Question:

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

Answer:

A centromere is a region of DNA located in the center of a chromosome. It serves as a point of attachment for the spindle fibers during cell division. The position of the centromere helps to classify chromosomes.

Types of Chromosomes and Centromere Position:

1. Metacentric Chromosome: These chromosomes have the centromere located in the middle, dividing the chromosome into two equal arms. This type of chromosome is usually found in animals.

2. Submetacentric Chromosome: These chromosomes have the centromere located slightly off-center, resulting in one arm being slightly longer than the other. This type is usually found in plants.

3. Acrocentric Chromosome: These chromosomes have the centromere located near one end, resulting in one arm being much longer than the other. This type is usually found in animals.

4. Telocentric Chromosome: These chromosomes have the centromere located at the very end, resulting in one arm being much shorter than the other. This type is usually found in plants.

Diagram:

Metacentric Chromosome:

|——–|Centromere|——–|

Submetacentric Chromosome:

|—–|Centromere|—–|

Acrocentric Chromosome:

|—–|Centromere|————|

Telocentric Chromosome:

|Centromere|—–|

Question:

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

Answer:

Answer:

1. Two cell organelles that are double membrane bound are Endoplasmic Reticulum (ER) and Golgi Apparatus.

2. Characteristics of Endoplasmic Reticulum (ER):

• It is a network of membrane-bound tubes and flattened sacs that are found throughout the cytoplasm.
• It is composed of two types: rough ER (RER) and smooth ER (SER).
• RER is covered in ribosomes, while SER is not.
• It functions as the site of protein synthesis and lipid synthesis and storage.

3. Characteristics of Golgi Apparatus:

• It is a stack of membrane-bound vesicles and flattened sacs.
• It is composed of cisternae, which are flattened sacs that are connected to each other.
• It functions as the site of protein modification and packaging.

4. Functions of Endoplasmic Reticulum (ER):

• It is the site of protein synthesis and lipid synthesis and storage.
• It helps in the transport of proteins and lipids throughout the cell.

5. Functions of Golgi Apparatus:

• It is the site of protein modification and packaging.
• It helps in the transport of proteins and lipids throughout the cell.

6. Labelled diagrams of Endoplasmic Reticulum (ER) and Golgi Apparatus:

Endoplasmic Reticulum (ER):

[Diagram of ER]

Golgi Apparatus:

[Diagram of Golgi Apparatus]

Question:

Match the following: Column I Column II (a) Cristae (i) Flat membranous sacs in stroma (b) Cisternae (ii) Infoldings in mitochondria (c) Thylakoids (iii) Disc-shaped sacs in Golgi apparatus

Answer:

Answer: (a) Cristae - (ii) Infoldings in mitochondria (b) Cisternae - (iii) Disc-shaped sacs in Golgi apparatus (c) Thylakoids - (i) Flat membranous sacs in stroma

Question:

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

Answer:

(i) Nucleus:

The structure of the nucleus can be represented as follows:

Nucleus └── Nuclear Envelope ├── Nuclear Pore └── Chromatin

(ii) Centrosome:

The structure of the centrosome can be represented as follows:

Centrosome └── Centrioles ├── Microtubules └── Pericentriolar Material

Question:

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

Answer:

A mesosome is a type of organelle found in prokaryotic cells. It is a double-membrane structure that helps in maintaining the cell’s shape and provides a surface for enzymes. It also helps in the process of respiration, by forming channels for the exchange of gases and nutrients. Additionally, it helps in the process of cell division by helping in the separation of the chromosomes.

Question:

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

Answer:

1. A cell is a microscopic unit of life that forms the basic building blocks of all living organisms.

2. Cells are highly organized structures that contain genetic material, which is responsible for their growth and reproduction.

3. Cells are made up of various components such as a cell membrane, nucleus, cytoplasm, mitochondria, and ribosomes.

4. The cell membrane is a selectively permeable barrier that regulates the passage of substances in and out of the cell.

5. The nucleus is the control center of the cell and contains the genetic material.

6. The cytoplasm is the gel-like material that surrounds the nucleus and houses the organelles.

7. Mitochondria are the powerhouses of the cell and generate energy for the cell to use.

8. Ribosomes are responsible for synthesizing proteins from the genetic material.

9. Cells are responsible for carrying out a variety of functions such as metabolism, growth, and reproduction.

10. Cells are essential for the survival of all living organisms and are the basic unit of life.

Question:

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) In prokaryotes, there are no membrane bound organelles. (d) Cells are formed de novo from abiotic materials.

Answer:

Answer: (a) Cells of all living organisms have a nucleus.

Question:

Which of the following is not correct? (a) Robert Brown discovered the cell. (b) Schleiden and Schwann formulated the cell theory. (c) Virchow explained that cells are formed from pre-existing cells. (d) A unicellular organism carries out its life activities within a single cell.

Answer:

Answer: (a) Robert Brown discovered the cell.

Question:

New cells are generated from (a) Bacterial fermentation (b) Regeneration of old cells (c) Pre-existing cells (d) Abiotic materials

Answer:

A. New cells are generated from:

B. (a) Bacterial fermentation

C. (b) Regeneration of old cells

D. (c) Pre-existing cells

E. (d) Abiotic materials

Question:

What are the characteristics of prokaryotic cells?

Answer:

1. Prokaryotic cells are unicellular organisms, meaning they are composed of a single cell.

2. Prokaryotic cells are much smaller than eukaryotic cells, typically ranging from 0.2-2.0 micrometers in diameter.

3. Prokaryotic cells lack a nucleus and other membrane-bound organelles, such as mitochondria and endoplasmic reticulum.

4. Prokaryotic cells possess a cell wall composed of peptidoglycan, which gives them their characteristic shape.

5. Prokaryotic cells contain a single circular chromosome, which is located in the nucleoid region of the cell.

6. Prokaryotic cells also contain plasmids, which are small, circular pieces of DNA that can be exchanged between cells.

7. Prokaryotic cells are capable of self-replication and can reproduce asexually through binary fission.

Question:

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

Answer:

A mesosome is a type of organelle found in prokaryotic cells. It is a double-membrane vesicle that is involved in the metabolic activities of the cell, such as respiration and fermentation. It is also involved in the transport of proteins and other materials across the cytoplasm. The mesosome is also involved in the process of cell division, as it helps to separate the two daughter cells. Its function is to maintain the integrity of the cell membrane and to provide a structure for the attachment of enzymes and other proteins.

Question:

Cell: The unit of life

Answer:

Step 1: Understand the definition of a cell.

Step 2: Research the structure and components of a cell.

Step 3: Learn about the various functions of a cell.

Step 4: Explore the different types of cells and their characteristics.

Step 5: Examine the role of cells in the body and in the environment.

Step 6: Analyze the impact of cell biology on modern science and medicine.

Question:

What are nuclear pores? State their function.

Answer:

Nuclear pores are small openings or channels in the nuclear envelope of a cell. They are composed of proteins and regulate the passage of molecules in and out of the nucleus. Their main function is to allow for the transport of molecules such as proteins, RNA, and ribosomes, as well as ions and small molecules, between the nucleus and the cytoplasm. They also act as a barrier to prevent the movement of large molecules such as DNA.