Question

1. Differentiate between the different forms of nitrogenous waste including ammonia, urea, and uric acid. Focus on their toxicity and energy costs to produce their waste product.

2. Differentiate between intracellular and extracellular digestion. For extracellular digestion, include information to compare those animals with a simple body plan and single opening to the digestive cavity to those having an alimentary canal.

Answer 1

1.

FEATURES	AMMONIA	UREA	URIC ACID
TOXICITY	Highly toxic in nature	Moderately toxic	Not very toxic
ENERGY COSTS	Requires less energy for production	3 ATP molecules	Energetically costly
EXCRETED BY	Mainly by aquatic invertebrates	Excreted by amphibians and mammals including humans	Excreted by insects, birds and reptiles.

2.

INTRACELLULAR DIGESTION	EXTRACELLULAR DIGESTION
Occurs in protozoans or unicellular organisms	Occurs in bacteria, fungi and the organisms that have alimentary canals like higher organisms(birds, reptiles and mammals)
Food vacuoles are present where this digestion occurs	Occurs outside the cell and in the alimentary canals that have the lumen
Involvement of vescicles and lysosymes are secreted into the vacuoles for digestion and the undigested food is excreted by exocytosis	Organs and glands are involved in this case where the various enzymes are secreted for digestion.