CBSE Class 8 Science Cell and Tissue Notes

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Revision Notes for Class 8 Science Chapter 8 Cell Structure and Functions

Class 8 Science students should refer to the following concepts and notes for Chapter 8 Cell Structure and Functions in Class 8. These exam notes for Class 8 Science will be very useful for upcoming class tests and examinations and help you to score good marks

Chapter 8 Cell Structure and Functions Notes Class 8 Science

INTRODUCTION

A cell is the structural and functional unit of life. It is the building block of which all living organisms are made, and the smallest unit of life capable of all the living functions. It is defined as a mass of protoplasm bounded by a plasma membrane.
Cell vary in size. Most cells are very small (microscopic), some may be very large. Some cells may exist as independent units of life. Some such cells like Euglena and Amoeba can change their shape, but most cells have a fixed shape. The number of cells vary from organism to organism. An amoeba is single-celled, while a human body weighing about 60 kg may have as many as 60 × 1015 cells. In unicelluar organisms, e.g. Amoeba, Paramoecium or Chalamydomonas, all the basic functions of a living being are performed in one cell, while multicellular organisms have well-developed division of labour. So, their different functions are performed by different organs. For example, we have a stomach to digest food, a heart to pump blood and a brain to think.
An English scientist, Robert Hooke, discovered the cell in 1665 while examining thin sections of cork under his simple microscope. He observed a mass of hexagonal chambers like a honeycomb and called them(compartments) cells. Cell is the Latin word for 'a little room'.
 
Types of cell

Prokaryotes and Eukaryotes

All living organisms are made of cells. And based on the kind of cells they are made up of, they are divided into two groups-prokaryotes and eukaryotes. Prokaryotes, which include bacteria other organisms are eukaryotes, and probably evolved from prokaryotes.
There are some structural differences between prokaryotic and eukaryotic cells. The most obvious difference is that unlike the eukaryotic cell, the prokayotic cell lacks a true nucleus. There is no nuclear membrane. The DNA or nuclear material lies in a circular loop in the cytoplasm. Such undefined nuclear region is called nucleoid. There are some other differences too. For instance, in prokaryotic cells the ribosomes are smaller and scattered in the cytoplasm. Besides, prokaryotic cells lack membrane-bound orgenelles like plastids, mitochondria and endoplasmic reticulum.
 
Structure of a cell

Cell membrane or plasma membrane:
A cell is essentially a tiny 'bag' of living matter. The covering of this 'bag' is called the cell membrane or plasma membrane. It maintains the shape and size of the cell and protects its contents. It acts like a sentry-allowing only some things to enter and leave the cell and stopping others. For example, it allows oxygen and nutrients to pass into the cell and lets wastes pass out of it. This is why it is called selectively permeable.
 
Cell wall:
Plant cells have an additional protective wll called the cell wall. It is thick, rigid and permeable, and is made up of a carbohydrate called cellulose.
 
Cytoplasm:
The matter inside the cell mebrane is called cytoplasm. It consists of a jellylike fluid with various structures, such as the nucleus, floating in it. These structures are called organelles.
Salts, proteins, sugar and other substances are dissolved in the fluid.
 
Nucleus:
Almost every cell has a nucleus. Red blood cells are among the exceptions. The nucleus is the largest and the most important organelle of the cell. It is usually spherical or oval in shape. Inside it there are thread like structures called chromosomes. Nucleus is the controlling central cell. Chromosomes have genes arranged in a linear fashion.
 
Vacuoles:
The central part of most plant cells is occupied by a large vacuole. You may have noticed it in some of the plant cells you observed. It is a sac like structure filled with fluid. Food, wastes pigments and other substances are dissolved in the fluid. Some plant cells have a number of large vacuoles.
Vaculoes are not so common in animal cells. When they ocour, they are much smaller in size.
 
Plastids:
These organelles are not present in animal cells. Chloroplasts (a type of plastid) contain the green pigment chlorophyll and are responsible for photosynthesis. Only green parts of plants have chloroplasts.
There are two other types of plastids called chromoplasts and leucoplasts.
Chromoplasts contain pigments which give fruits and flowers their colours. Leucoplasts store food and are found in the storage organs of plants.
 
Endoplasmic reticulum (ER)
The endoplasmic reticulum is a network of tubelike structures running through the cytoplasm. If ribosomes are attached to it, the reticulm is rough, otherwise it is smooth.
Function - It gives internal support to the colloidal matrix (cytoplasm).
Rough endoplamic reticulum
(RER) is associated with the synthesis of proteins.
 
CBSE Class 8 Science Cell and Tissue Notes Set B
 
CBSE Class 8 Science Cell and Tissue Notes Set B-
 
Ribosomes
 
Ribosomes are extremely amall, round bodies found either in the state in the cytoplasm or attached to the surface of the ER. They are composed of ribonucleoprotein (ribonucleic acid and protein).
Functions - The main function of ribosomes is to act as a platform or work place for the synthesis of proteins.
 
Mitochondria
 
Mitochondria are small, rod-shaped organelles found in large numbers. Each mitochondrion is bounded by two membranes-outer and inner. The outer membrane is smooth and the inner membrane is pushed inwards at intervals forming crests called cristae. The cristae lie in a ground substane called matrix. Mitochondria process enzymes necessary for the oxidation of carbohydrates. This process releases energy in the form of ATP. This is why mitochondria are known as the powerhouses of the cell. Mitochondria have their own DNA and ribosomes. They can synthesize their own proteins and thus they are semiautonomous organelles.
Function- Mitochondria provide energy for the vital activities of living cells.
 
Golgi body
 
They store, modify, package and condense the proteins synthesized in the ribosomes.
 
Lysosomes
 
These saclike, small spherical, single membrane-bound vesicles contain enzymes. These enzymes are synthesized in the RER, which are brought to the Golgi complex.
Lysosomes are formed by the Golgi complex. They occur in animal cells and in the meristematic cells of a few plants.
Function- They help in breaking down (digesting) large molecules of the cell. They work in defence againt bacteria and viruses. During stavation, lysosomes act on their own cellular organelles and digest them. This results in cell death.
Hence lysosomes are called suicide bags or demonlition squads.
 
Centrioles
 
The centrosome is a distinct region of the cytoplasm close to the nucleus of animal cells. It usually has two central granules called centrioles. The centrioles are hollow, cylindrical structure made of microtubules arranged in a specific manner. They are arranged at right angles to each other.
Function- At the time of cell division, centrioles move to the poles and form spindle fibre which help in the movement of chromatids (daughter chromosomes) in the daughter cells. They help in the formation of cilia and flagella.
 
Plant Cell & Animal Cell
 
CBSE Class 8 Science Cell and Tissue Notes Set B-1
 
Movement of subtances across the cell membrane

Diffusion:
 
Diffusion is the process of mixing up or different substances due to the random motion of their component atoms, molecules and ions. Diffusion takes place in solids, liquids and gases.
Ex. Burning of incense stick.
 
Osmosis:
 
Diffusion of water across a semipermeable membrane is called Osmosis. The movement of water in living beings depends on osmosis. The movement of water molecules across the cell membrane is affected by the amount of solute dissolved in it. Here also the water molecules are free to pass across the membrane in both directions. But the net movement of water molecules takes place from the dilute solution to the concentration one, i.e., from the region of greater concentration of water towards the region of lower concentration of water.
Ex. Grains in water.
 
Plant Tissues
 
Plant tissue are basically of two types-meristematic and permanent. This differentiation is based on the ability of the mature cells of the tissue to divide and produce new cells. Meristematic tissue cells are capable of dividing, while permanent tissue cells are not.
 
Meristematic
 
Tissue This tissue consists of actively dividing cells and is present in the growing regions of plants, e.g., the tips of roots and stems.
The cells can be round, oval, polygonal or rectangular, but there are a few things they have in common. They are packed closely without intercellular spaces, have thin cellulose walls, dense cytoplasm and prominent nuclei. Vacuoles are almost absent in such cells because they are completely filled with sap. Depending on the region of the plant where it is present, meristematic tissue can be of three types- apical, lateral and intercalary.
CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-B_1
 
Apical (from apex) meristem, as the name suggests, is present at the growing tips of stems and roots. Apical meristem is primary meristem.

Lateral meristematic tissue occurs along the sides of the cental (longitudinal) axis of the plant. It gives rise to v ascular tissues.

Intercalary meristem occurs at the base of leaves or internodes. These cells grow fast and soon change into permanent tissues.

Permanent Tissue

The div ision and differentiation of the cells of meristematic tissues given rise to permanent tissues. Cell division is the formation of two or more daughter cells from one mother cell. Simple permanant tissue consist of similar permanent cells that perform the same function or a similar set of functions. Parenchyma, collencyma and sclerenchyma are three types of simple permanent tissues. Complex permanent tissue are a group of different types of cells that perform a common function. Xylem and phloem are two types of complex permanent tissue.

Parenchyma

This tissue is composed of large, thin-walled cells which are generally oval or spherical. The cells are not packed closely, i.e., there are intercellular space. These living cells with a nucleus and a v acuole are found in the soft parts of the plant. They store food, fill up spaces between other tissue and provide temporary support to the plant. W hen they contain chloroplasts, as in leaves, they help manufacture food.

Collenchyma

This tissue is composed of cells that are elogated and thickened with cellulose at the corners. There is no intercellular space. Collenchyma provides mechnical support to plant organs and is found in leaf stalks and below the epidermis of stems. It helps leav es and stems bend without breaking. It prov ides support, protection and flexibility ot plant organs. It is generally absent in roots.

Sclerenchyma

This tissue is composes of long, narrow cells whose walls are ev enly thickened with lignin. Lignin is a chemical that acts like cement, sticking fibres and hardening them. Sclerenchyma cells are dead. They are packed together closely, and prov ide strength and flexibility to plant parts. They are present in stems, v eins of leav es, the hard covering of seeds and nuts, and the husk of coconut. Fibre-yielding plants like jute and flax contain this tissue in abundance.

CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-B_2

Xylem

Xylem, or wood, as it is often called, is a complex tissue. The cells are thick-walled, tubular and often dead. This tissue has four types of cells– tracheids, v essels, xylem parenchyma and xylem fibres. Of these only tracheids and vessels transport sap.

Phloem

Phloem too is a complex tissue made up of four types of cells, or elements–siev e tubes, companion cells, phloem fibres and phloem parenchyma. It is not necessary for the phloem to contain all four types of cells. Phloem to contain all four types of cells. Phloem cells are living cells (except phloem fibres) which help transport food from leav es to the storage organs and growing regions of the plant.

Animal Tissues

While doing the activities in this chapter, you have come across two types of animal tissue, the cheek cells are a type of epithelial tissue, while blood is a kind of connective tissue. There are two other types of animal tissue–muscular and nerv ous.

Epithelial Tissue:

This tissue covers the surface of the body and lines the internal organs. Its main function is protection. The cells that form the different types of epithelial tissue differ in shape. Some are thin and flat, some cubelike, while others are columnar.

CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-B_3

Connective Tissue:

Blood, bones cartilages, tendons (which connect muscles with bones) and ligaments (which tie bones together) are diferent types of connectiv e tissue. Adipose tissue, or what is generally known as fat, is also a kind of connective tissue. Though different in structure, connective tissues have one thing in common-the cells are suspended or embedded in a matrix. In blood, the matrix is liquid and is called the plasma.

CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-B_4

Muscular Tissue:

Muscular tissue is also of different types. However, the different types of muscular tissue (or muscles) have the same basic functoin. They contract and relax to make different parts of the body mov e. The muscles in our arms, legs thighs, back and so on help us move. The muscles in the heart help it pump blood. The muscles in the alimentary canal help the passage of food. The muscles in the blood v essels help them dilate and get constricted.

Nervous Tissue:

Nerve cells make up nerv ous tissue. A nerve cell has a long tail and short branches coming out of it.The tail too has branches. These help to carry message from one cell to the other. The brain and spinal cord are make up of nervous tissue.

CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-B_5

 
DISCOVERY OF CELL

1. Robert Hooke (1665) :– An English man and first curator of Royal society of London.
Observed a thin transverse section of bark of a tree under self designed microscope.
He noticed honey - comb like compartments.
He coined the term cell.
He wrote a book - Micrographia.
He actually observed dead cells.
2. Antony Van Leeuwenhoek (1674) was first to observe living cells like bacteria [from tartar of teeth]
erythrocytes [fish], sperms and protozoans [eg. Vorticella]
3. N. Grew (1682) :– Proposed cell concept which states that cell is unit of structure of organisms.
4. Rudolf Virchow (1858) :– Proposed that new cells formed from the pre-existing cells.
 
 CBSE Class 8 Science Cell and Tissue Notes Set A
 
MICROSCOPE

A microscope is an instrument to view small objects by magnifying them. It enables us to see the different types of living cells and the structures they contain.
 
CBSE Class 8 Science Cell and Tissue Notes Set A-
 
TYPES OF MICROSCOPES

There are mainly three types of microscopes. They are :

Light microscope : The light microscope uses light to produce images.
♦ Transmission Electron Microscope (TEM) : The electron microscope was designed by Knoll & Ruska (1932). A TEM makes use of a beam of highly energetic electrons to examine objects. The image produced is of a very fine scale.
♦ Scanning Electron Microscope (SEM) : Like the TEM, the SEM also uses electrons to produce images.
 
In the case of a SEM, electrons are reflected off the surface of the specimen, because of which SEM images usually manage to capture the physical features of a cell in great detail.
 
 
CBSE Class 8 Science Cell and Tissue Notes Set A-1
 
 
STRUCTURE OF A CELL
 
 Cell membrane or plasma membrane:
 
A cell is essentially a tiny 'bag' of living matter. The covering of this 'bag' is called the cell membrane or plasma membrane. It maintains the shape and size of the cell and protects its contents. It acts like a sentry-allowing only some things to enter and leave the cell and stopping others. For example, it allows oxygen and nutrients to pass into the cell and lets wastes pass out of it. This is why it is called selectively permeable.
 
♦  Cell wall:
 
Plant cells have an additional protective wll called the cell wall. It is thick, rigid and permeable, and is made up of a carbohydrate called cellulose.
 
♦  Cytoplasm :
 
The matter inside the cell mebrane is called cytoplasm. It consists of a jellylike fluid with various structures, such as the nucleus, floating in it. These structures are called organelles.
Salts, proteins, sugar and other substances are dissolved in the fluid.
 
♦  Nucleus:
 
Almost every cell has a nucleus. Red blood cells are among the exceptions. The nucleus is the largest and the most important organelle of the cell. It is usually spherical or oval in shape.
Inside it there are thread like structures called chromosomes. Nucleus is the controlling central cell. Chromosomes have genes arranged in a linear fashion.
CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-A_1
 
It is the most important part of the living cell.
 
It is usually spherical or oval in shape.
 
It controls all the vital functions of the cell.
 
It has four components:
 
(i) Nulcear Membrane (ii) Nulceoplasm
 
(iii) Nulceolus (iv) Chromosomes
 
(i) Nuclear membrane: Surrounds the nucleus and separates it from the cytoplasm. It is permeable and controls the passage of materials between cytoplasm and nucleoplasm
 
(ii) Nucleoplasm: The part of protoplasm which is enclosed by nuclear membrane is called nucleoplasm. It contains chromatin threads and nucleolus.
 
(iii) Nulceolus: It is a spherical body in the nucleus. It is composed of RNA and is responsible for protein synthesis.
 
(iv) Chromosomes: Nucleus contains thread like structures called chromosomes.
 
The hereditary units of chromosomes are the genes. They are responsible for the transmission of characters from parents to the offsping.
Nucleus along with tis role in inheritance regulates and controls differeny metabolic activities of the cell.
 
On the basis of well organised nucleus, cells can be of two types
(i) Prokaryotic cell (ii) Eukaryotic cell
 
(i) Prokaryotic cells: These are cells having primitive nucleus without nuclear membrane.
Organism with primitive nucleus are known as prokaryotes.
Ex. Bacteria and blue green algae.
 
(ii) Eukaryotic cells: These are cells having a well organised nucleus with nuclear membrane.
Organsims with true nucleus are known as eukaryotes.
Ex. Man, elephant, onion.

¶ Vacuoles:
 
The central part of most plant cells is occupied by a large vacuole. You may have noticed it in some of the plant cells you observed. It is a sac like structure filled with fluid. Food, wastes pigments and other substances are dissolved in the fluid. Some plant cells have a number of large vacuoles.
Vaculoes are not so common in animal cells. When they ocour, they are much smaller in size.

¶ Plastids:
 
These organelles are not present in animal cells. Chloroplasts (a type of plastid) contain the green pigment chlorophyll and are responsible for photosynthesis. Only green parts of plants have chloroplasts.
There are two other types of plastids called chromoplasts and leucoplasts. Chromoplasts contain pigments which give fruits and flowers their colours. Leucoplasts store food and are found in the storage organs of plants.
 
¶  Endoplasmic reticulum (ER)
 
The endoplasmic reticulum is a network of tube-like structures running through the cytoplasm.
If ribosomes are attached to it, the reticulm is rough, otherwise it is smooth.
Function - It gives internal support to the colloidal matrix (cytoplasm).
Rough endoplamic reticulum (RER) is associated with the synthesis of proteins.

¶  Ribosomes
 
Ribosomes are extremely amall, round bodies found either in the state in the cytoplasm or attached to the surface of the ER. They are composed of ribonucleoprotein (ribonucleic acid and protein).
Functions - The main function of ribosomes is to act as a platform or work place for the synthesis of proteins.

¶  Mitochondria
 
Mitochondria are small, rod shaped organelles found in large numbers. Each mitochondrion is bounded by two membranes-outer and inner. The outer membrane is smooth and the inner membrane is pushed inwards at intervals forming crests called cristae. The cristae lie in a ground substane called matrix. Mitochondria process enzymes necessary for the oxidation of carbohydrates.
 
This process releases energy in the form of ATP. This is why mitochondria are known as the powerhouses of the cell. Mitochondria have their own DNA and ribosomes. They can synthesize their own proteins and thus they are semiautonomous organelles. Function- Mitochondria provide energy for the vital activities of living cells.
 
¶  Golgi body
 
They store, modify, package and condense the proteins synthesized in the ribosomes.
 
¶  Lysosomes
 
These saclike, small spherical, single membrane-bound vesicles contain enzymes. These enzymes are synthesized in the RER, which are brought to the Golgi complex. Lysosomes are formed by the Golgi complex. They occur in animal cells and in the meristematic cells of a few plants.
Function- They help in breaking down (digesting) large molecules of the cell. They work in defence againt bacteria and viruses. During stavation, lysosomes act on their own cellular organelles and digest them. This results in cell death. Hence lysosomes are called suicide bags or demonlition squads.
 
¶  Centrioles
 
The centrosome is a distinct region of the cytoplasm close to the nucleus of animal cells. It usually has two central granules called centrioles. The centrioles are hollow, cylindrical structure made of microtubules arranged in a specific manner. They are arranged at right angles to each other.
Function- At the time of cell division, centrioles move to the poles and form spindle fibre which help in the movement of chromatids (daughter chromosomes) in the daughter cells. They help in the formation of cilia and flagella.
 Movement of subtances across the cell membrane
 Diffusion:
Diffusion is the process of mixing up or different substances due to the random motion of their component atoms, molecules and ions. Diffusion takes place in solids, liquids and gases.
Ex. Burning of incense stick.
 
¶  Osmosis:
Diffusion of water across a semipermeable membrane is called Osmosis. The movement of water in living beings depends on osmosis. The movement of water molecules across the cell membrane is affected by the amount of solute dissolved in it. Here also the water molecules are free to pass across the membrane in both directions. But the net movement of water molecules takes place from the dilute solution to the concentration one, i.e., from the region of greater concentration of water towards the region of lower concentration of water.
Ex. Grains in water.

¶ Plant Tissues

Plant tissue are basically of two types-meristematic and permanent. This differentiation is based on the ability of the mature cells of the tissue to divide and produce new cells. Meristematic tissue cells are capable of dividing, while permanent tissue cells are not.

¶ Meristematic Tissue

This tissue consists of actively dividing cells and is present in the growing regions of plants, e.g., the tips of roots and stems. The cells can be round, oval, polygonal or rectangular, but there are a few things they have in common. They are packed closely without intercellular spaces, have thin cellulose walls, dense cytoplasm and prominent nuclei. Vacuoles are almost absent in such cells because they are completely filled with sap. Depending on the region of the plant where it is present, meristematic tissue can be of three types- apical, lateral and intercalary.

Apical (from apex) meristem, as the name suggests, is present at the growing tips of stems and roots. Apical meristem is primary meristem.

Lateral meristematic tissue occurs along the sides of the cental (longitudinal) axis of the plant. It gives rise to vascular tissues.

Intercalary meristem occurs at the base of leaves or internodes. These cells grow fast and soon change into permanent tissues.

¶ Permanent Tissue

The division and differentiation of the cells of meristematic tissues given rise to permanent tissues. Cell division is the formation of two or more daughter cells from one mother cell. Simple permanant tissue consist of similar permanent cells that perform the same function or a similar set of functions. Parenchyma, collencyma and sclerenchyma are three types of simple permanent tissues. Complex permanent tissue are a group of different types of cells that perform a common function. Xylem and phloem are two types of complex permanent tissue.

¶ Parenchyma

This tissue is composed of large, thin-walled cells which are generally oval or spherical. The cells are not packed closely, i.e., there are intercellular space. These living cells with a nucleus and a vacuole are found in the soft parts of the plant. They store food, fill up spaces between other tissue and provide temporary support to the plant. When they contain chloroplasts, as in leaves, they help manufacture food.

¶ Collenchyma

This tissue is composed of cells that are elogated and thickened with cellulose at the corners. There is no intercellular space. Collenchyma provides mechnical support to plant organs and is found in leaf stalks and below the epidermis of stems. It helps leaves and stems bend without breaking. It provides support, protection and flexibility ot plant organs. It is generally absent in roots.

¶ Sclerenchyma

This tissue is composes of long, narrow cells whose walls are evenly thickened with lignin. Lignin is a chemical that acts like cement, sticking fibres and hardening them. Sclerenchyma cells are dead. They are packed together closely, and provide strength and flexibility to plant parts. They are present in stems, veins of leaves, the hard covering of seeds and nuts, and the husk of coconut. Fibre-yielding plants like jute and flax contain this tissue in abundance.

CBSE-Class-8-Science-Cell-and-Tissue-Notes-Set-A_2

 Xylem
Xylem, or wood, as it is often called, is a complex tissue. The cells are thick-walled, tubular and often dead. This tissue has four types of cells– tracheids, vessels, xylem parenchyma and xylem fibres. Of these only tracheids and vessels transport sap.

 Phloem
Phloem too is a complex tissue made up of four types of cells, or elements–sieve tubes, companion cells, phloem fibres and phloem parenchyma. It is not necessary for the phloem to
contain all four types of cells. Phloem to contain all four types of cells. Phloem cells are living cells (except phloem fibres) which help transport food from leaves to the storage organs and growing regions of the plant.

 Animal Tissues
While doing the activities in this chapter, you have come across two types of animal tissue, the cheek cells are a type of epithelial tissue, while blood is a kind of connective tissue. There are two other types of animal tissue–muscular and nervous.

 Epithelial Tissue:
This tissue covers the surface of the body and lines the internal organs. Its main function is protection. The cells that form the different types of epithelial tissue differ in shape. Some are thin and flat, some cubelike, while others are columnar.

CBSE Class 8 Science Cell and Tissue Notes Set A

 Connective Tissue:
Blood, bones cartilages, tendons (which connect muscles with bones) and ligaments (which tie bones together) are diferent types of connective tissue. Adipose tissue, or what is generally known as fat, is also a kind of connective tissue. Though different in structure, connective tissues have one thing in common-the cells are suspended or embedded in a matrix. In blood, the matrix is liquid and is called the plasma.

 Muscular Tissue:
Muscular tissue is also of different types. However, the different types of muscular tissue (or muscles) have the same basic functoin. They contract and relax to make different parts of the body move. The muscles in our arms, legs thighs, back and so on help us move. The muscles in the heart help it pump blood. The muscles in the alimentary canal help the passage of food. The muscles in the blood vessels help them dilate and get constricted.

 Nervous Tissue:
Nerve cells make up nervous tissue. A nerve cell has a long tail and short branches coming out of it.The tail too has branches. These help to carry message from one cell to the other. The brain and spinal cord are make up of nervous tissue.

CBSE Class 8 Science Cell and Tissue Notes Set A

Question. Make a sketch of the human nerve cell. What funtion do nerve cells perform? 

CBSE Class 8 Science Cell and Tissue Notes Set A
Answer. Functions of human nerve cell:
(i) Nerve cells receive message from different parts of body.
(ii) They further transfer these messages to brain and accordingly brain send commands for functioning of different organs of body.

Question. Write short notes on the following:
(i) Cytoplasm (ii) Nucleus of a cell
Answer. (i) Cytoplasm: Cytoplasm is a jelly like substance which is present between the cell membrane and the nucleus. Various other organelles of cells are present in the cytoplasm. Cytoplasm is made up of chemical substances like carbohydrates, proteins and water. These chemical substances are present in cells of all types and sizes. Cytoplasm contains many important tiny substances called Organelles.
(ii) Nucleus of a cell: Nulceus is the master of the cell. It commands all the functioning of the cell. It is generally located in the center of the cell and is spherical in shape. A membrane called nuclear membrane separates it from cytoplasm. It contains the genetic material DNA and RNA in it. This porous membrane allows the transfer of material in the nucleus and cytoplasm. Nucleus contains a dense body called Nucleolus which actually contains Chromosomes, the genetic material.

Question. Which part of the cell contains organelles?
Answer. Cytoplasm.

Question. State a difference between eukaryotes and prokaryotes.
Answer. Prokaryotes do not have a well designed nuclear membrane while, eukaryotes have a well designed nuclear membrane.

Question. Where are the chromosomes found in cell? State their functions?
Answer. Chromosomes are found in the nucleus of a cell. Their function is to carry characteristic features of parent cells to the daughter cell means, from parent to offspring.

Question. Cells are the basic structural units of living organism. Explain.
Answer. In Biology, the basic unit of which all living thins are composed is knows as cell. The cell is the smallest structural unit of living matter that is capable of functioning independently. A single cell can be a complete organism in itself, as in bacteria and protozoans. A unicellular organism also captures and digests food, respires, excretes, grows, and reproduces. Similar functions in multi-cellular organisms are carried out by groups of specialized cell which are organized into tissues and organs such as, the higher plants and animals. Hence, ‘cell’ is known as the basic structural and functional unit of life.

Question. Explain why chloroplast are found only in plant cells.
Answer. Chloroplasts are found only in plant cells because they are required for photosynthesis.

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Chapter 01 Crop Production and Management
CBSE Class 8 Science Crop Production And Management Notes
Chapter 02 Microorganisms: Friend or Foe
CBSE Class 8 Science Microorganism Friend Or Foe Notes
Chapter 03 Synthetic Fibres and Plastics
CBSE Class 8 Science Synthetic Fibres And Plastics Notes
Chapter 04 Materials Metals and Non-Metals
CBSE Class 8 Science Metal And Non Metals Notes
Chapter 05 Coal and Petroleum
CBSE Class 8 Science Coal And Petroleum Notes
Chapter 07 Conservation of Plants and Animals
CBSE Class 8 Science Conservation Of Plants And Animals Notes
Chapter 10 Reaching the Age of Adolescence
CBSE Class 8 Science Reaching The Age Of Adolescence Notes
Chapter 11 Force and Pressure
CBSE Class 8 Science Force And Pressure Notes
Chapter 14 Chemical Effects of Electric Current
CBSE Class 8 Science Chemical Effects of Electric Current Notes
Chapter 15 Some Natural Phenomena
CBSE Class 8 Science Some Natural Phenomena Notes
Chapter 17 Stars and the Solar System
CBSE Class 8 Science Stars and the Solar System
Chapter 18 Pollution of Air and Water
CBSE Class 8 Science Pollution of Air and Water Notes

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CBSE Class 8 Science Chapter 8 Cell Structure and Functions Notes

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Notes for Science CBSE Class 8 Chapter 8 Cell Structure and Functions

Our team of expert teachers have referred to the NCERT book for Class 8 Science to design the Science Class 8 notes. If you read the concepts and revision notes for one chapter daily, students will get higher marks in Class 8 exams this year. Daily revision of Science course notes and related study material will help you to have a better understanding of all concepts and also clear all your doubts. You can download all Revision notes for Class 8 Science also from www.studiestoday.com absolutely free of cost in Pdf format. After reading the notes which have been developed as per the latest books also refer to the NCERT solutions for Class 8 Science provided by our teachers

Chapter 8 Cell Structure and Functions Notes for Science CBSE Class 8

All revision class notes given above for Class 8 Science have been developed as per the latest curriculum and books issued for the current academic year. The students of Class 8 can rest assured that the best teachers have designed the notes of Science so that you are able to revise the entire syllabus if you download and read them carefully. We have also provided a lot of MCQ questions for Class 8 Science in the notes so that you can learn the concepts and also solve questions relating to the topics. All study material for Class 8 Science students have been given on studiestoday.

Chapter 8 Cell Structure and Functions CBSE Class 8 Science Notes

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Notes for CBSE Science Class 8 Chapter 8 Cell Structure and Functions

CBSE Class 8 Science latest books have been used for writing the above notes. If you have exams then you should revise all concepts relating to Chapter 8 Cell Structure and Functions by taking out a print and keeping them with you. We have also provided a lot of Worksheets for Class 8 Science which you can use to further make yourself stronger in Science

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