Which of the following is a steroid hormone? MCQ with Answer and Explanation

Explanation:
The alveoli are the terminal, microscopic, thin-walled, highly vascularized air sacs in the lungs. They are the primary and actual sites of gas exchange, where oxygen diffuses from the inhaled air into the blood, and carbon dioxide diffuses from the blood into the alveolar air to be exhaled. Their large surface area and thin walls facilitate this diffusion.

Explanation:
Paramecium is a unicellular ciliated protozoan found in freshwater. Earthworm and Hydra are multicellular animals, mushroom is a multicellular fungus. Unicellular organisms carry out all life processes within a single cell.

Explanation:
Myosin is the motor protein forming thick filaments; its heads bind to actin thin filaments and generate force via the cross-bridge cycle. Actin forms thin filaments, troponin and tropomyosin regulate contraction. The sliding filament theory describes muscle shortening without filament length change.