Class 12 Biology - Sexual Reproduction in Flowering Plants

Activities

Activity 1.1: Variation in Stamens

Aim: To appreciate the large variation in size and shape of stamens in different flowers. Materials Required:

Fresh flowers from 5 different families (e.g., Hibiscus, Pea, Mustard, Lily, Datura)
Dissecting microscope (10x - 40x magnification)
Fine forceps and needles
Glass slides and coverslips
0.5% Safranin stain (optional)

Procedure:

Carefully dissect the flower to expose the androecium.
Note the number of stamens and their arrangement (e.g., monadelphous in Hibiscus, diadelphous in Pea).
Extract one stamen from each flower and place it on a glass slide.
Observe the filament length and anther attachment (basifixed, dorsifixed, versifixed) under a dissecting microscope.
Record the dimensions (length in mm) using a miniature scale.

Scientific Note The variation in stamen morphology is an evolutionary adaptation to specific pollinators. For example, long filaments in wind-pollinated plants (anemophily) ensure anthers are exposed to wind currents, while specialized attachments like versatile anthers in grasses allow for maximum pollen dispersal.

Activity 1.2: Study of Pollen Architecture

Aim: To study the architecture of pollen grains from different species. Materials Required:

Mature anthers from Hibiscus, Tradescantia, Crotalaria, or Balsam
10% Sucrose solution
Glycerine (50% v/v)
Light microscope (100x and 450x magnification)
Glass slides and coverslips

Procedure:

Collect freshly dehisced anthers.
Dust the pollen grains onto a drop of 50% Glycerine on a glass slide.
Place a coverslip and observe under 10x and then 40x objective lens.
Note the shape (spherical, oval), size, and surface patterns (exine ornamentation).

Lab Best Practice Use Glycerine to prevent the pollen grains from drying out and to provide a suitable refractive index for observing fine exine details.

Activity 1.3: In Vitro Pollen Germination

Aim: To study pollen germination and pollen tube growth using a synthetic medium.

Materials Required:

Fresh pollen grains from Vinca rosea (Periwinkle) or Balsam
Germination Medium: 10% Sucrose, 100 mg/L Boric acid ( $H_3BO_3$ ), 300 mg/L Calcium nitrate ( $Ca(NO_3)_2 \cdot 4H_2O$ ), 200 mg/L Magnesium sulfate ( $MgSO_4 \cdot 7H_2O$ ), 100 mg/L Potassium nitrate ( $KNO_3$ )
Cavity slides (Depression slides)
Petri dish with moist filter paper (Humidity chamber)
Microscope

Procedure:

Place 2-3 drops of the germination medium in the center of a cavity slide.
Dust fresh pollen grains from Vinca onto the drops.
Place the slide in a petri dish containing moist filter paper to maintain 100% relative humidity.
Incubate at room temperature (25°C - 30°C) for 30 to 60 minutes.
Observe under the microscope every 15 minutes to track the emergence of pollen tubes.

Scientific Note Boron is essential for pollen germination as it facilitates the uptake of sugars and plays a structural role in the synthesis of pectin in the growing pollen tube tip. Calcium ions establish a tip-to-base gradient that directs the polarized growth of the tube (chemotropism).

Safety First Handle Boric acid and Calcium nitrate with care. Use gloves and avoid inhalation of chemical dust during medium preparation.

Activity 1.4: Observation of Ovules and Pistils

Aim: To study the internal structure of the ovary and ovule attachment (placentation). Materials Required:

Ovaries of Hibiscus (syncarpous), Pea (marginal), Dianthus (free central)
New razor blades (high precision)
Dissecting microscope
Brush and water

Procedure:

Take a mature ovary and perform a Transverse Section (T.S.) and a Longitudinal Section (L.S.) using a sharp razor blade.
Transfer the thin sections to a drop of water on a slide.
Count the number of locules and observe the arrangement of ovules on the placenta.
Identify the type of placentation (Axile, Marginal, Parietal, Free-central, or Basal).

Lab Best Practice Use a new, sharp razor blade for every 2-3 sections. A dull blade will crush the delicate placental tissue, making it impossible to identify the ovule attachment.

Activity 1.5: Polyembryony in Citrus

Aim: To observe multiple embryos within a single seed. Materials Required:

Mature seeds of Orange (Citrus reticulata) or Lemon
Forceps and dissecting needles
0.5% Acetocarmine stain
Beaker of water

Procedure:

Soak Citrus seeds in water for 2-4 hours to soften the seed coat.
Carefully remove the seed coat using forceps.
Gently tease apart the contents of the seed using needles.
Add a drop of Acetocarmine to differentiate the embryos.
Observe the embryos of different sizes and shapes.

Scientific Note In Citrus, polyembryony often occurs due to the development of nucellar cells into embryos (sporophytic budding). These embryos are genetically identical to the parent (apomictic), while the zygotic embryo (if present) is the result of sexual fusion.

Class 12 Biology - Sexual Reproduction in Flowering Plants

Activities

Activity 1.1: Variation in Stamens

Aim: To appreciate the large variation in size and shape of stamens in different flowers. Materials Required:

Fresh flowers from 5 different families (e.g., Hibiscus, Pea, Mustard, Lily, Datura)
Dissecting microscope (10x - 40x magnification)
Fine forceps and needles
Glass slides and coverslips
0.5% Safranin stain (optional)

Procedure:

Carefully dissect the flower to expose the androecium.
Note the number of stamens and their arrangement (e.g., monadelphous in Hibiscus, diadelphous in Pea).
Extract one stamen from each flower and place it on a glass slide.
Observe the filament length and anther attachment (basifixed, dorsifixed, versifixed) under a dissecting microscope.
Record the dimensions (length in mm) using a miniature scale.

Activity 1.2: Study of Pollen Architecture

Aim: To study the architecture of pollen grains from different species. Materials Required:

Mature anthers from Hibiscus, Tradescantia, Crotalaria, or Balsam
10% Sucrose solution
Glycerine (50% v/v)
Light microscope (100x and 450x magnification)
Glass slides and coverslips

Procedure:

Collect freshly dehisced anthers.
Dust the pollen grains onto a drop of 50% Glycerine on a glass slide.
Place a coverslip and observe under 10x and then 40x objective lens.
Note the shape (spherical, oval), size, and surface patterns (exine ornamentation).

Lab Best Practice Use Glycerine to prevent the pollen grains from drying out and to provide a suitable refractive index for observing fine exine details.

Activity 1.3: In Vitro Pollen Germination

Aim: To study pollen germination and pollen tube growth using a synthetic medium.

Materials Required:

Fresh pollen grains from Vinca rosea (Periwinkle) or Balsam
Germination Medium: 10% Sucrose, 100 mg/L Boric acid ( $H_3BO_3$ ), 300 mg/L Calcium nitrate ( $Ca(NO_3)_2 \cdot 4H_2O$ ), 200 mg/L Magnesium sulfate ( $MgSO_4 \cdot 7H_2O$ ), 100 mg/L Potassium nitrate ( $KNO_3$ )
Cavity slides (Depression slides)
Petri dish with moist filter paper (Humidity chamber)
Microscope

Procedure:

Place 2-3 drops of the germination medium in the center of a cavity slide.
Dust fresh pollen grains from Vinca onto the drops.
Place the slide in a petri dish containing moist filter paper to maintain 100% relative humidity.
Incubate at room temperature (25°C - 30°C) for 30 to 60 minutes.
Observe under the microscope every 15 minutes to track the emergence of pollen tubes.

Safety First Handle Boric acid and Calcium nitrate with care. Use gloves and avoid inhalation of chemical dust during medium preparation.

Activity 1.4: Observation of Ovules and Pistils

Aim: To study the internal structure of the ovary and ovule attachment (placentation). Materials Required:

Ovaries of Hibiscus (syncarpous), Pea (marginal), Dianthus (free central)
New razor blades (high precision)
Dissecting microscope
Brush and water

Procedure:

Take a mature ovary and perform a Transverse Section (T.S.) and a Longitudinal Section (L.S.) using a sharp razor blade.
Transfer the thin sections to a drop of water on a slide.
Count the number of locules and observe the arrangement of ovules on the placenta.
Identify the type of placentation (Axile, Marginal, Parietal, Free-central, or Basal).

Lab Best Practice Use a new, sharp razor blade for every 2-3 sections. A dull blade will crush the delicate placental tissue, making it impossible to identify the ovule attachment.

Activity 1.5: Polyembryony in Citrus

Aim: To observe multiple embryos within a single seed. Materials Required:

Mature seeds of Orange (Citrus reticulata) or Lemon
Forceps and dissecting needles
0.5% Acetocarmine stain
Beaker of water

Procedure:

Soak Citrus seeds in water for 2-4 hours to soften the seed coat.
Carefully remove the seed coat using forceps.
Gently tease apart the contents of the seed using needles.
Add a drop of Acetocarmine to differentiate the embryos.
Observe the embryos of different sizes and shapes.

Class 12 Biology - Sexual Reproduction in Flowering Plants

Class 12 Biology - Sexual Reproduction in Flowering Plants

Activities

Activity 1.1: Variation in Stamens

Activity 1.2: Study of Pollen Architecture

Activity 1.3: In Vitro Pollen Germination

Activity 1.4: Observation of Ovules and Pistils

Activity 1.5: Polyembryony in Citrus

On this page

Class 12 Biology - Sexual Reproduction in Flowering Plants

Class 12 Biology - Sexual Reproduction in Flowering Plants

Activities

Activity 1.1: Variation in Stamens

Activity 1.2: Study of Pollen Architecture

Activity 1.3: In Vitro Pollen Germination

Activity 1.4: Observation of Ovules and Pistils

Activity 1.5: Polyembryony in Citrus

On this page