Solved Examples (Dedicated Problem Set)

Chapter-Wide Solved Examples — Test Your Mastery

This dedicated problem set spans every theme of the chapter. The 12 problems below are deliberately chosen to be multi-step, cross-section, and trap-aware — designed to catch the kind of mistakes that lose NEET marks.

For each problem:

1. Read carefully — every problem includes a small detail that can trip you up.
2. Solve before reading the solution — pencil and paper out, please.
3. Read the solution and note the reasoning — solutions include both the answer and the underlying logic.
4. Note the [Board] / [NEET] tag — to know exam relevance.

These problems are arranged from easier to harder. By the end, you should be able to walk into any Board or NEET paper on this chapter and feel like the questions are old friends.

Problem 1 — Ploidy across the chapter

State the ploidy of each of the following: (a) PMC, (b) microspore, (c) pollen grain's vegetative cell, (d) MMC, (e) functional megaspore, (f) egg cell, (g) zygote, (h) PEN, (i) endosperm, (j) seed coat.

Solution:

Cell/Structure	Ploidy	Reasoning
(a) PMC	$2n$	Sporophytic, pre-meiotic
(b) Microspore	$n$	Post-meiotic
(c) Vegetative cell	$n$	From haploid microspore by mitosis
(d) MMC	$2n$	Sporophytic, pre-meiotic
(e) Functional megaspore	$n$	Post-meiotic
(f) Egg cell	$n$	Mitotic descendant of haploid megaspore
(g) Zygote	$2n$	Egg ($n$) + male gamete ($n$)
(h) PEN	$3n$	2 polar nuclei + 1 male gamete = $n+n+n$
(i) Endosperm	$3n$	From PEN
(j) Seed coat	$2n$	From integuments (sporophytic)

Master rule: Anything pre-meiotic or sporophytic = $2n$. Anything inside the embryo sac (before fertilisation) = $n$. Anything that includes a male gamete contribution = $2n$ (embryo) or $3n$ (endosperm).

Answer: $2n, n, n, 2n, n, n, 2n, 3n, 3n, 2n$.

[NEET Important] Ploidy MCQs are guaranteed every NEET. Drill until you can answer in under 5 seconds per cell.

Problem 2 — Microsporogenesis numbers

If an anther of a flower has 50 PMCs per microsporangium and the anther is bilobed and dithecous, calculate (a) the total number of microsporangia per anther, (b) the total number of PMCs per anther, (c) the total number of pollen grains produced per anther.

Solution:

We apply the structure of an anther:

• Bilobed = 2 lobes per anther.
• Dithecous = 2 theca per lobe.
• Tetrasporangiate = 1 microsporangium per theca → 4 microsporangia per anther.

NCERT states "bilobed, dithecous, tetrasporangiate" — meaning bilobed AND dithecous AND tetrasporangiate. So:

(a) Microsporangia per anther: Bilobed → 2 lobes. Each lobe has 2 microsporangia (dithecous). So 2 × 2 = 4 microsporangia per anther.

(b) PMCs per anther: 4 microsporangia × 50 PMCs each = 200 PMCs per anther.

(c) Pollen grains per anther: Each PMC → 4 pollen grains (by meiosis). So 200 PMCs × 4 = 800 pollen grains per anther.

The mistake to avoid: Not confusing "bilobed" (= 2 lobes) with "dithecous" (= 2 theca per lobe). These are TWO separate counts.

Answer: (a) 4 microsporangia, (b) 200 PMCs, (c) 800 pollen grains.

[NEET Important] Multi-step numerical problems on the anther structure appear regularly — drill this calculation.

Problem 3 — Embryo sac cell tracking

Mark each of the following as TRUE or FALSE:

(a) The egg cell is at the chalazal end of the embryo sac. (b) The 3 antipodals are at the micropylar end. (c) The central cell has 2 polar nuclei. (d) The mature embryo sac is 7-celled, 7-nucleate. (e) The pollen tube enters the egg cell directly.

Solution:

(a) FALSE — the egg cell is at the MICROPYLAR end (in the egg apparatus). Chalazal end has the antipodals.

(b) FALSE — antipodals are at the CHALAZAL end. Micropylar end has the egg apparatus (1 egg + 2 synergids).

(c) TRUE — the central cell uniquely contains 2 polar nuclei.

(d) FALSE — mature embryo sac is 7-celled, 8-NUCLEATE (the extra nucleus is the second polar nucleus in the central cell).

(e) FALSE — the pollen tube enters one of the 2 SYNERGIDS via the filiform apparatus, NOT the egg cell directly. The synergid degenerates and releases the 2 male gametes.

Common confusion: Students mix up the micropylar and chalazal ends. Memorise: "MICRO → MEN (egg apparatus, near micropyle); ANTI → ANTI (antipodals at the opposite/chalazal end)." Cheesy but memorable.

Answer: (a) F, (b) F, (c) T, (d) F, (e) F.

[Board Important] Embryo sac trivia is heavily tested. Drill these 5 facts.

Problem 4 — Double fertilisation products

A flower has 4 ovules. Each ovule undergoes successful double fertilisation. State the total numbers of: (a) zygotes formed, (b) PENs formed, (c) male gametes used.

Solution:

Per ovule:

• 1 egg + 1 male gamete → 1 zygote ($2n$).
• 2 polar nuclei + 1 male gamete → 1 PEN ($3n$).
• Total male gametes used per ovule = 2.

For 4 ovules:

(a) Zygotes: 4 ovules × 1 zygote each = 4 zygotes.

(b) PENs: 4 ovules × 1 PEN each = 4 PENs.

(c) Male gametes: 4 ovules × 2 male gametes each = 8 male gametes used.

The trap: Students sometimes forget that EACH ovule needs 2 male gametes (one for syngamy + one for triple fusion). 4 ovules → 4×2 = 8 male gametes, NOT 4.

How many pollen grains? Since each pollen grain delivers 2 male gametes, you need at least 4 pollen grains to fertilise 4 ovules (one pollen grain per ovule). In reality, many more pollen grains land on the stigma — but only 4 successful pollen tubes are needed.

Answer: (a) 4 zygotes, (b) 4 PENs, (c) 8 male gametes used.

[NEET Important] Double-fertilisation arithmetic appears in NEET every year. Master this.

Problem 5 — Identifying mystery cells from ploidy

A botany student isolates 4 tissues from a developing seed. The chromosome counts per cell are: (a) 30, (b) 20, (c) 10, (d) 30. The base haploid number ($n$) for this species is 10. Identify each tissue.

Solution:

Given $n = 10$, so $2n = 20$ and $3n = 30$.

Sample	Chromosomes	Ploidy	Possible tissue
(a) 30	$3n$	Endosperm or PEN-derived tissue
(b) 20	$2n$	Embryo, seed coat, nucellus, perisperm, or pericarp
(c) 10	$n$	Egg cell, synergid, antipodal (if before fertilisation, embryo sac cells)
(d) 30	$3n$	Same as (a) — endosperm

Reasoning:

• (a) = (d) = $3n$ → ENDOSPERM (the only $3n$ tissue in a seed). Two samples from the same tissue.
• (b) = $2n$ → EMBRYO (or any sporophytic tissue — seed coat, nucellus). Most likely the embryo, since we're inside a developing seed.
• (c) = $n$ → A leftover EMBRYO SAC CELL — could be a degenerating synergid or antipodal. Could also be a male gamete from an attached pollen tube.

Answer: (a) and (d) are both endosperm ($3n$). (b) is the embryo (or sporophytic seed tissue, $2n$). (c) is a leftover haploid embryo sac cell (synergid, antipodal, or similar).

[NEET Important] Ploidy detective work appears as application-style NEET MCQs. Practice the master ploidy table until you can match cells to ploidies in seconds.

Problem 6 — Outbreeding device match

Match each outbreeding device with its example:

(a) Dichogamy → ? (b) Herkogamy → ? (c) Self-incompatibility → ? (d) Monoecy → ? (e) Dioecy → ?

Pool of examples: Sunflower (protandry), Hibiscus (some species), Many crops (S-allele system), Maize, Papaya, Castor.

Solution:

Device	Mechanism	Example
(a) Dichogamy	Temporal mismatch (protandry/protogyny)	Sunflower (protandry)
(b) Herkogamy	Spatial mismatch	Hibiscus (some configurations)
(c) Self-incompatibility	Genetic block on pollen tube growth	Many crops (e.g., Brassica species, with the S-allele system)
(d) Monoecy	Unisexual flowers, SAME plant	Maize (and castor)
(e) Dioecy	Unisexual flowers, SEPARATE plants	Papaya

Quick mnemonic for the 5 devices:

• "D-H-S-M-D" = Dichogamy, Herkogamy, Self-incompatibility, Monoecy, Dioecy.

Why these distinct examples matter:

NCERT names examples only for unisexuality (maize/castor, papaya); the others below are beyond-NCERT illustrations:

• Cotton (protandry) — clearest natural example of temporal separation.
• Maize — clearest natural example of monoecy (separate sex flowers, one plant).
• Papaya — clearest natural example of dioecy.

Memorise these pairings — they appear together in NEET MCQs.

Answer: (a) Cotton, (b) Hibiscus, (c) Many crops (S-allele system), (d) Maize/Castor, (e) Papaya.

[Board Important] Match-the-column on outbreeding is a recurring CBSE pattern.

Problem 7 — Tracing the pollen tube

A pollen grain lands on the stigma of a compatible flower. Trace the path of the pollen tube and identify which cells it passes through or encounters at each stage. End with the events of fertilisation.

Solution:

We trace the journey step by step.

Step 1 — Pollen germination on stigma:

Pollen grain (n) absorbs water → intine emerges through germ pore → forms the pollen tube → vegetative nucleus moves to tube tip; generative cell (or 2 male gametes) trails behind.

Step 2 — Growth through style:

Pollen tube grows downward through the stylar transmitting tissue, guided by chemoattractants secreted by the style.

Step 3 — Entry into ovary:

Pollen tube enters the ovary cavity and travels along the placenta.

Step 4 — Approach to ovule:

Pollen tube travels along the funicle to reach the ovule.

Step 5 — Entry into ovule (porogamy):

Pollen tube enters the ovule via the MICROPYLE — this is porogamy (the most common mode in the vast majority of angiosperms).

Step 6 — Entry into embryo sac:

Pollen tube enters one of the 2 synergids via the FILIFORM APPARATUS at its micropylar tip.

Step 7 — Release of male gametes:

The synergid degenerates. 2 male gametes are released into the embryo sac cytoplasm.

Step 8 — Double fertilisation:

• Male gamete 1 + egg cell → zygote ($2n$) [SYNGAMY].
• Male gamete 2 + 2 polar nuclei → PEN ($3n$) [TRIPLE FUSION].

Both events happen SIMULTANEOUSLY.

Master flow:

$$\text{Stigma} \to \text{Style} \to \text{Placenta} \to \text{Funicle} \to \text{Micropyle} \to \text{Synergid (via filiform apparatus)} \to \text{Egg + Central cell (double fertilisation)}$$

Answer: Pollen tube path follows: Stigma → Style → Ovary (via placenta) → Funicle → Micropyle → Synergid (via filiform apparatus) → Release of 2 male gametes → Syngamy with egg + Triple fusion with polar nuclei.

[Board Important] A classic 5-mark CBSE question. Memorise the entire path word-for-word.

Problem 8 — True vs false fruits identification

Classify each of the following as TRUE FRUIT or FALSE FRUIT, and identify the source of the fleshy edible part:

(a) Mango (b) Apple (c) Tomato (d) Strawberry (e) Cashew

Solution:

Fruit	Type	Source of fleshy edible part
(a) Mango	TRUE fruit	Mesocarp (middle layer of pericarp), from the ovary wall
(b) Apple	FALSE fruit	Thalamus (NOT the ovary) — the core with seeds IS the true ovary-derived part
(c) Tomato	TRUE fruit	Pericarp (entire ovary wall becomes fleshy)
(d) Strawberry	FALSE fruit	Thalamus (the red fleshy berry-like part); tiny black "seeds" on surface are individual true fruits
(e) Cashew	FALSE fruit	Thalamus (the cashew "apple"); the kidney-shaped nut is the true fruit

The pattern:

• True fruits develop from the ovary only. Examples: mango, tomato, orange, grape, banana, papaya.
• False fruits have a major fleshy contribution from the THALAMUS. Three NCERT examples to memorise: apple, strawberry, cashew.

Cross-check via NCERT-canonical phrase:

"In some species such as apple, strawberry, cashew, etc., the thalamus also contributes to fruit formation. Such fruits are called false fruits."

Memorise this triplet — apple, strawberry, cashew — for instant NEET recognition.

Answer: True fruits: mango, tomato. False fruits: apple, strawberry, cashew.

[NEET Important] "Which of these is a false fruit?" — recurring NEET MCQ pattern.

Problem 9 — A Parthenium NEET trap

What is Parthenium hysterophorus commonly called, where did it come from to India, and what is the medical issue it causes? Include any specific MCQ traps to watch for.

Solution:

Common name: Parthenium hysterophorus = carrot grass (also called congress grass).

Origin and entry into India: Parthenium is NOT native to India. It entered India in the mid-20th century as a contaminant with imported wheat shipments. Once established, it spread rapidly across India.

Medical issues caused:

The plant's pollen is a major allergen. Effects include:

• Asthma (severe respiratory disorder).
• Allergic bronchitis (inflammation of bronchial tubes).
• Allergic rhinitis / hay fever (sneezing, runny nose).
• Contact dermatitis (skin rash from touching the plant — sesquiterpene lactones in the plant tissue cause this).

NCERT-canonical phrase: "Pollen grains of Parthenium or carrot grass that came into India as a contaminant with imported wheat, has become ubiquitous in our surroundings and cause pollen allergy."

NEET trap to watch for:

• Parthenium is a CONTAMINANT origin (NOT a deliberate introduction). NEET sometimes asks "How did Parthenium enter India?" — the correct answer is "contaminant with imported wheat" not "deliberate import for medicinal use" or "ornamental import."
• The Latin name has TWO parts: Parthenium (genus) + hysterophorus (species). Both can be tested.

Answer: Parthenium hysterophorus = carrot grass / congress grass, entered India as a wheat contaminant, causes asthma, bronchitis, hay fever, dermatitis — pollen allergy.

[NEET Important] This is one of the highest-frequency NEET MCQ topics in the entire chapter. Memorise the Latin name + origin story + medical effects.

Problem 10 — Endosperm vs Perisperm comparison

Differentiate between endosperm and perisperm with respect to (a) origin, (b) ploidy, (c) typical examples.

Solution:

Feature	Endosperm	Perisperm
(a) Origin	From PEN (triple fusion product)	Persistent NUCELLUS (maternal sporophytic tissue)
(b) Ploidy	Triploid ($3n$)	Diploid ($2n$)
(c) Examples	Wheat, rice, maize, castor, coconut	Black pepper, beet

The key differences:

1. Origin — endosperm forms AFTER fertilisation (from PEN). Perisperm forms FROM the maternal nucellus, which existed BEFORE fertilisation. So perisperm is a leftover; endosperm is a new tissue.

2. Ploidy — endosperm is uniquely $3n$. Perisperm, being maternal sporophytic, is $2n$.

3. Frequency — endosperm is found in MANY seeds (essentially all angiosperms have endosperm at some stage). Perisperm is RARE — limited to a few species.

NEET trap to watch for:

Don't say "perisperm is haploid" — that's wrong. Perisperm = $2n$. The only haploid tissue in a developing seed is the leftover embryo sac cells (degenerating synergids, antipodals) — and these typically aren't called "perisperm."

Where do you find perisperm?

Two NCERT-canonical examples:

• Black pepper (Piper nigrum).
• Beet (Beta vulgaris).

Both have persistent nucellus tissue serving as additional food storage.

Answer: Endosperm = from PEN, $3n$, common (e.g., wheat). Perisperm = persistent nucellus, $2n$, rare (e.g., black pepper, beet).

[NEET Important] Classic NEET MCQ: "Which is found in black pepper?" → Perisperm. Drill this pairing.

Problem 11 — Apomixis explanation chain

In simple terms, explain why developing apomictic varieties of food crops is considered one of the most important goals in modern plant biotechnology. Build the answer chain.

Solution:

We build the reasoning chain step by step.

Step 1: Hybrid F1 seeds are agriculturally superior.

F1 hybrid varieties (made by crossing two specific parental lines) show hybrid vigour: higher yield, better disease resistance, uniform growth. This is the foundation of modern agriculture (Green Revolution).

Step 2: F1 hybrid seeds are EXPENSIVE.

To produce F1 seeds, breeders must do laborious controlled crosses every season (emasculation, bagging, hand-pollination). This makes hybrid seeds many times more expensive than ordinary seeds.

Step 3: Farmers cannot save and replant F1 seeds.

If a farmer saves seeds from F1 plants, the resulting F2 plants are genetically variable (Mendel's law of segregation). Yields drop, traits become inconsistent — hybrid vigour is LOST.

Step 4: So farmers MUST BUY fresh F1 seeds every year.

This is the burdensome cost cycle. Especially for small farmers in developing countries, the annual hybrid seed cost can be a major expense.

Step 5: How apomixis breaks the cycle.

If a hybrid variety could be made APOMICTIC:

• Its seeds would be CLONES of the F1 mother.
• These clonal seeds would produce identical F1 plants when planted.
• Farmers could save and replant year after year.
• Hybrid vigour would be preserved indefinitely.
• No need to buy fresh hybrid seeds → MASSIVE COST SAVINGS.

Step 6: Why this is still a goal.

No major food crop (wheat, rice, maize, soybean) is naturally apomictic. Engineering apomixis into these is one of the holy grails of modern plant biotechnology.

NCERT-canonical phrase: "If we develop apomictic varieties of hybrid plants, the farmers need not buy hybrid seeds every year and can keep on using the hybrid seeds to raise new crop year after year."

Answer: Apomictic hybrid crops would let farmers save and replant seeds without losing hybrid vigour, eliminating the need for annual seed purchases. This would be a transformative cost reduction for small farmers globally. The challenge: no major food crop is naturally apomictic, so this remains an active research goal.

[Board Important] A classic CBSE 5-mark essay question. Practise the full reasoning chain.

Problem 12 — Comprehensive species identifications

Identify the plant from each description:

(a) Has the world's tallest inflorescence, emits the smell of rotting flesh. (b) Pollinator is Tegeticula moth in an obligate mutualism. (c) Water-pollinated; pollen floats on surface; aquatic plant. (d) Water-pollinated; ribbon-like pollen carried underwater; marine seagrass. (e) Causes pollen allergy; came to India as wheat contaminant. (f) Cleistogamous; assured autogamy without external pollinator. (g) Dioecious fruit-bearing plant; commercially valuable. (h) Has the longest known seed viability (10,000 years).

Solution:

#	Description	Plant	Genus name
(a)	Tallest inflorescence, foul odour	Amorphophallus	Amorphophallus titanum
(b)	Tegeticula mutualism	Yucca	Yucca sp.
(c)	Surface water-pollinated, aquatic	Vallisneria	Vallisneria sp.
(d)	Underwater pollination, marine	Zostera	Zostera sp.
(e)	Pollen allergy, wheat contaminant	Parthenium / Carrot grass	Parthenium hysterophorus
(f)	Cleistogamous, assured autogamy	Viola, Oxalis, or Commelina	Commelina
(g)	Dioecious, commercially valuable fruit	Papaya	Carica papaya
(h)	Longest seed viability (10,000 yr)	Arctic lupine	Lupinus arcticus

Why this matters:

NEET and Boards heavily test these species-specific facts. Each species has a unique "narrative hook" (e.g., the moth mutualism, the wheat contamination, the 10,000-year viability) that examiners use to construct MCQs.

Other names to memorise (bonus):

• Date palm = Phoenix dactylifera (2,000-year-old seed viability at Masada).
• Sunflower = Helianthus annuus (entomophilous, can show protandry).
• Maize = Zea mays (monoecious, 3-celled pollen at shedding, anemophilous).
• Pea = Pisum sativum (non-albuminous, dicot, 2-celled pollen).

Answer: (a) Amorphophallus, (b) Yucca, (c) Vallisneria, (d) Zostera, (e) Parthenium hysterophorus, (f) Commelina, (g) Carica papaya, (h) Lupinus arcticus.

[NEET Important] Species-identification MCQs are NEET-favourite. Memorise every Latin name explicitly mentioned in NCERT.