Case Study Questions for Class 9 Science Chapter 2 Cell – The Building Block of Life (Exploration Book) 2026-27

Imagine two tiny dots drawn on a piece of paper. As the dots are moved closer, there comes a point at which they can no longer be seen as separate. When viewed from about 25 cm (the near point of the human eye), two points separated by about 0.1 mm can be seen as distinct; otherwise, they appear as a single point. This is called the limit of resolution of the human eye, which is 0.1 mm. A cell is usually too small to be seen by the unaided eye.

Over the years, scientists have improved the microscope by improving its three main features: resolution (measure of clarity), contrast (the difference in brightness between various parts of an object), and magnification. The total magnification of a microscope depends on the magnifying power of the eyepiece and the objective lens. If both the eyepiece and the objective lens have a magnifying power of 10X, then the total magnification will be 100X. This means that a cell with an estimated size of 200 µm will appear 100 times larger.

When you get a small cut on your skin, it heals after a few days. When hair falls out, new hair grows back. This happens because cells in our body can grow and divide to replace old, dead, or damaged cells. When our body grows, it is not just because cells get bigger. Cells can grow only up to a certain size, but growth happens because cells divide to form new cells.

Cell division allows living organisms to grow, repair damaged tissues, and reproduce. There are two major types of cell division: mitosis and meiosis. Mitosis is important for normal growth, repair, maintenance, and asexual reproduction, while meiosis is important for sexual reproduction to create genetic diversity. Every human begins life as a single fertilised egg. This one cell divides repeatedly through mitosis to form trillions of cells in the body. Mitosis produces two genetically identical daughter cells from one parent cell, ensuring that each new cell gets the same DNA and the same number of chromosomes.

Eukaryotic cells carry out various life processes independently at the same time through specialized sub-cellular components called organelles. These organelles help in building new materials, removing waste, and providing energy to the cell. In other words, a cell is like a tiny living factory, with each of its parts doing a specific job.

The Endoplasmic Reticulum (ER) is a large network within the cytoplasm. The Rough ER looks rough under an electron microscope because it has ribosomes attached to its surface, and is mainly involved in protein synthesis. The Golgi apparatus, consisting of stacks of flattened sacs, acts like the cell’s post office. It modifies, sorts, and packages proteins and lipids into vesicles. Meanwhile, lysosomes act as the clean-up system. They are single membrane-bound sacs filled with enzymes that break down unwanted materials and damaged organelles.

Mitochondria and plastids are essential organelles with unique characteristics. Mitochondria are known as the ‘powerhouses of the cell’ because they supply the energy needed for most cellular activities. During cellular respiration, glucose and other molecules are broken down to release energy, which is stored in the form of ATP (Adenosine Triphosphate).

Plants use special organelles called plastids for food synthesis and storage. Chloroplasts contain the green pigment chlorophyll and are responsible for photosynthesis. In flower petals and fruits, plastids called chromoplasts contain pigments other than chlorophyll, such as yellow, orange, or red, providing bright colours to attract pollinators. Conversely, leucoplasts are colourless plastids that store food materials like starch, oils, or proteins. Interestingly, both mitochondria and plastids have their own DNA and ribosomes, suggesting they share an evolutionary history with single-celled bacteria.