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A Level Biology > Exchange And Transport In Plants > Flashcards

Exchange And Transport In Plants Flashcards

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1
Q

Describe the uptake of water and minerals in dicotyledonous plants. (Write it out)

A

Water from the soil is drawn in through the root hair cells via osmosis, across its partially permeable membrane. There are also lots of mitochondria for active transport in order to uptake minerals. In addition, root hair cells are long, which increase its surface area. This increases the area in which water can move from an area of higher water potential to an area of lower water potential.

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2
Q

Why do plants require a transport system?

A
  • Metabolic demands
  • Size
  • SA:V
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3
Q

What is a dicotyledonous plant?

A

A plant that contains two cotyledons - organs that act as food stores while the embryo plant develops.
- Usually woody, with lignified tissues and a long life cycle.

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4
Q

What is the function of translocation?

A
  • Transport or organic material (e.g. sugars)

- Sugar is transported in the form of sucrose

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5
Q

What plant vessel does translocation take place in?

A

Phloem

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6
Q

What is the purpose of transporting sugar in the form of sucrose?

A
  • Glucose doesn’t get used up in respiration
  • Less reactive than glucose
  • Less osmotic effect
  • More energy efficient
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7
Q

What is a source?

A

A source is where sucrose is being transported from and loaded into the phloem.

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8
Q

What are examples of sources?

A

Photosynthetic tissues and leaves

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9
Q

What is a sink?

A

Where sucrose is being transported to and unloaded from the phloem.

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10
Q

What are examples of sinks?

A

Roots, meristematic tissues, any growing regions

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11
Q

What are two pathways in which sucrose can enter the phloem?

A
  • Symplastic pathway

- Apoplastic pathway

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12
Q

What type of process is the symplastic pathway?

A

Passive process

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13
Q

What type of process is the apoplastic pathway?

A

Active pathway

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14
Q

Describe the symplastic pathway in translocation?

A

Sucrose moving through the cytoplasm of the mesophyll cells by diffusion, through plasmodesmata.

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15
Q

Describe the apoplast pathway in translocation

A
  • Sucrose travelled through the cell walls and intercellular spaces to the companion cells
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16
Q

How does sucrose reach the companion cell?

A
  1. ATP is broken down, it is turned into ADP + P, which releases energy.
  2. Hydrogen ions are then able to be pumped out of the companion cells, via a proton pump.
  3. This creates a steep hydrogen concentration gradient outside the cell.
  4. In order for hydrogen ions to return to companion cell, they must have a cotransporter - sucrose.
  5. Sucrose is now present in the companion cell and then can be loaded into the phloem.
17
Q

How does sucrose move along the phloem?

A
  1. Sucrose is loaded into the sieve tube element, which reduces water potential.
  2. Water follows by osmosis and increases hydrostatic pressure.
  3. Water moves down sieve tube down from higher hydrostatic pressure at source to lower hydrostatic pressure at sink.
  4. Sucrose is removed from the sieve tube by the surrounding cells, which increases the water potential.
  5. Water moves out of sieve tube and reduces the hydrostatic pressure.
18
Q

What is a xerophyte?

A

Plants that live in hot and dry conditions

19
Q

How do xerophytes allow for water conservation and survival?

A

Reduced transpiration:

  • Thick waxy cuticle
  • Reduced numbers of stomata
  • Reduced leaves
  • Leaf loss
  • Root adaptions:
    Long deep roots to reach water table
    Shallow wide roots to collect water from large surface area

Creation of microclimates (reduces water potential gradient - reducing transpiration):

  • Hairy leaves
  • Sunken stomata
  • Curled leaves
20
Q

What are hydrophytes?

A

Plants that live in extremely wet conditions

21
Q

What is an example of a xerophyte?

A

Marram grass

22
Q

What is an example of a hydrophyte?

A

Water lilies

23
Q

How do hydrophytes allow for survival in wet conditions?

A
  • Very thin waxy cuticle - more transpiration
  • Always open stomata
  • Wide, flat leaves - more photosynthesis
  • Small roots
  • Air sacs - allows leaves to float
24
Q

How do succulents allow xerophytes to survive in dry conditions?

A
  • Contain special parenchyma tissue in stems and roots.

- Have a swollen appearance and can be used in a time of drought.

25
Q

How does aerenchyma allow hydrophytes to survival in extremely wet conditions?

A

Contains parenchyma tissues which contain air spaces that provide buoyancy

26
Q

How does water move INTO the roots?

A
  • Soil water has a high water potential (due to its low number of solutes), however root-hair cells have a low water potential.
  • As a result, water moves in via osmosis, down the water potential gradient.
  • Minerals require active transport to be transported into the root hair cells.
27
Q

How are root hair cells adapted for water uptake?

A
  • Microscopic size to penetrate roots.
  • Large SA:V - tiny hairs.
  • Thin surface layer
  • Concentration of solutes maintains water potential gradient.
28
Q

What pressure is created as a result of water moving into the plant via the root hair cells?

A

Root pressure.

29
Q

What 2 pathways can water move across the root?

A

Symplast pathway

Apoplast pathway

30
Q

Describe the symplastic pathway across the root.

A
  • Water moves through continuous cytoplasm (connected by plasmodesmata)
  • Movement by osmosis due to differences in water potential in adjacent cells.
31
Q

Describe the apoplast pathway across the root

A
  • Water moves through cell walls and intercellular spaces, filling spaces between an open network of cellulose fibres.
  • As water moves through the xylem, cohesive forces create a tension force, pulling water molecules through the apoplast pathway.
32
Q

What is the purpose of the Casparian strip?

A
  • Forces water into the apoplast pathway into cytoplasm of cells, joining the symplast pathway.
  • As the water will now have to cross a selectively permeable membrane, this excludes any potential toxic solutes from reaching living tissues.
33
Q

What is the casparian strip?

A

A band of waxy material called Suberin found on the endodermal cells, forming a water proof layer.

34
Q

What is root pressure?

A

Pressure created due to active pumping of mineral ions into the xylem, through active transport, alongside water transporting down the water potential gradient, via osmosis into the xylem.

35
Q

Why is the transpiration stream necessary?

A
  • Photosynthesis in the leaves (requires water)
  • Maintain/regulate temperature (homeostasis)
  • Maintain turgidity (water in cells)
  • Growth and elongation of cells
  • To transport minerals
36
Q

What are the 3 ways that water movement can occur up the transpiration stream?

A
  • Cohesion tension theory
  • Adhesion
  • Root pressure
37
Q

How does adhesion cause water movement up the stream?

A

Water’s adhesive properties allow it to form hydrogen bonds with the carbohydrates in the walls of narrow xylem vessels. This results in water rising up the xylem against the force of gravity.

38
Q

How does the cohesion tension model allow water to move up the transpiration stream?

A
  • Water evaporates from spongy mesophyll layer into air spaces.
  • Diffuses into surrounding air via diffusion.
  • Loss of water by evaporation leads to a reduced water potential, leading to water moving into the cell.
  • Due to water’s cohesive properties, hydrogen bonds are formed between water molecules, meaning there’s a CONTINUOUS COLUMN of water.
  • This will create a “transpiration pull” when evaporation occurs.
39
Q

What factors affect rate of transpiration?

A
  • Light intensity (high light=high rate)
  • Relative humidity (high humidity=low rate)
  • Air movement (high air movement=high rate)
  • Temperature (high temp.= high rate)

A Level Biology (13 decks)

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