Sindh MDCAT 2026 Solved Answer Key & Question Paper Breakdown (IBA Sukkur / STS)

The Sindh Medical and Dental College Admission Test (MDCAT 2026) was successfully conducted across the province by SIBA Testing Services (STS) on Sunday, September 20, 2026. Candidates who appeared for today’s entry test can now review the complete question paper along with detailed, verified step-by-step solutions below.

Official carbon sheet answer keys, color-coded answer keys (Yellow, Blue, Pink, Green), and score conversion cards are available directly on the official portal links:

Complete MDCAT 2026 Question Paper & Verified Solutions

Question 1

The left atrium receives oxygenated blood from the:

  • A) Pulmonary veins
  • B) Superior vena cava
  • C) Inferior vena cava
  • D) Pulmonary artery

Correct Answer: A) Pulmonary veins

Explanation: Oxygenated blood returning from the lungs is carried into the left atrium via four pulmonary veins.

Question 2

The autonomic nervous system is mainly controlled by which part of the brain?

  • A) Cerebellum
  • B) Hypothalamus
  • C) Medulla oblongata
  • D) Cerebrum

Correct Answer: B) Hypothalamus

Explanation: The hypothalamus acts as the chief integration center for the autonomic nervous system, regulating visceral activities like heart rate, blood pressure, and body temperature.

Question 3

The cell membrane of a muscle cell is also known as:

  • A) Sarcoplasm
  • B) Sarcolemma
  • C) Sarcomere
  • D) Sarcoplasmic reticulum

Correct Answer: B) Sarcolemma

Explanation: The plasma membrane enclosing a muscle fiber (cell) is specifically called the sarcolemma.

Question 4

The aorta is connected to which chamber of the heart?

  • A) Right atrium
  • B) Right ventricle
  • C) Left atrium
  • D) Left ventricle

Correct Answer: D) Left ventricle

Explanation: The left ventricle pumps oxygenated blood into the systemic circulation via the main aorta.

Question 5

Which part of the brain controls body temperature?

  • A) Cerebellum
  • B) Medulla oblongata
  • C) Hypothalamus
  • D) Pons

Correct Answer: C) Hypothalamus

Explanation: The body’s central thermostat is located within the preoptic and anterior regions of the hypothalamus.

Question 6

Which is not part of alimentary canal?

  • A) Jejunum
  • B) Stomach
  • C) Liver
  • D) Oesophagus

Correct Answer: C) Liver

Explanation: The liver is an accessory digestive gland, whereas the oesophagus, stomach, and jejunum form direct continuous sections of the alimentary canal tube.

Question 7

The cooling effect of sweating is mainly due to the:

  • A) High specific heat of water
  • B) High heat of vaporization of water
  • C) Low boiling point of water
  • D) High density of water

Correct Answer: B) High heat of vaporization of water

Explanation: Water requires a high amount of heat energy to evaporate ($2260\text{ J/g}$), which removes significant heat energy from the body surface during sweat evaporation.

Question 8

Which structure is found only in animal cell?

  • A) Microtubules
  • B) Mitochondria
  • C) Cell wall
  • D) Centrosome

Correct Answer: D) Centrosome

Explanation: Centrosomes containing centrioles are characteristic organelle structures present in animal cells but absent in higher plant cells.

Question 9

The “DUB” sound of the heart is produced by the closure of which valve?

  • A) Atrioventricular valves
  • B) Semilunar valves
  • C) Tricuspid valve only
  • D) Mitral valve only

Correct Answer: B) Semilunar valves

Explanation: The second heart sound ($S_2$ / “DUB”) is generated by the closing of the aortic and pulmonary semilunar valves at the onset of ventricular diastole.

Question 10

Which is not a part of brain?

  • A) Hypothalamus
  • B) Pituitary gland
  • C) Medulla oblongata
  • D) Corpus Callosum

Correct Answer: B) Pituitary gland

Explanation: The pituitary gland is an endocrine gland situated in the sella turcica of the sphenoid bone at the base of the brain, rather than a structural neural component of the brain itself.

Question 11

Which structure connects the two cerebral hemispheres of the brain?

  • A) Medulla oblongata
  • B) Corpus callosum
  • C) Hypothalamus
  • D) Cerebellum

Correct Answer: B) Corpus callosum

Explanation: The corpus callosum is a wide nerve tract consisting of commissural fibers that links the right and left cerebral hemispheres.

Question 12 & 16

Which group of neurons in the brain is involved in emotional responses, including pleasure and punishment-related feelings?

  • A) Hippocampus
  • B) Amygdala
  • C) Ganglion cells
  • D) Corpus callosum

Correct Answer: B) Amygdala

Explanation: The amygdala, part of the limbic system, processes emotional stimuli, fear conditioning, reward, and motivation-based responses.

Question 13

General formula of carbohydrates:

  • A) $\text{C}_n\text{H}_{2n}\text{O}_n$ (written as $\text{C}_n(\text{H}_2\text{O})_n$)
  • B) $\text{C}_n\text{H}_n\text{O}_n$
  • C) $\text{C}_{2n}\text{H}_{2n}\text{O}_n$
  • D) $\text{C}_n\text{H}_n\text{O}_{2n}$

Correct Answer: A) CnH2nOn

Explanation: Carbohydrates follow the empirical chemical formula $\text{C}_x(\text{H}_2\text{O})_y$, which simplifies to $\text{C}_n\text{H}_{2n}\text{O}_n$ for simple monosaccharides.

Question 14

TMV shape:

  • A) Helical
  • B) Polyhedral
  • C) Icosahedral
  • D) Tadpole

Correct Answer: A) Helical

Explanation: Tobacco Mosaic Virus (TMV) possesses a cylindrical rod-like shape with helical capsid symmetry.

Question 15

Which layer of the heart is responsible for contraction of the heart muscle?

  • A) Pericardium
  • B) Endocardium
  • C) Myocardium
  • D) Epicardium

Correct Answer: C) Myocardium

Explanation: The myocardium consists of cardiac muscle fibers capable of generating contractile forces to pump blood.

Question 17

Monoclonal antibodies specifically bind to which part of a pathogen?

  • A) Surface of host cell
  • B) Surface of pathogen
  • C) Nucleus of host cell
  • D) Cytoplasm of pathogen

Correct Answer: B) Surface of pathogen

Explanation: Monoclonal antibodies specifically target unique surface antigens/epitopes exposed on the pathogen exterior.

Question 18

Renal tubules empty in:

  • A) Renal medulla
  • B) Renal cortex
  • C) Renal parenchyma
  • D) Renal pelvis

Correct Answer: D) Renal pelvis

Explanation: Collecting ducts in the renal tubules drain urine into the minor calyces, which converge into the major calyces and empty directly into the expanded funnel of the renal pelvis.

Question 19

Which of the following is not a part of GIT?

  • A) Small intestine
  • B) Oesophagus
  • C) Stomach
  • D) Liver

Correct Answer: D) Liver

Explanation: The gastrointestinal tract (GIT) consists strictly of the hollow continuous digestive tube. The liver is an accessory organ.

Question 20

Which of the following is not STD?

  • A) Gonorrhea
  • B) AIDS
  • C) Syphilis
  • D) Hemophilia

Correct Answer: D) Hemophilia

Explanation: Hemophilia is a genetic, X-linked recessive bleeding disorder, whereas Gonorrhea, AIDS, and Syphilis are sexually transmitted infections.

Question 21

LH surge impacts which phase of menstrual cycle?

  • A) Ovulatory
  • B) Proliferative
  • C) Menstrual
  • D) Secretory

Correct Answer: A) Ovulatory

Explanation: A sudden peak in Luteinizing Hormone (LH surge) around day 14 triggers ovulation and ruptures the mature Graafian follicle.

Question 22

Which controls autonomic functions?

  • A) Hypothalamus
  • B) Cerebellum
  • C) Pons
  • D) Cerebrum

Correct Answer: A) Hypothalamus

Explanation: The main subcortical regulatory organ for autonomic functions is the hypothalamus.

Question 23 (Bio/Physiology)

Which of the following regulate temperature?

  • A) Hypothalamus
  • B) Cerebellum
  • C) Pons
  • D) Cerebrum

Correct Answer: A) Hypothalamus

Explanation: Thermoregulation centers reside inside the anterior/preoptic regions of the hypothalamus.

Question 24

If both heterozygous (AaBb) crossed then ratio of AABB is?

  • A) $1/16$
  • B) $3/16$
  • C) $9/16$

Correct Answer: A) 1/16

Explanation: In a dihybrid cross ($AaBb \times AaBb$), the probability of getting $AA$ ($1/4$) and $BB$ ($1/4$) together is $1/4 \times 1/4 = 1/16$.

Short Concept Summary Questions (Section II)

  • 1. Non-competitive inhibition: Inhibitor binds to an allosteric site rather than the active site, altering enzyme conformation.
  • 2. Pepsinogen activation: Activated by Hydrochloric Acid ($\text{HCl}$) produced by parietal cells.
  • 3. Bone breakdown cell: Osteoclasts.
  • 4. Hepatic vein emergence: Emerges directly from the Liver.
  • 5. Effect of pH change on Enzyme activity: Alters ionization states of amino acids at the active site, denaturing enzyme structure if shifted away from optimum.
  • 6. Genes/Genome of HIV: Single-stranded RNA ($ssRNA$).
  • 7. Use and disuse of organs concept: Lamarckism / Lamarck’s Theory of Inheritance of Acquired Characteristics.
  • 8. Inheritance of Carrier Daughter: Inherits the affected X-chromosome from her Father (or a carrier mother).
  • 9. Cells producing antibodies on re-infection: Memory B Cells / Plasma Cells.
  • 10. Antibody secretion cell type: Plasma B Cells.
  • 11. Purpose of Test Cross: To check the unknown genotype of a phenotypically dominant individual (whether homozygous or heterozygous).

Chemistry & Physics Portion

Question 23 (Chemistry)

What is the oxidation state of hydrogen atom in BeH2?

  • A) $+1$
  • B) $-1$
  • C) $+2$
  • D) $-2$

Correct Answer: B) -1

Explanation: In metal hydrides ($\text{BeH}_2$), hydrogen is more electronegative than the Group 2 metal Beryllium, adopting an oxidation number of $-1$.

Question 24 (Physics)

When two electrons move towards each other, the:

  • A) KE increases
  • B) PE decreases
  • C) PE increases
  • D) No change

Correct Answer: C) PE increases

Explanation: Electrostatic repulsion opposes bringing like charges closer together. Work done against repulsive force increases electrostatic potential energy ($U = \frac{k q_1 q_2}{r}$).

Question 25 (Enzymology)

Effect of increasing temperature on enzymatic reaction?

  • A) Molecular collision between enzyme and substrate increases
  • B) Collision between enzyme and substrate decreases

Correct Answer: A) Molecular collision between enzyme and substrate increases

Explanation: Raising temperature increases kinetic energy, causing faster molecular motion and higher collision frequency.

Question 26

Carboxylic partial reduction produce:

  • A) alkane
  • B) alkene
  • C) Alcohol

Correct Answer: C) Alcohol

Explanation: Partial reduction of carboxylic acids using mild or controlled reducing agents yields primary alcohols.

Question 27

Which of the following contain more dipole moment?

  • A) $\text{NH}_3$
  • B) $\text{C}_4\text{H}_{10}$
  • C) $\text{CO}_2$

Correct Answer: A) NH3

Explanation: Ammonia ($\text{NH}_3$) has a trigonal pyramidal structure with a net dipole moment ($1.47\text{ D}$), whereas $\text{CO}_2$ is linear ($\mu = 0$) and $\text{C}_4\text{H}_{10}$ is non-polar.

Question 28

Principal Quantum number describes what?

Correct Answer: Main shell / Energy level and size of atomic orbital

Explanation: The principal quantum number ($n$) determines the main energy level of an electron and the average distance of the electron from the nucleus.

How to Download Official STS Carbon Sheet Keys

  1. Visit the STS Candidate Portal Login Page.
  2. Enter your CNIC number and account password.
  3. Click on Results & Announcements.
  4. Select MDCAT-2026 Answer Key matching your paper code color.