All Free Biology MCQs with Answers
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19844 questions · page 702 of 1985
7011. An enzyme required Mg to catalyze the substrate. The Mg2+ is best identified as:
- A. Prosthetic group
- B. Activator
- C. Coenzyme
- D. Inhibitor
Explanation: Some enzymes use metal ions as cofactors like Mg2+,Fe2+,Cu2+,Zn2+ etc. The detachable cofactor is known as an activator if it is an inorganic ion.
Correct answer: Activator7012. Bond sensitive to change in temperature and pH are respectively:
- A. Hydrogen, Ionic
- B. Hydrogen, Covalent
- C. Ionic, Hydrogen
- D. Covalent, Ionic
Explanation: Enzymes are proteins in nature, and different types of bonds (Hydrogen and Ionic) maintain their structure. Rise in temperature from optimum breaks hydrogen bonds, while a change in pH disturbs ionic bonds.
Correct answer: Hydrogen, Ionic7013. In a man the abducens nerve is injured. Which one of the following functions will be affected?
- A. Movement of the eyeball
- B. Movement of the tongue
- C. Swallowing
- D. Movement of the neck
Explanation: Abducens is the sixth cranial nerve that innervates the external rectus muscle of the eyeball. It is responsible for turning the eye outwards. The movement of the tongue is controlled by the hypoglossal nerve. Neck movements are controlled by the facial nerve. Swallowing is done by the glossopharyngeal.
Correct answer: Movement of the eyeball7014. Hypersecretion of growth hormone in adults does not cause further increase in height because:
- A. Epiphyseal plates close after adolescence
- B. Bones loose their sensitivity to growth hormone in adults
- C. Muscle fibres do not grow in size after birth
- D. Growth hormone becomes inactive in adults
Explanation: Epiphyseal plate is a hyaline cartilage plate in the metaphysis at each end of long bone. It is part of long bone where new bone growth takes place until puberty .When the plate ossifies and fuses into the epiphyseal line the growth of bone stops. In adults, elevated levels of GH results in acromegaly where no increase in height occurs because of ossified epiphyseal plate .Instead bones grow in thickness.
Correct answer: Epiphyseal plates close after adolescence7015. The posterior pituitary gland is not a 'true' endocrine gland because :
- A. It is provided with a duct
- B. It only stores and releases hormones
- C. It is under the regulation of hypothalamus
- D. It secretes enzymes
Explanation: The posterior pituitary is not a true endocrine gland because it does not produce its own hormones. Instead, it functions as a storage area for hormones, specifically antidiuretic hormone (ADH) and oxytocin, which are synthesized in the hypothalamus. These hormones are transported down nerve fibers from the hypothalamus to the posterior pituitary, where they are then released into the bloodstream when stimulated.
Correct answer: It only stores and releases hormones7016. Which of these functions will be affected if the medulla oblongata is damaged?
- A. Thermoregulation
- B. Vision
- C. Memory
- D. Autonomic functions like breathing and heart rate
Explanation: Sensory processing occurs in the spinal cord and somatosensory cortex, but reflex responses like withdrawing from pain involve brainstem pathways, including the medulla. Partially affected, but not directly controlled by the medulla.
Correct answer: Autonomic functions like breathing and heart rate7017. A man has to face an interview, but during his first five minutes before the interview, he experiences sweating, increased heart rate, and respiration. Which hormone is responsible for his restlessness?
- A. Adrenocorticotropic hormone
- B. Insulin and glucagon
- C. Epinephrine and norepinephrine
- D. Aldosterone
Explanation: Epinephrine and norepinephrine are responsible for the physical symptoms described because they trigger the 'fight-or-flight' response in stressful situations. These hormones increase heart rate, respiration, and other responses to prepare the body for action. The other options, such as ACTH, insulin, glucagon, and aldosterone, do not directly cause the specific symptoms mentioned in the question.
Correct answer: Epinephrine and norepinephrine7018. ADH most directly affects:
- A. Glomerulus
- B. Bowman's capsule
- C. Thymus
- D. Collecting tubules of the nephron
Explanation: Antidiuretic hormone (ADH) is a chemical produced in the brain that causes the kidneys to release less water, decreasing the amount of urine produced. A high ADH level causes the body to produce less urine.
Correct answer: Collecting tubules of the nephron7019. All of the following are correct about the endocrine system except:
- A. Endocrine glands are ductless
- B. Parathormone is the flight or fight hormone
- C. The islet cells in the pancreas produce both glucagon and insulin
- D. Ecdysone controls metamorphosis in some insects
Explanation: Adrenaline and noradrenaline are dubbed emergency hormones or Fight or Flight hormones. These hormones are rapidly released in reaction to stress of any kind and during emergency situations.
Correct answer: Parathormone is the flight or fight hormone7020. Which would occur if the parasympathetic system were stimulated
- A. Increase in blood sugar
- B. Increase in digestion
- C. Increase in breathing rate
- D. Increase in adrenaline
Explanation: The parasympathetic nervous system predominates in quiet "rest and digest" conditions while the sympathetic nervous system drives the "fight or flight" response in stressful situations. The main purpose of the PNS is to conserve energy to be used later and to regulate bodily functions like digestion and urination.
Correct answer: Increase in digestion