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Important Questions Class 11 Biology Chapter 8 Cell Unit Life

A cell is the structural and functional unit of life. Each cell is surrounded by a cell membrane which separates the internal and external environments of the cell. The interior environment of a cell is known as the cytoplasm which consists of cellular machinery and structural elements. The nucleus is present at the centre of the cell which contains all the hereditary information of an organism. Proteins, carbohydrates, sugars and starch are the organic molecules present in the cell.

Q.1. What is the importance of a vacuole in a plant cell? A.1.  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. Q.2. What is a satellite chromosome? A.2.  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. Q.3. Match the following:

A.3.  Cristae- Infoldings in mitochondria Cisternae- Disc-shaped sacs in Golgi apparatus Thylakoids- Fat membranous sacs in the stroma. Q.4. State the characteristics of prokaryotic cells. A.4.  The characteristics of a prokaryotic cell are as follows:

Q.5. Multicellular organisms exhibit division of labour. Comment. A.5.  The cells of a multicellular organism are organised to form tissues such as bones, blood etc. The tissues collectively form an organ such as kidney, liver, etc. and these organs organize to form an organ system, for eg., digestive system, circulatory system etc. Every single cell has its own function. Different organs and organ systems carry out different functions which help in the proper functioning of an individual. Q.6. Why is cell the basic unit of life? A.6.  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. Q.7. What do you mean by plasmids? What role do they play in bacteria? A.7.  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 Q.8. Describe the cell theory in brief. A.8.  The cell theory is based on the following postulates:

Q.9. Differentiate between Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum. A.9.

Q.10. What is the biochemical composition of the plasma membrane? A.10.  The plasma membrane comprises of the following biochemical components:

Q.11. What is a mesosome? A.11.  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. Q.12. What are histones? What role do they play? A.12.  Histones are alkaline proteins found inside the nucleus of eukaryotic cells. They package the DNA into structural units called nucleosomes. They are the main proteins in chromatin. Q.13. What does “S” stand for in the 70S and 80S ribosome? A.13.  “S” is the Svedberg’s unit for sedimentation coefficient. It depicts the rate of sedimentation of a cell during ultracentrifugation. Heavier the cell structure, higher is the sedimentation coefficient. Q.14. Why are mitochondria known as the “powerhouse of the cell”? A.14.  Mitochondria carry out the process of anaerobic respiration and generate ATP for cell functioning. That is why it is called “powerhouse of the cell”. Q.15. What is the fluid mosaic model of the plasma membrane? A.15.  The fluid mosaic model was proposed by Singer and Nicholson. It explains the structures and functions of various cell membranes. According to this model, the protein molecules are embedded in the lipid bilayer. This lipid bilayer gives elasticity and fluidity to the cell membrane. Q.16. Who proposed the fluid mosaic model of the plasma membrane A.16. The fluid mosaic model was first proposed by S.J. Singer and Garth L. Nicolson in the year 1972. Q.17. Define tonoplast? A.17. Tonoplast, also called as the vacuolar membrane is the cytoplasmic membrane filled with cell sap and functions as a membrane boundary of the vacuole of plant cells Q.18. What is the significance of vacuole in a plant cell? A.18. The vacuole is the primary storage organelle of a cell. In the plant cell, this organelle plays a primary role in storing water, food and other essential minerals required for their cellular activities. Q.19. What is the main function of the chloroplast in a plant cell? A.19. The chloroplast is green coloured plastids, which comprises of green-coloured pigments within the plant cell and are called as the chlorophyll. The most important function of the chloroplast is the production of food by the process of photosynthesis. Q.20. How many types of plastids are there in a plant cell? A.20. There are three types of plastids- chloroplast, chromoplast and leucoplast. Q.21.Who Discovered the cell? A.21.  Robert Hooke, an English natural philosopher, was the first person to discover the cell in the year 1665. Later, Antonie van Leeuwenhoek, a Dutch scientist observed cells under another compound microscope Q.22.List out the functions of a Cell. A.22. The cell is the fundamental unit of life. It performs various important functions, which are essential for both the growth and development of an organism. Listed below are few of the functions of a Cell.

Q.23.What are Thylakoids? A.23. Thylakoids are the membrane-bound organelles present within the chloroplasts of a plant cell.hey are the site of the light-dependent reactions of photosynthesis. Q.24.What is ATP? A.24.  ATP – Adenosine triphosphate is the organic molecules, which provide energy for various biochemical processes in the body. Therefore, these molecules are called the energy currency of the cell. Q.25.Where does the transpiration occur in the plant cell? A.25. The process of transpiration occurs in the stomata of a plant cell. They are the tiny opening or a minute pores found on the under-surface of leaves. Q.26.List out the main differences between plant cell and animal cell. A.26.

Q.27.Define cell theory? A.27.  The cell theory was proposed by the two scientists – Theodor Schleider and Matthias Schwann in the year 1839. According to this theory:

Q.28.Which cell organelle is found only in animal cells? A.28.  Cell organelles which are present exclusively in animal cells are Centrosomes. Q.29.What are the functions of Plant Cell? A.29. The major functions of the plant cell are:

Q.30.How many types of cells are there? A.30.  There are different types of cells and are differentiated mainly based on the structure, functions, their compositions, etc. The two main types of cell are- Prokaryotes and Eukaryotes. This differentiation is based on the presence and absence of a nucleus.  

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Disc-shaped sacs in Golgi apparatus

Ribosomes are attached to their surface.

Ribosomes are not attached to their surface.

Formed of cisternae and a few tubules.

It participates in the protein and enzyme synthesis.

Takes part in the synthesis of glycogen, lipids, and steroids.

May develop from the nuclear envelope.

It is connected to the nuclear envelope.

It is connected to the plasmalemma.

Mode of nutrition is Heterotrophic.

The nucleus is found on one side of the cell.

The nucleus is found in the centre of the cell.