Biology » Plant Reproduction » Pollination and Fertilization

Summarizing Pollination and Fertilization

Summary

For fertilization to occur in angiosperms, pollen has to be transferred to the stigma of a flower: a process known as pollination. Gymnosperm pollination involves the transfer of pollen from a male cone to a female cone. When the pollen of the flower is transferred to the stigma of the same flower, it is called self-pollination.

Cross-pollination occurs when pollen is transferred from one flower to another flower on the same plant, or another plant. Cross-pollination requires pollinating agents such as water, wind, or animals, and increases genetic diversity. After the pollen lands on the stigma, the tube cell gives rise to the pollen tube, through which the generative nucleus migrates. The pollen tube gains entry through the micropyle on the ovule sac.

The generative cell divides to form two sperm cells: one fuses with the egg to form the diploid zygote, and the other fuses with the polar nuclei to form the endosperm, which is triploid in nature. This is known as double fertilization. After fertilization, the zygote divides to form the embryo and the fertilized ovule forms the seed. The walls of the ovary form the fruit in which the seeds develop. The seed, when mature, will germinate under favorable conditions and give rise to the diploid sporophyte.

Glossary

accessory fruit

fruit derived from tissues other than the ovary

aggregate fruit

fruit that develops from multiple carpels in the same flower

aleurone

single layer of cells just inside the seed coat that secretes enzymes upon germination

coleoptile

covering of the shoot tip, found in germinating monocot seeds

coleorhiza

covering of the root tip, found in germinating monocot seeds

cotyledon

fleshy part of seed that provides nutrition to the seed

cross-pollination

transfer of pollen from the anther of one flower to the stigma of a different flower

dormancy

period of no growth and very slow metabolic processes

double fertilization

two fertilization events in angiosperms; one sperm fuses with the egg, forming the zygote, whereas the other sperm fuses with the polar nuclei, forming endosperm

endocarp

innermost part of fruit

endosperm

triploid structure resulting from fusion of a sperm with polar nuclei, which serves as a nutritive tissue for embryo

endospermic dicot

dicot that stores food reserves in the endosperm

exocarp

outermost covering of a fruit

epicotyl

embryonic shoot above the cotyledons

gravitropism

response of a plant growth in the same direction as gravity

hypocotyl

embryonic axis above the cotyledons

mesocarp

middle part of a fruit

multiple fruit

fruit that develops from multiple flowers on an inflorescence

nectar guide

pigment pattern on a flower that guides an insect to the nectaries

non-endospermic dicot

dicot that stores food reserves in the developing cotyledon

pericarp

collective term describing the exocarp, mesocarp, and endocarp; the structure that encloses the seed and is a part of the fruit

plumule

shoot that develops from the germinating seed

pollination

transfer of pollen to the stigma

radicle

original root that develops from the germinating seed

scarification

mechanical or chemical processes to soften the seed coat

scutellum

type of cotyledon found in monocots, as in grass seeds

self-pollination

transfer of pollen from the anther to the stigma of same flower

simple fruit

fruit that develops from a single carpel or fused carpels

suspensor

part of the growing embryo that makes connection with the maternal tissues

tegmen

inner layer of the seed coat

testa

outer layer of the seed coat

vernalization

exposure to cold required by some seeds before they can germinate

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