All Free Biology MCQs with Answers

921. Aldosterone increases

• A. Water excretion
• B. Sodium reabsorption
• C. Potassium reabsorption
• D. Glucose excretion

Explanation: Aldosterone increases Na+ reabsorption and K+ secretion in the distal tubule and collecting duct.

922. Urea is formed in the

• A. Kidneys
• B. Liver
• C. Muscles
• D. Brain

Explanation: Urea is formed in the liver from ammonia (toxic) via the ornithine/urea cycle.

923. Renin is secreted by

• A. Adrenal cortex
• B. Juxtaglomerular cells
• C. Pituitary
• D. Hypothalamus

Explanation: Juxtaglomerular cells in the afferent arteriole secrete renin in response to low blood pressure.

924. Glycosuria occurs when

• A. Blood glucose is normal
• B. Blood glucose exceeds renal threshold
• C. ADH is high
• D. Aldosterone is low

Explanation: Glycosuria (glucose in urine) occurs when blood glucose exceeds the renal threshold (~180 mg/dL), saturating reabsorption capacity.

925. The RAAS pathway ultimately increases

• A. Blood pressure
• B. Urine output
• C. Sodium excretion
• D. Potassium reabsorption

Explanation: The renin-angiotensin-aldosterone system (RAAS) ultimately increases blood pressure through vasoconstriction and Na+/water retention.

926. Diabetes insipidus is caused by

• A. Insulin deficiency
• B. ADH deficiency
• C. Aldosterone excess
• D. Renin deficiency

Explanation: Diabetes insipidus results from ADH deficiency or resistance, causing inability to concentrate urine and excessive dilute urine.

927. Mendel's law of segregation states that

• A. Alleles separate during gamete formation
• B. Different genes assort independently
• C. Dominant alleles always mask recessive
• D. Genes are on chromosomes

Explanation: The law of segregation states that allele pairs separate during gamete formation, so each gamete carries one allele.

928. A test cross is used to determine

• A. The genotype of a dominant phenotype individual
• B. The number of chromosomes
• C. Mutation rates
• D. Linkage groups

Explanation: A test cross between an individual showing dominant phenotype and a homozygous recessive reveals whether the dominant is homozygous or heterozygous.

929. Incomplete dominance results in

• A. Only dominant phenotype
• B. Only recessive phenotype
• C. Intermediate phenotype
• D. Both phenotypes expressed

Explanation: In incomplete dominance, the heterozygote shows an intermediate phenotype, e.g., pink flowers from red and white parents.

930. ABO blood group inheritance demonstrates

• A. Complete dominance only
• B. Incomplete dominance
• C. Codominance and multiple alleles
• D. Sex linkage

Explanation: ABO system shows codominance (IA and IB both expressed in AB) and multiple alleles (IA, IB, i).