Unit 4: Plant Biology Flashcards
Major events in history of (plant) life
4550 MY: Earth forms
3500 MY: photosynthesis appears
1500 MY: 1st plastid; plants and red algae diverge
500 MY: Colonization of land: plants, fungi, animals
Features of all plants
1) Starch as main energy-storage molecule
2) Chlorophyll b
- Chl a: all photosynthetic eukaryotes
- Chl b: accessory pigment; passes energy to chl a
- Chl b absorbs slighly different wavelengths
3) Cellulose is a major component of cell wall
- Polysaccharide: unbranched glucose residues
4) Thylakoids in stacks (“grana”)
- Thylakoids are membranes inside chloroplast - contain chlorophyll
Ancestors of land plants
Charophytes are the closest relatives of land plants
- Evidence:
1) both nuclear and chloroplast genes
2) structure
- Land plants are not descended from modern charophytes, but share a common ancestor with them
Features of charophyte and land plants
- Cell plate and phragmoplast (short microtubules)
- Plasmodesmata (extensions of the cell membrane through pores in cell wall)
- Sperm structure
- Peroxisome enzymes
- Rose-shaped cellulose synthesizing complexes
- Sporopollenin: durable polymer
Sporopollenin
- Durable polymer
- Found in walls of:
1) plant spores
2) pollen - chemically inert
- stable
- persists in the environment
protects from desiccation, decay, etc.
The move to land: potential advantages
- Air filters less sunlight than water. There’s more light for photosynthesis
- Air has more CO2 than water. There’s more fuel for photosynthesis
- Early terrestrial habitats lacked pathogens or predators/herbivores
- Terrestrial soil is richer in nutrients than aquatic soil
Land Plants Adaptations
- Air not as supportive as water: Turgor (positive pressure); cell walls with lignin; xylem; stems
- Lose water: Cuticle; Vascular tissue; Roots; Stomates
- Reproduction harder: sperm cannot swim in air, young not dispersed easily, eggs and embryos might dry out: Egg and embryo retained on parent; Sporopollenin; protected embryo; seed coat; pollen; flower; fruit
Features of all LAND plants
- Cuticle
- Sporopollenin
- Multicellular, jacketed sex organs = “gametangia” (antheridia, archegonia)
- Embryophyte condition (Zygote retained in maternal tissue)
- Alternation of generations
Antheridium
- Male sex organ (haploid)
- Produces sperm
Archegonium
- Female sex organ
- Produces egg
Alternation of generations
- Definition: MULTICELLULAR haploid and diploid stages
- Gametophyte is haploid and multicellular
- The 2 generations: Sporophyte (diploid, makes spores by mitosis) and Gametophyte (haploid, makes gametes by mitosis)
A green alga WITHOUT alternation of generations
- Chlamydomonas (chlorophyta)
- Most of life: single cell, haploid
How did alt of gen. originate?
- Zygote delays meiosis and divides and grows
- Result: Multicellular diploid
Spore
In land plants, meiosis produces spores:
- Single-cell that can divide to produce a multicellular organism (often with protective coat)
Gamete
Single-cell that can unite with another gamete to produce a diploid zygote
Land plants: 4 major divisions
1) Bryophyta: the mosses
2) Pterophyta: ferns, horsetails, etc.
3) Coniferophyta: the conifers
4) Anthophyta (angiosperms)
Bryophyta (the mosses)
- Around 15,000 species
- Low growing
- Confined to damp areas
- Swimming sperm
- No true vascular tissue (rudimentary vascular system)
- No true leaves
- Gametophyte dominant
- Homosporous (1 spore size)
Moss lifecycle
- Spores from sporangium give rise to two “buds” which eventually become a bisexual gametophyte
- female part of gametophyte has archegonia, male part of gametophyte has antheridia
- Fertilization occurs within archegonium
- zygote becomes embryo which becomes a young sporophyte, which eventually matures
Pterophyta (ferns, horsetails, etc.)
- Around 20,000 species, most tropical
- Appeared around 400 mya
- Vascular tissue
—-Xylem and phloem
—-Support and supply - Swimming sperm
- Sporophyte dominant
- Homosporous or heterosporous
Fern reproduction
- Sporangium opens and disperses spores
- Spore develops into a gametophyte
- Gametophyte has a male part (at back) with antheridia and a female part (at front) with archegonia
- Zygote develops within archegonium, new sporophyte, mature sporophyte (fern leave), back to sporangium
Spore sizes
Homospory: 1 size of spore from meiosis
Heterospory: 2 sizes of spore from meiosis
Homosporous spore production
1) Sporangium on sporophyll
2) Single type of spore
3) Typically a bisexual gametophyte
4) Eggs and sperm
Mosses and most Ferns
Heterosporous spore production
1) Megasporangium on megasporophyll
2) Megaspore
3) Female gametophyte
4) Eggs
1) Microsporangium on microsporophyll
2) Microspore
3) Male gametophyte
4) Sperm
Seed plants
- Seed plants have both seeds and pollen
- Seed:
—-Embryo + nutrition + seed coat - Develops from ovule:
—–Novel structure appearing in seed plants
—–Site of female meiosis
—–Thus contains female gametophyte, female sex organs, egg and embryo
Ovule
- Micropyle at top
- Integument (2n) on outside
- Megasporangium (=nucellus) (2n)
- Just after meiosis in megasporangium: single functional megaspore (1n): will become megagametophyte (1n)
- Ovule becomes the seed
Seeds and pollen
- Seed:
1) Embryo + nutrition + seed coat
2) Develops from ovule - Pollen
1) Mature male gametophyte
2) Few cells in size
Coniferophyta (conifers)
~550 species
* Reproductive
organs in cones
* Sporophyte
dominant
* Heterosporous
* Microgametophyte = pollen!
* Megagametophyte
—–within ovule
—–makes egg & the nourishes embryo
Conifer lifecycle
- Mature sporophyte (2n) has Ovulate cone and Pollen cone
1) Pollen cone has microsporangia, with microsporocytes in them, meiosis happens to produce pollen grains (n)
2) Ovulate cone has ovule, with integument, megasporangium (2n) with megasporocyte (2n)
3) Pollen grain enters the ovule through pollen tube (pollination BEFORE female meiosis!)
4) inside ovule is one surviving megaspore (n), which become megagametophyte
4) Archegonium in inside ovule, so is female gametophyte
5) sperm nucleus (n) and egg nucleus (n) meet, after pollen enters through pollen tube
6) seed coat forms around embyro (2n) with food reserves (n)
7) 2 seeds form, grows into seedling, becomes mature sporophyte
Nutrition for embryo in conifers
The megagametophyte provides nutrition for the embryo
Conifer gametophytes
megagametophyte:
1) Makes egg in archegonium
2) Nourishes embryo
Microgametophyte
1) Pollen grain (makes sperm)
Gymnosperms
- A plant that has seeds unprotected by an ovary or fruit
- Gymnosperms include the conifers, cycads and ginkgo
Angiosperms
- A plant that has flowers and produces seeds enclosed within a carpel
- Includes herbaceous plants, shrubs, grasses, and most trees
Jack Pine: Slow reproduction in conifers
- Male cones:
—-takes a year to develop and pollinate - Female cones:
—-takes a year to be pollinated, another year for female meiosis to occur
—-After 2 years, matures into woody cone with mature seeds
Seed Plants evolution
1) Gymnosperms (seed, pollen)
2) Angiosperms (flower)
Angiosperm terrestrial revolution
- Appeared around 150 mya then exploded into many species
- Today over 85% of plant, animal, and fungal species live on land rather than in the sea
— Half live in tropical rainforests - An explosive boost to terrestrial diversity occurred from 100-50 mya
— The biosphere expanded to a new level of productivity
— Coincided with innovations in flowering plant biology and evolutionary ecology, including
1) Their flowers and efficiencies in reproduction;
2) Coevolution with animals, especially pollinators and herbivores;
3) Photosynthetic capacities
4) Adaptability; the ability to modify habitats - The rise of angiosperms triggered a macroecological revolution on land and drove modern diversity
Anthophyta (angiosperms)
- 300,000 (named),
400,000 (estimated) species - Reproductive organs in flowers
- Sporophyte dominant
- Heterosporous
- Microgametophyte = pollen!
- Megagametophyte: 8 nuclei
Flower structure
- 4 whorls of modified leaves
- sepal (leaves on outside)
- petal (coulourful outside)
- Stamen (male part), stem is called filament, top is anther
- Carpel (female part), ovary on bottom, stem is style, stigma on top
- Ovules inside the ovary
Hermaphroditic
- A flower with both female and male sex organs
- 85% of angiosperm species have co-sexual = hermaphroditic flowers
Monoecy
Separate male and female flowers on the same individual plant
Dioecy
Male and female sex organs on different individuals
Pollination
- Definition: arrival of pollen on stigma (flowering plants) or on receptive female cone (conifers)
- Occurs only in seed plants
- Conifers: wind
- Flowering plants:
–insects
–birds
–bats
–wind
Pollination in angiosperms
- Reward for pollinators:
a) Nectar (sugar water)
b) Pollen - Advertisement by plant
a) Showy flower
b) Possibly odor - Both reward and advertisement are costly
Pollination syndromes
- Integrated sets of floral traits (e.g., morphology, colour, odour, size, rewards) associated with particular pollinator groups
- An example of convergent evolution: The traits have evolved separately many times. Can thus occur in unrelated plant species
Pollination by bees
Syndrome:
- Shape: various: can be highly specialized or not
- Color: various, including yellow, blue, orange (not red)
Odor: none or highly specialized
Pollination by bats or moths
Syndrome:
- Shape: tubular, open at night
- Color: yellow or white
- Odor: strong and sweet
- Nectar: large quantity
Pollination by birds
Syndrome:
- Shape: tubular
- Color: red most common, also yellow
- Odor: none
- Nectar: large quantity, often weak (20% sugar)
Pollination by wind
Syndrome:
- Shape: not showy (very reduced petals)
- Odor: none
- Nectar: none
- Pollen: very large quantity
Deceit pollination
- Plant provides no reward, instead is colorful and tricks pollinator into taking pollen with no reward
- Ex: Pink lady’s slipper orchid: bee enters bottom, has to exit through top where pollen packets (pollinia) and stigma are located
Angiosperm lifecycle
1) Mature flower on sporophyte
2) Anther in flower has microsporangium, with microsporocytes, go through meiosis and make microspores
3) microspore has a generative cell and a tube cell
4) male gametophyte is in pollen grain (n)
5) Pollen grains enter through pollen tube through stigma, pollen tube extends through the style toward the ovule
6) 2 Sperm in the pollen grains fertilizes megaspore in ovary and central cell
7) Ovule (2n) in ovary goes through meiosis and forms megaspore (n)
8) 2 cells join together to form central cell and get fertilized by one sperm, other sperm fertilizes egg
9) female gametophyte (embryo sac) consists of antipodal cells, central cell, synergids, eggs (n)
10) zygote forms, and endosperm (3n), which feeds the embryo
11) results in embryo (2n), endosperm (3n), and seed coat (2n)
Double fertilization
2 sperm nuclei in pollen
– 1 fertilizes egg, embryo (2n, diploid)
– 1 fertilizes central cell, endosperm (3n, triploid)
