Class 9 Science Chapter 5 MCQ

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

Grana are stacks of membrane bounded flattened discoid sacs containing the molecules of chlorophyll.

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.

Chloroplasts are present in green algae and higher plants. They have a green pigment called chlorophyll and they are involved in the photosynthesis of food. Therefore, they are also known as the ‘kitchens of the cells’. Each chloroplast is bounded by two-unit membranes like the mitochondria. It shows two distinct regions: i)Grana are the main functional units of chloroplast. They are stacks of membrane bounded, flattened discoid sacs (called thylakoids) containing the molecules of chlorophyll. ii)Stroma is the homogeneous matrix in which grana are embedded. It contains a large variety of photosynthetic enzymes, starch grains DNA and ribosomes.

The cell walls of adjacent cells are glued together by the plasmodesmata.

Diffusion can occur in any medium and the diffusing molecules may be solids, liquids or gases. Remember, semi-permeable membrane is not required in diffusion.

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.

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.

Along with the function of secretion of various enzyme proteins and producing vacoules, Golgi apparatus is also involved in the synthesis of cell wall, plasma membrane and lysosome. Nucleus, mitochondria and plastids have their own genome (i.e., DNA) and ribosomes. They are self-replicating organelles i.e., they have power to divide and are able to synthesise their own structural protein (semi-autonomous organelles). Mitochondria is site of cellulose respiration and synthesis of energy rich compounds (ATP). Therefore, it is called as power house of the cell. The part of cell which between the plasma membrane and nuclear envelope is called the cytoplasm

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.