Question

Given below are certain situations. Analyse and describe what would happen when:
(i) Spores are liberated from blob-like structures of the bread mould?
(ii) Leaves of bryophyllum fall on wet soil?
(iii) A pollen from different species land on the stigma of totally unrelated species?
(iv) Copper-T is placed in the uterus of a human female?
(v) Spirogyra breaks into smaller fragments upon maturation?

Hint:

(i) Bread mould spores \(\Rightarrow\) dispersal and new colonies. (ii) Bryophyllum leaves \(\Rightarrow\) plantlets from marginal buds. (iii) Unrelated pollen \(\Rightarrow\) rejection by stigma. (iv) Copper-T \(\Rightarrow\) contraception via spermicidal action. (v) Spirogyra fragments \(\Rightarrow\) each grows into new filament.

Answer 1

Part (i): Spores liberated from blob-like structures of bread mould
Step 1: Understand the structure.
Bread mould (Rhizopus) reproduces asexually by forming spores in blob-like structures called sporangia (singular: sporangium). These sporangia are borne on specialized hyphae called sporangiophores.
Step 2: Process of spore liberation.
When mature, the sporangium ruptures or bursts open, releasing thousands of tiny, lightweight spores into the air.
Step 3: What happens after liberation.

• Dispersal: Spores are carried away by air currents, water, or other agents to new locations.
• Germination: When spores land on a suitable substrate (moist bread, food, organic matter) with adequate moisture and nutrients, they germinate.
• New mycelium formation: Each spore produces a germ tube that develops into a new hypha, eventually forming a new mycelium (colony) of bread mould.
• Rapid colonization: Since thousands of spores are released, bread mould can quickly colonize new food sources.

Step 4: Final answer.
\[ \boxed{\text{Spores are dispersed by air and germinate on suitable substrates to form new bread mould colonies.}} \] Part (ii): Leaves of Bryophyllum fall on wet soil
Step 1: Understand Bryophyllum reproduction.
Bryophyllum (also called Kalanchoe) is a plant that reproduces asexually through vegetative propagation. Its leaves have special structures called epiphyllous buds or adventitious buds along the leaf margins.
Step 2: Process when leaves fall on wet soil.

• Rooting: When a mature leaf falls on moist soil, the buds along the leaf margins come in contact with soil.
• Germination of buds: Each bud develops into a new plantlet, producing roots that go into the soil and shoots that grow upward.
• Independent plants: Each plantlet eventually becomes an independent new plant, using nutrients from the parent leaf initially.
• Clonal propagation: All new plants are genetically identical to the parent plant (clones).

Step 3: Final answer.
Adventitious buds on leaf margins germinate, producing multiple new plantlets that grow into independent Bryophyllum plants. Part (iii): Pollen from different species lands on stigma of totally unrelated species
Step 1: Understand pollen-stigma interaction.
For successful pollination and fertilization, the pollen grain must be compatible with the stigma. Plants have mechanisms to recognize and accept or reject pollen.
Step 2: What happens in this situation.

• Pollen rejection: The stigma recognizes the pollen as foreign (from a different/unrelated species) through chemical signals.
• No germination: The pollen grain either fails to germinate or the pollen tube fails to grow.
• No fertilization: Since the pollen tube cannot reach the ovule, fertilization does not occur.
• No seed formation: No seeds or fruits are produced from this pollination event.
• Reproductive isolation: This mechanism maintains species boundaries and prevents hybridization between unrelated species.

Step 3: Exception (rare cases).
In very rare cases, if the species are closely related, hybridization might occur, but for totally unrelated species, it is impossible.
Step 4: Final answer.
The pollen grain is rejected by the stigma due to incompatibility. It does not germinate, and no fertilization occurs. Part (iv): Copper-T is placed in the uterus of a human female
Step 1: Understand Copper-T.
Copper-T (Intrauterine Device - IUD) is a small T-shaped contraceptive device made of plastic and copper, inserted into the uterus by a healthcare provider.
Step 2: Mechanism of action.

• Spermicidal effect: Copper ions released by the device are toxic to sperm, reducing their motility and ability to fertilize the egg.
• Inhibition of sperm movement: Copper alters the uterine and tubal fluid, making it unfavorable for sperm survival and movement.
• Prevention of implantation: It causes changes in the endometrium (uterine lining), making it unsuitable for implantation of a fertilized egg.
• Inflammatory response: It induces a mild sterile inflammatory reaction in the uterus, which is hostile to sperm and zygote.

Step 3: Result of placement.

• Effective contraception (pregnancy prevention)
• Long-term protection (5-10 years depending on type)
• Reversible fertility (fertility returns after removal)
• May cause heavier menstrual bleeding or cramps in some women

Step 4: Final answer.
Copper-T prevents pregnancy by releasing copper ions that kill sperm and prevent implantation. It provides long-term, reversible contraception. Part (v): Spirogyra breaks into smaller fragments upon maturation
Step 1: Understand Spirogyra reproduction.
Spirogyra is a filamentous green alga that reproduces asexually by fragmentation, as well as sexually by conjugation.
Step 2: Process of fragmentation.

• Natural fragmentation: Upon maturation, the filament of Spirogyra breaks into smaller pieces or fragments due to mechanical injury, aging, or environmental factors.
• Each fragment grows: Each fragment contains one or more cells and is capable of independent growth.
• Cell division: Cells in the fragment undergo division and elongation, forming new filaments.
• New individuals: Each fragment develops into a complete, independent Spirogyra filament.

Step 3: Advantages of fragmentation.

• Rapid multiplication (asexual reproduction)
• All offspring are genetically identical (clones)
• Helps in colonizing new areas quickly

Step 4: Final answer.
Each fragment grows into a new independent Spirogyra filament through cell division, leading to asexual reproduction and population increase.