Those issues which are made from the same kind of cell are called simple tissues. They are found both in plants and animals.
Compound Tissues: –
Those issues which are made from different kinds of cells are called compound tissues. They are present in plants but absent in animals.
Q3: Define microscopy? Explain Microscope and their types?
The use of a microscope to observe very minute living organisms is known as microscopy.
It is an instrument that is used for the observation of those things which cannot be seen with naked eyes.
Zacharias Janssen and his son Hans Janssen were two eye glass makers in Holland. They discovered the first microscope in 1595. It was simply a tube with lenses at each end and its magnification from 3x to 9x.
Anton van leeuwenhoek (1632-1723):
Anton van Leeuwenhoek was a Dutch scientist who made a much better microscope and observed small organisms under it. The magnification power of Leeuwenhoek’s microscope was more than 250x. He is considered to be the first microscopist.
Q4: Define magnification and resolution of microscope?
Ans: Magnification: –
The capacity of a microscope to enlarge the apparent size of a small object is called magnification. The magnification power of an electron a light microscope is 1500x.
The capacity of a microscope to differentiate between two close objects is called Resolution. The human eye can differentiate between two points, which are at least o.1 mm apart. This is known as the resolution of the human eye. The resolution power of a light microscope is o.2μm.
Q5: Write the characteristic features of light and electron microscope?
Ans: Light microscope:
Those microscopes which use light to make the image of an object is called a light microscope.
Light passes through the simple and then through two glass lenses.
Lens produces an enlarged image of the sample and the second lens magnifies the image more. After passing through the object and lenses, the light is projected into the viewer’s eye when an enlarge and clear image is formed.
The magnification of a light microscope is 1500x. It can magnify objects only about 1500 times.
The resolution of light microscope is 0.2μm.
It is the most advanced form of microscope which use the beam of an electron to make an image of an object.
In the electron microscope, the object and the lenses are placed in a vacuum chamber and a beam of electrons is passed through the object. Electrons pass through or are reflected from the object and make the image.
Magnetic lenses focus the electron beam on a screen and make a much enlarged image.
Resolution of electron microscope is 0.2mm.
Types of Electron Microscope: –
There are two types of an electron microscopes.
Scanning electron microscope (SEM): –
It uses an electron beam to scan the surface that has been coated with metal. ⮚ The SEM does not have great magnifying power.
Transmission Electron Microscope (TEM): –
It is used for the study of the internal structure of cells or any other object.
Q6: Differentiate between Light and Electron microscope?
Ans: Comparison between light and electron microscope:
Beams of Electron
10,000 times greater than the naked eye
100 times greater than light microscope
500 times of the naked eye
400 times of the light microscope
2 D images
TEM show 2D While SEM Shows 3D Images
400 – 700`
Q7: Write a brief history of cell theory?
Ans: History of Cell Theory: –
Robert Hook was an English scientist who discovered cells in 1665. He observed a piece of cork under his self-made microscope. He observed small chambers like honeycomb structures and he named it cell.
Anton van Leeuwen Hook:-
Leeuwen Hook was a Dutch scientist. He studied a drop or pond water under his own made microscope. The magnification power of his microscope was 300x. He noticed tiny creature swimming in the drop of pond water. Leeuwen Hook was the first man to observe single-celled organisms called unicellular organisms.
Jean Baptist de-Lamarck:
In 1809, jean Baptist de-Lamarck proposed that “Nobody can have life if its constituent parts are not formed by cellular tissues.”
Dolland in 1827 improved the quality of lenses. After that, all the scientists were interested in microscopy.
In 1831, a British botanist Robert Brown discovered the nucleus in the plant cell.
In 1839 a German Botanist Matthias Schleiden studied plant tissues and made the first statement of the cell theory. He stated that “all plants are made up of cells”
Theodor Schwann: –
In 1839 a German Zoologist Schwann found that all animals are made from cells. Thus, Schleiden and Schwann proposed cell theory in its Italian form i.e., “all living things are composed of living Cells”.
Purkyne was an English scientist. In 1840 he proposed that all the cellular contents are living materials and gave them the name of “Protoplasm”.
In 1855, Rudolf Virchow, a German physician gave his hypothesis that every cell comes from a pre-existing cell. (“Omnis Cellula a celula”).
In 1862, a French scientist Louis Pasteur experimentally proved the hypothesis of Rudolf Virchow. He experimented on bacteria and found that bacteria are produced from pre-existing bacteria.
Q8: Write the main points of cell theory?
Ans: Cell Theory:-
Cell theory was first proposed by two German scientists, Botanist Matthias Schleiden and Zoologist Theodor Schwan.
All living organisms are made from one or more cells.
⮚ A cell is the basic structural and functional unit of all living organisms.
⮚ New cells arise from pre-existing cells by cell division.
Q9: What do you mean by acellular or sub-cellular particles?
Ans: According to the first principle of the cell theory all organisms are composed of one or more cells. The Discovery of virus prions and viroid claims that the statement is not universal. They are not composed of cells rather they are sub-cellular or acellular particles. As they show some characteristics of living organisms i.e., they can increase in number and can transmit their characteristics to the next generation.
Q10: Describe the structure of the Cell Wall?
Ans: Structure of Eukaryotic Cell:-
It is a nonliving structure present in bacteria, plants, fungi, and some protists.
The cell wall of plant cells is made from cellulose while the cell wall of Fungi and prokaryotes are made from chitin and murein respectively.
Structural of Cell Wall:-
A cell Wall is mainly composed of three main layers.
i). Primary Wall:-
It is the outer layer of cell wall which is composed of cellulose. Cellulose molecules are arranged in a crisscross manner.
ii. Secondary wall:-
It is the second layer of the cell wall which lies inner to the primary wall. It is comparatively thick and more rigid than the primary wall.
iii. Middle Lamella:-
It is the inner layer between the primary walls of two adjacent cells.
The function of Cell Wall:-
Protection: It protects the cellular contents from the outer environment.
Support: It gives support to the plant cell.
Shape: It gives proper shape to the cell.
Rigidity: It provides rigidity to the cell.
Q 11: Explain the structure and function of the cell membrane?
Ans: Cell Membrane:-
All prokaryotic and eukaryotic cells have a thin and elastic cell membrane covering the cytoplasm. It is the outermost layer of the animal cell. In the cells of bacteria plants fungi and some protists, the cell membrane lies beneath the cell wall.
Chemically cell walls are composed of 20-40% lipids and 60-80% proteins and also contain some carbohydrates.
Structure of Cell Membrane:-
Many scientists presented different models for the structure of cell membranes. Among them, the most acceptable model is the Fluid mosaic model.
Fluid Mosaic Model:-
In 1972 singer and Nicolson presented a model of the structure of cell membrane which is known as the fluid mosaic model. According to this model, the lipids bilayer is a sea and the protein is floating over it while some stay embedded in the bilayer. Carbohydrate molecules are joined with proteins or with lipids.
Cell membrane as semi-permeable membrane:-
A cell membrane is a semi-permeable membrane because it controls the inflow and outflow of material of the cell. It is thin delicate and elastic. It controls the movement of the molecule passing through it. It allows only the passage of water and other small molecules such as gases while other substances such as glucose, amino acids, etc can slowly diffuse through it.
⮚ Protection: It protects the inner parts of cell.
⮚ Shape: It gives proper shape to the cell.
⮚ Regulation: It regulates the inflow and outflow of substances.
⮚ Binding site: It provides binding sites for ATP and other biological molecules.
Q 12: Define cytoplasm? Describe the structure of the cytoplasm.
The portion of the cell which lies between the nuclear membrane and cell membrane is called cytoplasm. It contains a variety of cell organelles and other substances.
It is a translucent, living, and viscous substance.
It consists of two main parts.
Soluble Parts contain about 70% Water and 30% organic and inorganic substances.
Cell organelles are the insoluble part of the cytoplasm.
The cytoplasm is divided into two portions.
i) Ectoplasm: The outer clear portion is called ectoplasm.
ii) Endoplasm: The inner granular portion is called the endoplasm.
The cytoplasm of the cell provides space for the proper functioning of the organelles.
It also act as the site for various metabolic reactions for example Glycolysis (breakdown of glucose during cellular respiration) Cytoplasm store useful substance like protein, lipid, vitamin, and carbohydrates.
Q13: Describe the structure and function of the Endoplasmic Reticulum? Ans: Endoplasmic Reticulum:-
Endo means internal
Plasm means cytoplasm
Reticulum means network.
It is a network of interconnected channels present throughout the cytoplasm.
These membranes enclosed flattened sacs called Cisternae.
Types of Endoplasmic Reticulum:-
There is two types of endoplasmic reticulum.
i. Rough endoplasmic reticulum:-
The endoplasmic reticulum which has small granules called ribosomes present on its surface is called the rough endoplasmic reticulum. It is attached to the nuclear membrane.
The rough endoplasmic reticulum is involved in protein synthesis.
Transport of materials from nuclear membrane to the cytoplasm.
They give support to the cell.
ii. Smooth Endoplasmic Reticulum:-
The endoplasmic reticulum which has no ribosomes present on its surface is called the smooth endoplasmic reticulum. It is attached to cell membrane.
It plays an important role in the formation of lipids.
They transfer materials from one part of the cytoplasm to another.
Detoxification of toxic materials.
They give support to the cell.
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