Lec: Ch. 38 Angiosperm reproduction and Biotechnology

Alternation of generation

• Diploid (2n) sporophytes produce spores by meiosis 2n——>n, grown into haploid gametophytes

• gametophytes produce haploid (n) gametes by mitosis

• fertilization of gamtes produces a zygote = sporophyte cell (2n)

Angiosperm life cycle is characterized by three F’s

1. flowers

2. double fertilization

3. fruits

Flower structure

Four floral organs

1. sepals - enclose flower

2. petals - attract pollinators

3. stamens- anther filament

4. carples- female portion

Anther

stamen consists of a filament topped with pollen sacs that produce pollen

Complete flowers

contain all four floral organs

Incomplete flowers

lack one or more flora organs

• ex: stamens or carpels

Inflorescences

clusters of flowers

development of female gametophytes

• megaspores are produced by meiosis and develop into embryo sacs, the female gametophytes

Pollination

• the transfer of pollen from anther to stigma (male—→female)

• aided by the environment such as wind, water, bees, moth, butterfly, fly, bird, bat

• by bees= color/signal to attract pollinators

• by flies= chemical signal/odor attracts flies

• birds= nectar/ chemical attraction

Double fertilization

• results from the discharge of two sperm from the pollen tube into the embryo sac in the ovule

• sperm + egg = zygote 2n

• sperm + two polar nuclei = endosperm 3n

Food - storing endosperm

• one sperm fertilizes the egg, and the other combines with the polar nuclei, giving rise to the triploid (3n)

• storage food for future zygote

Seed development

• after double fertilization, each ovule develops into a seed

• ovary develops into a fruit

Seed coat

• the embryo and its food supply are enclosed

• the seed enters a state of dormancy

Eudicots

• the embryo consist embryonic axis attached to two thick cotyledons

• ex: common garden bean

Seed Dormancy

• increases the chances that germination will occur at a time and place most advantageous to the seedling

• breaking of dormancy can be from environmental cues, temperature or light changes

Imbibition

• the uptake of water due to low water potential of the dry seed

• radicle emerges first

• next the shoot tip breaks through the soil

Fruit

• develops from the ovary

• protects the enclosed seeds

• aids in seed dispersal by wind or animal

Fruit: classified by their development

• Simple: a single or several fused carpels

• Aggregate: a single flower with multiple separate carpels

• Multiple: a group of flowers = inflorescence

Plants reproduce

• reproduce both asexually and sexually

• results in offspring that are genetically different from their parents

Asexual reproduction

results in a clone of a genetically identical organisms

Asexual reproduction - Fragmentation

• separation of parent plant into parts that develop into whole plants

• common type of asexual reproduction

Apomixis

asexual production of seeds from a diploid cell

Advantage of asexual reproduction

• vegetative reproduction

• beneficial to a successful plant in a stable environment

• generates genetic variation that makes evolutionary adaption possiable

Disadvantage of asexual reproduction

• clone of plants is vulnerable to local extinction if there is an environmental change

• only a fraction of seedlings survive