Question 6 - Case Based Questions (MCQ) - Chapter 6 Class 10 - Life Processes

Read the given passage and answer any of the four  questions from (a) to (e).  

Oxygen-rich blood from the lungs comes to the  thin-walled upper chamber of the heart on the left. The left upper chamber (A) then relaxes. It then contracts and the blood is allowed to enter the next  chamber (B), as it expands. When the muscular left lower chamber of the heart contracts the blood is  pumped out to the body via the aorta.  

Deoxygenated blood reaches from the body to the  upper chamber on the right side of the heart (C) and it expands. As this part contracts, the corresponding  lower chamber (D) dilates. This transfers the blood  to the right ventricle, which in turn pumps it to the  lungs for oxygenation.  

(a) Which of these correctly represents the label A, B,  C and D in the above passage?  

(i) A- Left atrium, B- Left Ventricle, C- Right  atrium, D- Right ventricle  

(ii) A- Right ventricle, B- Left atrium, C- Left  Ventricle, D- Right atrium  

(iii) A- Right atrium, B- Right ventricle, C- Left  atrium, D- Left ventricle  

(iv) A- Left ventricle, B- Right atrium, C- Right  ventricle, D- Left atrium  

Answer

• The oxygenated blood enters the heart from the left atrium and enters the left ventricle which pumps into the body . 
• After deoxygenation , it goes to the right atrium , and then to the right ventricle , which sends it for purification through the pulmonary veins to the lungs . 
• It returns oxygenated to the left atrium.

Thus, the correct answer is:

(a) A- Left atrium, B- Left Ventricle, C- Right atrium,  D- Right ventricle 

(b) Which chambers of the human heart contain blood?   

(i) A and B 

(ii) A and C  

(iii) C and B 

(iv) C and D  

Answer

A (Left atrium) and B (Left ventricle) contain  oxygenated blood from the lungs.

Thus, the correct answer is (i)

(c) What is the correct route of blood in a human?  

(A) A → B → Lungs → C → D  

(B) A → B → D → C → Lungs  

(C) C → D → B → A → Lungs  

(D) C → D → Lung → A → B  

Answer

• The oxygenated blood enters the heart from the lungs.
• Blood enters the left atrium and goes to the left ventricle which pumps the blood  into the body . 
• After deoxygenation , it goes to the right atrium , and then to the right ventricle , which sends it for purification through the pulmonary veins to the lungs . 
• It returns oxygenated to the left atrium.

(iv) C (Right atrium) → D (Right ventricle) → Lungs  → A (Left atrium) → B (Left ventricle).

(d) What prevents backflow of blood inside the heart  during contraction?  

(i) Valves in heart  

(ii) Thick muscular walls of ventricles  

(iii) Thin walls of atria  

(iv) All of the above  

Answer

Valves are flap-like structures that prevent the backflow of blood inside the heart during contraction of heart chambers  (atria or ventricles).

So, the correct answer is (i) valves in heart

(e) Assertion (A): Human heart does not allow mixing of oxygen rich blood with carbon dioxide rich  blood.  

Reason (R): Human heart has different chambers. 

(i) Both A and R are true and R is the correct  explanation of the assertion.  

(ii) Both A and R are true but R is not the correct  explanation of the assertion.  

(iii) A is true but R is false.  

(iv) A is false but R is true.  

Answer

Due to the presence of different chamber s of heart i.e. atria and ventricles , the mixing of oxygenated and deoxygenated blood is prevented.

Hence,

• The assertion is True
• The reason is True
• Reason is the correct explanation for the assertion

So, the correct answer is (i).