Class 10 Biology - How do Organisms Reproduce

Activities

Activity 7.1: Growth of Yeast and Bread Mould

Aim/Objective: To observe and compare the morphological characteristics of asexual reproduction in Saccharomyces and Rhizopus.

Materials Required:

10.0g Sucrose (Cane sugar)
1.0g Dry active yeast granules (Saccharomyces cerevisiae)
250 mL Conical flask with a cotton plug
1 Slice of preservative-free white bread
5 mL Sterile water in a spray bottle
Airtight transparent container
Compound microscope, slides, and 1% Methylene Blue stain

Procedure:

Yeast Culture: Dissolve 10g of sugar in 100mL of warm distilled water (30°C–32°C). Add 1g of yeast to 20mL of this solution in a conical flask. Plug with cotton and incubate at 30°C for 120 minutes.
Microscopy: Place 10µL of the yeast culture on a slide, add 5µL of Methylene Blue, and observe at 400x magnification.
Fungal Culture: Lightly spray the bread slice with sterile water. Place it in the airtight container and store in a dark, humid corner (RH > 80%) for 5 days at 25°C.
Observe the bread daily using a 10x magnifying glass to track mycelial expansion.

Scientific Note Yeast budding is an asymmetric mitotic process where the cell wall expands locally to form a daughter cell. In contrast, Rhizopus produces specialized upright hyphae called sporangiophores, which terminate in a columella and sporangium containing thousands of haploid spores.

Observation:

Yeast: Chains of budding cells (pseudomycelia) with distinct vacuoles.
Bread Mould: White cottony mycelium turning black as sporangia mature.

Explanation:

Yeast utilizes budding for rapid colonization in sugar-rich liquid media. Bread mould utilizes spore formation to survive environmental stress and achieve wide dispersal on solid substrates.

Conclusion:

Asexual reproduction strategies are optimized for the specific nutrient density and physical state of the environment.

Activity 7.3: Binary Fission in Amoeba

Aim/Objective: To analyze the stages of cytokinesis and karyokinesis in Amoeba proteus.

Materials Required:

Permanent slides of Amoeba (Vegetative state)
Permanent slides of Amoeba (Binary fission stages)
Compound microscope with 10x and 45x objectives
Camera lucida or drawing materials

Procedure:

Focus the vegetative Amoeba slide. Identify the nucleus, contractile vacuole, and pseudopodia.
Switch to the binary fission slide. Identify the Prophase (nuclear elongation) and Telophase (nuclear separation) stages.
Observe the formation of the cleavage furrow in the plasma membrane.
Measure the length-to-width ratio of the dividing cell compared to the vegetative cell.

Lab Best Practice When observing permanent slides, always start with the 10x objective to locate the specimen before switching to high power. Avoid using coarse adjustment with the 45x objective to prevent cracking the coverslip.

Observation:

The dividing nucleus appears as a "dumbbell" shape. The cytoplasm is constricted into two nearly equal volumes by an invaginating furrow.

Explanation:

Binary fission involves the replication of the single circular chromosome (or multiple chromosomes depending on the species) followed by the coordinated division of the nucleus (Karyokinesis) and then the cytoplasm (Cytokinesis). This results in two genetically identical clones.

Conclusion:

Binary fission is a precise geometric division that ensures genetic continuity in unicellular eukaryotes.

Activity 7.4: Identification of Spirogyra Filaments

Aim/Objective: To observe the structural simplicity and fragmentation capability of Spirogyra.

Materials Required:

Stagnant pond water sample with green "silk" filaments
1% Glycerine (as a mounting medium)
0.5% Iodine solution (to stain starch in pyrenoids)
Glass slides and coverslips

Procedure:

Tease out a few green filaments from the pond sample using a needle.
Place on a slide, add a drop of 0.5% Iodine, and wait 1 minute.
Add a drop of glycerine, apply a coverslip, and observe under 100x and 400x magnification.
Look for breaks in the filament and count the number of cells per fragment.

Scientific Note Spirogyra is characterized by its ribbon-like, spiral chloroplasts. The small dark spots within the chloroplast are pyrenoids, which are centers for starch synthesis and carbon fixation.

Observation:

Multicellular filaments with cells joined by transverse walls. Spiral chloroplasts are clearly visible. Iodine turns the pyrenoids dark blue/black.

Explanation:

Fragmentation occurs when the filament reaches a critical length or is physically disturbed. Because there is minimal cellular differentiation, any fragment containing at least one healthy cell can undergo repeated mitosis to regenerate the entire filament.

Conclusion:

Fragmentation is an effective reproductive strategy for multicellular organisms with low levels of tissue specialization.

Activity 7.5: Vegetative Propagation in Potato

Aim/Objective: To identify the role of axillary buds (eyes) in the asexual propagation of Solanum tuberosum.

Materials Required:

2 Fresh potatoes with active "eyes"
Sterile scalpel or knife
10% Sodium Hypochlorite (for surface sterilization of the knife)
Tray with 2cm layer of moist Vermiculite or Cotton
Labeling stickers

Procedure:

Surface-sterilize the knife with alcohol or dilute bleach.
Cut the potato into 4 segments:
- Segment A: Contains 2+ eyes.
- Segment B: Contains 1 eye.
- Segment C: Contains no eyes (internal pith only).
Place segments on moist vermiculite. Maintain at 20°C in the dark.
Check daily for 14 days and record the date of shoot emergence (sprouting).

Safety First Do not eat potatoes that have turned green or have large sprouts, as they contain high concentrations of Solanine, a toxic glycoalkaloid that can cause gastrointestinal and neurological distress.

Observation:

Segments A and B produce vigorous green shoots within 7–10 days. Segment C begins to rot without any signs of growth.

Explanation:

The potato tuber is a modified underground stem. The "eyes" are nodes containing dormant axillary buds. These buds contain meristematic cells that respond to moisture and warmth by initiating primary growth.

Conclusion:

Vegetative propagation is dependent on the presence of functional meristematic tissue (buds) in the storage organ.

Activity 7.6: Vegetative Propagation in Money Plant

Aim/Objective: To demonstrate the necessity of nodal meristems for adventitious root formation in Epipremnum aureum.

Materials Required:

Healthy Money Plant vine
Sharp scissors
3 Beakers (100 mL) filled with 80 mL distilled water
Marker

Procedure:

Cut the vine into 3 types of segments (approx. 5cm each):
- Type 1: Stem including a node and a leaf.
- Type 2: Stem including a node but the leaf removed.
- Type 3: Stem only (internodal region).
Place all segments in the water-filled beakers. Change the water every 48 hours to prevent algal growth.
Observe the base of the stems for 15 days.

Lab Best Practice Always make the cut at a 45° angle. This increases the surface area for water absorption and reduces the likelihood of the stem "sealing" itself before roots can emerge.

Observation:

Type 1 and Type 2 develop white, fleshy adventitious roots from the nodes. Type 3 segments darken and eventually decompose without root development.

Explanation:

Nodes contain clusters of undifferentiated cells (meristems) capable of differentiating into root or shoot tissue depending on environmental cues (Auxin gradients). The internode consists of differentiated vascular and ground tissue with no regenerative capacity.

Conclusion:

Stem cuttings must contain a node to serve as a viable propagule for vegetative reproduction.

Activity 7.7: Germination of Bengal Gram Seeds

Aim/Objective: To analyze the anatomy of a dicot seed (Cicer arietinum) and the sequence of embryo activation.

Materials Required:

20 High-quality Bengal gram seeds
100 mL Beaker with water
Petri dish with moist filter paper
Fine-tipped forceps and a hand lens

Procedure:

Soak 20 seeds in 50 mL water for 16 hours.
Transfer to a petri dish and maintain at 25°C for 24 hours.
Use forceps to carefully remove the softened seed coat (Testa).
Gently pry the two cotyledons apart to reveal the embryonal axis.
Identify the plumule (future shoot), radicle (future root), and the point of attachment (epicotyl/hypocotyl).

Scientific Note Bengal gram exhibits hypogeal germination, where the cotyledons remain below the soil surface while the epicotyl elongates. The cotyledons serve as the primary source of nutrients (protein and starch) for the developing axis until the first true leaves are formed.

Observation:

The radicle is the first structure to emerge through the micropyle. The cotyledons are thick and fleshy, storing nutrients for the embryo.

Explanation:

Germination begins with imbibition (water absorption), which activates enzymes like alpha-amylase to break down stored starch. This provides the energy required for the rapid cell division at the radicle and plumule tips.

Conclusion:

The seed is a highly evolved reproductive unit containing a dormant embryo and a localized nutrient reservoir designed for high-probability survival.

Class 10 Biology - How do Organisms Reproduce

Activities

Activity 7.1: Growth of Yeast and Bread Mould

Aim/Objective: To observe and compare the morphological characteristics of asexual reproduction in Saccharomyces and Rhizopus.

Materials Required:

10.0g Sucrose (Cane sugar)
1.0g Dry active yeast granules (Saccharomyces cerevisiae)
250 mL Conical flask with a cotton plug
1 Slice of preservative-free white bread
5 mL Sterile water in a spray bottle
Airtight transparent container
Compound microscope, slides, and 1% Methylene Blue stain

Procedure:

Yeast Culture: Dissolve 10g of sugar in 100mL of warm distilled water (30°C–32°C). Add 1g of yeast to 20mL of this solution in a conical flask. Plug with cotton and incubate at 30°C for 120 minutes.
Microscopy: Place 10µL of the yeast culture on a slide, add 5µL of Methylene Blue, and observe at 400x magnification.
Fungal Culture: Lightly spray the bread slice with sterile water. Place it in the airtight container and store in a dark, humid corner (RH > 80%) for 5 days at 25°C.
Observe the bread daily using a 10x magnifying glass to track mycelial expansion.

Observation:

Yeast: Chains of budding cells (pseudomycelia) with distinct vacuoles.
Bread Mould: White cottony mycelium turning black as sporangia mature.

Explanation:

Yeast utilizes budding for rapid colonization in sugar-rich liquid media. Bread mould utilizes spore formation to survive environmental stress and achieve wide dispersal on solid substrates.

Conclusion:

Asexual reproduction strategies are optimized for the specific nutrient density and physical state of the environment.

Activity 7.3: Binary Fission in Amoeba

Aim/Objective: To analyze the stages of cytokinesis and karyokinesis in Amoeba proteus.

Materials Required:

Permanent slides of Amoeba (Vegetative state)
Permanent slides of Amoeba (Binary fission stages)
Compound microscope with 10x and 45x objectives
Camera lucida or drawing materials

Procedure:

Focus the vegetative Amoeba slide. Identify the nucleus, contractile vacuole, and pseudopodia.
Switch to the binary fission slide. Identify the Prophase (nuclear elongation) and Telophase (nuclear separation) stages.
Observe the formation of the cleavage furrow in the plasma membrane.
Measure the length-to-width ratio of the dividing cell compared to the vegetative cell.

Observation:

The dividing nucleus appears as a "dumbbell" shape. The cytoplasm is constricted into two nearly equal volumes by an invaginating furrow.

Explanation:

Binary fission involves the replication of the single circular chromosome (or multiple chromosomes depending on the species) followed by the coordinated division of the nucleus (Karyokinesis) and then the cytoplasm (Cytokinesis). This results in two genetically identical clones.

Conclusion:

Binary fission is a precise geometric division that ensures genetic continuity in unicellular eukaryotes.

Activity 7.4: Identification of Spirogyra Filaments

Aim/Objective: To observe the structural simplicity and fragmentation capability of Spirogyra.

Materials Required:

Stagnant pond water sample with green "silk" filaments
1% Glycerine (as a mounting medium)
0.5% Iodine solution (to stain starch in pyrenoids)
Glass slides and coverslips

Procedure:

Tease out a few green filaments from the pond sample using a needle.
Place on a slide, add a drop of 0.5% Iodine, and wait 1 minute.
Add a drop of glycerine, apply a coverslip, and observe under 100x and 400x magnification.
Look for breaks in the filament and count the number of cells per fragment.

Observation:

Multicellular filaments with cells joined by transverse walls. Spiral chloroplasts are clearly visible. Iodine turns the pyrenoids dark blue/black.

Explanation:

Fragmentation occurs when the filament reaches a critical length or is physically disturbed. Because there is minimal cellular differentiation, any fragment containing at least one healthy cell can undergo repeated mitosis to regenerate the entire filament.

Conclusion:

Fragmentation is an effective reproductive strategy for multicellular organisms with low levels of tissue specialization.

Activity 7.5: Vegetative Propagation in Potato

Aim/Objective: To identify the role of axillary buds (eyes) in the asexual propagation of Solanum tuberosum.

Materials Required:

2 Fresh potatoes with active "eyes"
Sterile scalpel or knife
10% Sodium Hypochlorite (for surface sterilization of the knife)
Tray with 2cm layer of moist Vermiculite or Cotton
Labeling stickers

Procedure:

Surface-sterilize the knife with alcohol or dilute bleach.
Cut the potato into 4 segments:
- Segment A: Contains 2+ eyes.
- Segment B: Contains 1 eye.
- Segment C: Contains no eyes (internal pith only).
Place segments on moist vermiculite. Maintain at 20°C in the dark.
Check daily for 14 days and record the date of shoot emergence (sprouting).

Observation:

Segments A and B produce vigorous green shoots within 7–10 days. Segment C begins to rot without any signs of growth.

Explanation:

The potato tuber is a modified underground stem. The "eyes" are nodes containing dormant axillary buds. These buds contain meristematic cells that respond to moisture and warmth by initiating primary growth.

Conclusion:

Vegetative propagation is dependent on the presence of functional meristematic tissue (buds) in the storage organ.

Activity 7.6: Vegetative Propagation in Money Plant

Aim/Objective: To demonstrate the necessity of nodal meristems for adventitious root formation in Epipremnum aureum.

Materials Required:

Healthy Money Plant vine
Sharp scissors
3 Beakers (100 mL) filled with 80 mL distilled water
Marker

Procedure:

Cut the vine into 3 types of segments (approx. 5cm each):
- Type 1: Stem including a node and a leaf.
- Type 2: Stem including a node but the leaf removed.
- Type 3: Stem only (internodal region).
Place all segments in the water-filled beakers. Change the water every 48 hours to prevent algal growth.
Observe the base of the stems for 15 days.

Lab Best Practice Always make the cut at a 45° angle. This increases the surface area for water absorption and reduces the likelihood of the stem "sealing" itself before roots can emerge.

Observation:

Type 1 and Type 2 develop white, fleshy adventitious roots from the nodes. Type 3 segments darken and eventually decompose without root development.

Explanation:

Nodes contain clusters of undifferentiated cells (meristems) capable of differentiating into root or shoot tissue depending on environmental cues (Auxin gradients). The internode consists of differentiated vascular and ground tissue with no regenerative capacity.

Conclusion:

Stem cuttings must contain a node to serve as a viable propagule for vegetative reproduction.

Activity 7.7: Germination of Bengal Gram Seeds

Aim/Objective: To analyze the anatomy of a dicot seed (Cicer arietinum) and the sequence of embryo activation.

Materials Required:

20 High-quality Bengal gram seeds
100 mL Beaker with water
Petri dish with moist filter paper
Fine-tipped forceps and a hand lens

Procedure:

Soak 20 seeds in 50 mL water for 16 hours.
Transfer to a petri dish and maintain at 25°C for 24 hours.
Use forceps to carefully remove the softened seed coat (Testa).
Gently pry the two cotyledons apart to reveal the embryonal axis.
Identify the plumule (future shoot), radicle (future root), and the point of attachment (epicotyl/hypocotyl).

Observation:

The radicle is the first structure to emerge through the micropyle. The cotyledons are thick and fleshy, storing nutrients for the embryo.

Explanation:

Germination begins with imbibition (water absorption), which activates enzymes like alpha-amylase to break down stored starch. This provides the energy required for the rapid cell division at the radicle and plumule tips.

Conclusion:

The seed is a highly evolved reproductive unit containing a dormant embryo and a localized nutrient reservoir designed for high-probability survival.

Class 10 Biology - How do Organisms Reproduce

Class 10 Biology - How do Organisms Reproduce

Activities

Activity 7.1: Growth of Yeast and Bread Mould

Activity 7.3: Binary Fission in Amoeba

Activity 7.4: Identification of Spirogyra Filaments

Activity 7.5: Vegetative Propagation in Potato

Activity 7.6: Vegetative Propagation in Money Plant

Activity 7.7: Germination of Bengal Gram Seeds

On this page

Class 10 Biology - How do Organisms Reproduce

Class 10 Biology - How do Organisms Reproduce

Activities

Activity 7.1: Growth of Yeast and Bread Mould

Activity 7.3: Binary Fission in Amoeba

Activity 7.4: Identification of Spirogyra Filaments

Activity 7.5: Vegetative Propagation in Potato

Activity 7.6: Vegetative Propagation in Money Plant

Activity 7.7: Germination of Bengal Gram Seeds

On this page