Q.How does zona pellucida of ovum help in preventing polyspermy?

Showing the 12 most recent of 20 on this concept.

1. KCET 2026Set UNKNOWN1 markMCQ
   Q.Identify the correct path of milk secretion by the mammary glands. (A) Alveoli -> mammary duct -> ampulla -> mammary tubule -> lactiferous ducts (B) Alveoli -> mammary tubules -> mammary duct -> ampulla -> lactiferous ducts (C) Alveoli -> ampulla -> mammary duct -> mammary tubules -> lactiferous ducts (D) Alveoli -> lactiferous ducts -> mammary duct -> ampulla -> mammary tubule

   ›Reveal solutionSolution

   Milk formed in the alveoli of the mammary gland travels through a graded system of ducts — mammary tubules, mammary duct, ampulla, and finally lactiferous ducts — before reaching the nipple.

   Step 1 — Where milk is formed

   Milk is synthesised and secreted by the secretory alveoli — clusters of milk-producing cells within each lobule of the mammary gland.

   Step 2 — The path milk follows to the nipple …

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2. KCET 2026Set UNKNOWN1 markMCQ
   Q.Which of the following does NOT produce seminal plasma? (A) Epididymis (B) Bulbourethral glands (C) Seminal vesicles (D) Prostate gland

   ›Reveal solutionSolution

   Seminal plasma is formed by the secretions of the accessory sex glands that add fluid to sperm on their way out; the epididymis is a storage/maturation duct, not a secretory gland contributing to seminal plasma.

   Step 1 — Trace the path of sperm after formation

   Sperm produced in the seminiferous tubules pass through the vasa efferentia into the epididymis, where they are stored and undergo maturation, and from there through the vas deferens toward the urethra.

   Step 2 — Identify the glands that secrete seminal plasma …

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3. KCET 2025Set C-41 markMCQ
   Q.Match the hormone with its site of production:

   Column-I (Hormone)	Column-II (Site of production)
   a. hCG and hPL	i. Ovary
   b. Progesterone	ii. Placenta
   c. Androgens	iii. Corpus luteum
   d. Relaxin	iv. Leydig cells

   (A) a-iii, b-i, c-iv, d-ii (B) a-iv, b-i, c-ii, d-iii (C) a-i, b-ii, c-iv, d-iii (D) a-ii, b-iii, c-iv, d-i

   ›Reveal solutionSolution

   Place each hormone with its gland — hCG/hPL→placenta, progesterone→corpus luteum, androgens→Leydig cells, relaxin→ovary — giving a-ii, b-iii, c-iv, d-i.

   Step 1 — a. hCG and hPL → Placenta (ii)

   Once the blastocyst implants, the placenta forms and acts as an endocrine tissue. It secretes human chorionic gonadotropin (hCG), human placental lactogen (hPL), oestrogens and progestogens. hCG and hPL are produced only during pregnancy, and their source is the placenta. ⇒ a – ii

   Step 2 — b. Progesterone → Corpus luteum (iii)

   After ovulation, the ruptured Graafian follicle becomes the corpus luteum, whose defining secretion is progesterone. This progesterone maintains the endometrium and is essential for the maintenance of pregnancy. ⇒ b – iii

   Step 3 — c. Androgens → Leydig cells (iv)

   In the testis, the Leydig (interstitial) cells lie outside the seminiferous tubules and synthesise androgens (chiefly testosterone) under the influence of LH. (Contrast: Sertoli cells secrete inhibin and nourish the germ cells.) ⇒ c – iv …

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4. KCET 2025Set C-41 markMCQ
   Q.Which of the following are the techniques for detection of cancer of internal organs?

   (a) Radiography, MRI

   (b) MRI, computed tomography

   (c) Widal test, radiography

   (d) MRI, widal test (A) a and c (B) b and c (C) b and d (D) a and b

   ›Reveal solutionSolution

   Cancer of internal organs is picked up by imaging — radiography, CT and MRI; the Widal test detects typhoid, so any option containing it is eliminated.

   Step 1 — What NCERT lists as cancer-detection techniques.

   Detection of cancer of internal organs relies on:

   • Radiography (X-rays) — shows dense/abnormal masses.
   • Computed Tomography (CT) — X-rays plus computer processing to build a 3-D internal image.
   • Magnetic Resonance Imaging (MRI) — strong magnetic fields + non-ionising radiation, giving very accurate soft-tissue detail. (Blood/tissue biopsy, histopathology and monoclonal-antibody/molecular tests are the other class of methods, but the imaging trio above is what the question is after.)

   Step 2 — Identify the odd technique.

   The Widal test is an agglutination test for antibodies against Salmonella typhi — it diagnoses typhoid fever. It is not a cancer-detection method.

   Step 3 — Evaluate each statement. …

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5. KCET 2024Set B-41 markMCQ
   Q.Select the correct statement from the following : (A) Methanobacterium is an aerobic bacteria found in the rumen of cattle (B) Biogas is produced by the activity of aerobic bacteria (C) Biogas is pure methane (D) Activated sludge in sediment tanks is a rich source of aerobic bacteria

   ›Reveal solutionSolution

   Three statements misuse the word aerobic/pure; only the description of activated sludge as a rich source of aerobic bacteria is true.

   Step 1 — Evaluate (A): "Methanobacterium is an aerobic bacteria found in the rumen of cattle."

   Methanobacterium is an anaerobic methanogen. It is indeed found in the rumen of cattle (where it helps break down cellulose, which is why cattle dung is so rich in these microbes and is used as the raw material for gobar gas plants) — but it is emphatically not aerobic. Methanogenesis is destroyed by oxygen. False on the pivotal word. ✗

   Step 2 — Evaluate (B): "Biogas is produced by the activity of aerobic bacteria."

   Biogas is produced by methanogens acting anaerobically — they grow in the anaerobic sludge and in the oxygen-free biogas plant, producing $\mathrm{CH_4}$ from the substrates ($\mathrm{CO_2}$, $\mathrm{H_2}$ and the products of bacterial cellulose breakdown). False. ✗

   Step 3 — Evaluate (C): "Biogas is pure methane."

   Biogas is a mixture of gases — predominantly methane ($\mathrm{CH_4}$), along with carbon dioxide ($\mathrm{CO_2}$) and hydrogen sulphide ($\mathrm{H_2S}$). It is combustible because of its methane content, but it is not pure methane. False. ✗

   Step 4 — Evaluate (D): activated sludge.

   Trace the secondary (biological) treatment of sewage:

   1. Primary effluent is passed into large aeration tanks and constantly agitated mechanically while air is pumped in.
   2. This allows vigorous growth of useful aerobic microbes into flocs — masses of bacteria associated with fungal filaments forming mesh-like structures. …

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6. KCET 2023Set B-41 markMCQ
   Q.With respect to Inbreeding, which among the following is not true? (A) It helps to evolve a pure line in an animal. (B) Inbreeding decreases homozygosity. (C) It helps in accumulation of superior genes. (D) It helps in elimination of less desirable genes.

   ›Reveal solutionSolution

   Inbreeding increases homozygosity (that is its whole purpose — to fix a pure line), so the statement that it decreases homozygosity is the untrue one.

   Step 1 — Define inbreeding

   Inbreeding = mating of more closely related individuals within the same breed for 4–6 generations. Superior males and superior females of the same breed are identified and mated in pairs; the superior progeny are used for further breeding.

   Step 2 — Its genetic consequence

   Related parents share alleles by descent. When they mate, an offspring has a raised chance of receiving the same allele from both parents:

   $\text{Inbreeding} \;\Rightarrow\; \text{homozygosity} \uparrow \;,\qquad \text{heterozygosity} \downarrow$

   This is exactly why inbreeding is used: it is necessary if one wants to evolve a pure line in any animal. Continued inbreeding increases homozygosity.

   Step 3 — Test each statement

   Option	Statement	True?
   (A)	It helps to evolve a pure line in an animal	TRUE — pure lines require homozygosity, which inbreeding delivers.
   (B)	Inbreeding decreases homozygosity	FALSE — it increases homozygosity. ⟵ the answer
   (C)	It helps in accumulation of superior genes	TRUE — by exposing and fixing desirable alleles in homozygous form.

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7. KCET 2023Set B-41 markMCQ
   Q.In the female reproductive system, a tiny finger like structure which lies at the upper junction of the two labia minora above the urethral opening is called (A) Vagina (B) Hymen (C) Mons pubis (D) Clitoris

   ›Reveal solutionSolution

   "Tiny finger-like structure at the upper junction of the labia minora, above the urethral opening" is the standard definition of the clitoris.

   1. Lay out the external genitalia (vulva) from outside in

   The female external genitalia consist of:

   • Mons pubis — a cushion of fatty tissue covered by skin and pubic hair, lying over the pubic symphysis.
   • Labia majora — fleshy folds of tissue extending down and back from the mons pubis, enclosing the vaginal opening.
   • Labia minora — a pair of membranous folds lying under (inside) the labia majora.
   • Clitoris — a tiny finger-like structure lying at the upper junction of the two labia minora, above the urethral opening. It is the homologue of the penis and is richly supplied with sensory nerve endings.
   • Hymen — a membrane that partially covers the opening of the vagina.

   2. Match the description

   The question gives three positional clues, and all three converge on one structure:

   1. "tiny finger-like structure" → the clitoris' characteristic shape;
   2. "at the upper junction of the two labia minora" → the clitoris sits exactly where the two labia minora meet anteriorly;
   3. "above the urethral opening" → the clitoris is anterior/superior to the urethral orifice.

   So the structure is the clitoris. …

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8. KCET 2023Set B-41 markMCQ
   Q.Consider the following statements with reference to female reproduction system : Statement 1. The presence or absence of hymen is not a reliable indicator of virginity or sexual experience. Statement 2. The sex of the foetus is determined by the father and not by the mother. Choose the correct option from the following : (A) Both the Statement 1 and Statement 2 are wrong. (B) Statement 1 is correct and Statement 2 is wrong. (C) Both the Statement 1 and Statement 2 are correct. (D) Statement 1 is wrong and Statement 2 is correct.

   ›Reveal solutionSolution

   Both statements are biologically accurate: the hymen can be absent for non-sexual reasons, and sex determination depends on whether the sperm carries an X or a Y chromosome. Therefore, both statements are correct.

   The question tests two distinct biological facts — one about a common misconception regarding the hymen, and the other about the genetic basis of sex determination. Let’s examine each statement separately.

   1. Statement 1: The presence or absence of hymen is not a reliable indicator of virginity or sexual experience.

      The hymen is a thin membrane that partially covers the vaginal opening. It can be torn or stretched by many non-sexual activities — vigorous exercise, tampon use, medical examinations, or even normal physical growth. Some girls are born without a visible hymen. Conversely, the hymen can remain intact even after sexual intercourse. Therefore, using its presence or absence as a marker of virginity has no scientific basis. This statement is correct.

   2. Statement 2: The sex of the foetus is determined by the father and not by the mother. …

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9. KCET 2022Set A-11 markMCQ
   Q.Stalk of the Stamen is : (A) Petiole (B) Filament (C) Peduncle (D) Pedicel

   ›Reveal solutionSolution

   A stamen = anther + filament; the filament is the stalk, so the answer is (B).

   Step 1 — The concept: parts of a stamen.

   The stamen is the male reproductive organ (microsporophyll) of a flower. It consists of exactly two parts:

   • the anther — the terminal, usually bilobed head containing the pollen sacs (microsporangia) where pollen grains are produced;
   • the filament — the long, slender stalk that attaches the anther to the thalamus or to the petal.

   So, by definition, the stalk of the stamen is the filament.

   Step 2 — Why each distractor is wrong. This question is really testing whether you can keep the flower's several "stalks" apart:

   Term	What it is actually the stalk of
   Petiole	the stalk of a leaf (attaching the lamina to the stem)
   Filament	the stalk of a stamen ✓
   Peduncle	the stalk of an inflorescence (the whole flower cluster)

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10. KCET 2022Set A-11 markMCQ
    Q.The testis are situated outside the abdominal cavity in scrotum as it helps to (A) Maintain the low temperature (B) Store sperm (C) Regulates harmone secretion (D) Release sperm

    ›Reveal solutionSolution

    Spermatogenesis is temperature-sensitive; the scrotum is an external pouch that keeps the testes cooler than the body core.

    Step 1 — What the scrotum is. The scrotum is a sac of skin and muscle suspended outside the abdominal cavity, connected to the abdomen by the inguinal canal. The testes descend into it before or shortly after birth.

    Step 2 — Why the position matters. Normal core body temperature (about $37^\circ\text{C}$) is too high for spermatogenesis. The germinal epithelium of the seminiferous tubules needs a temperature roughly $2\text{-}2.5^\circ\text{C}$ lower than the core. The scrotal position, aided by the dartos and cremaster muscles (which raise or lower the testes with ambient temperature) and by the counter-current pampiniform plexus, maintains this cooler environment.

    Step 3 — Eliminating the other options.

    • (B) Store sperm — sperm are stored mainly in the epididymis (cauda epididymis), not because the testis is outside. …

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11. KCET 2022Set A-11 markMCQ
    Q.Identify the odd one from the following : (A) Infundibulum (B) Fimbriae (C) Isthmus (D) Labia minora

    ›Reveal solutionSolution

    Three options are regions of the oviduct; the labia minora belong to the external genitalia — that is the odd one out.

    Step 1 — Find the common category. Trace the human female oviduct (fallopian tube) from the ovary to the uterus:

    1. Infundibulum — the funnel-shaped part closest to the ovary.
    2. Fimbriae — the finger-like projections on the edge of the infundibulum that help collect the ovum after ovulation.
    3. Ampulla — the wider middle part (site of fertilisation).
    4. Isthmus — the last, narrow part that opens into the uterus.

    So (A), (B) and (C) are all parts of the fallopian tube. …

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12. KCET 2022Set A-11 markMCQ
    Q.Cell theory was formulated by (A) Schleiden and Robert Brown (B) Schleiden and Schwann (C) Schwann and Robert Brown (D) Robert Hook and Robert Brown

    ›Reveal solutionSolution

    Cell theory = Schleiden (plants, 1838) + Schwann (animals, 1839); Virchow later added that cells arise from pre-existing cells.

    Step 1 — Separate discovery from theory.

    Several names cluster around early cell biology, and the question turns on knowing who did what:

    • Robert Hooke (1665) — first saw and named "cells" while examining a slice of cork under his microscope. He observed dead cell walls, not living cells.
    • Anton von Leeuwenhoek (1674) — first saw living cells.
    • Robert Brown (1831) — discovered the nucleus.
    • Matthias Schleiden (1838) — a German botanist; after studying many plants, concluded that all plants are composed of cells.
    • Theodore Schwann (1839) — a British zoologist; studied animal cells, reported that cells have a thin outer layer (today's plasma membrane), that plant cells additionally have a cell wall, and hypothesised that the bodies of animals and plants are composed of cells and products of cells.

    Step 2 — The formulation.

    Together, the Schleiden–Schwann statements form the cell theory:

    1. All living organisms are composed of cells.
    2. The cell is the basic structural and functional unit of life.

    Step 3 — The later amendment. …

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