I am pretty confident that the answer is D) mouthpieces for breathing. This is the only way they can stay underwater for long periods of time. If they came up every 10 seconds for breath, they would waste a lot of time.
The nucleus plays the same role in animal cells as it does in other eukaryotes. What was handled in the RNA world is mostly handled by the eukaryotic nucleus. The nucleolus was the nucleus of the compartment that would later become the nucleus. The cytosol was introduced to accomplish protein synthesis and everything else related with it, according to the Eukaryotic Expansion Theory. Organelles were generated during the protein world, i.e. when translation was possible, and some of them evolved into bacteria, as explained by the Organelle Escape Theory. The endosymbiosis theory is no longer necessary with these views. This is demonstrated via an examination of OET. In the realm of RNA, the nucleus has retained its role. As a result, it has complete control over the cell.
Mitochondria
Mitochondria (plural: mitochondrion) are membrane-bound cell organelles that provide the majority of the chemical energy required to fuel the cell's metabolic activities. Adenosine triphosphate is a tiny molecule that stores the chemical energy created by mitochondria (ATP). Mitochondria have two membranes, one exterior and the other inner, both with deep inner folds. The inner membrane surrounds a region where the mitochondrial matrix is present and is impervious to most substances. Mitochondria are the energy plants of the cell, breaking down nutrients and converting them to energy. Citric acid, also known as Krebs cysteine, is created in the matrix and plays a crucial role in energy generation.
Endoplasmic Reticulum
In the cytoplasm of eukaryotic cells, the endoplasmic reticulum (ER) is a continuous membrane structure that produces a series of flattened sacs. ER is found in all eukaryotic cells. The ER typically accounts for more than 50% of the cell's membranous material in animal cells.
Golgi Apparatus
A Golgi body, also known as a Golgi apparatus, is a cell organelle that aids in the processing and packaging of proteins and lipid molecules, particularly those intended for cell export. The Golgi body is a collection of stacked membranes named after its discoverer, Camillo Golgi.
