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31.
Which cellular structure is responsible for producing ribosomal RNA and is often called the "factory" of the cell?
a. Nucleus
b. Endoplasmic reticulum
c. Golgi apparatus
d. Nucleolus
The nucleolus, located within the nucleus, synthesizes ribosomal RNA (rRNA) and assembles ribosomes. It's often referred to as the cellular "factory" because it produces essential components for protein synthesis. While the nucleus plays a role in cellular activities, it doesn't specifically produce rRNA like the nucleolus. The endoplasmic reticulum is a membrane-bound organelle found in eukaryotic cells. It consists of an extensive network of membranes and comes in two forms: rough endoplasmic reticulum (RER), studded with ribosomes on its surface, involved in protein synthesis, and smooth endoplasmic reticulum (SER), which lacks ribosomes and is associated with lipid synthesis, detoxification, and storage of calcium ions. Golgi apparatus further processes and sorts proteins received from the endoplasmic reticulum for transport to their eventual destinations; lysosomes, the plasma membrane, or secretion.
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33.
In cellular respiration, which stage produces the majority of ATP (adenosine triphosphate)?
a. Glycolysis
b. Krebs cycle
c. Electron transport chain
d. Fermentation
The electron transport chain, the final stage of cellular respiration, produces the majority of ATP. This process involves the movement of electrons through protein complexes, generating the energy required for ATP synthesis. While glycolysis and the Krebs cycle contribute to ATP production, they don't produce as much as the electron transport chain. While fermentation helps regenerate NAD+ and allows glycolysis to continue, it is less efficient in terms of ATP production compared to aerobic respiration, where the electron transport chain produces a significant amount of ATP. Therefore, in the absence of oxygen, cells resort to fermentation to sustain energy production, albeit at a lower efficiency.
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48.
Which phylum do insects belong to in the animal kingdom classification?
a. Mollusca
b. Arthropoda
c. Chordata
d. Annelida
Insects belong to the phylum Arthropoda, which is characterized by segmented bodies and exoskeletons made of chitin. This diverse phylum includes not only insects but also arachnids, crustaceans, and myriapods. Options a, c, and d correspond to other animal phyla--Mollusca, Chordata, and Annelida, respectively--each with distinct characteristics such as soft bodies, notochords, or segmented worms, setting them apart from insects in the animal kingdom.
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