Skip to main content

9th Class Notes Cell- the fundamental unit of life

 CLASS 9TH                  CELL –BASIC AND STRUCTURAL UNIT 


Introduction    
The word cell is derived from the Latin word “cellula” which means “a little room”
It was the British botanist Robert Hooke who, in 1664, while examining a slice of bottle cork under a microscope, found its structure resembling the box-like living quarters of the monks in a monastery, and coined the word “cells”

In the year 1838, Matthias Schleiden, a German botanist, first proposed the idea that all plants consist of cells


The Dutch scientist A.V.Leeuwenhoek, in 1674, discovered the minute forms of life such as bacteria and single celled animals in a drop of water


In 1839, Theodar Schwann, another German botanist, asserted that all plants and animals are made up of cells
In 1831, Robert Brown discovered the nucleus in the cell 


J.E.Purkinje, in 1840, used the term protoplasm to describe the juicy, slimy gelatinous contents of the cell
In 1885, Rudolf Virchow expressed that all cells arise from pre-existing cells


In 1932, two German Scientists, Ruska and Knoll, invented the electron microscope 


Endoplasmic Reticulum (ER) This is a complex network of tubes, the lumen of which is filled with fluid. Two types of endoplasmic reticula are seen.They are:   

Cell - A Unit of Life
Organisms may be broadly classified into two kinds:  Unicellular  and  Multicellular
Ameoba
Chlamydomonas another type unicellular organism
Chlamydomonas
structure of Paramecium a unicellualr organism
Paramecium
structure of onion peel

Cells of onion peel

All living organisms, whether plants or animals, are made up of microscopic units called cells. The cell occupies the same central position in biology as the atom in the physical sciences.
All living beings, plants and animals, start their life with a single cell. Some organisms exist as a single cell and carry out the various metabolic life processes such as assimilation, respiration, reproduction, excretion, etc., that are essential for their survival. These are known as unicellular organisms.

Structure of Cell
Cells vary in shape and size. They may be oval, spherical, rectangular, polygonal, spindle shaped, star shaped, rod-shaped or totally irregular like the nerve cell. The diversity in cells is in accordance with the role or function it has to perform as part of the tissue or organ system. In general, there is no typical shape for cells.
Cell Membrane (Plasma Membrane)  
Cell membrane is present in both plant and animal cells. It is living, elastic and made of proteins and lipids (fats). Its function is to provide a mechanical barrier for the protection of the inner cell contents and to regulate the movement of molecules in and out of the cell.  
Cytoplasm  
The part of the cell between the cell membrane and the nuclear membrane is called the cytoplasm. 
The cytoplasm consists of the matrix and the organelles. The matrix is a transparent semi fluid substance. 
When active, it is always in a state of movement. The organelles are found embedded in the cytoplasm. They have definite shape, structure and function. All the metabolic activities of the cell such as synthesis, secretion, digestion and energy generation, are performed by the different cell organelles. Cell organelles can be seen only with the help of an electron microscope.

Following are the Important Cell-organelles:

> Tubes with a smooth surface are called smooth endoplasmic reticula. They secrete lipids.
> Tubes with spherical bodies (ribosomes) attached are known as rough endoplasmic reticula.   

The functions of the endoplasmic reticulum are to form the skeletal framework of the cell, to provide a pathway for the distribution of nuclear material from one cell to the other and to synthesize fats, steroids and cholesterol with the help of enzymes secreted by the cell.  

Golgi Apparatus   

Also known as Golgi Complex or Golgi Bodies, they consist of tiny, elongated, flattened sacs (cisternae), which are stacked parallel to one another along with some vacuoles and clusters of vesicles.
The function of the golgi body is to secrete certain hormones and enzymes. It also forms lysosomes and peroxisomes. The golgi body is usually found close to the nucleus.  

Lysosomes   

These are tiny, spherical, sac-like structures scattered all over the cytoplasm. Their main function is digestion. They contain powerful destructive enzymes capable of digesting all organic material, and hence called “digestive bags”.  

Lysosomes 

present in white blood cells are capable of digesting bacteria and viruses. During starvation, lysosomes digest proteins, fats and glycogen in the cytoplasm, and supply energy to the cell. They are also capable of digesting worn out cell organelles, or even digesting the entire damaged cell containing them. Hence, “suicide bag” is a sobriquet that is often used for Lysosomes.  
Peroxisomes   
These organelles are found in the liver and kidney cells. They are small, membrane-bound sacs, and contain powerful oxidative enzymes.
Their chief function is to remove toxic substances.

Ribosomes   

These are spherical, granular particles which occur freely in the matrix or remain attached to the rough endoplasmic reticulum. Ribosomes contain RNA (ribonucleic acid) and proteins. Their function is to provide the surface for protein synthesis.  

Centrosome   

This is found in the cytoplasm near the outer surface of the nucleus and contains two cylinders called centrioles. The centrosome is found only in the animal cell. The centrosome and the centrioles play an important role by forming the poles of the spindle during cell division.  

Mitochondria   

These may be cylindrical, rod-shaped or spherical and distributed in the cytoplasm. Each mitochondrion is bound by a double membrane. The inner membrane is folded into ridges called cristae, which increase the surface area of the membrane.

 It is in the mitochondria that the sugar is finally burnt during cellular respiration. The energy thus released is stored as high-energy chemicals called ATP (adenosine triphosphate). Hence, mitochondria are termed as the “power house” or the “power plant” of the cell. The body cells use the energy stored in ATP for synthesis of new chemical compounds, the transport of these compounds and for mechanical work.  

Plastids  

These organelles are found only in plant cells.   

Plastids are of three types:   Chloroplasts   Chromoplasts   Leucoplasts  

Chloroplasts   They are green and found in leaves. The green colour is due to the presence of chlorophyll.

Chromoplasts   They are yellow, orange and red, and found in flowers and fruits.  

Leucoplasts   They are colourless and found in roots, seeds and underground stem

The function of the chloroplast is to trap solar energy for photosynthesis. Chromoplasts impart colour to flowers to attract insects for pollination. Leucoplasts store food in the form of carbohydrates, fats and proteins.   

Nucleus   This is a prominent, spherical or oval structure found at the centre of the cell. It is the controlling centre of all cell activities and has been described as the brain of the cell. It regulates all metabolic and hereditary activities of the cell.   

The nucleus is composed of the following structures:   

Nuclear Membrane   : Nucleoplasm   Nucleolus   Chromatin network

Nuclear Membrane   This is a double-layered membrane which separates the nucleoplasm from the cytoplasm. The nuclear membrane has minute pores which allow the selective transfer of material between the nucleoplasm and the cytoplasm.  

Nucleoplasm   Within the nuclear membrane, completely filling up the space, is a clear, semi-solid, granular substance or matrix called the nucleoplasm. The nucleolus and the chromatin network lie suspended in the nucleoplasm.  

Nucleolus   This dense, spherical granule found in the nucleus contains RNA (ribonucleic acid) which is responsible for protein synthesis in the cytoplasm.  

Chromatin Network   These are very fine thread-like, coiled filaments uniformly distributed in the nucleoplasm. At the time of cell division, the chromatin becomes thick and ribbon like and are known as chromosomes. The chromosomes contain genes, which are composed of DNA (deoxy-ribonucleic acid). Genes are responsible for storing and transmitting hereditary characteristics from one generation to another. A gene is the functional unit of a chromosome. Genes are arranged in single linear order along the chromosome. One gene may be responsible for a single characteristic, or a single characteristic may be transmitted by a set of genes. 

Prokaryotic and Eukaryotic Cells

The structure of the cell that we have studied so far is that of a eukaryotic cell. How is a prokaryotic cell different from a eukaryotic cell?   The main difference between these two cell types is that prokaryotic cells do not have a nuclear membrane. The nuclear material consists of a single chromosome and lies in the cytoplasm. The nuclear region in the cytoplasm is called nucleoid. Membrane-bound organelles are absent. Prokaryotic cells are found in bacteria and cynobacteria (blue-green algae).


 Related Post: 9th Biology You may like to Read

Comments

CBSE ADDA :By Jsunil Sir : Your Ultimate Destination for CBSE Exam Preparation and Academic Insights

Class 10 Chapter 02 Acid Bases and Salts NCERT Activity Explanation

NCERT Activity Chapter 02 Acid Bases and Salt Class 10 Chemistry Activity 2.1 Indicator Acid Base Red litmus No Change Blue Blue Litmus Red No change Phenolphthalein Colourless Pink Methyl Orange Pink   Yellow Indictors are substance which change colour in acidic or basic media. Activity 2.2 There are some substances whose odour changes in in acidic or basic media. These are called olfactory indicators. Like onion vanilla, onion and clove. These changes smell in basic solution. Activity 2.3 Take about 5 mL of dilute sulphuric acid in a test tube and add few pieces of zinc granules to it. => You will observe bubbles of hydrogen gas on the surface of zinc granules. Zn + H2SO4 --> ZnSO4 + H2 => Pass the Hydrogen gas through the soap solution. Bubbles formed in the soap solution as Hydrogen gas it does not get dissolved in it

Living science ratna sagar class 6 solutions

Ratna sagar living science 6 answers by jsunil. Class6 Living science solution Term-1 Living Science Solution chapter-1 Source of food Download File Living Science Solution chapter-2 Component of food Download File Living Science Solution chapter-3 Fibre to fabric Download File Living Science Sol ch-4 Sorting of material into group Download File Living Science Soln ch-5 Separation of substance Download File Living Science Solution chapter-6 Change around Us Download File Living Science Solution ch-7 Living and Non Living Download File Living Science Solution ch-8 Getting to Know Plants Download File Living Science Sol ch-9 The Body and Its movements Download File Visit given link for full answer Class6 Living science solution Term-II

Class 10 Metal and Non MetalsChapter 03 NCERT Activity Solutions

X Class 10 NCERT Activity Explanation Class 10 Metals and Non Metals Activity 3.1 Page No. 37 Take samples of iron, copper, aluminium and magnesium. Note the appearance of each sample. They have a shining surface. Clean the surface of each sample by rubbing them with sand paper and note their appearance again. They become more shiny. => Freshly cut Metal have shiny surface Activity 3.2 Page No. 37 Take small pieces of iron, copper, aluminium, and magnesium. Try to cut these metals with a sharp knife and note your observations. They are very hard to cut. Hold a piece of sodium metal with a pair of tongs and try to cut it with a knife. Sodium can be cut easily with knife. Hence K and Na are soft metal cut with knife Activity 3.3 Page No. 38 Take pieces of iron, zinc, lead and copper try to strike it four or five times with a hammer. These metals are beaten into thin sheet on hammering. This property of metal is called malleability and metals are called malleable. Activity 3.4 Page

CBSE I NCERT 10th Numerical Problem solved Reflection and reflection of light

Q. 1. A concave mirror of focal length 20cm is placed 50 cm from a wall. How far from the wall an object be placed to form its real image on the wall?  Solution: V= -50 cm F= -20cm From mirror formula 1/u = 1/f – 1/v = -1/20+ 1/50 = - 3/100  U = - 33.3 cm Therefore, the distance of the object from the wall x =  50 – u X = 50 – 33.3 = 16.7 cm. Q.2. An object is placed at a distance of 40cm from a concave mirror of focal length 15cm. If the object is displaced through a distance of 20 cm towards the mirror, By how much distance is the image displaced? Answer: Here f = - 15 cm, u = - 40 cm Now 1/f = 1/u + 1/v Then 1/v = 1/f – 1/u Or V= uf/u-f =( - 40 x -15)/25 = -24 cm Then object is displaced towards the mirror let u1 be the distance object from the Mirror in its new position. Then u1 = -(40-20) = -20cm If the image is formed at a distance u1 from the mirror then v1 = u1f/u1-f = -20X-15/-20+15 = -60 cm. = - 20 x-15/-20+15 = -60 cm. Therefor

Electricity numerical for class 10 CBSE Trend Setter 50 Problems

1. The current passing through a room heater has been halved. What will happen to the heat produced by it? 2. An electric iron of resistance 20 ohm draws a current of 5 amperes. Calculate the heat produced in 30 seconds. 3. An electric heater of resistance 8 ohm takes a current of 15 A from the mains supply line. Calculate the rate at which heat is developed in the heater. 4. A resistance of 40 ohms and one of 60 ohms are arranged in series across 220 volt supply. Find the heat in joules produced by this combination in half a minute. 5. A resistance of 25 ohm is connected to a 12 V battery. Calculate the heat energy in joules generated per minute. 6. 100 joules of heat is produced per second in a 4 ohm resistor. What is the potential difference across the resistor? 7. An electric iron is connected to the mains power supply of 220 V. When the electric iron is adjusted at minimum heating’ it consumes a power of 360 W but at ‘maximum heating’ it takes a power of 840 W. Ca