Question

Which one of the following options represents the tissues/organs of a healthy adult human, arranged in the correct decreasing order of their Young's modulus?

• A. Bone > Cartilage > Liver > Lung
• B. Bone > Cartilage > Lung > Liver
• C. Bone > Lung > Cartilage > Liver
• D. Bone > Lung > Liver > Cartilage

Hint:

Rank by typical stiffness scale: bone in GPa, cartilage in MPa, then liver in low kPa, with lung even softer since it is mostly air-filled.

Answer 1

The Correct Option is A

Step 1: Recall what Young's modulus measures.
Young's modulus is a measure of stiffness, how much a material resists stretching or compressing under stress. A high Young's modulus means the tissue is stiff and barely deforms; a low value means the tissue is soft and deforms easily under small loads.

Step 2: Rank bone first.
Bone is a mineralised, load-bearing structural tissue, packed with hydroxyapatite crystals in a collagen matrix. Its Young's modulus is in the gigapascal (GPa) range, roughly \(10\)-\(20\ \text{GPa}\) for cortical bone, far stiffer than any soft tissue in the body. So bone is always first in this ranking.

Step 3: Rank cartilage next.
Cartilage is a connective tissue, softer than bone since it is not mineralised, but still much stiffer than most soft organ tissue because of its dense collagen and proteoglycan network. Its Young's modulus falls in the megapascal (MPa) range, well below bone but well above the liver or the lung.

Step 4: Compare liver and lung.
Liver is a dense, fluid-filled parenchymal organ built of tightly packed hepatocytes with only a fine connective-tissue scaffold, and its Young's modulus is usually reported in the low kilopascal (kPa) range, roughly a few kPa in a healthy adult.
Lung tissue, by contrast, is mostly air-filled alveolar sacs held up by a very thin, sparse network of elastin and collagen septae. Because so much of its volume is air rather than solid tissue, the bulk lung parenchyma is even more compliant than liver, with an even lower effective Young's modulus, well under 1 kPa in its relaxed, healthy state.
So liver is stiffer than lung, not the other way round, since liver's denser cellular packing resists deformation more than the sponge-like, air-filled lung structure does.

Step 5: Put the full order together.
From stiffest to softest: bone (GPa) > cartilage (MPa) > liver (low kPa) > lung (well under 1 kPa).

Step 6: Why the other options are wrong.
Option (B) swaps liver and lung, placing lung above liver, which reverses their actual relative stiffness since the air-filled lung is the more compliant of the two.
Option (C) swaps cartilage and lung, putting lung above cartilage, but cartilage's MPa-range stiffness is far above lung's sub-kPa stiffness.
Option (D) swaps both cartilage's and liver's positions, giving an order that is wrong at two places at once.

Final Answer:
The correct decreasing order of Young's modulus is Bone > Cartilage > Liver > Lung.