Cell the Unit of Life| PYQs

The endomembrane system includes the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and the plasma membrane. Mitochondria, chloroplasts, and peroxisomes are not part of this system. Therefore, the correct choice is 3: A, C and E only (mitochondria, chloroplasts, and peroxisomes are not part of endomembrane). Options that include ER or Golgi (B and D) or mix in these with non-endomembrane organelles are not correct.

In NCERT, mitochondria and chloroplasts have their own DNA and ribosomes and are not components of the endomembrane system.

Endomembrane system: nuclear envelope, ER, Golgi, lysosomes, vacuoles, and plasma membrane.

The cytoskeleton provides mechanical support and enables movement of the cell and its parts. It helps in motility, such as movement of the cell itself (e.g., in certain cells with flagella or cilia) and in the movement/positioning of organelles. Among the options, motility is the primary function highlighted by NCERT as a role of the cytoskeleton. Protein synthesis is carried out by ribosomes; nuclear division involves spindle apparatus but is not the main named function of the cytoskeleton in this context; transportation of materials occurs along cytoskeletal elements, but the option that best captures the core idea is motility.

Microtubules and actin filaments form tracks along which organelles and vesicles are moved inside the cell.

Cytoskeleton helps in movement and support of the cell, aiding motility and organelle transport.

Statement I is correct: Mycoplasma are very small bacteria that can pass through filters with pore sizes less than 1 micron (e.g., 0.45 μm). Their lack of a cell wall contributes to their flexible shape and small size. Statement II is incorrect: Mycoplasma do not have a cell wall; NCERT states they are the smallest bacteria that lack a cell wall. Therefore, the correct choice is: Statement I is correct but Statement II is incorrect.

Because they lack cell walls, Mycoplasma are resistant to many antibiotics that target cell wall synthesis (like penicillin), and they have variable shapes due to their membrane-rich structure.

Mycoplasma are the smallest bacteria that lack cell walls.

The incorrect statement is option 2. In NCERT, Endoplasmic Reticulum (ER) is present in eukaryotic cells. Prokaryotes do not have ER at all; they lack membrane-bound organelles like ER. The RER has ribosomes on its outer surface and is involved in protein synthesis for secretion and membranes, while the SER lacks ribosomes and is the site for lipid synthesis and detoxification. Thus, options 1, 3, and 4 are true, and option 2 is false.

RER with attached ribosomes synthesizes secretory and membrane proteins; SER handles lipid metabolism and detoxification processes.

ER is a network of sacs and tubules, consisting of RER (with ribosomes) and SER (without ribosomes).

Option 1 is incorrect. Mature sieve tube elements lack a nucleus and have very few cytoplasmic organelles; they rely on companion cells for metabolic needs. This is described in NCERT in the discussion of phloem tissue.

Companion cells support sieve tube elements and help with loading/unloading of substances in phloem.

Mature sieve tube elements are enucleate and devoid of usual organelles; their metabolic functions are supported by companion cells.