General Q&A for Class 12 · Page 260
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is nucleoid? How is it different from the nucleus of eukaryotic cell?
This division of labour operates at multiple organizational levels—specialized cells group together to form tissues (like cardiac muscle tissue), different tissues combine to create organs (like the heart), and organs work together in systems (like the circulatory system). This hierarchical organization allows for remarkable efficiency and complexity. Consider digestion: salivary gland cells produce enzymes, stomach lining cells secrete acid, intestinal cells absorb nutrients, and pancr
- GeneralClass 12All
What is 'division of labour' in multicellular organisms?
Division of labour in multicellular organisms refers to the specialization of cells into different types, each performing specific functions efficiently rather than every cell attempting to do everything. This cellular specialization allows the organism to operate more effectively than if all cells were identical and multifunctional. For example, in humans, nerve cells specialize in transmitting electrical signals for communication and coordination, muscle cells are structured for contraction
- GeneralClass 12All
Define unicellular and multicellular organisms. Give examples.
Unicellular organisms are life forms consisting of a single cell that performs all the functions necessary for life independently—including nutrition, respiration, excretion, growth, reproduction, and response to stimuli. Despite being structurally simple, these organisms are functionally complete, with that one cell containing all the genetic information and cellular machinery needed for survival. Examples include bacteria (like Escherichia coli), protozoans (like Amoeba and Paramecium
- GeneralClass 12All
Draw a plant cell and label the parts.
The part that synthesizes food is the chloroplast, the double-membrane organelle containing chlorophyll that carries out photosynthesis, converting light energy, carbon dioxide, and water into glucose and oxygen through biochemical reactions in the thylakoids and stroma. The part that produces energy is the mitochondrion, often called the powerhouse of the cell, which generates ATP through cellular respiration by breaking down glucose and other organic molecules through the Krebs cycl
- GeneralClass 12All
What are different types of Endoplasmic reticulum? Write their function.
The endoplasmic reticulum (ER) exists in two structurally and functionally distinct forms: rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER). The rough ER appears granular under a microscope because its surface is studded with ribosomes attached to the cytoplasmic side of the membrane. These bound ribosomes synthesize proteins destined for secretion outside the cell, incorporation into the cell membrane, or delivery to specific organelles like lysosomes. The RER modifie
- GeneralClass 12All
Explain "A cell is a basic unit of an organism"
The statement "a cell is the basic unit of an organism" means that the cell is the smallest structural and functional unit capable of independent existence and performing all essential life processes. Just as atoms are the building blocks of matter, cells are the fundamental building blocks of life—every organism, from the simplest bacteria to complex humans, is composed of one or more cells. A single cell contains all the machinery necessary to carry out metabolism, growth, reproductio
- GeneralClass 12All
Write the main function of each of the following.
The plasma membrane functions as a selectively permeable barrier controlling the exchange of materials between the cell and its environment, while also facilitating cell recognition, communication, and maintaining cellular integrity through receptor proteins and structural support. The cell wall provides rigid structural support and protection to plant cells, maintains cell shape, prevents excessive water uptake and bursting in hypotonic conditions, and acts as a defensive barrier aga
- GeneralClass 12All
Write short notes on mitochondrion and chloroplast.
Mitochondria are double-membrane-bound organelles known as the "powerhouses of the cell" because they generate most of the cell's ATP (adenosine triphosphate) through cellular respiration. The outer membrane is smooth, while the inner membrane is highly folded into cristae, providing extensive surface area for ATP production. The inner compartment, called the matrix, contains enzymes for the Krebs cycle, mitochondrial DNA, and ribosomes, enabling mitochondria to produce some of their own prot
- GeneralClass 12All
Name the cell organelle found in plant cells only. Write its types and function.
Plastids are the cell organelles found exclusively in plant cells and some protists. These double-membrane-bound organelles are classified into three main types based on the pigments they contain and their specific functions. Chloroplasts are green plastids containing chlorophyll that carry out photosynthesis, converting light energy into chemical energy and producing food for the plant. Chromoplasts are colored plastids (yellow, orange, or red) containing carotenoid pigments that give color
- GeneralClass 12All
Write function of plasma membrane.
The plasma membrane serves as a selective barrier that regulates the passage of substances into and out of the cell, maintaining the distinct internal environment necessary for cellular survival. This selective permeability allows essential nutrients like glucose, amino acids, and oxygen to enter while permitting waste products like carbon dioxide and urea to exit, all while preventing harmful substances from entering. The membrane accomplishes this through various transport mechanisms includ
- GeneralClass 12All
Differentiate between hypertonic and hypotonic solution.
A hypertonic solution has a higher solute concentration (and consequently lower water concentration) compared to the cell's interior, while a hypotonic solution has a lower solute concentration (higher water concentration) than the cell. When a cell is placed in a hypertonic solution, water moves out of the cell through osmosis, causing the cell to shrink or become plasmolyzed in plant cells—a process where the cell membrane pulls away from the cell wall. Conversely, in a hypotonic solu
- GeneralClass 12All
What is prokaryotic cell? Differentiate between prokaryotic cell & eukaryotic cell.
A prokaryotic cell is a simple, primitive cell type that lacks a membrane-bound nucleus and other membrane-enclosed organelles. The genetic material in prokaryotes exists as a single circular DNA molecule located in a region called the nucleoid, which is not separated from the cytoplasm by any membrane. Bacteria and blue-green algae (cyanobacteria) are examples of prokaryotic organisms, representing some of the earliest and most abundant life forms on Earth. The fundamental difference
- GeneralClass 12All
What are the differences between cell wall and cell membrane?
The cell wall and cell membrane are distinct structures with different compositions, locations, and functions. The cell membrane (plasma membrane) is a thin, flexible lipid bilayer composed primarily of phospholipids, proteins, and cholesterol, present in all cells—both plant and animal. It serves as the selective barrier controlling what enters and exits the cell. In contrast, the cell wall is a rigid outer layer made of cellulose in plants, chitin in fungi, and peptidoglycan in bacter
- GeneralClass 12All
How does cell to cell movement of water take place in plants?
Water moves from cell to cell in plants primarily through osmosis, facilitated by three interconnected pathways: the apoplast, symplast, and transmembrane routes. In the symplastic pathway, water travels through the cytoplasm of cells via plasmodesmata—tiny cytoplasmic channels that connect adjacent plant cells, creating a continuous network of living protoplasm. The apoplastic pathway involves water movement through cell walls and intercellular spaces without crossing any membranes, wh
- GeneralClass 12All
Why is osmoregulation necessary in aquatic organisms?
Osmoregulation is essential for aquatic organisms because they constantly face water and solute imbalances with their surrounding environment, which can be fatal if left uncontrolled. Freshwater organisms live in a hypotonic environment where water continuously enters their bodies through osmosis, potentially causing cells to swell and burst. Conversely, marine organisms in saltwater face the opposite challenge—they lose water to the hypertonic ocean environment and must prevent dehydra
- GeneralClass 12All
1. Which organelle is called 'digestive bag' and why?
Lysosomes are called the 'digestive bags' of the cell because they contain powerful hydrolytic enzymes capable of breaking down all types of biological macromolecules including proteins, carbohydrates, lipids, and nucleic acids. These membrane-bound organelles function as the cell's waste disposal system, digesting unwanted materials, worn-out organelles, and foreign particles that enter the cell through phagocytosis. The enzymes work optimally in acidic conditions (pH 4.5-5.0), which is main
- GeneralClass 12All
Name the nucleic acids that are present in an animal cell.
Animal cells contain both DNA (Deoxyribonucleic Acid) and RNA (Ribonucleic Acid), the two types of nucleic acids essential for storing, transmitting, and expressing genetic information. DNA is primarily located in the cell nucleus, where it is organized into chromosomes and serves as the master blueprint containing all genetic instructions for the organism. Additionally, small amounts of DNA are found in mitochondria (mitochondrial DNA or mtDNA), which is inherited maternally and encodes some
- GeneralClass 12All
Give full form of ATP.
ATP stands for Adenosine Triphosphate. This molecule serves as the primary energy currency of all living cells, storing and transferring energy needed for virtually every cellular process including muscle contraction, nerve impulse transmission, chemical synthesis, and active transport across membranes. Structurally, ATP consists of adenosine (a nitrogenous base adenine attached to a ribose sugar) bonded to three phosphate groups. The high-energy bonds between the phosphate groups, pa
- GeneralClass 12All
Give two examples of cells where 'cell shape' changes frequently.
Amoeba is a classic example of a cell that constantly changes its shape through a process called amoeboid movement. This unicellular organism extends temporary projections of its cytoplasm called pseudopodia (false feet) in different directions to move, engulf food through phagocytosis, and respond to environmental stimuli. The shape changes are facilitated by the dynamic rearrangement of its cytoskeleton, particularly actin filaments, which allow the cell membrane to bulge outward and flow i
- GeneralClass 12All
Give two points of importance of osmosis.
Osmosis plays a vital role in maintaining cell turgidity and shape, which is especially critical in plant cells where the influx of water creates turgor pressure against the rigid cell wall, keeping plants upright, firm, and structurally sound. Without adequate turgor pressure maintained through osmosis, plants wilt and droop because their cells become flaccid. This same principle allows plant cells to perform growth movements and maintain the rigidity needed for leaves to capture sunlight ef