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AS Biology > 2.10 - Adaptations for transport in plants > Flashcards

2.10 - Adaptations for transport in plants Flashcards

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1
Q

What is the vascular bundle and what does it do?

A
  • xylem and phloem, found adjacent to eachother
  • vascular tissue transports materials around the body
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2
Q

How are xylem and phloem positioned in the root and why is this optimal?

A
  • xylem is central and star shaped with phloem in between
  • helps resist vertical strees and anchors the plant in the soil
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3
Q

How are the xylem and ploem positioned in the stem and why is this optimal?

A
  • vascular bundles are in a ring at the periphery
  • xylem towards the centre and phloem towards the outside
  • gives flexible support and bending
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4
Q

How are the xylem and phloem positioned in the leaves and why is this optimal?

A
  • vascular tissues are in the midrib and in a network of veins
  • gives flexibility and resistance to tearing
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5
Q

What are the 2 main cell types in xylem?

A

Vessels and tracheids

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6
Q

Describe 3 features of tracheids.

A
  • cell walls containing lignin (hard,strong and water proof)
  • gaps called pits where water travels
  • spindle shaped so water twists up the plant
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7
Q

Where do tracheids occur?

A

Ferns, conifers and aniosperms (flowering plants) but not in mosses
- mosses have no water conducting tissue and are therefore poorer at transporting water and cannot grow as tall as other plants

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8
Q

Describe 4 features of vessels in xylem.

A
  • only occur in angiosperms
  • as lignin builds up in the cell walls, the contents die, leaving an empty space called the lumen
  • the end walls break down, leaving a hollow tube
  • lignin is stained red and is spiral shape
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9
Q

What is the xylems 2 functions?

A
  • transport of water and dissolved minerals
  • providing mechanical strength and support
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10
Q

How is water uptaked through the root of a plant?

A
  • soil water has a dilute solution of mineral salts and a high water potential
  • the root hair cell (containinf vacuole and cytoplasm) contains a more concentrated solution of solutes and a lower, more negative water potential
  • therefore water passes into the root hair cell by osmosis , down a water potential gradient
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11
Q

What are the 3 pathways of movement in the root of a plant?

A
  • the apoplast
  • the symplast
  • the vacuolar
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12
Q

What is the apoplast pathway?

A

Water moves in the cells, cellulose fibres in the cell wall are separated by spaces through which the water moves

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13
Q

What is the symplast pathway?

A

Water moves through the cytoplasm and plasmodemata.

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14
Q

What is the plasmodesmata?

A

Strands of cytoplasm through pits in the cell wall joining adjacent cells so the symplast is a continual pathway across the root cortex

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15
Q

What is the vacuolar pathway?

A

Water moves from vacuole to vacuole.

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16
Q

What is the endodermis?

A

A single layer of cells around the pericycle and vascular tissue of the route. Each cell has an impermable waterproof barrier in its cell wall.

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17
Q

What is the casparian strip?

A

The impermeable band of suberin in the cell walls of endodermal cells, blocking movement of water in the apoplast driving it into the cytoplasm.

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18
Q

How does the water move from the root epidermis to the xylem?

A

Osmosis across the enderdermal cell membranes.

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19
Q

How is the water potential gradient achieved between the xylem and the endodermal cells?

A

1) The water potential of endodermis cells is raised by water being driven in by the casparian strip
2) The water potential of the xylem is decreased by active transport of mineral salts mainly sodium ions, from the endodermis and pericycle , into the xylem

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20
Q

How are minerals mainly uptaked into the cytoplasm?

A

Minerals are absorbed into the cytoplasm by active transport, against the concentration gradient.

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21
Q

What is the secondary route minerals can take to get into the cytoplasm?

A

They can move along the apoplast pathway in solution
When they reach the endodermis, the casparian strip prevents further movement, so enter the cytoplasm by active transport.

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22
Q

What benefit comes with active transport for minerals?

A

Allows the plant to absorb ions selectively at the endodermis, depending on the needs of the cell

23
Q

What are the 3 theories supporting the movement of water from the roots into the leaves?

A

1) Cohesion/tension
2) Capillarity
3) Root pressure

24
Q

What is the cohesion tension theory?

A
  • water vapour evaporates from leaf cells into the air spaces and diffuses out of the stomata into the air
  • draws water from the 3 pathways into the xylem
  • water sticks together by cohesion
  • water sticks to the cells walls by adhesion
25
Q

What is cohesion of water molecules?

A

Attraction of water molecules for eachother, seen as hydrogen bonds, resulting from the dipole structure of the water molecule.

26
Q

What is adhesion of water moelcules?

A

The charges on the water molecules cause attraction to the hydrophilic lining of the vessels.

27
Q

What is the capillarity theory?

A
  • movement of water up small tubes, by capillary action
  • only operates over small distances (like a straw)
28
Q

What is the root pressure theory?

A
  • operates over short distances
  • consequence of osmotic movement of water into the xylem pushing the water already there further up
  • caused by osmotic movement of water down the concentration gradient across the root into the base of the xylem
29
Q

What is transpiration?

A

The evaporation of water vapour from the leaves or other above ground sources/ parts of the plants, out through the stomata into the atmosphere.

30
Q

What is the dilemma with the stomata?

A

The stomata must be open during the day to allow gas exchange between the leaf tissues and the atmosphere, but this means the plant loses valuable water.

31
Q

What are the 2 types of factors affecting the rate of transpiration?

A
  • genetic factors such as those controlling the number, size and distribution of the stomata
  • environmental factors such as temperature, humidity, air movement and light intensity. THese affect the water potential gradient between the water vapour in the leaf and in the atmosphere.
32
Q

How does temperature effect transpiration?

A
  • temperature increase lowers the water potential of the atmosphere
  • increases the kinetic energy of the water molecules, accelerating the rate of evaporation from the walls of the mesophyll cells
  • if the stomata is open, KE speeds up the rate of diffusion into the atmosphere
  • higher temperature causes water molecules to diffuse away from the leaf more quickly, reducing the water potential around the leaf.
33
Q

How does humidity effect transpiration?

A

Air inside the leaf has humidity of 100%, whilst outside never exceeds 100%, so a water potential gradient is formed
- transpiration in still air results in the accumulation of a layer of saturated air at the surface of the leaves
- the water vapour gradually diffuses away, leaving concnetric rings of decreasing humidity the further away from the leaf you go
- the higher the humidity, the higher the water potential, which creates a concentration gradient

34
Q

How does air movement affect transpiration?

A
  • blows away layer of humid air at the leafs surface
  • the faster the air is moving, the faster the concentric shells of water vapour get blown away, the faster transpiration occurs
  • the water potential gradient between outside and inside increases and water vapour diffuses out through stomata more quickly
35
Q

How does light intensity affect transpiration?

A
  • the stomata open wider as the light intensity increases, increasing the rate of transpiration
  • stomata open widest in the middle of the day, less widely in the morning and closed in the evening
36
Q

What is a potometer?

A

Measures water uptake by the movement of an airbubble
Allows altering of surrounding environment, example changing factors like humidity.

37
Q

What are the 3 types of flowering plants and what are they?

A

Mesophytes - plants living in conditions of adequate water supplies
Xerophytes - plants that live in conditions where water is scarce
Hydrophytes - water plants

38
Q

What are the features of mesophytes?

A
  • shed their leaves before winter, so that they do not lose water by transpiration, when liquid may be scarce
  • aerial parts of many non-woody plants die off in winter, so they are not exposed to frost, but their underground organs, like bulbs or corms, survive
  • mesophytes over winter lay as dormant seeds with a low metabolic rate that almost no water is required
39
Q

What are the features of xerophytes and an example of one?

A
  • may live in hot, dry desert regions where soil water is frozen for much of the year or exposed, windy locations
  • example marram grass
40
Q

How does marrram grass (an xerophyte) adapt to its environment?

A
  • rolled leaves (reduces surface area)
  • sunken stomata (reduces potential gradient)
  • hairs (trap water)
  • thick cuticle (waterproof)
  • stiff fibres (shape is maintained when leaf becomes flaccid)
41
Q

What are the features of hydrophytes?

A
  • water is a supportive medium so they have little or no lignified support tissues
  • surrounded by water, there is little need for transport tissues so xylem is poorly developed
  • leaves have little or no cuticle, because there is no need to prevent water loss
  • stomata are on the upper surface of floating leaves, because the lower surface is in the water
  • stems and leaves have large air spaces, continuous down to their roots forming a reservoir of oxygen and CO2, which provides buoyancy
42
Q

What is translocation?

A

The movement of soluable products of photosynthesis such as sucrose and amino acids, through phloem, from sources and sinks

43
Q

What is phloem?

A

Plant tissue containing sieve tube elements, containing companion cells, translocating of sucrose and amino acids from the leaves to the rest of the plant. It is living.

44
Q

How do we know companion cells are biochemically active?

A

A large nucleous, dense cytoplasm, many RER and mitochondria.

45
Q

What are the 3 experiments proving transport in the phloem?

A
  • ringing experiments
  • radioactive tracers and autoradiography
  • aphid experiments
46
Q

What are ringing experiements?

A

Removing the outer bark removes the phloem
After photosynthesis, the phloem contents contained lots of sucrose, whilst below was none
Created a bulge of excess fluids

47
Q

How is radioactive tracers and autoradiography used?

A

Using isotopes like c14 to track movement up the phloem, as it can be detected by tracers

48
Q

What are aphid experiments?

A

A stylet is inserted into a sieve plate to exude sucrose, showing the presence of a phloem
Slightly unethical

49
Q

What are the 4 theories of translocation?

A

Mass flow hypothesis
Active processes
Protein filaments
Cytoplasmic streaming

50
Q

What is the mass flow hypothesis?

A

There is a passive mass flow of sugars from the phloem of the leaf , where there is highest concentration (the source) to other areas, such as growing tissues, where there is a lower concentration (the sink)

51
Q

What are the 5 key problems with the mass flow hypothesis?

A
  • phloem transport is much faster than if the substances were moving by diffusion
  • it does not take into account sieve plates
  • sucrose and amino acids move at different rates and in different directions in the same tissue
  • phloem has a relatively high oxygen consumption and translocation is slowed or stopped at high temperatures or if respiratory poisons, like potassium cyanide, are applied
  • the companion cells are biochemically active, yet the mass flow model shows no need for them
52
Q

What is the active process theory?

A

Cyanide and low temperature inhibit translocation, indicating that energy generated by respiration is used

53
Q

What is the protein filaments theory?

A

Protein filament pass through sieve pores so perhaps different solutes are carried at different rates through the same sieve sube elements

54
Q

What is cytoplasmic streaming?

A

Responsible for the movement in different directions in individual sieve tube elements, providing there was some mechanism to transport solutes through the sieve plates.

AS Biology (11 decks)

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