry.

61
Q

How does having reduced structural support help hydrophytes?

A
  • Stems can be bendy/flexible as they are not needed for support — they are supported by water. It needs to have lots of air spaces for movement of gases throughout the plant to the roots which add buoyancy, but are also a reserve of gases (O and CO).
  • Very little xylem or other tissues for strengthening as it is unnecessary which means the stems are flexible and can move with the water currents without getting broken.
62
Q

How does having wide, flat leaves help hydrophytes?

A
  • Increased surface area to maximise light absorption.
63
Q

How does having small roots help hydrophytes?

A
  • Roots are often also reduced as their main function is anchorage.
  • Root hairs which function in absorption are absent.
64
Q

Give examples of xerophytes.

A
  • Cacti
  • Marram grass
  • Pine trees
65
Q

Describe the leaves in xerophytes.

A
  • Spines like those found in some cacti (photosynthesis occurs in their stems which contains photosynthetic cells).
  • Needles like those found in pine/fir trees.
  • Absent e.g. some succulents.
66
Q

What are 7 adaptations of xerophytes?

A
  1. Thick waxy cuticle
  2. Sunken stomata
  3. Reduced numbers of stomata
  4. Reduced leaves
  5. Hairy leaves
  6. Curled leaves
  7. Extensive roots
67
Q

How does having thick waxy cuticles help xerophytes?

A
  • Shine of the cuticle will reflect light and heat.
  • Increases the diffusion distance across which water moves therefore decreasing the rate of transpiration.
  • Waxy material is also waterproof.
  • E.g. holly leaves
68
Q

How does having a sunken stomata help xerophytes?

A
  • Maintains humid air around stomata.
  • E.g. marram grass, cacti.
69
Q

How does having reduced numbers of stomata help xerophytes?

A
  • Stomata are gaps in the surface of the leaf which allow gas exchange, but every time a stomata is opened, water will escape.
  • The lower the number of stomata in a given area, the less water moves out of the leaves by transpiration.
70
Q

How does having hairy leaves help xerophytes?

A
  • Trap water vapour and so reduce the water potential gradient.
  • Makes the leaves lighter/shiny so reflecting more light and heat.
  • Maintains humid air around stomata, reducing water potential gradient and transpiration.
  • E.g. marram grass, couch grass
71
Q

How does having curled leaves help xerophytes?

A
  • Marram grass has roled leaves which trap moist air inside, reducing rate of transpiration.
  • Exposes a smaller surface area of the leaf to the drying effects of the wind
72
Q

Summarise how water moves through a plant.

A
  • Enters the plant through root hairs and crosses the root hairs, the epidermis, the cortex, the endodermis, the pericycle, and into the tracheary elements (the vascular bundles where we would find xylem and phloem).
  • Water is carried upwards through the xylem to the leaves.
  • When water gets to the leaves, it is able to pass through the xylem out into the tissues, coating the cells, allowing them to get the water they need.
  • Some of that water is lost from the leaves out through pores (stoma) between guard cells.
73
Q

Why is floating helpful for hydrophytes?

A
  • Leaves are closer to the light for photosynthesis, meaning they have direct access to the gases in the air.
  • They can out-compete any plants which live lower in the water than them.
  • They can move around if the water flows.
74
Q

What are adaptations of duckweed?

A
  • Floats so it has access to light.
  • Long roots to enable it to have a large surface area for absorption of minerals.
  • No stem — it has been more successful without investing in the growth of a stem.
  • They can reproduce very quickly, often covering a pond in a very short time.
  • They don’t need a very thick cuticle — doesn’t need to conserve water.
75
Q

Why can adaptations help a plant?

A

It can conserve its energy —> less tissues produced —> less need for resources.

76
Q

How are water lily leaves adapted?

A
  • Thin cuticle and stomata on upper surface makes gas exchange more efficient.
  • The stomata can be open all the time — the plant is never dry.
  • Lots of photosynthetic cells on the upper surface —> higher success in production of sucrose and other organic materials.
  • Layer of buoyancy —> lots of air space which makes the leaf float (between mesophyll cells).
77
Q

How is rice adapted?

A
  • Rice plants need a lot of ATP for biosynthesis so they need a lot of oxygen. In water there is less oxygen so they need to channel gas from the air down to the roots.
  • The stem and root tissues have large air spaces/tubes.
  • The tubes within the stem and roots are called aerenchyma —> supply oxygen rich air to the spaces and then to the root hair cells which need to carry out aerobic respiration.
  • The root hair cells can then absorb minerals using active transport.
78
Q

How are pine trees adapted?

A
  • Pine trees need to conserve water in winter. They have needles instead of flat open leaves.
  • They have very few stomata which are in pits. This keeps air saturated with water which collects close to the stomata, reducing water potential gradient between the inside and outside of the leaf.
79
Q

Describe the epidermis of cacti.

A
  • Rhipsalis dissimilis
  • Crater-shaped depressions with a guard cell each at their base can be seen.
  • Cross-section through the epidermis and underlying tissues.
  • The guard cells are countersunk, the cuticle is thickened.
80
Q

How is marram grass adapted?

A
  • Marram grass on the sand dunes have very little available water.
  • Their leaves are rolled so that inside the curve their is less wind and a more humid atmosphere.
  • Stomata on the inside of rolled leaf creates local humidity and decreases exposure to air currents because water vapour evaporates into air space rather than atmosphere
81
Q

How do grooves help xerophytes?

A
  • Grooved leaves allow water vapour to accumulate reducing the water potential gradient.
82
Q

How are cacti adapted?

A
  • Cacti have stems that are swollen and full of water.
  • Can be great source of water for animals which life in dry habitats as, when the leaf is broken, water will ooze out — so cacti have thorns which prevent animals from taking their water.
83
Q

Describe the roots of plants living in dry regions.

A
  • Long tap root growing deep into the sand to get groundwater sources (e.g. Marram grass).
  • Shallow roots spread over wide distances which allows them to collect lots of water very quickly when it rain in addition to the deep roots (Marram grass has a mat of shallow roots to obtain water).
84
Q

What are 2 other unique strategies xerophytes use to withstand dry conditions?

A
  1. Leaf loss: To prevent water loss in extreme dry conditions, some plants will lose their leaves completely. Coupled with this, some plants will concurrent photosynthesis from stems. Others become dormant until rain arrives.
  2. Avoiding drought: Some plats will survive periods of drought as storage organs, like tubers or bulbs, that will grow again when there is greater water availability.
85
Q

Describe aerenchyma in hydrophytes.

A

Specialised parenchyma in leaves, stems, and roots with thin walls and large intracellular spaces form. These make leaves and stems more buoyant and form a pathway for internal gas circulation

86
Q

State 3 ways most plants conserve water or gain better access to water.

A
  1. Cuticles
  2. Roots
  3. Not too many stomata — can close if necessary
87
Q

Describe the environmental conditions where water loss/access can become a real problem for plant species.

A
  • Desserts, sand dunes
  • Cold and icy
88
Q

State the form in which carbohydrates are transported in plants.

A

Sucrose

89
Q

Define ‘translocation’

A

The movement of organic solutes around a plant in the phloem.

90
Q

Define ‘source’

A

Region of a plant that produces assimilates by photosynthesis or from storage materials.

91
Q

Define ‘sink’

A

Region of a plant that requires assimilates for its metabolic needs.

92
Q

Define ‘assimilates’

A

The products of photosynthesis that are transported around a plant.

93
Q

State 3 examples of sources.

A
  1. Green leaves
  2. Storage organs e.g. tubers
  3. Seeds when germinating
94
Q

State 3 examples of sinks.

A
  1. Growing shoots
  2. Growing roots
  3. Fruits
95
Q

Define ‘phloem loading’ and state the two main ways this occurs.

A
  • The transport of sucrose into the phloem to be transported.
  • Actively and passively.
96
Q

Describe the symplast route for phloem loading and explain how it occurs.

A
  • Diffusion through cytoplasm and plasmodesmata of successive cells down concentration gradients.
97
Q

Describe the Apoplast route for phloem loading and explain how it occurs.

A
  • Using ATP, hydrogen ions are actively transported out of companion cells into the surrounding tissue.
  • Hydrogen ions diffuse back into companion cells down the diffusion gradient.
  • They pass through cotransporter proteins in the membrane bringing sucrose with them into the companion cells which the diffuses through the plasmodesmata into sieve cells.
98
Q

Describe how companion cells are adapted for their function.

A
  • Many mitochondria to produce ATP for active transport.
  • Infoldings in cell membranes to increase surface area for transport.
99
Q

Describe how the water and assimilates in phloem move from source to sink.

A
  • As source enters the sieve elements it reduces the water potential causing water to enter by osmosis.
  • This increases the hydrostatic pressure at the source causing mass flow towards the sink where there is lower hydrostatic pressure (due to sucrose being used by cells).
  • Water potential rises in sieve and water moves out into surrounding tissues by osmosis down a gradient.
100
Q

Describe the process of phloem unloading and explain how a concentration gradient is maintained from the phloem into cells requiring sucrose.

A
  • Sucrose leaves sieve tubes by active transport or diffusion to surrounding cells where it is used.
  • This maintains the concentration gradient.
  • As sucrose leaves, water potential of tubes increase so water follows by osmosis.
101
Q

Give 2 examples of what sucrose can be converted into, and what purpose each serves.

A
  1. Glucose: Respiration
  2. Starch: Storage
102
Q

Describe and explain sources of evidence for the processes involved in translocation.

A
  • Microscopy allows us to see adaptations of companion cells for active transport.
  • If mitochondria are poisoned, translocation stops, suggesting there is an active process which requires ATP.
  • Flow of sugars in phloem is 10000x faster than diffusion alone, suggesting there is an active process driving mass flow.
  • Positive pressure from inside the phloem forces sap out through aphid stylets (mouth parts), and the pressure lowers closer to the source.

Biology (25 decks)

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