Question

Miguel is evaluating two claims that he read about animal systems. Both claims are made by reliable sources.

Claim 1: No animal can make the enzymes that are necessary for the digestion of cellulose.

Claim 2: Cattle, goats, sheep, and other ruminants are able to digest grasses, which are mostly cellulose.

Which additional statement is most useful for evaluating the two claims?

A. Ruminants digest cellulose without the use of enzymes.
B. Ruminants have flat teeth that are ideal for grinding plant matter.
C. Symbiotic microorganisms in the ruminants make the enzymes for digesting cellulose.
D. Symbiotic microorganisms in the ruminants remove cellulose from grasses without digesting it.

Answer 1

Answer: c.

Explanation: Grass is mainly composed of water and lignin, a woody protein that is common in the cell walls of plants, according to ChemistryisLife.com Lignin can be hard to break down by human stomachs. Not only that, but the lignin in food can actively inhibit the access nutritional benefits of other types of digestible fiber, such as cellulos, according to a 2001 study in the Journal of Range Management(opens in new tab).

Animals such as cows, on the other hand, have a specialized stomach with four chambers to aid in the digestion of grass (a process called rumination). This helps them access the starch and cellulose in grass, even when the lignin takes much longer to break down, according to "Tropical Dairy Farming: Feeding Management for Small-Holder Dairy Farmers n the Humid Tropics" (Landlinks Press, 2005).

Aside from the digestion issues, a second problem with grass as a food source is the mastication. Your dentist would not be pleased; grass contains a lot of silica(opens in new tab), an abrasive which quickly wears down teeth. Grazing animals have teeth that are adapted to continually grow, replacing the worn tooth surfaces quickly, according to the Burke Museum(opens in new tab).