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Biology OCR > Transport In Plants > Flashcards

Transport In Plants Flashcards

1
Q

What substances are required by a plant

A

Carbon dioxide, water, oxygen, organic molecules, minerals ions

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2
Q

Why don’t plants require a transport system for oxygen and carbon dioxide

A

Plants have a low metabolic rate, oxygen and carbon dioxide can be transported due to a small diffusion distance (opening in the stomata)

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3
Q

What does the xylem transport

A

Water and minerals

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4
Q

What does the phloem transport

A

Sugars

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5
Q

What does the term ‘sources’ mean

A

Leafs

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6
Q

What does the term ‘sinks’ mean

A

Storage organs

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7
Q

What do plants require a mass transport system for

A

Water, mineral ions and organic molecules

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8
Q

What are cotyledons

A

Leaves that come out of the seed that provide nutrients to the plant till it can photosynthesise

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9
Q

What are some characteristics of monocotyledonous plants

A

One cotyledon leaf, parallel leaf veins

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10
Q

What are some characteristics of dicotyledonous plants

A

Two cotyledon leaves, net like leaf veins

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11
Q

Describe how vascular tissue is arranged in a leaf of a dicotyledonous plant

A

The veins branch from a central vein to form a branching network

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12
Q

What’s the epidermis

A

tissue that forms the outer layer of root and contains root hair cells for the absorption of mineral ions

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13
Q

What’s the phloems function

A

Transports sucrose up or down

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14
Q

What’s the xylems function

A

Transports water and mineral ions upwards from the roots

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15
Q

What’s the cortex

A

tissue that lies beneath epidermis and contains unspecialised cells that play a role in storage

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16
Q

What’s the endodermis

A

A layer of cells that surrounds the vascular bundle in the root, and plays a key role in transporting water to the xylem

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17
Q

What’s the pericycle

A

tissue that is made of meristem cells, and lies just inside the endodermal layer in the root

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18
Q

What’s the vascular cambium

A

tissue that lies between the xylem and phloem and is made up of meristem cells

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19
Q

Describe how vascular tissue is arranged in a root of a dicotyledonous plant

A

Xylem forms an ‘X’ at centre of root and phloem lies between arms

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20
Q

Describe how vascular tissue is arranged in a stem of a dicotyledonous plant

A

Vascular bundles arranged in a ring towards outside of stem. Xylem nearer centre of stem.

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21
Q

Identify a suitable stain to show the position of xylem tissue and explain why it is used.

A

Toluidine. Acts as a differential stain.
Stains different cells different colours so they can be distinguished.
Non-lignified tissue is stained pink/purple. Lignified tissue (xylem) is stained green/blue.

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22
Q

What specialised cells does a xylem have and what’s their function

A

dead xylem vessels to transport water and mineral ions upwards from the roots;
dead sclerenchyma with thickened cell walls for support and living parenchyma cells that act as packing tissue.

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23
Q

What specialised cells does the phloem have and what’s their functions

A

sieve tube elements for the transport of the products of photosynthesis and companion cells that are important in loading assimilates e.g. sucrose into the phloem sieve tubes.

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24
Q

Identify three features of xylem vessels that ensure the flow of water is not impeded.

A

No end cell walls
No cell contents
Thickening and lignification of cell wall prevents the wall from collapsing

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25
Q

What is the role of lignification?

A

Waterproofs wall to reduce water loss from xylem vessel
Supports and strengthens wall to prevent collapse under tension
Increases adhesion of water molecules to vessel walls to allow capillary action

26
Q

What are bordered pits and what is their role?

A

Non-lignified areas of cell wall
Permeable to water to allow water to leave a xvlem vessel and enter an adiacent vessel e.g. to by-pass an air lock or to pass into neighbouring (living) cells.

27
Q

Suggest why young plants have spiral, annular or reticulate thickening but older plants contain more vessels with pitted walls.

A

Allows xylem to stretch as plant grows and enables stem to bend so it doesn’t break

28
Q

Explain why companion cells contain large numbers of mitochondria and ribosomes?

A

Mitochondria to produce ATP for active loading of sucrose into sieve tube
Ribosomes on RER to synthesise transport proteins e.g. proton pump, sucrose H* cotransporter protein that are required for active loading

29
Q

Describe the apoplast pathway

A

Water moves through cell walls and extracellular spaces.
No membranes are crossed so mineral ions can be carried by water.

30
Q

Describe the Symplast pathway

A

Water crosses the plasma membrane into the cytoplasm and can move from one cell to another through the plasmodesmata

31
Q

Describe the Vacuolar pathway

A

Water crosses the plasma membrane into the cytoplasm and vacuoles and can move from one cell to another through the plasmodesmata

32
Q

How are root hair cells adapted?

A

Large surface area
Many mitochondria to produce
ATP for active transport
Many carrier proteins for active transport

33
Q

What is the Casparian strip? Describe its role.

A

Cells in endodermis contain a band of suberin in cell wall that forms a waterproof barrier called the Casparian strip.
This blocks the apoplast pathway. Water and mineral ions must cross the plasma membrane and enter the endodermal cells to follow the symplast pathway.

34
Q

How are mineral ions carried across the root cortex?

A

Via apoplast pathway until endodermis when both water and mineral ions must enter endodermal cells

35
Q

How is the movement of mineral ions into the xylem controlled?

A

Mineral ions require carrier proteins to cross the plasma membrane and enter endodermal cells. The type / number of carrier proteins can be controlled by the cell.

36
Q

What is transpiration?

A

Transpiration is the loss of water by evaporation from the aerial parts of a plant (mainly the leaves)

37
Q

explain why transpiration is an inevitable consequence of gas exchange?

A

Stomata open during the day to allow gas exchange for photosynthesis but water is also lost via transpiration.

38
Q

explain how water vapour lost through open stomata is replaced with water taken from the xylem.

A

Water evaporates from the cell walls of mesophyll cells into the air spaces in the leaf
Water vapour diffuses down a water vapour potential gradient out of the leaf through an open stoma
Lost water is replaced by water taken from the xylem vessel, that moves through the mesophyll cells of leaf by osmosis down a water potential gradient via either the symplast or apoplast pathways.

39
Q

State the three processes that contribute to water movement up a stem

A

Root pressure / Transpiration pull / Capillary action

40
Q

True or false “Mineral ions diffuse into xylem lowering the water potential”

A

False

41
Q

True or false “Mineral ions are actively transported into xylem lowering the water potential”

A

True

42
Q

True or false “Water enters xylem by osmosis via the apoplast pathway”

A

False

43
Q

True or false “Water enters xylem by osmosis down the water potential gradient”

A

True

44
Q

True or false “Water entry increases the hydrostatic pressure at the base of the xylem vessel”

A

True

45
Q

True or false “Water entry decreases the hydrostatic pressure at the base of the xylem vessel”

A

False

46
Q

Is the movement of water up the xylem a passive or active process

A

Passive

47
Q

Explain the cohesion tension theory

A

The water molecules are attracted to each other by forces of cohesion, due to the hydrogen bonds between them.
Water is pulled up xylem vessels as a continuous column by mass flow, under tension due to transpiration.

48
Q

What is capillary action

A

Water molecules are also attracted to lignin in the walls of the xylem vessel - this is called adhesion and is responsible for capillary action
Capillary action is increased by narrow xylem vessels and helps prevent the water column dropping back down.

49
Q

What happens if a water column is broken

A

Water can move sideways through the bordered pits to another xylem vessel to by-pass the air lock

50
Q

What is the transpiration stream

A

Movement of water up stem in xylem vessels from roots to leaves

51
Q

Why is the transpiration stream useful in plants

A

Supplies water to cells in leaf for photosynthesis
Enables plant cells to elongate
Keeps plant cells turgid supporting the plant
Transport of mineral ions from soil
Evaporation cools leaf

52
Q

Does the number of leaves increase or decrease the rate of transpiration

A

Increase as it increases the surface area available for evaporation

53
Q

Does a high number and large size of the stomata increase or decrease transpiration

A

Large stomata and lots of them increase diffusion

54
Q

What is the role of the stomata

A

Stomata open during the day to allow gas exchange for photosynthesis but water is also lost via transpiration
If water uptake from the soil is sufficient: guard cells are turgid and the stomata are open
If water loss in transpiration is greater than uptake via the roots: guard cells become flaccid and the stomata close to reduce water loss

55
Q

Comment on the number/size of stomata found in the upper and lower epidermis.

A

More and larger stomata in lower epidermis.
Cooler (not in direct sunlight) and less air movement so less water loss

56
Q

Why do deciduous plants lose their leaves in winter?

A

Light intensity is lower for photosynthesis so leaves are lost to reduce water loss by transpiration when less water may be available if the ground is frozen

57
Q

What is a potometer

A

A simple apparatus used to measure the rate of water uptake from a cut leafy shoot and so estimate the rate of water loss by transpiration

58
Q

Why is it important to form an airtight seal? How can this be achieved? (Potometer)

A

The airtight seal is necessary, or water will not be drawn up the capillary tube and no air bubble movement will be possible.
Use Vaseline / Plumber’s Mate to help make a tight seal

59
Q

Why does the apparatus only provide an estimate of transpiration?

A

Potometer measures water uptake not water loss. We assume all water taken up is lost in transpiration, but some is used by cells e.g. in photosynthesis, to maintain turgor

60
Q

How could water loss be estimated directly in this apparatus?

A

Weigh the potometer at the beginning and then after a set period of time. The fall in mass will be due to water loss (assuming no leaves etc are lost).

61
Q

Compare the use of bubble and mass potometers.

A

A potometer where movement of a bubble is measured is more difficult to set up since it must be air-tight but quicker to obtain data.
A mass potometer must be left longer (e.g. 2 days) to produce a measurable change in mass.

62
Q

How do you calculate water uptake

A

volume = distance moved by bubble x pieR2

Biology OCR (12 decks)

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