Q.Write the features that distinguish between the two
a. Plasma and Serum
b. Open and closed circulatory system
c. Sino-atrial node and Atrio-ventricular node

a. Plasma is the whole fluid matrix of blood, including the clotting factors; serum is what remains once these clotting factors have been removed from plasma.

b. In an open circulatory system (arthropods, molluscs), the heart pumps blood into vessels that empty into open sinuses or body cavities, bathing the tissues directly; in a closed circulatory system (annelids, chordates), blood stays confined within a closed network of vessels throughout its journey, allowing its flow to be regulated far more precisely. …

a. Plasma and Serum. Plasma is the full fluid matrix of blood, carrying water, proteins (including the clotting factors such as fibrinogen), minerals and dissolved nutrients. Serum is simply plasma with its clotting factors removed — the fluid that remains once the blood has been allowed to clot and the clot (containing the fibrin and trapped cells) has been separated out.

b. Open and closed circulatory system. In an open circulatory system, found in arthropods and molluscs, the heart pumps blood into large vessels that empty into open spaces or body cavities called sinuses, so the blood bathes the tissues directly rather than staying confined to vessels. In a closed circulatory system, found in annelids and chordates, the blood pumped by the heart stays within a closed network of vessels throughout its journey — an arrangement regarded as more advantageous because, when the fluid is confined to vessels, its flow can be regulated much more precisely. …

Method: Building a Differentiation Table for Paired Biological Terms

Use this approach whenever a question asks you to "distinguish" or "write the features that distinguish" two or more paired terms.

Steps

Step 1: Choose consistent axes of comparison for each pair

For "Plasma vs Serum": composition (whether clotting factors are present). For "Open vs Closed circulatory system": where the blood travels (open spaces/sinuses vs confined vessels) and how precisely flow can be regulated. For "SAN vs AVN": location within the heart and functional role (initiates the impulse vs relays it onward).

Step 2: Anchor each distinction in a single causal relationship

Plasma becomes serum specifically by removing clotting factors -- state the transformation, not just two static descriptions. Open vs closed circulation differ by whether blood ever leaves the vessels -- state this as the defining criterion, not a side detail. SAN vs AVN differ by being first-in-sequence-and-fastest vs second-in-sequence-and-relaying. …