Class 8 Science Chapter 8 Important Questions
Class 8 Science Chapter 8 Important Questions of Cell: Structure and Functions for academic session 2020-2021 free to use online for CBSE and State Board. In class 8 science chapter 8 extra question answers, we will cover all the topic in the format of question and answers.These important extra questions includes all the keywords and main points of chapter 8 science class viii.
Class 8 Science Chapter 8 Important Questions for 2020-2021
|Chapter: 8||Cell: Structure and Functions|
|Contents:||Extra Question and Answers|
Class 8 Science Chapter 8 Important Questions Set – 1
When and how were the cells discovered? Explain.
Discovery of the Cell Robert Hooke in 1665 observed slices of cork under a simple magnifying device. Cork is a part of the bark of a tree. He took thin slices of cork and observed them under a microscope. He noticed partitioned boxes or compartments in the cork slice. These boxes appeared like a honey- comb.
He also noticed that one box was separated from the other by a wall or partition. Hooke coined the term ‘cell’ for each box. What Hooke observed as boxes or cells in the cork were actually dead cells. Cells of living organisms could be observed only after the discovery of improved microscopes. Very little was known about the cell for the next 150 years after Robert Hooke’s observations.
What do you mean by “cell”?
Cells, in the living organisms, are called basic structural units. The buildings, though built of similar bricks, have different designs, shapes and sizes. Similarly, in the living world, organisms differ from one another but all are made up of cells. Cells in the living organisms are complex living structures unlike non-living bricks. The egg of a hen represents a single cell and is big enough to be seen by the unaided eye.
Write something about “single-cell” and “multi-cell” of organisms.
Organisms made of more than one cell are called multicellular (multi: many; cellular: cell) organisms. The number of cells being less in smaller organisms does not, in any way, affect the functioning of the organisms. An organism with billions of cells begins life as a single cell which is the fertilized egg. The fertilized egg cell multiplies and the number of cells increase as development proceeds. Both organisms are made up of a single cell. The single-celled organisms are called organisms. A single-celled organism performs all the necessary functions that multicellular organisms perform.
What do you know about the shapes of the cells?
Generally, cells are round, spherical or elongated. Some cells are long and pointed at both ends. They exhibit spindle shape. Cells sometimes are quite long. Some are branched like the nerve cell or a neuron. The nerve cell receives and transfers messages, thereby helping to control and coordinate the working of different parts of the body.
Explain the size of the cell and tell whether the size of the cell can be seen with unaided eye?
The size of cells in living organisms may be as small as a millionth of a meter (micrometer or micron) or may be as large as a few centimeters. However, most of the cells are microscopic in size and are not visible to the unaided eye. They need to be enlarged or magnified by a microscope. The smallest cell is 0.1 to 0.5 micrometer in bacteria. The largest cell measuring 170 mm ×130 mm, is the egg of an ostrich. It can be seen with unaided eye.
Class 8 Science Chapter 8 Important Questions Set – 2
How does an organism begin its life?
An organism with billions of cells begin life as a single cell which is the fertilized egg. This fertilized egg cell multiplies and the number of cells increases as development proceeds.
Neha wants to know, how does each organ in the performs different functions? Explain with an example of plants and human organs.
We know that each living organism has many organs. The digestive organs which together constitute the digestive system. Each organ in the system performs different functions such as digestion, assimilation and absorption. Similarly, different organs of a plant perform specific or specialized functions.
For example, roots help in the absorption of water and minerals. Leaves are responsible for synthesis of food. Each organ is further made up of smaller parts called tissues. A tissue is a group of similar cells performing a specific function.
Neha realized that an organ is made up of tissues which in turn, are made up of cells. The cell in a living organism is the basic structural unit.
What do you mean by “cytoplasm”?
It is the jelly-like substance present between the cell membrane and the nucleus. Various other components, or organelles, of cells are present in the cytoplasm. These are mitochondria, golgi bodies, ribosomes, etc.
What do you know about “cell membrane” and “cell wall”?
The basic components of a cell are cell membrane, cytoplasm and nucleus. The cytoplasm and nucleus are enclosed within the cell membrane, also called the plasma membrane. The membrane separates cells from one another and also the cell from the surrounding medium. The plasma membrane is porous and allows the movement of substances or materials both inward and outward. The boundary of the onion cell is the cell membrane covered by another thick covering called the cell wall. The central dense round body in the center is called the nucleus. The jelly-like substance between the nucleus and the cell membrane is called cytoplasm.
The cell membrane gives shape to the cell. In addition to the cell membrane, there is an outer thick layer in cells of plants called cell wall. This additional layer surrounding the cell membrane is required by the plants for protection. Plant cells need protection against variations in temperature, high wind speed, atmospheric moisture, etc. They are exposed to these variations because they cannot move. Cells can be observed in the leaf peel of Tradescantia, Elodea or Rhoeo.
What is “Nucleus”?
It is an important component of the living cell. It is generally spherical and located in the center of the cell. It can be stained and seen easily with the help of a microscope. Nucleus is separated from the cytoplasm by a membrane called the nuclear membrane. This membrane is also porous and allows the movement of materials between the cytoplasm and the inside of the nucleus. With a microscope of higher magnification, we can see a smaller spherical body in the nucleus. It is called the nucleolus.
In addition, nucleus contains thread-like structures called chromosomes. These carry genes and help in inheritance or transfer of characters from the parents to the offspring. The chromosomes can be seen only when the cell divides. Nucleus, in addition to its role in inheritance, acts as control center of the activities of the cell.