MCQs

Plasmodesmata are microscopic channels crossing the plant cell wall, lining up the plasma membrane and endoplasmic reticulum of neighboring cells.

Glycogen, a highly branched glucose polymer, serves as the primary multi-branched energy storage polysaccharide in animal tissues.

Plants store excess photosynthetic carbohydrates as insoluble starch (amylose and amylopectin), while animals store energy as glycogen.

Higher plant cells completely lack centrioles, utilizing alternative microtubule-organizing centers (MTOCs) to manage spindle formation during division.

Chloroplasts are specialized green plastids containing chlorophyll pigments that execute the light and dark reactions of photosynthesis in plants.

The tonoplast is the specialized semi-permeable membrane enclosing the plant vacuole, containing active transport pumps to maintain cell turgidity.

Mature plant cells feature a massive central vacuole that maintains turgor pressure, whereas animal cells contain multiple small, transient vacuoles.

Cellulose is a linear polymer of β-D-glucose units that organizes into microfibrils to give the plant cell wall its high tensile strength.

Plant cells possess an extracellular, rigid cell wall made primarily of cellulose that protects the cell from mechanical stress and osmotic lysis.

Animal cells lack a cell wall entirely; their outermost living boundary is the selectively permeable phospholipid bilayer known as the plasma membrane.

Triple-stranded H-DNA forms when a third single strand winds into the major groove of a duplex, binding via alternative Hoogsteen hydrogen bonds.

Hypoxanthine pairs with cytosine, meaning the original template A-T pair becomes a G-C pair after a few rounds of replication, causing a transition mutation.

The Shine-Dalgarno sequence base-pairs with the 16S rRNA of the 30S subunit, aligning the bacterial ribosome with the start codon to initiate translation.

Because the glycosidic bonds project unevenly, the backbones wind asymmetrically around the axis, creating alternating major and minor grooves.

NMD is a surveillance mechanism that detects premature stop codons on transcripts and degrades them, preventing the accumulation of toxic, truncated proteins.

Polymerization relies on the cleavage of pyrophosphate (PPi​→2Pi​) to provide the forward driving force; blocking this halts the reaction.

Mutilating a splice site prevents the spliceosome from recognizing the intron-exon boundary, leading to intron retention or exon skipping during splicing.

G-C pairs are bound by three hydrogen bonds, meaning G-C rich fragments require higher temperatures to denature than A-T rich sequences of the same length.

XP is caused by defects in the NER pathway, which is responsible for cutting out UV-induced pyrimidine dimers and bulky DNA distortions.