chapter 3 Flashcards
(205 cards)
1
Q
What systems does the vascular plant consist of?
A
1) A root system
2) A shoot system
2
Q
What does a root system do?
A
-anchors the plant
-absorbs water and ions from the soil
3
Q
What does a shoot system do?
A
-consists of supporting stems, photosynthetic leaves, and reproductive flowers.
-the repetitive shoot units consist of internode, node, leaf, and axillary bud
4
Q
What are the repetitive shoot units?
A
internode, node, leaf, axillary bud
5
Q
What is the node?
A
area where leaf attaches
6
Q
What is the internode?
A
area between 2 nodes
7
Q
What is the axillary bud?
A
lateral shoot apex, found at a leaf axil (basis); it produces a new branch (stem) or a flower at the time of reproduction.
8
Q
What is the shoot apex?
A
It bears the terminal bud.
9
Q
What is the area where leaf attaches?
A
Node
10
Q
What is the area between 2 nodes?
A
internode
11
Q
What is the lateral shoot apex, found at the leaf axil, and which produces a new stem/flower at the time of reproduction?
A
axillary bud
12
Q
What bears the terminal bud?
A
The shoot apex
13
Q
What are the 3 types of tissues that the roots, shoots and leaves are comprised of?
A
Dermal tissue
ground tissue
Vascular tissue
14
Q
Dermal tissue
A
epidermis and stomata forming the outer protective layer
15
Q
Ground tissue
A
functions in storage, photosynthesis, and secretion. In addition to fibers that support the plant; structural support.
parenchyma collenchyma
and schlerenchyma.
16
Q
Vascular tissue
A
conducts fluids and dissolved substances.
17
Q
Why are these 3 tissues called the tissue system?
A
Because each of these tissue extends through the root and shoot systems.
18
Q
What are tissues made of?
A
Cells
19
Q
What is the 3 main factors that can help us differentiate between the plant cell types?
A
1-the size of their vacuole
2-the thickness of their cell walls (with secondary cell wall or not)
3-whether they are living or dead at maturity
20
Q
What does the plant cell wall consist of?
A
cellulose
21
Q
what is the primary cell wall of plant cells?
A
strong, protective, waterproof cover surrounding the cell
22
Q
what is the position of microtubules wrt cellulose fibers?
A
parallel
23
Q
Where is the secondary cell wall located?
A
It is laid in between the plasma membrane and the primary cell wall (outermost).
24
Q
What does the secondary cell wall contain?
A
contains more layers of cellulose, in addition to other strengthening molecules, like lignin and pectin
25
lignin and pectin
strengthening molecules
26
Where does new plant growth occur?
Meristems
27
What are meristems?
Meristems are undifferentiated cells that can divide indefinitely to give rise to different types of cells.
Hence, they are cells that retained the ability to divide by mitosis or actively dividing embryonic tissues
28
What does each Meristematic cell give rise to?
Each meristematic cells gives rise to 2 daughter cells:
- 1 remains meristematic
- the other differentiate and contribute to the plant body
29
What does the meristem consist of?
Meristematic cells have dense cytoplasm and large nuclei.
30
What are the 2 types of meristems?
1)Apical meristems:
Responsible for the increase in length, called primary growth.
Extension of shoot and root produced by apical meristems.
Found in herbaceous and woody plants.
2)Lateral meristems:
Responsible for the increase in width (girth), called secondary growth.
Lateral meristems produce an increase in shoot and root diameter.
Found only in woody plants.
31
What are the tissues produced by the apical meristems?
primary tissues
32
primary tissues
The tissues produced by the apical meristem
33
What does the elongation of the shoot and root form?
primary plant body
34
What protects the root apical meristem?
Root cap
35
What protects the shoot apical meristem?
Leaf Primordia
36
Leaf primordia
Leaf primordia are embryonic leaves that protect the stem apical meristem.
37
Where is the bud primordia located? And what does it give rise to?
located at the base of a leaf axil (base), gives rise to a branch or a flower.
38
Where are root apical meristems found?
behind the root cap
39
What produces the root cap cells
Root cap cells are produced by the root meristem and are sloughed off and replaced as the root moves through the soil.
40
What are the 3 types of embryonic tissues that apical meristems give rise to?
The apical meristems gives rise to 3 types of embryonic tissues called primary meristems. The 3 primary meristems:
1.The protoderm: forms the epidermis.
2.The procambium: forms the primary vascular tissues(xylem and phloem)
3.The ground meristem: forms the ground tissue.
Few plants have an additional primary meristem:
4.intercalated meristems
Found in some plants only. Ex. corn and horsetails.
Found in the stem internodes
They add to internode length
(further increase in stem elongation in a short time).
41
Which embryonic tissue forms the epidermis?
the protoderm
42
Which embryonic tissue forms the primary vascular tissues(xylem and phloem)?
The procambium
43
What embryonic tissue forms the ground tissue?
the ground meristem
44
What does secondary growth result from?
Secondary growth results in the formation of the secondary tissues or secondary plant body.
Secondary growth results from the activity of lateral meristems.
45
What are the 2 types of lateral meristems?
a)CORK CAMBIUM: forms the outer bark
b)VASCULAR CAMBIUM: forms the secondary vascular tissues.
It divides to give 2⁰ xylem to its inside, known as wood,
and 2⁰ phloem to its outside, known as inner bark
46
What forms the outer bark?
cork cambium
47
What forms the 2ndary vascular tissues?
Vascular cambium
48
What is the secondary xylem known as?
wood
49
What is the secondary phloem known as?
inner bark
50
What type of growth do herbaceous plants exhibit? And what happens to them?
-Herbaceous plants exhibit only primary growth: increase in length.
-Some herbaceous plants become woody (ex. apple tree).
51
What type of growth do woody plants exhibit?
both primary and secondary growth
52
primary growth
Increase in length due to:
stem and root apical meristems
53
secondary growth
Two lateral meristems:
-Cork cambium:
forms the outer bark
-Vascular cambium:
inner bark (2⁰ phloem)
and wood (2⁰ xylem)
54
What is the epidermis?
the outer protective covering that covers all the surfaces in herbaceous plants.
55
How thick is the epidermis?
one cell-thick
56
What is the epidermis made of?
It is made of epidermal cells:
-transparent(and living) cells
-originating from the protoderm
57
What do the epidermal cells secrete?
a fatty and waxy cutin layer known as cuticle.
The cuticle is waterproof –> it prevents desiccation
58
What is the cuticle?
a fatty and waxy cutin layer; it is waterproof –> it prevents desiccation(drying out)
59
What are the specialized cells that the epidermis contains as well?
guard cells, trichomes and root hairs
60
Guard cells
---Are green, paired, sausage-shaped, and the only epidermal cells with chloroplasts.
---They allow gas exchange
-When they separate, they show an opening = stoma
61
Where are the guard cells found?
-In epidermis of leaves, sometimes stems and fruits.
-Usually more numerous on the lower leaf epidermis to decrease water loss.
62
Why are the guard cells more numerous on the lower leaf epidermis?
to decrease water loss
63
What happens when guard cells separate?
stoma shows=opening
64
Trichomes
-hair-like outgrowth of the epidermis
-unicellular/multicellular
-vary regarding the plant species
-found on leaves, stems, fruits.
65
What are the trichomes' major functions?
---Reduce evaporation by covering stomatal openings
---Protect leaves from high-intensity light and ultraviolet radiation
---Can buffer against temperature fluctuations
---Some are glandular; secreting sticky or toxic substances to deter herbivory
66
Root hairs
are tubular extensions of epidermal cells. They increase the surface area for absorption of water and minerals.
67
Where are root hairs found?
in the zone of maturation, just behind the tip of a young root
68
Important notes about root hairs
-A root hair is not a cell!
-Root hairs are not lateral roots (/root branches).
69
What the cells that ground tissues primarily contain?
parenchyma cells
collenchyma cells
sclerenchyma cells,
70
Parenchyma cells
-most common and abundant
-thin walls and large vacuoles
-only have primary cell wall
-less specialized than the other cells
-Have a living protoplasm:
remain alive after they mature and may live for many years
71
What does having a protoplasm mean?
Have a living protoplasm:
remain alive after they mature and may live for many years
72
What are parenchyma cells' major functions?
i) Storage(water; food; resins; nectar…)
ii)Photosynthesis: some are green and contain chloroplasts; they are also called chlorenchyma.
iii) Secretion(water; food; resins; nectar…)
73
Collenchyma cells
---Have a living protoplasm
---only have primary cell wall=lack secondary cell wall
---longer than wide with cell wall varying in thickness/ unevenly thickened 1°cell wall (thicker at the corners).
74
Where are collenchyma cells found?
---Not found everywhere in the plant.
---Found beneath the stem epidermis and along leaf veins
Ex. Found in celery strings
75
Sclerenchyma cells
*Have tough and thick walls.
*Have secondary cell wall with lignin ---> rigid
*Are usually dead at maturity= NO protoplasm
76
What is the function of Sclerenchyma cells?
provide rigid and mechanical support and protection
---> strengthening the tissues
77
What are the 2 types of sclerenchyma cells?
i) FIBERS: long and slender cells, found in groups (strands).
Ex. Linen is woven from fibers of flax phloem
ii) SCLEREIDS: vary in shape, often branched (star-shaped).May occur singly or in groups.
Found in hard seed coats (pits of fruits)
Ex: In pear fruits: there is special type of sclereid in soft flesh giving the fruit its gritty texture.
78
What is the xylem tissue made of?
Tracheids
Vessel members
Fibers
Parenchyma
78
Vascular Tissues
a)XYLEM:
-conducts water and dissolved minerals
a)PHLOEM:
-conducts sugars (mainly sucrose) used by plants as food;
-also transports hormones, amino acids and other substances needed for plant growth.
79
Tracheids
1-Dead cells with tapered ends
2-Hollow
3-thick, lignified 2°cell wall (for support)
4-have pits(small areas with no 2°cell wall) to allow continuous water flow from one tracheid to another.
5-Found in clusters
6-Function in water conduction and support
7-Found in all vascular plants.
80
what are the pits in tracheids for?
(small areas with no 2°cell wall) to allow continuous water flow from one tracheid to another.
81
Vessel members
1-dead and hollow at maturity.
2-have a lignified 2°cell wall.
3-shorter and wider than tracheids
4-arranged end to end, forming tubes called vessels= a stack of vessel members.
5-have open ends (at the end of the cell), called perforation plates to allow for water to move up from cell to cell.
-have pits for lateral water transport
-more efficient in water conduction.
-ONLY found in angiosperms
82
Perforation plates
open ends at the end of the cell that allow water to move up from cell to cell.
83
Fibers
1-Provide support
2-Dead and elongated cells with lignified 2°cell wall.
84
Parenchyma
1-Function in storage(of food: starch, fats…)
2-In woody stems, the parenchyma also function in lateral water conduction and food storage.
3-They are usually found in horizontal rows called rays.
4-Rays are produced by ray initials in the vascular cambium.
85
What is the phloem tissue made of?
Sieve cells
Sieve tube members
Companion cells
fibers
parenchyma
86
Sieve cells
1-Function in food conduction
2-Found in ferns, horsetails, and gymnosperms.
3-Are living at maturity, but their nucleus dies.
4-Long cells with clusters of pores called sieve areas.
5-Unlike the pits of xylem cells, which contain 1mary cell walls, phloem pores are completely open.
87
Sieve tube members
1-Function in food conduction
2-Found in angiosperms.
3-Are living at maturity, but their nucleus dies.
4-They are more efficient in food conduction.
5-The cells are arranged end to end forming continuous tubes called sieve tubes.
6-The pores at the end of the cells are larger, called sieve plates.
88
Companion cells
-each sieve tube member is associated with an adjacent parenchyma cell called companion cell.
-Function: carry out some of the metabolic functions needed to maintain sieve-tube member (ex. Loading and unloading sugars).
-Living cells with many cytoplasmic connections called plasmodesmata (to connect to sieve tube members).
-They are found in angiosperms(only).
89
Plasmodesmata
cytoplasmic connections; to connect to sieve tube members
90
Fibers
provide support
91
Parenchyma
function in storage
92
What are roots adapted for?
Roots are adapted for growing underground and absorbing water and minerals.
93
What is the root structure?
1.Root cap
2.Zone of cell division
3.Zone of cell elongation
4.Zone of maturation
94
What is the root cap composed of?
a)The inner columella cells
b)The outer, lateral root cap cells
These cells are continuously being formed by the root apical meristem
95
What are the main functions of the root cap?
-to protect the delicate tissues of the root apical meristem from abrasion with soil particles.
96
What do outer root cap cells have?
-Golgi bodies that continuously secrete a slimy substance called mucigel that is released through the cell wall to the outside.
-Mucigel acts as lubricant, facilitating root movement through the soil.
-It also provides a medium for the growth of nitrogen-fixing bacteria in legume roots.
97
How does the root cap function in the perception of gravity?
The root cap also functions in the perception of gravity. Columella cells contain amyloplasts (plastids with starch grains) that collect on the sides of cells facing the pull of gravity. Amyloplasts indicate the direction of gravity (so that roots bend toward gravity).
98
what are amyloplasts?
plastids with starch grains that collect on the sides of cells facing the pull of gravity. They indicate the direction of gravity.
99
What does the zone of cell division contain? And where is it located?
It contains the apical meristem and consists of actively dividing cells at a rate every 12-37 hours.
Most of the cells are cuboidal, with small vacuoles and large nuclei.
These rapidly dividing cells are daughter cells of the apical meristem.
In the center of the apical meristem, there is a quiescent center = a group of cells that divide infrequently.
----It is located behind the root cap
100
What do the apical meristem daughter cells subdivide in to?
The apical meristem daughter cells subdivide in to the 3 primary tissues: protoderm, procambium and ground meristem
101
In Arabidopsis, what has been identified?
In Arabidopsis, 2 genes have been identified as regulating patterning of these 3 tissue systems (1°meristems).
102
Where does the patterning of these cells begin?
The patterning of these cells begins in this zone of cell division, but the expression of this patterning is not fully revealed until the cells reach the zone of cell maturation.
103
In Arabidopsis, What are the 2 genes that have been identified as regulating patterning of these 3 tissue systems (1°meristems)?
1)WEREWOLF (WER) GENE
-WER suppresses root hair development in nonhair and hair epidermal cells.
-Plant with the WER mutation have an excess of root hairs
2)SCARECROW (SCR) GENE
-is required for the differentiation of ground meristem cells into ground tissue cells and endodermis via asymmetrical cell division.
-SCR mutants form a single layer of cells that have both endodermal and ground cell traits (instead of forming an outer layer of ground tissue and inner layer of endodermis).
104
Zone of cell elongation
*Roots lengthen in this zone, only!
*no cell division.
*The cells increase in size.
*Cells become longer than wide.
105
Zone of cell maturation
*Cells differentiate into specific cell type.
*Cells at the surface become epidermal cells.
*Root hairs develop in this area.
*Other cells form: parenchyma (cortex); endodermis; and vascular tissue (to the center).
106
Epidermis
-thin cuticle to allow water absorption
-Epidermal cells with root hairs or non-hair epidermal cells.
-Root hairs increase the surface area for water and mineral absorption
107
Cortex
-It is made of parenchyma cells(produced in the ground meristem)
-Cortex functions in food storage.
108
Endodermis
-The inner layer of the cortex differentiates into endodermis.
-Endodermal cells have a 1°cell wall impregnated with suberin, a fatty and water proof substance.
-Suberin is produced in bands called Casparian strips, surrounding every endodermal cell (at the end of the cell).
-Function of endodermis: controls what ions and other substances enter the core of the root (then xylem) ---> regulates intercellular flow of water and solutes in the vascular core of the roots; blocks harmful and toxic substances.
109
Suberin
a fatty and water proof substance impregnated in endodermal cells' primary cell wall. It is produced in bands called casparian strips.
110
Casparian strip
---fills the space between the cells of the endodermis.
---a waterproofing band that forces water and minerals to pass through the plasma membranes of endodermal cells, rather than through the spaces in the cell walls
111
Where is the pericycle located?
behind (just after) the endodermis.
112
Stele
-Is the tissues interior (after) to endodermis
-Inside the stele, there is a layer of parenchyma cells that can divide; it is the pericycle.
113
What is the function of the pericycle?
--giving rise to lateral roots (root branches)
--giving rise in (woody) dicots to the lateral meristems: vascular cambium and cork cambium.
--After the pericycle, there are vascular tissues (xylem and phloem); but their arrangement differs in monocot and dicot roots.
114
What happens in monocot roots?
--There is a pith made of parenchyma cells (storage function) at the core of the root.
--It is surrounded by a primary xylem found in discrete vascular bundles (veins) arranged in a ring.
--Phloem are found in patches in between the xylem
115
What happens in dicot roots?
-There is no pith at the center of the root.
-Instead, xylem occupies the core of the root and it forms radiating arms, often star-shaped.
-Phloem is found in patches between the xylem arms
116
Root cross section of monocots and dicots similarities
Both have epidermis, cortex, endodermis, and stele.
Inside the stele, there is a layer of pericycle.
117
Root cross section of monocots and dicots differences
--There is a pith at core of a monocot root; surrounded by xylem veins in a circle, and phloem in patches.
-The xylem (radiating arms) is at the core of a dicot root, surrounded by phloem in patches between the xylem arms
118
How is the root vascular cambium formed?
In woody dicots, some roots become woody (2ndary growth).
This involves the formation of a root vascular cambium from the pericycle and some parenchyma cells found in between xylem and phloem veins.
119
What does the root vascular cambium form?
---The root vascular cambium forms 2ndary xylem (wood) to its inside and 2ndary phloem (inner bark) to its outside.
---The root increase in width.
---The outside of the pericycle will be lost and replaced with bark.
120
What are the 2 types of roots that most plants produce?
Taproot or fibrous root
121
Taproot system
Taproot system consists of a single large root with smaller branches. (ex. apple tree).
122
Fibrous root system
Fibrous root system consists of many smaller roots of similar diameter. (ex. onion).
123
What is an adventitious root?
---Any root that arises along a stem or in some other place than a root.
---Not all roots come from pre-existing roots.
124
What are the roots modified for functions other than water and mineral absorption?
1.Prop roots
2.Aerial roots
3.Pneumatophores
4.Contractile roots
5.Parasitic roots
6.Food storage roots
125
Prop roots
-Keep the plant upright
-Support the plant against wind
-are adventitious; thick roots emerging from lower part of stems;
-Found in some monocots like corn
126
Aerial roots
-Obtain water from air
-Found in epiphytes (plants that grow attached on top of another plant); ex. orchids
-Have aerial roots for support
-Roots have a thick epidermis (many cell thick) to reduce water loss
-If aerial roots are green, like in vanilla orchids, they are photosynthetic.
127
epiphytes
plants that grow attached on top of another plant
128
Pneumatophores
-Are spongy outgrowths of roots
-Usually extend few cm above water surface
-Facilitate oxygen uptake to underwater roots
-Found in some plants growing in swamps
-ex. mangrove tree.
129
Contractile roots
--Pull plant deeper in soil
--Roots from bulbs (lilies) and some plants (dandelion) form contractile roots that contract and push by spiraling new bulbs deep in the soil until they attain a suitable soil temperature for growth
130
Parasitic roots
--Called haustoria
--Found in some plants that lack chlorophyll
Ex. Dodder
-Penetrate the host plant (to which they are attached to); they make contact with the conducting tissue of the host to steal carbohydrates.
131
Food storage roots
---Store carbohydrates
---Root contain many parenchyma cells in the xylem of branch roots(storing starch).
Ex. Sweet potato; carrot; radish; turnip; beet; parsnip
132
Water storage roots
----Store water in roots
-Found in pumpkin family (Curcurbitaceae)
-In plants growing in arid (dry) regions.
133
Buttress roots
-Huge (above ground) roots at the base of a tree trunk
-Give great stability and support
-Found in fig tree and other tropical trees
134
Similarly to roots, what do stems contain?
Similar to roots, stems contain the 3 types of plant tissues.
135
What are stems' functions?
-the backbone of the shoot
-Transport nutrients and water
-Support the aerial plant parts (leaves, fruits…)
136
What does the shoot apical meristem produce?
The shoot apical meristem produces new stem tissues and primordia.
137
What does primordia produce?
Primordia produce leaves, other shoots or flowers
138
What are the leaves attached to?
leaves are attached to the stem
139
What is the pattern of leaf arrangement called?
phyllotaxy.
140
What is the leaf arrangement designed for?
It is designed to optimize exposure of leaves to the sun.
141
What are the 3 ways that leaves may be arranged around the stem?
-Alternate arrangement (spiral)
most common
1 leaf per node
-Opposite arrangement
2 leaves per node
-Whorled arrangement(in circle)
many leaves per node
142
node
point of attachment of leaf to stem
143
internode
area of stem between 2 nodes
144
blade
flattened part of leaf
145
petiole
stalk of leaf
146
Axil
angle between petiole/blade and stem
147
Axillary bud
develops into branches with leaves or may form flowers
148
Terminal bud
extends the shoot system during the growing season
149
What do Monocots and herbaceous dicots have in common?
Monocots and herbaceous dicots have the epidermis (with cuticle) as outermost layer.
150
What does the stem epidermis commonly have?
The stem epidermis commonly have stomata, and sometimes trichomes.
151
How do the stems of monocots and herbaceous dicots differ in the arrangement of their vascular tissues?
*In monocots (like grasses), the vascular bundles (veins) are scattered throughout the ground tissue.
*In dicots, the vascular bundles are arranged in a ring (circle), with internal ground tissue termed pith, and external ground tissue called cortex.
*Each vein in monocot stem contains xylem to the center and phloem to the outside.
*Each vein in dicot stem contains xylem to the center; a layer of vascular cambium, and phloem to the outside.
152
What does the herbaceous dicot stem consist of?
--Epidermis
--Cortex (collenchyma and parenchyma)
--Veins in a circle (xylem to center; vascular cambium; phloem to outside)
--Pith (at the center): parenchyma (storage)
153
What does the monocot stem consist of?
--Epidermis
--Veins scattered in ground tissue (parenchyma)
--Each vein: xylem to center; phloem to outside.
154
How can the herbaceous stem become woody? What must develop in order for this to happen?
----A herbaceous stem can become woody as the plant undergoes secondary growth (increase in width
---For this, the lateral meristems need to develop.
155
The vascular cambium divides to give what?
-to the inside: 2dary xylem = wood
-to the outside: 2dary phloem = inner bark
156
What happens as the secondary vascular tissue expands?
--the pith and the 1 ⁰ xylem at the center become crushed; the 1 ⁰ phloem breaks apart.
---The 1 ⁰ vascular tissues become non-functional and the 2⁰ xylem and 2⁰ phloem replace them in function.
157
What happens when the stem increases in diameter?
the epidermis, cortex and 1⁰ phloem break apart/slough off
158
What happens to the cork cambium when the stem increases in diameter?
The cork cambium develops in the outer cortex (from a few epidermal cells and cortex cells).
The cork cambium divides to give:
-To the inside: parenchyma-like cells called phelloderm cells.
-To the outside: cork cells.
159
What do the cork cambium, cork cells and phelloderm cells form?
Periderm/outer bark
160
What does the periderm replace?
The periderm replaces the epidermis and the cortex in function.
161
What is the state of cork cells at maturation?
Cork cells are dead at maturity; they are impregnated with suberin, a water proof substance (replacing the cuticle).
162
Lenticels
--located In the outer bark,
--unsuberized cork cells.
--allow for gas exchange; they replace the stomata.
163
Why do the lenticels allow for gas exchange?
they replace the stomata
164
What does the secondary growth involve?
The vascular cambium divides and connects to form a ring.
It divides to give to the inside 2 xylem and to the outside 2 phloem.The secondary vascular tissues replace the primary vascular tissues in function.
The cork cambium is formed and it divides to give to its inside phelloderm cells and to its outside cork cells.
The outer bark (or periderm) replaces the epidermis and cortex in functions.
Lenticels (unsuberized cork cells) replace the stomata.
165
simple definition of periderm/outer bark
*Periderm or outer bark = cork cambium, cork, and phelloderm
166
Simple definition of lenticels
Lenticels – Cork cambium produces unsuberized cells that permit gas exchange to continue
167
In a cross-section of a woody tree trunk, what can we recognize?
Heartwood
sapwood
Springwood
Summer wood
168
Heartwood
--- inner, non-conducting primary xylem, which is darker and resistant to decay.
---Its function is support, only.
169
Sapwood
---functional 2°xylem, which is lighter in color.
---Its functions are conduction and support.
170
Springwood
---xylem cells are larger as there is plenty of
water in soil in spring; (also called earlywood)
171
Summerwood
---xylem cells are smaller(less water in soil);
(also called latewood).
172
Why ,in temperate regions, is annual growth of a tree (increase in width) is seen as annual rings?
because of springwood and summer wood
173
Dendrochronology
Dendrochronology is the science of determining the age of trees.
174
What are the 3 stem modifications?
---Most stems grow upright.
---Some grow horizontally. However, we can differentiate them from roots because (unlike roots) stems have leaves, nodes, internodes and buds in leaf axils.
---Some stems are modified for several purposes, such as vegetative reproduction(propagation).
175
Bulbs
Ex. Onions, lilies, tulips.
---Are swollen, underground stems.
---produce adventitious roots at their base.
---consists of fleshy leaves (for storage) around a small knob-like stem.
---The fleshy leaves store carbohydrates.
----They are surrounded by thin, papery brown leaves (protection).
176
Corms
-they superficially resemble bulbs
-they lack fleshy leaves
-they are swollen, underground stems
-they produce adventitious roots
-they are protected by brown, papery leaves.
-Ex. Crocus, gladiolus
177
Rhizomes
-are horizontal, underground stems, with adventitious roots.
-they produce a small scale-like leaf with an axillary bud at each node.
-ex. Perennial grasses; irises; ferns
178
Runners and Stolons
-Runners are horizontal stems with long internodes that grow along the ground surface (above ground).
-At each node, a new plant is produced.
-Ex. Strawberries
-Some botanists refer to stolonsfor the underground stems with long internodes; such as in white potatoes.
(In potatoes, tuber develop at the end of stolons).
179
Tubers
-are swollen, underground stems, that store carbohydrates;
or swollen tips of stolonsthat store carbohydrates.
-they form at the tip of stolons.
-they produce ‘eyes’ or axillary buds in the axils (base) of scale-like leaves.
-each ‘eye’ gives rise to new potato plant.
180
Tendrils
-are modified stems that function in support and climbing.
-ex. Grapes and ivy.
-note: in peas and pumpkins, tendrils are modified leaves
181
Cladophylls
-are flattened, green, photosynthetic stems of cacti.
-note: the spines of cacti are modified leaves.
182
How do leaves start from primordia?
by apical meristems.
183
What do leaves have unlike stems and roots?
Unlike stems and roots, leaves have determinate growth.
They stop growing at maturity.
They are the principal site of photosynthesis
184
There are 2 types of leaves
Microphyll= leaf with 1 vein (only found in clubmosses/Lycophyta)
Megaphyll= leaf with many veins(found in seed plants and ferns
185
How do leaves of monocots and dicots differ?
In monocots (ex. Grasses): leaves are long and narrow with parallel venation; lacking a petiole.
In dicots (ex. Sunflowers): leaves have a flat and expanded blade with netted (or branched) venation. Leaves are usually with a petiole; and sometimes they may have stipules (outgrowths at the base of the petiole in form of leaf-like or spine).
186
Simple leaf
A simple leaf has an undivided blade.
The blade may have teeth, indentations, or lobes
187
Compound leaf
A compound leaf has blade divided into leaflets.
188
Summarize the internal leaf structure
A leaf is composed of an upper epidermis, lower epidermis, a photosynthetic tissue called mesophyll in between, and veins (vascular bundles
189
Epidermis
EPIDERMIS
-it is the outside cover
-it is made of transparent cells with no chloroplasts.
-the epidermal cell secretes the waxy cuticle (waterproof)
-the epidermis may contain trichomes and glands.
-it has slit-like openings, stomata, for gas exchange.
-a stoma is found between guard cells (only epidermal cells with chloroplasts).
-stomata are more numerous in the lower epidermis (to reduce water loss).
190
Mesophyll
MESOPHYLL
-Is the photosynthetic tissue between the upper and lower epidermis
-It is made of chlorenchyma cells(parenchyma with chloroplasts).
-In most dicots, it is differentiated into 2 regions:
a)Palissade mesophyll
-bellow the upper epidermis
-made of tightly packed (columnar) parenchyma cells (usually 2 rows)
b)Spongy mesophyll
-toward the lower epidermis
-chlorenchyma cells are loosely arranged
-there are many air spaces: help in gas exchange and exit of water vapor from leaves
191
Palisside mesophyll
-bellow the upper epidermis
-made of tightly packed (columnar) parenchyma cells (usually 2 rows)
192
Spongy mesophyll
-toward the lower epidermis
-chlorenchyma cells are loosely arranged
-there are many air spaces: help in gas exchange and exit of water vapor from leaves
193
In monocots, what happens to the mesophyll?
In monocots, there is no differentiation of the mesophyll into palisade and spongy layers, and there is little distinction between the upper and lower epidermis.
194
Veins(vascular bundles)
In both dicot and monocot leaves, there are veins (or vascular bundles/with xylem and phloem tissue) that run in the mesophyll
195
Modified leaves
1)Floral leaves or bracts
2)Spines
3)Reproductive leaves
4)Window leaves
5)Shade leaves
6)Insectivorous leaves
196
Floral leaves/bracts
-Leaves are large and colored; they surround tiny yellow flowers.
-They have the same function as petals (attract pollinators).
-Ex. Poinsettia
197
Spines
-Sharp leaves with small surface area to reduce water loss and deter predators.
-Ex. Cacti
198
Reproductive leaves
-Some plants produce plantlets along leaf margins.
-When plantlets fall, they give rise to new plants (propagation function).
-Ex. Kalanchoe plant; ferns.
199
Window leaves
-Many plants in arid regions produce succulent, cone-shaped leaves with transparent tips.
-Leaves often become buried in sand (when blown by wind).
-Window leaves (with thick cuticle) allow light to pass so that photosynthesis can proceed below the soil surface
200
Shade leaves
-When there is too much shade, the leaves become larger in surface area(to receive more light), but thinner as there is less mesophyll.
201
Insectivorous leaves
*There are around 200 plants that have leaves to trap insects.
*These plants often grow in acid swamps and areas deficient in some minerals, mainly nitrogen.
*The plant catches and digests insects to supply the missing nutrients
202
Pitcher plant
Have cone-shaped leaves in which rainwater accumulates; inside the leaves, there are stiff, down-oriented hairs.
Insect that drowns cannot escape.
Plant releases enzymes to digest insect
203
Sundews
Have glandular trichomes on leaves that secrete sticky material to trap insects
204
Venus fly trap
Leaf is made of 2 halves, with trigger hairs.
Hairs are stimulated when insects move.
The 2 halves snap shut, trapping insect
