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A-Level Biology - Three > 9.1-9.5 Transport in plants > Flashcards

9.1-9.5 Transport in plants Flashcards

1
Q

Why do plants require a transport system?

A
  • to ensure that all the cells of a plant receive a sufficient amount of nutrients
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2
Q

How do plants receive sufficient amounts of nutrients?

A
  • xylem tissue
  • phloem tissue
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3
Q

What is the role of xylem tissue?

A
  • enables water as well as dissolved minerals to travel up the plant in the passive process of transpiration
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4
Q

What is the role of phloem tissue?

A
  • enables sugars to reach all parts of the plant in the active process of translocation
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5
Q

Description of the vascular bundle in the roots.

A
  • xylem and phloem are components of the vascular bundle which serves to enable
    transport of substances as well as for structural support
    he xylem vessels are arranged in an X shape in the center of the vascular bundle.
  • this enables the plant to withstand various mechanical forces such as pulling
  • the X shape arrangement of xylem vessels is surrounded by endodermis, which is an
    outer layer of cells which supply xylem vessels with water.
  • an inner layer of meristem cells known as the pericycle
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6
Q

Description of the vascular bundle in the stem.

A
  • xylem is located on the inside in non-wooded plants to provide support and
    flexibility to the stem
  • phloem is found on the outside of the vascular bundle
  • there is a layer of cambium in between xylem and phloem, that is meristem cells
    which are involved in production of new xylem and phloem tissue
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7
Q

Description of the vascular bundle in the source/ leaf.

A
  • the vascular bundles form the midrib and veins of a leaf
  • dicotyledonous leaves have a network of veins, starting at the midrib and spreading
    outwards which are involved in transport and support
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8
Q

Features of the xylem tissue are …

A
  • transport water and minerals
  • serve to provide structural support
  • long cylinders made out of dead tissue with open ends = can form continuous column
    -vessels contain pits which enable water to move sideways into other vessels
  • thickened with a tough substance (lignin) which is deposited in spiral patterns to allow the plant to remain flexible
  • water can only flow upwards
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9
Q

Features of phloem tissue are …

A
  • tubes made of living cells
  • involved in translocation which is the movement of nutrients to storage organs and growing parts of the plant
  • consist of sieve tube elements and companion cells
  • sieve tube elements form a tube to transport sugars such as sucrose, in the dissolved
    form of sap and can be transported upwards or downwards
  • companion cells are involved in ATP production for active processes such as loading
    sucrose into sieve tubes
  • cytoplasm of sieve tube elements and companion cells is linked through structures
    known as plasmodesmata
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10
Q

Plasmodesmata is …

A

are gaps between cell walls which allow
communication and flow of substances such as minerals between the cells

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11
Q

Transpiration is …

A
  • the process where plants absorb water through the roots, which then moves up through the plant and is released into the atmosphere as water vapour through pores in the leaves
  • carbon dioxide enters, while water and oxygen exit through a leaf’s stomata.
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12
Q

Transpiration stream is …

A
  • the movement of water up the stem, enables processes such as photosynthesis, growth and elongation as it supplies the plant with water which
    is necessary for all these processes
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13
Q

What does the transpiration stream provide the plant with?

A
  • required minerals
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14
Q

How does the plant control it’s temperature?

A
  • via evaporation of water
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15
Q

When does transpiration involved osmosis?

A
  • water moves from the xylem to the mesophyll cells
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16
Q

When does transpiration involve evaporation?

A
  • from the surface of mesophyll cells into intercellular spaces and diffusion of water vapour down a water vapour potential gradient out of the stomata
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17
Q

How can the rate of transpiration be measured?

A
  • by using a potometer
  • where water vapour lost by the leaf is replaced by water in the capillary tube
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18
Q

What is physically measured on the potometer?

A
  • measuring the movement of the meniscus can be used to determine the rate of transpiration
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19
Q

Factors affecting the rate of transpiration include …

A
  • number of leaves
  • number/size or position of
    stomata
  • presence of waxy cuticle, the amount of light present
  • the temperature
  • humidity
  • air movement
  • water availability.
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20
Q

Xerophytes are …

A
  • plants adapted to living in dry conditions
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21
Q

What are the adaptations of xerophytes benefiting?

A
  • minimises water loss
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22
Q

What are the adaptations of xerophytes?

A
  • smaller leaves to reduce the surface area for water loss
23
Q

What do xerophytes respond to?

A
  • low water availability by closing the stomata to prevent
    water loss
24
Q

How does xerophytes prevent water loss via evaporation?

A
  • densely packed mesophyll
  • thick waxy cuticle
25
Q

What xerophytes contain to trap moist air and what does this do?

A
  • hairs
  • pits
  • reduces water vapour potential
26
Q

What do the leaves of xerophytes do and why?

A
  • roll up leaves
  • to reduce the exposure of lower epidermis to the atmosphere
  • by trapping air
27
Q

Hydrophytes are …

A
  • plants that actually live in water such as water lilies
28
Q

What adaptations do hydrophytes have for their environment?

A
  • very thin or absent waxy cuticle as they don’t need to conserve water
  • many constantly open stomata are found on the upper surfaces of leaves to maximise gas exchange
  • wide, flat leaves give a large surface area for light absorption
  • air sacs are found in some hydrophytes to enable leaves to stay afloat
  • many large air spaces to make leaves and stems more buoyant
29
Q

How does water enter the roots?

A
  • root hair cells
  • moves into the xylem tissue located in the center of the root
30
Q

What does the water uptake through the root hair cells cause and why?

A
  • water potential gradient
  • the water potential is higher inside the soil than inside the root hair cells due to the dissolved substances in the cell sap
31
Q

What is the purpose of root hair cells in movement of water in the roots?

A
  • to provide a large surface area for the movement of water to occur
32
Q

How are minerals absorbed through the root hair cells and why?

A
  • active transport
  • as they need to be pumped against the concentration gradient
33
Q

What are the two ways that water can be taken up by the root hair cells can move across the cortex of the root into the xylem?

A
  • symplast pathway
  • apoplast pathway
34
Q

How does water transport through the symplast pathway?

A
  • enters the cytoplasm through the plasma membrane
  • passes from one cell to the next through plasmodesmata
35
Q

Plasmodesmata is …

A
  • the channels which connect the cytoplasm of one cell to the next
36
Q

How does water transport through the apoplast pathway?

A
  • water moves through water filled spaces between cellulose molecules in the cell walls
37
Q

What is the benefit of water not passing through the plasma membrane?

A
  • it can carry dissolved mineral ions and salts
38
Q

What happens when the water reaches the endodermis?

A
  • it encounters a layer of
    suberin which is known as the Casparian strip which cannot be penetrated by water
39
Q

What has to occur for the water to cross the epidermis?

A
  • the water that has been moving through the cell walls must now enter the symplast pathway
40
Q

What happens once the water has moved across the epidermis?

A
  • the water continues down the water potential gradient from cell to cell until it reaches a pit in the xylem vessel which is the entry point of water
41
Q

How is water removed from the top of the xylem vessels into the mesophyll cells?

A
  • down the water potential gradient
42
Q

What is the push of water upwards aided by?

A
  • root pressure
43
Q

What is root pressure causing?

A
  • where the action of the endodermis moving minerals into the xylem by active
    transport drives water into the xylem by osmosis, thus pushing it upwards
44
Q

How is the flow of the water maintained and what do these two forces in combination support?

A
  • with the help of surface tension of water
  • the attractive forces between water molecules known as cohesion
  • tension-cohesion theory and capillary action
45
Q

What is tension-cohesion theory and capillary action?

A
  • the forces involved in cohesion cause the water molecule to adhere to the walls of xylem, thus pulling water up
46
Q

Translocation is …

A
  • an energy requiring process which serves as a means of transporting assimilates such as sucrose in the phloem between sources which release sucrose - - such as leaves and sinks e.g. roots and meristem which remove sucrose from the phloem
47
Q

How does sucrose enter the phloem?

A
  • active loading
  • where companion cells use
    ATP to transport hydrogen ions into the surrounding tissue, thus creating a diffusion
    gradient, which causes the H+ ions to diffuse back into the companion cells
48
Q

Where does the sucrose diffuse into after facilitated diffusion in the companion cells?

A
  • sucrose diffuses out of the
    companion cells down the concentration gradient into the sieve tube elements through
    links known as plasmodesmata
48
Q

Active loading is a form of what?

A
  • facilitated diffusion
  • involving cotransporter proteins which allows the returning H+ ions to
    bring sucrose molecules into the companion cells, causing the concentration of sucrose in the companion cells to increase
49
Q

What happens in the sieve tube elements once sucrose has entered?

A
  • water potential inside the tube is reduced
  • causing water to enter via osmosis
  • increasing the hydrostatic pressure of the sieve tube
50
Q

How does water move around the sieve tube?

A
  • from an area of higher
    pressure to an area of lower pressure
51
Q

How is sucrose eventually removed from the sieve tube?

A
  • active transport or diffusion
  • into the surrounding cells
  • increasing the water potential of the sieve tube
52
Q

How does water leave the sieve tube?

A
  • osmosis
  • reducing the pressure in the phloem at the sink
53
Q

Summarise translocation.

A
  • the mass flow of water from the source to the sink down the
    hydrostatic pressure gradient is a means of supplying assimilates such as sucrose to where they are needed

A-Level Biology - Three (3 decks)

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