In a cockroach, how many alary muscles are present in the heart, expressed as the total number of paired alary muscles supporting the dorsal blood vessel?

Introduction / Context:
Invertebrate anatomy, especially of common laboratory specimens like cockroach, is a favourite topic in biology based general knowledge. Students are often asked to memorise the number and arrangement of specific structures, such as heart chambers, segments, and associated muscles. This question focuses on the alary muscles of cockroach, which help suspend and support the dorsal blood vessel and assist in circulation. Knowing the correct number of paired alary muscles is a standard fact required in many exams.

Given Data / Assumptions:

• The organism is the cockroach, a commonly studied insect.
• The structure in question is the alary muscles associated with the heart or dorsal blood vessel.
• Options include several possible counts, such as 12 individual muscles, 12 pairs, 6 total, and 24 pairs.
• We assume the typical adult cockroach as described in standard zoology textbooks.

Concept / Approach:
The cockroach heart is a dorsal, elongated tube with multiple chambers. It is held in position beneath the dorsal body wall by fan shaped muscles called alary muscles. These muscles arise from the body wall and attach to the heart, helping to keep it suspended and assisting in the movement of haemolymph. Textbooks describe that a cockroach has 12 pairs of alary muscles, one pair per open heart chamber. Therefore, the correct way to express the number is 12 pairs, not 12 single muscles or any other count.

Step-by-Step Solution:
Step 1: Recall that the cockroach heart is divided into multiple chambers arranged in a series along the dorsal side. Step 2: Remember that each chamber is connected to the body wall by a pair of alary muscles, which support and suspend the heart. Step 3: From standard descriptions, note that there are 12 such chambers that have associated alary muscles. Step 4: Therefore, the total count is 12 pairs of alary muscles, which means 24 individual muscles but is usually written as 12 pairs. Step 5: Compare with the options and select the one that explicitly states 12 pairs of alary muscles as the correct anatomical detail.

Verification / Alternative check:
An easy verification is to connect the number of alary muscle pairs to the number of heart chambers in the cockroach. Diagrams in zoology practical manuals show 13 chambers in total, with the first chamber lacking alary muscles and the remaining 12 chambers having one pair each. This yields 12 pairs overall. Exam oriented summaries also directly state that cockroach has 12 pairs of alary muscles. This consistent portrayal across diagrams and text confirms that 12 pairs is the correct answer.

Why Other Options Are Wrong:
12 individual muscles is wrong because it undercounts by a factor of two and ignores the paired nature of these muscles. 6 alary muscles in total is incorrect and does not match any standard description of cockroach anatomy. 24 pairs of alary muscles is also wrong; while there are 24 individual muscles, they are organised as 12 pairs, not 24 pairs. These options either misrepresent the count or confuse individual muscles with paired units.

Common Pitfalls:
A common pitfall is mixing up individual muscle numbers with pairs, leading students to wrongly think of 24 as 24 pairs instead of 24 single muscles. Another mistake is to extend the count to all 13 chambers without remembering that the first chamber lacks alary muscle support. To avoid confusion, focus on the standard phrase used in textbooks: cockroach possesses 12 pairs of alary muscles. Memorising the phrase exactly as written helps ensure you choose the correct option in multiple choice questions.

Final Answer:
The correct choice is 12 pairs of alary muscles, which is the standard description of the number of alary muscles supporting the cockroach heart.