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Biology - Topic 4 > Xylem and Phloem > Flashcards

Xylem and Phloem Flashcards

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1
Q

How are xylem vessels adapted to their function? (Cell type)

A
  • Large cells, thick cell walls

- Form a column

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2
Q

How are xylem vessels adapted to their function? (Production)

A
  • Production of lignin
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3
Q

What is the role of lignin?

A
  • Impregnates cellulose wall, restricting solute and water entry
  • Provides Stability
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4
Q

What is autolysis?

A

Tonoplast breaks down. Organelles, cytoplasm, membrane are broken down by enzymes

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5
Q

What happens to end cell walls in xylem?

A
  • They are lost or highly perforated
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6
Q

What two things give xylem strength?

A
  • Cellulose microfibrils

- Lignin

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7
Q

What is the casparian strip?

A

Cell wall material deposited around endodermal cells

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8
Q

Why is the casparian strip different to cell walls?

A
  • Made of suberin, and sometimes lignin
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9
Q

What does the casparian strip do?

A
  • Forces solutes and water to pass through plasma membrane via symplastic route to cross endodermic level
  • Regulates water and mineral intake by roots
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10
Q

Why is there low water potential at the bottom of the xylem?

A
  • Loss of water by transpiration and the transpiration stream draw water up, causing low potential. Water diffuses in by osmosis
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11
Q

How do root hair cells gain water?

A
  • Large surface area for diffusion
  • Soil water is dilute with large water potential
  • Cytoplasm of root hairs have low water potential due to dissolved ions
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12
Q

How does water move from root hair to xylem?

A
  • Apoplast, diffusion between cell walls. Symplast, movement between cytoplasm
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13
Q

Why is cytoplasm continuous?

A

Plasmodesmata, narrow fluid-filled channels maintain a continuous cytoplasm

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14
Q

Where does water evaporate from?

A

Diffuses through the stomata in the leaves, then evaporated from the surface of cells lining the substomal cavity

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15
Q

How does water mass flow work?

A
  • Continuous column of water drawn up through column
  • Capillary action due to surface tension, cohesion, adhesion
  • Pulling force on water behind
  • Energy comes from the sun
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16
Q

What components is phloem made up of?

A
  • Sieve elements
  • Companion cells
  • Parenchyma cells
  • Fibres
17
Q

What is the role of phloem?

A

Transports sucrose and amino acids

18
Q

What is the source?

A

The cell that photosynthesyses

19
Q

How is sucrose transported into companion cells?

A

Active transport

20
Q

How does sucrose move from companion cells to sieve elements?

A

Diffusion

21
Q

What does the diffusion of sucrose into the sieve elements cause?

A

Reduction of water potential

22
Q

When there is low water potential, what occurs into the cells?

A

Osmosis

23
Q

What happens to the sieve element cell following osmosis?

A
  • Becomes turgid, hard, high pressure
24
Q

What is a sink?

A

Region where sugars are respired or stored as starch

25
Q

What do sinks include?

A

Roots, tubas, actively growing buds etc

26
Q

What happens when there is a low concentration of sucrose in the sinks?

A

Sucrose passes from sieve tubes into sinks by diffusion

27
Q

Why is there lower water potential in phloem by sinks?

A

Low sucrose means high water concentration and diffuses out

28
Q

Why does sap move down the plant?

A

Higher pressure compared to low pressure means mass movement

29
Q

What is the organelle difference between xylem and phloem?

A
  • Xylem is dead with no organelles
  • Phloem remains alive. Nucleus and most contents disintegrate, with a few organelles in a thin layer of cytoplasm. Membrane, cytoplasm, ER, mitochondira
30
Q

What is most of the space in a phloem sieve tube?

A

Liquid filled space called a lumen

31
Q

What do phloem sieve cell walls do to interact?

A
  • Aligned holes, allowing transfer of material
32
Q

What is the section between two sieve plates?

A

Sieve tube element

33
Q

What do companion cells do?

A

Line the elements with more mitochondria and ribosomes, and produce and transfer materials required by sieve elements

34
Q

Why are xylem vessels narrow?

A

More contact with the water means more adhesion

Biology - Topic 4 (6 decks)

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