Lecture 9- Plant Diversity II

Question 1

Derived Traits of Seed Plants

Answer 1

• Seeds
• Reduced Gametophyte
• Heterospory
• Ovules and Egg Production
• Pollen and Sperm Production

Question 2

Advantages of Seeds

Answer 2

Self contained structures
Embryo + protective coat + stored food= full terrestrial

Question 3

Advantages of Reduced Gametophyte

Answer 3

Microscopic
Develop from spores internally
Dependent on sporophyte
Protects gametophyte from environment
Ensures nutrients for gametophyte

Question 4

Heterospory

Answer 4

Production of 2 different types of spores
Megaspore grows into female gametophyte
Microspore grows into male gametophyte

Question 5

What does the microspore grow into?

Answer 5

Male gametophyte (spore)

Question 6

What does the megaspore grow into?

Answer 6

Female gametophyte

Question 7

What are the components of an ovule?

Answer 7

Megasporangium (2n) + megaspore (n) + integument (2n)

Question 8

What are integuments?

Answer 8

Protective sporophyte tissue around megasporangium, form seed coat

Question 9

How many integuments are in gymnosperms? Angiosperms?

Answer 9

1 integument in gymnosperms
2 integuments in angiosperms

Question 10

Pollen grain

Answer 10

Male gametophyte within pollen wall (sporopollenin)
Develops from microspore

Male gametophyte - 2 cells
Tube cell: produces pollen tube
Generative cell: produces sperm

Question 11

Pollination

Answer 11

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

Question 12

Advantages of Seeds (compare to spores)

Answer 12

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

Question 13

Gymnosperms

Answer 13

“naked seeds”
One clade of seed plants
Seeds exposed on modified leaves -> cones
Most are conifers

Question 14

Gymnosperm Life Cycle

Answer 14

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

Question 15

Angiosperms

Answer 15

“vessel seeds”- Flowering/fruiting plants

Question 16

Derived Traits of Angiosperms

Answer 16

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

Question 17

What is a complete flower vs. incomplete flower?

Answer 17

A complete flower in angiosperms has all 4 organs, an incomplete flower lacks 1 or more organs

Question 18

How are angiosperms pollinated?

Answer 18

Structure, color, odor often adapted to pollinator
Most angiosperms animal pollinated
Some wind pollinated (e.g. grasses)

Question 19

Fruits in angiosperms

Answer 19

Ovary wall thickens, matures into fruit as seeds develop
Protects seeds
Facilitates dispersal
Many mechanisms
- Wind
- Water
- Animals

Question 20

Angiosperm Life Cycle

Answer 20

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