Class 9 Science Chapter 5 MCQ

In the year 1670, Anton Van Leuwenhoek, a Dutch biologist discovered the living cell when he looked at the pond water under the microscope, he made of lenses.

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.

In 1938 Schleiden proposed the idea that plants consist of cells. Later in the year 1839, Schwann independently asserted that all animals and plants are made up of cells. This joint finding forms the basis of cell theory. The cell theory was refined further in 1855, when R. Virchow presented the idea that all cells arise from pre-existing cell. His amorphism was (Omnis Cellula-e-Cellula).

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.

Vacuoles may be small or large. These are filled with liquid or sap and are membrane-bound organelles. In animal cells, vacuoles are smaller in size and lesser in number than in plant cells. In some plant cells, only one large vacuole is present. The major portion of a plant cell is occupied by vacuoles. The (approx. 90% in some cases) either may be contractile (can contract) or non-contractile. When the pressure of the contents of a contractile vacuole increases, it contracts and releases its contents. In unicellular organisms like Amoeba, food particles are present inside food vacuoles. But are not associated with locomotion. The main functions of vacuoles are 1.In animals, vacuoles are often associated with the maintenance of water balance. 2.They work in osmoregulation, i.e., the maintenance of internal pressure. 3.They store various substances including waste products.

The volume of a cell is fairly constant for a particular cell type and is dependent to the size of an organism. For example, kidney or liver cells are approximately the same size in a bull, horse and mouse. The difference in the total mass of the organ or organisms dependent on the number, not on the volume of the cells. The cells of an elephant are not necessarily larger than those of other tiny animals or plants. The large size of an element is due to the larger number of cells present in its body.

The endoplasmic reticulum performs the following functions: (i)It increases the surface area of the cytoplasm for various metabolic activities of the cell. (ii)It gives internal support to the colloidal matrix i.e., cytoplasm. (ii)It is associated with the synthesis, storage and transport of metabolic products. (iv)It helps in the formation of the cell plate and nuclear membrane during cell division. (v)Routh Endoplasmic Reticulum (RER) is associated with the synthesis of proteins. (iv)Smooth Endoplasmic Reticulum (SER) secretes lipids which along with proteins constitute cell membrane by a process called membrane biogenesis.

Viruses are an exception to cell theory.

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