4/9 - Living Environment

The molecules represented in the diagram below can interact to cause a biochemical process to occur. Molecule A and molecule B most likely represent

• a nerve signal and a gene

• a receptor and a hormone

• a chromosome and an antigen

• a starch and an amino acid

Pneumocystis is an organism normally found in the human lungs that can cause pneumonia. It seldom causes problems in individuals with healthy immune systems. However, people with AIDS sometimes become seriously ill with pneumonia. This is most likely due to the fact that individuals with AIDS have

• inherited a tendency to contract pneumonia

• difficulty fighting off infections

• an allergy to this organism

• hormones that strengthen the infection

Rabbits have evolved strategies that get them through periods of time when there is little food. The diagram below represents essential life functions that rabbits need to perform. Which life function in the diagram could be eliminated without affecting an individual rabbit’s ability to survive when food is scarce?

• digestion

• excretion

• circulation

• reproduction