The tiny air sacs in the lungs are surrounded by:

Here are the answers to your questions:

13. Which respiratory condition is primarily caused by long-term smoking?
The options for this question are incomplete in the image. Only option A. Asthma is visible.

• While smoking can exacerbate asthma, it is not its primary cause. Common respiratory conditions primarily caused by long-term smoking include chronic bronchitis and emphysema, which are often grouped under Chronic Obstructive Pulmonary Disease (COPD). Without the other options, a definitive answer cannot be selected.

14. The tiny air sacs in the lungs are surrounded by:
The correct option is B.

• The alveoli, which are the tiny air sacs where gas exchange occurs, are surrounded by a dense network of capillaries to facilitate the diffusion of oxygen and carbon dioxide between the air and the blood.
• The answer is B. Capillaries

15. What is the correct pathway of air through the respiratory system?
The correct option is B.

• Air typically enters through the nose, passes through the pharynx (throat), then the larynx (voice box), down the trachea (windpipe), into the bronchi, and finally reaches the alveoli in the lungs.
• The answer is B. Nose $\to$ pharynx $\to$ larynx $\to$ trachea $\to$ bronchi $\to$ alveoli

16. Which disease is caused by the Mycobacterium tuberculosis bacteria?
The correct option is B.

• Mycobacterium tuberculosis is the specific bacterium responsible for causing the infectious disease known as tuberculosis.
• The answer is B. Tuberculosis

17. The amount of air that can be forcefully exhaled after a maximum inhalation is called:
The correct option is C.

• Vital capacity is the maximum amount of air a person can exhale from the lungs after a maximum inhalation.
• The answer is C. Vital capacity

18. What is the primary function of surfactant in the alveoli?
The correct option is A.

• Pulmonary surfactant is a substance that reduces the surface tension of the fluid lining the alveoli, which prevents the tiny air sacs from collapsing during exhalation.
• The answer is A. Prevents alveolar collapse

19. Which of these is NOT a function of the respiratory system?
The correct option is C.

• The respiratory system is primarily involved in gas exchange, regulating blood pH by controlling carbon dioxide levels, and producing sound through the vocal cords in the larynx. Hormone production is a function of the endocrine system.
• The answer is C. Hormone production

20. During exercise, breathing rate increases primarily due to:
The correct option is B.

• During exercise, increased metabolic activity produces more carbon dioxide. This rise in blood carbon dioxide levels (and the resulting decrease in blood pH due to increased hydrogen ions) is the primary stimulus that triggers an increase in breathing rate to expel the excess CO2.
• The answer is B. Increased carbon dioxide levels in blood