General Q&A for Class 12 · Page 67
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Who gave the fluid mosaic model of the plasma membrane?
S.J. Singer and Garth L. Nicolson proposed the fluid mosaic model of the plasma membrane in 1972. This model describes the cell membrane as a dynamic structure composed of a lipid bilayer with embedded proteins that can move laterally, creating a mosaic-like pattern. The "fluid" nature refers to the flexible, liquid-like consistency of the lipid layer, while "mosaic" describes the diverse arrangement of proteins and other molecules within the membrane.
- GeneralClass 12All
Which cell organelle contains enzymes for ATP production?
Mitochondria contain the enzymes necessary for ATP (adenosine triphosphate) production. These enzymes are located in the inner mitochondrial membrane and the mitochondrial matrix, where they facilitate the electron transport chain and the Krebs cycle, the key processes in cellular respiration that generate ATP.
- GeneralClass 12All
Why is the plasma membrane called a selectively permeable membrane?
The plasma membrane is called selectively permeable (or semi-permeable) because it allows certain substances to pass through while restricting others. This selective nature is crucial for maintaining cellular homeostasis. Small, non-polar molecules like oxygen and carbon dioxide can easily diffuse through, while larger molecules, ions, and polar substances require specific transport proteins. This selectivity enables the cell to control what enters and exits, maintaining optimal internal cond
- GeneralClass 12All
What is the difference between diffusion and osmosis?
Diffusion is the movement of particles (solute molecules) from an area of higher concentration to an area of lower concentration until equilibrium is reached. This process can occur with any type of particle in any medium. Osmosis, on the other hand, is specifically the movement of solvent molecules (typically water) across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration. While diffusion involves solute movement, osmosis
- GeneralClass 12All
Which cell organelle is called the headquarters of the cell?
The nucleus is called the headquarters (or control center) of the cell. It contains the cell's genetic material (DNA) in the form of chromosomes and controls all cellular activities including growth, metabolism, protein synthesis, and reproduction. The nucleus directs cellular functions by regulating gene expression and maintaining the integrity of genetic information.
- GeneralClass 12All
What is endocytosis?
Endocytosis is the process by which cells internalize substances from their external environment by engulfing them within the cell membrane. During this process, the plasma membrane folds inward to form a pocket around the target material, which then pinches off to create a membrane-bound vesicle inside the cell. This mechanism allows cells to intake large molecules, nutrients, or even entire particles that cannot pass through the membrane by simple diffusion. There are different types of end
- GeneralClass 12All
Which cell organelle is called the powerhouse of the cell?
Mitochondria are called the powerhouse of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which serves as the primary energy currency for cellular processes. Through cellular respiration, mitochondria convert nutrients and oxygen into ATP, providing energy for all metabolic activities.
- GeneralClass 12All
What is the movement of solvent into the cell called?
The movement of solvent (typically water) into the cell is called endosmosis. This occurs when the cell is placed in a hypotonic solution, where the external solute concentration is lower than inside the cell, causing water to move inward through the selectively permeable membrane by osmosis.
- GeneralClass 12All
What are secondary sexual characteristics?
Secondary sexual characteristics are physical features that develop during puberty and distinguish males from females, but are not directly involved in reproduction. In boys, these include facial and body hair growth, deepening of voice, broadening of shoulders, development of Adam's apple, and increased muscle mass. In girls, secondary sexual characteristics include breast development, widening of hips, growth of pubic and underarm hair, and redistribution o
- GeneralClass 12All
What is the role of hormones in initiating reproductive function?
Hormones play a fundamental role in initiating and regulating reproductive function during adolescence. When a child reaches puberty, the hypothalamus in the brain signals the pituitary gland to release hormones that stimulate the reproductive organs. In males, luteinizing hormone (LH) and follicle-stimulating hormone (FSH) trigger the testes to produce testosterone and begin sperm production. In females, these same hormones stimulate the ovaries to produce e
- GeneralClass 12All
What is goitre and what causes it?
Goitre is an abnormal enlargement of the thyroid gland, which appears as a visible swelling in the neck. The thyroid gland, located at the front of the neck, produces hormones that regulate metabolism. The most common cause of goitre is iodine deficiency in the diet. Without adequate iodine, the thyroid cannot produce sufficient hormones, causing the gland to enlarge in an attempt to compensate. Other causes include thyroid disorders like hyperthyroidism (ove
- GeneralClass 12All
What is the largest cell in the living world?
The ostrich egg is the largest cell in the living world. This single cell can measure up to 15-18 centimeters in diameter and weigh approximately 1.4 kilograms. Despite its enormous size, it remains a single-celled structure containing all the necessary components for developing into a complete organism.
- GeneralClass 12All
Who wrote the book Micrographia?
Robert Hooke wrote the book "Micrographia" in 1665. This groundbreaking publication documented his microscopic observations of various objects, including the famous discovery of cells in cork tissue. Hooke coined the term "cell" because the tiny compartments he observed reminded him of the small rooms (cells) inhabited by monks in monasteries.
- GeneralClass 12All
Why is the cell called the structural and functional unit of life?
The cell is called the structural and functional unit of life because it serves as both the basic building block and the smallest living component capable of independent function. Structurally, all living organisms are made up of cells, either single or multiple cells organized into tissues and organs. Functionally, cells carry out all essential life processes including nutrition, respiration, growth, reproduction, and waste elimination. Even in multicellular organisms, each cell maintains it
- GeneralClass 12All
How can you calculate full adult height during adolescence?
To estimate full adult height when you know a child's current height and what percentage of their final height it represents, use this formula: Full Height = (Current Height ÷ Percentage) × 100. For example, if a 9-year-old boy is 120 cm tall and this represents 75% of his full height, the calculation would be: (120 ÷ 75) × 100 = 160 cm. This means the boy will likely reach approximately 160 cm at the end of his growth period. However, this is an est
- GeneralClass 12All
Is Amoeba a unicellular or multicellular organism?
Amoeba is a unicellular organism, meaning it consists of only one cell that performs all life functions. Despite being microscopic and single-celled, an amoeba can independently carry out feeding, movement, respiration, excretion, and reproduction without requiring other cells for survival.
- GeneralClass 12All
What is a cell?
A cell is the smallest structural and functional unit of life that can perform all essential life processes independently. It consists of a membrane-bound structure containing cytoplasm and genetic material. Cells can exist as single-celled organisms (like bacteria and amoeba) or combine to form complex multicellular organisms (like plants and animals). Every living organism is composed of one or more cells, making them the fundamental building blocks of all life forms.
- GeneralClass 12All
What is a balanced diet and why is it important during adolescence?
A balanced diet contains all essential nutrients in the right proportions to meet the body's needs. It includes carbohydrates (for energy), proteins (for growth and repair), fats (for energy and cell function), vitamins and minerals (for various bodily functions), and water (for hydration). A balanced diet should feature diverse foods: whole grains, fruits, vegetables, dairy products, lean proteins (meat, fis
- GeneralClass 12All
What are the effects of increased activity of sweat and sebaceous glands during adolescence?
During adolescence, both sweat glands and sebaceous (oil) glands become more active due to hormonal changes, particularly increased androgen hormones. Sweat glands produce more perspiration, which can lead to body odor, especially in areas like armpits and feet, making regular bathing and use of deodorants important. Sebaceous glands produce more sebum (oil), which can make skin and hair oilier. When excess oil combines with dead skin cells and bacteria, it c
- GeneralClass 12All
What developmental changes occur in females at age 13?
At age 13, girls typically experience significant developmental changes as part of puberty. These include breast development (often one of the first signs), growth of pubic and underarm hair, widening of the hips and pelvis, increased height (growth spurt), development of body curves due to fat redistribution, onset of menstruation (menarche) if it hasn't occurred already, activation of sweat and oil glands leading to possible acne, and emotional changes due to hormonal fluct