Short & Long Question Answers with Solution: Cell - The Unit of Life | Science for ACT PDF Download

Q1. What is a satellite chromosome?
Ans: The chromosomes that have an additional or secondary constriction at the distal part of the arm formed by a chromatin thread are known as satellite chromosomes. These appear as an outgrowth or a small fragment. These are also known as marker chromosomes. The chromosomes 13, 14, 15, 16, 21, and 22 are satellite chromosomes.

Q2. Give the fundamental similarities that occur in all cells.
Ans: The fundamental similarities that occur in all cells are:

• Hereditary characters are transmitted through nucleic acids containing DNA and RNA.
• The basic structure of cell membranes is the same in all cell organelles.
• The process and method of aerobic respiration are similar.
• The mechanism of synthesis of nucleic acids and the formation of proteins within the cells are also much the same. .

Q3. What is the importance of a vacuole in a plant cell?
Ans: The vacuole is a membrane-bound space in the cytoplasm of a plant cell. It contains sap, water, excretory products and other materials not useful for the cell. Vacuoles occupy 90% of the cell volume during osmosis. They maintain the turgor pressure against the cell wall thereby maintaining the shape of the cell and cell fluid balance.

Q4. What are the cytoskeletal structures present in eukaryotic cells?
Ans:  Cytoskeletal Structures help the eukaryotic cells to adopt different types of shapes and to perform directed movement.

Cytoskeletal structures contain three major types of protein filaments which are classified as microfilaments, microtubules, and intermediate filaments.

The microfilaments are 7 nm in diameter and either scattered or organised into the network or parallel arrays within the matrix. They also play a major role in cell motion and help the eukaryotic cells adopt different shapes. Such cellular movements are associated with the microfibres movements of pigment granules, amoeboid movements, and protoplasmic streaming. The microfilaments consist of actin-like proteins.

Q5. State the characteristics of prokaryotic cells.
Ans: The characteristics of a prokaryotic cell are as follows:

• A prokaryotic cell is surrounded by a cell membrane.
• Mitochondria, chloroplast and nucleus are not present.
• The DNA is circular and not associated with basic proteins.
• The cytoplasm is filled with dense granules most of which are ribosomes.
• The thylakoids are scattered in the chloroplast, and not placed in the form of stacks.

Q6. What are the major functions of the cell wall?
Ans: The major functions of the cell wall are as follows:

• The cell wall gives a definite shape and helps protect the internal organelles.
• The cell wall provides a structural framework and supports the plasma membrane.
• It prevents the cell from the process of desiccation.
• The cell wall physically counteracts the osmotic pressure produced by the cell organelles.
• It also helps transport materials and metabolites in and out of the cell through diffusion.

Q7. Why is cell the basic unit of life?
Ans: A human body is made up of trillions of cells. There are various organisms with a single cell such as amoeba. All cells divide to form new cells and possess several organelles to carry out various life functions. The cells of an organism carry the same genetic material which carries all the hereditary information of an individual. That is why it is called the basic unit of life.

Q8. What do you mean by plasmids? What role do they play in bacteria?
Ans: A plasmid is an autonomously replicating, extra-chromosomal, circular, double-stranded DNA found in the cytoplasm of the bacterial cell. These usually remain separate from the chromosome.
Role- Plasmids act as vectors to transfer important genes and in recombination experiments. It also helps in bacterial conjugation. For eg., pBR322

Q9. List the different functions of the golgi bodies.
Ans: The functions of Golgi bodies are as follows:

• Golgi bodies help in storing, condensing, and packaging important materials.
• Many different enzymes are found in Golgi bodies that help during spermatogenesis.
• Due to the action of the Golgi bodies, mucilage and gums are secreted in plant cells.

Q.10. What is a mesosome?
Ans: Mesosome is formed by the extension of the plasma membrane into the cell in prokaryotes. It facilitates cell wall formation, DNA replication, and distribution of DNA to the daughter cells. It also helps in respiration and secretion and increases the surface area of the plasma membrane and enzymatic content.

Q11. Describe the structure and functions of the organelles stated below-
(a) nucleus
(b) mitochondria
(c) plastid
Ans:

(a) Nucleus
Electronic studies reveal that the nucleus is an organelle bounded by two membranes forming the nuclear envelope. The outer and inner membranes of the nucleus are separated by a narrow space called perinuclear space.

The outer membrane of the nucleus continues with the organelle endoplasmic reticulum (ER), while the inner membrane surrounds the nucleus organelles. At some points, the nuclear envelope is surrounded by small structures called nuclear pores.

Circular pores surround these pores. The circular pores or circular structures are called annuli. The pores or the annuli unite to form a structure called a pore complex. These pores also help exchange materials between the nucleoplasm and cytoplasm. The nuclear membrane disappears during the cell.-division process. It then reappears during nuclear recognition in the telophase stage of cell division.

The nucleoplasm contains chromatin and nucleolus, where the nucleolus is a rounded structure, and it is not separated from the rest of the nucleoplasm by a single membrane. It is also associated with a specific nucleolar organising region called the NOR of some chromosomes. The nucleolus is also called the “site for ribosomal RNA synthesis”, where the cells which remain engaged in protein synthesis have a larger and more numerous nucleoplasm.

(b) mitochondrion 
Ultrastructure of the organelle mitochondria: They are commonly spherical, elongated, or rod-like cell organelle, known as the “powerhouse of the cell.” Mitochondria were first discovered by the scientist Hofmeister in 1851 in the cells of a pteridophyte. They were later named ‘mitochondrion’ by Benda in 1897.

Mitochondria is a double membranous cell organelle where the outer membrane is smooth, and the space between the two membranes is called the outer chamber. On the other hand, the space surrounded by the inner membrane is called an inner chamber filled with homogeneous fluid.

The double membrane of the mitochondria is actively associated with aerobic respiration and the release of energy for cellular activity. This biological oxidation of the fats & carbohydrates releases a small amount of energy utilised by mitochondria for ATP synthesis. 

(c) plastid.
Ultrastructure of plastids: They are green-coloured cell organelles in the form of plastids bounded by two membranes with about 300 A in total thickness. Each plastid membrane is about 40 to 60 A’ thick and is separated by a clear space of about 25 – 27 A.

The plastid’s inner membrane is intricately elaborated to form a system of lamellae, and the chloroplasts are divisible into two main parts. Stroma- This is a colourless, ground substance found in the chloroplast’s inner side. 

And the Membrane system is made of closed flattened sacs called thylakoids. These thylakoids are closely packed & appear as piles of coils. . These piles of coil structures are called Grana.

The arrangement of this form can be in the form of simple parallel sacs running lengthwise or in a complex interconnecting network of sacs. These chloroplasts invariably have starch granules, which often accumulate near a special region known as pyrenoid in algae.

Q12. How is a multicellular organisation more advanced than a unicellular organisation?
Ans: The multicellular organisation of the human body is more advanced than the unicellular organisation because:

There is a presence of division of labour that occurs among cells which increases efficiency. Also, in a multicellular organism, cells are differentiated, and specialised cells are formed. These specialised cells perform specific functions that increase their survival capacity. Multicellular cells contain a varied type of cells which is more efficient than a single-celled organism. One of the major advantages of multicellular organisms is that the death of a few cells does affect the whole organism.

Q13. Who proposed cell theory? Also, give its postulates.

Ans: J. Schleiden and Theodore Schwann gave the famous cell theory, which states:

1. All living things present are made of cells and cell products. 
2. The cell is all living organisms’ basic structural and functional units. Also, the cell is the basic unit of the living organism. 
3. All metabolic reactions in living beings occur within the cell. The cell theory was later modified by the scientist Rudolf Virchow, who was the first to state that “all-new cells arise from the pre-existing cells”, explaining why all cells contain hereditary material that passes from one generation to another by the process of cell division. It also ensures the transfer of characters with genetic material from parents to their offspring.

Q14. Which cell organelle is known as the powerhouse of a cell and why? 
Ans: The double membrane of the mitochondria is actively associated with aerobic respiration and the release of energy for cellular activity. This biological oxidation of the fats & carbohydrates releases a small amount of energy utilised by mitochondria for ATP synthesis. They are commonly spherical, elongated, or rod-like cell organelles known as the “powerhouse of the cell.” Mitochondria were first discovered by the scientist Hofmeister in 1851 in the cells of a pteridophyte. They were later named ‘mitochondrion’ by Benda in 1897.
Mitochondria is a double membranous cell organelle where the outer membrane is smooth, and the space between the two membranes is called the outer chamber. On the other hand, the space surrounded by the inner membrane is called an inner chamber filled with homogeneous fluid.

Q15. Why is the plasma membrane described as a” protein iceberg in the sea of lipids”?
Ans: The plasma membrane was first described by Singer & Nicolson as a fluid mosaic model type. The lipids and proteins were arranged in a mosaic fashion. The matrix is a highly viscous fluid consisting of two layers of phospholipid molecules with two types of globular proteins. The two types of globular proteins are- 

• peripheral or extrinsic proteins 
• intrinsic or integral proteins. 

The proteins present superficially with the membrane are enzymatic and can move across the matrix & help in the active & passive transport of ions through the membrane.