Cell Structure — Set 4
Biology · कोशिका संरचना · Questions 31–40 of 60
What is the name of the fluid that fills the space inside the chloroplast and surrounds the thylakoids?
Correct Answer: D. Stroma
The stroma is the site of the light-independent reactions of photosynthesis, also known as the Calvin cycle. It contains enzymes, DNA, and ribosomes necessary for chloroplast function. It is analogous to the matrix found in mitochondria.
Which structure in animal cells is involved in the formation of the 'cleavage furrow' during cytokinesis?
Correct Answer: B. Microfilaments
Microfilaments, made of the protein actin, form a contractile ring that pinches the cell into two. This process is the final step in dividing the cytoplasm between daughter cells. It differs significantly from the cell plate formation seen in plants.
Which organelle is responsible for the storage of water, waste, and nutrients in a large central compartment in plants?
Correct Answer: C. Vacuole
The large central vacuole can occupy up to 90 percent of the volume of a mature plant cell. It provides turgor pressure to keep the plant upright and stores various defensive compounds. It is surrounded by a single membrane called the tonoplast.
Which organelle is found in large numbers in sperm cells to provide energy for movement?
Correct Answer: D. Mitochondria
Sperm cells have many mitochondria in their midpiece to power the flagellum. This energy is required for the long journey toward the egg. Without ATP from these organelles, fertilization would not be possible.
Which protein makes up the 'microtubules' of the cytoskeleton?
Correct Answer: D. Tubulin
Tubulin dimers assemble into hollow tubes that provide rigidity and act as tracks for organelle movement. Microtubules are also the main components of cilia, flagella, and centrioles. They play a critical role in separating chromosomes during cell division.
Which organelle is primarily responsible for the oxygenase activity of RuBisCO that initiates the photorespiration pathway?
Correct Answer: B. Chloroplast
Photorespiration is initiated in the chloroplast where the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) acts on oxygen instead of CO2, producing 2-phosphoglycolate. This compound is then processed sequentially in the peroxisome (where it is converted to glycine) and mitochondria (where CO2 is released). Although all three organelles participate in the full photorespiration cycle, the primary initiating organelle is the chloroplast where the oxygenase activity of RuBisCO takes place.
What is the term for the movement of water across a selectively permeable membrane?
Correct Answer: A. Osmosis
Osmosis is the diffusion of water from a region of low solute concentration to high solute concentration. It is a passive process that does not require the expenditure of cellular energy. This movement is essential for maintaining cell volume and pressure.
Which part of the nucleus allows for the regulated exchange of large molecules like RNA and proteins?
Correct Answer: A. Nuclear Pore
Nuclear pores are complex protein channels that span the double membrane of the nuclear envelope. They control the traffic of materials between the nucleus and the cytoplasm. Small molecules can pass freely, but larger ones require specific signal sequences.
Which cellular structure is responsible for the movement of mucus across the surface of human respiratory tracts?
Correct Answer: C. Cilia
Cilia are short, hair-like projections that beat in a coordinated rhythm. In the lungs, they move trapped dust and particles upward toward the throat. They share the same internal '9+2' microtubule arrangement as flagella.
Which organelle is the site of the 'Light Reactions' of photosynthesis?
Correct Answer: B. Thylakoid
The thylakoids are flattened sacs where chlorophyll captures sunlight and converts it into chemical energy. This energy is stored in molecules like ATP and NADPH for use in the stroma. Thylakoids are often stacked into structures called grana.