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My AS level biology - OCR A > 3.3 - Plants > Flashcards

3.3 - Plants Flashcards

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1
Q

Name the two specialised transport vessels in plants

A

Xylem and phloem

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2
Q

Why do plants need transport systems?

A

They need a transport system to move food, water and minerals around the plant.
They have no heart, or circulatory system, so a specialised transport system makes up for it

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3
Q

What do plants need to transport around their structure?

A

Water and minerals from the roots up to the leaves(in xylem)

Sugars from the leaves to the rest of the plant(in phloem)

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4
Q

Definition of dicotyledonous plant

A

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

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5
Q

Definition of vascular bundle

A

Consists of cells specialised for transporting fluids by mass flow
- e.g. xylem and phloem

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6
Q

Definition of meristem

A

A layer of dividing cells, called the pericycle as well.

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7
Q

What do the xylem transport and in which direction?

A

The xylem vessels transport water and mineral ions up the plant

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8
Q

Where are the xylem and phloem found in the stem?

A

Vascular Bundle found at the outer edge of the stem
Xylem - towards the inside of the vascular bundle; closest to centre
Phloem - found towards outside of vascular bundle

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9
Q

Where are xylem and phloem tissue found in the root?

A

Vascular bundle found in the centre of the root
Xylem - ‘x’ shape in middle of vascular bundle
Phloem - in between arms of ‘x’ shaped tissue

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10
Q

List all structures of a root

A 
Cortex
Medulla
Phloem
Xylem
Endodermis
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11
Q

List all structures of a stem

A 
Sclerenchyma
Collenchyma
Cortex
Phloem
Xylem
Medulla
Cambium
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12
Q

List all structures of the leaves

A

Phloem
Xylem
Central Midrib
Small vein in leaf lamina

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13
Q

Adaptations of the xylem vessel

A

Made from dead cells formed end to end to form a continuous column - allows smooth flow of water in xylem vessel
Tubes are narrow - water column does not break easily and capillary action can be effective
Bordered pits in walls - allow water to move sideways form one vessel to another
Lignin deposited in walls in spiral - allows stem or branch to bend

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14
Q

How do xylem vessels form?

A

Lignin impregnates early xylem
Waterproofs and kills the cells
Long column of dead cells with no contents forms - called xylem vessel
This prevents vessel from collapsing
Lignin thickens and forms spiral in cell wall
This allows some flexibility to stem or branch
Where lignification is not complete, bordered pits form
These allow water to move sideways into cells

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15
Q

How does the xylem allow for a continuous flow of water?

A

There are no cross - walls
There are no cell contents, nucleus or cytoplasm(empty lumen)
Lignin thickening prevents walls from collapsing

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16
Q

Where are xylem and phloem found in the leaves?

A

Vascular bundles form midrib and veins of a leaf
Xylem - on top of phloem, further in centre
Phloem - under xylem, nearer outside of centre

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17
Q

Function of sieve tube elements

A

Make up the tubes in the phloem tissue that carry sap up and down the plant
Separated by sieve plates

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18
Q

Features of the sieve tube elements

A

Elongated sieve tube elements lined up end to end to form sieve tubes
Contain no nucleus, very little cytoplasm, (space for mass flow to occur)
Sieve plates - perforated cross walls
(Allow movement of sap from one element to next)
Very thin walls

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19
Q

Function of companion cells

A

Cells that help load sucrose into sieve tubes

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20
Q

Features of the companion cells

A

Numerous mitochondria to produce ATP
(Needed for metabolic processes)
Carry out metabolic processes needed to load assimilates actively into the sieve tubes

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21
Q

Definition of plasmodesmata

A

Gaps in the cell wall containing cytoplasm that connects two cells

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22
Q

What are the three pathways water can take in a plant?

A

Apoplast Pathway
Symplast Pathway
Vacuolar Pathway

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23
Q

Describe the apoplast pathway

A

Water passes through spaces in cell walls and between cells
Does not pass through plasma membranes
Water then moves by mass flow rather than osmosis
Dissolved mineral ions and salt can be carried with the water

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24
Q

Describe the symplast pathway

A

Water enters the cell cytoplasm through plasma membrane.

Passes through plasmodesmata from one cell to the next

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25
Q

Describe the vacuolar pathway

A

Similar to symplast pathway
However, water not confined to cytoplasm of the cell
Able to enter and pass through vacuole as well

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26
Q

List two main features of the phloem vessel

A

Sieve Tube Elements

Companion Cells

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27
Q

What do the phloem transport and which direction?

A

They phloem vessels transport sucrose and other assimilates up and down the plants

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28
Q

Definition for diffusion

A

Movement of gas particles from an area of high concentration to an area of lower concentration - down the concentration gradient

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29
Q

Definition for osmosis

A

The movement of water particles from an area of higher water potential to an area of lower water potential

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30
Q

Definition for active transport

A

The movement of particles form an area of lower concentration to higher concentration, against the concentration gradient.
(Opposite direction to that of diffusion or osmosis)

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31
Q

Outline movement of water through water potential in the cell

A

Water always moves form region of higher water potential to area of lower water potential.
Plant cell contains mineral ions and solutes that reduce water potential.
Fewer ‘free’ water molecules available means water potential in plant cells is always negative

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32
Q

What happens if you place a plant in pure water(description of water uptake)?
Why?

A

Takes in water by osmosis, higher water pot in water than in cell, so water moves into cell
Cell becomes turgid, and water in cell exerts pressure on cell wall
Pressure pot increases, reducing influx of water

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33
Q

Describe water loss in a plant

A

Water lost by osmosis, down a water potential gradient
Cytoplasm and vacuole shrink, and cytoplasm no longer touching cell wall
Cell is no longer turgid
The cell is now flaccid

34
Q

Definition of transpiration

A

Loss of water vapour from the upper parts of the leaf, usually leaves.

35
Q

Movement water between cells

A

If touching each other, water passes from one cell to another
Move from area of higher water pot to lower water pot, by osmosis

37
Q

Importance of transpiration

A

Transports mineral ions up the plant
Maintains cell turgidity
Supplies water for growth, cell elongation and photosynthesis
Helps cool plant down on hot day

38
Q

What apparatus would be used to measure water uptake in a plant?

A

A potometer

39
Q

Why is the rate of water uptake in a potometer only an estimate for rate of transpiration.

A

Not all water uptake by the plant is by transpiration, some used by other metabolic processes, e.g photosynthesis

40
Q

What effect does light intensity have on rate of transpiration?

A

Higher light intensity means more transpiration

Stomata open more so more water vapour leaves the cell

41
Q

What effect does temperature have in the rate of transpiration?

A

Higher temperature means higher rate of transpiration
Water molecules have more KE, so increases diffusion through stomata
Increases rate of evaporation, so water pot in leaf rises
Decreases water vapour pot in air, allows faster diffusion of molecules out of leaf

42
Q

How does humidity affect rate of transpiration?

A

Higher humidity in air decreases rate of water loss.

Smaller water vapour pot gradient between air spaces in the leaf and the air outside

43
Q

How does wind affect transpiration?

A

More windy conditions = more water loss = more transpiration
Carries water vapour that has just diffused out of the leaf.
This maintains a high water vapour pot gradient

44
Q

How does water availability affect transpiration?

A

If little water in soil, plant cannot replace water that is lost.
If insufficient water in soil, stomata close and leaves wilt

45
Q

What is the transpiration stream?

A

The movement of water from the soil, through the plant,

to the air surrounding the leaves

46
Q

How does water enter the plant?

A

Via the root hair cells

47
Q

Definition for adhesion

A

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

48
Q

Definition for cohesion

A

The attraction between water molecules caused by hydrogen bonds

49
Q

What is the outermost layer of cells in a plant?

A

The epidermis

50
Q

Adaptations of the root hair cell

A

Long and narrow - larger SA:V ratio for faster absorption of substances
Cell sap in vacuoles - high conc. of nutrients and sugars, lowers water pot in cell so more water enters by osmosis into cell
Many mitochondria - more ATP production for active transport of mineral ions into root hair cell

51
Q

How does water move into the root hair cells?(part of transpiration stream)

A

Soil particles are surrounded by water
Root hair cells contain cell sap in vacuoles,
This lowers water pot in cell, so water moves into cell by osmosis

52
Q

How do minerals move into root hair cell?(Transpiration stream)

A

Mineral ions are actively absorbed from the soil, lower pot in soil than in cell(vacuole)
This makes water pot of cytoplasm more negative

53
Q

Outline the transpiration stream

A

Minerals actively transported into xylem
Lowers water pot in xylem
Water follows by osmosis
Water moves by mass flow through cohesion
Pulled upwards from tension above
Low hydrostatic pressure created as water leaves xylem, so tension created
Water moves across leaf, and diffuses from stomata

54
Q

What is the function of the casparian strip?

A

Stops flow of water in apoplast pathway

Water then has to go through symplast pathway

55
Q

Function of endodermis

A

Contain within their walls:
-Casparian strips - water-impermeable deposits of suberin that regulate water and mineral uptake by the roots via the apoplast pathway

56
Q

What is capillary action?

A

Adhesion pulls water up the sides of the xylem vessel

57
Q

What is plasmolysis in plant cells?

A

Where too much water leaves the cell, and the plasma membrane loses contact with the cell wall

58
Q

What are xerophytes?

A

They are plants that are adapted to living in arid conditions

59
Q

What are hydrophytes?

A

Plants that live in water
Have to adapt to get oxygen
Have to adapt and to stay afloat,
Need to get sunlight for photosynthesis

60
Q

Adaptations of xerophytes

A 
Leaf is rolled
Thick waxy cuticle
Stomata on inside of rolled leaf
Stomata in pits
Dense spongy mesophyll
61
Q

Adaptations of hydrophytes

A

Many large air spaces -
Stomata in upper epidermis - exposed to air to allow gaseous exchange
Leaf stem has many large air spaces - helps with buoyancy

62
Q

Give an example of a xerophyte

A

Cactus

Marram Gas

63
Q

Example of a hydrophilic plant

A

Water lily

64
Q

Definition of assimilates

A

Substances that have become a a part of the plant.

Made from substances from the environment

65
Q

Source definition

A

Part of the plant that materials into the transport system

E.g. leaves

66
Q

Definition of a sink

A

Where materials are removed from the transport system

E.g. roots store sucrose as starch

67
Q

What is an example of both a source and a sink?

A

Roots:
Store sucrose as starch during summer
Starch converted back into sucrose and other assimilates during winter

68
Q

What is translocation?

A

The movement of assimilates through the plant

69
Q

Active loading process

A

Hydrogen ions actively pumped out of companion cell using ATP
High conc of h+ ions causes facilitated diffusion of H+ ions back into cell with sucrose through contransport
Higher conc of sucrose in companion cell means sucrose moves through plasmodesmata into sieve tube.

70
Q

Mechanism for water moving from soil to xylem

A

-Minerals actively transported into root hair cell (through carrier proteins)
• Water moves via osmosis from soil into root hair cells across cell surface
membrane (through aquaporins) down the water potential gradient
• Water can move via cell walls in the apoplast pathway
• Water can move via the cytoplasm in the symplast pathway, through plasmodesmata, linking the cytoplasm in neighbouring cells
• Water also moves through vacuoles via the vacuolar pathway
• At the endodermis, the Casparian strip (made of suberin) blocks the apoplast pathway
• This makes the water enter the symplast pathway
• Water potential is most negative in the xylem due to the active transport of minerals into it
• This causes water to move into the xylem from the cells of the endodermis and cortex

71
Q

How does transpiration result in the movement of water up a stem?
(model answer)

A

• Water evaporates from the surface of the mesophyll cells in the leaf and forms water vapour
• Water vapour diffuses from a high water potential to a lower water potential out of the leaf, through the stomata
• More water is drawn from the mesophyll cells via the symplast/apoplast pathways in the leaf replacing the water that has evaporated
• Bonus: This occurs via osmosis down the water potential gradient in the symplast pathway and mass flow in the apoplast pathway
• This water is replaced by water from the xylem vessels (moving out via osmosis)
• The loss of water from the xylem causes a low hydrostatic pressure at the top of the xylem
• Water moves from a higher pressure (roots) to a lower pressure (down the pressure gradient) under tension
• Water is therefore pulled up the xylem by mass flow
• The cohesion of water molecules due to the
hydrogen bonds between them causes them to stay as a long unbroken column of water during this process ­ the transpiration stream

71
Q

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
72
Q

How sucrose moves along phloem at a sink?

A
  • Sucrose is unloaded at the sink by diffusion/active transport and used in respiration/stored
  • This increases the water potential in the sieve tube element
  • Water moves out of the sieve tube element via osmosis down the water potential gradient
  • This reduces the hydrostatic pressure in the sieve tube element
  • 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
73
Q

How are guard cells adapted to their role?

A
  • Able to change Shape/ bend
  • Ion pumps to transport proteins in plasma membrane
  • Many mitochondria for ATP production for energy
74
Q

Two places where water can be lost from a leaf

A
  • Stomata

- Epidermis/cuticle

75
Q

The cohesion-tension theory is often used to explain the mechanism by which water moves up the xylem from the roots to the leaves.
Use this theory to explain how water moves from the roots to the leave
(3 Marks)

A

evaporation of water vapour at top of plant from stomata
creates tension in xylem
water molecules stick together as they are cohesive due to hydrogen bonding between water molecules
form a chain or long column of water
column / chain pulled up by tension

76
Q

Difference between transpiration and transpiration stream

A

Transpiration:
- loss of water vapour via diffusion from the stomata in the leaf surface

Transpiration stream:
-how water moves up the xylem vessels from the roots to the leaves

77
Q

Function of sunken pits in the xylem

A
  • Allows water to move out sideways between xylem vessels to supply water to other tissues in the plant
78
Q

Function of the spiral band of lignin in xylem

A
  • lignin waterproofs and kills the cell/wall
  • lignin thickens and strengthens the xylem wall - prevents collapse of xylem under tension
  • spiral pattern allows for increased flexibility and movement of vessel
  • improve adhesion of water molecules - increase capillarity
79
Q

Explain how mass flow of phloem sap occurs in plants with a vascular system.
(3 Marks)

A
  • Sucrose and assimilates collect in the sieve tube elements
  • Assimilates enter sieve tube at source and lowers water potential inside
  • Water enters sieve tube by osmosis - down water potential gradient
  • hydrostatic pressure increases
  • assimilates leave sieve tube at the sink
  • increases water potential in sieve tubes at sink
  • water leaves sieve tube by osmosis
  • lowers hydrostatic pressure
  • assimilates move from high to low hydrostatic pressure/down pressure gradient
  • moves from source to sink
80
Q

Give three properties of cellulose that make it suitable as the basis for plant cell walls.
(3 Marks)

A
  • Insoluble - do not affect water potential of the cell
  • high tensile strength - provide support and maintain structural integrity of the cell
  • Unreactive
  • Flexible - allows plant to bend
  • Can form hydrogen bonds with neighbouring chains - increased structural support
81
Q

Definition for osmosis

A

Movement of water from a less negative (higher) water potential to a more negative (lower) water potential down the water potential gradient

My AS level biology - OCR A (19 decks)

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