Processes of Plant Development L1

Question 1

What do plant embryos consist of?

Answer 1

Cotyledons (The seed leaves)

Shoot Apical Meristem which is separated from a:

Root Apical Meristem by a short stem.

Hypocotyl (Figure 1).

Question 2

Explain the two types of Arresting cells

Answer 2

The arresting cells also fall into two types: (1) those that promptly expand and differentiate.

(2) those for which arrest is a temporary phase. These occupy fixed positions, and resume cell division again later to build additional structures: branch roots, branch shoots, and extra girth.

Question 3

Where is the size of a Apical Meristem?

Answer 3

Small: approx 100 - 250um

Question 4

What is a Apical Meristem?

Answer 4

Dome of dividing cells at the very tip of every shoot or root

Question 5

What does the root and shoot of a Apical meristem consist of?

Answer 5

Root and shoot consist of a central group of cells

-function: Organisational and outer layers of cells dividing rapidly to generate new
Tissue.

Question 6

Where is the distinction of Apical meristem marked?

Answer 6

The distinction is more marked in roots, where the central cells are called a quiescent center.

Question 7

What do the Meristematic cells form?

Answer 7

The meristematic cells form 2 bowl shaped layers:

• The root initials
• Cap initials

Question 8

What are Angiosperm shoots?

Answer 8

The central zone grades off less distinctly into the meristematic regions.

Question 9

Why are zonations much easy to see in gymnosperms?

Answer 9

The zonation is much easier to see in gymnosperm shoot apical meristems. This is because the central mother cells will divide more slowly than their angiosperm counter parts

Question 10

Isolated SAMs and RAMs can be cultured, plants and roots on nutrient media. What does this show?

Answer 10

This shows their independence to the rest of the plant, meaning they are able to self-contain as a developmental unit.

Question 11

When moving back from the apex, what emerges?

Answer 11

the patterns of mitotic arrest emerge.

Question 12

When the patterns of mitotic arrest emerge, what is this different from?

Answer 12

This is different from qc and cz = cycling slowly: further back, cells are rapidly or not cycling.

Question 13

In relation to a root apical meristem and a shoot apical meristem.
Why do cells which continue to divide show up?

Answer 13

Cells which continue to divide show up because they are smaller than other cells

Question 14

What do roots show?

Answer 14

Roots show a clear and simple sequence of overlapping zones:

• Apical zone of cell elongation
• Tissue more basal, a separate zone of differentiation of root hairs
• Casparian strip as well as xylem and phloem

Question 15

What makes development more complicated up in shoot?

Answer 15

Leaf Morphogenesis
When it comes to leaf shape and size, this is generated by a sequence of meristems, which are each independently controlled

Question 16

During morphogeneis, a not yet fully formed lead is called a?

Answer 16

primordium

Question 17

Explain phase 1 in leaf morphogenesis?

Answer 17

Accelerated cell division and expansion, some few cell layers under the surface of the flanks of the apical dome heaves up a bump or buttress, the position of which is determined only by the 2 nearest primordia (Inhibitory), so that the leaves arise in a constant arrangement

Older leaves, a pattern of leaf position/ arrangement known as phyllotaxis

Question 18

What does phase 1 of leaf morphogenesis determine?

Answer 18

LF position

Question 19

Explain phase 2: The apical meristem of the leaf

Answer 19

The positive and negative random divisions shown on phase one stop and is taken over by growth by a cell, or a small number of cells, this is just under the outermost layer.

The proximal (Back) cells stop dividing however the distal (Front) cells keep dividing and the bump or buttress will grow to form a peg, this will expand to become the mid-rib.

Cells of the apical meristem of the leaf then crease to divide and vacuolate before the leaf is 1mm long in dicots, 0.3mm in gymnosperms and monocots

Question 20

What does phase two determine?

Answer 20

Phase two determines LF length

Question 21

Explain phase 3: The marginal meristem

Answer 21

A stripe of cells down the sides of the peg as well as the extending 4 cells into it re-commence active cell division.

The accumulated cells form 2 wings laterally

Cell division concentrated along the margin of the growing curved plate which will later expand to become the leaf blade or lamina.

Question 22

Explain phase 4: Plate enlargment

Answer 22

The plate is enlarged by a phase of anticlinal (add area) divisions scattered throughout.

Anticlinal: Divisions add to the area

Periclinal: divisions add to the thickness

Question 23

What does phases 3 and 4 determine?

Answer 23

Phases 3 and 4 determine LF width

Question 24

Explain phase 5: The plate meristem

Answer 24

A sudden wave of periclinal divisions from the tip to the base will generate the final 7 to 10 cell thickness

Question 25

What does phase 5 determine?

Answer 25

This phase determines LF thickness

Question 26

How are different leaf shapes determined?

Answer 26

This is achieved by restricting the duration and/or distribution of individual phases

Conifer needles are generated by a similar sequence except the activity of the marginal meristem is very limited.

The differences between species are genetically determined, however phases 4 and 5 can be under environmental control for production of specific features.

Question 27

What can counter predation include?

Answer 27

Counter predation can include fenestrations in leaf, for example nettles.

Question 28

What follows cell division phase?

Answer 28

Cell division phase is followed by a phase of cell expansion as well as differentiation. The spongy mesophyll cells stop expanding earlier than other cells and therefore get ripped apart, this gives rise to larger intercellular spaces.

Question 29

What happens when the LF tip cell expansion stops first?

Answer 29

In the LF tip cell expansion stops first, this is then passing as a wave back down the petiole. If there is one, the plants entire development is very much later than the rest of the leaf.

Question 30

Why does cell expansion phase of the petiole often lasts the entire life of the LF?

Answer 30

this is that the growth adjustments for the direction of light can be made.

Question 31

what happens to Petioles supported by collenchyma

Answer 31

Petioles supported by collenchyma, whos walls thicken very early and phloem fibres. An example of this is raffia palm.

Question 32

Describe the primary cell walls

Answer 32

Cell walls in tissues which are still expanding are known as primary walls

Typically for primary walls they are thin and consist of cellulose microfibrils in a pectin and water matrix (gel).

Question 33

How is the secondary cell wall formed?

Answer 33

Once cell expansion is finished, the thicker secondary wall is laid down over the inside of the wall in certain cell types, except where there are clusters of plasmodesmata pit fields.

The “Windows” in the secondary wall are called simple pits.

Question 34

Describe secondary cell walls?

Answer 34

Secondary walls are made mostly of cellulose microfibrils which includes a much smaller proportion of matrix polysaccharide, water and contains lignin.

Secondary wall provides strength, however will stop cell expansion. This is why there are problems in providing mechanical support for the growing primary tissues

Question 35

What do Fibres cells belong too?

Answer 35

These types of cells belong to the class of support tissues which are called sclerenchyma, this include massively thickened, hard, cellulose walls also often but not always lignified.

Question 36

Describe fibres cells

Answer 36

The wall is inextensible so the cell goes on extending to cope with the expansion of the surrounding tissue by apical intrusive growth.

The ends of the cell are pointed, also thin walled and cytoplasmic, they carry on growing, boring intrusively between the expanding cells while the middle section thickens up.

This way allows primary tissue fibre cells to reach great lengths which is exploited by us in the case of flax and hemp.

Question 37

Describe and explain Collenchyma cells

Answer 37

These cells are known for being very thick however have extendable walls. Beginning at the corners often, parenchyma cells lay down a wall of alternating layers of pectin as well as cellulose which is strong also capable of supporting up to 10-12 kg/mm before breaking.

An example of this is celery petioles.

Collenchyma is distributed in stems as a strengthening tube. These cells are very long and thin in LS by the time stem elongation is complete.

Question 38

What are subsidiary meristems?

Answer 38

zones of cell division basal to the shape determining apical meristem.

Question 39

A subsidiary meristem in dicots is known as subapical meristem, what is its function?

Answer 39

One of these which are known in dicots as the subapical meristem, controls internode elongation in a simple, quantitative way. .

Question 40

What does it mean by Divisions are predominantly anticlinal?

Answer 40

meaning add to the length but not to the thickness of the axis separating out this activity keeps the upper internodes very short.

As a result the developing lfs protect the apical dome and younger lfs.

Question 41

For many plants, especially grasses the meristematic activity leads to?

Answer 41

internode elongation persists, becoming confined to a region at the base of the internode with fully diff’ned tissue above as as below

Question 42

The intercalated m’ stematic tissue is called an?

Answer 42

intercalary meristem and also occurs in the base of grasses if sheath.

Question 43

What two types of cells are generated by cells in the apical meristem that divide?

Answer 43

Those that continue to divide,maintaining the meristem

Those that stop dividing and build the plant

Question 44

All types of cells at any stage of development are able to respond to changes in the environment. But how?

Answer 44

This can be individually or collectively as a group (as in a meristem) this is done by altering the progress or nature of development, in order to increase the survival chance of the plant.

Question 45

Primary growth takes place at:

a) Lateral meristems
b) Apical meristems
c) Leaves
d) Vascular tissue
e) Cork cells

Answer 45

b)Apical meristems

Question 46

The apical meristem is located:

a) At the tip of the leaf
b) At the tip of the stem
c) At the tip of the root
d) All of above
e) Both 2 and 3

Answer 46

e) Both 2 and 3

Question 47

Growth is a complex process involving:

a) Cell division
b) Cell elongation
c) Cell differentiation
d) All of the above
e) None of the above

Answer 47

d)All of the above

Question 48

Secondary growth increases —– of the plant:

a) Length
b) Girth
c) Root hairs
d) Leaf size
e) None of the above

Answer 48

b)Girth

Question 49

The pattern/arrangement of leaves on a plant stem is termed the:

a) Leaf position
b) Epistasis
c) Glycosylation
d) Phyllotaxis
e) None of the above

Answer 49

d)Phyllotaxis