Question

Write a note on the following:
(i) Spore formation in Rhizopus
(ii) Seed germination

Hint:

In Rhizopus, sporangia play an essential role in reproduction, while seed germination ensures the continuation of plant life through suitable conditions.

Answer 1

(i) Spore Formation in Rhizopus:
Rhizopus is a type of fungus that reproduces both sexually and asexually. Asexual reproduction in Rhizopus occurs through the formation of spores called sporangia. The process of spore formation can be described as follows:
1. Formation of Sporangium: In Rhizopus, sporangia are formed at the tip of specialized hyphal branches known as sporangiophores. These hyphae grow upright from the mycelium (the fungal body).
2. Development of Sporangium: The sporangium develops as a spherical structure at the end of the sporangiophore. It contains hundreds of tiny spores, also called conidia.
3. Maturation and Release of Spores: As the sporangium matures, it fills with spores and the sporangium eventually bursts, releasing the spores into the surrounding environment. These spores are carried by air, water, or other mechanisms to new locations where they can germinate and form new Rhizopus colonies.
4. Germination of Spores: When a spore lands in a suitable environment with adequate moisture and nutrients, it germinates, giving rise to a new hypha that grows and forms a new mycelium. This allows the Rhizopus to spread and grow in different areas.
(ii) Seed Germination:
Seed germination is the process by which a seed develops into a new plant. It involves several stages that begin with the seed absorbing water and end with the emergence of the seedling. The main stages of seed germination are: 1. Water Absorption: The seed absorbs water from the environment, a process known as imbibition. This causes the seed to swell and activate the metabolic processes necessary for germination.
2. Activation of Enzymes: The absorbed water activates enzymes within the seed that begin to break down stored nutrients, such as starches, into simpler forms like sugars, which the seedling can use for energy.
3. Growth of Embryo: The embryo within the seed begins to grow. The radicle (embryonic root) is the first part of the plant to emerge, followed by the shoot (the stem and leaves).
4. Emergence of Seedling: The radicle penetrates the soil, anchoring the plant and allowing it to take up water and nutrients. The shoot pushes upward toward the surface, where it will develop leaves for photosynthesis.
5. Photosynthesis and Seedling Growth: Once the seedling emerges and the leaves begin to develop, the plant starts to carry out photosynthesis, producing its own food, and it continues to grow into a mature plant.
Conclusion:
- Spore formation in Rhizopus enables the fungus to spread quickly, as the spores are easily dispersed to new areas.
- Seed germination is a critical process for plant reproduction, marking the transition from a dormant seed to an actively growing plant. The success of this process depends on various environmental factors, including water, temperature, and light.