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AS Biology > Transport In Plants > Flashcards

Transport In Plants Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is transported in the Xylem?

A

Water and dissolved mineral ions

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2
Q

What is transported in the Phloem?

A

Assimilates ( mainly amino acids and sucrose dissolved in water to form sap)

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3
Q

Give the 3 components of Xylem structure

A

Vessels - To carry the water and mineral ions
Fibres - To help support the plant
Living Parenchyma cells - Act as packing tissue to separate and support the vessels

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4
Q

Why is the flow of water not impeded in the Xylem?

A
  • There are no cross walls
  • No cell contents, Nucleus, or Cytoplasm
  • Lignin thickening prevents the walls collapsing
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5
Q

State 3 ways in which the structure of the xylem enables it to carry water etc from root to tip of the plant

A
  • The dead cells align to make a continuous column
  • Tubes are narrow so the water column doesn’t break easily
  • Lignin allows xylem to stretch as plant grows and allows stem to bend
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6
Q

Name the 3 characteristics you would see in a microscope image of the Xylem

A
  • Thick Lignified Walls
  • Empty Lumen
  • Parenchyma
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7
Q

What two things compose the Phloem?

A

Sieve tube elements and Companion cells

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8
Q

What 3 characteristics would you see in a microscope image of the Phloem?

A
  • Companion Cells
  • Sieve Plate/s
  • Parenchyma (packing cells)
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9
Q

Why do Xylem vessels have bordered Pits?

A

The pits allow water to move sideways from one vessel to another

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10
Q

Why are Sieve tube elements not true cells?

A

They contain no nucleus (Or Cytoplasm)

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11
Q

Suggest why Phloem doesn’t have Lignin or Pitted walls

A

It is not required in the phloem, as it has companion cells in which its contents can diffuse into by the plasmodesmata and thus into the tissues of the plant.
- Essentially, Phloem has live cells not dead, so diffusion can happen in them.

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12
Q

WHY do plants ( and all living things) need transport systems?

A
  • Because all the cells need a constant supply of oxygen, and waste products to be taken away before they build up and become toxic
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13
Q

In what direction do the Xylem contents travel?

A
  • Upwards ONLY
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14
Q

In what direction do the Phloem contents travel?

A
  • Upwards or downwards
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15
Q

Describe the distribution of Xylem in the young root

A

Found in an ‘X’ shape core of the vascular bundle, found at the centre of the young root

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16
Q

Describe the distribution of Xylem in the stem

A

In the vascular bundles, near the outer edge of them stem, found toward the inside of each vascular bundle

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17
Q

Describe the distribution of Xylem in the leaves

A

The vascular bundles make up the midrib and veins, inside each vein, the xylem is on top of the phloem

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18
Q

Describe the distribution of Phloem in the young root

A

The phloem is found in between the arms of the ‘X’ shaped xylem tissue

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19
Q

Describe the distribution of Phloem in the stem

A

Found towards the outside of the vascular bundles

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20
Q

Describe the distribution of Phloem in the leaves

A

Below the Xylem in the veins formed of vascular bundles

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21
Q

What is Plasmodesmata?

A

Gaps in the cell wall containing cytoplasm that connects two cells

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22
Q

Describe the Apoplast pathway

A

Water passes through the spaces in the cell walls and between the cells, not passing through plasma membranes into the cells

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23
Q

What is water moving by in the Apoplast pathway?

A

Mass flow, because it’s not passing through plasma membranes into the cells

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24
Q

Describe the Symplast pathway

A

Water enters the cell cytoplasm through the plasma membrane. Then passes through the plasmodesma from one cell to the next

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25
Q

Describe the Vacuolar pathway

A

Water enters cell cytoplasm but is not confined to the cytoplasm. It can pass through vacuoles as well

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26
Q

What is meant by Plasmolysis?

A

When water exits the cell, and the plasma membrane loses contact with the cell wall

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27
Q

How would a cell become plasmolysed?

A
  • Placed in a salt solution with a very negative ( low ) water potential, then it will lose water by osmosis.
  • As water loss continues eventually the cytoplasm and vacuole shrink, eventually cytoplasm is no longer turgid and touching the cell wall
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28
Q

Give 3 reasons why Transpiration is important

A
  • Transports useful mineral ions up the plant
  • Maintains cell turgidity
  • Supplies water for growth and photosynthesis
29
Q

Name 2 places on the leaf that water may leave from

A
  • Stomata

- Waxy cuticle

30
Q

Why must the water vapour potential be higher in a leaf air space than that of the air outside?

A
  • Because water leaves the leaf surface cells so a concentration gradient must be maintained
31
Q

Explain the effect of light intensity on the rate of Transpiration

A

Higher light intensity increases the transpiration rate, because, in light, the stomata open to allow gaseous exchange

32
Q

State 3 ways in which a higher temp will increase the rate of transpiration

A
  • Increase rate of evaporation from the cell surfaces so that the water vapour potential in the leaf rises
  • Increase the rate of diffusion through stomata as the water molecules have a higher kinetic energy
  • Decreases the relative water vapour potential of the air allowing more rapid diffusion of molecules out of the leaf
33
Q

What effect will relative humidity have on the rate of transpiration?

A
  • Higher humidity DECREASES the rate of transpiration
  • Higher relative humidity will reduce the rate of water loss
  • as there will be a smaller water vapour potential gradient between air spaces IN the leaf and air spaces OUT of them
34
Q

What effect will wind have on the rate of transpiration?

A

The wind outside the leaf will carry away water vapour that has just diffused out. This will maintain a high water vapour potential gradient

35
Q

What effect will water availability have on the rate of transpiration?

A

Low water availability will decrease the rate as small amounts of water in the soil means the plant cannot replace the water that is lost. This means the stomata will close and the leaves will wilt

36
Q

What piece of equipment is used to estimate the rate of transpiration?

A

A Potometer

37
Q

What is meant by Adhesion?

A

The attraction between water molecules and the walls of the Xylem

38
Q

What is meant by Cohesion?

A

The attraction between water molecules caused by hydrogen bonds

39
Q

How are root hair cells specialised?

A
  • The long extension ( the root hair ) increases the surface area of the root, making for a faster rate of osmosis
40
Q

Name the 3 processes that help to move water up the stem

A
  • Root pressure
  • Transpiration Pull
  • Capillary action
41
Q

Use the cohesion-tension theory to explain how water moves from the roots to the leaves

A
  • Evaporation at the top of the plant / Leaves
  • Creates tension in the Xylem
  • Water molecules stick together due to their cohesive nature and hydrogen bonds and form a chain/column
  • (column/chain) is pulled up by the tension
42
Q

Explain how root pressure helps to move water up the stem

A
  • The Endodermis draws water INTO the medulla by osmosis

- The pressure in the root medulla builds up and forces water into the xylem.

43
Q

Explain how capillary action helps move water up the stem

A
  • Because the xylem vessels are very narrow, adhesion can have an effect and pull water up the sides of the vessel
44
Q

What are the two ways that water may reach cells in the leaf?

A
  • Water can be drawn from the xylem in the leaf by osmosis.

(Due to evaporation of water from the leaf reducing the water potential of those cells causing water to enter them from neighbouring cells)

  • By the Apoplast pathway from the Xylem
45
Q

Explain the significance of the Casparian strip

A
  • It blocks the Apoplast pathway between the cortex and the medulla, forcing water to take the symplast pathway
46
Q

What property of water causes cohesion?

A
  • Its’ Hydrogen bonds
47
Q

Why is it important that the water column in the xylem vessel is not broken

A
  • Because then the transpiration stream would stop because the hydrogen bonds in the water that form the stream are broken
48
Q

What 2 things, must plants living on land be adapted to?

A
  • Reducing loss of water

- Replacing water that is lost

49
Q

Name 4structural and behavioural adaptations in which most terrestrial plants can reduce their water loss

A
  • Waxy cuticle on the upper epidermis reduces water loss by evaporation
  • Stomata being on the under-surface of leaves, reducing evaporation by direct heating from the sun
  • Stomata closed at night as photosynthesis isn’t needed
50
Q

Give 3 ways in which Marram grass (a Xerophyte) is adapted to living in arid conditions

A
  • Thick waxy cuticle on upper epidermis to reduce water loss by evaporation
  • Stomata are on the lower epidermis so they’re protected by the enclosed, humid air space of rolled leaf
  • Stomata are in pits covered by hair, reduce air movement and thus loss of water vapour
51
Q

Name 3 adaptions of Cacti to arid conditions

A
  • Succulent (stores water in stem)
  • Leaves reduced to spines reducing surface area for loss of water by transpiration to happen
  • Widespread roots take advantage of any rain that does fall
52
Q

Give 3 adaptations of Water Lillies (Hydrophytes) to living in water

A
  • Many large air spaces in leaf keeps the leaves afloat to be in the air to absorb sunlight
  • Stomata on upper epidermis, so they’re exposed to air to allow the gaseous exchange
  • Many large air spaces in the stem gives buoyancy and allows oxygen to diffuse quickly to the roots for aerobic respiration
53
Q

Why would many plants not survive in arid conditions?

A
  • Because the cells need a constant supply of oxygen, which is obtained from water
54
Q

Explain why leaves in water cannot transpire

A
  • The leaf needs to be in contact with air in order to perform gaseous exchange for photosynthesis
55
Q

What are Assimilates?

A

Substances that have become part of the plant, including sugars (mainly as Sucrose) and Amino acids

56
Q

What is a ‘Sink’?

A

A part of the plant where Assimilates are removed from the transport system

57
Q

What is a ‘Source’?

A

A part of the plant that loads material onto the transport system

58
Q

What is the definition of Translocation?

A

The transport of Assimilates throughout a plant

59
Q

Why is Translocation important in the life of plants?

A

Because the Assimilates it carries (Sucrose and Amino Acids) are vital for life

60
Q

‘How’ is Sucrose moved along the Phloem?

A

By Mass flow

61
Q

In what direction may ‘Sap’ flow in a plant?

A

Both up and down the plant as required

62
Q

What causes the Mass flow of Sap along the Phloem?

A

A difference in Hydrostatic Pressure between the two ends of the tube, which produces a pressure gradient

63
Q

Explain how a Pressure gradient is produced in the Phloem to move sap by mass flow?

A
  • Water enters the tube at the source, increasing pressure
  • Its leaves the tube at the sink, reducing the pressure
  • Therefore the sap flows from the Source the the Sink
64
Q

What qualifies the movement of Sap as Mass flow?

A
  • All the sap is travelling in the same direction
65
Q

Why may the direction of the sap change at different times?

A
  • It depends on where the Sucrose is being produced and where it is needed
66
Q

Explain how a sieve tube can transport sucrose upwards at one time of the year and downward at another

A
  • A source is any place in the plant that loads sucrose into the sieve tube
  • In early spring this could be the roots where energy stored as starch is converted into sucrose and moved to other parts of the plant to enable growth in spring
  • Sugars made in photosynthesis are converted to sucrose and loaded into the phloem sieve tubes in LATE spring, summer and autumn and is transported to plant areas that are growing eg. Meristem or to roots for starge
67
Q

Outline the process of movement of sap in the Phloem

A
  • Sucrose ACTIVELY LOADED into sieve tube element and REDUCES WATER POTENTIAL
  • Water follows by osmosis and increases the hydrostatic pressure in the sieve tube element
  • Sap moves down sieve tube from HIGHER TO LOWER hydrostatic pressure at source to sink
  • Sucrose removed from sieve tube by surrounding cells and increases water potential in the sieve tube
  • Water moves OUT of sieve tube and REDUCES hydrostatic pressure
68
Q

Outline the process of Active Loading

A
  • Movement of Assimilates into phloem STCs is an ACTIVE PROCESS that requires the ATP from CCs.
  • ATP is used to pump out H+ ions out of CCs causing a concentrations gradient (Higher outside the CCs)
  • Thus H+ ions DIFFUSE back into CCs through COTRANSPORTER PROTEINS in the cell membrane
  • They only pass if the H+ ions are associated with sucrose
    (This is known as cotransport or 2ndry Active Transport0
  • High conc of H+ causes Facilitated Diffusion back to CC!
  • This Sucrose moves against its gradient. Concentration increases in CCs, so DIFFUSE through plasmodesma into the STCs!

AS Biology (12 decks)

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