Plant water relationaships

       Water is one of the most essential components of plant life. It constitutes about 80–95% of the fresh weight of actively growing plant tissues. Water acts as -a  solvent, a transport medium, a reactant in photosynthesis, a temperature regulator and a source of turgidity

The study of absorption, transport, utilization, and loss of water in plants is known as Plant–Water Relations.

Water Potential (Ψw)

Water potential is the potential energy of water that determines the direction of movement of water in a system.

Water always moves from:

• Higher water potential → Lower water potential

Pure water has the highest water potential:
[Psi_w = 0]

Water potential helps explain how water moves from soil into roots and from one plant cell to another. The presence of dissolved substances and pressure affects the water potential of cells.

It determines the direction of water movement.

Water always moves:

• From higher water potential
• To lower water potential

Pure water has the highest water potential:

$$\Psi_w = 0$$

Water potential is measured in:

• Pascal (Pa)
• Megapascal (MPa)

Components of Water Potential

Water potential is mainly composed of:

$$\Psi_w = \Psi_s + \Psi_p$$

Where:

• $\Psi_w$ = Water potential
• $\Psi_s$ = Solute potential (osmotic potential)
• $\Psi_p$ = Pressure potential

Example

• Water moves from pure water into a concentrated sugar solution because the sugar solution has lower water potential.

Solute Potential (Ψs)

Solute potential is the decrease in water potential due to dissolved solutes.

It is always negative.

When solutes like salts or sugars dissolve in water, they reduce the free energy of water molecules. Therefore, water tends to move toward the region containing more solutes.

• Also called osmotic potential.
• Addition of solute decreases water potential.
• Always negative.

Example:

• Pure water = 0
• Sugar solution = negative value

Example

• Salt water has lower solute potential than pure water.

Pressure Potential (Ψp)

Pressure potential is the pressure exerted by the cell wall on the cell contents.

Pressure exerted by cell wall on cell contents.

Usually positive in living cells.

Responsible for turgidity.

Explanation

When water enters a plant cell, the vacuole expands and presses the cytoplasm against the cell wall. This creates turgor pressure which keeps plants upright.

Example

• Fresh green leaves remain firm because of positive pressure potential.

Osmosis

Osmosis is the movement of water molecules through a semipermeable membrane from higher water concentration to lower water concentration.

Explanation

Osmosis is the major method by which roots absorb water from soil. Cell membranes allow water molecules to pass while restricting many dissolved substances.

Example

• Raisins swell when kept in water due to osmosis.

Diffusion

Diffusion is the movement of molecules from higher concentration to lower concentration.

Explanation

Diffusion occurs without energy expenditure and continues until equilibrium is reached.

Example

• Perfume smell spreading throughout a room.

Imbibition

Imbibition is the absorption of water by hydrophilic substances resulting in swelling.

Explanation

Certain substances such as cellulose and proteins attract water molecules and absorb them rapidly.

Example

• Dry seeds swell after soaking in water.

Root Pressure

Definition

Root pressure is the positive pressure generated in roots due to active absorption of mineral ions and water.

Explanation

Mineral accumulation in xylem lowers water potential, causing water to enter xylem vessels. This creates pressure that pushes water upward.

Example

• Water droplets ooze out from cut stems of herbaceous plants.

Guttation

Definition

Guttation is the loss of liquid water droplets from leaf margins through hydathodes.

Explanation

When transpiration is low and soil moisture is high, root pressure forces excess water out through hydathodes.

Example

• Water droplets seen at the tips of grass leaves early in the morning.

Transpiration

Definition

Transpiration is the loss of water in the form of water vapor from aerial parts of plants.

Explanation

Most transpiration occurs through stomata. It creates transpiration pull and helps cool the plant body.

Example

• Water vapor loss from leaves of sunflower plants during daytime.

Transpiration Pull

Definition

Transpiration pull is the suction force generated due to evaporation of water from leaves.

Explanation

As water evaporates from mesophyll cells, tension develops in xylem vessels, pulling water upward from roots.

Example

• Water transport to the top of tall trees such as eucalyptus.Cohesion

Definition

Cohesion is the attraction between water molecules.

Explanation

Hydrogen bonding between water molecules keeps the water column continuous inside xylem vessels.

Example

• Continuous water column during ascent of sap.

Adhesion

Definition

Adhesion is the attraction between water molecules and other surfaces.

Explanation

Water molecules adhere to xylem walls, helping maintain the water column against gravity.

Example

• Water sticking to inner walls of xylem vessels.

Aquaporins

Definition

Aquaporins are specialized membrane proteins that facilitate rapid movement of water across membranes.

Explanation

They form channels in the plasma membrane allowing quick transport of water molecules.

Example

• Rapid water absorption by root cells.

Apoplast Pathway

Definition

Movement of water through cell walls and intercellular spaces.

Explanation

Water does not cross membranes in this pathway and therefore moves rapidly.

Example

• Water movement through cortex before reaching endodermis.

Symplast Pathway

Definition

Movement of water through the cytoplasm connected by plasmodesmata.

Explanation

Water enters the cytoplasm once and then moves cell-to-cell through plasmodesmata.

Example

• Water movement among cortical cells of roots.

Transmembrane Pathway

Definition

Movement of water across plasma membranes repeatedly from one cell to another.

Explanation

Water alternates between cytoplasm and cell wall while moving through tissues.

Example

• Water transport across root cortical cells.

Hydathodes

Definition

Hydathodes are specialized openings present at leaf margins through which guttation occurs.

Explanation

They remain permanently open and are connected to xylem endings.

Example

• Hydathodes present at the leaf margins of grasses.

Turgor Pressure

Definition

Turgor pressure is the pressure exerted by cell sap against the cell wall.

Explanation

It maintains rigidity and prevents wilting in plants.

Example

• Young shoots remain erect due to turgor pressure.

Flaccid Cell

Definition

A flaccid cell is a cell that has lost water and become limp.

Explanation

Loss of water decreases turgor pressure causing wilting.

Example

• Wilted leaves during drought conditions.

Antitranspirants

Definition

Antitranspirants are chemicals that reduce transpiration in plants.

Explanation

They help conserve water by reducing stomatal opening or forming protective films on leaves.

Example

• Phenyl mercuric acetate (PMA) used as stomatal closing antitranspirant.

Eukaryotic Cell

A eukaryotic cell is a complex type of cell that contains a true nucleus enclosed by a nuclear membrane and several membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi bodies, chloroplasts (in plants), etc.

The word “Eukaryotic” comes from the Greek words:

• Eu = true

• Karyon = nucleus

Thus, eukaryotic cells possess a well-defined nucleus.

Eukaryotic cells are found in:

• Animals

• Plants

• Fungi

• Protists

Characteristics of Eukaryotic Cells

1. Presence of a true nucleus.

2. DNA arranged in chromosomes.

3. Presence of membrane-bound organelles.

4. Larger and more complex than prokaryotic cells.

5. Cell division occurs through mitosis and meiosis.

6. Cytoplasm is well organized.

Diagram of a Typical Eukaryotic Cell

Fig: A typical eukaryotic cell

Major Organelles of a Eukaryotic Cell and Their Functions

Organelle	Function
Cell Membrane	Controls movement of substances into and out of the cell
Cytoplasm	Jelly-like matrix where organelles remain suspended
Nucleus	Controls all cellular activities and contains DNA
Nucleolus	Formation of ribosomes
Mitochondria	Site of cellular respiration and ATP production
Ribosomes	Protein synthesis
Endoplasmic Reticulum (ER)	Transport of materials inside the cell
Rough ER	Protein synthesis due to attached ribosomes
Smooth ER	Lipid synthesis and detoxification
Golgi Apparatus	Packaging and secretion of proteins
Lysosomes	Intracellular digestion
Vacuoles	Storage of food, water, and wastes
Centrosome/Centrioles	Help in cell division (mainly animal cells)
Chloroplast (plant cells)	Photosynthesis
Cell Wall (plant cells)	Provides rigidity and protection

Types of Eukaryotic Cells

1. Animal Cell

• No cell wall

• Small vacuoles

• Centrosome present

2. Plant Cell

• Cell wall present

• Large central vacuole

• Chloroplast present

Difference Between Prokaryotic and Eukaryotic Cells

Feature	Prokaryotic Cell	Eukaryotic Cell
Nucleus	Absent	Present
Size	Small	Large
Organelles	Absent	Present
DNA	Naked circular DNA	Linear chromosomes
Examples	Bacteria	Plants, animals, fungi

        Eukaryotic cells are highly organized cells possessing a true nucleus and membrane-bound organelles. Their complex internal structure enables advanced cellular functions in plants, animals, fungi, and protists.

Diagrammatic presentation of a eukaryotic cell & functions

Do you want to know more?

Important Scientists Related to the Discovery of Eukaryotic Cells

1. Robert Hooke (1665)

• Observed cork cells using a microscope.
• Coined the term “cell” in his book Micrographia.
• These were dead plant cells.

2. Antonie van Leeuwenhoek (1674)

• First observed living cells and microorganisms.
• Called them “animalcules”.

3. Édouard Chatton (1925)

• Introduced the terms:
  • Prokaryote
  • Eukaryote
• Distinguished cells based on the presence of a true nucleus.

Therefore, Édouard Chatton is credited with distinguishing and defining eukaryotic cells, while Robert Hooke first discovered cells in general.

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Cultivation of Commercial F lower Crops — I

China Aster

Botanical Name: Callistephus chinensis

Family: Asteraceae

Introduction

China aster is one of the most important annual ornamental flower crops cultivated throughout the world. It is native to China and belongs to the family Asteraceae. In India, it is mainly grown as a traditional flower crop for loose flowers, while internationally it is also popular as a cut flower crop.

In Northeast India and Assam, China aster has good commercial potential because of:

• Favourable climatic conditions

• Availability of fertile soils

• Increasing demand for flowers in local markets

• Scope for protected cultivation and floriculture entrepreneurship

It is commonly used for:

• Garlands

• Religious and social functions

• Floral decoration

• Bedding and border planting

• Bouquet preparation

Scope of China Aster Cultivation in Northeast India and Assam

The agro-climatic conditions of Assam and Northeast India are highly suitable for flower cultivation due to:

• Moderate temperature

• High humidity

• Adequate rainfall

• Fertile alluvial soils

Districts around:

• Dibrugarh

• Tinsukia

• Jorhat

• Sivasagar

• Kamrup

• Cachar

have good potential for commercial cultivation of China aster.

The crop is especially suitable for:

• Small and marginal farmers

• Kitchen gardens

• Nursery business

• Commercial floriculture units

Flowers are sold in:

• Local markets

• Temple markets

• Marriage ceremonies

• Festival decorations

Demand increases during:

• Durga Puja

• Bihu

• Weddings

• Religious functions

Important Varieties

Important varieties suitable for Indian conditions include:

• Kamini

• Poornima

• Phule Ganesh Pink

• Phule Ganesh Purple

• Phule Ganesh Violet

• Phule Ganesh White

• Shashank

• Violet Cushion

These varieties perform well under Assam conditions with proper drainage management.

Climate Requirement

China aster prefers cool and mild climate.

Optimum Conditions

• Day temperature: 20–30°C

• Night temperature: 10–18°C

• Relative humidity: 50–60%

• Bright sunlight is essential

In Assam and Northeast India

• Winter season is ideal for cultivation.

• Excessive monsoon rainfall may cause fungal diseases and root rot.

• Therefore, proper drainage is essential.

Soil Requirement

Best suited soils are:

• Well-drained sandy loam or loamy soils

• Rich in organic matter

• Soil pH: 6.8–7.5

In Assam

Alluvial soils of Brahmaputra valley are suitable for cultivation if:

• Drainage is maintained

• Organic manure is adequately applied

Waterlogging should be strictly avoided due to heavy rainfall conditions.

Propagation

China aster is propagated through seeds.

Seed Requirement

• 2.5–3.0 kg seed per hectare

Nursery Raising

• Seeds are sown in raised nursery beds during September–October.

• Seedlings become ready in about one month.

• Seedlings of about 10 cm height are transplanted to the main field.

In Northeast India

Raised nursery beds are very important to avoid:

• Water stagnation

• Damping-off disease

Land Preparation

• Land should be ploughed 3–4 times for fine tilth.

• Proper drainage channels should be prepared.

• Farmyard manure (FYM) @ 10–15 tonnes/ha should be mixed during land preparation.

• Vermicompost can also be used.

Special Recommendation for Assam

Because of heavy rainfall:

• Raised beds are highly recommended.

• Drainage channels should be maintained throughout the field.

Planting Time

Assam and Northeast India

• Nursery sowing: September–October

• Transplanting: October–November

Flowering generally occurs during winter when climatic conditions remain favourable.

Spacing

Recommended spacing:

• 30 × 30 cm

• 45 × 45 cm

According to soil type:

• Light soils: 45 × 20 cm

• Medium soils: 60 × 20 cm

Manures and Fertilisers

Organic Manure

• FYM @ 10–15 tonnes/ha

Fertiliser Dose

• NPK @ 120:80:120 kg/ha

Application

• Full phosphorus and potassium as basal dose

• Nitrogen in 2–3 split doses

In Assam

Use of organic manures and vermicompost improves:

• Soil structure

• Water-holding capacity

• Flower quality

Irrigation

China aster requires moderate irrigation.

General Recommendation

• Irrigation at 10–12 day intervals during winter

In Northeast India

• Irrigation requirement is less during winter due to residual soil moisture.

• Excess irrigation should be avoided.

Pinching

Pinching is done one month after transplanting.

Advantages

• Promotes branching

• Increases flower production

• Improves flower yield

Disadvantage

• Slight delay in flowering

Harvesting

Loose Flowers

Harvested when flowers are fully open.

Cut Flowers

Harvested when flower colour fully develops.

Post-Harvest Handling

• Stems should be immediately placed in clean water.

• Flowers should be graded and packed carefully.

Yield

Average loose flower yield:

• 15–20 tonnes/ha

Yield depends on:

• Variety

• Soil fertility

• Drainage

• Weather

• Crop management

Important Insect-Pests

Major Pests

• Black blister beetle (Epicauta pennsylvanica)

• Asiatic beetle (Autoserica castanea)

• Tarnished plant bug (Lygus lineolaris)

• Leafhopper (Macrosteles fascifrons)

• Leaf miners

• Semilooper caterpillars

Control Measures

• Field sanitation

• Light traps

• Need-based insecticide application

• Removal of infected plant parts

Nematode Problems

Root-knot Nematode

(Meloidogyne incognita)

Foliage Nematode

(Aphelenchoides ritzemabosi)

Control

• Application of Furadan @ 1 g/m²

• Proper field sanitation

• Crop rotation

Diseases

Major Diseases

• Wilt

• Collar rot

• Stem rot

• Gray mould

• Leaf spot

• Rust

• Canker

Common Disease Problems in Assam

High humidity and rainfall favour:

• Fungal diseases

• Root rot

• Leaf spot diseases

Control Measures

Spraying with:

• Mancozeb

• Carbendazim

• Captan

• Zineb

• Wettable sulphur

Proper drainage and wider spacing reduce disease incidence.

Viral Diseases

Important Viruses

• Chrysanthemum mosaic virus

• Aster yellows

• Spotted wilt

• Curly top virus

Control

• Removal and destruction of infected plants

• Control of insect vectors such as leafhoppers

Conclusion

China aster is a profitable ornamental flower crop with excellent scope in Assam and Northeast India. The favourable climate, fertile soils, and increasing market demand make it suitable for commercial cultivation.

For successful production in Northeast India:

• Raised beds and drainage are essential

• Proper nutrient management should be followed

• Fungal diseases must be carefully managed during humid conditions

With scientific cultivation practices, China aster cultivation can become an important source of income for farmers and floriculture entrepreneurs in Assam and the Northeast region.

HS II Agriculture

 

Male Papaya bears fruit, how?

In papaya, sex expression can sometimes change due to physical injury, environmental stress, or hormonal imbalance. Normally, a male papaya plant produces only staminate (male) flowers and does not bear fruits. However, when the plant body or growing tip is injured, the balance of plant hormones may be disturbed. This can induce the development of bisexual (hermaphrodite) or female flowers on a male plant.

These newly formed flowers contain functional ovaries, so after pollination they can develop into fruits. This phenomenon is called sex reversal or sex modification in papaya.

Why this happens

• Injury affects the apical meristem and hormone regulation.
• Papaya is highly sensitive to environmental and physiological changes.
• Stress conditions (injury, temperature fluctuation, nutrition imbalance, pruning, etc.) may alter flower sex expression.

Important point

The fruits produced on such injured male plants are usually:

• fewer in number,
• irregular in shape,
• and sometimes temporary in occurrence.

This is a well-known characteristic of papaya (), which shows considerable plasticity in sex expression.

Pollen–Pistil Interaction

Introduction

After pollination, pollen grains land on the stigma of a flower. But every pollen grain may not be suitable for fertilization.

The pistil has the ability to identify whether the pollen grain is:

• Compatible (right type)   or

• Incompatible (wrong type)

This process is called Pollen–Pistil Interaction.

What is Pollen–Pistil Interaction?

Pollen–pistil interaction is the series of events from:

• deposition of pollen on stigma to entry of pollen tube into the ovule.

It includes:

• Recognition of pollen

• Acceptance or rejection of pollen

• Growth of pollen tube

• Entry into ovule

Compatible and Incompatible Pollen

Compatible Pollen

Compatible pollen is pollen from the same species that can successfully fertilize the ovule.

Result

• Pollen germinates

• Pollen tube grows

• Fertilization occurs

Example

Pollen of Pea on another pea flower.

Incompatible Pollen

Incompatible pollen may come:

• From another species   OR

• From the same plant in self-incompatible plants

Result

• Pollen germination is prevented   OR

• Pollen tube growth stops

Example

Pollen of Mustard rejected by its own stigma in self-incompatible varieties.

Recognition of Pollen by Pistil

The pistil recognizes pollen through chemical interaction between:

• pollen grains and

• pistil tissues

This chemical communication helps the pistil decide whether to:

• accept pollen OR

• reject pollen

Steps of Pollen–Pistil Interaction

1. Pollination

Pollen grains are deposited on the stigma.

Diagram

Anther →→→ Stigma (Pollen transfer)

2. Pollen Germination

If pollen is compatible, it germinates on the stigma through a germ pore and forms a pollen tube.

Diagram

     Pollen grain
          ●
         / \
        /   \
     Pollen tube

Example

Pollen germination can be observed in:

• Pea

• Chickpea

• Balsam

• Vinca

3. Growth of Pollen Tube

The pollen tube grows through:

• stigma

• style

• ovary

to reach the ovule.

Diagram

 Stigma
    |
    |
  Style
    |
    |
  Ovary
    |
  Ovule

(Pollen tube grows downward)

4. Formation of Male Gametes

In Two-Celled Pollen

Pollen grain contains:

• One vegetative cell

• One generative cell

During pollen tube growth, the generative cell divides to form:

• Two male gametes

In Three-Celled Pollen

Pollen already contains:

• One vegetative cell

• Two male gametes

So pollen tube carries the male gametes from the beginning.

5. Entry into Ovule

The pollen tube enters:

• Ovule through micropyle

• One synergid through filiform apparatus

Role of Filiform Apparatus

It guides the pollen tube into the embryo sac.

Diagram

        Ovule
      __________
     |          |
Micropyle →  Pollen tube
     |          |
     | Synergid |
     |__________|

Importance of Pollen–Pistil Interaction

• Ensures correct fertilization

• Prevents wrong pollination

• Helps in hybrid formation

• Important in plant breeding

Artificial Hybridisation

Artificial hybridisation is a technique used by plant breeders to produce plants with desirable characters.

Example

Developing disease-resistant or high-yielding crops.

Techniques Used in Artificial Hybridisation

1. Emasculation

Removal of anthers from bisexual flower buds before anther dehiscence.

Purpose

Prevents self-pollination.

Diagram

Flower bud
   ↓
Removal of anthers
(using forceps)

Example

Used in hybridization of:

• Pea

• Hibiscus

2. Bagging

After emasculation, flowers are covered with butter paper bags.

Purpose

Prevents unwanted pollen contamination.

Diagram

   Flower
     ↓
 [Covered with bag]

When stigma becomes receptive:

• Desired pollen is dusted

• Flower is rebagged

Artificial Hybridisation in Unisexual Flowers

In unisexual flowers:

• Emasculation is not required

• Female flowers are directly bagged before opening

Example

• Maize

• Papaya

Simple Summary Table

Process	Function
Pollen recognition	Identifies compatible pollen
Pollen germination	Produces pollen tube
Pollen tube growth	Carries male gametes
Emasculation	Prevents self-pollination
Bagging	Prevents unwanted pollination

    

           Pollen–pistil interaction is a very important process in flowering plants. It helps the pistil recognize the correct pollen and ensures successful fertilization. Knowledge of this process is very useful in plant breeding and artificial hybridisation for developing improved crop varieties.

Outbreeding Devices in Flowering Plants

Introduction

Most flowering plants produce hermaphrodite flowers, which contain both male and female reproductive parts. In such flowers, self-pollination may easily occur because pollen grains can reach the stigma of the same flower.

Continuous self-pollination leads to inbreeding depression, which causes weak offspring and reduces genetic variation.

To avoid self-pollination and encourage cross-pollination, flowering plants have developed several special mechanisms called outbreeding devices.

What are Outbreeding Devices?

Outbreeding devices are special adaptations in flowering plants that:

• Prevent self-pollination

• Encourage cross-pollination

• Increase genetic variation

• Produce healthy offspring

Types of Outbreeding Devices

1. Dichogamy (Different Timing of Maturity)

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

Two conditions may occur:

• Pollen is released before stigma becomes receptive
  OR

• Stigma becomes receptive before pollen release

This prevents pollen from fertilizing the same flower.

Importance

• Prevents autogamy (self-pollination within same flower)

• Encourages cross-pollination

Examples

• Sunflower

• Salvia

Stage 1                         Stage 2

Pollen released             Stigma receptive

   Anther                       Stigma

       ↓                                ↓

 [ Flower ]                  [ Flower ]

(At different times)

2. Herkogamy (Different Position of Anther and Stigma)

In some flowers, the anther and stigma are placed at different positions.

Because of this arrangement, pollen grains cannot easily reach the stigma of the same flower.

Importance

• Prevents self-pollination

• Promotes cross-pollination

Examples

• Hibiscus

• Gloriosa

         Stigma

              |

              |

          --------

        /           \

   Anther      Anther

(Anther and stigma are separated)

3. Self-Incompatibility

Self-incompatibility is a genetic mechanism in plants.

In this mechanism, pollen grains from the same flower or same plant fail to fertilize the ovule.

This happens because:

• Pollen does not germinate
  OR

• Pollen tube growth is stopped inside the pistil

Importance

• Prevents inbreeding

• Encourages cross-pollination

Examples

• Brassica

• Petunia

Pollen grain → Stigma

      ✖ Pollen tube growth stops

          No fertilization occurs

4. Unisexuality

Some plants produce separate male and female flowers.

This helps in preventing self-pollination.

Unisexuality is of two types:

a) Monoecious Condition

In monoecious plants:

• Male and female flowers are present on the same plant

This condition:

• Prevents autogamy

• Does not prevent geitonogamy

Examples

• Castor

• Maize

• Coconut

                Male Flower

                      (Tassel)

                         ↑

                         |

                 Maize Plant

                         |

                         ↓

           Female Flower

                    (Cob)

b) Dioecious Condition (Dioecy)

In dioecious plants:

• Male and female flowers are present on different plants

• One plant is only male

• Another plant is only female

This condition:

• Prevents both autogamy and geitonogamy

Examples

• Papaya

• Date Palm

             Male Plant                       Female Plant

             [Male Flower]  →→→   [Female Flower]

Inbreeding Depression

Continuous self-pollination causes inbreeding depression.

Effects of Inbreeding Depression

• Weak plants

• Reduced fertility

• Poor growth

• Lower resistance to diseases

Cross-pollination helps to overcome these problems.

Summary Table

Outbreeding Device	Main Function	Example
Dichogamy	Different timing of pollen release and stigma receptivity	Sunflower
Herkogamy	Different position of anther and stigma	Hibiscus
Self-incompatibility	Prevents self-fertilization genetically	Brassica
Monoecy	Male and female flowers on same plant	Maize
Dioecy	Male and female flowers on different plants	Papaya

    Outbreeding devices are important adaptations in flowering plants that prevent self-pollination and promote cross-pollination. These mechanisms increase genetic variation, improve plant health, and help plants survive better in changing environments.

MCQs on Double Fertilisation

 

1. Double fertilisation is a characteristic feature of:

A. Gymnosperms
B. Bryophytes
C. Pteridophytes
D. Angiosperms

2. Double fertilisation occurs inside the:

A. Ovary
B. Embryo sac
C. Anther
D. Endosperm

3. The pollen tube usually enters the embryo sac through the:

A. Chalaza
B. Funicle
C. Micropyle
D. Hilum

4. The pollen tube releases male gametes into:

A. Egg cell
B. Central cell
C. Antipodal cells
D. Synergid

5. How many male gametes are released by the pollen tube?

A. One
B. Two
C. Three
D. Four

6. Fusion of one male gamete with the egg nucleus is called:

A. Triple fusion
B. Fertilisation
C. Syngamy
D. Pollination

7. Syngamy results in the formation of:

A. Endosperm
B. Embryo sac
C. Zygote
D. Ovule

8. The zygote formed after syngamy is:

A. Haploid
B. Diploid
C. Triploid
D. Tetraploid

9. The second male gamete fuses with:

A. Egg cell
B. Synergids
C. Antipodals
D. Two polar nuclei

10. Fusion involving one male gamete and two polar nuclei is called:

A. Syngamy
B. Pollination
C. Triple fusion
D. Germination

11. Triple fusion produces:

A. Zygote
B. Embryo
C. Primary endosperm nucleus
D. Ovule

12. The ploidy of Primary Endosperm Nucleus (PEN) is:

A. Haploid
B. Diploid
C. Triploid
D. Tetraploid

13. PEN stands for:

A. Primary Egg Nucleus
B. Primary Endosperm Nucleus
C. Polar End Nucleus
D. Primary Embryo Nucleus

14. PEC develops into:

A. Embryo
B. Ovule
C. Seed coat
D. Endosperm

15. The zygote develops into:

A. Fruit
B. Embryo
C. Endosperm
D. Ovary

16. Endosperm mainly functions in:

A. Protection
B. Pollination
C. Nourishment of embryo
D. Seed dispersal

17. Double fertilisation includes:

A. Pollination and fertilisation
B. Syngamy and triple fusion
C. Germination and fertilisation
D. Pollination and germination

18. The central cell after triple fusion becomes:

A. Zygote
B. Synergid
C. Primary Endosperm Cell
D. Antipodal cell

19. Triple fusion involves the fusion of:

A. Two haploid nuclei
B. Three haploid nuclei
C. Four haploid nuclei
D. One diploid nucleus

20. Which one of the following is unique to flowering plants?

A. Pollination
B. Seed formation
C. Double fertilisation
D. Photosynthesis

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DOUBLE FERTILISATION IN FLOWERING PLANTs

Definition

Double fertilisation is a unique phenomenon in flowering plants in which two fusions occur inside the embryo sac:

1. Syngamy

2. Triple fusion

Because two fertilisation events occur simultaneously, the process is called double fertilisation.

Step-wise Process of Double Fertilisation

1. Entry of Pollen Tube

• The pollen tube enters the embryo sac through the micropyle.

• It penetrates one of the synergids.

• The tip of the pollen tube bursts and releases two male gametes into the cytoplasm of the synergid.

2. First Fusion – Syngamy

• One male gamete moves towards the egg cell.

• The nucleus of the male gamete fuses with the nucleus of the egg.

Result

• A diploid zygote (2n) is formed.

Equation

[n + n = 2n]

3. Second Fusion – Triple Fusion

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

• It fuses with the two polar nuclei.

Result

• A triploid Primary Endosperm Nucleus (PEN) (3n) is formed.

Equation

[n + n + n = 3n]

Why is it Called Double Fertilisation?

Two fusion events occur in the same embryo sac:

1. Syngamy

2. Triple fusion

Therefore, the phenomenon is called double fertilisation.

After Effects of Double Fertilisation

Formation of Embryo

• The zygote develops into the embryo.

Formation of Endosperm

• The central cell after triple fusion becomes the Primary Endosperm Cell (PEC).

• PEC develops into the endosperm.

• Endosperm provides nourishment to the developing embryo.

Important Terms

Term	Meaning
Syngamy	Fusion of male gamete with egg
Triple Fusion	Fusion of one male gamete with two polar nuclei
Zygote	Diploid cell formed after syngamy
PEN	Primary Endosperm Nucleus
PEC	Primary Endosperm Cell
Endosperm	Nutritive tissue for embryo

Diagrammatic Flow of Double Fertilization

Pollen tube enters synergid
            ↓
Two male gametes released
            ↓
 ┌───────────────────────┐
 │ First male gamete     │
 │ + Egg nucleus         │
 │ = Zygote (2n)         │
 └───────────────────────┘
            ↓
        Syngamy

 ┌───────────────────────┐
 │ Second male gamete    │
 │ + Two polar nuclei    │
 │ = PEN (3n)            │
 └───────────────────────┘
            ↓
      Triple Fusion
            ↓
      Double Fertilisation
            ↓
 Zygote → Embryo
 PEC → Endosperm

Significance of Double Fertilisation

• It is unique to angiosperms (flowering plants).

• Ensures formation of:

  • Embryo

  • Nutritive endosperm

• Helps in proper nourishment and development of the embryo.

Double fertilisation is an important reproductive event in flowering plants where one male gamete forms the zygote and the other forms the endosperm. This process ensures successful seed development and nourishment of the embryo.

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Scientific Nomenclature of Living Organisms

Scientific nomenclature is the standardized system of naming living organisms using internationally accepted rules and principles. It provides every organism with a unique scientific name so that scientists throughout the world can identify and communicate about organisms without confusion caused by local or common names.

The modern system of scientific nomenclature was introduced by through the method of binomial nomenclature.

In binomial nomenclature, every organism is given two names:

1. Generic name (Genus)
2. Specific epithet (Species)

Example:

• Mango — Mangifera indica
• Human — Homo sapiens

Here, Mangifera and Homo are genus names, while indica and sapiens are species names.

Principles of Scientific Nomenclature

The scientific naming of organisms follows certain universal principles.

General Principles

1. Universality

Scientific names are accepted and used worldwide irrespective of language or country.

2. Binomial System

Each species is represented by two words:

• Genus name
• Species name

Example: Oryza sativa (rice)

3. Latinization

Scientific names are usually derived from Latin or are latinized because Latin is considered a universal and stable language.

4. Uniqueness

Each organism must have only one correct scientific name.

5. Priority

The earliest validly published name is accepted as the correct name.

6. Typification

Every scientific name is based on a type specimen or type concept that serves as a reference.

7. Standardized Rules

Naming must follow internationally accepted codes.

Process of Scientific Nomenclature

The process of naming organisms generally includes the following steps:

1. Discovery and Identification

A new organism is discovered and carefully studied.

2. Classification

The organism is placed into appropriate taxonomic categories such as kingdom, phylum/division, class, order, family, genus, and species.

3. Determination of Novelty

Scientists compare it with previously known organisms to confirm whether it is a new species.

4. Selection of Scientific Name

A binomial name is chosen according to international rules.

Rules for Writing Scientific Names

• Genus name begins with a capital letter.
• Species name begins with a small letter.
• Both words are italicized when printed.
• When handwritten, each word is underlined separately.

Example:

• Azadirachta indica

5. Description and Publication

A detailed scientific description is published in a recognized scientific journal or book.

6. Designation of Type Specimen

A preserved specimen is deposited in a herbarium or museum as a permanent reference.

Legal Authority for Scientific Nomenclature

Different groups of organisms are governed by separate international codes.

Scientific Nomenclature of Plants

Legal Authority

Plant nomenclature is governed by the:

through the

Previously, it was called the International Code of Botanical Nomenclature (ICBN).

The ICN is adopted during the International Botanical Congress held periodically.

Important Principles of Plant Nomenclature

1. Botanical nomenclature is independent of zoological nomenclature.
2. Names are based on priority of publication.
3. Each taxon has only one correct name.
4. Scientific names are treated as Latin.
5. Typification is essential.

Example

• Tea plant — Camellia sinensis
• Rice — Oryza sativa

Scientific Nomenclature of Animals

Legal Authority

Animal nomenclature is regulated by the:

through the

The ICZN provides rules for naming all animals.

Important Principles of Animal Nomenclature

1. Each animal species has a unique scientific name.
2. The principle of priority is followed.
3. Names are latinized.
4. Type specimens are mandatory.
5. Scientific names must be validly published.

Example

• Human — Homo sapiens
• Tiger — Panthera tigris

Difference Between Plant and Animal Nomenclature

Feature	Plant Nomenclature	Animal Nomenclature
Governing Code	ICN	ICZN
Governing Authority	International Botanical Congress/IAPT	International Commission on Zoological Nomenclature
Starting Point of Priority	1753 (Species Plantarum)	1758 (Systema Naturae)
Type Specimen	Herbarium specimen	Museum specimen

Conclusion

Scientific nomenclature is an essential system in biology that ensures accurate identification and universal communication about living organisms. The naming of plants and animals follows internationally accepted principles and legal codes such as the ICN for plants and the ICZN for animals. This standardized system avoids confusion and promotes scientific research across the world.