General Q&A for Class 12 · Page 230
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
How is a eukaryotic cell different from a prokaryotic cell?
Eukaryotic and prokaryotic cells represent the two fundamental categories of cellular organization, differing in complexity and structure. The most significant difference is that eukaryotic cells have a membrane-bound nucleus that houses their genetic material, while prokaryotic cells lack a true nucleus—their DNA exists as a circular chromosome in a region called the nucleoid that is not separated from the cytoplasm by a membrane. This distinction is so fundamental that it divides all
- GeneralClass 12All
Name two structures present only in (a) Plant cells (b) Animal cells
Plant cells contain two distinctive structures not found in animal cells: cell wall and chloroplasts. The cell wall is a rigid outer layer composed primarily of cellulose that surrounds the plasma membrane, providing structural support, protection, and shape to plant cells. This tough barrier allows plants to maintain upright growth without a skeletal system and protects against mechanical stress and pathogen invasion. Chloroplasts are the photosynthetic organelles containing chlorophyll that
- GeneralClass 12All
Which structure is the controlling centre of the cell and why?
The nucleus is the controlling center of the cell, often described as the cell's "brain" or command center. This spherical, membrane-bound organelle contains the cell's genetic material (DNA) organized into chromosomes, which carry all the instructions needed for cellular activities. The nucleus is typically the largest and most prominent structure within eukaryotic cells, separated from the cytoplasm by a double membrane called the nuclear envelope. The nucleus earns its designation
- GeneralClass 12All
What is cytoplasm? What is its function?
Cytoplasm is the jelly-like, semi-fluid substance that fills the interior of a cell between the plasma membrane and the nucleus. It consists of the cytosol (the aqueous fluid component) along with all the organelles suspended within it, excluding the nucleus. This complex mixture contains water (about 70-80%), dissolved nutrients, salts, enzymes, and various organic molecules necessary for cellular metabolism. The cytoplasm serves multiple critical functions in cellular life. It provi
- GeneralClass 12All
What is the shape of red blood cells in human blood? What function do red blood cells perform?
Human red blood cells (erythrocytes) have a distinctive biconcave disc shape, meaning they are round and flat with both sides curved inward like a doughnut without a hole. This unique shape, resembling two saucers pressed together rim-to-rim, provides a large surface area-to-volume ratio that optimizes their primary function. Mature red blood cells in mammals lack a nucleus and most organelles, maximizing internal space for their oxygen-carrying machinery. The primary function of red
- GeneralClass 12All
Explain why chloroplasts are found only in plant cells.
Chloroplasts are found only in plant cells (and some protists) because these organisms are autotrophic, meaning they produce their own food through photosynthesis. Animals are heterotrophic organisms that obtain energy by consuming other organisms, so they have no biological need for chloroplasts or the ability to convert light energy into chemical energy. The presence of chloroplasts is the fundamental adaptation that allows plants to harness solar energy and synthesize glucose from carbon d
- GeneralClass 12All
Name the structure on which genes are present. Why are genes considered as the most important part of any living cell?
Genes are present on chromosomes, which are thread-like structures composed of tightly coiled DNA molecules associated with proteins called histones. In eukaryotic cells, chromosomes are located in the nucleus, while in prokaryotic cells, the genetic material exists as a single circular chromosome in the nucleoid region. Each chromosome contains hundreds to thousands of genes arranged linearly along the DNA molecule. Genes are considered the most important part of any living cell beca
- GeneralClass 12All
Can you name two cell organelles that contain their own genetic material?
Mitochondria and chloroplasts are the two cell organelles that contain their own genetic material in the form of circular DNA molecules. This DNA is separate from and much smaller than the nuclear DNA found in the cell's nucleus. Mitochondria are present in nearly all eukaryotic cells (both plant and animal), while chloroplasts are found only in plant cells and some protists. The presence of independent DNA in these organelles strongly supports the endosymbiotic theory, which proposes
- GeneralClass 12All
State the role of Biosphere Reserves.
Biosphere Reserves serve multifaceted roles as model landscapes that integrate biodiversity conservation with sustainable human development, representing UNESCO's innovative approach to balancing environmental protection with economic needs. Their primary conservation role involves protecting representative examples of major ecosystem types—tropical rainforests, grasslands, wetlands, mountains, and coastal areas—preserving genetic diversity within species populations and maintaini
- GeneralClass 12All
. What is a Wildlife Sanctuary? Name any two Wildlife Sanctuaries in India. Where are these Sanctuaries located?
A Wildlife Sanctuary is a protected area established to conserve wildlife species and their habitats, where animals receive legal protection from hunting, poaching, and habitat destruction while certain traditional human activities may continue under regulation. These areas specifically focus on protecting particular species or groups of animals—whether endangered mammals, birds, reptiles, or amphibians—within their natural ecosystems. Unlike National Parks which prohibit nearly a
- GeneralClass 12All
With the help of a labeled diagram, describe the basic design of a Biosphere Reserve.
While I cannot create a visual diagram here, I'll describe the basic three-zone design structure of a Biosphere Reserve that you can visualize or sketch. Imagine a target or bullseye pattern with three concentric zones, though in reality these zones follow natural landscape features rather than perfect circles. The Core Zone forms the innermost area—typically one or more legally protected national parks, wildlife sanctuaries, or strict nature reserves where ecos
- GeneralClass 12All
From cellular point of view, how are Amoeba and earthworm different from each other?
From a cellular perspective, Amoeba and earthworms represent fundamentally different levels of biological organization. Amoeba is a unicellular organism, meaning its entire body consists of just a single cell that performs all life functions—nutrition, respiration, excretion, and reproduction—independently. In contrast, an earthworm is a multicellular organism composed of millions of specialized cells organized into distinct tissues and organ systems, where different groups of cel
- GeneralClass 12All
Where are proteins synthesized inside the cell?
Proteins are synthesized on ribosomes, which serve as the cellular machinery for protein production. These ribosomes can be found in two locations within the cell: either floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming what's called the rough endoplasmic reticulum (RER). The location of protein synthesis often depends on the protein's intended destination—proteins meant for use within the cell are typically made on free ribosomes, while proteins destin
- GeneralClass 12All
What is the name of Golgi apparatus in a plant cell?
In plant cells, the Golgi apparatus is often referred to as dictyosomes. These structures perform the same essential functions as the Golgi apparatus in animal cells, serving as the cell's processing and packaging center for proteins and lipids. The term "dictyosome" specifically describes the individual stacks of flattened, membrane-bound sacs that make up the Golgi complex in plants. Plant cells typically contain numerous separate dictyosomes distributed throughout the cytoplasm, ra
- GeneralClass 12All
Why is plasma membrane termed as differentially permeable membrane?
The plasma membrane is called a differentially permeable (or selectively permeable) membrane because it allows certain substances to pass through while restricting or blocking others. This selective permeability is essential for maintaining the cell's internal environment and controlling what enters and exits. Small, non-polar molecules like oxygen and carbon dioxide can diffuse freely across the lipid bilayer, while charged ions and large polar molecules require specific protein channels or
- GeneralClass 12All
Name the scientist who observed a thin slice of cork through a microscope and coined the term 'cell'.
Robert Hooke, an English scientist, was the first person to observe and name cells in 1665. He examined a thin slice of cork under a primitive compound microscope of his own design and noticed a honeycomb-like pattern of tiny compartments. These box-like structures reminded him of the small rooms or "cells" where monks lived in monasteries, leading him to coin the term "cell" to describe these biological units. What Hooke actually observed were the dead cell walls of cork tissue, not
- GeneralClass 12All
What controls the flow of substances in and out of a cell?
The plasma membrane (also called the cell membrane) controls the flow of substances in and out of the cell. This thin, flexible boundary consists of a phospholipid bilayer embedded with proteins, cholesterol, and carbohydrates, creating a selectively permeable barrier that regulates molecular traffic. The membrane's structure allows it to maintain the cell's internal environment while facilitating necessary exchanges with the external surroundings. Control mechanisms include passive p
- GeneralClass 12All
Name the organelle of a plant cell where photosynthesis takes place.
Photosynthesis takes place in chloroplasts, the specialized organelles found in plant cells and some protists. These double-membrane-bound structures contain chlorophyll, the green pigment that captures light energy from the sun and converts it into chemical energy stored in glucose molecules. Chloroplasts are most abundant in the leaf cells of plants, particularly in the mesophyll tissue where maximum light exposure occurs. Inside chloroplasts, photosynthesis occurs in two main regio
- GeneralClass 12All
What do the chloroplasts contain?
Chloroplasts contain chlorophyll, the green pigment essential for capturing light energy during photosynthesis. Beyond chlorophyll, they also house other accessory pigments like carotenoids and xanthophylls, which help capture light at different wavelengths and protect the chloroplast from excessive light damage. These pigments are embedded in the thylakoid membranes, organized structures stacked into formations called grana. Additionally, chloroplasts contain their own DNA, ribosomes
- GeneralClass 12All
What are the units of inheritance in living organisms?
Genes are the units of inheritance in living organisms. These are specific segments of DNA that contain coded instructions for producing proteins or functional RNA molecules, thereby determining inherited characteristics and traits. Each gene occupies a particular position on a chromosome and carries information that is passed from parents to offspring during reproduction. Genes control everything from physical characteristics like eye color and height to biochemical processes like en