Chapter 5 The Fundamental Unit of Life PDF

C hapter 5 THE FUNDAMENTAL UNIT While examining a thin slice of cork, Robert Hooke saw that the cork resembled the structure of a honeycomb consisting of many little compartments. Cork is a substance which comes from the bark of a tree. This was in the year 1665 when Hooke made this chance observati...

C hapter 5 THE FUNDAMENTAL UNIT While examining a thin slice of cork, Robert Hooke saw that the cork resembled the structure of a honeycomb consisting of many little compartments. Cork is a substance which comes from the bark of a tree. This was in the year 1665 when Hooke made this chance observation through a self-designed microscope. Robert Hooke called these boxes cells. Cell is a Latin word for ‘a little room’. This may seem to be a very small and insignificant incident but it is very important in the history of science. This was the very first time that someone had observed that living things appear to consist of separate units. The use of the word ‘cell’ to describe these units is being used till this day in biology. Let us find out about cells. Eyepiece Coarse adjustment Body tube Fine adjustment Clip Microscope slide Condenser Arm Objective lens Stage Swivel Mirror Base Activity ______________ 5.1 Let us take a small piece from an onion bulb. With the help of a pair of forceps, we can peel of f the skin (called epidermis) from the concave side (inner layer) of the onion. This layer can be put immediately in a watch-glass containing water. This will prevent the peel from getting folded or getting dry. What do we do with this peel? Let us take a glass slide, put a drop of water on it and transfer a small piece of the peel from the watch glass to the slide. Make sure that the peel is perfectly flat on the slide. A thin camel hair paintbrush might be necessary to help transfer the peel. Now we put a drop of safranin solution on this piece followed by a cover slip. Take care to LIFE avoid air bubbles while putting the cover slip with the help of a mounting needle. Ask your teacher for help. We have prepared a temporary mount of onion peel. We can observe this slide under low power followed by high powers of a compound microscope. 5.1 What are Living Organisms Made Up of? OF Fig. 5.1: Compound microscope What do we observe as we look through the lens? Can we draw the structures that we are able to see through the microscope, on an observation sheet? Does it look like Fig. 5.2? Rationalised 2023-24 Nucleus Cells Fig. 5.2: Cells of an onion peel