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CELS191 > Cell walls and their role in regulating plant cell shape > Flashcards

Cell walls and their role in regulating plant cell shape Flashcards

Lecture 8

1
Q

Major component in the cell wall

A

Cellulose

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2
Q

Describe cellulose

A
  • The most abundant organic macromolecule on Earth
    -Glucose polymer
    -Highly ordered
    Long, ribbon like structures
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3
Q

Cellulose forms

A

Microfibrils

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4
Q

Microfibrils

A

Highly organised structures that are strong and form a major component of both primary and secondary cell walls

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5
Q

Two phases of the cell wall structure

A

Microfibrils and matrix

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6
Q

What consists of microfibrils

A

Cellulose

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7
Q

What consists of matrix

A
  • Pectin polysaccharides
  • Hemicellulose polysaccharides plus a network of Extensin
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7
Q

Hemicellulose

A

Heterogeneous group of polysaccharides. Long chain of one type of sugar and short side chains that form a rigid structure

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8
Q

Pectin

A

Branched, negatively charged polysaccharides. Bing water and have gel like properties.

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8
Q

The extensibility (expansion) of cells can be controlled by

A

extensin cross linking

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8
Q

Effect of extensin cross linking of pectin and cellulose

A

It dehydrates the cell wall, reducing extensibility and increasing strength. The cell cannot expand in size

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8
Q

The synthesis of the primary cell wall consists of the o-ordinated synthesis and delivery of: A

A

Cellulose microfibrils at plasma membrane

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8
Q

The synthesis of the primary cell wall consists of the o-ordinated synthesis and delivery of: B

A

Polysaccharide (pectin and hemicellulose) in the golgi apparatus are transported to the wall in vesicles

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8
Q

The vesicles fuse to

A

the plasma membrane

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9
Q

The synthesis of the primary cell wall consists of the o-ordinated synthesis and delivery of: C

A

Cell wall proteins (extensins) from the rough endoplasmic reticulum

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9
Q

Exocytosis

A

Transports material out of the cell or delivers it to the cell surface

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9
Q

Constitutive exocytosis releases

A

extracellular matrix proteins

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9
Q

Cytoskeleton

A

A network of microtubules, microfilaments and intermediate filaments that extend throughout the cytoplasm

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10
Q

Functions of the cytoskeleton

A

Maintaining the position of organelles and providing structural support

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11
Q

The cellulose producing rosettes move

A

parallel to the cortical microtubules

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11
Q

Cellulose producing rosettes are

A

protein complexes (enzymes) that span the plasma membrane

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11
Q

Orientation of the cellulose microfibrils influences..

A

cell morphology

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12
Q

Cell wall functions in regulating cell shape

A
  • Influences cell morphology
  • Provides structural support
  • Prevents excessive water uptake
13
Q

If the cellulose microfibrils are orientated where the right angles to the ultimate long axis to the cell,

A

the cell will expand longitudinally along that axis

13
Q

if the cellulose microfibrils are randomly oriented,

A

the cell will expand equally in all directions

14
Q

The cell wall provides..

A

structural support

15
Q

The protoplast pushes against the cell wall.

A

The cells become rigid and this maintains the plant structure

16
Q

Wilting occurs when..

A

the protoplast is not pushing against the cell wall.

17
Q

Water loss from cells reduces the protoplast volume ..

A

and the protoplast does not press on the cell wall

18
Q

The cell wall prevents ..

A

excessive water uptake

19
Q

As water enters the cell by osmosis,

A

the protoplast expands and pushes against the cell wall.

20
Q

Pressure from the cell wall limits..

A

the volume of water that can be taken up

21
Q

Vacuoles are important because..

A

they contain water and make up such a large portion of the protoplast.

22
Q

A vacuole is..

A

an organelle surrounded by a single membrane

23
Q

Vacuole is highly selective,

A

controlling much of what enters and leaves the vacuole

24
Q

Water moves in the vacuoles by..

A

osmosis (passive transport)

25
Q

Typical mature plant cell has..

A

a single large vacuole

26
Q

Osmosis is..

A

the diffusion of water across a selectively permeable membrane

27
Q

Movement in osmosis occurs from

A

a high water (low solute) concentration to a low water (high solute) concentration

28
Q

There is high concentration of solutes in the vacuole. This results in…

A

water uptake into the vacuole by osmosis

29
Q

The plant cell wall limits…

A

water uptake and prevents the cell bursting.

30
Q

Plant cell builds up a large internal pressure that contributes to..

A

plant structural support

31
Q

Not all plants cells have..

A

a secondary cell wall

32
Q

The secondary cell wall is produced only after…

A

cell growth has stopped

33
Q

The secondary cell wall is ….. than primary cell walls

A

thicker and stronger

34
Q

The secondary cell wall provides more..

A

structural support than primary cell wall

35
Q

The secondary cell wall structure

A
  • Made up of multiple layers
  • Microfibrils in each layer have different orientations
    -This strengthens the secondary wall
36
Q

Chemical characteristics of the secondary cell wall

A
  • more cellulose
    -less pectin
    -lignin
37
Q

Lignin is the second most

A

abundant organic macromolecule

38
Q

Lignin is a complex

A

polymer

39
Q

Lignin confers…

A

strength and rigidity to the secondary cell wall and acts to exclude water

40
Q

The secondary cell wall provides structural support for:

A

specific cell types such as water transporting cells, and for the whole plant

41
Q

Plasmodesmata

A

are intercellular connections, that enable cell to cell communication

42
Q

Is the plasma membrane continuous

A

Yes

43
Q

The plasmodesmata is small enough to prevent organelle movements,,

A

although endoplasmic reticulum is connected through plasmodesmata.

44
Q

Plasmodesmata allows

A

the free exchange of small molecules

CELS191 (9 decks)

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