Which of the following describes a response to external stimuli

A. a person yawns when oxygen levels in the blood are low

B. a child becomes hyperactive due to a chemical imbalance

C. a boy sneezes when exposed to cat dander

D. A girl eats food when she is hungry

1. amino acid refers to the fundamental building block of proteins, comprising of an amino group and a carboxyl group.

2. catalyst refers to any substance, which increases the rate of chemical reaction without being used up in the reaction.

3. a complex molecule containing he genetic code is dna or deoxyribonucleic acid.

4. an enzyme refers to a molecule of protein, which is unique in accelerating up a particular chemical reaction in the biological systems.

5. nucleic acid refers to an sequence of sugars, phosphates, and nitrogenous bases, for example, dna and rna.

6. a protein refers to a large, composite organic molecule comprising of a huge number of amino acids associated together with the of peptide bonds.

7. rna refers to a nucleic acid that takes part in the production of proteins.

8. substrate refers to a compound, which takes part in a chemical reaction, and is chemically modified by the reaction.

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.  

answer; aerobic conditions; citric acid cycle (krebs cycle) electron transport chain;         anaerobic conditions; fermentation; both glycolysis;