Midterm Flashcards
(149 cards)
1
Q
Population Genetics
A
a change in population allele
frequencies over time
-modification is the result of genetic changes
2
Q
Phylogeny
A
a hypothesis
of ancestor-descendent
relationships
3
Q
Nodes
A
represent
common ancestors
4
Q
Tips
A
represent the
descendants of that
ancestor
5
Q
Roots
A
As we move from
root to tip we are moving
forward in time
6
Q
Vascular Plants
A
- plants with
plumbing (trachea refers to
“windpipe”)
-contain xylem and phloem
7
Q
Xylem
A
transports water through the plant
8
Q
Phloem
A
transports soluble organic compounds (made from photosynthesis)
9
Q
Tracheids
A
elongated cells that transport water and mineral salts through the Xylem
10
Q
When did the first seed appear?
A
Upper Devonian
11
Q
When did trees evolve and what were they considered?
A
Near the end of the Devonian Period (355 mybp)
-first tress where experiments, combining wood and growth like features like conifers with fern-like reproductive structures.
-These first trees are treated as
progymno-sperms, the earliest
members of the lignophyte
clade.
12
Q
Southern Ontario forest
A
dominated by beech, maple and oak trees
13
Q
Tropical Forests
A
-dozens of spp of flowering plant trees are
co-dominant
-biodiversity is very high
14
Q
Grasslands
A
-too dry for tress
-cover 1/5 of our terrestrial environment
-12000 species
15
Q
Ethnobiology
A
the study of the relationships between living things and human culture
16
Q
What are plants?
A
-Plants produce oxygen while packaging the sun’s energy into compounds needed for life.
-They make up more than 80% of the total biomass on earth.
17
Q
What are bacterial cell wall composed of?
A
are composed of peptidoglycan, a complex of protein and sugars.
18
Q
What are Archaeal cell walls composed of?
A
are composed of polysaccharides
(sugars)
19
Q
What are eukaryotic cell walls composed of?(plants&fungi)
A
in plants they are composed of cellulose, and the cell walls of fungi are composed of chitin.
20
Q
Archaeplastida super-group (3 groups?)
A
consist of 3 groups: Viridiplantae (green algae
and plants), red algae (Rhodophyta), and Glaucocystophytes (glaucophyta).
21
Q
3 domains of organisms?
A
Bacteria and archaea (prokrayotes) and Eukaryota (cells with nuclei).
22
Q
Prokaryotes facts
A
-First forms of life on earth were prokaryotes (3.5 billion years ago)
-For about 1.3 billion years no other organisms existed
-Eukaryotes evolved from prokaryotes
-prokaryotes are less complex than eukaryotes
23
Q
prokaryotic cells features
A
-Prokaryotic cells do not have organelles
-surrounded by a cell membrane that controls the movement of water, gases, and molecules in and out of the cell
24
Q
Archaeplastida Super-Group: Key Features
A
-All members have plastids (organelles for photosynthesis).
-Most plastids are functional.
-Plastids have two membranes, indicating a single endosymbiotic event.
-Event involved phagocytosis of a cyanobacterium (a gram-negative bacteria, not true algae).
-Cyanobacteria caused the Great Oxidation Event (~2.2-2.4 billion years ago) in the Proterozoic era
25
The Great Oxygenation Event (GOE): Overview
-Cyanobacteria are oxygenic phototrophs.
-Before ~2.4 bya, anoxygenic photosynthesis and chemosynthesis dominated, using H₂S, H₂, and Fe²⁺ as electron donors.
-Cyanobacteria introduced oxygen into the atmosphere over 200-300 million years, displacing methane.
-This led to a global extinction of many anaerobic taxa due to the toxic oxygenated atmosphere.
26
Endosymbiotic Theory: Overview (Lynn Margulis, 1970s)
-Proposed to explain the origin of organelles (e.g., mitochondria, chloroplasts, possibly nuclei).
-Organelles with double membranes such as mitochondria, and chloroplasts (even nuclei) themselves probably originated
as prokaryotes that invaded another prokaryotic cell
27
Phagocytosis
is a form of endocytosis where cells
surround food particles and package them in vesicles that bud off from the cell membrane.
28
Mitochondria
-the energy factories of the cell
-Mitochondrial DNA (mtDNA) is haploid and matrilineal
-double membrane
-inner membrane is folded, form the cristi where membrane bound reactions takes place
29
Chloroplast
-site of photosynthesis
-have their own maternally haploid cpDNA. It can range from 120k-170k bp
-can reproduce by binary fission within the cell but controlled by the nucleus
-double membrane
-a series of stacks(grana) of inner membranes called thylakoid membranes(light-dependant reactions)
-Thylakoid membranes are folded like this to increase surface area for electron transport chain reactions.
-Light-independent reactions take place outside the grana
-The end product of photosynthesis is glucose
30
Transition from Water to Land: Basic Needs & Adaptations
Basic Requirements for Plants:
Light
Water
Carbon dioxide
Oxygen
Minerals
Adaptations for Life on Land:
-Developed roots (for water/mineral absorption) and stems (for support).
-Leaves for photosynthesis.
-Waxy cuticle to reduce water loss.
-Stomata for gas exchange (O₂, CO₂).
-Sporopollenin to protect against drying.
-Symbiosis with fungi (mycorrhizae) for better nutrient absorption.
Challenges on Land:
-Water scarcity, lack of structural support.
-Exposure to harsh conditions like sunlight, wind, and temperature extremes.
31
Roots
Anchor the plant and collect water
32
Stems
Stems support the plant and its leaves, which perform photosynthesis. In young, non-woody plants, stems also help with photosynthesis. They also contain the vascular system that transports water, nutrients, and food throughout the plant
33
Epidermis
outer layer of above-ground cells
surrounded by a waxy cuticle to prevent water
loss
34
eipphytes
grow on hard surfaces, such as other plants or rocks. They get most of the water and nutrients they need from rain and the air.
35
2 flowering plants that grow in antarctic
pearlword and antarctic hairgrass and about 130 species of bryophytes (mosses, hepatics and liverworts).
36
Poa annua: Key Facts
Reported on the island in 2017/2018 and subsequently destroyed.
An aggressive invasive species often used as turf grass on golf courses.
One of the most widely distributed plant species in the world.
Considered a synanthropic pioneer species (thrives in human-altered environments).
37
Key Features of Plant Cells
Cell wall: Offers strength, shape, protection, regulates transport
Plasma membrane: An inner layer beneath the cell wall.
Vacuole: A large space for storage and enzyme sequestration.
Cytosol/Cytoplasm: The fluid area between the vacuole and plasma membrane.
Nucleus: Houses genetic material and regulates gene expression.
Chloroplasts: Aid in photosynthesis and starch storage.
Mitochondria: Responsible for energy production via respiration.
Endoplasmic reticulum: Produces proteins and stores calcium; connected to the nucleus.
Golgi apparatus: Involved in cell wall polysaccharide synthesis
38
Totipotency
is the ability for single
cell to change from one cell type to
another and even develop into a
whole plant
39
Cellulose(cell wall)
Main Component: Composed of 100 – 1500 glucose monomers.
Makes up approximately 30% of the dry weight of plant cell walls.
40
Hemicellulose(cell wall)
a matrix containing a gluelike substance that holds cellulose fibrils together
41
Pectin (cell wall)
the middle lamella is the first layer formed as cells develop. This layer, made of pectin, is shared between two neighboring cells. Afterward, each cell builds a primary wall on either side of the middle lamella, which contains:
Cellulose
Hemicellulose
Pectin
Glycoproteins
42
secondary cell wall
if present, is between the plasma membrane and primary cell wall
43
The Plasma Membrane: componments and functions
Components:
called the Fluid Mosaic Model
Lipid Bilayer: Hydrophilic ‘heads’ face outward; hydrophobic ‘tails’ face inward.
Functions:
Detection and Transduction: Responds to hormonal and environmental signals.
Transport Regulation: Regulates the movement of substances in and out of the cell.
Cellulose Synthesis: Helps produce and assemble cellulose for the cell walls.
Intercellular Connections: Creates plasmodesmata for communication between cells.
Attachment to Cell Wall: Connects to the cell wall through hechtian strands
44
What are the structure and functions of a vacuole in plant cells?
Structure:
Can take up 90% or more of the cell’s volume.
Surrounded by a membrane called the tonoplast.
Functions:
-Maintains cell pressure (turgor pressure) and pH.
-Controls movement of water in and out of the vacuole, regulating turgor pressure (force that pushes the plasma membrane against the cell wall).
-Stores metabolites (salts, sugars, organic acids, soluble proteins) and waste products.
-Contains cell sap, a watery fluid with dissolved substances, slightly to moderately acidic.
-May store anthocyanins, water-soluble pigments responsible for red, blue, or purple colors in flowers and leaves. These pigments accumulate in response to cold temperatures, contributing to fall color changes.
45
What is the structure and function of the nucleus in a cell?
Structure:
-Surrounded by two membranes that form the nuclear envelope.
-The outer membrane is connected to the endoplasmic reticulum (especially the rough ER) and may have ribosomes on its surface.
Function:
-Acts as the control center of the cell.
-Sends coded messages from DNA with instructions to other parts of the cell.
46
What are the components and functions of the endomembrane system?
separates the cell into different compartments, or organelles, such as the nucleus, the endoplasmic reticulum (ER), the Golgi apparatus, and lysosomes (see Table 2.2). The endomembrane system is derived from the ER and flows to the Golgi apparatus, from which lysosomes bud.
-Facilitates cellular communication and material transport.
-Primary site of membrane synthesis within the cell.
47
What are the types and functions of the endoplasmic reticulum (ER)?
Types of ER:
Rough ER – Consists of cisternae (flattened sacs) with ribosomes for protein synthesis, secretion, and storage.
Smooth ER – Tubular structure, lacks ribosomes, and is involved in lipid synthesis and secretion.
Function
● Storage
● Cell signalling
● Lipid biosynthesis
● Movement of molecules and
proteins
48
Golgi Apparatus
that helps process and package proteins and lipid molecules, especially proteins destined to be exported from the cell
49
Plastids
are plant organelles that make/store food or pigments
50
Ribosomes
● Catalyzes synthesis of proteins
● Made of two sub-units (60S and
40S)
● “S” stands for Svedberg (a unit
size based on sedimentation
rate under acceleration)
● Ribosome genes are some of
the slowest evolving genes
51
Grana
membranes that
appear like stacked discs
(called thylakoids) with
double membranes. 40-60
grana linked together by
arms. The thylakoids only
appear like discs, they are
actually part of the
continuous membrane
52
Stroma:
colorless fluid
matrix within the chloroplast
53
Chloroplasts structure and function
Structure:
● Double membraned.
● Can be different shapes.
● 5x larger than mitochondria
Function:
● Light capture and
photosynthesis.
54
Chloroplast Lipid Bi-layer structure
Around 50% lipid/ 50% protein
Lipid content:
● 55% monogalactosyl
diglycerides (MGDG)
● 28% digalactosyl diglycerides
(DGDG)
● 10% sulfolipids
inner membrane
● Engulfed cyanobacterial cell
● More similar in fatty acid composition
to the thylakoid membranes
Outer membrane
● Original eukaryotic cell membrane
● Less MGDG and sulfo-lipid
55
photosynthesis
Atmospheric or aqueous
carbon dioxide is
converted into organic
matter using energy from
sunlight
CO 2 + H 2O + light C6H12O 6 + O2
56
Primary producer
or autotroph, is an organism that can synthesize its
own food from inorganic sources
- form the basis of ecosystems by transforming the
energy in sunlight or inorganic compounds into the chemical energy stored
in sugars
57
gross primary productivity (GPP)
The total amount of chemical energy produced in a given area and time period
58
Primary producers use this chemical energy in two ways:
1. The plant uses energy to stay alive through cellular respiration
2. The remaining energy can be put into growth and reproduction. In primary producers, this energy is called net primary productivity (NPP)
59
Net primary productivity can be calculated as:(and npp facts)
NPP=GPP-R
where R is energy used in cellular respiration, or lost
NPP results in biomass—organic material
that non-photosynthetic organisms can eat
* NPP represents the amount of energy
available to consumers and decomposers
* Can be expressed as kcal/m 2 /year, but more
often g/m 2 /year
60
The Cytoskeleton (“cell skeleton”)
Determine cell shape, cell division, organelle anchoring and movement
* Network of thread-like proteins found throughout the cytoplasm
Three main components:
* Microtubules
* Intermediate filaments (not well studied in plants)
* Microfilaments
61
Microtubules
-Made of α and β tubulin proteins, arranged in 13 rows to form a hollow, tube-like structure (15-25 nm diameter).
-Involved in vesicle transport, chromosome movement, and cell wall deposition.
-Part of flagella and cilia for cell motility.
-Form spindles and phragmoplasts during cell division (mitosis).
62
Intermediate Filaments
* Form an elaborate network of several types of linear proteins combined
* Not well studied in plants
* Thinner than microtubules (12 nm in diameter)
* Hold the nucleus in position and control nuclear shape (nuclear lamins)
63
What are microfilaments made of and what is their function in the cell?
-Made of actin protein, organized into helical chains (8 nm in diameter)
-Control cell shape and Move cell contents around central vacuole
(cytoplasmicstreaming/cyclosis) "barber pole"
-Driven by motor proteins
64
Motor Proteins
-Proteins associated with microtubules and microfilaments
-Attach to the cargo to be moved (i.e. transport vesicles going from ER to Golgi)
-These proteins move, release, reattach and move again using ATP
-Motor proteins are a eukaryotic invention allowing for larger cell size and differentiation
65
Homology
similarity in structure, function,
physiology, development in different
species because of common ancestry
66
analogy (or homoplasy)
refers to similarities in features that evolved independently in different species, not because they inherited it from a common ancestor, but because they faced similar challenges.
67
Plant Homology
Organs or parts of a plant that have dissimilar
structure or function but have the same evolutionary origin are considered homologous
68
synapomorphy
a shared derived characteristic
69
Plesiomorphy
refers to the ancestral character state
70
Autapomorphy
a uniquely derived character state
71
Apomorphy
a character state different than the ancestral
state, or DERIVED STATE
72
Monophyletic/clades
a group that includes
ALL of the descendants of a
common ancestor.
73
Paraphyletic
A group that includes
some, but not all of the descendants
of a common ancestor
74
Polyphyletic
refers to a collection of organisms that have been grouped together but do not share a recent common ancestor. Instead, the organisms have similar traits due to convergent evolution or other reasons
75
Cyclosis (Cytoplasmic Streaming)
-Increases the movement of molecules and organelles within the cell
-Optimizes chloroplast exposure to light
-Most efficient at neutral pH
-May play a role in gravisensing (detecting gravity direction)
-Involves filament-mediated streaming of the cytoplasm
76
Serotinous cones
heat-dependent resin
sealed cones
77
Ecosystem Service:
Conditions and processes through which natural
ecosystems and the species that make them up, sustain and fulfill human life
78
Symplastic pathways (symplast)
Small cytoplasmic strands that
connect cells
79
Apoplast
the space outside the plasma membrane that allows free movement of material
-any fluid filled space
80
Phragmoplast
the structure that builds a cell wall between daughter cells.
81
Meristems
Meristems are located at the tips of roots and stems, and along the surface called the vascular cambium. They are present in all plants and are areas where growth happens through active cell division.
82
cork cambium
In most woody plants, there exists a second
meristem called the cork cambium
83
Higher Plant Cells Versus Animal Cells
Animals:
* Internal or external skeletons; no cell walls
* Plasma membrane called cell membrane.
* Divide by pinching in two; no cell plate nor
plasmodesmata
* Centrioles present during cell division
* No plastids nor large central vacuoles
84
Plants have three or four major groups
of organs
- Roots
- Stems
- Leaves
- Flowers
85
Apical meristems
Found at the tips of roots and shoots
Responsible for primary growth, which makes the plant grow taller or longer.
86
Primary meristems
grow from apical meristems and include:
Protoderm
Ground Meristem
Procambium
87
Primary meristems produce
primary tissue
Dermal (epidermis)
* Ground (cortex, pith)
* Vascular (xylem, phloem)
88
Lateral Meristems
Produce secondary tissues that
increase the width of roots and stems (=
secondary growth)
89
What do the vascular cambium and cork cambium do in a plant?
Vascular Cambium: Produces tissues for support and conduction (thin layer of cells running along stems and roots).
Cork Cambium: Found outside the vascular cambium, it creates the bark
90
Intercalary Meristems:
Located at the nodes (where leaves attach) and help the stem grow longer.
91
Meristematic cells
are undifferentiated and can become any type of cell (totipotent).
92
Ground tissue
Functions:
Photosynthesis,Storage ,Support
Space filling tissue (occupies areas between dermal and vascular tissues) known as the cortex
* Inside vascular cylinder it is called pith
93
Parenchyma Cells
The most common and least specialized type of plant cell.
Acts like a “filler” tissue in plants.
Have thin walls and can take on different shapes.
Contain living cytoplasm with large vacuoles and some secretions.
94
What is Aerenchyma?
A type of parenchyma tissue with large connected air spaces; commonly found in aquatic plants to aid buoyancy and gas exchange
95
What is Chlorenchyma?
A type of parenchyma that contains chloroplasts and is involved in photosynthesis.
96
What are Transfer Cells?
Specialized parenchyma cells with irregular wall extensions that increase the surface area of the plasma membrane, enhancing nutrient transfer; often found in nectaries of flowers.
97
Collenchyma
Main Function: Provides flexible support for growing organs.
-Alive at Maturity
-No secondary walls; walls are unevenly thickened at cell corners.
-Plants often produce more collenchyma in response to mechanical stresses.
97
Wilting
is caused by a loss of
turgidity
98
What is Sclerenchyma?
Cell Walls: Thin primary walls, thick secondary walls with lignin.
Types: Fibers and sclereids (stone cells).
Function: Provides support; dead at maturity.
Location: Found in nutshells and fruit pits
99
Taproot Systems
-Taproots penetrate deeply
into the soil
-Small plants can have
significant taproot systems
-Taproots enable plants to
survive in harsh
environments (drought
tolerance)
100
Fibrous Root System
Structure: Consists of many thin roots that spread out and form lateral roots.
Depth: Typically shallower than taproot systems.
Water Acquisition: More effective at collecting water.
Soil Stabilization: Helps reduce soil erosion.
Induction: Can develop in response to various conditions, such as:
Wounding (from cuttings).
Flooding.
Nutrient deprivation
101
root hairs
Root hairs take in water and minerals.
Secrete acids (like citric acid) to dissolve minerals.
Stick to soil particles.
Increase the area for better absorption.
New root hairs continuously form as older ones die.
102
Monocots
Have one seed leaf (e.g., grasses, sugar cane, lilies, orchids).
103
Dicots (Eudicots):
Have two seed leaves (e.g., buttercups, poppies, roses, pumpkins, legumes).
104
Cotyledon
The first leaf or leaves that appear in a germinating seed
105
(Xylem)Tracheids and Vessel Elements:
Tracheids: First water-conducting cells in vascular plants; found in ferns, conifers, and non-flowering plants.(Dead at maturity)
vessel elements (dead at maturity) Evolved later; found in most flowering plants and some gymnosperms (e.g., gnetophytes). They transport water and minerals more rapidly than tracheids.
Vessels evolved from tracheids by losing their end walls.
Vessels are key innovations that helped angiosperms become dominant
106
Vessel Elements down side
Flow through vessel elements is more prone to
blockage by air or ice crystals than tracheids
Water is less well supported by secondary walls
because they are wider, prone to the formation
of air bubbles
Ice formation has to occur separately in each
tracheid whereas ice in one vessel element
affects flow in the entire column
107
Phloem: Two Cell Types
Sieve-Tube Members:
Modified, enucleate (lacking a nucleus) cells.
Alive at maturity.
Companion Cells:
Smaller cells that have nuclei.
Closely associated with sieve-tube members.
108
Sieve Tube
● Conduct sugars from leaves (source) to other parts (sink) of the plant
● Are stacked end to end forming a continuous tube (sieve tubes)
● Form a continuous connection of cytoplasm along the entire plant
● Form callose (carbohydrate) and p- protein plugs in
response to perturbations
109
What happens during sieve tube formation?
Cell Elongation and Connection: Sieve tube elements (cells in the phloem) elongate and connect end-to-end to form a continuous tube.
Formation of Pores: At the ends of these cells, plasmodesmata (tiny channels) enlarge into pores, forming sieve plates that allow nutrients to pass through the tube.
Organelles Breakdown: The sieve tube cells lose their nucleus and some other organelles to make space for the smooth flow of nutrients.
Companion Cell Development: Companion cells, which support the sieve tube cells by handling metabolic activities, develop alongside each sieve tube element.
110
Sieve plates
are cell walls with lots of membrane-lined
pores and are a distinctive feature of sieve-tube members.
111
How do companion cells help in sucrose transport?
Source to Sink: Companion cells facilitate sucrose movement from source (production) to sink (usage).
Active Transport: Sucrose enters phloem, drawing water from xylem, creating pressure that pushes sap down.
At the Sink: Sucrose is actively transported out and converted to starch, reducing osmotic effects.
Pressure Maintenance: Sieve plates help maintain pressure gradients in phloem
112
Sieve Cells
Found in ferns and (gymnosperms)
long, conducting cells with narrow diameter that do not have sieve plates.
113
Casparian strips
Radial and transverse cell walls
of endodermis are impregnated
by suberin bands called Casparian strips.
Made of suberin (waxy, waterproof), Acts as a hydrophobic barrier, controlling movement
114
Apoplastic herbicides
will move through the cell walls and xylem
115
Symplastic herbicides
will move through the phloem
116
Passage Cells
Passage cells are endodermal
(or exodermal) cells that retain
thin cell walls that lack suberin
to allow the passage of nutrients
(Calcium and magnesium)
- They have Casparian strips, but
lack the suberin lamellae
117
Roots with specialized functions
Serving other needs
1. Water storage
2. Food storage
3. Asexual propagation
4. Access to air or water in the air
5. Additional support
6. Parasitism
118
Grafting
a horticulture technique where you graft the stem of one plant to the root system
of another plant.
119
Pneumatophores (air roots)
In plants with roots growing in
water/swampy areas
Air roots extend above the water’s
surface to obtain oxygen for
respiration
120
Parasitic roots
Parasitic roots are specialized roots that attach to host plants to extract water and nutrients.
120
Ectomycorrhizae type of mycorrhizae
fungi stay on the surface of roots and form a protective layer called a mantle. This helps the plant absorb more minerals from the soil
120
Aerial roots
are specialized roots that grow above the ground instead of in the soil. They serve various purposes support, adapation and nutrient
121
Endomycorrhizae
-Fungi enter the cells of plant roots.
-They create branching structures called arbuscules.
-Arbuscules push against the cell membrane to get nutrients.
-They are the main points for nutrient exchange (like phosphorus, water, and carbon).
-These fungi depend on the plant for survival.
The plant benefits by absorbing more minerals, -=especially phosphorus, and needs fewer root hairs, improving phosphorus uptake efficiency.
122
Root Nodules
-contain large numbers of nitrogen-fixing bacteria.
– Legume Family (Fabaceae)
123
Stipules
Stipules are small, leaf-like structures found at the base of a leaf stalk (petiole)
124
phyllotaxy
the arrangement
of leaves on a plant stem
125
Central Zone
undifferentiated cells in the center that produce
cells
126
Peripheral Zone
A ring of cells
below the central zone where
the leaf primordia is formed
127
Protosteles
Solid xylem core, phloem
surrounds xylem (in primitive seed plants,
ferns, club mosses and whish ferns)
128
Siphonosteles
Tubular xylem and phloem with
pith in center (Common in ferns)
129
Eusteles
divided vascular bundles
130
Seedless Vascular Plants
-do not have seeds or flowers
-Have true leaves.
– Developed roots that function in absorption and anchorage
The major phyla of seedless vascular plants:
* Lycophyta (clubmosses)
* Polypodiophyta (ferns)
131
4 major groups of vascular plants
-Lycophyte
-Gymnosperm
-Ferns
-Angiosperm
132
Bicollateral Vascular Bund
Arrangement in vascular plants where xylem is
bordered by phloem on both the inner side and the periphery
-two vascular cambium strips in this arrangement
133
What are key features of monocot vascular bundles?
No vascular cambium or cork cambium.
Bundles scattered throughout the stem, with no distinct cortex or pith.
Bundles are surrounded by a sclerenchyma sheath.
134
Rhizomes
horizontal stems that grow below ground
and have long to short internodes. Similar to roots but have buds and nodes
135
Stolons/Runners
Horizontal stems that grow above ground and have long internodes
136
Stem Tubers
are underground stems that
store food (potato). Eyes of potato are nodes
137
Bulbs
are large buds with fleshy leaves
attached to a short stems
138
Corms
Resemble bulbs, but composed
almost entirely of stem tissue, with papery
leaves
139
Cladophylls
Flattened, leaf-life stems
Greenbriers, orchids, prickly pear cactus
140
secondary growth
-increases in girth of stem or root from secondary tissues
-20% dicots, 5%monocot, all gymnosprem
-Lateral or secondary meristems produce
secondary growth
-New cells are added toward center and
surface
-Secondary xylem tends to have thicker walls
(more lignin)
141
Vascular cambium & Cork cambium
Vascular cambium is derived from
cortex and procambium
Cork cambium forms from cortical
parenchyma cells and phloem
142
Anticlinal division
-produces two cambial cells
-the division plane is
perpendicular to the
surface of the plant orga
143
Periclinal division
produces one secondary xylem or
phloem and one cambial cells
-the division plane is parallel to the surface of
the plant organ
144
What is the role and structure of the stem vascular cambium?
-Produces secondary xylem (wood) on the inside and secondary phloem on the outside.
-In dicots and conifers, it begins when vascular cambium cells arise from procambium cells between primary xylem and phloem.
-It can also originate from parenchyma cells between vascular bundles.
-The vascular cambium is formed by the fusion of fascicular and interfascicular cambiums.
145
What are the key points about secondary phloem?
Only the most recent layers of living secondary phloem conduct food.
Primary and older secondary phloem become stretched and broken as the vascular cambium pushes them outward.
146
What are the key points about secondary xylem (wood)?
Wood is composed of secondary xylem.
It mainly consists of dead cells.
Only the most recently formed layers of secondary xylem conduct water and minerals.
Primary and older secondary xylem become inactive.
