Which one of the following statements about the human vascular system and blood volume is NOT correct?

Introduction / Context:
Questions about the vascular system often test factual knowledge of blood volume, blood cell life span, and general properties of blood as a connective tissue. This item asks you to identify the statement that is NOT correct. That means three statements should be reasonably accurate according to standard physiology, and one should contain an incorrect or misleading fact. Understanding normal blood volume and basic characteristics of blood is important for both general science and medical entrance preparation.

Given Data / Assumptions:
– The topic is the human vascular system and blood in a healthy adult.
– Statements mention red blood cell life span, percentage of body weight formed by blood, description of blood as vascular connective tissue, and total blood volume in litres.
– We assume average values used in standard textbooks, allowing for small variation but not large numerical errors.
– The task is to find which one statement is factually incorrect or most inconsistent with accepted reference values.

Concept / Approach:
In an average adult, total blood volume is about 5 to 6 liters, which corresponds to roughly 7 to 8 percent of body weight. Red blood cells have a life span of about 120 days, and some books give a range around this value, such as 110 to 120 days, so a description of 115 to 120 days fits within a reasonable approximation. Blood is classified as a vascular connective tissue because it consists of cells suspended in a fluid matrix called plasma and circulates through vessels. Although blood itself is red and lymph is sometimes called a white connective tissue, the phrase highlighting white and red vascular connective tissue is conceptually acceptable as a reference to these fluid tissues. However, stating that there are about 6.8 liters of blood in an average healthy adult clearly exceeds the standard average, which is closer to 5 to 6 liters. That makes the statement about 6.8 liters the best choice as the incorrect one.

Step-by-Step Solution:
Step 1: Remember that the average blood volume of a healthy adult is about 5 to 6 liters, not close to 7 liters. Step 2: Compare this to the statement, There are about 6.8 liters of blood in an average healthy adult, and see that it is outside the usual range. Step 3: Review that blood is about 7 to 8 percent of body weight, which matches common physiology facts, so that statement is acceptable. Step 4: Recall that red blood cell life span in humans is usually given as approximately 120 days, so a range of 115 to 120 days is a reasonable approximation. Step 5: Conclude that the clearly incorrect statement is the one giving total blood volume as about 6.8 liters in an average adult.

Verification / Alternative check:
If you consult any standard physiology or biology text, you will find tables listing normal blood volume as approximately 70 to 80 millilitres per kilogram of body weight. For a person weighing 70 kilograms, this gives about 4.9 to 5.6 liters of blood, which supports the typical 5 to 6 liter figure. Texts also describe blood forming around 7 to 8 percent of total body weight and confirm the approximate 120 day life span of red blood cells. This independent verification from reference values makes it clear that the statement claiming 6.8 liters as an average value is the one that does not match standard data.

Why Other Options Are Wrong:
Life span of a human red blood cell is about 115 to 120 days: This aligns well with the commonly cited life span of about 120 days, so it is essentially correct.
The vascular system forms about 7 to 8 percent of total body weight: This reflects the usual estimate of blood volume as a percentage of body mass, so it is accurate for exam purposes.
Blood is white or red vascular connective tissue: In basic classification, blood and lymph are grouped as vascular connective tissues, so this phrasing is acceptable even if simplified, and therefore not the incorrect statement targeted by the question.

Common Pitfalls:
Students often focus only on memorising single numbers and may not appreciate normal ranges. Some may assume that a larger number sounds more impressive and therefore more correct, leading them to accept 6.8 liters without checking it against the standard 5 to 6 liter reference. Others may be distracted by wording and think the phrase about white or red vascular connective tissue is wrong, without considering that blood and lymph are both fluid connective tissues. To avoid these mistakes, always compare numerical statements with typical textbook values and remember that exam questions often use slightly exaggerated numbers to create incorrect options.

Final Answer:
The incorrect statement about the human vascular system and blood volume is There are about 6.8 liters of blood in an average healthy adult.