The correct option is (c) 2 and 3 only.
Explanation
Photosynthesis is the physicochemical process by which green plants use light energy to synthesize organic compounds. The immediate product of photosynthesis is glucose, which is often converted into starch for storage within plant tissues. Consequently, the presence of starch serves as an indicator that photosynthesis has taken place.
Statement-wise Analysis
- Statement 1 is Incorrect. The presence of starch in leaves is evidence that photosynthesis has occurred. During photosynthesis, plants produce glucose, which is polymerized into starch. Therefore, finding starch in a leaf indicates the occurrence of photosynthesis, not its absence.
- Statement 2 is Correct. Starch is a complex carbohydrate (polysaccharide) synthesized by plants. It serves as the primary storage form of energy in plants, analogous to glycogen in animals.
- Statement 3 is Correct. Iodine solution is the standard reagent used to test for the presence of starch. When iodine comes into contact with starch, it forms a complex that turns the solution a characteristic blue-black color. This reaction is widely used in laboratory experiments to demonstrate photosynthesis.
Key Takeaway: Starch is the stored carbohydrate product of photosynthesis in plants. Its presence is experimentally verified using the iodine test, which yields a blue-black color.