Important Questions from Cell - The Unit of Life
A cell is the smallest unit of life. It is the fundamental structural, functional, and biological unit of all living organisms that are known till now. Through the study and analysis of cells, the unit of life and its components, we can ascertain the physiological and behavioral processes of living organisms in molecular terms. This is known as the physio-chemical approach. Additionally, the physio-chemical method of studying living organisms is known as reductionist biology.
The following important question from chapter 7 cell the unit of life will enable you to have a thorough idea of the cell and its various components.
Short Answer Questions
State Cell Theory
Ans. Cell theory states that all living organisms are composed of cells and are products of cells. It also suggests that all cells arise from pre-existing cells.
What are Passive Transport and Active Transport?
Ans. When molecules pass through membranes of the cell the unit of life without the help of energy, it is known as passive transport. On the other hand, active transport is when molecules require energy to move from a lower concentration region to a higher concentration region.
What Are Microbodies?
Ans. Microbodies are membrane-bound tiny vesicles which contain several enzymes. These microbodies can be found in both plant and animal cells.
Mention The Functions of Mesosomes.
Ans. Functions of mesosomes include distribution of daughter cells, replication of DNA and facilitation of cell wall formation. Moreover, it also increases the total surface area and aids in respiration and excretion.
Which is The Powerhouse of The Cell and Why?
Ans. Mitochondria is known as the powerhouse of the cell unit of life as it manufactures cellular energy which is in the form of ATP or Adenosine triphosphate.
What is A Satellite Chromosome?
Ans. In some cases, the fragment of a chromosome is separated from the main body by a secondary constriction. It is known as a satellite chromosome.
Give The Fluid Mosaic Model of A Plasma Membrane
Ans. Singer and Nicholson presented the fluid mosaic model, which shows the structure of the cell membrane as a mosaic of different components – protein, lipid bilayer, cholesterol, sugar. The ratio of each element varies as per cell type. Additionally, the semi-fluid nature of lipids enables the movement of protein.
Long Answer Questions
Describe The Structure of a Prokaryotic Cell With The Help of a Diagram.
Ans. Organisms which have prokaryotic cells are unicellular organisms such as bacteria, mycoplasma, blue-green algae etc. Prokaryotic cells have a wall which surrounds the cell membrane. The fluid matrix within the cell is called cytoplasm. Besides the genomic or single chromosome DNA located in a nucleoid, bacteria have a smaller DNA known as plasmids. It carries unique phenotypic characteristics.
Prokaryotic cells of organisms like bacteria have three-layered cell envelopes. The outermost layer is called glycocalyx, which can be a thick or thin layer. Next comes the cell wall, which acts as a protection and gives shape and structure to the organism. The final layer is the plasma membrane which is semi-permeable and interacts with the external world. The plasma membrane also contains the ribosome and inclusion bodies.
The flagellum of a motile bacteria is made up of three parts – basal body, filament and hook. Other structures in bacteria are Pili which are elongated tubular structures composed of protein. Fimbriae resemble bristle-like structures. These two help the bacteria to function like hosting tissues, rocks in water, etc.
Explain The Structure of A Eukaryotic Cell With A Diagram.
Ans. In contrast to prokaryotic cells, eukaryotic cells contain a nucleus which is membrane-bound. In addition to that, other membrane organelles can also be observed in the cytoplasm such as mitochondria, ribosomes, golgi bodies, chloroplasts, endoplasmic reticulum and so on.
The cytoplasm is bound by a plasma membrane, which is semi-permeable and allows transportation of nutrients and fluids. Plant cells contain a cell wall in addition to plastids and a large central vacuole. Animal cells do not have these. Instead, it has centrioles which are not present in plant cells.
Cell wall protects cells which are the basic unit of life from infection and damage, while also giving it shape. The primary cell wall of a young plant is capable of growth.
The endomembrane system contains the golgi complex, endoplasmic reticulum, lysosomes and vacuoles.
Mitochondria is a double membrane-bound structure. It is called the powerhouse of the cell as it produces cellular energy.
Plastids are found in plants which are responsible for giving each plant-specific colours.
Ribosomes are not bound by membranes and contain RNA and proteins.
Cytoskeleton is a network of filaments which are made up of proteins.
Cilia and flagella are hair-like structures of the cell membrane. They are responsible for cell movement.
Centrosomes contain centrioles which are responsible for cell division.
Nucleus is the largest organelle present in a eukaryotic cell. It is responsible for controlling all the activities of a cell. It also contains DNA.
3. Write a Short Note on Plastids.
Ans. They are present in plant cells and carry pigments which give colour to plants. Plastids can be classified into three types based on the colour of a pigment – chloroplast, chromoplast and leucoplast.
Chloroplasts have carotenoid pigments in addition to chlorophyll which helps in capturing light energy and thereby aid in the process of photosynthesis. Chromoplasts contain carotenoid pigments such as xanthophylls and carotene, which are responsible for red, yellow and orange colour. Leucoplasts have no colour. Its function is to store nutrients.
You will find more cell questions apart from the ones given here on our website along with detailed study materials on each topic. You can also check out solved solutions on class 11 Biology, which will enable you to gain an idea about exam structure.
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FAQs on Cell - The Unit of Life
1. What is a cell and why is it called the structural and functional unit of life?
A cell is the most basic, membrane-bound entity that contains the fundamental molecules of life and of which all living things are composed. It is called the structural unit because all organisms are made up of one or more cells. It is known as the functional unit because all vital metabolic processes required for an organism to live, such as respiration and energy production, occur within the cell.
2. What are the main principles of the Cell Theory as per the NCERT syllabus?
The Cell Theory, a cornerstone of modern biology, is based on three fundamental principles:
- All living organisms are composed of one or more cells.
- The cell is the basic structural and functional unit of all living organisms.
- All cells arise from the division of pre-existing cells, a concept summarised by the maxim 'Omnis cellula-e cellula'.
3. What is the primary difference between a prokaryotic and a eukaryotic cell?
The primary difference lies in the presence of a nucleus and other membrane-bound organelles.
- Prokaryotic cells are structurally simpler and lack a true, membrane-bound nucleus. Their genetic material is located in a region called the nucleoid. They also lack other membrane-bound organelles.
- Eukaryotic cells possess a well-defined, membrane-bound nucleus that houses the chromosomes, as well as specialised organelles like mitochondria, chloroplasts, and the endoplasmic reticulum.
4. Explain the key structural differences between a plant cell and an animal cell.
While both are eukaryotic, plant and animal cells differ in several important ways:
- Cell Wall: Plant cells have a rigid cell wall made of cellulose that provides structural support, which is absent in animal cells.
- Vacuole: Plant cells typically have a large, permanent central vacuole that maintains turgor pressure, whereas animal cells have small, temporary vacuoles, if any.
- Chloroplasts: Plant cells contain chloroplasts, the sites of photosynthesis. Animal cells do not have chloroplasts as they are heterotrophic.
- Centrioles: Animal cells contain centrioles, which are involved in cell division. These are absent in most higher plant cells.
5. What is the importance of the fluid mosaic model for the cell membrane?
The fluid mosaic model is important because it describes the cell membrane not as a rigid barrier, but as a dynamic and fluid structure. This fluidity, which allows lipids and proteins to move, is crucial for functions like cell signalling, transport of substances, cell growth, and secretion. The 'mosaic' of proteins embedded within the lipid bilayer allows the membrane to perform its diverse and specific functions, acting as a selective gatekeeper for the cell.
6. What are mitochondria, and why are they known as the 'powerhouse of the cell'?
Mitochondria are double-membraned organelles found in eukaryotic cells. They are called the 'powerhouse of the cell' because they are the primary site of aerobic cellular respiration. Through this process, they break down glucose and other nutrients to produce ATP (adenosine triphosphate), which is the main energy-carrying molecule used to power all of the cell's metabolic activities and functions.
7. What are the major components and functions of the endomembrane system?
The endomembrane system is a network of organelles that work together to synthesise, modify, package, and transport proteins and lipids. Its major components are:
- Endoplasmic Reticulum (ER): The Rough ER synthesises proteins, while the Smooth ER synthesises lipids and detoxifies substances.
- Golgi Apparatus: Modifies, sorts, and packages materials from the ER into vesicles for transport.
- Lysosomes: Contain digestive enzymes to break down waste materials and cellular debris.
- Vacuoles: Primarily involved in storage and maintaining internal pressure.
8. How do ribosomes and the endoplasmic reticulum cooperate in protein synthesis?
Ribosomes are the cellular machinery responsible for synthesising proteins. Their cooperation with the endoplasmic reticulum (ER) is vital. Ribosomes attached to the Rough Endoplasmic Reticulum (RER) synthesise proteins that are destined for secretion or insertion into membranes. As a protein is made, it is threaded into the ER's internal space, where it undergoes folding and modification. From the ER, these proteins are then transported to the Golgi apparatus for further processing and distribution.
9. What is the role of the nucleus in a eukaryotic cell?
The nucleus serves as the main control centre of the cell. Its primary functions include:
- Storing Genetic Material: It houses the cell's chromosomes, which contain the DNA.
- Controlling Cell Activities: It regulates gene expression, thereby controlling all metabolic activities and determining the cell's structure and function.
- Facilitating Cell Division: It is the site of DNA replication and transcription, which are essential processes for cell division and protein synthesis.
