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Alevel Biology OCR A > 3.1.3 Transport in Plants COMPLETE > Flashcards

3.1.3 Transport in Plants COMPLETE Flashcards

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1
Q

Why plants need a transport system

A
  • Plants are multicellular so not all in direct contact with the environment
  • Allows metabolic reactions to occur and the removal of waste.
  • So plants continue growing, allows them to become large, water transported a long way
  • Their large size means they have a small SA:V
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2
Q

What plants need to transport

A
  • Water & Minerals from soil to cells via roots
  • CO2 during daytime
  • O2 for respiration
  • Assimilates such as sucrose and amino acids
  • Plant Hormones to where they’re needed
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3
Q

Xylem

A

Transport water and mineral ions up the plant

Vascular Tissue

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4
Q

Phloem

A

Transports assimilates such as sucrose up and down the plant

Vascular Tissue

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5
Q

How substances are transported around the plant

A

Diffusion, osmosis, active transport, bulk transport

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6
Q

Vascular Tissue in a young root

A

Xylem forms a cross in the centre, contains an
Endodermis- sheath surrounding the vascular bundle to help get water in
Pericycle- Layer of meristem which is undifferentiated

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7
Q

Vascular Tissue in young stem

A

Multiple bundles circle around a pith in the centre, contains
Cambium- Layer of undifferentiated meristem
Parenchyma- Packing and support
Collenchyma- provide structure for growth in shoots and leaves

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8
Q

Distribution of vascular tissue in the leaf

A

Vascular bundles form the midrib (main vein) and the side veins, the branched network helps to support the leaf. Airspaces are of photosynthesis

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9
Q

Structure of the Xylem Vessels

A

Starts as a column of live cells which lay down lignin, this makes them waterproof, the cell dies along with its contents. No endplates mean theres a continuous column, there are gaps in the lignin called pits these let water move across

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10
Q

Adaptions of the Xylem Vessels

A
  • Continuous column with no contents so the flows not impeded
  • Lignin prevents walls collapsing and allows adhesion of water
  • Pits allow lateral sideways movement
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11
Q

Xylem Parenchyma

A

Living cells that form packaging tissues and stores food, bitter tasting to prevent attack

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12
Q

Structure of the Phloem Tissue

A

Consists of more than one cell:

  • Sieve tube elements
  • Companion Cells
  • Parenchyma Cells
  • Scleroid’s and fibres
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13
Q

Sieve Tube Elements

A

Contains a thin layer of cytoplasm, mitochondria and endoplasmic reticulum. No nucleus or ribosomes. Thin non lignified walls with perforated edges forming sieve plates

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14
Q

Companion Cells

A

Linked to the STE by plasmodesmata, have dense cytoplasm with large nucleus, contain more mitochondria and ribosomes than usual and have no large permanent vacuole.

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15
Q

Transporting water up Plants

A
  1. Water uptake near roots
  2. Water enters the xylem
  3. Water moves up the xylem
  4. Water moves from the xylem to leaf cells via pits
  5. Evaporation of water into leaf airspaces
  6. Transpiration of water vapour through open stomata
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16
Q

Water Potential

A

The tendency of water molecules to leave a solution, the more solute in a solution the lower the water potential

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17
Q

Turgid

A

Water enters as a higher water potential outside the cell, this prevents the plant wilting

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18
Q

Plasmolysed

A

Water moves out the cell as a lower water potential outside

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19
Q

Mineral ion and water uptake from the soil

A

The epidermis has root hair cells to increase SA, Mineral ions are absorbed by active transport alongside amino acids and sugar. These lower the water potential of the cytoplasm so water follows via osmosis.

20
Q

Movement of water across a root

A
  1. Apoplast pathway
  2. Symplast Pathway
  3. Vacuolar Pathway
21
Q

The Apoplast Pathway

A

The cellulose cell wall is fully water permeable so water and dissolved minerals move through them. It doesn’t go through the cell membrane as is not osmosis. As the water moves up and is cohesive theres a continuous flow.
Stops at the endodermis

22
Q

The Symplast Pathway

A

Water travels through the cytoplasm, plasmodesmata connect the cells and they’re made of thin strands of cytoplasm. Not osmosis as there’s no barrier

23
Q

The Vacuolar Pathway

A

Similar to the symplast pathway but can also travel through vacuoles.

24
Q

Casparian Strip

A

Made from waxy Suberin, blocks the apoplast pathway and forces water into cells via symplast pathway. Water then has to pass through the cell surface membrane which is selectively permeable. Active transport moves the mineral ions.
water cannot pass back into the apoplast pathway

25
Q

How does water get pulled up the stem

A
  1. Root pressure
  2. Transpiration Pull
  3. Capillary Action
26
Q

Root Pressure

A

Water is forced up through the stem when mineral ions are moved into the xylem by active transport.
Metabolic poison, temp and O2 conc affect it.
Cannot support really tall trees

27
Q

Transpiration Pull

A

Cohesive forces attract water, this forms a large column in the xylem. When water is lost via transpiration more water is pulled up.
This creates tension, lignin prevents collapse.
If one column breaks water can move through pits into another

28
Q

Capillary Action

A

Adhesive forces between water and the narrow walls of the xylem help pull it up, allows water to move against gravity, narrower container means more contact so greater adhesive forces.

29
Q

Transpiration

A

The loss of water vapour from the upper parts of the plant, especially the leaves
Water evaporates into the air spaces and then leaves by diffusion out of the stomata
This maintains the water potential gradient

30
Q

Measuring rate of transpiration

A

Easiest way is to measure water uptake as they’ll roughy be the same.
Fill apparatus up with waterhen put a freshly cut shoot in it, seal joints with vaseline, dry the leaf, and then measure how much water is moving under constant conditions

31
Q

Factors affecting Transpiration rate

A
  • Number of leaves
  • Number of stomata
  • Presence of a waxy cuticle
  • Light
  • Temperature
  • Relative Humidity
  • Wind
  • Water availability
32
Q

Xerophytes

A

Plants that are adapted to dry conditions such as marram grass

33
Q

Features of Xerophytes

A
  • Spikes to reduce SA
  • Hairs and rolled leaves to create a microclimate of humid air
  • Succulents store water in special parenchyma tissues
  • Thick waxy cuticle minimise diffusion
  • Long tap roots to access water
34
Q

Hydrophytes

A

Plants that live in water, either submerged or on the surface. They need to ensure enough O2, and maintain transpiration for mineral ions

35
Q

Features of Hydrophytes

A
  • Wide leaves to capture more light
  • Air spaces for buoyancy
  • Stomata on the upper surface for gas exchange
  • No waxy cuticle as plenty of water
  • Reduced structure as water supports them
36
Q

Translocation

A

The movement of assimilates (product of photosynthesis) up and down the plants phloem. Glucose is converted into sucrose

37
Q

Sources

A

Where sugars are produced, and assimilates are loaded. Is an active process in the STE and water follows by osmosis increasing hydrostatic pressure
e.g. in germinating seeds

38
Q

Sinks

A

Where the assimilates are removed from the phloem and the sugars are used. Sucrose leaves STE by diffusion water potential increases in sap and water follows down the gradient, decreasing hydrostatic pressure.
e.g. in the meristem or growing roots

39
Q

Mass Flow

A

Water moves in at the source and out at the sink provides a pressure difference forcing the sap to move

40
Q

Loading sucrose into phloem

A

Either via the symplast route where it moves through the plasmodesmata
or the apoplast route where it passes through the cell walls

41
Q

Movement of H ions

A

ATP is used to pump hydrogen ions out of the companion cells, this leads to a higher concentration outside. They move back into the companion cells from STE with a co transporter protein, these also carry sucrose with them.

42
Q

Supporting evidence: How do we know the Phloem is used

A

RADIOACTIVE CARBON is incorporated into carbohydrates, aphids drink phloem sap, head snapped and sample can be taken to see if its present.
TREE RINGING is when bark is removed (phloem) the tree dies due to lack of energy

43
Q

Supporting evidence: How do we know it needs metabolic energy

A

Lots of mitochondria in the companion cells, when metabolic poisons used translocation is stopped

44
Q

Supporting evidence: How do we know translocation uses this mechanism

A

The pH of the sap is 8 which is expected as H ions are being pumped out, also more negative inside as H+ are outside . Theres also a higher concentration of sucrose in the source than sink,

45
Q

Supporting evidence: Against this mechanism for translocation

A

Not all solutes move at the same rate, sucrose moves at a constant rate regardless of concentration. Its also unclear what the role of the sieve plates is

Alevel Biology OCR A (26 decks)

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