Angiosperm Plant Reproduction (Chap. 28)

Know the following in a typical plant:

• sepal, petal, stamen, anther, filament, pollen, pistil, stigma, style, ovule, and ovary

Sexual Reproduction

Pollination

• the transfer of pollen from an anther to a stigma

• some flowers’ color, shape, and fragrance attract pollinators and others simply use wind

Fertilization • a zygote is formed by the fusion of a male

gamete (a pollen grain produced by the anther) and a female gamete (ovules in the ovaries)

• Process – after pollination, one cell in the pollen grain

called the tube cell makes enzymes that digest the tissue ahead of it and the pollen grain progresses through the style towards the ovary

– two other cells in the pollen grain called sperm cells finally penetrate the ovule (various maternal cells) in the ovary in a process called double fertilization • one sperm fertilizes the egg cells that

eventually becomes the zygote• other sperm fertilizes the central cell that

produce the endosperm (nutritive tissue in seeds)

(sperm cell)

Seed Dormancy and Dispersal

• lose most of their water and can lie dormant up to 10,000 years

• primarily dispersed by wind, water, and animals (inside and outside)

Germination of the Seed

• Water to re-hydrate the dry tissue and the hydrolysis of storage compounds such as starch into their simple monomers such as glucose.

• Oxygen is needed for aerobic respiration• Seeds have an optimum temperature for enzymatic

activity leading to germination.

Conditions needed for germination

Metabolic events of germination

1. Absorption of water to rehydrate living cells in the seed and cause it to burst

2. Water activates a plant hormone gibberellin

3. Gibberellin stimulates the production of amylase (that catalyzes the digestions of starch into maltose) and then maltose is hydrolyzed by maltase into glucose.

4. The embryo absorbs glucose and uses it for respiration

5. Cell division, growth and elongation occur in the embryo . The radicle starts growing downwards into a root and the plumule starts growing upwards into a shoot.

6. As the nutrients in the cotyledons are consumed and exhausted, the first leaves start to appear and the plant starts to photosynthesize and make its own food.

Asexual Reproduction

• the development of new individuals from a fragment of the plant

• genetically identical to the parent plant

• ensures desirable qualities of a crop

• 5 types that occur in some plants 1. cuttings – cut and put pieces of stem in

water

Vegetative propagation

2. adventitious buds (suckers) – buds form on underground roots or stems

3. leaf generation – shoots emerge on the margins of a leaf

4. runner or stolons – wispy stems that snake away from the parent plant and eventually develop roots and stems. ex) strawberries

5. tubers – thick underground stems. ex) potatoes

Apomixis

• seeds produced without the union of sperm and egg

• egg fails to under go meiosis and diploid condition is retained

• occurs naturally in about 400 plant species • can be good in extreme environmental

conditions however lack the variability that is necessary for evolution of the plant