Reproduction in Animals - 1

Vivipary means giving birth to live young that develop within the mother's body, receiving nourishment directly. Humans (Man) exhibit vivipary. Frogs are typically oviparous (egg-laying), earthworms have different reproductive strategies, and duck-billed platypus (not mole) is a monotreme that lays eggs. Option D is the correct answer.

A zygote is a fertilized egg formed by the fusion of male and female gametes during sexual reproduction. This fusion is the defining characteristic of sexual reproduction. Asexual reproduction (budding, fission, etc.) and vegetative propagation do not involve zygote formation since they don't require gamete fusion.

Viviparity is found in rabbits as they give birth to young ones.

Complete metamorphosis (holometabolous) has four stages: egg, larva, pupa, and adult. Butterflies undergo complete metamorphosis (caterpillar → chrysalis → butterfly). Bed bugs, grasshoppers, and silverfish undergo incomplete metamorphosis (hemimetabolous) where juveniles resemble small adults without a pupal stage.

Neoteny is the retention of larval characteristics in sexually mature adults, where the larva develops gonads and reproduces while still in larval form. Regeneration is regrowing lost parts. Autotomy is self-amputation (like lizards dropping tails). Paedogenesis is reproduction by larvae, but neoteny specifically describes the retention of juvenile features in adulthood.

In oviparous reproduction (egg-laying), the embryo develops inside an egg outside the mother's body, nourished by yolk - not directly from the mother. In viviparous reproduction (live birth), the embryo receives nourishment directly from the mother via placenta. In ovoviviparous reproduction, eggs hatch inside the mother's body, and embryos get nourishment from yolk, not directly from mother.

Sexual dimorphism is the condition where males and females of the same species show differences in size, appearance, or other morphological traits (like peacock feathers, lion manes). Heterogamy refers to mating between different types. Homogamy means mating between similar types. Hermaphroditism is having both male and female reproductive organs.

Sexual reproduction fundamentally requires the fusion of gametes from two parents. This means one male reproductive cell (sperm) must unite with one female reproductive cell (ovum/egg). Options involving two cells of the same sex or multiple cells of both sexes describe processes that don't occur in standard sexual reproduction.

Syngamy is the fusion of the nuclei of sperm and ovum (male and female gametes). This nuclear fusion is the key event in fertilization, combining genetic material from both parents. Option A describes cytoplasmic fusion which may accompany but doesn't define syngamy. Option C is incorrect (syngamy is cellular, not organismal). Option D describes conjugation, a different process in some microorganisms.

Sponges like Leucosolenia reproduce asexually primarily through budding, where a new organism grows from the body of the parent.

Testis is the primary sex organ because it produces gametes (sperm) and secretes reproductive hormones. Scrotum, penis, and prostate are secondary or accessory sex organs that support reproduction but do not produce gametes.

Taenia (tapeworm) is hermaphroditic and can practice self-fertilization. Ascaris has separate sexes, earthworms are hermaphroditic but typically cross-fertilize, and honeybees have separate sexes with complex reproductive systems.

Most terrestrial animals use internal fertilization to protect gametes from desiccation (drying out) in terrestrial environments. External fertilization is primarily an aquatic adaptation, while dichogamy and pollination are not standard modes of animal reproduction.

Human sperm cells contain 23 chromosomes (haploid number), which is half the 46 chromosomes found in somatic cells. This ensures that when sperm fertilizes an egg (also 23 chromosomes), the resulting zygote has the normal diploid number of 46.

Anisogamy (fusion of morphologically different gametes) is found in humans (sperm and egg), earthworms (though they are hermaphroditic, they produce different sperm and egg types), and pila (apple snail). All these organisms produce distinct male and female gametes.

Natural parthenogenesis (development from unfertilized eggs) occurs in aphids (cyclical parthenogenesis), honey bees (drones develop from unfertilized eggs), and wasps (some species reproduce parthenogenetically). All three groups exhibit this reproductive strategy.

Ejaculation is controlled by the sympathetic nervous system, which coordinates the emission of semen and propels it through the urethra. The somatic nervous system controls voluntary movements, and the sensory nervous system transmits sensory information.

Thymosin is the hormone secreted by the thymus gland that stimulates the maturation and differentiation of lymphocytes (T-cells) in the fetus. Adrenaline, non-adrenaline (norepinephrine), and thyroxine are not involved in lymphocyte maturation.