What Is Cell The Unit Of Life Definition Structure And Types
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.
You can access our hot questions on cell structure as pdf with our phone application and practice according to your convenience, along with easy access to online interactive sessions.
FAQs on Cell The Unit Of Life Complete Guide for Biology Students
1. What is a cell in biology?
A cell is the basic structural and functional unit of life. It is the smallest living unit capable of performing all vital life processes. All living organisms are made up of one or more cells, and each cell contains:
- Plasma membrane that encloses the cell
- Cytoplasm where metabolic activities occur
- Genetic material (DNA) that controls cell functions
2. Why is the cell called the unit of life?
The cell is called the unit of life because it is the smallest unit capable of carrying out all life processes independently. According to the cell theory:
- All living organisms are made of cells.
- The cell is the basic unit of structure and function.
- All cells arise from pre-existing cells.
3. What are the main parts of a cell?
The main parts of a cell are the plasma membrane, cytoplasm, and nucleus (in eukaryotes). Each part has a specific role:
- Plasma membrane – Controls entry and exit of substances.
- Cytoplasm – Contains organelles and is the site of metabolic reactions.
- Nucleus – Stores DNA and regulates cell activities.
4. What is the difference between prokaryotic and eukaryotic cells?
The main difference between prokaryotic and eukaryotic cells is the presence of a true nucleus and membrane-bound organelles. Key differences include:
- Prokaryotic cells – No true nucleus, no membrane-bound organelles (e.g., bacteria).
- Eukaryotic cells – True nucleus and membrane-bound organelles (e.g., plant and animal cells).
- Eukaryotic cells are generally larger and more complex.
5. What is the function of the cell membrane?
The cell membrane controls the movement of substances into and out of the cell. It is selectively permeable and performs the following functions:
- Protects the cell from the external environment
- Maintains internal balance (homeostasis)
- Allows diffusion, osmosis, and active transport
6. What is the role of the nucleus in a cell?
The nucleus acts as the control center of the cell by storing and regulating genetic information. It performs key functions such as:
- Containing DNA and genes
- Controlling protein synthesis
- Regulating cell growth and division
7. What are cell organelles and what do they do?
Cell organelles are specialized structures within a cell that perform specific functions. Important organelles include:
- Mitochondria – Produce energy (ATP)
- Ribosomes – Synthesize proteins
- Endoplasmic reticulum – Synthesizes proteins and lipids
- Golgi apparatus – Modifies and packages proteins
- Lysosomes – Digest waste materials
8. How does diffusion and osmosis occur in cells?
Diffusion and osmosis are passive transport processes that move substances across the cell membrane without energy. They occur as follows:
- Diffusion – Movement of molecules from higher to lower concentration.
- Osmosis – Movement of water across a selectively permeable membrane from high to low water concentration.
- Both help maintain cellular balance.
9. What is the difference between plant cells and animal cells?
Plant and animal cells differ mainly in structure and certain organelles. Key differences include:
- Plant cells – Have a cell wall, chloroplasts, and a large central vacuole.
- Animal cells – Lack cell wall and chloroplasts, usually have small vacuoles.
- Both are eukaryotic and contain nucleus and mitochondria.
10. What is cell division and why is it important?
Cell division is the process by which a parent cell divides to form new daughter cells. It is essential for growth, repair, and reproduction. Types of cell division include:
- Mitosis – Produces two identical somatic cells for growth and repair.
- Meiosis – Produces four haploid gametes for sexual reproduction.
- Ensures continuity of genetic information.
