Class 9 Science Chapter 5 MCQ

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

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.

Lipid molecules in the cell are synthesized by the smooth endoplasmic reticulum present in the 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.

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.

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”.

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.

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.

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.

Endoplasmic reticulum exists as a membranous network, which is connected to the outer membrane of nucleus from one side and plasma membrane to the other. It occurs in three forms (i)Cisternae-closed fluid filled sac (ii)Vesicles (iii)Tubules It is of two types, smooth endoplasmic reticulum i.e., without ribosomes on its surface and rough endoplasmic reticulum with ribosomes on its surface.