Cell Structure Practice Questions

Correct answer: Nucleus

The nucleus houses the cell's DNA in the form of chromatin and coordinates activities like growth, intermediary metabolism, and reproduction. It is separated from the cytoplasm by a double membrane called the nuclear envelope.

Correct answer: Cell wall

Plant cells possess a rigid cell wall made of cellulose that provides structural support and protection. Animal cells lack this structure, possessing only a flexible plasma membrane.

Correct answer: ATP synthesis by aerobic respiration

Mitochondria oxidise the products of glucose and fatty acid breakdown, passing electrons down the inner-membrane transport chain to build a proton gradient that ATP synthase converts into ATP. Ribosomes and rough endoplasmic reticulum handle protein synthesis, chloroplasts photosynthesis, and lysosomes the breakdown of cellular waste.

Correct answer: Ribosome

Ribosomes are small complexes of RNA and protein that serve as the site of protein synthesis. They can be found floating freely in the cytoplasm or attached to the rough endoplasmic reticulum.

Correct answer: Lack of membrane-bound organelles

Prokaryotes, such as bacteria, do not have a nucleus or other membrane-bound organelles like mitochondria or chloroplasts. Their genetic material is typically located in a nucleoid region as a single circular chromosome.

Correct answer: Plasma membrane

The plasma membrane is described as a 'mosaic' of phospholipids, cholesterol, and proteins that are free to move laterally. This fluidity is essential for cell signaling, transport, and maintaining integrity.

Correct answer: Lysosome

Lysosomes act as the cell's recycling center, containing acid hydrolases that can digest proteins, nucleic acids, lipids, and complex sugars. They are crucial for intracellular digestion and apoptosis.

Correct answer: Synthesis and modification of proteins

The Rough ER is studded with ribosomes, which synthesize proteins destined for secretion or membrane insertion. As these proteins enter the RER lumen, they undergo folding and initial modifications.

Correct answer: Sorted, tagged, and packaged for delivery

The Golgi apparatus functions like a post office, receiving proteins from the ER. It modifies them (e.g., glycosylation) and packages them into vesicles destined for specific locations inside or outside the cell.

Correct answer: Microfilaments (Actin)

Microfilaments are the thinnest components of the cytoskeleton, made of actin. They are essential for cytokinesis, amoeboid movement, and the contraction of muscle cells.

Correct answer: Granum

Chloroplasts contain green-colored grana, which are stacks of disc-like thylakoids. This is the site where the light-dependent reactions of photosynthesis occur.

Correct answer: Smooth Endoplasmic Reticulum

The Smooth ER lacks ribosomes and is the major site of phospholipid and steroid synthesis. In liver cells, it also contains enzymes that help detoxify harmful substances.

Correct answer: Ribosomal RNA (rRNA) synthesis

The nucleolus is a dense region where rRNA is transcribed and assembled with proteins to form ribosomal subunits. These subunits then exit the nucleus through pores to function in the cytoplasm.

Correct answer: Maintaining turgor pressure and storing nutrients

The central vacuole can occupy up to 90% of a plant cell's volume. It stores water, ions, and waste, and its turgidity provides structural support to the plant.

Correct answer: Microtubules

Cilia and flagella are microtubule-based extensions of the plasma membrane. The '9+2' arrangement consists of nine doublets of microtubules surrounding two central singlets, powered by dynein motor proteins.

Correct answer: Plasmodesmata

Plasmodesmata are channels that pierce the cell walls of plant cells. They create a cytoplasmic continuum (symplast) that enables communication and nutrient exchange between neighboring cells.

Correct answer: Cristae

Cristae increase the surface area of the inner mitochondrial membrane. This provides more space for the proteins of the electron transport chain and ATP synthase, maximizing energy production.

Correct answer: Rough Endoplasmic Reticulum

Since enzymes are proteins, cells that produce and secrete them require extensive Rough ER for synthesis. These proteins are then modified and moved to the Golgi for export.

Correct answer: The Endosymbiotic Theory

The Endosymbiotic Theory suggests these organelles were once free-living bacteria that were engulfed by a host cell. Evidence includes their own circular DNA, double membranes, and bacterial-like ribosomes.

Correct answer: Peroxisome

Peroxisomes contain enzymes like catalase that convert toxic hydrogen peroxide into water and oxygen. They also play a significant role in the initial stages of lipid metabolism.