Reproductive differences between gymnosperms and angiosperms: gymnosperms: 1) ovules attached to...

reproductive differences between gymnosperms and angiosperms:

gymnosperms:

1) ovules attached to a megasporophyll

- megasporophylls often arranged in a megastrobilus (ovulate cone)

2) a) megagametophytes consist of many cells;

b) eggs produced in archegonia

3) microsporangia attached to surface of a microsporophyll

- microsporophylls often arranged in a microstrobilus (staminate cone)

4) microgametophytes are very small

- produce sperm (not in antheridia)- are pollen grains

5) pollination by wind dispersal of pollen

6) pollen tube grows to an ovule and sperm is released

- sperm have flagella and swim to egg, but not through external water

7) seeds develop on surface of megasporophylls

- seeds are not enclosed (“naked”)

gymnosperm = naked seed

CHARACTERISTIC GYMNOSPERMS

Placement of ovules Attached to megasporophylls, in a megastrobilus

Size of megagametophyte Many cells

Archegonia Present

Placement of microsporangia (pollen sacs)

Attached to microsporophylls, in a microstrobilus

Size of microgametophytes Very small; several cells

Antheridia Absent

Pollination Mostly by wind dispersal of pollen

Sperm Have flagella; swim through ovule to reach egg

Seed location On surface of megasporophylls;not enclosed (naked)

angiosperms:

1) ovules (and seeds) are enclosed within ovaries;

- part of flower structure

angiosperm = “vessel seed”

2) megagametophytes consist of only a few cells

- produce eggs, but not in archegonia

3) microsporangia carried on stamens;

part of flower structure

4) sperm do not have flagella

5) double fertilization occurs

CHARACTERISTIC GYMNOSPERMS ANGIOSPERMS

Placement of ovules Attached to megasporophylls, in a megastrobilus

Located in an ovary, within a flower

Size of megagametophyte

Many cells A few cells

Archegonia Present Absent

Placement of microsporangia (pollen sacs)

Attached to microsporophylls, in a microstrobilus

Located on a stamen, within a flower

Size of microgametophytes

Very small; several cells Extremely small, a few cells

Antheridia Absent Absent

Pollination Mostly by wind dispersal of pollen

Various mechanisms - wind, insect, bat, rodent, etc.

Sperm Have flagella; swim through ovule to reach egg

No flagella; deposited at egg

Seed location On surface of megasporophylls; not enclosed in a fruit ("naked")

Located enclosed in a fruit that develops from the ovary

Double fertilization Absent Present

Flower Structure:

flower stalk (peduncle) and floral appendages attached to it

receptacle

floral appendages = sterile appendages and fertile appendages

sterile appendages = sepals and petals

sepals

petals

fertile appendages = stamens and carpels

stamens - are “specialized microsporophylls”

- include: filament

anther

carpels “modified megasporophylls”?

- produce a tubular pistil

- each has a stigma ;

an ovary;

a style

5) double fertilization

- megagametophyte of angiosperms usually has seven cells

- one egg, two synergids, three antipodals - each with one 1n nucleus

- one central cell containing TWO 1n nuclei = polar nuclei

pollination - pollen is transferred from pollen sac to a stigma

pollen germination

pollen tube grows through style, to an ovule

- releases two sperm into the ovule

1) one sperm (1n) fuses with the egg (1n) - produces zygote (2n)

2) second sperm fuses with two polar nuclei-produces a triploid (3n) primary

endosperm nucleus

following double fertilization:

- zygote develops into embryo (within the ovule)

- the primary endosperm nucleus produces endosperm tissue (all cells with 3n nuclei)

- will provide nutrients to the embryo

- integuments harden to form seed coat

** produces a seed, consisting of:

- seed coat

- endosperm (not present in gymnosperms)

- sometimes a perisperm

- embryo

In flowering plants, ovules are enclosed in ovaries

- ovaries undergo changes as seeds form- produces a fruit

- will usually enlarge

may become fleshymay become dry, or hard

fruit - provides additional protection for the embryo

- contributes to seed dispersal

“typical” flower structure varies with species

common variations include variation in appendages:

# of each type

size

color

shape

other variations:

placentation type:

placenta

placentation

parietal placentation:

- ovules attached to side walls of ovary

- ovary with one or more locules

axile placentation:

- ovules attached to partitioning walls in ovary

- ovary has two or more locules

free central placentation:

- ovules attached to central column of tissue

- ovary has one locule

basal placentation:

- ovule(s) attached to base of ovary

- ovary has one locule

fusion of various floral appendages

coalescence

e.g. formation of tubular corolla

adnation

variations in ovary placement:

hypogynous flowers

- ovary is superior - other appendages attached lower

epigynous flowers

- receptacle tissue surrounds ovary

- other appendages attached above the ovary

- ovary is inferior

perigynous flowers

- basal portion of sepals, petals, and stamens form structure that surrounds the ovary

- ovary is superior

variations related to presence or absence of floral appendages:

complete flowers

incomplete flowers

perfect flowers

imperfect flowers

staminate flower

carpellate flower

species with imperfect flowers may be monoecious or dioecious:

monoecious species

dioecious species

Embryo structure

- seed and embryo structure also varies with species

- embryo includes a root-shoot axis, and one or two cotyledons

- root-shoot axis consists of

a) the radicle

b) the plumule

- includes epicotyl and embryonic leaves attached

c) the hypocotyl

- one or two cotyledons attached at hypocotyl/epicotyl junction

- two classes of flowering plants

- dicots, have two cotyledons

- monocots, have one cotyledon

- cotyledons are food-storage organs

- may remain small

- may become thick and fleshy

monocot embryos include additional protective tissue layers:

- the coleoptile

- the coleorhiza