35 Plant Structure, Growth and Development Flashcards
1
Q
What is a tissue?
A
A group of cells consisting of one or more type of cell.
2
Q
What are the main systems of a plant?
A
The shoot system and the root system.
3
Q
What is the major terminology that describes the shoot system?
A
The main shoot is called the stem. It has ‘vegetative shoots’ that grow of. They are joined to the stem by ’nodes’. The region between the nodes is called the ‘internode’
At the top of the stem and at the end of each vegetative shoot is an ‘apical bud’. (end of vegetative shoot may be leaf) Along the stem there may be ‘auxillary buds’
Besides ‘vegetative shoots’, ‘reproductive shoots’ also branch of from the stem and terminate in flowers.
4
Q
What are the two most basic patterns of root systems?
A
’Taproot systems’ and ‘’fibrous root systems’
5
Q
Describe a ’taproot system’?
A
A single vertical ’tap root’ is a thick root that is an extension of the stem.
Along its length ‘lateral (branch roots)’ branch of it more-or-less horizontally.
6
Q
Describe a ‘fibrous root system’
A
A mat of thin roots spread out under the soil.
7
Q
How do ’taproots’ and ‘fibrous roots systems’ differ in their adaption to specific climates?
A
Fibrous roots systems do not usually penetrated as far and are thus best adapted to shallow soils or regions where rainfall is light do does not moisten the soil far below ground level.
Tap roots often anchor the plant better. The fibrous roots are could at holding the topsoil in place hence why grasses prevent erosion.
8
Q
In what plants are taproots typically seen?
A
Most eudicots and gymnosperms
9
Q
In what plants are fibrous roots systems typically seen?
A
Monocots such as grasses.
10
Q
What adaptation is found on many roots to increase the rate at which they can absorb nutrients?
A
Fine projections called ‘root hairs’
11
Q
What are some specific forms of roots with evolutionary advantages?
A
Prop roots, storage roots, ’Strangling aerial roots’ buttress roots and pneumatophores
12
Q
What are prop roots?
A
Roots that extend from the lower trunk of a tree.
This helps support the tree such as the Hala trees that live in unstable sand soils in the South Pacific.
13
Q
What are storage roots?
A
Roots that can store water and nutrients underground, often by swelling.
These include potatoes.
14
Q
What are ’Strangling’ aerial roots?
A
The seeds of these species germinate in the branches of tall trees of other species and send many aerial roots to the ground. These snakelike roots gradually wrap around the host tree and kill it by blocking its light
15
Q
What are buttress roots?
A
Like prop roots they extend from the trunk although buttress roots often start lower.
Unlike prop roots which a are normal sticks the area under the ‘buttress root’ is filled so that they are ◢
16
Q
What are ‘penumatophores’?
A
Roots that stick out of the ground i.e. the ones mangroves have.
They are important for roots to obtain oxygen which is lacking the thick, waterlogged roots.
17
Q
What types of roots do mangroves have?
A
‘Pneumatophores’
18
Q
What does ’node’ refer to on a plant?
A
Where the leaf joins the stem
19
Q
What does ‘internode’ refer to on a platns?
A
The stem segment between nodes.
20
Q
What are the shoots that branch of the plant called?
A
Lateral shoots or more often ‘branches’
21
Q
What is a bud composed of?
A
Developing leaves and a compact series of nodes and internodes
22
Q
What is found at the top of the stem and of each lateral shoot?
A
Apical buds aka ’terminal buds’
23
Q
What are buds on the sides of the stem called?
A
Auxillary buds.
24
Q
What determines which bud develops?
A
Generally speaking the growth is concentrated at the ‘apical bud’ as it exerts ‘apical dominance’ that suppresses the growth of the auxiliary buds.
If the apical bud becomes shaded its will lessen this suppression. This allows the auxiliary buds to develop into a ’lateral shoot’ (branch) to allow the plant to get light.
25
What are the basic structures plants have to perform asexual reproduction?
Rhizomes, bulbs, stolons and tubers.
26
What asexual reproduction structure is a root?
None: they are all technically stems event if they are underground.
27
What are ‘rhizomes’?
An underground asexual structure that consist of a shoot that grows just under the soil surface.
Along the rhizomes are auxiliary buds that can develop into vertical stems and thus new plants.
28
What are 'bulbs'?
Vertical underground shoots that consist of the enlarged bases of leaves that store food.
The individual leaves, called ’storage leaves’ explain the many layers of an onion: each layer is a leaf.
29
What are stolons?
Horizontal shoots that grow along the surface.
They allow asexual reproduction as ‘plant lets’ form at nodes along each ‘runner' (stolon)
30
What are tubers?
Enlarged ends of rhizomes or stolons that are specialised for storing food in the form of starch.
31
What is the basic structure of a leaf?
It is connected to a ‘node’ by a 'petiole’.
The actual leaf may con of a ‘main rib’ (eudicot only?) and a series of smaller veins to transport nutrients to and from the leaf cells.
The actual leaf blade is called the lamina?
32
How does leaf structure differs between plant species?
In Monocots there are typically veins that pun in parallel from the petiole. for example the flax leaves
In Eudicot leaves there is typically a ’net like web’ of veins.
33
What are the fundamental ways in which leaves are structured ?
Simple leaf, compound leaf and ‘doubly compound leaaves'
34
What are ’simple leaves’?
When the leaf has a simple undivided lamina and is to only one that extends from the petiole.
35
What compound leaves?
In a compound leaf, the blade consists of multiple leaflets. A leaflet has no axillary bud at its base.
Each leaflet connects to the petiole not the stem.
36
What are double compound leaves?
Each leaflet is divided into smaller leaflets.
Therefore ‘compound leaves’ branch of from the petiole.
37
What are some advantages to compound leaves?
Since each leaflet is smaller than a normal leaf this prevents it from catching in the wind and falling off easily.
Pathogens might only infect one small leaflet, not the entire leaf.
38
What are some special adaptions of leaves?
Tendrils, Spines, Storage leaves, reproductive leaves and Bracts.
39
What are tendrils?
Modified leaves that that cling onto neighbouring plants etc. and thus support the plant.
(note that tendrils are often leaves but can be stems in some species)
40
What are spines?
The spines of cacti are actually leaves; photosynthesis is carried out by the fleshy green stems which constitute to main body of the cactus.
41
What are storage leaves?
Swollen leaves that many succulents have to store water
42
What are reproductive leaves?
Leaves that aid in asexual reproduction.
For example Kalanchoë daigremontiana, produce adventitious plantlets, which fall off the leaf and take root in the soil.
43
What does ‘adventitious’ refer to?
A plant organ that grows in an unusual location, such as roots arising from stems or leaves.
44
What is the word that means growing from an unusual place i.e. roots from the stem?
‘Adventitious'
45
What are the basic types of plant tissue?
Dermal tissue, ground tissue and vascular tissue.
46
What is the 'dermal tissue’?
The outer layer of the plant that acts as its protective coating.
47
What are some examples of dermal tissue?
In nonwoody plants there is tissue called the epidermis (tightly packed cells). In woody plants, protective tissues called periderm replace the epidermis in older regions of stems and roots.
In leaves and most stems, the cuticle (waxy coating on epidermis surface) helps prevent water loss.
48
What is an example of a specialised structure pro ducted by some plants on the dermal tissue?
Trichomes
49
What are trichomes and what advantage do they offer?
Hairlike outgrowths of the shoot epidermis.
In some desert species, they reduce water loss and reflect excess light,
However their primary function is to provide defense against insects by forming a barrier or by secreting sticky fluids or toxic compounds.
For instance, the trichomes on aromatic leaves such as mint secrete oils that protect the plants from herbivores and disease.
50
What is the purpose of the vascular tissue system?
To carry nutrients throughout the plant.
51
What are the main components of the vascular tissue system?
Xylem and Phloem
52
What is the vascular system of a root or stem collectively called?
Its ’stele'
53
What does ’stele’ refer to?
The collective vascular system of a root or stem.
54
How does the arrangement of the ’stele’ vary between plants and regions?
In angiosperms the root stele is a solid central vascular cylinder of xylem and phloem. T
he stele of stems and leaves consists of vascular bundles, separate strands containing xylem and phloem.
55
What does the ground tissue system consist of?
Pretty much anything that isn’t vascular or dermal.
It is divided into ‘pith’ and 'cortex'
56
What is the difference between ‘pith’ and ‘cortex’ in the ground tissue system?
Ground tissue that is internal to the vascular tissue is known as pith, and ground tissue that is external to the vascular tissue is called cortex.
57
What is the function of the ground tissue?
It is not just a filler and thus is involved in storage, photosynthesis and support of the plant.
58
What are the basic types of plant cells?
Parenchyma, Collenchyma and Sclerenchyma.
59
What is the structure of parenchyma cells?
They have thin and flexible primary cell walls with most lacking secondary cell walls.
They typically have a large central vacuole.
Most parenchyma cells retain the ability to divide and differentiate into different plant cell types i.e. for wound repair
60
What functions do parenchyma cells perform?
They perform most of the metabolic functions of the plant, synthesizing and storing various organic products
For example photosynthesis occurs within the chloroplasts of parenchyma cells. Some parenchyma cells in stems and roots have colourless plastids that store starch.
Therefore parenchyma a cells are typically alive when mature
61
What is the fleshy tissue of most fruits mad up of?
Parenchyma cells
62
What is the structure of collenchyma cells?
They are elongated cells that are often found in stands. They have thicker primary cells walls than parenchyma cells but the walls are unevenly thickened.
63
What is the purpose of collenchyma cells?
Young stems and petioles have strands of collenchyma cells below their epidermis. to support theses structures. They are flexible so don’t restrain growth.
At maturity, these cells are living and flexible, elongating with the stems and leaves they support
64
What is the structure of sclerenchyma cells?
They are more rigid than collenchyma as they have thick secondary cell walls with large amounts of lignin.
Sclerenchyma cells are divided into two types: sclereids and fibres
65
In what organisms are sclerenchyma cells found?
All vascular plants but no bryophytes.
66
What is the function of sclerenchyma cells?
They can not elongate and thus support regions of the plant that have stopped growing. For example they make up a large component of wood.
Since their main function is to support the cell most produce thick secondary cell walls and then die as they mature, leaving behind a skeleton.
67
What are the basic types of sclerenchyma cell?
Sclereids and fibres.
68
How do ’sclereids’ and ‘fibres differ'
Both are forms of sclerenchyma and thus have thick lignified secondary cell walls as they function in support.
Sclereids, are boxier than fibers and irregular in shape, have very thick, lignified secondary walls.
Fibers, are usually grouped in strands and are long, slender, and tapered.
69
Where are sclereids found?
They are what make nutshells and seed coats hard and give pears their gritty texture.
70
Where are fibres (sclerenchyma) found?
They are uses for making ropes. Flax fibres are used for weaving into linen.
71
What is xylem composed of?
Two different types of 'water-conducting cells': tracheids and vessel elements.
72
In what plants are tracheids found in xylem?
Almost all vascular plants
73
In what plants are vessel elements found in xylem?
Most angiosperms, a few gymnosperms and some seedless vascular plants.
74
What is the structure of tracheids?
They are long, thin cells with tapered ends.
Water moves from cell to cell through 'pits' which are regions where the the secondary cell wall is missing and thus water has to pass only through the primary cell wall.
75
What is the structure of vessel elements?
Vessel elements are generally wider, shorter, thinner walled, and less tapered than the tracheids.
They are aligned end to end in a stack, forming long micropipes known as vessels.
The end walls of vessel elements have 'perforation plates’ (the walls have lots of holes) so enable water to flow freely through the vessels.
76
What prevents the tracheids and vessel elements from collapsing?
They are hardened with lignin which not only prevents them from collapsing but also supports the platen.
77
What type of structure are the stalks of celery?
Petioles as they support the leaves.
78
What makes up the ’strings’ of celery?
Collenchyma cells.
79
Besides tracheids and ‘xylem vessels’, what structures are found in xylem?
Xylem fibres and Xylem parenchyma.
80
What are xylem vessels also known as?
Xylem Tracheae
81
What are xylem fibres?
Dead sclerenchyma fibres that found between the vessels and the tracheids that provide mechanical support.
82
What are xylem parenchyma?
This is the only living component in the xylem tissue and consists of parenchyma cells.
They store reserves of food.
83
What is xylem divided into?
Primary xylem and secondary xylem
Primary xylem is further divided into protoxylem and metaxylem
84
How do protoxylem and metaxylem differ?
When xylem first forms it starts as protoxylem then develops into metaxylem and eventually secondary xylem.
Protoxylem has a narrower lumen. Protoxylem undergoes ‘annular and spiral thickening’ whereas metaxylem undergoes ’sclariform, reticulate and pitted thickening'
85
What is phloem composed of?
Two types of 'water conducting cells:’ Sieve tubes or sieve cells
86
How does the structure of phloem differ between plants?
Seedless vascular plants and gymnosperms have phloem with ’sieve cells’
Angiosperms have ’sieve tubes’ which are composed of chains of cels called ’sieve tubes elements’ (aka sieve tube members)
87
What is the detailed structure of phloem in angiosperms?
The phloem consists of stacks of individual cells called ’sieve tube elements.’ The sieve tube elements are alive but have no nucleus, ribosomes, distinct vacuole or cytoskeletal elements. The absence of these structures allows food to move more easily
Where the sieve tube elements join in the stack is a ’sieve plate’ with pores to allow food to move between the sieve-tube elements.
The sieve tube elements are surrounded by 'companion cells’ which are connected to the sieve tube elements by plasmodesmata. This allows proteins synthesised in the companion cell to be transported to the nucleus-less sieve tube element.
In some plants the companion cells in leaves also help load sugars into the sieve-tube elements.
88
A sieve tube element has no nucleus or ribosomes but is still alive. How is this possible?
The companion cell supplies it with proteins using plasmodesmata between the sieve-tube element and the companion cell.
89
Plants growth throughout their lives. What is this called?
Indeterminate growth.
90
Animals generally stop growing when they reach certain size. What is this called?
Determinate growth i.e. to a ‘determined’ size
91
What allows plants to keep on growing?
They leave undifferentiated regions i.e. 'meristems'
92
What meristems are found in plants and what form of growth are they involved in?
Apical meristems are found at the top of stems etc. and thus allow primary growth.
Lateral meristems are composed of ‘cork cambium’ dab ‘vascular cambium’ and thus allow secondary growth.
93
What are the basic types of growth a plant undergoes? What is the result of each?
In primary growth the plant gets taller and in secondary growth its structures i.e. the stems get thicker.
94
How can cells undergoing mitosis be identified?
By staining for ‘cyclin’, a key protein in cell division
95
What are the types of cambium seen in stems and what does each form?
Vascular cambium forms secondary xylem and secondary phloem
Cork cambium adds secondary dermal tissue.
96
Rephrase the statement ’the cells of the cambium become specialised cells’ using correct terminology?
The cells of the cambium are ‘initials’ (aka stem cells, even in plants) this means that they can become more specialised cell.
These ‘initials’ then differentiate in to ‘derivatives’ which are more specialised cells i.e. secondary xylem
97
What are ‘leaf scars’?
Scars left on the plant from petioles that have detached i.e. when trees lose their leaves
98
What is the formal term for when tress lose their leaves?
Defoliation
99
How can plants be grouped based on how long their life cycle is?
‘Annuals’ complete their lifecycle i.e. germinate → flower → die within a year or less
‘Biennials’ complete their lifecycle through years.
‘Perennials’ live many years
100
What are some examples of ‘annuals’?
Many wildflowers, legumes, wheat and rice
101
What are some examples of ‘biennials'?
Turnips
102
What are some examples of ‘perennials’?
Trees, shrubs and some grasses.
103
What protects the root as it travels through the soil?
The root cap which is found on the tip of the apical meristem of the root.
104
What is the purpose of the root cap?
To protect the root as it pushes through the soil and to secrete a polysaccharide slime to lubricate the soil.
105
What are the stages of primary growth?
Division, elongation, differentiation.
106
The stages of primary growth do not occur at once. What is the consequence of this in terms of where each form of growth occurs.
The newly formed cells are undergoing the first stage: division and thus form the ‘zone of cell division’.
Eventually as new cells are formed these original cells will begin elongation and hence form the ‘zone of elongation’.
Eventually cells in the ‘zone of differentiation’ differentiate into specific cells.
107
What occurs during the ‘division’ stage of primary growth?
Cells of the apical meristem become generic root cells.
The apical meristem cells undergo mitosis to form new cells while retaining a constant supply of undifferentiated cells.
108
What occurs during the ‘elongation’ stage of primary growth?
The cells take in water and expand to up-to 10 times their size.
It is this expansion that forces the root deeper into the soil.
109
What happens during differentiation?
The generic cells differentiate into specific cells.
This is, for example, where root hairs are formed
110
When in a root are root hairs found?
In its entirety excluding the zone of elongation and the zone of division because root hairs only form after differentiation.
111
What happens during differentiation?
The generic cells differentiate into specific cells.
This is, for example, where root hairs are formed
112
What aid the basic cross-sectional structure of a stem that has undergone secondary growth?
- At the centre is pith
- Then the primary xylem in individual vascular bundles arranged like a ferris wheel.
- Then a complete ring of secondary xylem
- A complete ring of vascular cambium
- A complete ring of secondary phloem
- A few individual bundles of primary phloem arranged like a ferris wheel
- The cortex
- The cork cambium
- The outermost layer is the periderm which is formed by the cork cambium.
113
What aid the basic cross-sectional structure of a stem that has only undone primary growth?
In order from centre to outside:
- Pith at the centre
- A ring of individual vascular bundles with primary xylem on the inside and primary phloem on the outside
- Cortex to the outside of the vascular bundles.
- Epidermis surrounding the stem
114
What does cork and bark develop from?
Periderm which is in turn produced by the cork cambium
115
What does the cork cambium form?
Periderm which later becomes cork and bark
116
What does cork and bark develop from?
Periderm which is in turn produced by the cork cambium
117
What is the basic cross-sectional structure of a root?
It has an outer epidermis layer. Then cortex.
Next is a thin ring of vascular tissue called the ’endodermis’ which is a form of ground tissue.
In side the endodermis is another ring of cells, this time vascular, called the ‘pericycle’.
In side the pericycle is the vascular cylinder, which differs between eudicots and monocots
118
What is the structure of the vascular cylinder in eudicots?
Inside the pericycle is a star shaped i.e. * collection of xylem.
Surrounding this star is phloem cells.
119
What is the structure of the vascular cylinder in monocots?
Inside the pericycle is a thick ring of phloem cells.
Inside this ring xylem cells are arranged in distinct vascular bundles like a ferris wheel.
At the core of the root is a core of parenchyma cells.
120
What type of tissue is cortex?
Ground
121
What type of tissue is endodermis?
Ground (not dermal)
122
What type of tissue is the core of parenchyma seen in monocot roots?
Vascular
123
What type of tissue is the pericycle?
Vascular
124
What type of tissue are the root hairs?
Dermal.
125
What type of tissue is Pith?
Ground.
126
What is the function of ground tissue in roots?
To store carbohydrates and absorb water and minerals from the soil.
127
What type of tissue is Pith?
Ground.
128
What is the function of ground tissue in roots?
To store carbohydrates and absorb water and minerals from the soil.
129
What do lateral roots form?
A lateral root originates form the pericycle (outermost layer of the vascular cylinder) It continues to grow through the cortex of the main root.
Eventually it grows out through the dermis of the root and thus a ‘lateral root’ appears on the side.
130
What is tissue in the root forms a boundary between the vascular and ground tissue?
The endodermis
131
How are leaves formed?
They develop from ‘leaf primordial’ which are finger-like projections along the sides of the apical meristem.
132
Where specifically in the stem does primary growth occur?
In the ‘internode’ regions between leaves. Therefore the leaf ’nodes’ become farther apart as primary growth occurs.
133
How does ‘branching occur’?
‘Axillary’ buds on the side of the stem begin to develop.
134
Is branching a form of secondary growth, primary growth or neither?
Primary growth.
135
Which buds are more likely to be inhibited: ones closer to the apical buds or ones further?
The ones closer to the active apical buds will likely be more strongly inhibited.
136
What adaption do some plants have to allow them to continue growing even if their tops are cut off?
Some monocots, particularly, grasses have meristems called ‘intercalary meristems’ at the base of the stems and leaves.
Therefore if the end of the leaf is chopped off i.e. through herbivory the grass etc. can continue growing.
137
How do lateral shoots develop?
They arise form from the epidermis tissue.
138
What is the advantage of lateral shoots developing from the epidermis as opposed to developing from the vascular cylinder as in roots?
The method in roots disrupts the vascular cylinder and thus does not allow nutrients to pass. To mitigate this many roots fork like -<.
Stems however have a branching pattern like --\-- and thus this disruption would be disadvantageous.
By forming from the epidermis, lateral stem formation does not impact the vascular system of the main stem.
139
What is a the typical structure of a monocot stem in cross section?
It has a thin layer of epidermis with an interior filled with ‘ground tissue’
Inside this ground tissue are scattered individual vascular bundles.
140
What type of tissue are sclerenchyma?
Vascular.
141
What type of cells are in the ground tissue of roots?
Mainly parenchyma. However, collenchyma cells just beneath the epidermis strengthen many stems.
Sclerenchyma cells (especially 'fibre cells’) also provide support in those parts of the stems that are no longer elongating.
142
What are ‘fibre cells’?
A form of sclerenchyma.
143
What is the cross sectional structure of a eudicot root?
Form outside to in:
They have an epidermis then a layer of ‘cortex’ Arranged in a ring like a ferris wheel are multiple vascular bundles.
Further inside is central layer of ‘pith’ in the gaps between the vascular bundles is “ground tissue connecting pith to cortex”
Each vascular bundle is like a stack (| | | | ) of tissues. The tissue closes to the epidermis is a layer of ’sclerenchyma (fibre cells)’ Next is a layer of phloem, then cambium then xylem.
144
In roots, what is on the outside: xylem or phloem?
In monocot roots the xylem is on the inside.
In eudicot roots the xylem is also on the inside forming star shape. This star is surrounded by phloem.
145
In roots, what is on the outside: xylem or phloem?
Phloem
146
In leaves, what is on the outside?
In leves the xylem is at the top (towards the palisade cells.)
147
From top to bottom, what are the tissues of the leaf?
```
Cuticle + (stoma)
Upper epidermis + (stoma)
Palisade mesophyll + sclerenchyma fibres
Vascular bundle + (spongy mesophyll)
Spongy mesophyll + sclerenchyma fibres
Lower epidermis + (guard cells, stoma)
```
148
What is the structure of the vascular bundle of a leaf?
It has an outer ring formed from ‘bundle sheath cells’ In side this is the actual vein.
The upper layer of the vein is ht xylem and the lower level is the phloem.
149
What type of tissue is the upper epidermis in the leaf?
Dermal
150
What type of tissue is the palisade mesophyll in the leaf?
Ground
151
What type of tissue is the spongy mesophyll in the leaf?
Ground
152
What type of tissue is the lower epidermis in the leaf?
Dermal
153
What type of tissue is the vein in the leaf?
Vascular (note that the vein is just the xylem and phloem - it does not include the surrounding bundle-sheat cells)
154
What type of tissue are the bundle sheath cells in the leaf?
Ground
155
What type of tissue is the xylem in the leaf?
Vascular
156
What type of tissue is the phloem in the leaf?
Vascular
157
What type of tissue is the guard cells in the leaf?
Dermal
158
Where are the sclerenchyma fibres found in a leaf and what function do they play?
They are found connecting the upper epidermis and lower epidermis to the vascular bundle. In this way they hold the vascular bundle in place whilst also providing support for the entire leaf.
159
What is mesophyll primarily composed of?
Parenchyma cells.
160
What type of cells constitute the bundle sheath cells of the leaf vein?
Typically parenchyma.
161
Where does the growth of secondary growth occur?
In the ‘lateral meristems’.
162
What species undergo secondary growth?
All gymnosperms, most eudicots but very few monocots
163
Note:
Primary growth and secondary growth occur simultaneously,
164
What provides the undifferentiated cells needed for secondary growth?
Vascular cambium
165
What are the cells in the vascular cambium a type of?
Conceptually: Meristematic cells, Physically: parenchyma cells.
166
What happens during secondary growth?
The stem thickens as the vascular cambium forms secondary xylem to the inside and secondary phloem to the outside.
Some initials of the vascular cambium give rise to vascular rays.
As secondary growth continues to increase the diameter of the vascular cambium the secondary phloem outside it ruptures as it doesn’t increase in diameter.
A second lateral meristem, the cork cambium, develops from parenchyma cells in the cortex. The cork cambium produces cork cells, which replace the epidermis.
Each cork cambium and the tissues it produces form a layer of periderm which is part of the bark.
167
What does ‘bark include’?
All the layers exterior to the vascular cambium. This includes the secondary phloem, cork cambium an the periderm produced by the cork cambium.
168
Besides secondary phloem and xylem, what does the vascular cambium produce?
'Vascular rays'
169
What are vascular rays?
Radial fibres of mostly parenchyma cells found between secondary xylem and secondary phloem.
These ‘vascular rays’ move water and nutrients between the secondary xylem and phloem, store carbohydrates and aid in wound repair.
170
What accounts for the strength of wood?
It has secondary xylem with highly lignified xylem cells.
171
What causes secondary tree rings?
In temperate regions, wood that develops early in the spring, known as early (or spring) wood consists of secondary xylem cells with larger diameters and thin cell walls to maximised delivery of water to new leaves.
Wood produced during the rest of the growing season is called late (or summer) wood. It is composed of thick-walled cells that do not transport as much water but provide more support.
In temperate regions, the vascular cambium becomes inactive during winter.
The larger thin walled cells are lighter in colour than the small cells. Therefore these seasonal variation leads to an alternating pattern of light and dark bands and thus tree rings.
172
When analysing tree rings, what are some important factors to consider?
- There is one dark band per year
- The newest ring will be the one on the outside i..e just internal to the vascular cambium. Therefore the oldest rings will be at the centre
- A thicker ring indicates better growth i.e. more available nutrients/photosynthesis performed.
173
Why is the production of bark important?
To replace the epidermis which cracks and falls off as the stem increases in diameter.
174
Does cork form in roots?
Yes.
175
What happens to the cork cambium as the stem/root expands?
It splits and cracks as the stem diameter increases and thus loses its meristematic ability.
Therefore new cork cambiums must be produced as the old ones become cork.
176
How does the cork cambium produce bark?
It differentiates to produce a thin layer of parenchyma cells to its interior called the ‘phellloderm’
To the exterior it forms cork cells. As cork cells mature, they deposit a waxy, hydrophobic material called ‘suberin' in their walls and then die. This makes the ‘cork tissue’ waterproof
177
Why is the formation of cork tissue important?
It protects the stem or root from water loss, physical damage, and pathogens
178
What is the material formed by cork cells to make them waterproof?
Suberin
179
The cork tissue is largely waterproof: what are the consequences of this and how are they mitigated?
Heavily wooded roots can’t perform water absorption and thus are primarily used for support and to extend the root system deeper.
This would block gases form entering the stem/root and thus would suffocate living cells i.e phloem inside. To mitigate this small raised areas called lenticels are places along the woody stem/root in which there are greater spaces between the cork cells and thus gases can permeate. These lenticel often appear as horizontal slits.
180
What are ‘lenticels’?
Regions of the stem/root with extra spaces between the cork cells to allow living cells i..e phloem in the woody stem or root to perform gas exchange.
181
What does ’development’ refer to?
A specific series of changes in which cells form tissue, organs and organisms.
182
What are the basic processes that occur during development?
‘Growth’, ‘morphogenesis’ and ‘differentiation'
183
What is ‘growth’ in terms of development?
A long-term increase in size
184
What is ‘morphogenesis’ in terms of development?
The process which gives a tissue, organ or organism its shape. It also involves determining the position of cell types.
185
What are B cells classed as?
Lymphocytes
186
What are T cells classed as?
Lymphocytes
187
What does ‘lymphocyte’ include?
B cells and T cells.
188
What is ‘differentiation’ in terms of development?
The process in which cells of one type develop into more specialised cells.
189
What causes differentiation to occur?
The new cell will have the same genes but changes in their expression leads to cellular differentiation.
190
What are the basic mechanisms in which plant growth occurs?
By ‘cell division’ and ‘cell expansion'
191
How do plant cells grow by expansion?
They intake water causing them to swell and thus elongated.
192
What is the ‘pre-prophase band'
Microtubules in the cytoplasm become concentrated into a ring called the preprophase band.
The band disappears before metaphase but predicts the future plane of cell division.
193
What is an important factor in growth by cell division?
It has a determined ‘plane’ which directs in which direction the cell plate will form and thus in which direction growth will occur.
194
What is the typical ‘plane’ of cell division?
The one which cuts through the shortest distance i.e. if it was a rectangle like [] it would be horizontal.
195
What does ’plane’ refer to?
The direction in which the cell plate forms and thus the direction of growth by cell division.
196
What is ’suberin’?
A chemical released to make bark waterproof.
197
What can lead to unusual planes of division during cell growth by division?
A mutant form called ’tangled-1'
198
What happens to those with ’tangled-1'
In plants of this mutates form plane of cell division is random and thus instead of forming a grid of cells and random “tangled mess” appears.
The leaves grow slower but actually end up looking normal to the naked eye.
199
What can cell division be divided into?
’Symmetric division’ and ‘asymmetric division'
200
How do symmetric division and asymmetric division differ?
In symmetric division the cell plate forms halfway along the cells and thus after cytokinesis two cells with an equal amount of cytoplasm form and thus are of equal size.
In asymmetric division the cytoplasm is not evenly shared and thus a big cell and a small cell results.
(note that both daughter cells have nuclei etc.)
201
What is an example of where ‘asymmetrical cell division’ is used?
The formation of guard cells.
202
How are guard cells formed?
An epidermal cell divides asymmetrically, forming a large cell that remains an unspecialized epidermal cell and a small cell that becomes the guard cell “mother cell.”
Guard cells form when this small mother cell divides in a plane perpendicular to the first cell division.
203
What does ‘fate’ refer to in terms of cells?
What the cell is destined to develop into.
204
What is it called when organisms have structural or chemical differences at each end?
Polarity
205
What does ’polarity’ refer to?
The condition of having structural or chemical differences at opposite ends of an organism.
206
How is directionality initiated in growth by expansion?
Cellulose microfibrils grow in bands around the cube shaped cell.
These rings do not expand. Therefore the cell can only grow up.
207
What are the basic processes which lead to specialised structures in plants called?
Morphogenesis and Pattern Formation
208
How does Morphogenesis differ from Pattern Formation?
During morphogenesis, cells acquire different identities in an ordered spatial arrangement i.e. dermal tissue forms on the exterior, and vascular tissue in the interior
The development of specific structures in specific locations is called pattern formation.
209
What is the basic concept which allows 'pattern formation’?
Cell fate in which a basic cell is destined to be a specific one.
210
What are the leading hypotheses which describe how cell fate leads to pattern formation?
The ‘lineage-based mechanisms’ and ‘position-based mechanisms’ hypothesises.
211
What is the ‘lineage-based mechanism’ of pattern formation?
The idea that cell fate is determined early in development and that cells pass on this destiny to their progeny.
This leads to ideas such as that cells at the top of the embryo will develop into ____ and those at the bottom will eventually becomes cells that develop into ___.
212
What is the ‘position-based mechanism’ of pattern formation?
The idea that cell fate is not determined based on where the originate but where they are currently located.
This is determined by chemical signals that are released form the neighbouring cells.
Therefore theoretically speaking if a random undifferentiated cell was placed in a vein it would theoretically become a phloem/xylem cell.
This also explains how cells formed by mitosis after injury become the correct type of cell.
213
How does cell differentiation occur conceptually?
With ‘differential gene expression’ in which certain genes are expressed more than others leading to different proteins and thus different features.
214
What is the ‘GALBRA-2’ gene involved in?
Controlling the distribution of root hairs on a root.
215
How can plant growth be described in terms of how the plant ages?
It ages in ‘phases’ which are specific stages with specific patterns of growth i.e. large leaves fro one phase, bug buds for the next.
Basically phases are just stages in the lifecycle i.e. child, adolescent and adult etc. in humans.
The transition between phases is called ‘phase change’ and is analogous to puberty
216
What does ’phase’ refer to?
A specific stage in plant development i.e “adult” or “child” if in human.
217
What does ’phase change’ refer to?
The transition between phases of plant growth, analogous to puberty.
