IB 103: Lec 12 & 13 — Gymnosperms

Megaspore Mother Cell

A diploid cell in the ovule that undergoes meiosis to produce megaspores.

Pollen

The male gametophyte of seed plants that delivers sperm to the ovule.

Exine

The tough outer layer of a pollen grain that protects it from environmental damage.

What is a seed?

A mature fertilized ovule containing an embryo, stored nutrients, & seed coat.

Three main parts of a seed?

• Seed coat (2n)

• Female Gametophyte (1n) — stored nutrients

• Embryo (2n)

Main function of seeds?

Protection of the embryo & dispersal of the next generation

Gymnosperm

A seed plant that produces “naked seeds” not enclosed in fruit.

Example of gymnosperm commonly used to study the life cycle?

Pine tree

What structure produces pollen in gymnosperms?

Male cones (pollen cones).

What structure produces ovules in gymnosperms?

Female cones (seed cones).

What is the microgametophyte in gymnosperms?

The pollen grain

How are gymnosperms microgametophytes different from those in ferns or lycophytes?

They are reduced and develop inside pollen grains rather than existing as free-living plants.

What is the ploidy of the embryo in a gymnosperm seed?

Diploid (2n)

What is the ploidy of the seed coat?

Diploid (2n), derived from the parent sporophyte.

What is the ploidy of the nutritive tissue in gymnosperm seeds?

Haploid (1n), derived from the female gametophyte.

What major reproductive challenge did seed plants solve?

The need for water for fertilization.

How did seed plants solve the water requirement for fertilization?

By evolving pollen that transports sperm through air rather than water.

What replaced swimming sperm in seed plants?

Air-dispersed pollen

What became the primary dispersal unit in seed plants?

Seeds

What did seeds replace as the primary dispersal unit?

Spores

What are common defense strategies used by many gymnosperms?

Chemical defenses such as resins & toxic compounds

What is resin used for in gymnosperms?

Protection against herbivores & pathogens.

Cataphyll

A small, reduced leaf that often protects emerging foliage, buds, or flowers, & a protective sheath for new growth & the SAM

Endemism

When a species is native to & restricted to a specific geographic area.

Long Shoots

Branches with elongated internodes that produce leaves spaced farther apart.

Short Shoots

Branches with very short internodes that produce clustered leaves.

Pollen Drop

A sticky fluid secreted by ovules that capture pollen for fertilization.

Pollen Chamber

A structure inside the ovule where pollen grains collect & germinate.

Vegetative cell in pollen

The cell that forms the pollen tube.

Generative cell in pollen

The cell that divides to protect sperm cells.

4 Major Gymnosperm Groups?

1. Conifers

2. Cycads

3. Ginkgo

4. Gnetophytes

Which gymnosperms have compound leaves?

Cycads

Which gymnosperm has fan-shaped leaves?

Ginkgo

Which gymnosperms have needle-like leaves?

Conifers

Which gymnosperms have extremely reduced leaves?

Some Gnetophytes (like Ephedra)

Which gymnosperms have leaves similar to flowering plants?

Some Gnetophytes (like Gnetum)

Which gymnosperm groups have swimming sperm?

Cycads & Ginkgo

What advantages do cycads have with a well-protected SAM?

It protects the growing tissue from environmental damage & herbivores

What is the function of the vegetative cell in pollen grains?

It forms the pollen tube that delivers sperm to the egg.

What is the function of the generative cell in pollen grains?

It produces the sperm cells.

What is the function of long shoots?

They extend plant growth & space out leaves for better light capture.

What is the function of short shoots?

They cluster leaves together, often improving photosynthesis efficiency.

What secretes the pollen drop?

The ovule

What is the function of a pollen drop?

It captures pollen & pulls it into the ovule for fertilization.

How is sperm delivered in cycads & Ginkgo?

Via swimming sperm that move to the egg.

How is sperm delivered in other seed plants (like conifers)?

Through a pollen tube that delivers sperm directly to the egg.

How is sperm delivered in non-seed plants?

Sperm swim through water to reach the egg.