All questions of Cell Theory (BIO) for MCAT Exam

Cell theory states that cells are the basic structural and functional units of all living organisms, and all cells arise from pre-existing cells. Observations that support cell theory include:

III. Spermatogonia undergoing mitosis: This observation demonstrates cell division, which is a fundamental process in cell reproduction and supports the idea that cells arise from pre-existing cells.

IV. The bulk of tissue samples from endocrine glands contain cells as their main building blocks: This observation confirms that cells are the basic building blocks of tissues. The presence of cells as the main constituents of tissue aligns with the concept that organisms are composed of cells.

t cell to replicate and complete their life cycle. Unlike living cells, viruses do not have the ability to reproduce on their own. Instead, they must infect a host cell and hijack its cellular machinery to produce new viral particles. The process of viral replication involves the synthesis of viral components using the host cell's resources and the assembly of new viruses within the host cell. Once the new viruses are assembled, they are released from the host cell, often causing cell lysis.

Therefore, viruses do not strictly adhere to cell theory because they do not arise directly from other viruses. They require a host cell to act as a replication machinery.

Schleiden and Schwann are both credited with making significant contributions to the development of cell theory. Schleiden, a botanist, studied plant tissues and concluded that all plant parts are composed of cells. Schwann, a zoologist, conducted similar studies on animal tissues and came to the conclusion that all animal tissues are made up of cells. Together, their observations and findings led to the formulation of the first two tenets of cell theory: "All plants are composed of cells" and "All animals are composed of cells."

Cell theory is a fundamental principle in biology that consists of three main statements:

I. All living cells must have a cell wall: This statement is incorrect. While some cells, such as plant cells and bacterial cells, have a cell wall, not all living cells possess this structure. Animal cells, for example, do not have a cell wall but are still considered living cells.

II. All living cells require glucose for survival: This statement is incorrect. While glucose is an important energy source for many cells, not all cells require glucose specifically for survival. Cells can utilize different energy sources and metabolic pathways to generate energy.

III. The basic unit of life is a cell: This statement is correct. Cell theory states that all living organisms are composed of one or more cells, and the cell is the basic structural and functional unit of life. Cells carry out all the necessary functions for life, such as metabolism, growth, reproduction, and response to stimuli.

The experiment described involves the use of boiled broth and non-boiled broth, both of which are covered to prevent the entry of air. The observation that no growth occurred in either flask cannot be solely attributed to the rejection of spontaneous generation. The absence of growth could be due to the lack of essential nutrients or gases necessary for cell growth, such as oxygen. Therefore, the conclusion that spontaneous generation is an invalid theory based solely on this experiment is not justified, as it does not account for the potential influence of other factors necessary for cell growth.

Cell theory states that all living organisms are composed of cells, and that cells are the basic units of structure and function in living organisms. However, mitochondria pose a potential exception to cell theory because they have their own genetic material (DNA) and can replicate independently of the cell. Mitochondria are thought to have originated from free-living bacteria that were engulfed by ancestral eukaryotic cells in a process called endosymbiosis. This led to the formation of a symbiotic relationship between the host cell and the engulfed bacteria, which eventually evolved into the mitochondria found in eukaryotic cells today. The presence of mitochondria with their own genetic material challenges the idea that all cellular functions are carried out solely by the cell itself. However, it's important to note that mitochondria are still considered essential organelles within cells, and their functions are tightly integrated with the overall functioning of the cell.

According to cell theory, all cells arise from preexisting cells. This fundamental principle states that cells are the basic units of life and that new cells are generated through cell division. In the given hypothesis, the suggestion is that new cellular material is not created from preexisting cells, but rather by attaching a new nucleus to preexisting cells and forming the cytoplasm and cellular membrane. This contradicts the principle of cell theory, which states that new cells are derived from preexisting cells through processes such as mitosis or meiosis. Therefore, this hypothesis is not supported by cell theory.

Louis Pasteur's crooked neck flask experiment was designed to disprove the theory of spontaneous generation, which proposed that living organisms could arise spontaneously from non-living matter. In his experiment, Pasteur used flasks with curved necks that prevented airborne microorganisms from directly entering the flask while still allowing the exchange of air. He boiled the broth contained in the flask to kill any existing microorganisms and then observed that no growth of microorganisms occurred in the broth over time, even when the flask remained open to the air. This experiment provided evidence against the concept of spontaneous generation, as it showed that the absence of microbial growth was not due to lack of oxygen but rather the prevention of contamination from pre-existing microorganisms in the air. Pasteur's experiment supported the idea that living cells only arise from pre-existing cells, reinforcing the concept that cells are the basic unit of life.

Cell theory states that cells arise from preexisting cells, not from nonliving materials through spontaneous generation. This principle was demonstrated through experiments by Louis Pasteur, which disproved the theory of spontaneous generation.