The blood vessel with the thinnest wall, allowing exchange of substances, is:
A. Capillary
B. Arteriole
C. Artery
D. Vein
Answer: Option A
Solution (By JKSSB Mock Tests)
Capillaries are the smallest blood vessels, with walls only one cell thick (endothelium), facilitating diffusion of oxygen, carbon dioxide, nutrients, and waste products between blood and tissues. Arteries and veins have thicker walls with smooth muscle and connective tissue. Capillaries form extensive networks (capillary beds) throughout the body.
Explanation:
Enterokinase (enteropeptidase) is secreted by the intestinal mucosa and activates the pancreatic proenzyme trypsinogen to trypsin, which then activates other zymogens. Pepsin is active in the stomach, renin is a milk-curdling enzyme (chymosin), carboxypeptidase is a pancreatic protease. This cascade ensures that protein-digesting enzymes are activated only in the appropriate location to prevent autodigestion.
Explanation:
The Cell Theory, one of the fundamental principles of biology, was proposed by Matthias Schleiden (a German botanist) in 1838 and Theodor Schwann (a British zoologist) in 1839. Schleiden concluded that all plants are composed of cells, and Schwann extended this to animals. Rudolf Virchow later added the third tenet in 1855: 'Omnis cellula e cellula' (all cells arise from pre-existing cells).
Consider the following statements about vitamins:
1. Vitamin K is essential for bone health.
2. Vitamin D deficiency can cause rickets.
3. Vitamin A is also known as tocopherol.
Which of the above is/are correct?
Explanation:
Vitamin K supports bone protein osteocalcin; D deficiency causes rickets. Vitamin A is retinol; vitamin E is tocopherol. So 3 is incorrect.
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