Cell Structure & Function — Part 3: 40 MCQs with Explanations

Approximately 98.5% of oxygen binds reversibly to hemoglobin in red blood cells forming oxyhemoglobin; only 1.5% dissolves in plasma.

Meiosis is a reduction division producing four haploid gametes with genetic variation from crossing over and independent assortment.

Mitochondria produce ATP via oxidative phosphorylation (Krebs cycle and electron transport chain) using energy from nutrient oxidation.

HCl secreted by parietal cells creates acidic environment (pH 1.5-2) that denatures proteins and activates pepsinogen to pepsin.

Bacteria have a single circular chromosome in the nucleoid region (not membrane-bound) and may contain plasmids (small circular DNA).

Prokaryotes have 70S ribosomes (50S + 30S subunits); eukaryotes have 80S ribosomes (60S + 40S) in cytoplasm (mitochondria/chloroplasts have 70S).

White blood cells (leukocytes) defend against pathogens via phagocytosis (neutrophils, macrophages), antibody production (B cells), and cell-mediated immunity (T cells).

Oxytocin from posterior pituitary stimulates myoepithelial cell contraction for milk ejection and powerful uterine contractions during labor.

Red bone marrow in axial skeleton (sternum, ribs, vertebrae, pelvis) and proximal ends of humerus/femur produces blood cells in adults.

Viruses contain either DNA or RNA (never both), lack cellular structure, cannot replicate without host machinery, and have no ribosomes.

Glucagon from pancreatic alpha cells stimulates glycogenolysis and gluconeogenesis in the liver to raise blood glucose during fasting.

Meiosis generates genetic variation through crossing over (prophase I) and independent assortment (metaphase I), producing non-identical haploid gametes.

Testosterone from Leydig cells promotes development of male secondary sexual characteristics (facial hair, deep voice, muscle mass) during puberty.

Osmosis is passive movement of water from lower solute concentration to higher solute concentration across a selectively permeable membrane.

Rods (for low-light vision) and cones (for color vision) are photoreceptor cells in the retina that convert light into neural signals.

Retroviruses (e.g., HIV) have ssRNA genomes that are reverse transcribed into DNA by reverse transcriptase after infecting host cells.

Light-dependent reactions (photosystems II and I, electron transport) occur in thylakoids, producing ATP and NADPH. Calvin cycle occurs in stroma.

Binary fission is asexual reproduction in prokaryotes where a single cell divides into two genetically identical daughter cells after DNA replication.

Calcitonin from thyroid parafollicular cells lowers blood Ca²⁺ by inhibiting osteoclast activity and promoting calcium deposition in bones.

Neurons (nerve cells) transmit electrical and chemical signals, forming the structural and functional basis of the nervous system.

The glomerulus is a capillary network where blood pressure forces water and solutes (except proteins/cells) into Bowman's capsule (ultrafiltration).

Sickle cell anemia is caused by missense mutation (GAG → GTG) in β-globin gene, substituting valine for glutamic acid at position 6.

Viruses lack ribosomes, ATP-generating systems, and metabolic enzymes; they must hijack host cell machinery to replicate.

Mitosis produces two diploid daughter cells genetically identical to parent cell for growth and repair. Meiosis produces genetically diverse haploid gametes.

The cochlea in the inner ear contains hair cells that transduce sound vibrations into neural signals for hearing.

Mature human erythrocytes (RBCs) lack nuclei and organelles to maximize hemoglobin content and flexibility for capillary passage.

Crossing over (exchange of genetic material between non-sister chromatids of homologous chromosomes) occurs during pachytene stage of prophase I.

Cardiac autorhythmic cells (SA node) exhibit pacemaker potential—spontaneous depolarization due to funny channels (Na⁺ influx) leading to action potentials.

Plasma cells (derived from B lymphocytes) produce and secrete antibodies specific to antigens.

Krebs cycle (citric acid cycle) occurs in mitochondrial matrix, producing NADH, FADH₂, and ATP/GTP from acetyl-CoA oxidation.

Na⁺/K⁺ ATPase pumps 3 Na⁺ out and 2 K⁺ into the cell per ATP hydrolyzed, maintaining resting membrane potential.

Anaphase: centromeres split and sister chromatids (now chromosomes) are pulled toward opposite poles by spindle fibers.

Resting potential is typically -70 mV (inside negative relative to outside) due to K⁺ leak channels and Na⁺/K⁺ pump.

Pyruvate decarboxylation (link reaction) occurs in matrix: pyruvate → acetyl-CoA + CO₂ + NADH.

Primary response has lag period (days), lower antibody titer (mainly IgM), and generates memory B/T cells for faster secondary response.

Casparian strip (suberin/wax) in endodermal cell walls blocks apoplastic pathway, forcing water/solutes through cells (symplastic pathway) for selective uptake.

Substrate-level phosphorylation directly transfers phosphate from substrate to ADP (e.g., in glycolysis and Krebs cycle), independent of oxygen or membranes.

Eustachian (auditory) tube equalizes pressure on both sides of tympanic membrane and drains mucus from middle ear.

Thyroid-stimulating hormone (TSH) from anterior pituitary stimulates thyroid follicular cells to produce T3/T4.

Glycolysis occurs in cytosol; other options occur in mitochondria.

Which of the following organisms have Chitin as a major structural component of their cell wall Fungi .

Interconversion of carbohydrates proteins and lipids in living cells are an example of Both A and B .

Leptotene zygotene pachytene diplotene diakinesis is the correct answer to “Which one of the following is correct sequence of stages of prophase 1 of meiosis”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

G2 phase is the correct answer to “Which one of the following stage preceeds mitosis during cell cycle”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Glycolipids and glycoproteins have structural role in the Extracellular matrix of animal and bacterial cell.

If a plasmolysed plant cell is placed in water the cell will Be deplasmolysed .

Sunlight is trapped is the correct answer to “Membranes of the grane are sites where”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Total number of amino acids discovered so far in cells and tissues are 170 .

Proteins comprise of 50% % of the total dry weight of a cell.

Chemical component/s less in eukaryotic cell as compared to prokaryotic cell is / are (i) lipids (ii) carbodydrates (iii) proteins (iv) DNA iv only .

The cell wall of oomycetes is chiefly composed of Cellulose .

Cellular digestion is associated with which organelle Lysosomes .

The unicellular organisms ingest large molecules into their cytoplasm from the external environment without previously digesting them. This process is called Phagocytosis .

Which chemical component has the greatest contribution in the total mammalian cell weight Water .

Polysome is the correct answer to “Ribosomes + m-RNA”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Strengthening material of prokaryotic cell wall is Peptidoglycan or Murein. .

In cell fractionation various components of cells including its organelles can be isolated in different layers depending upon Both a and b .

Robert Brown is the correct answer to “Who opposed the idea the cell is an empty space bounded by thick wall”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

A group of ribosomes attached to mRNA is known as Polysomes .

Cellular organelles related with H2O2 are Peroxisomes .

Number of nuclear pores/nucleus in an RBC are 3?4 .

Yellow cytoplasm in ascidian gives rise to Muscle cells .

Mitochondria Chloroplast is the correct answer to “Which of the following combination is an example of self replicating organelles”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Sickle cell anemia is an example of Point mutation .

The stent energy in the form of ADP is regenerated by mitochondria into ATP .

Number of mitochondria is constant is the correct answer to “Of the following which one is not the characteristic of mitochondria”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Ribosomes are assembled in Nucleolus .

Rudolph Virchows is the correct answer to “Who first observed and thus hypothesized that new cells are formed from previously existing living cell”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

Percentage of proteins in cell membrane is 60-80% .

Movement of the material across the cell membrane which does not requiring expenditure of metabolic energy is called Passive transport .

The first layer of cell wall which is formed is Primary wall .

95% of the cytoplasm of RBCs is Hemoglobin .

Sieve element cells of phloem are directly involved in transport of organic solutes.

Robert Hook is the correct answer to “Who coined the term CELL”. Items of this type are drawn from the Cell Structure & Function — Part 3 syllabus of Pakistani competitive exams, where the fact is tested verbatim.

The arrangement of Organelles speaks of the division of labour within cell.

A structure formed by groups of similar cells organized into loose sheetsor bundles performing similar functions is called as A Tissue .

Intake of liquid material by cell membrane is called Pinocytosis .

Golgi complex is concerned with cell secretions.

Cytoskeleton involved in assembly and disassembly of the spindle during mitosis is of Microtubules .

Ribosomes were discovered by Palade .