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What is a mesosome in a prokaryotic cell? Mention the functions that it performs.

Mesosomes are special membranous structure formed by the extension of plasma membrane. These extensions are in the form of vesicles, tubules, and lamella


(1) They help in the formation of cell wall

(2) They take part in the replication of and distribution DNA to the daughter cells.

(3) Mesosomes help in respiration, and secretion processes.

(4) They increase the surface area of the plasma membrane and enzymatic content.


How do neutral solutes move across the plasma membrane? Can the polarmolecules also move across it in the same way? If not, then how are thesetransported across the membrane?

Neutral solutes move across the membrane by the process of simple diffusion along the concentration gradient which is from higher concentration to lower concentration.

Polar molecules cannot move across the membrane in the same way. They require a carrier protein of the membrane to facilitate their transport.


Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labeled diagrams of both.

The double membrane bound cell-organelles are

(1) Mitochondria

(2) Chloroplast.

Characteristics of Mitochondria and Chloroplast
The outer membrane forms the limiting membrane. The inner membrane encloses a lumen. It is known as matrix in mitochondria and stroma in chloroplast.

Functions of Mitochondria

(1) It is the site of aerobic respiration.

(2) They produce cellular energy in the form of ATP; hence they are called as the "power house of the cell".

Functions of Chloroplast

(1) They are the site of photosynthesis.

(2) They store the enzymes required for the synthesis of carbohydrates.


What are the characteristics of prokaryotic cells.

(1) Prokaryotes have cell wall surrounding the cell membrane.

(2) They do not have a well defined nucleus.

(3) The genetic material is not covered by a nuclear membrane.

(4) Extra chromosomal DNA called plasmids is present in the cytoplasm.

(5) Prokaryotes do not have membrane bound organelles.


Multi cellular organisms have division of labour. Explain.

Multi cellular organisms have different types of cells and each of these cells have different functions to perform. For e.g. red blood cells helps in the transport of oxygen, white blood cells help in protection of the body against pathogens, nerve cells for bodily co-ordination etc. A group of cells, which are of the same type, perform the same function like the cells of the kidney helping in excretion, the cells of the respiratory system helping in respiration, the cells in the digestive system helping in nutrition etc. Thus we can see that in multi cellular organisms each function is performed by each system, which exhibits division of labour.


Cell is the basic unit of life. Discuss in brief.

All living organisms are composed of small, tiny structures or compartments called cells. These cells are called the ‘building blocks’ of life.

The cells in a true sense are considered as the basic unit of life because all the life processes, i.e., metabolism, responsiveness and reproduction are carried out by the cells. Cells are the seat of all metabolic processes. Respiration, nutrition and release of energy are carried out within the cells. Even the animals and plants reproduce because the cells reproduce individually. Growth occurs because cells grow and multiply.

Let us take the example of amoeba, a unicellular organism. In amoeba, all the life processes are performed within the boundaries of the single cell. On the other hand, the body of a multi cellular organism is made up of many cells. In these organisms, the cells do not behave independently, but get organized into tissues. Each tissue is specialized to perform specific functions. Different tissues then get organized into organs, which perform certain specific functions. Different organs are finally organized to form organ systems. These tissues, organs and organ systems of the organisms work because the cells work.

On account of the above discussion, it can be said that cells are the structural and functional unit of living beings. Hence it is the basic unit of life.


What are nuclear pores? State their function.

The minute pores formed by the fusion of the two nuclear membranes which envelopes the nucleus is called as the nuclear pores.

It forms the passage for the movement of RNA and proteins in both the directions between the nucleus and the cytoplasm.


Both lysosomes and vacuoles are endo membrane structures, yet they differ in terms of their functions. Comment.

Lysosomes are membrane bound vesicular structure, which contains all types of hydrolytic enzymes. The main function of these enzymes is the digestion of carbohydrates, proteins, lipids, and nucleic acids.

Vacuoles are membrane bound space found in the cytoplasm, which contain water, sap, excretory products, and other materials not necessary for the cell. Its helps in the excretion of unwanted waste products.

In some organisms like amoeba it forms food vacuole for digestion of food and also contractile vacuole for excretion of waste.


Describe the structure of the following with the help of labeled diagrams.

(i) Nucleus                            

(ii) Centrosome

(i) Structure of Nucleus
In 1831 Robert Brown first described the nucleus. During the inter phase stage in the nucleus we can see the nucleoprotein fibers called chromatin, nuclear matrix, and one or more spherical bodies called nucleoli. It is covered by a nuclear envelope, which consists of two membranes with a space in between called peri nuclear space. The outer membrane is usually continuous with the endoplasmic reticulum and it bears ribosome's on it.

The nuclear envelope is interrupted at a number of places by number of pores, formed by the fusion of its two membranes.

The nucleoplasm contains nucleolus and chromatin. The content of the nucleolus that is spherical structures is continuous with the rest of the nucleoplasm. The nucleolus is not a membrane bound structure. The chromatin during cell division gets condensed and is called chromosomes.

(ii) Structure of Centro some
Centrosome consists of two cylindrical structures called centrioles which are surrounded by amorphous pericentriolar materials. In a Centrosome both the centrioles lie perpendicular to each other. The centrioles are made up of nine evenly peripheral fibrils of tubulin. Each fibril is a triplet and the adjacent triplets are linked. The central portion of the centriole is proteinaceous.


What is a Centromere?

(i) How does the position of Centromere form the basis of classification of chromosomes?

(ii) Support your answer with a diagram showing the position of Centromere on different types of chromosomes.

(i) The primary constriction present in the chromosome is called Centromere. On either sides of the Centromere there are disc shaped structures called kinetochores.

There are four types of chromosomes based on the position of the Centromere they are

Met centric
The chromosome has the Centro mere in the middle forming two equal arms of the chromosome.
  Sub-met centric
The chromosome has the Centro mere nearer to one end of the chromosome resulting in the formation of one long arm and another short arm.
The Centromere lies extremely close to one end of the chromosome resulting in the formation of one long arm and the other very short arm.
In this type the Centro mere lies in the terminal end of the chromosome.

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