Lecture 22 - Plant Diversity (part 2) Flashcards
Further life on land is possible due to…
seeds & pollen
Seed plants have a set of adaptations further than those of bryophytes & seedless vascular plants. What are they?
- Seeds
- Reduced gametophytes
- Heterospory
- Ovules and pollen
Describe the reduced gametophytes in seed plants.
• Microscopic
• Tiny gametophytes can develop directly in the sporangium
- Protection from the elements such as UV radiation, desiccation
• Gametophytes nutritionally dependent on the sporophyte now
Describe heterospory
- Recall most seedless plants were homosporous
* Most seed plants are heterosporous
Describe the cycle starting from female spore leaves –> female gametophyte (n)
MegasporoPHYLLS (2n) (Female spore LEAVES) ->
MegaSPORANGIA (2n) (Female spore bearing STRUCTURES) ->
MegasporoCYTES (2n) (Female sporeproducing CELLS) ->
MegaSPORES (n) (Female spore) ->
Female gametophyte (n)
Describe the cycle starting from male spore leaves –> male gametophyte (n)
MicrosporoPHYLLS (2n) (Male spore LEAVES) ->
MicroSPORANGIA (2n) (Male spore bearing STRUCTURES) ->
MicrosporoCYSTS (2n) (Male spore producing CELLS ) ->
MicroSPORES (n) (Male SPORE) ->
Male gametophyte (n)
Seed plants retain the megasporangium within the…
parent sporophyte
Integument
is a 2n sporophytic tissue that envelopes and protects the megasporanium
How many integuments does Gymnosperms have?
1 integument
How many integuments does Angiosperms have?
2 integuments
Ovule
-> megasporangium (2n) + megaspore (n) + integuments (2n)
Where will the female gametophyte develop?
within the ovule
Pollen grain (n)
develops from a microspore and contains the male gametophyte
Pollen grain doesn’t equal…
male gametophyte
What is inside & outside of the pollen grain?
Inside = male gametophyte (n)
Outside pollen wall = secrete by microsporocytes (2n), contains sporopollenin
What can the shape of pollen grains & outer wall spikes do?
can ID the plant species it came from
Pollination
transfer of pollen to the ovule through a pollen tube in the micropyle of the ovule
What is an advantage of pollen grains?
can travel large distances without needing to swim in water
What are evolutionary advantages of seeds?
- If a sperm fertilises an egg, zygote will grow into a sporophyte
- In non-vascular plants, spores could be released in a dormant state that germinates when conditions are good; their small size allows for this
- In seed plants, the ovule develops into a multicellular seed, which can remain dormant for longer periods of time
- Seed plants share characteristics that arose during the Devonian period (380 million years ago)
- First evidence of seed plants themselves arose around 360 million years ago based on fossil record
Gymnosperms
“naked seed”
What is apart of the Gymnosperms?
- Cycads
- Gnetophytes
- Ginkgos
- Conifers
Cycads
palm like leaves, large cones
- part of gymnosperms
Gnetophytes
Gnetum, Ephedra, Welwitchia
- part of gymnosperms
Ginkgos
Ginkgo biloba, “maiden-hair” tree
- part of gymnosperms
Conifers
Pines, Spruce, Fir, junipers, larch, sequoia
- part of gymnosperms
Earliest Gymnosperm fossils are approx. 305 million years old. Where did they live and where did they survive better in?
• Lived in moist Carboniferous ecosystems still dominated by lycophytes and
other seedless vascular plants
• Survived better in drier climates due to seeds and pollen, thicker cuticles and
small surface area of their needles (leaves)
What are some things to note amongst all gymnosperms?
- Increasing dominance of the sporophyte
- Seed as a resistant, dispersible stage in the life cycle
- Pollen as an airborne agent brining sperm to the female gametophyte
- All are heterosporous
- Most produce cones: ovulate cones (female) and pollen cones (male)
* The scales on the cones are specialised sporophylls - Wind is the primary mode of dispersal
Are gymnosperms heterosporous or homosporous?
HETEROsporous
What is the primary mode of dispersal?
wind
Describe the Pine Life Cycle as an example of Gymnosperm cycles
1) In most conifer species, each tree has both ovulate (female) and pollen (male)
cones
2) Microsporocytes divide by meiosis to produce microspores (n). The microspore develops into a pollen grain (the male gametophyte (n) + surrounding wall (2n))
3) An ovulate cone scale has 2 ovules, each containing a megasporangium.
- Only 1 ovule is shown here
4) Pollination occurs when the pollen grain reaches the ovule, germinating to form a pollen tube that grows through the megasporangium
5) While the pollen tube develops, the megasporocyte (2n) undergoes meiosis. - Producing 4 haploid cells.
- Only 1 survives as the megaspore (n)
6) The megaspore develops into a female gametophyte that contains 2-3 archegonia, each of which will form an egg
7) By the time eggs are mature, sperm cells are fully developed and travel down the pollen tube for fertilisation
8) Fertilisation usually occurs 1 year after pollination. All the eggs may be fertilised, but only 1 zygote develops into an embryo (2n).
- The ovule becomes a seed (embryo + food supply + seed coat)
What is part of Gymnosperms?
- Cycadophyta
- Ginkgophyta
- Gnetophyta
- Pinophyta (formerly Coniferophyta)
Describe Cycadophyta
~300 species
• Large cones, palm-like leaves
• Have flagellated sperm (suggests descent from seedless vascular plants
• Most endangered -> 75% species threatened by habitat destruction
Describe Ginkgophyta
single species, Ginkgo biloba
• Have flagellated sperm
• Deciduous, fan-like leaves that turn gold in autumn
• Tolerant to pollution
• Only plant males because female seeds stink as they decay
Describe Gnetophyta
Gnetum, Ephedra, Welwitschia spp.
• Tropical and desert habitats
• Welwitschia mirabilis can live 1000s of years, deserts in SW Africa
• Ephedra has ~40 spp., desert shrubs
• Gnetum has ~35 spp., tropical trees, vines, shrubs in Africa and Asia
Describe Pinophyta (formerly Coniferophyta)
- The largest and most diverse gymnosperm phylum (~600)
- Most species have woody cones (junipers have fleshy cones) and are evergreen
- Some species are deciduous (larch, tamarack, some redwoods)
- Leaves are needle-like (Pines, spruce) or scale-like (redwoods)
- Huge economic importance (lumber, chemical compounds (taxol from Pacific yew))
Angiosperms
“Flowering plants”
What are the dispersal vectors for Angiosperms?
- Wind: common in grasses, temperate tree species
- Animals: fruit-eating animals, hummingbirds
- Insects: bees, moths, flies
What is apart of the flower?
• Floral organs are specialised sporophylls
- Sepals
- Petals
- Stamens (anthers & filaments)
- Carpels (stigma, style, & ovary)
Sepals
outermost whorl of sporophylls; usually green (like on a bud)
- part of the flower
Petals
showy, inner whorl; attracts pollinators
- part of the flower
Stamens
microsporophylls that produce microspores that develop into pollen grains
- Composed of anthers and filaments
- part of the flower
Carpels (syn. Pistal)
megasporophylls that produce megaspores that develop into female gametophytes
- Composed of the stigma, style, and ovary
- part of the flower
The flower can…
- Can vary in their symmetry
- Can vary in their floral parts
- Can be annual (1 year), biennial (every 2 years), or perennial (every year)
Fruits
ovary wall that has thickened around the seeds
- part of the Angiosperms
What does the fruit function as in the Angiosperms?
- Protects the seeds and aids in dispersal
- Can be fleshy or dry
- Have adaptations to allow for dispersal
What are the adaptations that Angiosperms have that allow for dispersal?
- Propellers (maple seeds)
- parachutes (Dandelions)
- rough coats to stick to animals (burrs on dogs)
- sweet tasting fruit (so animals eat and poop out the seeds in a new location)
Describe the Angiosperm Life Cycle
1) In the megasporangium, the
megasporocyte divides by meiosis, producing 4 megaspores of only which 1 survives
2) On the anther, each microsporangium contains microsporocytes that divide by meiosis, producing microspores
3) A microspore develops
into a pollen grain. The generative cell of the male gametophyte will divide, forming 2 sperm.
- The tube cell will produce
the pollen tube
4) After pollination, eventually two sperm cells are discharged in each ovule
5) Double fertilisation occurs. - - One sperm fertilises the egg, forming the zygote.
- The other sperm fertilises the central cell, forming a 3n endosperm (food supply)
6) Zygote develops into an embryo that is packaged into the seed with the food supply (fruit not shown)
7) The seed germinates and grows into a new sporophyte (2n)
What is the structure of the male gametophyte?
- Prothallial cells
- Generative cell
- Tube cell
- Exine
Prothallial cells
produce the generative and tube cells
- part of the structure of the male gametophyte
Generative cell
produces sperm
- part of the structure of the male gametophyte
Tube cell
produces the pollen tube
- part of the structure of the male gametophyte
Exine
outer wall composed of sporopollenin
- part of the structure of the male gametophyte
What is the structure of the female gametophyte?
- Antipodal cells
- Polar nuclei (inside the central cell)
- Synergids
- Egg
What is the female gametophyte also called?
embryo sac
Antipodal cells
cells at the far end of the gametophyte
- part of the structure of the female gametophyte
Polar nuclei (inside the central cell)
forms the endosperm following double fertilisation
- part of the structure of the female gametophyte
Synergids
near the egg, aid in fertilisation
- part of the structure of the female gametophyte
Egg
female gamete
- part of the structure of the female gametophyte
Angiosperm had a widespread appearance in the fossil record (approx. 140 million years ago). Where did they orginate? AND What is Archaefructus?
- Originated in the Cretaceous period
* Archaefructus is a fossil angiosperm, with a herbaceous and bulbous growth habit
One current hypothesis of the phylogeny of Angiosperms is based on…
morphological and molecular evidence
Living Angiosperms are…
monophyletic
What was evolution often a result of for Angiosperms?
of plant-animal interactions
Angiosperm evolution often was a result of plant-animal interactions. Describe
- Anti-herbivory compounds, mutualistic co-evolution of animal pollinators
- Flower shape and colour can be very specific to pollinator preference
What is part of Angiosperms?
- Basal Angiosperms
- Magnoliids
- Monocots
- Eudicots
Describe Basal Angiosperms
(~100)
• Water lilies, Star anise and relations, Ambrorella
• Oldest Angiosperm linegage
• Spiral arrangement of floral parts
Describe Magnoliids
(~8000 species) • Magnolias, Laurels, Black Pepper plants (Piper nigrum, plant of the day) • Woody and herbaceous species • Spiral arrangement of floral parts - part of Angiosperms
Describe Monocots
(~70,000 species)
• Orchids, grasses, palms
• Fibrous root system
• Simple leaves with parallel veins
Describe Eudicots
(~170,000 species)
• Legumes, roses, flowering trees (oak, walnut, etc)
• Tap root system
• Leaf venation is netted
What are characteristics of Monocots?
- 1 cotyledon
- veins usually parallel
- vascular tissue scattered
- root system usually fibrous (no main root)
- pollen grain with 1 opening
- floral organs usually in multiples of 3
What are characteristics of Eudicots?
- 2 cotyledons
- veins usually netlike
- vascular tissue usually arranged in ring
- taproot (main root) usually present
- pollen grain with 3 openings
- floral organs usually in multiples of 4 or 5
If a sperm fertilises an egg…
zygote will grow into a sporophyte
In non-vascular plants, spores could be released in a…
dormant state that germinates when conditions are good; their small size allows for this
• However, spores are a single cell
• No food supply
In seed plants, the ovule develops into a…
multicellular seed, which can remain dormant for longer periods of time
• Embryo
• Food supply
• Protected seed coat (develops from the integument)
Seed plants share characteristics that arose during the…
Devonian period (380 million years ago) - Archaeopteris was heterosporous, though it did not make seeds
First evidence of seed plants themselves arose around…
360 million years ago based on fossil record
• 55 million years before Gymnosperms
• > 200 million years before Angiosperms
