Class 9 Science Chapter 5 MCQ

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

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.

The prokaryotic cells lack true nucleus and a circular DNA lies naked in the cytoplasm. The unidentified nuclear region of the cell is called nucleoid. The prokaryotic cell lacks chromosomes and nucleolus or nuclear membrane and nucleoplasm remains undifferentiated from the cytoplasm.

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.

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

The movement of water molecules through selectively permeable membrane along concentration gradient is called osmosis. It is the passage of water from region of high-water concentration through semipermeable membrane to a region of low water concentration (only through semipermeable membrane). Unicellular freshwater organisms and most plant cells tend to gain water through osmosis. Absorption of water by plant roots is also an example of osmosis.