The correct option is (a).
Explanation
Waste removal in animals involves two distinct processes: excretion (removal of metabolic wastes produced by cells) and egestion (removal of undigested food residue). Various organs such as the lungs, kidneys, and liver play specific roles in maintaining the body's internal environment.
Statement-wise Analysis:
- Statement 1 is Correct: Carbon dioxide is a major metabolic waste product generated during cellular respiration. It is transported by the blood to the lungs, where it diffuses into the alveoli and is expelled from the body during exhalation.
- Statement 2 is Incorrect: The kidneys are responsible for filtering the blood to remove nitrogenous metabolic wastes (like urea and uric acid) and excess salts in the form of urine. Undigested food is not processed by the kidneys; it is eliminated from the body as faeces through the anus via the digestive tract.
- Statement 3 is Incorrect: The liver functions as a detoxification center. It converts toxic substances (such as ammonia) into less harmful forms (such as urea) or modifies drugs and toxins for excretion. It does not store toxic waste permanently; the processed wastes are released into the blood for kidney filtration or secreted into bile for elimination.
Key Takeaway:
Excretion deals with metabolic by-products (CO2, urea) removed by lungs and kidneys, while egestion deals with undigested food removed via the alimentary canal.