The period of growth to natural death is known as the life span.

The life span is not correlated with size.

Crow and Parrot are much similar in size. But their life spans have a huge difference. Parrot has a life span of 140 years and crow has a life span of 15 years.

Reproduction is a biological process required for the continuation of species.

Reproduction is not essential for a species, but it is essential for a population as the entire population might be extinct in its absence of it.

There is no natural death in single-celled organisms like Amoeba as they continue to live as their daughter cells.

Every organism has its mechanism to multiply.

There are two types of reproduction:

• Asexual Reproduction:

  • A single parent is involved

  • With/ without the involvement of gametes

• Sexual Reproduction:

  • Opposite sexes are involved

  • Involves fusion of gametes

  • Alternation of generation is involved

  • Dioecious condition is not mandatory to be followed in sexual reproduction as organisms following sexual reproduction could be monoecious as well.

ASEXUAL REPRODUCTION:

• Offspring are generally identical to their parents.

• These are called clones.

• Clones are morphologically and genetically similar.

• The individual member of a clone is called a ramet.

• No evolutionary role.

• Somatogenic Reproduction.

• It is called vegetative reproduction in plants.

• It is very common in single-celled organisms, plants, and animals with simple organizations.

• Cell division is itself a mode of reproduction in Monera and Protista.

• In yeast, it takes place in form of budding. The division is irregular.

• Binary fission

  • It takes place in Amoeba in favorable conditions. In unfavorable conditions, Amoeba undergoes encystation where a three-layered structure forms on Amoeba to protect it from adverse conditions. When favorable conditions return, it undergoes multiple fission from minute pseudopodia spores to undergo sporulation.

  • In Paramecium, transverse binary fission takes place.

  • In Euglena, longitudinal binary fission takes place.

• Asexual reproductive structures:

  • Zoospores: Chlamydomonas

    • Motile, flagellated

    • Microscopic

    • Fungi, and simple plants

  • Conidia: Penicillium

    • Conidiophore → Rami → Metulae → Phalides → Conidia

    • Non-flagellate spores

    • Thin-walled, unicelled, uninucleate

  • Buds: Hydra

  • Gemmules: Sponges

• Vegetative propagules: Give rise to new offspring

  • Rhizome: Ginger, Banana

  • Tuber: Potato

  • Leaf buds: Bryophyllum, Kalanchoe

  • Bulbil: Agave

  • Bulb: Onion

  • Offset: Pistia, Eichhornia, Water Hyacinth

If the body breaks into distinct fragments, it’s called fragmentation. e.g.: Hydra, filamentous mosses, spirogyra etc.

Terror of Bengal: Water Hyacinth

• One of the most invasive weeds.

• Propagates vegetatively at a phenomenal rate

• Multiplies in stagnant water.

• Deprives oxygen which leads to the death of fish.

• It was introduced in India due to its beautiful flowers and the shape of its leaves.

Asexual reproduction is found in both higher and lower plants.

Only sexual reproduction is found in higher animals.

SEXUAL REPRODUCTION:

• Complex, Elaborate, Slow

• The offspring is not identical to the parents.

• In primates, the cycle takes care of the associated reproductive changes in the menstrual cycle.

• In non-primates, the cycle takes care of the associated reproductive changes in the estrous cycle.

• In the juvenile or vegetative phase, the organism changes to get reproductively active followed by the reproductive phase, and then when the metabolic processes slow down is called senescence.

• The prominent stages in sexual reproduction include:

  • Pre- fertilization: This includes gametogenesis and gamete transfer

  • Fertilization:

    • External fertilization: When fertilization takes place in an outside medium like water.

    • Internal fertilization: When fertilization takes place inside the body.

  • Post-fertilization: Embryogenesis

• Key terms:

  • Viviparous: The organisms which give birth to young ones.

  • Oviparous: The organisms which lay eggs and young ones hatch from eggs.

  • Ovoviviparous: The females retain the eggs inside their body after fertilization and allows the development of an embryo inside the body without providing extra embryonic care as the placenta is absent. E.g. sharks.

  • Monoecious: In plants, the male and female reproductive structures are present on the same plant. It is a homothallic structure and is often referred to as a bisexual condition in animals.

    • E.g.: Chara, Sweet potato, Pinus, Cucurbits, Cucumber. [CSPCC]

    • Hermaphrodite animals: Leech, tapeworm, sponges, earthworm [LTSE]

  • Dioecious: In plants, the male and female reproductive structures are present in different plants. It is a heterothallic structure and is often referred to as a unisexual condition in animals.

    • E.g.: Vallisneria, Cycas, Date palm, Papaya [VCDP]

• Strobilanthus kunthiana:

  • It flowers in 12 years.

  • Found in KKT (Karnataka, Kerela, Tamil Nadu).

  • Monocarpic but Perennial plant.

• In diploid organisms, specialized cells called meiocytes (gamete mother cells) undergo meiosis.

• At the end of meiosis, only one set of chromosomes gets incorporated into each gamete.

• In flowering plants

  , the ovary develops into fruit after fertilization,

  and ovules mature into seeds.

• Inside the mature seed is the progenitor of the next generation, the embryo.

Fungi and Algae reproduce through asexual reproductive structures.

Fleshy buds in aquatic plants called turion.

The nucule in chara has a cap of five coronary cells.

Isogamous condition with non-flagellated is found in spirogyra.

Self-fertilization is seen in the bisexual flower.

Hermaphrodite: Earthworm

The juvenile/Vegetative phase is variable in different organisms.

Dioecious organisms are seen in both plants and animals.

A Pistil may produce more than one seed.

Each carpel may have more than one ovule.

The endosperm found in the angiosperm seed is different from that of gymnosperms in the sense that, in the former, it is formed after fertilization.

Syngamy can occur outside the body of the organism in Algae.