11. Do membranes form only the outer wrapping of cells?
Lipid membranes do not form only the outer cover of cells. Cell organelles, such as the Golgi complex, mitochondria, chloroplasts, lysosomes, the endoplasmic reticula and the nucleus, are delimited by membranes too.
12. Which type of cell came first in evolution - the eukaryotic cell or the prokaryotic cell?
This is an interesting problem of biological evolution. The most accepted hypothesis asserts that the more simple cell, the prokaryotic cell, appeared earlier in evolution than the more complex eukaryotic cell. The endosymbiotic hypothesis, for example, affirms that aerobic eukaryotic cells appeared from the mutualist ecological interaction between aerobic prokaryotes and primitive anaerobic eukaryotes.
13. Concerning the presence of the nucleus what is the difference between animal and bacterial cells?
13. Concerning the presence of the nucleus what is the difference between animal and bacterial cells?
Animal cells (cells of living beings of the kingdom Animalia) have an interior membrane that delimits a cell nucleus and thus they are eukaryotic cells; in these cells the genetic material is located within the nucleus. Bacterial cells (cells of living beings of the kingdom Monera) do not have organized cellular nuclei and so they are prokaryotic cells and their genetic material is found dispersed in the cytosol.
14. What are the three main parts of a eukaryotic cell?
The eukaryotic cell can be divided into two main portions: the cell membrane that separates the intracellular space from the outer space physically delimiting the cell; the cytoplasm, the interior portion filled with cytosol (the aqueous fluid inside the cell); and the nucleus, the membrane-delimited internal region that contains the genetic material.
15. What are the main structures within the cell nucleus?
15. What are the main structures within the cell nucleus?
Within the cell nucleus the main structures are: the nucleolus, an optically dense region, spherical shaped, where there are concentrated ribosomal RNA (rRNA) associated to proteins (there may be more than one nucleolus in a nucleus); the chromatin, made of DNA molecules dispersed in the nuclear matrix during the cell interphase; the karyotecha, or nuclear membrane, the membrane that delimits the nucleus.
16. What are the substances that constitute the chromatin? What is the difference between chromatin and chromosome?
The chromatin, dispersed in the nucleus, is a set of filamentous DNA molecules associated to nuclear proteins called histones. Each DNA filament is a double helix of DNA and thus a chromosome.
17. What is the fluid that fills the nucleus called?
The aqueous fluid that fills the nuclear region is called karyolymph, or nucleoplasm. In the fluid there are proteins, enzymes and other important substances for the nuclear metabolism.
18. Of what substances is the nucleolus made? Is there a membrane around the nucleolus?
18. Of what substances is the nucleolus made? Is there a membrane around the nucleolus?
Nucleolus is a region within the nucleus made of ribosomal RNA (rRNA) and proteins. It is not delimited by membrane.
19. What is the name of the membrane that delimits the nucleus? To which component of the cell structure is that membrane contiguous?
19. What is the name of the membrane that delimits the nucleus? To which component of the cell structure is that membrane contiguous?
The nuclear membrane is also called karyotheca. The nuclear membrane is continuous to the endoplasmic reticulum membrane.
20. What are the main cytoplasmic structures present in animal cells?
20. What are the main cytoplasmic structures present in animal cells?
The main cytoplasmic structures of the cell are the centrioles, the cytoskeleton, lysosomes, mitochondria, peroxisomes, the Golgi apparatus, the endoplasmic reticula and ribosomes.
Compiled by My Preparation of Maharashtra Public Service Commission (MPSC) Examination for the blog http://maharashtrapublicserviceexams.blogspot.com
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