Class 9 Science Chapter 5 MCQ

Here, are all the statements are correct. Hence, your answer will be option [D].

The micrometer commonly known as micron in SI derived unit of length equaling to 10^-6 of a metre.

Schleiden (1836) and Schwann (1834) gave the cell theory, which was further refined by R. Virchow (1855). The main postulates of cell theory are (i)All organisms are composed of cells and cell products. (ii)All metabolic reactions take place in cells. Thus, cell are structural and functional units of life. (iii)All cell arise from pre-existing cells only. No cell can originate spontaneously but they comes into being only by division of pre-existing cells. (iv) Every organism starts its life as a single cell.

Generally, inside the cell there exist a membranous network enclosing a fluid-filled lumen which almost fills up the intracellular cavity, called endoplasmic reticulum (ER). Endoplasmic reticulum is absent in the red blood cells of mammals.

Other than nucleus mitochondria contains DNA and are able to synthesise their own proteins they are regarded as semi-autonomous organelles.

Endocytosis is the ingestion of material by the cells through their plasma membrane. It is a collective term that describes three similar processes “phagocytosis” (cell eating), “potocytosis” (cell drinking) and receptor-mediated endocytosis. These processes are pathways to specifically internalise solid particles, small molecules and ion, and macromolecules, respectively. All of them require energy, so they may be regarded as different forms of active transport. Out of these phagocytosis is the common method of feeding among the Protozoa (e.g., Amoeba) and lower “Metazoa” (e.g., sponges). In pseudopodial movement the phagocyte enguls the particle lysosomes, join with the vacoule containing ingested particle and pour their contents into the vacoule to destroy the particle.

In nucleoid, its DNA content is equal to a single DNA molecule. Generally, in nucleus, its DNA content is equal to two or several DNA molecules.

In eukaryotic cell membrane bound cell organelles such as mitochondria and plastids endoplasmic reticulum, Golgi apparatus etc. are present. In prokaryotic cell membrane bound cell organelles are absent.

When a cell is immersed in hypertonic (very concentrated) solution, water diffuses out of the cell by the process of osmosis. This is because there is a lower concentration of water outside the cell. Although water molecules pass the cell membrane in both direction but more amount of water goes out of the cell than the amount of water which enters it. As a result of this the cell shrinks. This process is called exosmosis. If exosmosis continues in a plant cell, the cytoplasm appears to be shrunken. This is called plasmolysis and the cell is said to be plasmolysed.

Viruses are considered as an intermediate between living and non-living cells because they cannot metabolize and reproduce on their own. They can reproduce only when enters in a host’s body. They are an exception to all cell theory. A virus crystal is a collection of thousands of viruses. Viral crystal is a pore collection used for chemical studies.