Question 1

Q1: Which of the following is not correct? (a) Robert Brown discovered the cell. (b) Schleiden and Schwann formulated the cell theory. (c) Virchow explain...

Accepted Answer

The correct answer is (a). Explanation: Robert Brown discovered the nucleus in 1831. The cell was first observed by Robert Hooke in 1665 (dead cork cells), and the first live cell was seen and described by Antonie Von Leeuwenhoek. Therefore, the statement that Robert Brown discovered the cell is inc...

Question 2

Q10: Cell is the basic unit of life. Discuss in brief.

Accepted Answer

The statement "Cell is the basic unit of life" is a cornerstone of biology, supported by the cell theory. This can be understood in two main aspects: 1.  Structural Unit: All living organisms, from the simplest bacteria to the most complex plants and animals, are composed of one or more cells. The c...

Question 3

Q11: What are nuclear pores? State their function.

Accepted Answer

Nuclear pores are minute perforations or channels found in the nuclear envelope, which is the double membrane surrounding the nucleus in eukaryotic cells. These pores are formed by the fusion of the two membranes (the inner and outer nuclear membranes) of the envelope. Function: The primary function...

Question 4

Q12: Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.

Accepted Answer

Yes, both lysosomes and vacuoles are single-membrane-bound organelles and are part of the endomembrane system. However, they have distinct structures and perform different functions. Lysosomes:    Structure: They are small, vesicular structures formed by the process of packaging in the Golgi apparat...

Question 5

Q13: Describe the structure of the following with the help of labelled diagrams. (i) Nucleus (ii) Centrosome

Accepted Answer

(i) Nucleus The nucleus is a large, double membrane-bound organelle that contains the cell's genetic material. It is the control center of the eukaryotic cell. Structure: 1.  Nuclear Envelope: The nucleus is enclosed by a double membrane called the nuclear envelope. It consists of two parallel membr...

Question 6

Q14: What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing...

Accepted Answer

A centromere is the primary constriction present in a chromosome. It is the region where the two sister chromatids of a replicated chromosome are held together. Disc-shaped structures called kinetochores are present on the sides of the centromere, which serve as attachment points for spindle fibres...

Question 7

Q2: New cells generate from (a) bacterial fermentation (b) regeneration of old cells (c) pre-existing cells (d) abiotic materials

Accepted Answer

The correct answer is (c). Explanation: Rudolf Virchow in 1855 modified the cell theory with his statement Omnis cellula-e cellula, which means that all new cells arise from the division of pre-existing cells. This principle is a fundamental tenet of the modern cell theory.

Question 8

Q3: Match the following Column I (a) Cristae (b) Cisternae (c) Thylakoids Column II (i) Flat membranous sacs in stroma (ii) Infoldings in mitochondria (ii...

Accepted Answer

The correct match is as follows:    (a) Cristae - (ii) Infoldings in mitochondria: The inner membrane of the mitochondria forms a number of infoldings called cristae, which increase the surface area for ATP synthesis.    (b) Cisternae - (iii) Disc-shaped sacs in Golgi apparatus: The Golgi apparatus...

Question 9

Q4: Which of the following is correct: (a) Cells of all living organisms have a nucleus. (b) Both animal and plant cells have a well defined cell wall. (c...

Accepted Answer

The correct answer is (c). Explanation:    (a) is incorrect because prokaryotic cells lack a membrane-bound nucleus. Also, some eukaryotic cells, like mature mammalian erythrocytes, lack a nucleus.    (b) is incorrect because animal cells do not have a cell wall; it is a characteristic feature of pl...

Question 10

Q5: What is a mesosome in a prokaryotic cell? Mention the functions that it performs.

Accepted Answer

A mesosome is a specialized membranous structure found in prokaryotic cells, such as bacteria. It is formed by the infoldings or extensions of the plasma membrane into the cytoplasm. These extensions can be in the form of vesicles, tubules, and lamellae. Functions of Mesosomes: Mesosomes perform sev...

Question 11

Q6: How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transp...

Accepted Answer

Neutral solutes move across the plasma membrane by a process called simple diffusion. This is a type of passive transport where molecules move along the concentration gradient, from an area of higher concentration to an area of lower concentration, without any expenditure of energy. No, polar molecu...

Question 12

Q7: Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled...

Accepted Answer

Two cell-organelles that are double membrane-bound are Mitochondria and Chloroplasts. 1. Mitochondria Characteristics:    They are typically sausage-shaped or cylindrical organelles.    They are enclosed by two membranes: a smooth outer membrane and an inner membrane that is folded into numerous inf...

Question 13

Q8: What are the characteristics of prokaryotic cells?

Accepted Answer

Prokaryotic cells are structurally simpler than eukaryotic cells. Their main characteristics are as follows: 1.  Organisms: They are represented by bacteria, blue-green algae (cyanobacteria), mycoplasma, and PPLO (Pleuro Pneumonia Like Organisms). 2.  Size: They are generally smaller (1-10 $\mu m$)...

Question 14

Q9: Multicellular organisms have division of labour. Explain.

Accepted Answer

Division of labour is a fundamental characteristic of multicellular organisms. It refers to the specialization of different cells, tissues, organs, and organ systems to perform specific functions for the body as a whole. This specialization allows the organism to function efficiently and carry out c...

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