Midterm 2 Flashcards
How long ago was the terrestrial surface lifeless?
~3BYA
How long ago did Cyanobacteria develop?
~1.2BYA
How long ago did small plants, fungi and animals develop?
500MYA
How long ago did plants get taller?
385MYA
Why did plants get taller 385MYA?
Access to more light
How long ago did the earliest trees appear?
~385MYA
What are the closest relatives to land plants?
Green algae called Charophytes
What 3 traits did plants acquire independently?
1) Multicellularity
2) Photosynthetic pigments
3) Cell walls made of cellulose
What are the 3 key traits that land plants share with charophytes?
1) Rings of cellulose-synthesizing proteins
2) Structure of flagellated sperm
3) Formation of phragmoplast
What are phragmoplasts and what do they do in plants?
They are structures that guide assembly of the cell plate during cell division
What is one adaptation that enabled plants to move to land?
Layer of durable polymer called sporopollenin which prevents zygotes from drying out
What are 4 reasons for plants to move to land?
1) Unfiltered sun
2) More plentiful CO2
3) Nutrient-rich soil
4) Few herbivores or pathogens
What are 2 issues plats had with moving to land?
1) Scarcity of water
2) Lack of structural support
What would happen if the plant weren’t able to make an adequate amount of sporopollenin?
1) Zygotes would dry out
2) Spores would be less viable
What is the word that we use to define plants with?
Embryophytes: plants w/ embryos
What are 5 key traits of all plants
1) Alternation of generations: alternation b/w 2 multicellular stages: gametophyte (n) and sporophyte (2n)
2) Multicellularity
3) walled spores produced in sporangium: spore walls made of sporopollenin through meiosis of sporophyte
4) Multicellular gametangium: Archegonia (female organ) and Antheridia (male organ)
5) Apical meristems: responsible for extension of roots and shoots
What are 3 more derived traits of plants?
1) Cuticle: waxy covering of epidermis
2) Mycorrhizae: fungi + land plants
3) Stomata: specialized spores that support photosynthesis by allowing gas exchange
What are the 2 purposes of a waxy cuticle
1) Decreases water loss
2) Decreases microbial attacks
What’s the purpose of Apical meristems?
Responsible for extension of roots and shoots
What are the female and male gametangium organs that produce gametes called?
Female: Archegonia
Male: Antheridia
How long ago did spores develop?
470MYA
How long ago did spores with plant cuticle develop?
425MYA
How are plants informally grouped?
They’re informally grouped by presence or absence of vascular tissue
Which grouping of plants has the most diversity within their group?
Gymnosperms
Which grouping of plants is the most diverse?
Angiosperms
What are the four major groups of plants?
1) Bryophytes
2) Seedless vascular plants
3) Gymnosperms
4) Angiosperms
What are the 3 phyla within Bryophytes?
1) Hepatophyta: liverworts
2) Bryophyta: Mosses
3) Anthocerophyta: Hornworts
What are the 5 economic importances of Mosses?
1) Retains N in soils
2) Soil conditioner
3) Fuel source
4) Packing material
5) Storage of organic carbon
What are the 2 groups that seedless vascular plants are divided into?
1) Lycophytes
2) Monilophytes
What plants are in Lycophytes?
club mosses, spike mosses, quillworts + relatives
What plants are in Monilophytes?
ferns, horsetails, whisk ferns + relatives
What are the significances of the ancestors of Lycophytes?
They grew to great heights during the Devonian and Carboniferous eras, forming the 1st forests and creating coal. AND they may have contributed to global cooling as their roots increased the rate of calcium and magnesium which react with CO2.
What are the 2 groups of seed vascular plants?
1) Gymnosperms
2) Angiosperms
Did early vascular plants have dependent or independent sporophytes?
Independent branching sporophytes
What are 3 characteristics of living vascular plants?
1) Life cycles with dominant sporophytes
2) Vascular tissue called xylem and phloem
3) well-developed roots and leaves
What does xylem do?
It conducts most H2O and minerals and includes dead tube-shaped cells called tracheids
What does phloem do?
it consists of living cells arranged into tubes and distribute sugars, amino acids, and other organic products
What does vascular tissue provide to plants?
It gives plants increased height
What are 2 evolutionary advantages of having vascular tissue
They’re taller so…
1) Get more sunlight
2) Spores dispersed faster
What are 2 functions of roots?
1) Anchors vascular plants
2) Enables vascular plants to absorb water and nutrients from the soil
What may have roots evolved from?
Subterranean stems
What’s the function of leaves?
It increases surface area of vascular plants, thereby capturing more solar energy used in photosynthesis
What are the 2 categories of leaves?
1) Microphylls: leaves w/ single vein
2) Megaphylls: leaves w/ highly branched vascular system; present in all vascular plants except lycophytes
What’s the definition of sporophylls?
Modified leaves with sporangium
What’s the definition of Sori?
clusters of sporangium on the undersides of sporophylls
What’s the definition of Strobili?
cone-like structures formed from groups of sporophylls
What are the characteristics of a heterosporous species?
They produce megaspores giving rise to female gametophytes and Microspores which give rise to male gametophytes
Are all seed plants and some seedless vascular plants hetersporous or homosporous?
Heterosporous
What are the characteristics of a Homosporous species?
They produce 1 type of spore that develops into a bisexual gametophyte
Are most seedless vascular plants Heterosporous or Homosporous?
Homosporous
What are monocots and Eudicots?
2 major groups of angiosperms
What 3 basic organs evolved in vascular plants?
1) Stems
2) Roots
3) Leaves
What are 3 important functions of roots?
1) Anchor plant
2) Absorb H2O and nutrients
3) Storing carbs
What’s the function of the taproot system, and is it mostly monocots or eudicots that have them?
Tall plants with large shoot masses have taproot systems which prevents it from toppling. This includes most eudicots.
Describe what a primary root is
It’s the first to emerge and it then branches to form lateral roots which improves anchorage and water storage.
What’s the function of the fibrous system, and is it mostly monocots or eudicots that have them?
The fibrous root system consists of adventitious roots that arise from stems, leaves, and lateral roots. This includes most monocots.
Fibrous root system, monocot or eudicot?
monocot
Taproot system, monocot or eudicot?
eudicot
Where along the root does the most absorption occur?
Root hairs as they increase surface area of roots allowing for more absorption
what do axillary buds do?
structures that have the potential to form lateral shoot or branch
What is the apical bud?
growing shoot tip which causes elongation of young shoot
What’s the function of apical dominance?
It helps maintain dormancy in most axillary buds
What are the 2 functions of plant stems?
1) structure
2) transport H2O and minerals
What are the 4 functions of leaves?
1) Intercept light
2) Exchange gasses
3) Dissipate heat
4) Defend plant from herbivores and pathogens
What kind of veins do monocots have?
Parallel veins
What kind of veins do Eudicots have
branching veins
When classifying angiosperms by their leaves, what are the 2 categories?
1) Simple
2) Compound
What does each plant organ have (3 things)?
Dermal, vascular, and ground tissues and each forms a tissue category
In non-woody plants what does the dermal tissue consist of?
epidermis
In non-woody plants, what is the function of the waxy coat/cuticle?
prevents water loss from epidermis
In non-woody plants, what is the periderm?
It’s protective tissue that replaces epidermis in older regions
In non-woody plants what are trichomes and what are its functions?
outgrowths of shoot epidermis which helps reduce water loss and insect defense
What are the 2 types of vascular tissue in non-woody plants and what are their functions?
Xylem: transports H2O and dissolved minerals from roots to shoots
Phloem: transports organic nutrients from sources to sinks (sugar)
What are the vascular tissues of stem and root in non-woody plants?
stele: central part of the root or stem
In angiosperms what is the stele of a root?
It’s a solid central vascular cylinder
In non-woody plants, what does the ground tissue system consist of?
-Internal to vascular tissue: pith
-Eternal to Vascular tissue: cortex
-Includes specialized cells for storage, photosynthesis, support and transport
What are the 5 types of plant cells?
1) Parenchyma
2) Collenchyma
3) Sclerenchyma
4) Water-conducting cells of the xylem
5) Sugar-conducting cells of the phloem
What are the characteristics and functions of Parenchyma cells?
Mature: thin flexible primary walls, lack secondary walls, are least specialized, perform most metabolic functions, and retains ability to divide and differentiate
What are the characteristics and functions of Collenchyma?
-Grouped in strands and help support young parts of plant shoot
-Have thicker and uneven cells walls
-Provide flexible support without restraining growth
-Flexibility and support
What are the characteristics and functions of Sclerenchyma?
-Rigid due to thick secondary walls strengthened with lignin, and are dead at functional maturity
-2 types:
1) Sclereids: short irregular shape w/ thick lignified secondary walls
2) Fibers: long and slender and arranged in threads
What are the characteristics and functions of Water-Conducting cells of the xylem?
-2 Types: Tracheids and Vessel Elements
-Tracheids: found in xylem of all vascular plants
-Vessel Elements: common to most angiosperms + some gymnosperms; they align end to end to form long micro pipes called vessels
-Sieve-tube elements: alive at functional maturity, but lack organelles
-Sieve plates: has a companion cell whose nucleus and ribosomes serve both cells
Where are tracheids found?
Found in xylem of all vascular plants
Structure of meristematic tissue?
1) Top: Apical meristem
2) middle: Intercalay meristem
3) bottom: Lateral meristem
What are the 2 different types of growth?
1) Indeterminate growth: grow throughout life
2) Determinate growth plant organs cease to grow at certain age
What are meristems and what do they allow for?
They’re perpetually embryonic tissue allowing for indeterminate growth
What are the 2 types of meristems?
Apical and lateral
Where are apical meristems found and what is their function
They’re located at tips of roots and shoots and at axillary buds. They elongate shoots and roots in process of primary growth (vertical)
What’s the function of lateral meristems?
add thickness to woody plants in process of secondary growth (lateral)
What are the 2 types of lateral meristems?
Vascular cambium and cork cambium
What’s the function of vascular cambium?
adds layers to vascular tissue called secondary xylem (wood) and secondary phloem
What’s the function of cork cambium?
replaces epidermis w/ periderm, which is thicker and tougher
What are 2 things that meristems give rise to?
1) Initials: stem cells that remain in the meristem
2) Derivatives: become specialized in mature tissue
What does the term annuals mean for flowering plants?
Complete lifecycle in year or less
What does the term biennials mean for flowering plants?
require 2 growing seasons
What does the term perennials mean for flowering plants?
live for many years
Primary growth: What’s the purpose of a root cap?
It protects the apical meristem as root pushes through soil
Primary growth: What 3 zones does growth occur behind the root tip?
1) Zone of cell division
2) Zone of elongation
3) Zone of differentiation and maturation
Primary growth: Where do lateral roots arise from?
arise from within the pericycle, the outermost cell layer in vascular tissue
Primary growth: What is the function and name of the innermost layer of the outer layer in vascular tissue?
Endodermis: regulates passage from soil into vascular cylinder
What does primary growth of roots look like in Eudicots?
xylem is starlike w/ phloem b/w the arms
What does primary growth of roots look like in monocots?
core of parenchyma cells is surrounded by rings of xylem then phloem
Primary growth of shoots: where do leaves develop from?
Leaf primordial along apical meristem
Primary growth of shoots: where do lateral shoots develop from?
axillary buds on stem’s surface
What does primary growth of shoots look like in monocots?
vascular bundles are scattered throughout the ground tissue
What does primary growth of shoots look like in Eudicots?
vascular tissue consists of vascular bundles arranged in a ring
What are the functions of stomata in leaves?
they are pores that allow CO2 and O2 exchange, and they are also major avenues for evaporative water loss
What is the purpose of guard cells?
they stretch and close the stomata
What is secondary growth a characteristic of? (monocots or eudicots, gymnosperms or angiosperms)
Characteristic of gymnosperms and angisperms and many eudicots, but NOT monocots
Why does secondary growth only occur in stems and roots of woody plants and not in leaves?
Secondary growth provides thickness which would be bad for leaves
What does secondary growth consist of?
consists of tissues produced by the 2 types of lateral meristems: vascular cambium and cork cambium
True of false: Primary growth and secondary growth occur simultaneously?
TRUE
What is dendrochronology used for and what does it study?
It’s the science that deals with the dating and study of the annual growth increments, or tree rings, in woody trees and shrubs
Do older layers of secondary xylem still transport H2O?
NO
Do outer layers of secondary growth known as sapwood still transport H2O?
YES
If bark is vut off in a ring around the tree, why does a bubble form?
Transport of water and nutrients continues where bark was not cut
Which plant revealed how secondary growth was triggered?
Arabidopsis plant
What is the cue for wood formation (secondary growth)?
Stem weight
Define growth:
an irreversible increase in size
Define Morphogenesis:
development of body form and organization
Define cell differentiation:
the process by which cells w/ same genes become different from each other
How tall did the tallest red cedar get?
115.7 meters
What is the major limitation of tall trees like red cedar?
Hydraulic limitation = major limiting factor for tall trees
How does transport through phloem work?
transport brings products from sources to sinks via translocation
What are the functions of stems?
serve as conduits for water and nutrients and as support structures for leaves
What does length and branching in shoots affect and what is a common trade off?
Length and branching pattern affect light capture; trade off b/w growing tall and branching
What is phyllotaxy and why is it important?
It’s the arrangment of leaves on stem which is important for light capture
What phyllotaxy do most angiosperms have?
alternate with spirally arranged leaves
Why are leaves so thin?
Green leaves are thin and broad to increase the surface area for absorption of light and carbon dioxide
Do horizontal leaves capture more light in low-light conditions or sunny conditions?
low-light
Why are vertical leaves more favourable in sunny conditions?
It’s because they’re less damaged by the sun and lower leaves can get light
What are the 3 transport routes for water and minerals?
1) Apoplast route: through cell walls and extracellular spaces
2) Symplast route: through cytosol
3) Transmembrane route: across cells
What consists of the Apoplast pathway?
everything external to plasma membrane; cells walls, extracellular space, and interior of vessel elements and tracheids
What consists of the Symplast pathway?
consists of cytosol of living cells in plants as well as plasmodesmata
What characteristic of the plasma membrane controls short-distance transport?
permeability
What are 4 short-distance ways of transporting solutes across the plasma membrane in plants?
1) Proton pump: membrane potential established by pumping H+ which in turn establishes a pH gradient driving transport of solutes
2) H+/sucrose Cotransporter: energy from H+ gradients used to cotransport ions by active transport. Example: Sugar in phloem
3) H+/NO3- Cotransporter: energy from H+ gradients used to cotransport solutes by active transport. Example: important in for uptake of NO3- in root cells
4) Ion Channels: only allow certain ions to pass. Example: K+ ion channel involved in release of K+ from guard cells when stomata close
How is water transported over short distances in plants?
Osmosis: plants must balance water uptake and loss to survive and they do so by osmosis. It’s the diffusion of water into or out of the cell affected by solute concentration and pressure
What happens if a flaccid/isotonic plant cell is placed in a hypertonic solution?
Plasmolysis: occurs when the protoplast shrinks and pulls away from the cell wall
What happens if a flaccid/isotonic plant cell is placed in a hypotonic solution?
Turgid
What do aquaporins do in plant cells in relation to short distance water transport?
they are transport proteins in cell membrane` that facilitate passage of H2O; these affect the rate of water movement across the membrane
With what mechanism is water transported over long distances in plant cells?
Bulk flow
How does Bulk flow via the xylem work?
Transports xylem sap, water and dissolved minerals, from roots to leaves. Bulk flow is driven by transpiration (evaporation of water from plant’s surface) and doesn’t require energy
What are the 4 differences between bulk flow and diffusion?
1) Bulk flow driven by pressure potential not solute potential
2) Bulk flow occurs across hollow dead cells not across living cell membranes
3) Bulk flow moves entire solution not just water and solutes
4) Bulk flow is much faster
What is the cohesion-tension hypothesis?
Transpiration and water cohesion pull water from roots to shoots; movement of xylem sap against gravity is maintained by the cohesion-tension mechanism
What is transpirational pull and how does it work?
water from air spaces in leaf evaporates causing air-water interface to retreat further into the mesophyll cell causing negative pressure. This negative pressure pulls water in the xylem into the leaf.
Transpirational pull on xylem sap goes from where to where?
leaves to roots
How does adhesion and cohesion work in plant cells long distance transport in xylem?
water molecules attracted to cellulose in xylem cell walls through adhesion. Adhesion of H2O to xylem cell walls helps offset the force of gravity
How does bulk flow via positive pressure work and in what kind of vascular tissue does it occur?
It occurs in the phloem as sap moves from sieve tube by bulk flow by positive pressure called pressure flow
True or False: Xylem is one way flow and negative pressure and Phloem is 2 way flow and positive pressure
TRUE
What rate is regulated by stomata?
The rate of transpiration is regulated by stomata
What are the functions of guard cells which flank stomata?
They open and close the stomata., helping balance water conservation with gas exchange for photosynthesis. When turgid, pore opens, and when flaccid, pore closes; this results primarily from reversible uptake and loss of K+ by guard cells
What ion is the most responsible for causing the guard cells to be flaccid and turgid?
K+
What percentage of water is lost via the stomata?
95%
What 3 conditions could cause stomata to close during the day?
drought, high temps, and wind
What hormone produced in response to water deficiency causes stoma to close at dawn?
Abscisic acid (ABA)
What 4 conditions will cause stoma to close?
1) light
2) CO2 depletion
3) An internal “clock” in guard cells; circadian rhythm
4) water loss
What kind of plants have developed adaptations for living in arid clinates?
xerophytes
What are 7 adaptations developed by a wide range of plants to reduce water loss?
1) thick cuticles
2) thin waterproof waxy cuticles
3) taproots
4) Some desert plants complete their lifecycle during rainy season
5) Some desert plants have fleshy stems to store water
6) Some plants have leaf modifications to reduce rate of transpiration
7) specialized form of photosynthesis called CAM where stomatal gas exchange occurs at night
What angle b/w leaves is best and why?
137.5 degrees and it minimizes shading on lower leaves
How do roots adjust to local cconditions?
they branch more in high nitrate soils than in low nitrate soils
True or false: roots are more competitive with roots of same plant?
FALSE; Less competitive
Why do some plants resort to carnivory?
They live in nutrient poor soils and use carnivory to obtain mineral nutrients
What’s an example of the corkscrew carnivore?
Genlisea; uses modified underground leaves to capture soil organisms and hairs lining the leaves ensures one-way passage
Which layer of soil do plants obtain most water and minerals?
Upper layers of soil (Topsoil/A Horizon)
What are 2 important features of soil?
Texture and composition
What 3 things does topsoil consist of?
Minerals, living organisms, and humus
What is the composition of topsoil?
Contain equal amount of sand, clay, and silt
What do inorganic components such as cations do in soil?
They adhere to negatively charged soil particles, preventing them from leaching out of the soil through percolating groundwater
What are 3 things organic components of soil such as humus do?
- Builds crumbly soil that retains H2O,
- increases capacity to exchange cation
- serves as reservoir of mineral nutrients
Through what process do nutrients get into roots?
Cation exchange: cations displaced from sol particles by other cations, particularly H+, enter the soil solution and can be taken up by rots
What part of the root achieves cation exchange?
Root hairs
What are 3 consequences of intensive agriculture?
1) Depletes mineral content in soil
2) Taxes water reserves
3) Encourages erosion
What percentage of farmland has reduced productivity due to soil mismanagement?
30%
What are the 7 functions of Soil for plants?
1) Anchorage
2) Nutrient source
3) Water retention
4) Gas exchange (particularly O2)
5) Microbial interactions helping with nutrient cycling
6) Physical protection
7) pH and soil exchange
What is the primary source of irrigation waters?
Aquifers
What 2 things can happen with the depletion of aquifers?
1) Results in subsidence; settling and sinking of land
2) Salinization
What form of irrigation is better?
Drip irrigation; less water and reduces salinization while providing more water to plants
What does fertilizer do?
Replaces depleted nutrients
What can excess minerals in fertilizers cause?
Algal blooms
What are organic fertilizers composed of?
Composed of manure, fish meal, or compost which release N, P and K as they decompose
What do commercial fertilizers contain?
N, P and K
What percentage of global freshwater is used for agriculture
75%
What does soil pH affect?
It affects cation exchange and chemical form of mineras
What are 4 solutions to control erosion? (Topsoil loss due to wind and water)
1) planting trees as windbreakers
2) terracing hillside crops
3) cultivating in a contour pattern
4) practicing no-till agriculture
What is phytoremediation?
Reclaims contaminated areas suing plants capable of extracting soil pollutants
What percentage of plant’s fresh mass is H2O?
80-90%
What percentage of a plant’s mass is inorganic substances from soil?
4%
What percentage of a plant’s dry mass comes from CO2 assimilated into carbs?
96%
What is the purpose of hydroponic cultures?
Helps determine what chemical elements are essential
How many nutrients are essential for a plant to complete their life cycle?
17
What are the 9 macronutrients (need in large amounts)?
Carbon, Oxygen, Hydrogen, Nitrogen, Phosphorous, Sulfur, Potassium, Calcium, and Magnesium
What are the 8 micronutrients (need in small amounts)?
Chlorine, Iron, Manganese, Boron, Zinc, Copper, Nickel, and Molybdenum
When mineral concentrations are higher inside root cells than in soil, what do plants need to do in order to bring in more?
Hydrolyze ATP in order to bring nutrients into the roots against their gradient
In what kind of leaves are mineral deficiencies most common?
Maize leaves
What are 2 modifications to plants?
1) resistance to aluminum toxicity: bacterial gene allowing plant to secrete acids that bind to free aluminum
2) smart plants: inform grower of nutrient deficiency w/ change in colour
What does aluminum do to crops?
Damages roots and reduces crop yield
What are 5 mutualistic relationships b/w plants and other organisms?
1) Plants and soil microbes
2) Plants with Rhizobacteria and Endophytes
5) plants and Nitrogen fixing Bacteria
6) Plants and fungi
7) Plants and vertebrates
What 4 things do Rhizobacteria and Endophytes give plants?
1) Produces chemical that stimulate plant growth
2) Produces antibiotics that protects from disease
3) Absorbing oxide metals
4) increasing nutrients
How do Bacteria help plants?
Turn nitrogen gas from atmosphere into NO3- or NH4+
What are nodules in relation to bacteria and plants mutualistic relationship?
Composed of plant cells infected by nitrogen-fixing bacteria; hey fix N and receive sugar
How do fungi help plants?
Mycorrhizae = fungi and plant roots
Plant receives increase in surface area and they also secrete growth factors hat stimulate root growth and branching
How do vertebrates help plants?
In coastal regions likeBC, salmon are dragged into the forest by predators providing Phosphorous to plants
What are3 examples of non-mutualistic plants?
1) Epiphytes: grows on plants
2) parasitic plants: absorb sugar ad minerals from living host plant
3) Carnivorous plants: photosynthetic but obtain N from insects
What’s an example of a parasitic plant?
Rafflesia (also biggest flower)
In angiosperms is it the gametophyte or sporophyte that we see?
Sporophyte
What are the 3 F’s that characterize angiosperm life cycles?
1) Flower
2) double Fertilization
3) Fruits
What are the 4 floral organs?
1) Carpels
2) Stamens
3) Petals
4) Stepals
What are stamens and carpels?
Reproductive organs
What’s the structure of a stamen?
Filament topped by an anther
What’s the structure of carpels?
Long style with a stigma which pollen may land
What is a group of fused carpels called
A pistil
What is a slugger of flowers called
Inflorescences
What is pollination?
The transfer of a pollen from an anther to a stigma
What are the 3 methods of transferring pollen from an anther to a stigma?
1) wind
2) water
3) animals
What % of angiosperms are wind-pollinated?
~20%
What % of flowering plants are pollinated by insects?
~65%
Which insect is the most important pollinator?
Bees
Define coevolution
Joint evolution in response to selection imposed by each other
What is an example of coevolution that Darwin predicted?
Darwin correctly predicted a moth w/ a 28cm long tongue based on the morphology of a particular flower
What are the 4 steps in an angiosperms lifecycle?
1) Gametophyte development
2) Pollination
3) doubling fertilization
4) seed development
What are 2 characteristics of angiosperm gametophytes?
1) Microscopic
2) development obscured by protective tissue
What does pollen develop from?
they develop from microspores within the microsporangium, or pollen sacs of the anthers
Each microspore undergoes mitosis to produce what 2 cells?
1) Generative cell
2) Tube cell
Where does the female gametophyte of angiosperms develop?
within the ovule
What surrounds the megasporangium in an ovule?
integumentary
1 cell in the megasporangium undergoes meiosis to 4 megaspores, how many survive?
1
What happens to the single surviving megaspore?
It divides without cytokinesis, producing 1 large cell w/ 8 nuclei, then it’s partitioned into a multicellular female gametophyte, the embryo sac
How does double fertilization work?
2 sperm reach the female gametophyte. 1 fertilizes egg and other combines w/ 2 polar nuclei giving rise to the triploid food-storing endospore (3n)
What does double fertilization ensure?
ensures that the endosperm only develops in ovules containing fertilized eggs
What occurs after double fertilization?
seed development; each ovule develops into a seed and the ovary develops into the fruit enclosing the seed
When a seed germinates, what does the embryo develop into?
A new sporophyte
What part of the female gametophyte in angiosperms develops into the fruit?
The ovary
What are the 6 steps in seed development?
1) Endosperm development
2) Embryo development
3) Seed dormancy
4) Seed germination
5) Seedling development
6) Flowering
When does endosperm development occur? And what does the endosperm store?
It usually precedes embryo development. In most monocots and eudicots, the endosperm stores nutrients that can be used by seedling
What does embryo development entail?
The 1st mitotic division of the zygote splits the fertilized egg into the basal cell and a terminal cell.
What does the basal cell produce?
The basal cell produces a multicellular suspensor which anchors the embryo to the plants
What is the hypocotyl of plants?
it is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root)
Why do some eudicot seeds have thin cotyledon?
Because they retain food in their endosperm; it also absorbs nutrients from the endosperm and transfers then to the rest of the embryo when the seed germinates
What % of a mature seed is water?
5-15%
How many cotyledons do monocot embryos have?
they have 1 cotyledon; grasses such as maize and wheat have a special cotyledon called a scutellum
What’s the name of the special cotyledon possessed by maize and wheat?
Scutellum
What is seed dormancy for?
increases the chance that germination will occur at a time and place most advantageous to the seedline
What environmental cues are required for breaking of the seed to occur?
temp or lighting changes
What does seed germination depend on?
imbibition: the uptake of water due to low H2O potential of a dry seed
What’s the order in which the seedline develops?
1) radicle emerges
2) developing root anchors the plant
3) shoot breaks through the soil
How does Eudicot seed germination occur?
a hook forms in the hypocotyl, and growth pushes the hook above ground. Light causes the hook to straighten an pull the cotyledons and shoot tip up
What is the coleoptile?
Cylindrical organs that ensheath the first leaf and shoot apex in grass seedlings
How does Monocot seed germination occur?
the coleoptile pushes up through the soil creating a tunnel for the shoot tip to grow through
What kind of angiosperms do maize and other grasses fall into?
Monocots
Why are flowers of a given plant species synchronized in their appearance at a specific time during the year?
To promote outbreeding
What is flowering triggered by?
A combination of environmental cues and internal signals
What is the carpel of a flower?
The female reproductive organ that contains an ovary, a stigma, and a style
What are fruits classified by and what are the 4 groups?
they’re classified by their development
1) Simple fruits: develop from a single or several fused carpels
2) Aggregate fruits: result from a single flower w/ multiple separate carpels
3) Multiple fruit: develop from a group of flowers (inflorescence)
4) An accessory fruit: contains other floral parts in addition to ovaries
What is the advantage of asexual reproduction (vegetative reproduction) in angiosperms?
Good for plants in stable envs
What is the disadvantage of asexual reproduction (vegetative reproduction) in angiosperms?
vulnerable to local extinction if there’s any environmental change
What is the advantage of sexual reproduction in angiosperms?
generates genetic variation that makes evolutionary adaptation possible
What is the disadvantage of sexual reproduction in angiosperms?
Only a fraction of the seed survives
Why do plants self fertilize?
to ensure every ovule develops into a seed
What are 4 mechanisms to prevent self fertilization “Selfing”?
1) Dioecious species = staminate and carpellate flowers on diff. plants
2) Self-incompatibility is the ability to reject its own pollen
3) Some plants reject pollen w/ S-gene matching allele in stigma cells
4) Recognition of self blocks pollen tube growth
Which mechanism to prevent selfing is the most common?
Self incompatibility: ability to reject its own pollen
Where is light sensed to initiate phototropism in grass seedlings?
Tip of the coleoptile which contains a blue light sensor
What mechanism/hormone allows the plant to bend?
The phototropic signal is a chemical that causes the coleoptile tip to bend due to the elongation of the cells on the side where light isn’t hitting, that way the plant bends towards the light
What is the Hormone hypothesis proposed by the Darwins for phototropism?
“some matter in the upper part which transmits its effects to the lower part”
What are the 3 evidences that support the hormone hypothesis for phototropism?
1) Coleoptiles bend in response to light if substances from the tip are allowed to move downward
2) If bending can take place in the darkness, then light isn’t directly required for réponse. Only hormone is required
3) During phototropic response, bending occurs bc cells on shaded side of coleoptile elongate
What gene was found by analyzing mutant arabidopsis thaliana individuals that don’t show a phototropic response to light?
PHOT1
What is photomorphogenesis?
The effects of light on plant morphology
What wavelengths of light induce curvature?
Only wavelengths below 500nm
What causes different plant responses to light?
These responses can be mediated by the same or different photoreceptors
What are the 2 major classes of photoreceptors?
1) Blue-light receptors: controls hypocotyl elongation, stomatal opening and phototropism
2) Phytochromes: contain pigments that mostly absorb red light and regulate seed germination and shade avoidance
Hypocotyl?
Stem of a germinating seed
What’s the difference between red light and far-red light effects?
Red light increases germination while far-red light inhibits it. The final light exposure determines response
What is a photoperiod?
The relative lengths of night and day and it is the environmental stimulus plants use most often to detect time of year
What is photoperiodism and what does it control?
It’ the physiological response to photoperiod, and flowering is controlled by photoperiodism
When do short-day plants flower?
When light is shorter than a critical length of light
When do long-day plants flower?
When light period is longer than a certain # of. Hours
Is it day length or night length that controls responses to photoperiod?
Night length
How are short-day plants governed by night length?
They’re governed by whether the critical night length sets a minimum # of hours of darkness
How are long-day plants governed by night length?
They’re governed by whether the critical night length sets a maximum # of hours of darkness
What is vernalization?
Cold pretreatment: it’s an example of flowers requiring additional environmental stimulus on top of the photoperiod in order to flower
With what organ do leaves detect photoperiod?
Photoperiod is detected by leaves which cue buds to develop into flowers
What is the hypothetical flowering hormone and what is the evidence for this hormone?
The hormone is called florigen
Evidence: a signal from a grafted leaf can induce flowering
What is geotropism/gravitropism?
Response to gravity
What is the statolith hypothesis in gravitropism?
It states that plants may detect gravity by the settling of statoliths, dense cytoplasmic components
What type (positive or negative) of gravitropism do roots and shoots demonstrate?
Roots: positive
Shoots: negative
What is thigmomorphogenesis?
Changes in form that result from mechanical disturbance
What is an example of thigmomorphogenesis?
Rubbing stems of young plants a couple of times daily results in plants that are shorter than controls
What is Thigmotropism? And in what plants does it occur?
Growth in response to touch which occurs in vines and other climbing plants
What does flooding do to plants?
Results in enzymatic destruction of root cortex which creates air tues that help plants survive oxygen deprivation during flooding
What does drought do to plants?
They reduce transpiration by closing stomata, reduce exposed surface area and shedding leaves. Growth of shallow roots is inhibited and deeper roots continue
What does heat stress do to plants, and what is something that helps protect against this?
Heat stress can denature a plant’s enzymes. Transpiration helps cool plants leaves by evaporative cooling. AND heat-shock proteins help protect other proteins against heat stress
What kind of proteins help other proteins in plants during heat stress?
Heat-shock proteins
What does salt stress do to plants and what is the plants response?
Salt can lower the water potential of the soil solution and reduce water uptake. In response, plants produce certain solutes at high concentrations which keeps the water potential of cells more negative than that of the soil solution
What does cold stress do to plants and how do plants prevent this?
Cold decreases membrane solubility. Altering lipid composition is a response to cold stress. Many plants have anti-freeze proteins to prevent ice formation and damage to cells
How do plants defend against herbivores?
Physical defenses: thorns and trichomes
Chemical defenses: distasteful or toxic compounds
Mind-altering: some plant products cause mind-altering effects.
Plants damaged by insects release volatile chemical to warn other plants
What is an amino acid that plant produce that kills insects upon digestion?
Canavanine
What’s the first line of defence against pathogens in plants?
The epidermis and periderm, but they can still enter through wounds or natural openings like stomata.
How is PAMP immunity triggered?
Once PAMPs are recognized, a chain of signalling events start leading to the production of anti microbial chemicals and toughening of cell wall
What does PAMPs stand for?
Pathogen associated molecular patterns
True or False: PAMPs are specific to certain pathogens?
TRUE
What mechanism did pathogens evolve in order to suppress PAMP-triggered immunity?
Pathogens developed the ability to deliver effectors into plant cells which suppress PAMP-triggered plant immunity
What are effectors that pathogen sinsrt in plant cells, and what do they do to the plant cell?
Effectors or pathogen-encoded proteins that cripple a host’s innate immunity system
What is the plant’s defence against effectors?
plant defence results from action of hundreds of disease resistant (R) genes. Each R-protein is activated by a specific effector. R-proteins trigger signal transduction pathways leading to local and general response
What are the 4 hypersensitive responses (Local responses) that result from R-gene triggering transduction pathways?
1) stomatal closure
2) production of toxin
3) Reinforcement
4) rapid suicide of infected cells
How is the general response triggered in plants?
The hypersensitive response (local response) produces a signal that induces Systemic Acquired Resistance (SAR)
What are the 8 major plant hormones needed for growth and development?
1) Auxin
2) Cytokinins
3) Gibberellins
4) Abscisic acid
5) Ethylene
6) Brassinosteroid
7) Jasmonates
8) Strigolactones
What is the major type of Auzin in plants?
Indoleacetic acid (IAA)
What does Auxin as a term refer to?
refers to any chemical that promotes elongation of coleoptiles
What are the 2 roles of Auxin?
1) Elongation
2) Alters gene expression and stimulates a sustained growth response
What is the hypothesis for how auxin plays a role in elongation of coleoptiles?
Acid growth hypothesis states that auxin stimulates proton pumps in the plasma membrane. The proton pumps lower pH of cell wall, activating expansins, enzymes that loosen the wall’s fabric. Then cell elongates.
Why were cytokinins named this?
It’s because they stimulate cytokinesis (cell division)
When are cytokinins produced?
they’re produced in actively growing tissues such as roots, embryos, and fruit
What are the 3 functions cytokinins play?
1) cell division and differentiation (w/ auxin)
2) Apical dominance (w/ auxins and strigolactones)
3) Anti-aging
What are the 3 things that cytokinins do to slow the aging process of some plant organs?
1) Inhibit protein breakdown
2) Stimulating RNA and protein synthesis
3) Mobilizing nutrients from surrounding tissue
Which hormone causes Foolish seedling disease?
Caused by Gibberella fijikuroi (fungus) which produced Gibberellins causing plants to grow excessively tall and thin
What 3 roles do Gibberellins play?
1) Growth of stems and leaves; In stems they trigger cell elongation and cell division
2) Fruit growth (w/ auxin)
3) Germination: after water is imbibed, release of gibberellins signals seeds to germinate
Where is auxin produced and where is it transported to?
Produced in shoot tips and transported down the stem
What is the major role of abscisic acid in plants?
It regulates growth, development, and stress responses within plants, specifically through inhibition of cell division
What are 2 of the many effects of abscisic acid?
1) Seed dormancy: ensures that seed will germinate only in optimal conditions
2) Drought tolerance: ABA is the primary internal signal that enables plants to withstand drought. An accumulation of ABA causes stomata to close rapidly.
What is precocious and what is it caused by?
It is early germination which can be caused by inactive or low levels of ABA
What is Ethylene produced in response to?
produced in response to stress such as drought, flooding, mechanical pressure, injury, and infection
What response does ethylene induce when a plant is under mechanical stress?
It induces the triple response which allows growing shoot to avoid obstacles. This response consists of a slowing of stem elongation, a thickening of the stem, and horizontal growth
What is senescence and what is it triggered by?
It is programmed cell or organ death often associated with a burst of ethylene
What causes leaf abscission?
change in balance of auxin and ethylene
What causes fruit ripening?
A burst of ethylene production triggers the ripening process. Ethylene triggers ripening which triggers release of more ethylene (positive feedback loop)
What kind of feedback loop is the process of fruit ripening?
Positive: this is because ripening is caused by a burst of ethylene then ripening triggers release of more ethylene
How old is the earliest Homo Sapien fossil?
196,000 years old
What were important staples in hunter-gatherer diets?
wild plants, fungi and animals
Who are the San?
They’re amongst the 1st people to have lived in southern africa and they’re one of the few hunter-gatherer societies
How many hours per week do the san spend gathering food from the wild?
12-19 hours
What are the 4 hypotheses used to explain the shift from hunter-gatherer to agriculture?
1) Changes in climate causing reduction in wild food sources
2) Greater pop density increasing food demand
3) Overhunting leading to decline in wild prey pops
4) Changing tech like domesticating seeds making agriculture a more viable lifestyle
How many years has agriculture been practiced?
Practiced sporadically for the past 13,000 years
Where did agriculture start independently (3 places)?
1) Northern China
2) Central America
3) Fertile Crescent
What were the 4 types of first crops?
1) Wheat
2) Barley
3) Lentils
4) Types of peas
What is crop domestication?
artificially selecting plants to increase their suitability to human requirements: taste, yield, storage, and cultivation practices
What are 4 features of domestication syndrome?
1) Loss of dispersal
2) Increase in size
3) Loss of seed dormancy
4) Loss of chemical or mechanical protection against herbivores
What was the great Famine and how much did the Pop fall?
Period of starvation in Ireland from 1845-1852. 1 million died and over 1 million fled causing pop to fall by 20-25%
What is a Canadian invention?
Canola oil derived from rapeseed
What is hybridization used for?
It’s common in nature and has been used by breeders to introduce new genes
How are mutations used in breeding plants?
they arise spontaneously and plants with beneficial ones are used in breeding experiments
What are the 2 uses of the word Plant Biotechnology?
1) refers to innovations in the use of plants to make useful products
2) Specifically refers to use of GM organisms in agriculture and industry.
What are transgenic organisms?
those who have been engineered to express a gene from another species
What are 3 benefits of transgenic crops?
1) Produce proteins (Bt toxic) to defend against insect pests
2) Tolerate herbicides
3) Resist specific diseases
What is being improved in plants?
Nutritional quality of plants is being improved
What is Golden rice?
Transgenic variety being developed to address vitamin A deficiencies amongst the world’s poor
how is cassava being engineered?
developed w/ increased levels of Fe and beta-carotene
