Plant Form

Question 1

What are the three stages of plant development?

Answer 1

1. embryogenesis
2. vegetative
3. reproductive

Question 2

What are the meristems?

Answer 2

origin of all post-embryonic organs

Question 3

Name the two primary and two lateral meristems.

Answer 3

primary:
1. root apical
2. shoot apical
(as well as the axillary meristem)

lateral (typical of woody plants):
1. vascular cambium
2. cork cambium

Question 4

Define phyllotaxy and name the different types.

Answer 4

the arrangement of leaves (and thus branches) around the stem

a) alternate
b) spiral - golden angle between two leaves that are generated along an equiangular angle
c) opposite (eg mint)
d) whorled - more than two leaves at each node

Question 5

What is the role of auxin?

Answer 5

it is a hormone that determines new cell/organ fate or growth rate

Question 6

What is a primordium?

Answer 6

the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow

Question 7

Name he different zones of the meristem and state their function.

Answer 7

Central zone - stem cells
peripheral zone - produces organs
L1 - divides anticlinally to generate the epidermis
L2 - divide periclinally to produce the bulk of the internal tissue
L3 - same as L2 but also gives rise to vasculature

Question 8

Define anticlinal and periclinal division in regard to the meristem

Answer 8

anticlinal - vertical divisions outwards of the meristem
periclinal - horizontal divisions across the meristem

Question 9

What are the roles of the epidermis?

Answer 9

• protection
• light reflection/harvesting
• water/gas exchange
• surface cleaning
• structural light/colouring effect

Question 10

What are the roles of the vascular tissue?

Answer 10

• transport of water via the xylem
• transport of photosynthetic products via the phloem
• structural support

Question 11

What is the benefit of a vein-like vascular structure?

Answer 11

• allows efficient spacing of xylem and phloem
• allows a circulation system that is harder to disrupt

Question 12

What are lenticels?

Answer 12

horizontal slits in wood/bark that are important for gas exchange

Question 13

Where does carbon fixation take place?

Answer 13

in the air spaces in mesophyll cells

Question 14

What is meant by an “open root apical meristem” and specify what type of plant it occurs in

Answer 14

not having specific tiers of initial cells in the root apical meristem, occurs in monocots

Question 15

How do root hairs develop?

Answer 15

can be environmentally induced
as part of the epidermal cell elongates via tip growth

Question 16

How are apical root meristems produced?

Answer 16

root apical meristem originates from the pericycle

Question 17

What is the pericycle?

Answer 17

a primary root tissue that forms the cell layer surrounding the xylem, phloem, and procambium cells

Question 18

Define heterophylly.

Answer 18

environmentally induced differential leaf shapes
eg two different leaf morphologies depending on growing in water/air

Question 19

Define photomorphogenesis.

Answer 19

light-mediated development, where plant growth patterns respond to the light spectrum

Question 20

What is dogma?

Answer 20

the fact that all living plant cells can regain totipotency
plants are highly regenerative

Question 21

State the roles of both vascular and cork cambium which develop as plants grow older.

Answer 21

vascular cambium: produces secondary vascular tissues (eg wood) which provide more transport and structural support

cork cambium: produces cork/bark which provides new epidermis and more protection

Question 22

What is apical dominance?

Answer 22

the process whereby the high concentrations of auxin in shoot tip inhibits the outgrowth of axillary buds further down the stem to control the number of growing shoot tips and branches

Question 23

What is propagation?

Answer 23

a plant regenerating itself from a piece of its body
each module has a meristem and is self-sufficient to replicate itself

Question 24

How do different types of stresses affect different types of trees?

Answer 24

deciduous (in tension) = increase of cellulose in cells and wood
conifer (in compression) = increase of lignin in cells and wood

Question 25

What is meant by “closed root apical meristem” and specify what type of plant it appears in

Answer 25

occurs in dicots
have specific layers in the meristem to which all cell files can be traced

Question 26

During formation of the apical meristems, what is cell fate determined by?

Answer 26

cell fate is position-dependant rather than lineage-dependant

Question 27

What is the phellogen?

Answer 27

the dividing zone of cells in the cork cambium

Question 28

How do phellogen cells divide and how does this affect the structure?

Answer 28

divide periclinal
results in production of phelloderm cells to the inside and phellem to the outside (cork cells)
as a result, epidermal cells divide anticlinal otherwise they would start bursting
This growth forms the Periderm

Question 29

What happens to cork cells at maturity?

Answer 29

they die and are heavily impregnated w suberin, a waxy hydrophobic compound
provides protection for stem and roots against water loss and pathogens

Question 30

How is the vascular cambium initially realised?

Answer 30

the cambium is first activated within the vascular bundle and spread in between dedifferentiating cells in the area
a cylinder of 1-2 cell thick cambium layer then gives rise to numerous numbers of xylem and phloem cells

Question 31

Difference between xylem and phloem?

Answer 31

Xylem is dead tissue enforced to carry water
Phloem have companion cells (containing nuclei) and transport the products of photosynthesis

Question 32

What are the 3 tissue types in the shoot apex of angiosperms?

Answer 32

Vasculature
Epidermis
Ground tissue (exists between the vasculature and epidermis and in the centre)

Question 33

What is secondary growth?

Answer 33

Growing older and larger; additional cells for transport, structure, support and protection are needed
Lateral meristem (vascular and cork cambiums) growth provides these

Question 34

Difference between compound leaf and branch?

Answer 34

Branches have auxiliary buds between leaves, no buds between the leaflets on a compound leaf

Question 35

How is the anatomy of the leaf organised?

Answer 35

Stomata openings on the bottom
Epidermis has a cuticle on the top layer
Mesophyll with chloroplasts (also BS cells)

Question 36

What is the root cap?

Answer 36

Provides cover for root
Arguably not part of root as it isn’t directly attached

Question 37

Which tissue starts lateral root formation?

Answer 37

The stele at the centre of the root is surrounded by the pericycle which causes lateral root formation as it doesn’t lose the ability to divide

Question 38

How are roots made to be selective

Answer 38

Casparian strips are impregnated with hydrophobic compound, doesn’t allow water to centre and allows selective ness in what is allowed through

Question 39

What is the purpose of root hairs?

Answer 39

Increase surface area
Absorb water and mineral ions
Decreasing concentration of nutrients will cause the plant to make more root hairs

Question 40

How does root branching take place?

Answer 40

Mediated by auxin
Pericycle begins to divide and root apical meristem begins to acquire shape
Apoptosis occurs around bulging structure to give way to it as to avoid bursts and ruptures

Question 41

What causes lateral root formation?

Answer 41

Elevated nutrients causes plant to respond with root formation
Low nutrient decreases root formation
Also induced in areas with more water
If a bend in the root of formed by an obstacle, auxin causes LR formation on convex side to explore