9th Class Biology Chapter 4 Notes
Important Notes of Chapter No.4: Cells And Tissues 9th Class Notes Urdu Medium or 9th Class Biology Chapter 4 Notes written by Honorable Sir Adnan Haider Suib. These notes are very helpful in the preparation of 9th Class Biology Chapter 4 Notes for students of the 9th class Biology Urdu Medium and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Very Important Multiple Choice Questions (MCQs) of Chapter No.4 Cells And Tissues Urdu Medium.
- The wing of a butterfly is a thin sheet
of cells, and so is the shiny layer of our
eyes. The meat we eat is composed of
cells and its contents soon become part
of our cells. Our eyelashes, fingernails,
orange juice, the wood of our pencil -
all are produced by cells. In this chapter
we will take a close look at cells and learn about their internal structure. We will also learn how
specific cells group together to form tissues.
- Microscopy And The Emergence Of Cell Theory: The use of microscope is known as microscopy. The first compound microscope was developed
by Zacharias Janssen, in Holland in 1595. It was simply a tube with lenses at each end and its
magnification ranged from 3X to 9X.
- Two important terms are used in microscopy i.e. magnification and resolving power. Magnification
is the increase in the apparent size of an object and it is an important factor in microscopy. Resolving
power or resolution is the measure of the clarity of an image. It is the minimum distance at which
two objects can be seen as separate objects. Human naked eye can differentiate between two
points, which are at least 0.1 mm apart. This is known as the resolution of human eye. If we place
two objects 0.05 mm apart, human eye would not be able to differentiate them as two separate
objects. Magnification and resolution can be increased with the help of lenses.
- Light microscopy and electron microscopy: Now two types of microscope i.e. light microscope (LM) and electron microscope (EM) are used in
microscopy.
- Light Microscope: A light microscope works by passing visible light through a specimen. It uses two glass lenses. One
lens produces an enlarged image of the specimen and the second lens magnifies the image and
projects it into viewer’s eye or on to photographic film. A photograph taken through a microscope
is called a micrograph.
- A light microscope can magnify objects only about 1500 times without causing blurriness i.e. its
magnification is 1500X. Its resolving power is 0.2 micrometer (μm) and 1μm = 1/1000 mm. In
other words, the LM cannot resolve (distinguish) objects smaller than 0.2 μm. It is about the size
of the smallest bacterium. The image of bacterium can be magnified many times, but light microscope cannot show the details of its internal structure.
- Electron Microscope: It is the most advanced form of microscope. In EM, object and lens are placed in a vacuum chamber
and a beam of electrons is passed through object. Electrons pass through or are reflected from
object and make image. Electromagnetic lenses enlarge and focus the image onto a screen or
photographic film.
- Electron microscope has much higher resolving power than light microscope. The most modern
EM can distinguish objects as small as 0.2 nanometer (nm) and 1 nm = 1/1000,000 mm. It is a
thousand-fold improvement over LM. EM can magnify objects about 250,000 times. Under special
conditions EM can detect individual atoms. Cells, organelles and even molecules like DNA and
protein are much larger than single atoms.
- Biologists use two types of electron microscopes i.e. Transmission Electron Microscope (TEM) and
Scanning Electron Microscope (SEM). In TEM, electrons are transmitted through the specimen.
TEM is used to study the internal cell structure.