REPRODUCTION AND ITS TYPES - Key Concepts
» Life span is the period from birth to the natural death of an organism.
» The life span of organisms varies from a few days to a few thousand years.
» Reproduction is the process that ensures continuity of living organisms generation
» Reproduction is defined as the biological process in which an organism gives rise to
young ones similar to itself.
» Reproduction is of two types in plants
1. Asexual reproduction
2. Sexual reproduction
» Asexual reproduction is a method in which a single individual parent is capable of
» The offsprings produced during asexual reproduction are identical to one another and
also exact copies of their parent.
Different kinds of asexual reproduction in lower plants:
1. Binary fission: Ex:- Protists and Monerans (Euglena and Bacteria)
2. Budding: Yeasts
3. Zoospores(motile): Chlamydomonas
4. Aplanospores (non- motile): Rhizopus (Bread mold)
5. Conidia : Pencillium
6. Fragmentation: some forms of colonial algae, moulds and mushrooms.
7. Gemmae: liverworts
» Asexual reproduction in flowering plants takes place by vegetative propagules like runners, stolons, suckers, offsets, rhizomes, corms, tubers, bulbs, bulbils and reproductive leaves.
» Plants produced vegetatively or asexually are called clones.
» Water hyacinth – "Terror of Bengal" is an example for profuse vegetative propagation
» Simple organisms like algae and fungi shift to sexual mode of reproduction just before the onset of adverse conditions.
» Sexual reproduction involves formation of the male and female gametes either by
the same individual or by different individuals of the opposite sex.
» The gametes unite to form a zygote which develops into a new organism.
» The offsprings produced by sexual reproduction are not identical to the parents or
» In annuals and biennials vegetative, reproductive and senescent phases are clear.
» In perennials these phases are not distinct.
» Hormones and environmental factors regulate reproductive process.
» Events in sexual reproduction:
1. Pre fertilization
3. Post – fertilization
¤ Pre fertilization events:
2. Gamete transfer
» It is the process of formation of two types of gametes.
» If both the gametes are similar they are called homogametes or isogametes.
» If the gametes are dissimilar and distinguished into male and female they are referred as
heterogametes e.g.: Funaris, Pteris, Cycas.
» If both male and female reproductive structures are present in the same plant it is
said to be bisexual. Homothallic in fungi and monoecious in plants. e.g.: Cucurbits and
» If male and female reproductive structures are present on different plants it is said to
be unisexual. Heterothallic in fungi and dioecious in plants.
e.g.: Papaya and date palm.
» A haploid parent produces gametes by mitotic division.
» A diploid parent produces gametes by meiosis (reduction division).
» Water is the medium of gamete transfer in algae, bryophytes and pteridophytes.
» In few fungi and algae both male and female gametes are motile.
» In many plants male gametes are motile and female gametes are stationary.
» In seed plants (angiosperms and gymnosperms) pollen grains produce male gametes
and ovule produces egg (female gamete).
» Hence the pollen grains are transferred to the stigma of a flower by pollination.
» Fusion of gametes to form a diploid zygote is called syngamy or fertilization.
» Fertilization is external in majority of algae (in water).
» Fertilization is internal in bryophytes, pteridophytes, gymnosperms and angiosperms.
» In seed plants the male gametes are carried by pollen tubes to the female gamete.
¤ Post fertilization events:
» Every sexually reproducing organism begins life as a single celled zygote.
» In fungi and algae the zygote develops a thick wall and undergoes a period of rest.
It later divides by meiosis to form haploid spores that grow into haploid individuals.
» Zygote undergoes cell division (mitosis) and cell differentiation to form an embryo.
» The process of development of embryo from the zygote is called embryogenesis.
» As the zygote develops into embryo, the ovules develop into seeds, the ovary
develops into fruit.
» Seeds germinate under favorable conditions to produce new plants.