CBSE Questions for Class 11 Medical Biology Chemical Coordination And Integration Quiz 14 - MCQExams.com

• Hormones which are made up of proteins or steroids are chemical messengers that enable communication between cells. Hormones are secreted by the glands of the endocrine system and help in maintaining homeostasis and regulates metabolism, reproduction, and development. 
• The protein hormones that are released bind to a specific receptor on target cells and trigger intracellular signals. Since the signal transduction begins when a hormone is released into the bloodstream, this hormone is called the first messenger. 
• The hormone further binds to specific cell membrane receptors. The binding of the hormone to the receptor sends across conformational changes that produce a response in the cytosolic side of the cell. 
• These responses bring about a change of concentration of small molecules called the second messengers such as cyclic AMP, cyclic GMP, Ca2+, inositol 1,4,5 triphosphate (IP3), and diacylglycerol, DAG which ultimately brings about upregulation or downregulation of certain genes or molecules. 
• Magnesium ions do not play a role as secondary messengers.

A.Correct option A
B.Explanation for correct option:

• The thymus gland is located in the chest, behind the sternum.
• T-cells are produced in the bone marrow. These cells migrate to the thymus. The thymus gland is responsible for the differentiation and maturity of the T-cells.
• These mature T-cells are released in the bloodstream to fight against infections.
• The T-cells work in coordination with the B-cells to destroy the bacteria, viruses and other foreign antigens. If any damage is caused to the thymus during childhood may cause a lack or less number of mature T-cells.
• This will cause the child to become more prone to infections. Thus, there will be a lack or loss of cell-mediated immunity provided by the T-cells. 

$$\textbf{Correct option:A}$$ 

$$\textbf{Solution:}$$

$$\textbf{Option (A)}$$

$$\bullet$$ Calcitriol is the active form of vitamin D which is made in the kidney,it increases calcium absorption from nephrons,intestine and gastrointstinal tract and helps with the deposition on the bone. Deficiency of this hormone leads to rickets in children and osteomalacia in adults.

$$\textbf{Option (B)}$$

$$\bullet$$ Aldosterone is secreted from the adrenal cortex that stimulates the reabsorption of sodium from nephrons which in turn promotes the reabsorption of water from the glomerular filtrate .Thus helps in balancing water and electrolyte level in the body.

$$\textbf{Option (C)}$$

$$\bullet$$ Cholecystokinin is secreted by the entire mucosa of small intestines and stimulates the secretion of bile from gallbladder and pancreas to release enzymes,this hormone controls appetite.

$$\textbf{Option (D)}$$

$$\bullet$$ Thyrocalcitonin(calcitonin) is secreted when calcium level in blood is higher .It is antagonist to parathormone and inhibits the release of calcium from bones .

$$\textbf{Hence, the correct option is (A)}$$

1. Steroid hormones are made up of cholesterol while peptide hormones are made up of amino acids. 
2. Since the steroid hormones are made of lipids they can easily pass through the plasma membrane and bind to the receptors on the nucleus and effects the DNA transcription. 
   
3. Protein hormones are made of amino acids they bind to the receptors of the plasma membrane of the receptor cell and activate secondary messenger system. 

Renin is produced in the kidney by the juxtaglomerular apparatus.  It participates in the renin–angiotensin–aldosterone system which maintains the blood pressure and fluid balance in the body. It breaks the angiotensinogen secreted from the liver into a peptide angiotensin I. Angiotensin I is further cleaved into angiotensin II. Angiotensin II acts on the adrenal glands and releases aldosterone which acts on the collecting tubules to absorb more sodium ions which in turn increases the absorption of water and increases the blood volume.  It also acts on the CNS to increase water intake by stimulating thirst. So, the correct answer is 'Renin'.

$$\textbf{Correct option:D}$$ 

$$\textbf{Solution:}$$

$$\bullet$$ Pineal gland situated in the diencephalon behind the anterior choroid plexus in between the region of eyebrows which used to be considered a third eye in ancient time.

$$\bullet$$ It is believed that reptiles, the pineal gland is present in the form of the parietal eye or the pineal eye which is photosensitive and is involved in regulating the diurnal cycle. In mammals, it does not form the photosensitive structure but it is involved in the secretory roles 

$$\bullet$$ But due to lack of use this organ slowly started atrophy and became of no use to nowadays organisms. Thus ,its an vestigial organ.

$$\bullet$$ Pineal gland acts as a endocrine gland it secretes melatonin and serotonin hormone. Meltonin which is also known as sleep hormone and promotes sleep ,the production is diurnal so it acts as a biological clock which may produce circadian rhythms .It also lightens the skin color of certain animals and delays sexual maturation.

$$\bullet$$ Serotonin helps brain cells and other nervous system cells to establish communication with each other and promotes sleeping ,eating and digestion.

$$\textbf{Hence, the correct option is (D)}$$

• Chymase is a chymotrypsin-like serine protease found in the mast cells and also present in basophil granulocytes.
  
• Chymase hydrolyzes chymotryptic substrates by activating chymotrypsinogen.
  
• So, the correct answer is 'Activator of chymotrypsinogen'.

• In the thyroid gland, the prohormone $$T_3$$ and $$T_4$$ remain in the colloid center till TSH stimulates the colloid to diffuse into the follicular cell and release $$T_3$$ and $$T_4$$ hormones.

$$\textbf{Correct option:D}$$ 

$$\textbf{Solution:}$$

$$\textbf{Option (A)}$$

$$\bullet$$ Peptide hormones are insoluble hormones which does not easily passes through the membrane of the target cells.

$$\bullet$$ Insulin and glucagon are antagonistic peptide hormones that are secreted from the islets of Langerhans and it is engaged with the sugar metabolism and homeostasis.

$$\textbf{Option (B)}$$

$$\bullet$$ Thyroxine is an iodothyronines which is secreted from thyroid glands and promotes high metbolism,mental growth and temperature maintenance. Insulin is related with sugar homeostasis in the blood.

$$\textbf{Option (C)}$$

$$\bullet$$ Somatostatin and oxytocin are peptide hormones which plays crucial role in the growth of tissues and contraction of uterine at the time of pregnancy and myoepithelial layer of mammary glands at the time of ejection of milk respectively.

$$\textbf{Option (D)}$$

$$\bullet$$ Steroid hormone can easily pass through the cell membrane of the target cell and bind to a receptor inside it(mostly in nucleus)

$$\bullet$$ Cortisol and testosterone are steroid hormones secreted from adrenal cortex and testis respectively.

$$\textbf{Hence, the correct option is (D)}$$