9th Class Biology Chapter 4 Notes English Medium
Important Notes of 9th Class Biology Chapter 4 Notes English Medium written by Honorable Sir Adnan Haider Suib. These notes are very helpful in the preparation of Cells and Tissues 9th Class notes for students of the 9th class Biology English 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:
- Here are the detailed tissue class 9th notes to help you prepare for your exams.
- Very Important Multiple Choice Questions (MCQs) of Chapter No.4 Cells And Tissues English Medium.
- History of the formulation of cell theory: In the history of biology, ancient Greeks were the first who organized the data of natural world.
Aristotle presented the idea that all animals and plants are somehow related. Later this idea gave
rise to questions like “is there a fundamental unit of structure shared by all organisms?”. But before
microscopes were first used in 17th century, no one knew with certainty that living organisms do
share a fundamental unit i.e. cell.
- Cells were first described by a British scientist, Robert Hooke in 1665. He used his self-made
light microscope to examine a thin slice of cork. Hooke observed a “honeycomb” of tiny empty
compartments. He called the compartments in cork as “cellulae”. His term has come to us as cells. The first living cells were observed a few years later by Dutch naturalist Antonie van
Leeuwenhoek. He observed tiny organisms (from pond water) under his microscope and called
them as “animalcules”.
- For another century and a half, the general importance of cells was not appreciated by biologists.
In 1809, Jean Baptist de-Lamarck proposed that “no body can have life if its parts are not cellular
tissues or are not formed by cellular tissues”.
- In 1831, a British botanist Robert Brown discovered nucleus in the cell. In 1838, a German botanist
Matthias Schleiden studied plant tissues and made the first statement of cell theory. He stated
that all plants are aggregates of individual cells which are fully independent. One year later, in
1839, a German zoologist Theodor Schwann reported that all animal tissues are also composed of
individual cells. Thus Schleiden and Schwann proposed cell theory in its initial form.
- Sub-cellular or Acellular Particles: According to the first principle of the cell theory all
organisms are composed of one or more cells. Virus, prions and viroids are not composed of cells;
rather they are sub-cellular or acellular particles. They do not run any metabolism inside them. They
show some characteristics of living organisms i.e. they can increase in number and can transmit
their characters to next generations. We know that such acellular particles are not classified in any
of the five kingdoms of organisms.
- Cellular Structures And Functions: We are well familiar with the basic organization of a eukaryotic cell. Here we will get some detailed
learning about cellular structure and functions. A cell is made by the assemblage of organelles.
There are some structures in cell that are not organelles, but are still very important for cell. These
structures are cell wall, cell membrane, cytoplasm, and cytoskeleton.
- Cell Wall: We know that not all living organisms have cell walls around their cells, e.g. animals and many
animal-like protists. Cell wall is a non-living and strong component of cell, located outside
plasma membrane. It provides shape, strength, protection and support to the inner living matter
(protoplasm) of cell.
- Plant cells have a variety of chemicals in their cell walls. The outer layer of plant cell wall is known as
primary wall and cellulose is the most common chemical in it. Some plant cells, for example xylem
cells, also have secondary walls on the inner side of primary wall. It is much thicker and contains
lignin and some other chemicals. There are pores in the cell walls of adjacent cells, through which
their cytoplasm is connected. These pores are called plasmodesmata.