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Elemental Composition: Living Tissue vs Earth's Crust

Biology · Biomolecules · NEET

Every element found in Earth's crust is also found in living tissue, so life uses no special "vital" element. The real difference is relative abundance: Hydrogen, Carbon, Oxygen and Nitrogen are much higher in living tissue than in the crust. Memory hook: "Life is made of the SAME bricks, just MORE H, C, O" (HCON build every biomolecule).
Same Elements, Different Abundance (NCERT Table 9.1)Living TissueEarth's CrustHydrogen ~ high (H)Carbon ~18.5% (C)Oxygen ~65% (O)Nitrogen ~3.3% (N)Oxygen ~47% (O)Silicon ~28% (Si) HIGHAluminium ~8% (Al)Carbon ~0.19% (C) LOWKey: H and C are far higher in life; Si is high in crust, trace in body
Living tissue and Earth's crust contain the same elements, but Hydrogen and Carbon are far more abundant in life, while Silicon dominates the crust yet is only a trace in the body.

Your doubts, answered

Is there any element in living tissue that is NOT in Earth's crust?

No. NCERT states clearly that all the elements present in a sample of Earth's crust are also present in a sample of living tissue. Life does not invent a new element. So there is no special 'vital element'. The difference is only in HOW MUCH of each element is present, not WHICH elements.

Which elements are more abundant in living tissue than in the crust?

Hydrogen (H), Carbon (C) and Oxygen (O) show much higher relative abundance in living tissue. NCERT specifically says the relative abundance of carbon and hydrogen with respect to other elements is higher in any living organism than in the crust. In the crust the top element is Oxygen (~47%) and Silicon (Si) is very high (~28%), but Si is very low in the body.

Why is carbon so high in living organisms but low in the crust?

Living things are built from carbon-based biomolecules: carbohydrates, proteins, lipids and nucleic acids all have a carbon backbone. Carbon can form four stable bonds and long chains, so life is carbon-based. The crust is mostly rock made of silicates (Si and O) and metals, so its carbon is low (~0.19%).

What is the difference between elemental composition of living and non-living matter?

Qualitatively (which elements) they are the SAME. Quantitatively (how much) they differ. Living tissue is rich in H, C, O, N. Earth's crust is rich in O, Si, Al, Fe. This higher H and C content is the chemical signature of life for NEET.

Is Silicon important in the human body?

No, Silicon is only a trace element in the body even though it is the second most abundant element in Earth's crust (~28%). This is a classic contrast: high in crust, negligible in living tissue. NEET may test this reversal.

⚠️ The NEET trap
✗ Living organisms contain a special element that is absent in non-living matter.
✓ Living tissue contains the SAME elements as Earth's crust; only the relative abundance (especially of H, C, O) is higher. No unique element exists in life.
🧠 When you read 'living vs non-living', the trap is 'unique element'. Correct idea = same elements, different amounts. Remember: composition qualitatively same, quantitatively different.

Real NEET questions

ReNEET 2026

Arrange the following elements in descending order of their contribution to the percentage weight of the human body: (a) Oxygen, (b) Carbon, (c) Hydrogen, (d) Nitrogen.

A · (a), (b), (c), (d) ✓
B · (c), (a), (b), (d)
C · (b), (c), (d), (a)
D · (b), (a), (c), (d)
Solution: By percentage of body weight: Oxygen (~65%) > Carbon (~18.5%) > Hydrogen (~9.5%) > Nitrogen (~3.3%). So the descending order is (a), (b), (c), (d). This shows H, C, O, N dominate living tissue, unlike Earth's crust where O and Si dominate.

Solved Biomolecules NEET PYQs

Try the real previous-year questions from this chapter — each with the answer and a full solution.

See all 51 Biomolecules NEET PYQs ›
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Frequently asked

What does NCERT say about living tissue vs Earth's crust?

NCERT says all elements in a sample of Earth's crust are also present in living tissue, but the relative abundance of carbon and hydrogen is higher in living organisms than in the crust (Table 9.1).

What is the most abundant element in Earth's crust?

Oxygen is the most abundant element in Earth's crust (~47%), followed by Silicon (~28%). In the body Oxygen is also number one, but Silicon is only a trace.

Which four elements make up most of living tissue?

Hydrogen, Oxygen, Carbon and Nitrogen make up the bulk of living tissue. Together they build carbohydrates, proteins, lipids and nucleic acids.

Why is this topic important for NEET?

NEET often asks a one-line fact: 'same elements, higher abundance of H and C in life' or an ordering of body elements. Knowing the crust-vs-body contrast lets you reject 'unique element' traps quickly.

Related concepts:
What Are Biomolecules? Meaning and ExamplesMost Abundant Elements in the Human Body (Order by Weight)Why Water Is the Most Abundant Molecule in CellsMicromolecules vs Macromolecules (Biomacromolecules)Acid-Soluble Pool vs Acid-Insoluble Fraction
Practise Biology for NEET:
Biology MCQs (free, chapter-wise)Biomolecules PYQs