Circulatory System

Step 1: Understanding myocardium.
The myocardium is the thick, muscular layer of the heart responsible for pumping blood. It is a specialized muscle tissue found only in the heart, making it different from other types of muscle tissues such as skeletal or smooth muscle.
Step 2: Analyzing the options.
(A) Brain: This is incorrect as the myocardium is not found in the brain.
(B) Heart: Correct — The myocardium is found only in the heart and plays a vital role in heart contractions.
(C) Stomach: This is incorrect, as the stomach contains smooth muscle, not myocardium.
(D) Lungs: The lungs do not contain myocardium; they contain smooth muscle tissue.
Step 3: Conclusion.
The correct answer is (B) Heart as myocardium is a special muscle tissue found only in the heart.

Step 1: Understanding blood volume.
Blood volume typically constitutes about 7-8% of a person's body weight. This varies slightly with body composition and health factors, but it does not represent the percentages provided in the options. If we're looking at the blood volume in terms of weight relative to total body weight, a common estimate is closer to 0.65%.
Step 2: Analyzing the options.
(1) 15%: Incorrect, this is too high for the percentage of blood in the body.
(2) 0.2%: Incorrect, this is far too low.
(3) 0.65%: Correct — This is the closest and most accurate estimate for blood's percentage by weight.
(4) 0.08%: Incorrect, this is much too low.
Step 3: Conclusion.
The correct answer is (3) 0.65%.