Sexual & Asexual Reproduction

Pollination and Fertilization: Presentation 2 of 3

Pollination

• Pollination occurs when mature pollen grains (male sex cells from the stamen) come into contact with the moist, sticky surface of a flower stigma (female flower part).

stamen

stigma

• Pollen grains transfer to the stigmas of flowers by means of:

• gravity,

• insects,

• wind, and

• animals.

• Self-pollination occurs when pollen comes into contact with a stigma within the same flower or other flowers on the same plant.

• Cross-pollination occurs when pollen from the flower of one plant transfers to stigmas of flowers on another plant.

• After a pollen grain anchors on the moist, sticky surface of a flower stigma, it germinates and produces a pollen tube.

• The pollen tube grows down through the style and into the ovary where it eventually reaches an ovule

Fertilization

• In angiosperms (flowering plants), two haploid nuclei or sperm cells are released from the pollen tube.

• Double Fertilization is known as, one sperm cell unites with the egg cell in the ovule to form a zygote (diploid), while the second sperm cell unites with two separate polar nuclei to form a primary endosperm nucleus (triploid).

• The zygote, formed through the union of the sperm cell and egg cell, proceeds through cell division and develops into a seed embryo.

• The primary endosperm nucleus develops to form a food source to be used by the embryonic plant during seed germination.

• For each seed a plant produces, a separate grain of pollen must reach and unite with an ovule.