General Q&A for Class 12 · Page 259
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Which chemical substance is deposited in the secondary walls of sclerenchyma?
Lignin is the primary chemical substance deposited in the secondary walls of sclerenchyma cells, making these tissues remarkably strong and rigid. This complex organic polymer is laid down in thick layers over the cellulose framework of cell walls, creating a hard, woody structure that provides exceptional mechanical strength and support to plant organs. The lignification process essentially converts flexible cell walls into rigid, waterproof barriers that can bear significant weight and resi
- GeneralClass 12All
Write one important character of permanent tissues
The most defining characteristic of permanent tissues is that they are composed of cells that have lost the ability to divide, having differentiated from meristematic tissues into specialized forms with specific functions. Once meristematic cells divide and mature, they undergo permanent structural and functional changes—developing thick or thin walls, forming specific shapes, and sometimes even losing their living contents—to perform dedicated roles such as protection, support, p
- GeneralClass 12All
Name the tissue responsible for growth in plants
Meristematic tissue is the primary tissue responsible for growth in plants. This specialized tissue consists of undifferentiated cells that retain their ability to divide continuously through mitosis, producing new cells that enable plants to increase in length and girth throughout their lifetime. Unlike animal cells, which generally lose their division capacity after maturation, meristematic cells remain perpetually young and metabolically active. Meristematic tissues are strategical
- GeneralClass 12All
Draw the structure of mitochondria.
Mitochondria are double-membrane-bound organelles with a distinctive structure optimized for energy production. The outer membrane is smooth and permeable to small molecules, forming the organelle's exterior boundary and separating it from the cytoplasm. The inner membrane is extensively folded into finger-like projections called cristae, which dramatically increase the surface area available for ATP synthesis. This inner membrane is selectively permeable and contains the electron transport c
- GeneralClass 12All
What are cell organelles? Write the names of different cell organelles.
Cell organelles are specialized, membrane-bound structures within eukaryotic cells that perform specific functions necessary for cellular survival and operation, much like organs in a body perform specific functions for an organism. These compartmentalized structures allow different chemical reactions and processes to occur simultaneously in optimal conditions without interfering with each other, greatly increasing cellular efficiency and complexity compared to prokaryotic cells that lack suc
- GeneralClass 12All
. What would happen to the life of a cell if there was no Golgi apparatus?
Without the Golgi apparatus, cells would face severe disruptions in protein processing, packaging, and distribution, likely leading to cellular dysfunction and death. Proteins synthesized by ribosomes and processed in the endoplasmic reticulum would not undergo essential modifications like glycosylation (adding sugar groups) that are critical for their proper folding, stability, and function. Many proteins require these post-translational modifications to become biologically active, so their
- GeneralClass 12All
Why do spinach look green, papaya yellow and edible part of water melon red?
These distinctive colors result from different types of plastids and the pigments they contain. Spinach appears green because its cells are packed with chloroplasts containing the green pigment chlorophyll, which absorbs red and blue wavelengths of light for photosynthesis while reflecting green wavelengths that our eyes perceive. Chlorophyll is essential for capturing light energy, explaining why actively photosynthesizing tissues like leaves are predominantly green. This color serves a func
- GeneralClass 12All
Write an activity showing osmosis.
Take a peeled potato or carrot and scoop out a cavity in its center, ensuring the walls remain intact. Fill this cavity halfway with concentrated sugar solution or saturated salt solution and mark the initial level with a pen or by measuring. Place the potato in a beaker containing plain water, ensuring the water level outside is higher than the sugar solution level inside the cavity, but does not overflow into it. Leave this setup undisturbed for 3-4 hours or overnight. After this period, ob
- GeneralClass 12All
What is ATP? Write its full form.
ATP stands for Adenosine Triphosphate, a nucleotide that functions as the universal energy currency of cells. This molecule consists of three components: adenine (a nitrogen-containing base), ribose (a five-carbon sugar), and three phosphate groups linked in a chain. The energy in ATP is stored in the high-energy bonds between the phosphate groups, particularly the bond connecting the second and third phosphate. When the cell requires energy for any process, ATP is hydrolyzed (broken down) in
- GeneralClass 12All
What is cell theory? Who formulated it?
Cell theory is one of the fundamental principles of biology, stating three core tenets: (1) all living organisms are composed of one or more cells, (2) the cell is the basic structural and functional unit of life, and (3) all cells arise from pre-existing cells through division. This theory established that cells are not just structural components but the fundamental units where all life processes occur—metabolism, growth, reproduction, and response to stimuli all happen at the cellular
- GeneralClass 12All
What happens when a cell is placed in different solutions? What mechanism is responsible for this?
When a cell is placed in a hypertonic solution (higher solute concentration outside), water moves out of the cell through osmosis, causing the cell to shrink. Animal cells become shriveled and crenated, while plant cells undergo plasmolysis—the cell membrane pulls away from the cell wall as the cytoplasm shrinks, causing the cell to become flaccid and potentially die if the condition persists. In contrast, when placed in a hypotonic solution (lower solute concentration outside), water e
- GeneralClass 12All
What is the importance of nucleus?
The nucleus is fundamentally important because it contains the cell's complete genetic blueprint in the form of DNA, which stores all the information necessary for building and maintaining an organism. This hereditary material controls all cellular activities by determining which proteins are produced, when they are produced, and in what quantities through the regulation of gene expression. The nucleus directs metabolic processes, growth, repair, and reproduction by sending RNA messages to th
- GeneralClass 12All
. What is the role of ribosomes and Golgi body?
Ribosomes are the cellular factories responsible for protein synthesis, translating genetic information from messenger RNA (mRNA) into functional proteins by linking amino acids in the precise sequence specified by the genetic code. Found either free-floating in the cytoplasm or attached to the rough endoplasmic reticulum, ribosomes consist of two subunits (large and small) made of ribosomal RNA and proteins. Free ribosomes typically produce proteins for use within the cell itself, such as en
- GeneralClass 12All
Differentiate between diffusion and osmosis. What is its importance?
Diffusion is the movement of molecules or ions from a region of higher concentration to lower concentration until equilibrium is reached, occurring with any type of substance—solids, liquids, or gases—through any medium. This spontaneous process requires no energy input and happens due to the random kinetic motion of particles. Examples include the spread of perfume fragrance through air, dye dispersing in water, or oxygen entering cells while carbon dioxide exits. Osmosis, in con
- GeneralClass 12All
Write short note on nucleus.
The nucleus is the most prominent and essential organelle in eukaryotic cells, serving as the control center that houses the cell's genetic material and directs all cellular activities. Enclosed by a double-layered nuclear envelope perforated with nuclear pores, the nucleus contains chromosomes made of DNA and associated histone proteins. These chromosomes carry genes that encode instructions for protein synthesis and inheritance of traits. The nucleus regulates which genes are expressed at a
- GeneralClass 12All
Write function of cell wall.
The cell wall provides mechanical strength and structural support to plant cells, fungi, and bacteria, maintaining a definite cell shape and preventing cells from bursting when water enters through osmosis. This rigid framework, composed of cellulose in plants, enables plants to grow upright against gravity and reach toward sunlight without requiring an internal skeleton. The wall's tensile strength comes from the arrangement of cellulose microfibrils embedded in a matrix of other polysacchar
- GeneralClass 12All
What is a gene? What is its chemical composition and function?
A gene is a functional unit of heredity that contains the instructions for building specific proteins or functional RNA molecules. Chemically, genes are composed of DNA (deoxyribonucleic acid), a double-stranded molecule made up of four nitrogen-containing bases—adenine (A), guanine (G), cytosine (C), and thymine (T)—linked to a sugar-phosphate backbone. Each gene represents a specific sequence of these bases that codes for a particular trait or protein, with the sequence determin
- GeneralClass 12All
If cell of onion peel and RBC are separately placed in hypotonic solution, what among the following will take place?
Option (c) is correct—both statements (a) and (b) are accurate. When placed in a hypotonic solution (where the external solution has lower solute concentration than the cell's interior), both onion peel cells and red blood cells (RBCs) will initially swell as water enters through osmosis. However, their subsequent behavior differs dramatically due to structural differences. The RBC will burst (undergo hemolysis) relatively quickly because it has only a flexible cell membrane without any
- GeneralClass 12All
Briefly describe three important parts of cell.
The nucleus is the cell's control center, containing genetic material (DNA) organized into chromosomes that direct all cellular activities. Enclosed by a double-layered nuclear membrane with pores, it regulates gene expression and coordinates cell growth, metabolism, and reproduction. The nucleolus within the nucleus produces ribosomes, essential for protein synthesis. Without the nucleus, cells cannot reproduce or maintain long-term function, though mature red blood cells demonstrate that sh
- GeneralClass 12All
What is protoplasm? Who gave the term protoplasm?
Protoplasm is the living substance within a cell, comprising all the contents enclosed by the cell membrane including both the cytoplasm and the nucleus. It represents the complete living material of the cell and consists of water (75-85%), proteins, lipids, carbohydrates, nucleic acids, and inorganic salts in a complex colloidal state. Often described as the "physical basis of life," protoplasm exhibits characteristic properties such as metabolism, growth, reproduction, responsiveness to sti