The correct option is (a).
Explanation
Saprotrophic nutrition is a specific mode of heterotrophic nutrition wherein organisms obtain food from dead and decaying organic matter. This process involves the breakdown of complex organic substances into simpler forms outside the organism's body.
Statement-wise Analysis:
- Statement 1 is Correct: Saprotrophic nutrition is defined as the mode of nutrition in which organisms take in nutrients in solution form from dead and decaying matter. Organisms following this mode are called saprotrophs.
- Statement 2 is Incorrect: Fungi do not ingest solid dead matter directly. Instead, they secrete digestive juices (enzymes) onto the dead and decaying matter. These enzymes convert the solid matter into a solution (extracellular digestion), which the fungi then absorb.
- Statement 3 is Incorrect: Not all fungi are harmful. While some fungi cause food spoilage (e.g., bread mould) and diseases in plants and animals (e.g., rust in wheat, ringworm in humans), many are beneficial. For instance, mushrooms are consumed as food, yeast is used in the production of alcohol and bakery products, and Penicillium is used to produce antibiotics.
Key Takeaway:
Saprotrophs, such as fungi, utilize extracellular digestion by secreting enzymes onto dead matter before absorbing nutrients. Fungi play diverse roles, acting as both pathogens and beneficial agents in ecosystems and industry.