Class 9 Science Chapter 5 MCQ

Each cell is bounded by an extremely delicate, thin elastic living membrane, called the plasma membrane. The plasma membrane is made up of two layers of liquid or fat molecules with protein molecules which is sandwitched between lipid layer. The structure of plasma membrane can be observed under and electron microscope only. It is a selectively permeable membrane which allows the flow of only some substances into the cell and out of the cell. Viruses do not have any membranes. Functions: a) It gives a definite shape to the cell. b) It provides protection to the in contents of the cell. c) It regulates entry and exit of substances in to and out of the cell. d) It can internalise solid and liquid materials by infolding or extending around them. This is the process of active intake of minerals. e) In animal cells, it is involved in adhesion, recognition and in the formation of vesicles, cilia, flagella, microvilli etc.

The Golgi apparatus is involved in formation of lysosome. Lysosomes are simple, tiny spherical sac-like structures evenly distributed in the cytoplasm each lysosome is surrounded by a double membrane and contains powerful enzymes capable of digesting or breaking down all organic material. These enzymes are made by rough endoplasmic reticulum. They perform following functions in our body: i)They help in breaking down or digesting large molecules of the cell. ii)They help in a defence against bacteria and viruses. iii)During starvation, lysosomes act on their own cellular organelles and digest them. This results in cell death. The lysosomes are also called suicide bags or demolition squads of the cell.

Generally, inside the cell there exist a membranous network enclosing a fluid-filled lumen which almost fills up the intracellular cavity, called endoplasmic reticulum (ER). It is of two types: i)Rough Endoplasmic Reticulum with ribosomes attached on its surface for synthesizing proteins. Ii)Smooth Endoplasmic Reticulum which is without ribosome and is meant for secreting lipids.

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

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”.

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

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

The undefined nuclear region is the cytoplasm of prokaryotic cells is called nucleoid. The prokaryotic cells consist of a single chromosome, which is direct content of the cytoplasm i.e., there is no nuclear membrane in a eukaryotic cell, the nuclear envelope separates the nucleus from the cytoplasm. The nuclear envelope contains many pores (the nuclear pores) and encloses the liquid ground substance, the nucleoplasm. Within nucleoplasm two types of nuclear structures are embedded-the nucleolus and chromatin material. The nucleolus may be one or more in number and is not bounded by any membrane. It is rich in protein and RNA (Ribonucleic Acid) molecules and acts as the site for ribosome formation, hence are also known as factory of ribosomes.

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.

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.