Plasma vs serum, and which plasma protein does what? Is serum just plasma without fibrinogen?
Aarav Kulkarni11th Sample
5 Oct 2026 · 1 min read
Making a checklist again (yes, I know) for the blood chapter and I want the plasma section to be airtight.
From NCERT: blood is a special connective tissue consisting of a fluid matrix, plasma, and formed elements. Plasma is a straw-coloured, viscous fluid constituting about 55 per cent of the blood. Ninety to ninety-two per cent of it is water, and proteins contribute 6–8 per cent. Fibrinogen, globulins and albumins are the major proteins. Plasma also contains small amounts of minerals like Na+, Ca++, Mg++, HCO3-, Cl-, etc., and glucose, amino acids, lipids are also present. Factors for coagulation are present in plasma in an inactive form. Plasma without the clotting factors is called serum.
What I want to check:
- Is my checklist right that plasma = 55% and formed elements = 45%?
- Plasma without clotting factors = serum. Does that mean serum has no proteins at all? A friend says it has none.
- What does each of the three proteins do? I only remember fibrinogen being related to clotting.
- How is plasma different from lymph and from tissue fluid? I think they're all "fluids that bathe cells" but I'm not sure.
6 answers & replies
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[+][–]Nisha Verma12thSample· 14d ago
- Yes: about 55% plasma and about 45% formed elements (RBCs, WBCs and platelets, with the RBCs being the great majority of the formed elements).
- Functions:
- Fibrinogen: needed for clotting (coagulation)
- Globulins: mainly involved in the body's defence (antibodies are globulins)
- Albumins: help in maintaining osmotic balance
- and 4. I'll leave to the others, there's a trap in 2 😅
[+][–]Pooja Iyer12thSample· 14d ago
the serum one is easy!! serum = plasma minus ALL proteins, so it is literally just water and salts and sugar. That's why it's clear and watery. Your friend is right 🙂
[+][–]Zoya Khan12thSample· 14d ago
Pooja, serum still has proteins. What is removed are the clotting factors (like fibrinogen), which are used up in forming the clot. Albumins and globulins are still present in serum, which is why doctors can test antibody levels in serum. NCERT's definition is "plasma without the clotting factors", so I'd write exactly that. Aarav, your friend is wrong on this one.
[+][–]Aarav Kulkarni11thSample· 14d agoAuthor
Serum has proteins, only clotting factors are gone. Updating the checklist and my friend gets a polite correction. thank you!
[+][–]Tanvi Deshmukh12thSample· 14d ago
Mnemonic: F-G-A
- Fibrinogen = Fix the wound (clotting)
- Globulins = Guard (defence)
- Albumin = Adjust the water (osmotic balance)
And a way to remember serum vs plasma: blood in a tube with anticoagulant gives plasma on top after spinning; blood left to clot gives serum. Plasma = fluid that still has clotting factors. Serum = the fluid left after clotting.
[+][–]Kavya NaikDropperSample· 14d ago
For question 4, short comparison:
- Plasma: fluid part of blood, inside the blood vessels, has the plasma proteins and clotting factors.
- Tissue (interstitial) fluid: the fluid that leaves the capillaries and bathes the cells; same mineral composition as plasma, formed from it.
- Lymph: fluid in the lymphatic vessels, colourless, has lymphocytes, no RBCs. It's tissue fluid that has drained into lymph capillaries.
You can think of it as one family, travelling through different channels.
