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Biology > 3.3 - C - Transport In Plants > Flashcards

3.3 - C - Transport In Plants Flashcards

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1
Q

What are dicotyledonous plants?

A

Plants with 2 seed leaves and a branching pattern of veins in the leaf

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2
Q

What is a meristem?

A

A layer of dividing cells

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3
Q

Define phloem

A

Transports dissolved assimilates, such as sugars, up and down a plant

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4
Q

Define vascular tissue

A

Consists of cells specialised for transporting fluids by mass flow (xylem and phloem)

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5
Q

Define xylem

A

Transports water and mineral ions upwards in a plant

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6
Q

Explain the cross-section (incl. vascular bundles) of a root of a plant

A

Xylem in x/+ shape
Phloem in 4 quadrants
Epidermis surrounds them (vascular tissue)
Around that is the thick cortex with an epidermis at the edge
Inside endodermis is the pericycle

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7
Q

Define pericycle

A

A ring of meristem cells - found inside the endodermis in roots

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8
Q

Explain the cross-section (incl. vascular bundles) of a stem of a plant

A

Vascular bundles found near outer cells of the stem
The xylem is near the inside of the bundle (closer to centre of stem), phloem on outside
In between the xylem and phloem is cambrium

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9
Q

What is cambium?

A

A layer of meristematic cells capable of differentiating into new xylem and phloem vessels

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10
Q

Explain the formation of vascular bundles in leaves

A

They form the veins of the leaf

The xylem is above the phloem

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11
Q

Define what companion cells are

A

The cells that help load sucrose into sieve tubes

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12
Q

Define what sieve tube elements are

A

They make up the tubes in phloem tissue that carry sap up and down the plant. They are separated by sieve plates

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13
Q

List 5 structural aspects of xylem vessels and explain their functions

A

Continuous, hollow tubes with no end walls or contents - less resistance to flow of water and more space
Walls impregnated with lignin - strengthens wall, waterproofs wall, improves adhesion of water molecules - increases capillarity
Lignification in spiral pattern - flexibility and stretching of stem
Narrow lumen - more effective capillary action
Bordered pits (pores) in walls - can move around and avoid blockages

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14
Q

List 5 structural aspects of sieve tube elements and explain their functions

A

Little cytoplasm, lots of absent organelles - less resistance and more space for transport
Siege plates - connects S.T.E to allow sucrose (as sap) through
Joined end to end to for tube - allow continuous transport
Bi-directional flow - allows sucrose to go both up and down the plant
Living - allows active processes

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15
Q

List 3 structural aspects of companion cells and explain their functions

A

Many mitochondria - a lot of respiration is needed to provide lots of ATP for active processes
Nucleus - controls the functions of both the companion cell and S.T.E
Plasmodesmata - allows continuation of cytoplasm between companion cell and sieve tube element

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16
Q

What is plasmodesmata?

A

Gaps in the cell wall containing cytoplasm that connects 2 cells

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17
Q

List the 3 pathways

A

The apoplast pathway
The symplast pathway
The vacuolar pathway

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18
Q

Explain the apoplast pathway

A

Water passes through the spaces in the cell walls and between cells. Doesn’t pass through any plasma membranes into cells. It moves by mass flow, not osmosis. This means dissolved mineral ions and salts can be carried with water

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19
Q

Explain the symplast pathway

A

Water enters the cell cytoplasm through the plasma membrane. It passes through the plasmodesmata from one cell to the next

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20
Q

Explain the vacuolar pathway

A

This is similar to the symplast pathway, but the water is not confined to the cytoplasm of the cells. It is able to enter and pass through vacuoles as well

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21
Q

Define water potential

A

A measure of the tendency of water molecules to move from one place to another

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22
Q

Define turgid

A

When a cell is full/saturated with water

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23
Q

Define transpiration

A

The loss of water by evaporation out of plant’s leaves via the stomata

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24
Q

What is a potometer?

A

A device that can measure the rate of water uptake as a leafy stem transpires

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25
Q

List 8 factors of transpiration

A 
Number of leaves
Number and size of stomata
Presence of a waxy cuticle
Light
Temperature
Humidity
Wind
Availability of water
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26
Q

Explain how and why the number of leaves affects water loss in transpiration

A

More leaves = more water loss

It’s a larger SA for water to evaporate out of

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27
Q

Explain how and why the number and size of stomata affects water loss in transpiration

A

More/bigger stomata = more water loss

A larger SA allows more water to evaporate out of them

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28
Q

Explain how and why the presence of a waxy cuticle affects water loss in transpiration

A

If it’s present - less water loss

It reduces water evaporating from stomata as its hydrophobic

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29
Q

Explain how and why light affects water loss in transpiration

A

The lighter it is = the more water lost
The stomata open wider in light to allow gas exchange for photosynthesis. If they are open there is a larger SA for water to evaporate out of

30
Q

Explain how and why temperature affects water loss in transpiration

A

Higher the temp = more water loss

More kinetic energy, water evaporates faster and water vapour diffuses out of leaves faster

31
Q

Explain how and why humidity affects water loss in transpiration

A

The higher the humidity = the less water lost
When humid, air is more saturated with water. Whilst saturation in the air spaces in the leaf is still higher, there is a shallower water potential gradient for diffusion if water vapour

32
Q

Explain how and why wind affects water loss in transpiration

A

More wind = more water loss
It carries water vapour that has just diffused from the leaf away, making the air immediately surrounding the leaf less saturated and maintaining a steeper water potential gradient

33
Q

Explain how and why water availability affects water loss in transpiration

A

More water in the soil = more water loss

The more water available, the more water it can lose

34
Q

List 5 things to do when setting up a potometer as to ensure the results are valid

A

Set it up under water so no air bubbles are inside it
Ensure the shoot is healthy
Cut the stem underwater to prevent air entering the xylem
Cut the stem at an angle so a large SA is in contact with the water
Dry the leaves

35
Q

How do you calculate volume in a cylinder?

A

V=pi x r^2 x length

36
Q

How do you calculate the rate of transpiration?

A

Rate = volume / time

37
Q

Explain why using a potemeter does not give an exact measure for rate of transpiration

A

Transpiration is the loss of water by evaporation from leaves.
A potometer measures water uptake to replace loss.
Some water may be used e.g. in photosynthesis rather than all evaporating from the leaves.
Also uptake by detached shoots may not be the same as that of the whole plant

38
Q

Define adhesion

A

The attraction between water molecules and the walls of the xylem vessel

39
Q

Define cohesion

A

The attraction between water molecules caused by hydrogen bonds

40
Q

Explain water uptake and movement across the root

A

Root hair cells absorb mineral ions and water from soil via osmosis. It moves across the root cortex down a water-potential gradient to the endodermis of the vascular bundle via the apoplast pathway blocked by caspian strip.

41
Q

What drives continual osmosis into root hair cells?

A

Minerals are actively transported into the root hair cell from the soil. This decreases the water potential of the root hair cell

42
Q

List 6 adaptations of root hair cells

A

Big SA - water and minerals can be exchanged
Lots of mitochondria - release energy during respiration needed for active transport
Tube-like protrusion - penetrate between soil particles, reducing distance water and mineral ions need to travel
Large vacuoles - have salts to speed up water absorption
No cuticles - would prevent water absorption
Thin walls - thin exchange surface

43
Q

What is the purpose of the casparian strip?

A

It blocks the apoplast pathway, ensuring nutrients pass through the cells

44
Q

Give 3 ways water is helped to move up xylem vessels in the stem

A

Root pressure - the push from the water entering the xylem vessels in the roots (doesn’t move water far)
Capillary action ‐ adhesion of water molecules to lignin in narrow xylem vessels can pull the water up the sides of the vessel
Transpiration pull ‐ most of the driving force - evaporation causes cohesion and pulls up water in chains. It creates tension and proves the purpose of lignin: to keep the xylem from collapsing.

45
Q

How does water move across and out of the leaf?

A

Osmosis

46
Q

Define water potential

A

The measure of the tendency of water molecules to move from one place to another

47
Q

Why is water loss via transpiration unavoidable?

A

Gas exchange of carbon dioxide and oxygen occur through open stomata.
Stomata open during the day when it is lightest and warmest.
More stomata open means a larger area for water vapour to diffuse through.

48
Q

What is a xerophyte?

A

A plant that is adapted to reduce water loss by transpiration so that it can survive in very dry (arid) conditions

49
Q

List 7 adaptations of xerophytes

A 
Epidermis covered in hair
Thicker waxy cuticle
Small leaves/needles
Sunken stomata (in pits)
Curled leaves
Small air spaces in mesophyll
Stomata shut in day, open in night
50
Q

What is a hydrophyte?

A

A plant that is adapted to living in water or where the ground is very wet

51
Q

List 3 adaptations of hydrophytes

A

Large air spaces in leaf - keeps leaf afloat so they are in the air and can absorb sunlight
Stomata on the upper epidermis - exposed to the air not the water for gas exchange
Leaf stem has many large air spaces - helps with buoyancy, also allows oxygen to diffuse quickly to the roots for aerobic respiration

52
Q

Explain how having the epidermis covered in hairs reduces transpiration to help xerophytes survive

A

Hairs trap water which stops the wind removing water vapour. More humid air around the leaf reduces water potential gradient - less evaporation and therefore transpiration

53
Q

Explain how a thicker waxy cuticle reduces transpiration to help xerophytes survive

A

Waxy cuticles are hydrophobic
This prevents even more water passing through the epidermis of a plant
Less evaporation causes less transpiration

54
Q

Explain how small leaves/needles reduce transpiration to help xerophytes survive

A

Small surface area and/or fewer stomata causes less evaporation and transpiration

55
Q

Explain how sunken stomata reduce transpiration to help xerophytes survive

A

Pits trap water vapour which stops the wind removing it. More humid air around leaves reduce water potential gradient so less evaporation and transpiration occurs

56
Q

Explain how curled leaves reduce transpiration to help xerophytes survive

A

Lower epidermis is not exposes to the atmosphere
This traps and stops wind removing water vapour
More humid air around the lead reduces the water potential gradient causing less evaporation and transpiration

57
Q

Explain how small air spaces in mesophyll reduce transpiration to help xerophytes survive

A

Less water can evaporate into air spaces and so the leaf quickly becomes saturated
This reduces area for loss of water

58
Q

Explain how having stomata shut during the day and open at night reduces transpiration to help xerophytes survive

A

Dry/hot climates cause more evaporation and transpiration during the day whereas it’s cooler during night

59
Q

Define translocation

A

The transport of assimilates between the sources and sinks of a plant in the phloem tissue. This requires energy

60
Q

What are assimilates

A

Carbon containing compounds produced by a plant using the carbon from carbon dioxide

61
Q

What is a source?

A

Where sucrose and other assimilates are loaded into the phloem e.g. leaf

62
Q

What is a sink?

A

Where sucrose and other assimilate are unloaded from the phloem e.g. flower

63
Q

Explain how sucrose enters the phloem from the source by active loading

A

H+ ions are actively transported (requires ATP) out of the companion cells
This produces a diffusion gradient for the H+ ions
They move back into the companion cell via facilitated diffusion through co‐transporter carrier proteins along with sucrose
Sucrose has been actively loaded into the companion cell
There is a high concentration of sucrose in the companion cell compared to the sieve tube element, so it diffuses into it down the concentration
gradient through the plasmodesmata

64
Q

Explain how sucrose moves along the phloem at the source

A

Sucrose is actively loaded into the sieve tube elements at the source
This reduces the water potential in the sieve tube element
Water enters the sieve tube elements by osmosis
This increases the hydrostatic pressure in the sieve tube element near the source

65
Q

Explain how sucrose moves along the phloem at the sink

A

Sucrose is unloaded at the sink by diffusion (or active transport) and used in respiration/stored
This increases the water potential in the sieve tube element
Water moves into the sink via osmosis down the water potential gradient
This reduces the hydrostatic pressure in the sieve tube element near the sink
Water in the sieve tube element at the source moves down the hydrostatic gradient from source to sink
This creates a flow which carries the sucrose and other assimilates along the phloem via mass flow either up or down the plant

66
Q

How are sieve tube elements adapted to allow mass flow to occur? (3)

A

Elongated elements, joined end to end to form a column
Sieve plates with pores in end walls allow sucrose through
Little cytoplasm and no nucleus ‐ less resistance to transport

67
Q

Give 3 pieces of evidence which prove phloem is used in translocation

A

Radioactively labelled carbon dioxide supplied for photosynthesis appears in phloem
Aphids feeding on plant stems insert mouthparts into phloem
Sugars collect above ring when tree is ringed to remove phloem

68
Q

Give 3 pieces of evidence which prove ATP is needed in translocation

A

Companion cells have many mitochondria
Translocation is stopped if a poison which stops ATP production is given
Flow of sugars is very high that ATP must be used ‐ much faster than would be possible with diffusion

69
Q

Give 2 pieces of evidence that prove translocation takes place

A

pH of companion cells is higher than surrounding cells (H+ ions reduce pH)
Concentration of sucrose is higher in source than sink

70
Q

Give 3 pieces of evidence against translocation

A

Not all solutes in phloem move at same rate
Sucrose moved to all parts of plant at same rate and doesn’t go to places with lowest concentration faster
The role of sieve plates is unclear

71
Q

Give 4 reasons why transpiration is important

A

It transports usefulness mineral ions up the plant
It maintains cell turgidity
Supplies water for growth, cell elongation and photosynthesis
Supplies water that, as it evaporates, can keep the plant cool on a hot day

Biology (25 decks)

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