frst 303: sexual reproduction

What is meiosis?

Type of cell division producing four haploid (N) cells from one diploid (2N) cell.

What is a gamete?

A haploid reproductive cell — sperm or egg.

What is the difference between spores and gametes?

Spores grow into new haploid organisms; gametes must fuse to form a zygote.

What is the plant life cycle called?

Sporic meiosis or alternation of generations — alternates between haploid (gametophyte) and diploid (sporophyte) stages.

In plants, what is the sporophyte?

The diploid (2N) tree or plant that produces spores by meiosis.

In plants, what is the gametophyte?

The haploid (N) stage that produces gametes (sperm & egg).

Example conifer species studied

Douglas-fir (Pseudotsuga menziesii)

How long is the Douglas-fir reproductive cycle?

About 17 months from bud initiation to seed dispersal.

What are the three bud types in Douglas-fir?

Vegetative, seed-cone (female), and pollen-cone (male) buds.

When do Douglas-fir buds start forming?

In spring, determined as vegetative or reproductive during the same year.

When do cones emerge and pollination occur?

The following spring, pollination occurs by wind.

How are cone crops influenced?

Increased by nitrate fertilizer before budburst and dry, sunny weather during early development.

How often do Douglas-fir trees produce heavy cone crops?

Roughly every 5 years, but varies 2-7 years.

Where are male cones located?

Usually dense near the base of the previous year's shoot.

What are conifer microgametophytes?

5-celled pollen grains containing two sperm (after meiosis + division).

What are conifer megagametophytes?

Nutritive tissues within seeds, haploid (N), supporting the embryo.

How are conifers pollinated?

By wind, often using winged pollen for dispersal.

How long do pine cones take to mature?

About two years.

Example of a conifer with swimming sperm

Ginkgo, which retains flagellated sperm like ferns.

Example angiosperm from lecture

Northern red oak (Quercus rubra)

Why are male oak flowers abundant and female flowers small?

To maximize pollen production for wind pollination; female flowers are small and inconspicuous.

Where are male flowers found?

On long catkins producing pollen.

What are the angiosperm gametophytes?

Male (microgametophyte): 3-celled pollen grain with 2 sperm; Female (megagametophyte): 7 cells, 8 nuclei.

What is the sporophyte in angiosperms?

The tree or plant itself (2N).

What happens during double fertilization?

One sperm + egg → zygote (2N); other sperm + 2 polar nuclei → endosperm (3N).

What develops after double fertilization?

Seeds within fruits, growth by mitosis.

Example of monocarpic tree

Tachigali versicolor ("suicide tree") - flowers once, fruits, then dies (4-6 yr cycle).

What is the main difference between wind and insect pollination?

Wind: many small, light pollen grains; Insect: fewer, sticky or structured pollen for targeted delivery.

Advantages of wind pollination

Doesn't depend on animals; can reach distant trees.

Disadvantages of wind pollination

Inefficient; wastes much pollen; depends on weather.

Advantages of insect pollination

Efficient, targeted fertilization → less pollen needed.

Disadvantages of insect pollination

Relies on pollinator availability and behavior.

Which flower parts are reduced or missing in wind-pollinated plants?

Petals (no need to attract insects).

How far can wind-borne pollen travel?

Up to a few thousand km.

Why is wind-borne pollen important for humans?

Causes allergies ("hay fever"); e.g., alder and birch produce billions of grains yearly.

What do anthers produce?

Pollen grains = microgametophytes.

What grows from a pollen grain to reach the egg?

A pollen tube.

What is pollinator specialization?

Evolution of specific pollinators matched to unique flower structures (e.g., orchids + long-tongued moths).

Dominant life stage in mosses

Gametophyte (N) — green plant body.

Dominant life stage in ferns

Sporophyte (2N) — leafy fern plant; independent gametophyte is small & heart-shaped.

Dominant life stage in conifers and angiosperms

Sporophyte (2N) — the tree.

Trend across plant evolution

Gametophyte shrinks, becomes more dependent on sporophyte.