Class 9 Science Chapter 5 MCQ

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

Mitochondria are absent in bacteria and the red blood cells of mammals.

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.

Plant cells, in addition to the plasma membrane, have another rigid rotor covering called the cell wall. The cell wall lies outside the plasma membrane. The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance and provides structural strength to plants. Bacteria is not a plant therefore its cell wall is made up of “Peptidoglycan”.

If the medium surrounding the cell has a higher water concentration, than the cell will gain water by osmosis, such a dilute solution is called hypotonic solution.

Smooth endoplasmic reticulum in liver cells of vertebrates helps in detoxification. It metabolises various toxic or poisonous substances such as drugs, aspirin, insecticides (DDT), petroleum products and pollutants. These toxic substances make their entry in animal’s body through food, air or water.

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.

Chromosomes are thread like structure as usually present in the nucleus which becomes visible only during cell division. Each chromosome is made up of two components. i)Deoxyribonucleic acid (DNA) ii) Proteins (e.g. histones and acidic proteins) These consists of two (unreplicated) or four (duplicate) arms and a primary constriction or centromere which gives them a particular shape due to its position. The paired condition of chromosome is called diploid and unpaired chromosome are said to be haploid.

Osmosis is a spontaneous process where movement of solvent molecules occurs into a region of higher solute concentration from lower solute concentration through a partially permeable membrane, so as to tend to equalise the solute concentration on the two sides. When movement of the solvent takes place from outside to inside the all (inward movement) the process is endosmosis. It occurs in hypertonic solution and causes the swelling of cell. When the movement of solvent takes place from inside to outside of the cell (outward movement) the process is exosmosis. It occurs in hypertonic solution. It results the shrinkage of the cell. When the concentration of water both in the surrounding medium and in the cell is same, the solution in the surrounding medium is said to be isotonic and no movement of water molecules takes place.