Cell Structure And Function Pdf Class 8
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- NCERT Solutions For Class 8 Science Chapter 8: Download Cell Structure And Functions PDF
- CBSE Class 8 Science Chapter 8 Cell – Structure and Functions Revision Notes
- Science - Class 8 (C ...
Our aim is to help students learn subjects like physics, maths and science for students in school , college and those preparing for competitive exams.
NCERT Solutions For Class 8 Science Chapter 8: Download Cell Structure And Functions PDF
Our aim is to help students learn subjects like physics, maths and science for students in school , college and those preparing for competitive exams. All right reserved. All material given in this website is a property of physicscatalyst. All living organisms are made up of cells.
Cells make tissues, tissues make organs, organs make organ systems and organ systems make a living organism. Thus, the cell is the building block, or the structural unit of the living body. Cells were discovered for the first time by Robert Hooke in He observed a piece of cork under his microscope. He saw that the cork was made up of many small boxes.
He called these little boxes cells. These box-like structures were actually dead cells. Living cells were observed by Anton Von Leeuwenhoek for the first time using improved microscopes. According to this theory: All living organisms are made up of cells. New cells arise from pre-existing cells. All cells are similar in structure and function but are not identical. The function of an organism depends on the way the cells work or the functions they perform.
Shapes and sizes Depending on their function, the cells show a variation in their shapes and sizes. They may be oval, spindle-shaped, spherical etc. Sizes of cells are measured in micrometer or microns. Bacterial cells are the smallest cells. The longest cells in our body are the nerve cells. The egg of ostrich is the largest cell- it is a single cell.
Cell Number According to the number of cells, organisms are broadly classified into two groups- unicellular and multicellular. Unicellular: Organisms made up of a single cell are called unicellular organisms. The single cell performs all the functions needed for sustaining life- growth, movement, digestion.
Amoeba, Paramecium and bacteria are examples of unicellular organisms. Multicellular: Organisms made up of many cells are called multicellular organisms. The cells of such organisms usually perform specialized functions. Most plants and animals are examples of multicellular organisms. Structure of a cell The basic components of cell are cytoplasm, cell membrane, nucleus and organelles.
Cell membrane The thin outer layer of the cell is called the cell membrane or the plasma membrane. It separates the cell and its contents from the surroundings.
It protects the inner cell contents. It protects the cell and gives it a shape. It is selectively permeable and allows water, minerals and other necessary substances to pass through it. It controls what passes in and out of the cell Cell Wall Cell wall is present only in plant cells. It is an additional wall outside the cell membrane.
It is thick wall made up of cellulose. The cell wall gives shape to the plant cell, offer protection and provide rigidity to the cell. The cell wall is important for plants since they do not have a skeleton for support and protection, nor they can move to escape environmental stress.
The cytoplasm has the nucleus and various other cellular components within it. These components are called cell organelles. Nucleus The nucleus is a spherical body present inside the cell. It is the control centre of the cell. The nucleus is surrounded by the nuclear membrane and the liquid present inside is called nucleoplasm. The nucleus and the cytoplasm together make up the protoplasm.
A smaller spherical structure present inside the nucleus, called Nucleolus plays an important role in protein synthesis. The nucleus also has a thread-like network called chromatin.
The chromatin organizes itself into rod-like structures when the cell has to divide. These rod-like structures are called chromosomes.
They contain the DNA inside them. DNA has the genes that help in transfer of characteristics from parent to the offspring. Therefore, DNA forms the hereditary material in most organisms. Note: The nucleus and cytoplasm together make up the protoplasm. There are various types of cell organelles that perform different functions. They provide energy in the form of ATP.
Therefore, they are known as powerhouse of the cell. Ribosomes are associated with protein synthesis. They can be of three types-chloroplasts, chromoplasts and leucoplasts.
They are concerned with secreting useful substances such as enzymes and hormones. In mature plant cells, they occupy most of the space within the cell and help to store food, water and wastes. In animal cells, vacuoles are smaller and may be greater in number. They help in waste removal and digestion.
The endoplasmic reticulum helps to transport substances in and out of cells. They are present only in animal cells and are absent in plant cells. They are small rounded sacs filled with tissue dissolving enzymes. They help in the digestion of foreign bodies and worn out cell parts. On receiving nutrition, it grows and reaches a certain size after which it divides to form two cells.
This process is known as cell division, and the cells formed are known as daughter cells. Cell division is also necessary for replacement of dead cells. Million of cells are die and replaced every second in our body. No Animal Cell Plant Cell 1 Smaller in size larger in size 2 Cell membrane is present but Cell wall is absent both cell membrane and cell wall are present 3 plastids are absent plastids are usually present 4 Vacuoles are smaller and more in number One large vacuole is present in the cell 5 Centrioles, centrosomes and lysosomes are present Centrioles, centrosomes and lysosomes are absent Check your Knowledge Fill in the blanks 1.
Check your Answers 1. Cell 2. Robert Hooke 4. DNA 9. Physicscatalyst Our aim is to help students learn subjects like physics, maths and science for students in school , college and those preparing for competitive exams.
CBSE Class 8 Science Chapter 8 Cell – Structure and Functions Revision Notes
Register Now. Hey there! We receieved your request. A cell is the Smallest Unit of life that can replicate independently, and cells are often called the "Building Blocks of Life". Figure1: Robert Hooke discovered cells in Hooke saw honeycomb-like structure when he observed thin slices of cork under a microscope.
Science - Class 8 (C ...
Question 1. Indicate whether the following statements are True T or False F. Answer: a True b True c False d True. Question 2. Make a sketch of the human nerve cell.
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.
Cell: i In the living organisms, Cells are basic structural units. Bricks are assembled to make a building. Similarly, cells are assembled to make the body of every organism. All organisms are made up of cells iv Sub cellular structures of cell include organelles, the plasma membrane, and, if present, the nucleus. Each cell contains genetic material that is passed down during reproduction process. Discovery of the Cell: i In , the English scientist Robert Hooke observed slices of cork which is part of bark of the tress, under a simple magnifying device. He noticed partitioned boxes or compartments in the cork slice.
The first section discusses how Robert Hooke discovered this fundamental unit of life. In the second section, various concepts of the cell are explained in detail. The similarity between the brick of a building and cell of living organisms is discussed. Variety in cell number, shape and size is covered in the third section. Here, the organisms are classified on the basis of a number of cells inside their body into. In the fourth section of the chapter, Cell- Structure and Functions, the structure of cell and functions of each part of the cell is extensively covered.
The topics covered under CBSE Class 8 Science important questions are the discovery of the cell, the cell, variety in cell number, shape, and size in different organisms, cell structure and function, parts of the cell, comparison between the animal cell and the plant cell. The cell is the basic unit of life, It is a small membrane-bound compartment. Which contains all the chemicals and molecules that help to support an organism's life. Understanding the structure and function of cells is one of the basic steps to comprehend the complex cellular interactions, which produces life. There are two types of cells namely unicellular and multicellular organisms, both the organisms have their own uniqueness and functions. Like unicellular organisms have the capability to sustain their life on their own. All the organisms are made up of cells, but the cell differs from the one organism to others like from plants to animals.
In the class 8th science chapter 8 notes, you will learn the basic functioning of the cell and how they are formed. Some of the basic features are listed below:. Living organisms are made of cells, and different body parts are formed through a combination of cells.