31 Years NEET Previous Year Questions: Cell: The Unit of Life - 4 - NEET MCQ

Cell theory was proposed by Schleiden and Schwann (1839) according to which “All living organisms are composed of cells.” Cell theory is also known as cell principle, cell doctrine etc.

The exceptions of cell theory is viruses which do not possess a cellular machinery. They consists of DNA or RNA core surrounded by a protein sheath and lack cellular organisation.

In salivary gland chromosomes / polytene chromosomes, somatic pairing is formed between homologous chromosomes and repeated replication of their chromonemata.

Cell recognition and adhesion occur due to biochemicals of cell membranes named glycoproteins and glycolipids. These are formed due to the small carbohydrate molecules present on lipids and extrinsic protein.

Golgi complex is absent in prokaryotic cell i.e (PPLO, bacteria and blue green algae). It is present in all eukaryotic cells except sieve tubes of plants, sperms of bryophytes and pteridophytes and red blood corpuscles.

Lysosomes are membranous bag with hydrolytic enzymes which is used for controlling intracellular digestion of macro-molecules.

In plant peroxisomes are associated with photorespiration. Peroxisomes are ubiquitous organelles in eukaryotes that function to rid the cell of toxic substances. They have a single membrane that separates their contents from the cytosol (the internal fluid of the cell) and that contains membrane proteins critical for various functions, such as importing proteins into the organelles and aiding in proliferation. Unlike lysosomes, which are formed in the secretory pathway, peroxisomes usually self-replicate by enlarging and then dividing, although there is some indication that new ones may be formed directly. Peroxisomes were discovered by the Belgian cytologist Christian de Duve in 1965

In the region of Balbiani ring the DNA strands uncoil, become active and produce number of copies of messenger RNA.

The inner  membrane of mitochondria  is infolded to form involutions called cristae. They are meant for increasing the active area of the inner membrane.

Mitochondrial cristae possess small particles called elementary particles which contain ATP- ase. Therefore, they are the centes of ATP synthesis during oxidative - phosphorylation.

Organelle having flattened membrane bound cisternae and lying near the nucleus is Golgi apparatus.

Several plant structures e.g. pollen, seeds contain fats. The fats are hydrolysed and consumed as source of energy. This is accomplished through oxidative degradation called glyoxylate cycle.

Three types of growth are present in multicellular animals :
(i) Auxetic growth : Increase in cell volume only not in number.
(ii) Multiplication growth : Increase in number not in volume.
(iii) Accretionary growth : Growth is due to mitotic division of some special type of cells occurring in specific locations of body.

The prokaryotic flagellum is single stranded made up of several parallel protein fibrils and helical in shape while in eukaryotes it is made up of axonema and sheath.

Rough endoplasmic reticulum bears ribosomes on its outer surface. These ribosomes take part in protein synthesis.

Granules of condensed chromatin (heterochromatin), are found scattered in interphase nuclei. A chromocentre, the polytene chromosomes appear attached.

Desmosomes are cementing substances, which adhere to each other and keep the latter tightly packed and they also prevent leakage of fluid from interphase.

Lysosomes are single membrane bound vesicular organelles rich in acid hydrolases. They are involved in phagocytosis.

Genes located on the mitochondrial  DNA are inherited through the cytoplasm. The zygote receives cytoplasm from the female gamete  hence it involves maternal inheritance.

Golgi bodies are cytoplasmic organelle which take part in elaboration and secretion of complex biochemicals. Microsomes are small single membraned cell organelles that absorb oxygen and perform direct oxidation of substrates. Glyoxisomes contain enzymes for b-oxidation of fatty acids.

Nucleus is enclosed by a double layered envelope. Sphaerosomes are small spherical single membrane bound cell organelles specialized to synthesize and store fat. Mitochondria is also surrounded by a two layered membrane - outer membrane and inner membrane. 

Ribosomes are the sites of protein synthesis mitochondria is the site of ATP synthesis . Golgi complex takes part in elaboration and secretion of complex biochemicalls. The distinctly staining region of cytoplasm surrounding the pair of centrioles together with the centrioles is called centrosome .

Glycosylation is the process or result of addition of saccharides to proteins and lipids. The process is one of four principal co-translational and posttranslational modification steps in the synthesis of membrane and secreted proteins and the majority of proteins synthesized in the rough ER undergo glycosylation. It is an enzyme-directed site-specific process, as opposed to the non-enzymatic chemical reaction of glycation. 

Microtubules are  formed of dimers of tubulin. Microtubules are present in centriole, flagella, spindle fibres but not in Mitochondria.

Zinc is an activator of enzymes like carbonic anhydrase. Copper takes part in electron transport as plastocyanin. Potassium maintains membrane permeability.