Q1: What is the limit of resolution of the human eye?
Ans: The limit of resolution of the human eye is 0.1 mm. This means two points closer than 0.1 mm appear as a single point to the naked eye.
Q2: Who was the first person to observe a cell and what did he use?
Ans: Robert Hooke was the first person to observe a cell in 1665 using a self-designed microscope capable of about 200-300X magnification.
Q3: What are thermophiles?
Ans: Thermophiles are mostly heat-loving bacteria that live in hot springs. They are unicellular organisms that can survive very high temperatures nearly at the boiling point of water.
Q4: What is the difference between unicellular and multicellular organisms? Give one example of each.
Ans: Unicellular organisms consist of only one cell, for example bacteria or yeast. Multicellular organisms are made up of millions of cells working together, for example humans or plants.
Q5: What is the plasma membrane? Why is it called selectively permeable?
Ans: The plasma membrane is a thin boundary that surrounds and protects the contents of a cell. It is called selectively permeable because it allows some substances to pass through while blocking others.
Q6: What is osmosis?
Ans: Osmosis is the movement of water through a selectively permeable membrane from an area of more water to an area of less water until concentrations become equal.
Q7: What is diffusion?
Ans: Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. It occurs even without a membrane.
Q8: What is the cell wall made of in plant cells?
Ans: The plant cell wall is primarily made of cellulose, a type of carbohydrate formed by many glucose units linked together.
Q9: Why do animal cells shrink when placed in a concentrated sugar solution but plant cells do not?
Ans: Animal cells shrink because they have no cell wall to maintain their shape. Plant cells do not shrink because their rigid cell wall holds them in their original shape even when inner content loses water.
Q10: What is the fluid-mosaic model of the cell membrane?
Ans: The fluid-mosaic model explains that the cell membrane has a lipid bilayer with proteins embedded in it. The molecules can move sideways and flip within the membrane, making it fluid, and the proteins are arranged like tiles in a mosaic.
Q11: What are organelles?
Ans: Organelles are sub-cellular components present in the cytoplasm of eukaryotic cells. Each organelle performs a specific function, making the cell work like a tiny living factory.
Q12: What is the function of ribosomes?
Ans: Ribosomes are the sites of protein synthesis in a cell. They may be found freely in the cytoplasm or attached to the endoplasmic reticulum.
Q13: What is the difference between Rough ER and Smooth ER?
Ans: Rough ER has ribosomes on its surface and is mainly involved in protein synthesis. Smooth ER has no ribosomes and is involved in the synthesis and storage of fats and hormones.
Q14: Why are mitochondria called the powerhouse of the cell?
Ans: Mitochondria are called the powerhouse of the cell because they supply the energy needed for most cellular activities by breaking down glucose during cellular respiration, releasing energy stored as ATP.
Q15: What are lysosomes and what is their function?
Ans: Lysosomes are single membrane-bound sacs filled with enzymes. They break down unwanted proteins, carbohydrates, fats, and damaged parts of the cell, keeping it clean and healthy.
Q16: What is the difference between prokaryotic and eukaryotic cells?
Ans: Prokaryotic cells do not have a well-defined nucleus or membrane-bound organelles, and most cellular activities occur in the cytoplasm. Eukaryotic cells have a well-defined nucleus and several membrane-bound organelles.
Q17: State the three points of the classical Cell Theory.
Ans: According to the classical Cell Theory: (i) all living organisms are made up of one or more cells, (ii) the cell is the basic unit of structure and function in living beings, and (iii) all cells arise from pre-existing cells.
Q18: What is the difference between mitosis and meiosis?
Ans: Mitosis produces two genetically identical daughter cells from one parent cell and is important for growth and repair. Meiosis is a two-step division that produces four daughter cells each with half the number of chromosomes, and is important for sexual reproduction.
Q19: What is contact inhibition?
Ans: Contact inhibition is the process by which cell division stops when cells come in contact with neighbouring cells. Cancer cells lose this control and keep dividing uncontrollably, forming tumours.
Q20: What is the nucleoid in prokaryotic cells?
Ans: The nucleoid is the region in a prokaryotic cell that contains its genetic material. Unlike eukaryotic cells, this DNA is present as a single circular molecule and is not enclosed by a membrane.