Plasma is the straw-coloured, slightly thick (viscous) liquid part of blood. It makes up about 55% of blood. Of plasma itself, 90-92% is water and 6-8% is proteins (fibrinogen, globulins, albumins), plus minerals, glucose, and clotting factors. Memory hook: "55-92-8" means plasma is 55% of blood, and inside plasma water is ~92% and proteins ~8%.
Blood is ~55% plasma and ~45% formed elements. Inside plasma, water is 90-92% and proteins 6-8%; the three main proteins are fibrinogen (clotting), globulin (defence) and albumin (osmotic balance). Read the percentages layer by layer, not all at once.
Your doubts, answered
Is plasma the same thing as blood?
No. Blood is a connective tissue with two parts: the fluid matrix (plasma) and the formed elements (RBCs, WBCs, platelets). Plasma is only the liquid part. Plasma is about 55% of blood; formed elements are about 45%. So plasma is a part of blood, not the whole blood.
What percentage of blood is plasma, and what is inside plasma?
Plasma is nearly 55% of blood. Inside plasma: 90-92% is water and 6-8% is proteins. The main proteins are fibrinogen, globulins and albumins. Plasma also has minerals (Na+, Ca++, Mg++, HCO3-, Cl-), glucose, amino acids and lipids in transit, plus clotting factors in an inactive form.
What is the difference between plasma and serum?
Serum is plasma without the clotting factors. Plasma contains fibrinogen and other clotting (coagulation) factors. When these are removed after clotting, the remaining straw-coloured fluid is serum. So: Plasma = Serum + Clotting factors (including fibrinogen). This exact point was asked in NEET 2016.
Are RBCs, WBCs and platelets part of plasma?
No. RBCs, WBCs and platelets are the formed elements (cells), not part of plasma. Plasma is only the fluid matrix left after you imagine removing all cells. This is a very common trap: 'plasma' means the liquid, 'formed elements' means the cells.
Why is plasma straw coloured and viscous?
Plasma looks pale yellow (straw coloured) mainly due to dissolved substances like bilirubin and proteins, not haemoglobin (haemoglobin is inside RBCs, which are removed). It is viscous (slightly thick) because of its 6-8% protein content. Water alone would be thin; the proteins make it flow slower than water.
What jobs do the three main plasma proteins do?
Fibrinogen is needed for clotting (coagulation) of blood. Globulins are mainly involved in the body's defence mechanism (antibodies). Albumins help maintain osmotic balance. NCERT states this directly, and NEET 2018 asked exactly this matching.
⚠️ The NEET trap ✗ Plasma is 90-92% water, so about 90-92% of BLOOD is water. ✓ The 90-92% water figure is the composition of PLASMA, not of whole blood. Plasma is only 55% of blood. Read the percentages one layer at a time: blood -> plasma (55%) -> inside plasma, water is 90-92%. 🧠 Percentages are nested: 55% of blood is plasma, then 92% OF THAT plasma is water. Never mix the two layers.
Real NEET questions
2016
Serum differs from blood in
A · Lacking globulins
B · Lacking albumins
C · Lacking clotting factors ✓
D · Lacking antibodies
Solution: Plasma contains clotting (coagulation) factors, including fibrinogen, in an inactive form. When these clotting factors are removed, the remaining straw-coloured fluid is called serum. So serum differs from blood/plasma by lacking the clotting factors. This tests the plasma-vs-serum idea directly.
2018
Match Column I with Column II: a. Fibrinogen, b. Globulin, c. Albumin | (i) Osmotic balance, (ii) Blood clotting, (iii) Defence mechanism
A · a-(i), b-(iii), c-(ii)
B · a-(i), b-(ii), c-(iii)
C · a-(iii), b-(ii), c-(i)
D · a-(ii), b-(iii), c-(i) ✓
Solution: NCERT states the functions of the three major plasma proteins: fibrinogen -> blood clotting (ii), globulins -> defence mechanism (iii), albumins -> osmotic balance (i). So the correct match is a-(ii), b-(iii), c-(i).
Solved Body Fluids and Circulation NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
