Lecture 9- Plant Diversity II Flashcards
Derived Traits of Seed Plants
- Seeds
- Reduced Gametophyte
- Heterospory
- Ovules and Egg Production
- Pollen and Sperm Production
Advantages of Seeds
Self contained structures
Embryo + protective coat + stored food= full terrestrial
Advantages of Reduced Gametophyte
Microscopic
Develop from spores internally
Dependent on sporophyte
Protects gametophyte from environment
Ensures nutrients for gametophyte
Heterospory
Production of 2 different types of spores
Megaspore grows into female gametophyte
Microspore grows into male gametophyte
What does the microspore grow into?
Male gametophyte (spore)
What does the megaspore grow into?
Female gametophyte
What are the components of an ovule?
Megasporangium (2n) + megaspore (n) + integument (2n)
What are integuments?
Protective sporophyte tissue around megasporangium, form seed coat
How many integuments are in gymnosperms? Angiosperms?
1 integument in gymnosperms
2 integuments in angiosperms
Pollen grain
Male gametophyte within pollen wall (sporopollenin)
Develops from microspore
Male gametophyte - 2 cells
Tube cell: produces pollen tube
Generative cell: produces sperm
Pollination
Transfer of pollen to part of plant containing ovules
By wind or animals
NOT fertilization
Significance:
- Sperm dispersal not water dependent
- Can colonize dry habitats
Advantages of Seeds (compare to spores)
Seed
- Multicellular embryo protected by seed coat
- Remain dormant days to years
- Supply of stored food
Spore
- Single-celled
- Shorter life span
- No stored food
Gymnosperms
“naked seeds”
One clade of seed plants
Seeds exposed on modified leaves -> cones
Most are conifers
Gymnosperm Life Cycle
Mature sporophyte= pine tree (2n)
Sporangia- scale-like in cones
Usually 2 types
- Pollen cones
- Ovulate cones
Pollination
Pollen grain reaches ovule via wind-> germinates
Tube cell produces pollen tube
During pollen tube growth
Megasporocyte -> meiosis -> 4 haploid cells -> 1 megaspore
-> female gametophyte with 2-3 archegonia (1 egg each)
Pollen Tube Reaches Archegonium
Sperm cells have developed
Fertilization -> zygote (2n)
Usually occurs >1 year after pollination
Ovule becomes Seed
Consists of embryo, food supply, seed coat
Angiosperms
“vessel seeds”- Flowering/fruiting plants
Derived Traits of Angiosperms
Flowers: Structures specialized for sexual reproduction
Specialized shoot, leaves
Usually 4 concentric layers
Fruits: Ovary wall thickens, matures into fruit as seeds develop
Protects seeds
Facilitates dispersal
Many mechanisms
What is a complete flower vs. incomplete flower?
A complete flower in angiosperms has all 4 organs, an incomplete flower lacks 1 or more organs
How are angiosperms pollinated?
Structure, color, odor often adapted to pollinator
Most angiosperms animal pollinated
Some wind pollinated (e.g. grasses)
Fruits in angiosperms
Ovary wall thickens, matures into fruit as seeds develop
Protects seeds
Facilitates dispersal
Many mechanisms
- Wind
- Water
- Animals
Angiosperm Life Cycle
Starting with mature sporophyte- large, 2n
Development of Female Gametophyte
Ovary (within flower) contains 1+ ovules
Each ovule= megasporangium
Contains megasporocyte (2n)
-> Undergoes meiosis
-> 4 n megaspores
3 disintegrate, 1 undergoes 3 mitotic divisions -> 8 haploid nuclei
Mature female gametophyte
8 haploid nuclei, 7 cells
6 have 1 nucleus
1 egg cell
3 antipodals (disintegrate)
2 synergies (disintegrate, affect pollen tube growth)
Central cell- 2 polar nuclei
Egg and central cell involved in fertilization
Development of Male Gametophyte
Anther (within flower) contains microsporangia
Each contains many microsporocytes (2n)
Meiosis -> 4 n microspores
Microspores -> pollen grains via mitosis
2 cells each
Tube cell: Forms pollen tube
Generative cell: Divides via mitosis -> 2 sperm
Pollination
Pollen release from stamen, carried to carpel
Some flowers self-pollinate
Most have mechanisms to ensure cross pollination
Pollen grain absorbs water, germinates
Tube cell produces pollen tube
Enters ovule through micropyle: pore in integument
2 sperm cells (via mitosis of generative cell) enter female gametophyte
Double Fertilization
1 sperm fertilizes egg -> 2n zygote
1 sperm fuses with 2 nuclei in central cell
-> triploid (3n) cell
Ovule matures into seed
Zygote -> sporophyte
Has early root, 1-2 cotyledons- seed leaves
3n cell-> endosperm: nourishes developing embryo
Summary
gHeterosporous
Pollen disperses sperm
Double fertilization
Ovary -> fruit
Ovule -> seed
Seed coat ruptures, seedling emerges
Seedlings use endoderm and cotyledons until they can photosynthesize
