sexual reproduction in flowering plants

🌱 Biological Importance:

• To a biologist, a flower is not just pretty — it’s a morphological and embryological marvel, site of sexual reproduction.

• You are asked to recall the two most important parts of a flower for sexual reproduction:

✅ Answer:

1. Androecium (Stamens) – produces pollen grains (male gametes)

2. Gynoecium (Carpels) – contains ovules (female gametes)

1. Androecium

1. (Stamens) – produces pollen grains (male gametes)

1. Gynoecium

1. (Carpels) – contains ovules (female gametes)

🌱 PRE-FERTILISATION: STRUCTURES AND EVENTS 📌 Key Idea:

Sexual reproduction in plants starts even before the flower visibly blooms!

🔄 Early Events Before Flowering:

1. Floral Induction:

   • The decision to flower happens early at the molecular and hormonal level.

   • Triggered by factors like day length (photoperiod), temperature, and internal hormonal signals.

1. Structural & Hormonal Changes:

1. • Lead to the formation of floral primordium (the earliest visible sign of a flower on the shoot apex).

   • This primordium develops into inflorescences (groups of flowers) or single floral buds.

1. Development of Reproductive Organs:

1. • Inside each flower:

     • Androecium (Male organ) → develops into stamens.

     • Gynoecium (Female organ) → develops into carpels/pistils.

📚 Quick Recall:

• Androecium = Stamens = Male reproductive organs

  • Produces pollen grains.

• Gynoecium = Carpels = Female reproductive organs

  • Contains ovules that develop into seeds.

🌸 Stamen, Microsporangium & Pollen Grain

🌿 1. Structure of a Stamen

• Parts:

  • Filament: Long, slender stalk that attaches to the thalamus or petal.

  • Anther: Terminal, generally bilobed structure with two theca per lobe ⇒ dithecous

🌼 2. Anther Structure

• T.S. (Transverse Section) shows:

  • A bilobed, tetragonal (four-sided) structure.

  • 4 microsporangia — one at each corner (2 per lobe).

🔬 3. Microsporangium Structure

• Has four wall layers (from outside to inside):

  1. Epidermis

  2. Endothecium

  3. Middle layers

  4. Tapetum (innermost) → provides nutrition to developing pollen grains

     • Tapetal cells are often bi-nucleate (can be due to mitotic divisions without cytokinesis or fusion of nuclei).

• Sporogenous tissue:

• • Found at the center of each microsporangium.

  • Diploid cells → undergo meiosis to form microspores.

🧬 4. Microsporogenesis

• Definition: Formation of microspores from sporogenous tissue.

• Process:

  • Sporogenous cells undergo meiosis (reductional division).

  • Forms microspore tetrads (4 haploid microspores in a group).

  • Ploidy of tetrad cells = haploid (n).

• Sporogenous Tissue

• • Inside the anther, the sporogenous tissue is the starting point.

  • These cells are special and will become pollen grains.

• Meiosis Time ➡ Let's split up!

  • The cells of the sporogenous tissue undergo meiosis.

  • This division creates microspore tetrads – four microspores grouped together.

• Microspore Tetrad

• After meiosis, we get a tetrad – a cluster of 4 microspores (like four friends stuck together).

  • Each one of these will become a pollen grain.

• Separation of Microspores

• As the anther matures, these microspores separate from each other.

  • They are now free to develop into individual pollen grains.

• Pollen Grains Form

Each microspore transforms into a pollen grain. This is the male gametophyte!

• Dehiscence of Anther

• The anther opens up (called dehiscence), releasing thousands of pollen grains into the air.

  • These pollen grains are ready to participate in fertilization!

Pollen Grain Overview

• Male Gametophyte: Pollen grains represent the male reproductive cells in flowering plants.

• Size: 25–50 micrometers in diameter, so they’re tiny!

• Shape & Color: They come in all sorts of shapes, colors, and sizes. Some are spherical, while others can be elongated or irregular.

🔬 Structure of Pollen Grain

1. Two Layers of Wall:

   • Exine (Outer Layer):

     • Hard and protective. Made of sporopollenin (resistant to high temperatures, acids, and alkalis).

     • Function: Protects the pollen grain, helping it survive harsh conditions and allowing it to be well-preserved in fossils.

     • Has germ pores where the sporopollenin is absent (they allow the pollen tube to form).

   • Intine (Inner Layer):

     • Thin, continuous, made of cellulose and pectin.

1. Inside the Pollen Grain:

1. • Cytoplasm: The space where everything floats!

   • Plasma Membrane: Surrounds the cytoplasm.

🧬 Types of Cells Inside the Pollen Grain

1. Vegetative Cell:

   • Larger and has food reserves.

   • Irregularly shaped nucleus.

   • Supports growth and development.

1. Generative Cell

• Smaller, spindle-shaped, with dense cytoplasm.

• Before shedding, it divides to form two male gametes in some species.

• In over 60% of plants, it remains undivided until after the pollen grain is shed.

💡 Fun Facts

• Why is Exine Hard?

• 
  The hard exine protects the pollen grain from damage and helps it resist environmental challenges.

• What’s the Role of Germ Pores?

The germ pores allow the pollen grain to form a pollen tube, which is crucial for fertilization.

Pollen Grains: The Little Powerhouses with Big Impacts 🌸

• Allergic Trouble:

  • Some pollen grains cause severe allergies 🥴, like asthma or bronchitis.

  • Ever heard of Parthenium (or carrot grass) in India? It came with wheat imports and is now a major culprit for pollen allergies!

Pollen = Nutrient-Rich:

• Fun fact: Pollen grains are packed with nutrients! 🥦🌾

• That’s why pollen tablets have become popular as food supplements. In some places, you’ll find them as tablets and syrups. They claim to boost energy and performance—perfect for athletes and even race horses!

• Pollen’s Lifespan:

• • How long do pollen grains last? Well, it depends! ⏳

    • Some pollen grains, like from rice and wheat, lose viability just 30 minutes after being released! 😱

    • But others, like those from rosaceae and solanaceae, can last months! 🗓

• Pollen Banks:

• • Just like storing sperm for artificial insemination, pollen grains can be stored for years in liquid nitrogen ❄ (at -196°C)!

  • These stored pollen grains are like nature’s backup and are super useful in crop breeding programs. 🌱

The Pistil: The Queen of the Gynoecium 👑

• The gynoecium is the female reproductive part of the flower 🌸.

• It may consist of a single pistil (monocarpellary) or more than one pistil (multicarpellary).

  • Syncarpous: Pistils fused together 💕

  • Apocarpous: Pistils free from each other 🎋

• Parts of the Pistil:

• 1. Stigma – The welcoming platform for pollen grains 🌾

  2. Style – The slender, elongated part below the stigma 🌟

  3. Ovary – The bulging base where the magic happens 💫

• Inside the Ovary:

• The ovarian cavity (locule) holds the placenta (the connection point between the ovule and the ovary).

  • From the placenta arise the ovules (the megasporangia) where the female gametophytes (embryo sacs) will develop.

The Megasporangium (Ovule): A Tiny Wonder! 🌱

• The ovule is a small structure connected to the placenta by a stalk called the funicle. 🌿

  • The junction where the ovule and funicle meet is called the hilum (kind of like the belly button of the ovule! 😉).

• Protective Layers:

• The ovule has integuments (outer protective layers) surrounding the nucellus (inner part of the ovule) 🛡.

  • Micropyle: A tiny opening at the tip of the ovule – think of it as the ovule’s "mouth" 🍽.

  • Chalaza: The basal end of the ovule, opposite the micropyle 🌍.

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• The Nucellus & Embryo Sac:

  • The nucellus contains food reserves for future development 🌾.

  • Embryo Sac: The ovule houses a single embryo sac, which is the female gametophyte. It is formed from a megaspore.

  • Note: The embryo sac is where fertilization happens, leading to the formation of the seed 🌱!

How many ovules are typically found in the ovary of wheat, paddy, and mango?

A. One
B. Many
C. Two
D. None

One

Megasporogenesis: Formation of the Female Gametophyte 🌸

• Step 1: The MMC (Megaspore Mother Cell)
  The MMC is a large diploid cell (2n) found in the micropylar region of the ovule. It has a prominent nucleus and dense cytoplasm, ready to undergo meiosis.

• Step 2: Meiosis 🔬
  The MMC divides meiotically to produce four haploid megaspores (1n). Out of these four, only one megaspore becomes functional, while the other three degenerate.

• Step 3: The Functional Megaspore (1n)
  The functional megaspore develops into the female gametophyte (embryo sac). This process is called monosporic development because the embryo sac forms from a single megaspore.

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Ploidy of Cells 🧬

• Nucellus: 2n (Diploid)

• MMC: 2n (Diploid)

• Megaspores: 1n (Haploid)

• Female Gametophyte (Embryo Sac): 1n (Haploid)

formation of the Embryo Sac 🌸

1. Start with the Functional Megaspore

   • The functional megaspore (1n) begins to divide by mitosis.

   • First division: The nucleus divides, forming 2 nuclei at opposite ends of the cell.

   • This creates the 2-nucleate embryo sac. (Still no cell walls, just free nuclear divisions!) 😲

1. Next Division Stages

1. Second division: The 2 nuclei divide again to form 4 nuclei.

   • Third division: These 4 nuclei divide again to form 8 nuclei.

   • These divisions are free nuclear (no cell walls yet!) 🔄

Cell Wall Formation

• After the 8-nucleate stage, cell walls are laid down to form distinct cells.

• Now we have a 7-celled embryo sac! ✨ (Even though it’s 8-nucleate!)

Structure of the Mature Embryo Sac 🧬

• Micropylar End (Egg Apparatus)

  • 2 Synergids + 1 Egg Cell = Egg Apparatus 👩‍🦰🍳

  • Synergids: Special cellular thickenings called filiform apparatus guide pollen tubes toward the egg! 🛠

• Chalazal End (Antipodals)

  • 3 Antipodal Cells at the opposite end of the embryo sac. 📍

• Central Cell

  • The large central cell holds 2 Polar Nuclei. ⚪

External Agents for Pollination

Flowers use a variety of external agents to move pollen around. Can you guess who helps? 🤔

• Insects (like bees 🐝)

• Wind 🍃

• Water 🌊

• Animals 🦋

Kinds of Pollination 🌼

1. Autogamy (Self-pollination) 🌱

   • Pollination happens within the same flower!

   • Pollen goes from anther to stigma of the same flower.

   • Example: Some plants like Viola and Oxalis can do this.

   • Bonus: Some flowers (like cleistogamous flowers) never open, and self-pollination happens when pollen touches the stigma within the closed bud. 🌺

   • Is it Advantageous or Disadvantageous?

     • Advantage: No pollinators required.

     • Disadvantage: No genetic variation, which can affect plant survival. ❌

Autogamy in a normal flower is rare because:
A. It always requires pollinators
B. Stigma is not receptive during pollen release
C. Anther and stigma lie far apart
D. Both B and C

✅ Answer: D. Both B and C
📘 Autogamy in open (chasmogamous) flowers needs synchrony in pollen release and stigma receptivity, and close proximity of anther and stigma.

Which of the following is always autogamous?
A. Chasmogamous flowers of Oxalis
B. Cleistogamous flowers of Viola
C. Cross-pollinated flowers of maize
D. Chasmogamous flowers of Commelina

✅ Answer: B. Cleistogamous flowers of Viola
📘 Since cleistogamous flowers never open, there's no chance of cross-pollination — they are invariably autogamous.

Match the columns:

Column I	Column II
a. Cleistogamy	i. Assured seed set
b. Chasmogamy	ii. Requires pollinators
c. Autogamy in open flower	iii. Rare due to synchrony issues

Choose the correct match:
A. a-i, b-ii, c-iii
B. a-ii, b-i, c-iii
C. a-iii, b-i, c-ii
D. a-i, b-iii, c-ii

✅ Answer: A. a-i, b-ii, c-iii

Assertion (A): Cleistogamous flowers ensure self-pollination even in absence of pollinators.
Reason (R): These flowers do not open and their anthers lie close to the stigma.

A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but R is not the correct explanation of A
C. A is true, R is false
D. A is false, R is true

✅ Answer: A. Both A and R are true, and R is the correct explanation of A

Which of the following is NOT a feature of cleistogamous flowers?
A. Do not open
B. Cross-pollination is impossible
C. Produce less number of seeds
D. Seed set occurs without external agents

✅ Answer: C. Produce less number of seeds
📘 Cleistogamous flowers produce assured seed set, not less seed set.

Geitonogamy (Same Plant, Different Flower) 🌿

• Pollination happens between flowers on the same plant.

• Example: Pollen goes from one flower’s anther to another flower’s stigma on the same plant.

• Technically Cross-pollination, but Genetically Same as Autogamy. 🚶‍♂

xenogamy (Cross-pollination) 🌍

• Pollen is transferred from anther to stigma of different plants.

• This brings genetically different pollen to the stigma, making the plant’s offspring more genetically diverse. 🌍

• Example: Transfer of pollen from one flower to another of the same species, but different plants.

🌼 Agents of Pollination

Plants use different agents to transfer pollen from anther to stigma. These agents can be abiotic (non-living) or biotic (living).

🔹 Abiotic Agents (Non-living)

1. Wind (Anemophily) 🌬

   • Most common abiotic pollination method

   • Flowers produce huge amounts of pollen to increase chances of landing on a stigma

   • Pollen features:

     • Light

     • Non-sticky

   • Flower features:

     • Well-exposed stamens 🌾

     • Large, feathery stigma to catch pollen

   • Examples: Grasses, Corn (the tassels on corn cobs = stigma + style!)

1. Water (Hydrophily) 💧

(Not explained in this extract, but it's the other abiotic method used by some aquatic plants)

🔹 Biotic Agents (Living) 🐝🦋

• Used by the majority of plants

• Agents include insects, birds, bats, etc.

📌 Fun Fact:

Pollination by wind is random and uncertain, so wind-pollinated plants overproduce pollen compared to the number of ovules – a strategy to ensure at least some successful pollination.

What is the main advantage of cleistogamy for a plant?

A. It allows for cross-pollination.
B. It ensures seed set even in the absence of pollinators.
C. It helps the plant produce more pollen.
D. It attracts more pollinators.

It ensures seed set even in the absence of pollinators.

Q. Which type of pollination brings genetically different pollen grains to the stigma?

A. Autogamy
B. Geitonogamy
C. Xenogamy
D. Cross-pollination

C. Xenogamy

Pollination by Water 🌊

• Water Pollination is quite rare in flowering plants and occurs in only about 30 genera, mostly monocotyledons.

• Common Examples:

  • Vallisneria (freshwater plant)

  • Hydrilla (freshwater plant)

  • Zostera (marine seagrass)

How Water Pollination Works:

• Vallisneria: The female flowers have long stalks and reach the surface of the water, while male flowers or pollen are released onto the water's surface. Pollen grains are carried by water currents, and some of them reach the stigma of female flowers.

• Seagrasses: Female flowers remain submerged, while the pollen is released into the water and carried by currents.

Characteristics of Water-Pollinated Plants:

• Pollen grains in these plants often have a mucilaginous covering to protect them from wetting.

• No bright colors or nectar in water-pollinated flowers because they don’t rely on visual or nectar-based attraction

Pollination by Animals 🐝

• Animal Pollination is the most common form of pollination in flowering plants.

• Common Pollinators:

  • Insects (Bees, butterflies, flies, beetles, wasps, ants, moths)

  • Birds (Sunbirds, hummingbirds)

  • Bats 🦇

  • Other animals (Lemurs, tree-dwelling rodents, reptiles like geckos)

Adaptations of Animal-Pollinated Flowers:

• Flowers are often brightly colored to attract pollinators.

• Flowers might produce nectar to reward the pollinators.

• Some flowers are specifically adapted to attract certain pollinators (e.g., shape, size, and scent of the flower).

• Pollinator-Specific Flowers:

• • Some flowers are adapted to a specific pollinator species. For example, certain flowers might have long, tubular shapes ideal for hummingbirds or specific scents that attract moths.

Insect Pollination in Flowers 🐝🌸

• Characteristics of Insect-Pollinated Flowers:

  • Typically large, colorful, and fragrant.

  • Often rich in nectar to attract pollinators.

  • When flowers are small, they may be clustered into inflorescences to become more conspicuous. 🌺

• Attraction Mechanism:

• • Color and fragrance play a significant role in attracting pollinators, especially insects like bees, butterflies, and flies.

  • Some flowers, such as those pollinated by flies and beetles, secrete foul odors to attract these specific animals. 👃

• Rewards for Pollinators:

• • Nectar and pollen grains are the typical rewards provided to pollinators.

  • The animals collect nectar and pollen while visiting flowers.

• Pollination Process:

• • When an animal visits a flower for nectar or pollen, its body gets coated with sticky pollen grains.

  • As the animal moves from flower to flower, it transfers pollen to the stigma, resulting in pollination. 🐝🌻

Floral Rewards & Pollinator Relationships

• Some flowers provide safe places for pollinators to lay eggs as part of mutualistic relationships. Example:

  • Amorphophallus: The tall flower (about 6 feet) attracts pollinators by providing a nesting site.

  • Yucca and Moth: The yucca plant and the yucca moth share a mutualistic relationship. The moth lays its eggs in the ovary locule of the flower, and in turn, it pollinates the flower. The larvae feed on the developing seeds.

Observing Flower Visitors for Pollination

• When observing flowers, try to identify the animals visiting them. Common plants to observe include:

  • Cucumber, Mango, Peepal, Coriander, Papaya, Onion, Lobia, Cotton, Tobacco, Rose, Lemon, Eucalyptus, and Banana.

• What to Look For:

  • Time of visit: Different animals might visit at different times of the day.

  • Type of visitor: Determine whether insects, birds, bats, etc., are the visitors.

  • Pollinator Interaction: Observe whether visitors touch the anthers and stigma (the parts responsible for pollination).

Pollen/Nectar Robbers

• Some floral visitors consume nectar/pollen without pollinating, referred to as pollen/nectar robbers. These animals take the rewards but don’t transfer pollen, hence not aiding pollination.

Important Points for NEET:

1. Mutualistic relationships: Some plants depend on specific animals (like moths) for both pollination and seed development.

2. Characteristics of pollinators: Be familiar with various types of pollinators such as insects (bees, butterflies), birds (hummingbirds), bats, and others.

3. Floral structure: Know how the flower structure (like anthers, stigma, and ovary) relates to the type of pollination (biotic or abiotic).

4. Pollen/nectar robbers: Understand the concept of non-pollinating visitors that still interact with the flowers.

Key Outbreeding Mechanisms:

1. Non-Synchronous Pollen Release and Stigma Receptivity

   • In some species, pollen release and stigma receptivity do not occur at the same time.

   • Result: This temporal separation prevents self-pollination.

     • Example: Cucurbita species (pumpkins and squashes) release pollen before the stigma becomes receptive.

1. Spatial Separation of Anther and Stigma

1. The anthers and stigma are placed at different positions within the flower.

   • Result: This physical separation ensures that pollen from the same flower cannot reach the stigma.

     • Example: Figs have their anthers and stigma at different positions within the flower.

1. Self-Incompatibility Mechanism

1. This genetic mechanism prevents self-pollen from fertilising the ovules.

   • Result: The pollen tube growth is inhibited, or pollen germination is blocked when self-pollen is deposited.

     • Example: Brassica species (cabbage, mustard) exhibit self-incompatibility.

1. Unisexual Flowers

1. Some plants produce unisexual flowers, i.e., male and female flowers are found on the same plant (monoecious) or on separate plants (dioecious).

   • Monoecious Plants: Male and female flowers are on the same plant, preventing autogamy but still allowing geitonogamy (cross-pollination within the same plant).

     • Example: Maize (corn), Castor.

   • Dioecious Plants: Male and female flowers are on separate plants, preventing both autogamy and geitonogamy.

     • Example: Papaya, Holly, Willows.

Which of the following mechanisms prevents self-pollination by temporal separation of pollen release and stigma receptivity in plants?

a) Self-incompatibility

b) Non-synchronous pollen release and stigma receptivity

c) Unisexual flowers

d) Spatial separation of anther and stigma

b) Non-synchronous pollen release and stigma receptivity

Pollen Recognition and Rejection:

• The pistil (female part of the flower) has the ability to recognize whether the pollen on the stigma is compatible (from the same species) or incompatible (from a different species or self-pollen if the plant is self-incompatible).

• Compatible pollen promotes germination and pollen tube growth, leading to fertilization.

• Incompatible pollen is rejected by the pistil, preventing pollen germination or inhibiting pollen tube growth.

• Pollen-Pistil Dialogue:

• • The interaction between the pollen grain and the pistil is a chemical dialogue where components from the pollen interact with those of the pistil.

  • This recognition process ensures only the right type of pollen (compatible) germinates.

• Pollen Germination and Tube Growth:

• After compatibility is confirmed, the pollen grain germinates on the stigma, producing a pollen tube.

  • The pollen tube grows through the stigma and style towards the ovary.

• Two-Cell vs. Three-Cell Pollen:

• In plants with two-celled pollen, the generative cell divides during pollen tube growth to form two male gametes.

  • In plants with three-celled pollen, the two male gametes are already present at the time of pollen release.

• Pollen Tube Entry into Ovule:

• • The pollen tube reaches the ovule via the micropyle.

  • The pollen tube enters one of the synergids through the filiform apparatus, which helps guide the tube to the correct location.

• Pollen-Pistil Interaction Process:

• The entire process from pollen deposition on the stigma to the entry of the pollen tube into the ovule is termed pollen-pistil interaction.

  • This process is dynamic and crucial for fertilization.

• Applications in Plant Breeding

• :

  • Understanding pollen-pistil interaction helps in manipulating pollen-pistil interactions to overcome incompatibility, allowing for the production of desired hybrids in plant breeding

Pollen Germination

• Pollen germination can be observed by dusting pollen from flowers like pea, chickpea, Crotalaria, balsam, and Vinca on a glass slide containing a 10% sugar solution.

• After 15–30 minutes, under the microscope, you should see pollen tubes emerging from the pollen grains

Artificial Hybridization

• Artificial hybridization is a key technique in crop improvement, aimed at combining desirable traits from different species or genera.

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Steps for Artificial Hybridization

1. Emasculation:

   • In bisexual flowers, remove the anthers before they dehisce (open) to ensure only the desired pollen is used.

   • This is called emasculation (the removal of male parts from the flower).

Bagging

Bagging:

• After emasculation, cover the flower with a bag (typically made of butter paper) to prevent contamination from unwanted pollen. This is referred to as bagging.

1. Pollination

When the stigma becomes receptive, pollen from the male parent (with desired traits) is dusted onto the stigma.

• The flower is then rebagged to allow fruit development.

For Unisexual Flowers:

• No emasculation is required for unisexual flowers.

• Female flower buds are bagged before they open. Once the stigma is receptive, pollination with desired pollen occurs, and the flower is rebagged.

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Key Takeaways for NEET:

• Emasculation is used to prevent unwanted pollen from reaching the stigma.

• Bagging ensures that only the desired pollen comes into contact with the stigma.

• Pollen germination can be easily observed on a sugar solution slide, which is a common experiment in labs.

Double Fertilisation in Flowering Plants 🌸

1. Pollen Tube Journey:

• The pollen tube enters one of the synergids and releases two male gametes. 🚹💨

In an angiosperm, the pollen tube releases two male gametes into:
A. Central cell
B. Antipodal cells
C. Egg apparatus
D. Cytoplasm of a synergid

✅ Answer: D. Cytoplasm of a synergid
📘 Both gametes enter one synergid before fertilisation events begin.

3. Step 2: Triple Fusion (Fusing with Polar Nuclei)

• The second male gamete moves towards the two polar nuclei in the central cell.

• It fuses with both of them to create a triploid primary endosperm nucleus (PEN). 🌱
  ➡ This is triple fusion as three haploid nuclei are involved! 🔺

The fusion of one male gamete with two polar nuclei is termed:
A. Syngamy
B. Triple fusion
C. Fertilisation
D. Endospermation

✅ Answer: B. Triple fusion
📘 Fusion of 3 haploid nuclei (male gamete + 2 polar nuclei) results in triploid PEN.

Match the following:

Column I	Column II
a. Syngamy	i. Diploid zygote
b. Triple fusion	ii. Triploid primary endosperm nucleus
c. Double fertilisation	iii. Syngamy + Triple fusion

Options:
A. a–i, b–ii, c–iii
B. a–ii, b–i, c–iii
C. a–i, b–iii, c–ii
D. a–ii, b–iii, c–i

✅ Answer: A. a–i, b–ii, c–iii

4. Why Double Fertilisation?

• Two fusions take place:

  1. Syngamy (fertilization of the egg cell)

  2. Triple fusion (fertilization of the polar nuclei)

• This unique process is called double fertilisation in flowering plants. 🌷

Assertion (A): Double fertilisation is a unique feature of angiosperms.
Reason (R): It involves both syngamy and triple fusion in the same embryo sac.

A. Both A and R are true, and R is the correct explanation of A
B. Both A and R are true, but R is not the correct explanation of A
C. A is true, R is false
D. A is false, R is true

✅ Answer: A. Both A and R are true, and R is the correct explanation of A

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The zygote and primary endosperm nucleus (PEN) formed after fertilisation are:
A. Both diploid
B. Both triploid
C. Zygote diploid, PEN triploid
D. Zygote triploid, PEN diploid

✅ Answer: C. Zygote diploid, PEN triploid
📘 Syngamy forms a 2n zygote, triple fusion forms a 3n endosperm.

tips

Syngamy

1 male gamete + 1 egg → diploid zygote (2n)

Triple fusion

1 male gamete + 2 polar nuclei → triploid PEN (3n)

Double fertilisation

Syngamy + Triple fusion (only in angiosperms!)

Endosperm

First tissue to develop after fertilisation