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Samacheer Kalvi 10th Science Chapter 16 Long Answer Questions — Reproduction with Answers

Long answer questions (5 marks) from Samacheer Kalvi Class 10 Science Chapter 16 Reproduction with detailed answers.

Updated 25 May 202613 min read
Question 1: Describe the different types of asexual reproduction with suitable examples.

Answer:

Asexual reproduction is a type of reproduction that involves only one parent organism, does not require the fusion of gametes, and produces offspring that are genetically identical to the parent (clones). It is faster and more efficient than sexual reproduction.

Types of Asexual Reproduction:

1. Binary Fission:
Answer
  • The parent organism divides into two equal daughter cells
  • Each daughter cell inherits a copy of the parent's genetic material
  • Simple (amitotic) binary fission: e.g., Amoeba — the cell divides in any plane
  • Transverse binary fission: e.g., Paramecium — division perpendicular to the long axis
  • Longitudinal binary fission: e.g., Euglena — division along the long axis
  • In bacteria, this is called prokaryotic binary fission — cell wall constricts inward
  • Can produce millions of offspring in a short time
2. Budding:
Answer
  • A small outgrowth (bud) forms on the parent body
  • The bud grows, becomes organised, and eventually detaches to become a new individual
  • In Animals: e.g., Hydra — a small bud grows on the body wall, develops tentacles and mouth, and detaches; e.g., Yeast (Saccharomyces cerevisiae) — a small bump forms on the yeast cell, grows, and pinches off
  • In Plants: e.g., some sponges; in horticulture (budding is used as a vegetative propagation method)
3. Fragmentation:
Answer
  • The parent organism breaks into fragments
  • Each fragment is capable of regenerating and growing into a complete new organism
  • e.g., Spirogyra (filamentous green alga): the filament breaks and each fragment grows into a new filament
  • e.g., Planaria: if cut into pieces, each piece regenerates into a complete organism (due to totipotency)
  • e.g., Starfish: each arm can regenerate into a new individual (if it contains part of the central disc)
4. Sporulation (Spore Formation):
Answer
  • Special reproductive cells called spores are produced inside sporangia (spore cases)
  • Spores are lightweight, have a resistant coat, can survive harsh conditions (heat, drought, chemicals)
  • Released spores germinate under favourable conditions to form new individuals
  • e.g., Rhizopus (bread mould): black sporangia form on stalks; spores released and dispersed by air
  • e.g., Mucor, Aspergillus (fungi)
  • e.g., Mosses and ferns (in their life cycle) also produce spores
5. Regeneration:
Answer
  • Some organisms can grow a complete new individual from a body part or fragment
  • Similar to fragmentation but can also occur from a detached body part
  • e.g., Planaria: cut into many pieces, each regenerates into a new Planaria
  • e.g., Starfish arm: can regenerate if it includes part of the central disc
  • e.g., Lizard regenerates a new tail (though this is incomplete regeneration — the tail is cartilaginous, not the original bone)
  • Not all animals can regenerate fully; humans cannot regenerate complex organs
6. Vegetative Propagation (in Plants):
Answer
  • New plants are produced from vegetative parts (root, stem, leaf) without seeds
  • e.g., Potato — tubers (stem modification with nodes/buds); Ginger — rhizomes
  • e.g., Bryophyllum — adventitious buds on leaf margins produce new plants
  • e.g., Strawberry — stolons (runners) produce new plants
  • e.g., Onion — bulbs produce new plants

Advantages of Asexual Reproduction:

  • Only one parent required
  • Rapid production of large numbers of offspring
  • Offspring are genetically identical (useful for preserving desirable traits)
  • Requires less time and energy than sexual reproduction

Disadvantages:

  • No genetic variation — all offspring are identical clones
  • If a disease affects one individual, all identical offspring are equally vulnerable
  • Cannot adapt to changing environments
Question 2: Describe the parts of a flower and explain sexual reproduction in plants including pollination and fertilisation.

Answer:

Parts of a Flower:

A flower is the reproductive organ of angiosperms (flowering plants). A complete flower has four whorls:

1. Calyx (Sepals):
Answer
  • The outermost whorl of leaf-like structures (usually green)
  • Collectively called the calyx; individually called sepals
  • Protect the flower bud before it opens
  • In some plants, sepals are coloured (petaloid) to attract pollinators
2. Corolla (Petals):
Answer
  • Second whorl inside the calyx
  • Usually brightly coloured and fragrant to attract pollinators
  • Collectively called the corolla; individually called petals
  • Shape and colour vary greatly and are adapted to specific pollinators
3. Androecium (Stamens) — Male reproductive organ:
Answer
  • Third whorl; collectively called the androecium
  • Each stamen consists of:
  • Filament: Slender stalk
  • Anther: Bilobed structure at the tip of the filament containing pollen sacs (microsporangia)
  • Pollen grains develop inside the anther in the pollen sacs
  • Pollen grains contain the male gametophytes (germinate to produce male gametes)
4. Gynoecium (Pistil/Carpel) — Female reproductive organ:
Answer
  • The innermost whorl; collectively called the gynoecium
  • Each pistil (carpel) consists of:
  • Stigma: Sticky, flattened top surface — receives pollen grains
  • Style: Slender tube connecting stigma to ovary
  • Ovary: Enlarged base containing one or more ovules
  • Each ovule contains the female gametophyte with the egg cell (female gamete)

Sexual Reproduction in Plants:

Step 1: Development of Pollen Grains (Microsporogenesis):

  • Pollen grains develop inside the anther from pollen mother cells by meiosis
  • Each pollen grain contains two cells: the vegetative cell (tube cell) and the generative cell
  • The generative cell later divides to produce two male gametes

Step 2: Development of Egg Cell (Megasporogenesis):

  • Inside the ovule, a megaspore mother cell divides by meiosis → one functional megaspore
  • The megaspore undergoes three mitotic divisions → 8-nucleate female gametophyte (embryo sac)
  • The embryo sac contains: 1 egg cell, 2 synergids, 3 antipodal cells, and 2 polar nuclei

Step 3: Pollination: Pollination is the transfer of pollen grains from the anther to the stigma of a flower.

Types of pollination:

  • Self-pollination (Autogamy): Pollen is transferred to the stigma of the same flower or another flower on the same plant. e.g., Wheat, rice, pea.
  • Advantages: Does not depend on external agents; ensures reproduction even when pollinating agents are absent
  • Disadvantage: No genetic variation
  • Cross-pollination (Allogamy): Pollen is transferred to the stigma of a flower on a different plant of the same species. e.g., Maize, sunflower.
  • Advantages: Genetic variation, healthier offspring (hybrid vigour)
  • Disadvantage: Dependent on external agents; less reliable

Agents of pollination:

  • Wind (Anemophily): Pollen is light, dry, smooth, produced in large quantities. e.g., Grasses, wheat, maize. Flowers are inconspicuous.
  • Insects (Entomophily): Flowers are brightly coloured, fragrant, with nectar. Pollen is sticky and has sculptured surface. e.g., Hibiscus, rose, Salvia.
  • Water (Hydrophily): e.g., Vallisneria, Hydrilla.
  • Birds (Ornithophily): e.g., Bignonia, Salvia.

Step 4: Germination of Pollen Grain:

  • Pollen grain germinates on the compatible stigma
  • Pollen tube grows down through the style → enters the ovule through the micropyle
  • The generative cell divides to produce two male gametes (inside the pollen tube)

Step 5: Double Fertilisation (unique to angiosperms):

  • First male gamete + egg cell → Zygote (2n) [syngamy] → develops into the embryo
  • Second male gamete + two polar nuclei → Primary Endosperm Nucleus (PEN) (3n) [triple fusion] → develops into the endosperm (food reserve for the seed)
  • This simultaneous occurrence of syngamy and triple fusion is called double fertilisation (discovered by Nawaschin, 1898)

Step 6: Post-Fertilisation Changes:

  • Zygote → divides mitotically → Embryo (inside the seed)
  • Ovule → matures into a Seed
  • Ovary → matures into a Fruit
  • Petals, stamens, sepals, style, stigma → usually wither and fall
Question 3: Describe the human male and female reproductive systems.

Answer:

Male Reproductive System:

The male reproductive system produces male gametes (sperms) and delivers them to the female reproductive tract.

Primary Sex Organs:

Testes (Gonads):

  • Two oval-shaped organs located outside the abdominal cavity in the scrotal sac (scrotum)
  • Temperature in scrotum is 2–3°C lower than body temperature — essential for normal sperm production (spermatogenesis fails at body temperature)
  • Each testis contains seminiferous tubules (250–300 metres of tightly coiled tubes) where sperm are produced
  • Sertoli cells (nurse cells) in the tubules support developing sperm
  • Interstitial cells of Leydig (between tubules) produce testosterone (male sex hormone)

Accessory Sex Organs and Ducts:

  • Epididymis: Coiled tube on the back of each testis where sperm mature and are stored
  • Vas Deferens (Ductus Deferens): Muscular tube carrying sperm from epididymis to the urethra
  • Seminal Vesicles (2): Secrete alkaline fluid rich in fructose (energy for sperm), prostaglandins, and proteins → forms 60% of semen volume
  • Prostate Gland (1): Secretes slightly acidic fluid with enzymes, zinc, and citric acid → forms 30% of semen volume; activates sperm
  • Bulbourethral Glands (Cowper's glands, 2): Secrete lubricating mucus → neutralises urine acidity in urethra before ejaculation
  • Urethra: Carries both urine and semen (not simultaneously) to the outside through the penis
  • Penis: Male copulatory organ; contains erectile tissue (corpora cavernosa) that fills with blood during erection

Semen: Mixture of sperm (from testes) + secretions from seminal vesicles + prostate + bulbourethral glands; slightly alkaline (pH 7.2–7.8); volume 2–5 mL per ejaculation; contains 200–500 million sperm.

Female Reproductive System:

Primary Sex Organs:

Ovaries (Gonads):

  • Two almond-shaped organs in the lower abdomen (pelvic cavity), on each side of the uterus
  • Produce female gametes (eggs/ova) — process called oogenesis
  • Produce female sex hormones: oestrogen and progesterone
  • Each ovary contains hundreds of thousands of follicles; each follicle contains a developing egg

Accessory Sex Organs:

Fallopian Tubes (Oviducts):

  • Two muscular tubes (10–12 cm long) connecting the ovaries to the uterus
  • Finger-like projections called fimbriae at the ovarian end sweep the released egg into the tube
  • Lined with ciliated epithelium and smooth muscle → move the egg toward the uterus
  • Site of fertilisation (in the ampulla region, the widest part of the tube)

Uterus (Womb):

  • A pear-shaped, thick-walled muscular organ in the pelvic cavity
  • Size: about 7.5 cm long, 5 cm wide (in non-pregnant woman)
  • Three layers:
  • Perimetrium (outer serous layer)
  • Myometrium (middle thick smooth muscle layer) — contracts during labour
  • Endometrium (inner mucous layer) — where the fertilised egg implants; shed during menstruation if no pregnancy
  • Divided into: fundus (top), body (middle), cervix (lower narrow part) opening into the vagina

Vagina:

  • Muscular canal connecting the uterus to the external environment
  • Receives penis during intercourse; acts as birth canal during delivery
  • pH is acidic (3.8–4.5) due to lactic acid bacteria — prevents infection

External Genitalia (Vulva): Mons pubis, labia majora, labia minora, clitoris, and vestibular glands (Bartholin's glands).

Question 4: Explain vegetative propagation in plants with suitable examples and its significance.

Answer:

Vegetative propagation is a form of asexual reproduction in plants in which new plants are produced from vegetative parts (root, stem, or leaf) of the parent plant, without involving seeds or spores.

Natural Methods of Vegetative Propagation:

1. By Roots:
Answer
  • Adventitious buds form on roots and develop into new plants
  • e.g., Sweet potato: the tuberous roots have buds that develop into new plants
  • e.g., Dahlia, Asparagus: tuberous roots
  • e.g., Rajnigandha: tuberous roots used for propagation
2. By Stems:
Answer
  • Rhizomes (Underground horizontal stems with nodes): e.g., Ginger, Turmeric, Banana, Ferns. Each node can produce new leaves and roots.
  • Tubers (Swollen underground stems with eyes/buds): e.g., Potato. Each "eye" is a node with an axillary bud. When planted, buds sprout into new plants.
  • Bulbs (Short underground stems with fleshy leaf bases): e.g., Onion, Garlic, Lily. The bulb contains stored food; the central bud grows into a new plant.
  • Corms (Solid underground stems): e.g., Colocasia (taro), Crocus, Gladiolus.
  • Stolons (Runners — horizontal above-ground stems): e.g., Strawberry, Mint, Lawn grass. The stolon grows along the soil surface, and nodes produce roots and shoots at intervals.
  • Bulbils (Small bulb-like structures on aerial parts): e.g., Agave, Oxalis. Develop in leaf axils or inflorescences and fall off to form new plants.
3. By Leaves:
Answer
  • Some plants can produce new plants from their leaves
  • e.g., Bryophyllum (Patharchatta): adventitious buds develop in the notches (sinuses) along the leaf margin; these fall and grow into new plants
  • e.g., Begonia: leaf cuttings planted in moist soil develop roots and shoots
  • e.g., Kalanchoe: leaf margins produce plantlets

Artificial Methods of Vegetative Propagation:

1. Cuttings:
Answer
  • A piece of stem, leaf, or root is cut and planted in moist soil
  • Stem cuttings: Rose, Hibiscus, Sugarcane, Bougainvillea
  • Root cuttings: Tamarind, Breadfruit
  • Leaf cuttings: Begonia, Sanseveria
2. Layering:
Answer
  • A branch is induced to form roots while still attached to the parent plant, then detached
  • Ground Layering: A low-growing branch is bent to the ground, covered with soil, and rooted before being cut; e.g., Jasmine
  • Air Layering (Gooty / Marcottage): A ring of bark is removed from a branch; the wound is covered with moist sphagnum moss and polythene; roots develop; the rooted branch is then cut; e.g., Mango, Litchi, Rose
3. Grafting:
Answer
  • The shoot system of one plant (scion — desired variety) is joined to the root system of another (rootstock — hardy variety)
  • Cambium of both parts must be in contact for the graft to succeed
  • Used in: Mango, Apple, Guava
  • Advantages: Combines the best characteristics of two plants; produces early-bearing plants; maintains the exact genetic characteristics of the scion variety
4. Tissue Culture (Micropropagation):
Answer
  • A small piece of plant tissue (explant) is grown in a sterile nutrient medium
  • Produces callus → regenerates into a complete plant
  • Produces thousands of identical plants in a short time
  • Used for orchids, banana, potato, and many ornamental plants

Significance of Vegetative Propagation:

1. Maintains genetic purity: All offspring are clones of the parent — useful for preserving superior varieties (e.g., seedless grapes, specific mango varieties like Alphonso) 2. Faster production: Plants flower and fruit earlier compared to seed-grown plants 3. Propagation of seedless plants: e.g., Banana, Grapes, Pineapple (which rarely produce viable seeds) 4. Ensures uniform crop: All plants have identical traits — important for commercial agriculture 5. Easy and economical: Most methods are simple and inexpensive 6. Year-round production: Not dependent on the flowering season

Disadvantages:

  • No genetic variation — all clones are equally susceptible to the same diseases
  • Vegetatively propagated plants may carry pathogens from parent
  • Overcrowding may occur if natural vegetative propagation is too prolific

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Frequently Asked Questions

Types of asexual reproduction include: Binary fission (Amoeba), Budding (Hydra, Yeast), Fragmentation (Spirogyra), Sporulation/Spore formation (Rhizopus/Bread mould), Regeneration (Planaria, Starfish), and Vegetative propagation in plants.