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Cell The Unit of Life Class 11 – Introduction
Cell The Unit of Life Class 11:- Important Questions and Answers for Class 11th Biology Chapter 8 , “Cell: The Unit of Life ”is available here for students exam preparations. They can go through these questions and prepare them well before exams. It will be a good revision for the students. Also, they will become confident enough to handle any type of problem asked from this chapter in the examination.
A Cell is the structural and the functional unit of life. Each cell is surrounded by a cell membrane which separates the internal and the external environments of a cell. The interior environment of a cell is known as cytoplasm which consists of cellular machinery and the structural elements. The nucleus is present at the centre of cell which contains all the hereditary information of an organism. Carbohydrates,Proteins, Starch and Sugars are the organic molecules present in a cell.
Cell The Unit of Life Class 11 Questions And Answers
Q.1. Write the importance of vacuole in a plant cell?
A.1. The vacuole is a membrane-bound space in cytoplasm of a plant cell. It basically contains water, sap, excretory products and other materials that are not useful for the cell. Vacuoles occupies 90% of the cell volume during osmosis. They maintain the turgor pressure against the cell wall thereby maintains the shape of the cell and maintains cell – fluid balance.
Q.2. Define satellite chromosome?
A.2. The chromosomes that have an additional or secondary constriction at distal part of the arm formed by a chromatin thread are called satellite chromosomes. These appear as an outgrowth or small fragment. These are also known as the marker chromosomes. The chromosomes 13, 14, 15, 16, 21, and 22 are called satellite chromosomes.
Q.3. Match the correct :
| Column I | Column II |
| 1.Cristae | Fat membranous sacs in stroma |
| 2.Thylakoids | Disc -shaped sacs in Golgi apparatus |
| 3.Cisternae | Infoldings in mitochondria |
A.3.
*Cristae- Infoldings in mitochondria. *Cisternae- Disc-shaped sacs in Golgi apparatus.
*Thylakoids- fat membranous sacs in stoma.
Q.4. State characteristics of a prokaryotic cell.
A.4. The characteristics of prokaryotic cell are:
- A prokaryotic cell is surrounded by the cell membrane.
- Nucleus,Mitochondria, and chloroplast are not present.
- DNA is circular and not associated with the basic proteins.
- Cytoplasm is filled with the dense granules ,most of which are the ribosomes.
- Thylakoids are scattered in chloroplast, and not placed in form of stacks.
Q.5. “The multicellular organisms exhibits division of the labour”. Comment on the following.
A.5. Cells of a multicellular organism are organised to form tissues such as bones, blood etc. The tissues collectively forms organs such as kidney, liver, etc. and these organs organize to form an organ system, for eg., digestive system, circulatory system, excretory 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 organism.
Q.6. Cell is the basic unit of life.Comment.
A.6. Human body is made up of trillions of the cells. There are some organisms with a single cell such as Amoeba. All cells divide to form new cells and possess several organelles to perform various life functions. The cells of an organism carry the same genetic material which carries all the hereditary information of an individual which is transferred from the parents to the offsprings. That is why Cell is called the basic unit of life.
Q.7. What are plasmids? Give it’s functions in bacteria?
A.7. Plasmid is an autonomously replicating, extra-chromosomal, circular, double-stranded DNA found in cytoplasm of the bacterial cell. These usually remain separate from chromosomes.
Functions-
*Plasmids acts as vectors to transfer important genes and in the recombination experiments.
* It also helps in the bacterial conjugation. For eg., pBR322.
Cell The Unit of Life Class 11 Quiz
Q.8.Explain the Cell Theory in brief.
A.8. Cell theory is based on the following postulates:
- Cell is the basic structural and the functional unit of life.
- All living beings are composed of the cells.
- All cells arises from the pre-existing cells.
Q.9. Give differences between Rough Endoplasmic Reticulum and Smooth Endoplasmic Reticulum.
A.9.
| Rough Endoplasmic Reticulum (RER) | Smooth Endoplasmic Reticulum (SER) |
| 1.Ribosomes are attached to their surface. | 1.Ribosomes are not attached to their surface. |
| 2.Formed of cisternae and a few tubules. | 2. It is formed of vesicles and tubules. |
| 3.It participates in the protein and enzyme synthesis. | 3. It takes part in the synthesis of glycogen, lipids, and steroids. |
| 4.May develop from the nuclear envelope. | 4. It may develop from RER. |
| 5.It is internal. | 5.It is peripheral. |
| 6.It is connected to the nuclear envelope. | 6.It is connected to plasmalemma. |
| 7.Lacks detoxification enzymes. | 7. It contains detoxification enzymes. |
| 8.Gives rise to lysosomes. | 8. It gives rise to the sphaerosomes. |
Q.10. The biochemical composition of the plasma membrane is ?
A.10. Plasma membrane comprises of following biochemical components:
- Water- 20%
- Proteins- 20-70%
- Carbohydrates- 1-5%
- Lipids-20-79%
Q.11. Define a mesosome?
A.11. Mesosomes are formed by extension, of the plasma membrane into the cell in prokaryotes. It facilitates the cell wall formation, DNA replication, and the distribution of DNA to the daughter cells. It also helps in the process of respiration and secretion, and increases the surface area of the plasma membrane and the enzymatic content.
Q.12. Define histones? Write their functions ?
A.12. Histones are the alkaline proteins found inside nucleus of the eukaryotic cells. They pack the DNA into structural units called the nucleosomes. They are the main proteins in the chromatin.
Q.13. “S” in the 70S and 80S ribosomes stands for?
A.13. “S” is the Svedberg’s unit. It represents sedimentation coefficient. It also depicts the rate of the sedimentation of a cell during ultracentrifugation.
*Heavier the cell structure, higher is the sedimentation coefficient of the cell .
Q.14. Mitochondria are known as the “powerhouse of the cell”.Comment.
A.14. Mitochondria carries out the process of anaerobic respiration and generate ATP for cell functioning. So it is called the “powerhouse of the cell”.
Q.15. Explain in brief the fluid mosaic model of the plasma membrane?
A.15. Fluid mosaic model was proposed by Singer and Nicholson. It explains the structures and the functions of various cell membranes.
According to this model, protein molecules are embedded in the lipid bilayer. This lipid bilayer provides elasticity ,fluidity to the cell membrane.
Cell The Unit of Life Class 11 Toppers Notes
Q.16.The fluid mosaic model of the plasma membrane was proposed by.
A.16.It was first proposed by S.J. Singer and Garth L. Nicolson, in the year 1972.
Q.17.What is tonoplast?
A.17.Tonoplast is also called as vacuolar membrane. It is the cytoplasmic membrane that is filled with the cell sap and functions as a membrane boundary of the vacuole of plant cells.
Q.18.The significance of vacuoles in a plant cell is ?
A.18.The vacuole is primary storage organelle of a cell. In plant cell, this organelle plays a primary role in the storage of water, food and other essential minerals required for the cellular activities.
Q.19. Function of the chloroplast in a plant cell.
A.19. Chloroplast is a green coloured plastids, which comprises of green-coloured pigments within the plant cell and are called as chlorophyll. The most important function of the chloroplast is the production of food by process of photosynthesis.
Q.20.How many types of plastids are found in a plant cell?
A.20. There are three types of plastids which are found in plants.These are – chromoplast, chloroplast and leucoplast.
Q.21.Cell was discovered by?
A.21. Robert Hooke, an English natural philosopher, was the first to discover the cell in the year 1665. Later, Antonie van Leeuwenhoek, a Dutch scientist observed the cells under the another compound microscope.
Q.22.List out common functions of Cell.
A.22. Cell is the structural and fundamental unit of life. It performs various important roles , which are essential for the growth and development of an organism. These are some of the functions of a Cell-
- It plays a vital role in the reproduction
- It facilitates growth by the process of cell division.
- The cell provides support to the body of the plant.
- It provides energy and allows the transportation of the substances.
- It includes the different organelles associated with the different functions within the cell.
Q.23. Define Thylakoids?
A.23. Thylakoids are membrane-bound organelles present within chloroplasts of the plant cell body.They are the sites of the light-dependent reactions of photosynthesis process.
Q.24 Expand ATP?
A.24. ATP is Adenosine triphosphate.It is the organic molecules, which provides energy for the various biochemical processes in the body. Therefore, these molecules are called ” energy currency of the cell”.
Q.25.Transpiration in plants occurs in which part of the plant ?
A.25.The process of transpiration occurs in stomata of the plant cell. They are the tiny openings or a minute pores found on the under-surface of the leaves.
Q.26.List out the main differences between plant cell and animal cell.
A.26.
| Plant Cell | Animal Cell |
| 1.It is rectangular in Shape. | Round or irregular in shape. |
| 2.Cell wall is present. | The cell wall is absent. |
| 3.Centrosomes are not present. | Centrosomes are present. |
| 4.Plastids are also present. | Plastids are absent. |
| 5.Vacuoles are large and very few in number. | Vacuoles are small and many. |
| 6.Mitochondria are very few in number. | Mitochondria are more in number. |
| 7. The mode of nutrition is autotrophic. | Mode of nutrition is Heterotrophic. |
| 8.The nucleus is present in one side of cell. | The nucleus is present in the centre of the cell. |
Q.27.Briefly describe the Cell Theory?
A.27. Cell Theory was proposed by the two scientists – Theodor Schleider and Matthias Schwann in year 1839. According to the theory:
- A new cell exists from the pre-existing cells.
- All cells have same basic chemical structures.
- Cell is the structural and the functional unit of all living things.
- Hereditary information is passed from parent cell to daughter cell.
- The fundamental biochemical reactions of the individual life takes place within the cells.
- All the living organisms existing on the planet Earth are composed of one or more than one cells.
Q.28 Cell organelle that is found only in the animal cells?
A.28. Cell organelles which are present exclusively in the animal cells are the Centrosomes.
Q.29 Functions of a Plant Cell are ?
A.29.Major functions of plant cell are:
- They are called the building blocks of plants.
- The cell wall provides shape to the cell and protect the inner cell organelles inside the cell.
- Stores food in the form of the energy.
- It helps in the process of photosynthesis, transpiration and the other biological process.
- It helps in the transportion of water and nutrients from the roots and leaves to different parts of the plants.
Q.30 Types of cells are ?
A.30. There are different types of cells and are differentiated mainly based structure, functions, and their compositions, etc. Prokaryotes and Eukaryotes are the two different types of cells . This differentiation is based on the presence or absence of a nucleus.
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