IB 103: Lec 16 — Angiosperms I

Chalazal End

The end of the ovule opposite the microphyle; where antipodal cells are located.

Micropylar End

The opening of the ovule where the pollen tube enters; contains the egg cell & synergids.

Antipodal Cells

Three cells at the chalazal end that may help nourish the embryo sac.

Synergids

Two cells near the egg that guide the pollen tube for fertilization.

Central Cell

A large cell containing two polar nuclei that becomes endosperm after fertilization.

Polar Nuclei

Two nuclei in the central cell that fuse with a sperm cell to form endosperm.

Endosperm

Nutritive tissue (usually triploid) that supports embryo development.

Double Fertilization

One sperm fertilizes the egg → embryo (2n)

Another fertilizes polar nuclei → endosperm (3n)

Cotyledon

An embryonic leaf that stores or absorbs nutrients for the seedling.

Carpel

The female reproductive organ of a flower (stigma, style, ovary).

Floral Meristem

A meristem that produces floral organs instead of leaves.

Whorl

A circular arrangement of floral organs around the stem.

Inflorescence Meristem

A meristem that produces multiple flowers.

Vernalization

Exposure to prolonged cold that induces flowering.

Bracts

Modified leaves associated with flowers or inflorescences.

Key difference between gymnosperm vs. angiosperm gametophytes?

Angiosperms have highly reduced gametophytes & double fertilization; gymnosperms do not.

How many cells are in the angiosperm female gametophyte?

7 cells, 8 nuclei

The 7 cells in the female gametophyte?

1. 1 egg

2. 2 synergids

3. 3 antipodals

4. 1 central cell

What are the products of double fertilization?

Embryo (2n) & endosperm (3n)

Difference between gymnosperm vs. angiosperm seeds?

Gymnosperms use haploid female tissue; angiosperms use triploid endosperm.

Persistent vs. transient endosperm

Persistent = remains in mature seed

Transient = absorbed by embryo

Advantages of endosperm as nutritive tissue?

Provides efficient, controlled nutrient allocation after fertilization.

What is a flower?

A reproductive structure composed of modified leaves.

4 main floral organs?

• Sepals

• Petals

• Stamens

• Carpels

Function of sepals?

Protect the developing bud.

Functions of petals?

Attract pollinators.

Function of stamens?

Produce pollen (male gametes).

Function of carpels?

Produce ovules & house female gametophyte.

Parts of carpel?

• Stigma

• Style

• Ovary

Function of stigma?

Receives pollen.

Function of style?

Pathway for pollen tube growth.

Function of ovary?

Contains ovules.

Difference between SAM & FM?

SAM — produces leaves/stems

FM — produces flowers

Why is false spring harmful?

Plants may flower early & then be damaged by returning cold.

Do plants measure light or darkness to flower?

Darkness (length of uninterrupted night).