Home › Biology › Q
BiologyDiversity in Living World
Which of the following is an example of asexual reproduction?
Options
1
Formation of seeds in flowering plants
2
Fusion of gametes in frog
3
Regeneration in Planaria
4
Formation of embryo from fertilised egg in humans
Correct Answer
Regeneration in Planaria
Solution
1

Check each option for absence of fertilisation (= asexual):

A: Seeds from flowering plants = after fertilisation = sexual

B: Fusion of gametes in frog = fertilisation = sexual

2

C: Regeneration in Planaria = from body fragment, mitosis only, NO fertilisation = asexual

D: Embryo from fertilised egg in humans = sexual

Answer: C - Regeneration in Planaria

Planaria regeneration = asexual (mitosis only, no gametes)
All other options involve fertilisation = sexual
Theory: Diversity in Living World
1. Types of Asexual Reproduction

Binary fission: cell divides into 2 equal daughter cells. Amoeba: equal fission. Paramecium: transverse. Euglena: longitudinal. Budding: Hydra (multicellular bud), yeast (unicellular). Fragmentation: Spirogyra (filament breaks), Planaria, starfish. Regeneration: Planaria (complete regeneration from any piece), starfish (can regenerate from arm + part of disc), lizard (regenerates tail - but not a new organism). Sporulation: Rhizopus, Mucor form sporangiospores. Plasmodium: multiple fission (schizogony) in host cells.

2. Regeneration in Detail

True regeneration (asexual reproduction): organism can regenerate complete individual from a fragment. Planaria: flatworm. Cut into pieces - each grows into new organism. Involves dedifferentiation (cells lose specialised function) then redifferentiation (form new cell types). Starfish: can regenerate complete individual from arm + portion of central disc. Hydra: fragments regenerate. Earthworm: can regenerate posterior end from anterior, but anterior cannot regenerate from posterior alone. Human: can regenerate liver (not whole organism), skin, blood cells - not true regenerative asexual reproduction. Stem cells important for regeneration.

3. Vegetative Propagation Types

Natural methods: Runners/stolons above ground - strawberry, Oxalis. Rhizomes horizontal underground - ginger, turmeric, fern, banana. Bulbs - short stem + fleshy leaves - onion, garlic, lily. Corms - swollen underground stem - Colocasia, Crocus. Tubers - potato (stem), sweet potato (root). Leaf buds - Bryophyllum (epiphyllous buds fall, grow into plants). Artificial: Cutting - rose, sugarcane, Bougainvillea. Grafting - mango, apple (scion + rootstock). Layering - jasmine (bend branch to soil, roots form before cutting). Tissue culture (micropropagation) - orchid, banana, potato.

4. Animal Reproduction Modes

Asexual: binary fission (Amoeba, Paramecium), budding (Hydra, sponges), fragmentation (Planaria, starfish), sporulation (Plasmodium). Sexual: most animals. External fertilisation: fish, frog, most aquatic animals. Requires water medium. Produces many eggs (to compensate for low survival). Internal fertilisation: reptiles, birds, mammals. More efficient, fewer eggs needed, better parental care possible. Oviparous: lay eggs (birds, reptiles, monotremes - duck-billed platypus). Viviparous: give birth to young (most mammals, some reptiles, some sharks). Ovoviviparous: eggs hatch inside mother (some snakes, rays).

5. Plant Life Cycles

Alternation of generations: sporophyte (2n) and gametophyte (n) alternate. Pteridophytes: sporophyte dominant, independent gametophyte (prothallus). Bryophytes: gametophyte dominant, sporophyte dependent on gametophyte. Gymnosperms: sporophyte dominant, tiny gametophyte inside ovule/pollen. Angiosperms: sporophyte dominant, extremely reduced gametophyte (embryo sac 7 cells, pollen 2-3 cells). Double fertilisation unique to angiosperms. Seed: protective structure - embryo + food reserve + seed coat. Advantage over spores: better protection, food reserve for germination.

6. Animal Development

Embryonic development stages: Fertilisation -> zygote -> cleavage (rapid mitosis, no growth) -> morula (16-cell solid ball) -> blastula/blastocyst (hollow, fluid-filled) -> gastrulation (3 germ layers: ectoderm, mesoderm, endoderm) -> organogenesis. Germ layers: Ectoderm: skin epidermis, nervous system, sense organs. Mesoderm: muscles, bones, circulatory system, kidneys, gonads. Endoderm: GI tract lining, respiratory tract, liver, pancreas. Metamorphosis: dramatic transformation. Complete (holometabolous): egg, larva (caterpillar), pupa (chrysalis), adult (butterfly). Incomplete (hemimetabolous): egg, nymph, adult (grasshopper, cockroach).

7. Reproductive Health Issues

STIs (Sexually Transmitted Infections): bacterial: gonorrhoea (Neisseria), syphilis (Treponema pallidum), chlamydia. Viral: HIV/AIDS, HPV (warts, cervical cancer), herpes, hepatitis B. Fungal: candidiasis. Parasitic: trichomoniasis. Prevention: condoms (most effective barrier), vaccination (HPV, Hepatitis B), monogamy, STI screening. HIV/AIDS: HIV (Human Immunodeficiency Virus) infects CD4+ T cells, macrophages. AIDS (Acquired Immunodeficiency Syndrome): CD4+ count below 200/microL. Transmission: sexual, blood (needles), mother to child. No cure but ART (Antiretroviral Therapy) extends life indefinitely. India: ~2.4 million HIV-positive people (3rd highest globally).

8. Infertility and ART

Infertility: inability to conceive after 1 year of unprotected sex. Male: low sperm count (oligospermia), no sperm (azoospermia), poor motility, abnormal morphology. Female: anovulation, PCOS, blocked tubes, endometriosis, uterine abnormalities. ART: IVF (In Vitro Fertilisation) - egg + sperm fertilised in lab dish. First IVF baby: Louise Brown (UK, 1978). India: Durga (1978, claimed - same year). ICSI: single sperm injected into egg cytoplasm - for severe male infertility. GIFT: gametes placed in fallopian tube. ZIFT: zygote placed in fallopian tube. Surrogacy: gestational surrogate carries embryo. India: Surrogacy (Regulation) Act 2021 - altruistic surrogacy allowed for close relatives only.

Frequently Asked Questions
1. What is the difference between regeneration as repair and regeneration as reproduction? ⌄
Repair regeneration: replacing lost parts without producing a new individual. Humans, most animals: heal wounds (skin regeneration), regrow blood cells, regenerate some organs (liver up to 75%). This is NOT asexual reproduction - no new individual formed. Reproductive regeneration: a fragment gives rise to a completely new individual. Planaria: any piece regenerates complete worm. Starfish: arm + central disc regenerates. Hydra: fragments regenerate. This IS asexual reproduction - new complete organism formed from parent fragment. The distinction: repair regeneration = homeostasis, not reproduction. Reproductive regeneration = new individual created, counts as asexual reproduction.
2. Why does Planaria have such remarkable regenerative ability? ⌄
Planaria have high proportions of neoblasts - pluripotent adult stem cells (20-30% of all cells). Neoblasts can divide and differentiate into any cell type. When Planaria is cut: neoblasts at the wound site divide rapidly. They form a regeneration blastema (mass of undifferentiated cells). Positional information (gradients of molecules like Wnt signalling along anterior-posterior axis) tells blastema cells what body part to form. Remarkable: a piece as small as 1/279th of Planaria can regenerate complete organism. Planaria is intensively studied as model for regeneration biology and stem cell research.
3. What is parthenogenesis and which organisms use it? ⌄
Parthenogenesis: egg develops into new organism without fertilisation. Natural parthenogenesis: Drone bees (male honeybees) develop from unfertilised eggs - haploid. Aphids: facultative parthenogenesis (can be sexual or asexual depending on season). Whiptail lizards (Cnemidophorus): all female species, obligate parthenogenesis. Komodo dragon: facultative parthenogenesis documented. Turkeys: rare accidental parthenogenesis documented. Plants: dandelion, some grasses (apomixis). In plants called apomixis: embryo develops without fertilisation from egg (diplospory) or from cells of nucellus/integument (adventive embryony/sporophytic apomixis). Artificial parthenogenesis: eggs of sea urchin, frog can be activated by chemical or electrical stimulation in lab.
4. How does binary fission differ in different organisms? ⌄
Prokaryotes (bacteria): FtsZ protein forms Z-ring at midcell. Chromosome duplicated, attached to membrane. Z-ring constricts, divides cell into two. No spindle (no mitosis). Amoeba: divides into 2 roughly equal halves. Nucleus divides first (mitosis), then cytoplasm. Paramecium: transverse fission - divides across width. Two macronuclei, two micronuclei first divide. Euglena: longitudinal fission - divides along length. Dinoflagellates: unusual transverse fission. Diatoms: mitosis followed by each half retaining one original silica valve, secreting new valve. This means diatoms get progressively smaller with each binary fission until they undergo sexual reproduction to restore size.
5. What makes tissue culture micropropagation commercially important? ⌄
Micropropagation via tissue culture allows: (1) Production of millions of genetically identical plants rapidly from one explant (e.g., one meristem). (2) Disease-free plants: growing from meristem tips (which are virus-free even in infected plants) produces virus-free plants. Critical for: banana, potato, strawberry, orchids. (3) Year-round production independent of season. (4) Conservation of rare/endangered plants. (5) Preservation of superior genotypes (e.g., disease-resistant or high-yield varieties). Commercial scale: orchid micropropagation (Singapore, Thailand) produces millions of plants yearly for global flower market. Banana: all commercial Cavendish bananas are tissue culture clones. Limitation: all plants are genetically identical = vulnerability to new pathogen that attacks the whole clone population (like Panama disease in Gros Michel banana variety - wiped out entire commercial crop in 1950s).
Previous Questions
Q.
Vegetative propagation asexual reproduction clones identical offspring both correct
Biology . Both correct
Q.
Species broad geographic range survival A true R false ecology
Biology . A true R false
Q.
Biodiversity hotspots India Western Ghats Eastern Himalayas A B D only
Biology . A, B and D only
Q.
Translation ribosome moves 5 to 3 incorrect statement B molecular biology
Biology . B incorrect
Q.
Angiosperm pollen formation meiosis mitosis microsporogenesis
Biology . 1 meiosis + 3 mitosis