Pepsin and trypsin are two of the digestive enzymes that break down protein. A group of students studied the pH requirements of these enzymes. The graph shows the results.  The students found that pepsin functions best in an acidic environment and trypsin functions best in a neutral environment.
Based on their observations, pepsin most likely aids in digestion in which part of the human body?

• Large Intestines (colon)
• Small Intestines
• Mouth
• Stomach

What two human systems work together to provide the body cells with a constant supply of oxygen while removing carbon dioxide waste products?

• Nervous and Endocrine
• Muscular and Skeletal
• Respiratory and Circulatory
• Excretory and Integumentary

When a person is suddenly cut by a sharp object, a nervous impulse is sent along a sensory neuron to the spinal cord. The impulse is immediately transmitted through motor neurons to produce a response.
Which of the following correctly identifies and describes this response?

• It is a conditioned response that occurs only to prevent injury.
• It is a learned response that does not occur in infants and small children.
• It is a voluntary response that is initiated only after the impulse has been carried to the relevant area of the brain.
• It is a reflex response that causes various muscles to contract in order to move away from an object.

H1N1 flu is highly contagious viral infection caused by the influenza A (H1N1) virus. The symptoms of H1N1 flu are listed in the box below. An antiviral agent administered within 48 hours of the appearance of symptoms can reduce the severity of the illness.  
Why is it important to administer the antiviral agent to an infected person within 48 hours of the appearance of symptoms?

• The H1N1 virus is dormant in cells.
• The H1N1 virus replicates quickly.
• The H1N1 virus does not mutate.
• The H1N1 virus is transmitted through a vector host, such as a mosquito.

Toxoplasmosis is an infection producing brain lesions caused by the parasitic protozoan Toxoplasma gondii. Mice with their gonads (reproductive organs) removed are more resistant to T. gondii and develop very few lesions on their brain tissue. The graph shows the results of a scientific study of normal adult mice infected with T. gondii.
Which systems most likely interact and cause the severity of infections to vary?

• Muscular and Skeletal
• Immune and Endocrine
• Excretory and Respiratory
• Nervous and Integumentary

A person infected with the human immunodeficiency virus (HIV) may not have any symptoms for a period of time.
During this period the virus affects the body by doing which of the following?

• The virus damages immune cells while using their machinery to produce copies of itself.
• The virus produces toxins that weaken the immune cells and prevent them from reproducing.
• The virus uses nutrients meant for immune cells to fuel its own cellular respiration.
• The virus changes the identity of the nucleotides of immune cells to prevent the immune system from functioning normally.

The human digestive system is approximately 900 cm long. Food is moved through the digestive tract primarily by –

• Bile produced by the pancreas
• The enzymes amylase and pepsin
• Hydrochloric acid in the stomach
• Smooth Muscular contractions

The diagram shows the internal feedback mechanism that maintains blood-calcium (Ca2+) homeostasis.
If a person has a blood calcium (Ca2+) level of 8 mg/100 mL of blood, which of the following mechanisms does the body use to maintain blood-calcium homeostasis?

• The kidneys take up more Ca2+ and release vitamin D.
• The bones release Ca2+.
• The intestines increase reabsorption of Ca2+.
• All of the above.

Severe acute respiratory syndrome (SARS) is an illness caused by a coronavirus. Symptoms including a high fever, headaches, and body aches typically occur two to seven days after infection by the virus. SARS is more serious in elderly patients.
This information suggests that the reproductive cycle of SARS virus is – 

• Lytic, because the virus causes respiratory illness
• Lysogenic, because the virus is a coronavirus
• Lytic, because of the quick onset of symptoms after infection
• Lysogenic, because the virus primarily affects older people

Which of the following functions at the same organizational level as the kidney in the human excretory system?

• Skeleton
• Urinary bladder
• Epithelial tissue
• A squamous cell