A difficulty in fossil comparisons is that the fossil may be from: a large plant or animal an old plant or animal an extinct plant or animal

an extinct plant or animal

Explanation:

Fossils of an animal or plant refers to its preserved or mineralized remains. Fossils have proven to be an integral part of tracing life back. Among the very many usefulness of keeping fossil records of plant and animals, one of them is discovering the evolutionary relationships between these organisms.

Fossils of plants or animals are compared with that of a present organism to discover how related they are. However, a difficulty that arises during this comparative procedure is that the fossils about to be compared may be from an extinct plant or animal.

enzyme active site and substrate specificity

enzymes bind with chemical reactants called substrates. there may be one or more substrates for each type of enzyme, depending on the particular chemical reaction. in some reactions, a single-reactant substrate is broken down into multiple products