Biology · Cell: The Unit of Life · NEET
It is made of BOTH lipids and proteins. The main lipids are phospholipids, plus some cholesterol. But which one is MORE by amount depends on the cell. NCERT gives one exact number you must remember: in the human RBC (erythrocyte) membrane, protein is about 52% and lipids about 40%. So in RBC, protein is slightly more than lipid. The ratio of protein to lipid varies a lot in different cell types, so do not memorise it as a fixed rule for all cells.
Phospholipids are arranged in a BILAYER, meaning two layers back to back. Each phospholipid has a polar head (likes water) and a non-polar hydrophobic tail (hates water). The polar heads face OUTWARD on both sides (towards the watery fluid inside and outside the cell). The hydrophobic tails point INWARD, towards each other, in the middle. This hides the non-polar tails from water. NEET loves this exact wording: 'polar head towards the outer sides and the hydrophobic tails towards the inner part.'
Because the tails are made of non-polar saturated hydrocarbons, and they do not mix with water. The inside and outside of a cell are both watery (aqueous). By turning the tails inward, away from water, the membrane keeps them protected from the aqueous environment. The water-loving polar heads face the water on both sides. This arrangement is stable and forms automatically.
Membrane proteins are classified by how easily you can remove (extract) them. PERIPHERAL proteins lie ON the surface of the membrane and are easy to remove. INTEGRAL proteins are partly or fully buried INSIDE the lipid bilayer and are hard to remove. Simple hook: peripheral = on the edge/surface (easy out); integral = built-in/inside (hard out). NCERT says proteins are classified as integral and peripheral 'depending on the ease of extraction.'
Yes. Besides phospholipids, the membrane also contains cholesterol (a lipid). Biochemical studies later showed the membrane also has protein AND carbohydrate. The carbohydrate is usually attached to lipids or proteins on the outer surface. So the full list is: phospholipids + cholesterol (lipids), proteins, and some carbohydrate. Do not forget cholesterol — NEET has tested it.
No, and this is a common trap. Glycocalyx is described in NCERT as the OUTERMOST layer of the PROKARYOTIC (bacterial) cell envelope, not as part of the eukaryotic plasma membrane. In the NEET 2026 question 'select correct statements about eukaryotic cell membrane', the statement 'Glycocalyx is present on the outer surface of the plasma membrane' was marked WRONG in that context. Keep glycocalyx with bacteria.
Select the correct statements regarding cell membrane in eukaryotic cell. A. Membrane of human RBCs has approximately 52% protein. B. Major phospholipids are arranged in a bilayer. C. Extensions of the plasma membrane into the cell form mesosomes. D. Tails towards the inner part of lipids are hydrophobic and thus protected from aqueous medium. E. Glycocalyx is present on the outer surface of the plasma membrane.
Match List-I with List-II: A. Centromere; B. Cilium; C. Cristae; D. Cell membrane | I. Mitochondrion; II. Cell division; III. Cell movement; IV. Phospholipid Bilayer. Choose the correct answer.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mainly lipids and proteins. The major lipids are phospholipids arranged in a bilayer, plus cholesterol. It also contains proteins (integral and peripheral) and some carbohydrate.
In the human erythrocyte (RBC) membrane, protein is about 52% and lipids about 40%. This exact number is frequently asked in NEET. The ratio varies in other cell types.
Peripheral proteins lie on the surface of the membrane and are easily removed. Integral proteins are buried within the lipid bilayer and are hard to extract. They are classified by ease of extraction.
The tails are non-polar and do not mix with water. Both sides of the membrane are watery, so the tails turn inward to stay protected from the aqueous environment, while the polar heads face the water.
Singer and Nicolson (1972) proposed the fluid mosaic model, which describes the phospholipid bilayer with proteins that can move sideways (laterally) within it.
