Why do heterotrophic organisms need to digest food?

Correct answer: Because large food molecules must be changed into small soluble molecules

The governing concept is digestion followed by absorption. Heterotrophic organisms obtain ready-made food, but nutrients such as starches, proteins, and fats are often large, complex molecules that cannot cross the intestinal lining efficiently. Enzymes break them into smaller soluble substances—sugars, amino acids, and fatty acids with glycerol—which can be absorbed and used for energy, growth, and repair. Therefore option A is correct; the other choices confuse digestion with plant transport or gas exchange.