Cells
Overview.
Cell specialisation.
Hierarchy of cellular structure.
Discovery of the cell.
Robert Hooke.
Cell theory.
Light microscope.
Electron microscope.
Cell metabolism.
Cell chemistry.
Carbohydrates.
Amino acids.
Proteins.
Enzymes.
Lipids.
Organism and the cell.
Components of a cell.
Cell membrane.
Nucleus.
Cytoplasm.
Cytoskeleton.
Mitochondria.
Centrioles.
Endoplasmic reticulum.
Ribsomes.
Golgi complex.
Vacuoles.
Lysosomes.
Animal cells and plant cells.
Cell wall.
Vacuole.
Plastid.
Leucoplasts.
Chromoplasts.
Chloroplasts.
Overview.
All Living organisms are made up of small units, called cells.
Cells are, the building blocks of a living organism.
Whether the organism, is a bacteria, insect, fish, plant, tree, bird, animal, or a human being, the unit of the organism, is still a cell.
Organisms, which have only one cell, are called unicellular organisms.
Bacteria, archaea, protozoa, amoeba are examples, of unicellular organisms.
Most other living organisms, insect, fish, plant, tree, bird, animal, or a human being, are multi cellular.
The cell size, of a human being, or a elephant, is about the same.
Larger organisms, have more number of cells.
A Human being, has about 100 trillion cells.
The basic components and functionality, of a cell of any living organism, is the same.
So, study of cells is like studying life itself.
Cell Specialisation.
Though the basic components, are the same in any cell, in larger organisms, cells specialise in functions.
For example, in our body,
Blood cells, transport oxygen and nutrition.
Brain Neurons, which are cells in the brain, are involved in the thinking process.
Cells, in the eye, help deduct light signals.
Cells, in the tongue, help deduct taste.
Cells, in the nose, help deduct odours.
Nerve Neurons, which are cells, in the nerves, transmit signals, to and from the brain.
The sense of touch, of say, heat or cold, is transmitted to the brain, by nerve cells.
Hierarchy of Cellular structure.
Cells are, the structural or functional unit, of an organism.
Many cells make a tissue.
For example, bone tissue.
Many tissues make an organ.
For example, a finger bone.
Many organs make an organ system.
For example, skeletal system.
An organism consists of many organ systems.
For example, the brain, the heart, the lung, the kidney, the liver, are organs in our body.
The blood system, the nerve system, the respiration system, the digestive system, are examples of organ systems in our body.
All the organ systems work together, in a inter related way, in the organism.
Discovery of the Cell.
Robert Hooke.
Robert Hooke, was an English scientist.
He designed, the microscope, which can enlarge the cell image.
He examined, a piece or dried cork, under a microscope.
He saw, honeycomb like structures, with many units.
He called, each of them as a cell.
The word cell, has a meaning, a small room.
The branch of science, which deals with the study of cells, is called cytology.
Robert Hooke, is considered as the father of cytology.
Cell theory.
Cell theory, was first developed by German scientists, Schleiden and Schwann in 1839.
Some basic concepts of cells are outlined below.
All living organisms, comprises of a basic living unit called a cell.
All the cells, originate from, a single main cell.
Cells, divide and create, more cells.
This is how, living organisms grow.
Whether it is a plant, animal, or human being, this concept of growth, from a single cell remains the same.
In higher level organisms, Cells specialise, in different functionalities.
For example, Blood cells, nerve cells, muscle cells, kidney cells etc., are specialised cells.
Light Microscope.
Cells are very small in size, they are usually, measured in microns.
A micron, is one millionth of a metre.
It is also, one thousandth of a milli metre.
A Human cell, is typically, 10 to 20 microns in size.
With the naked eye, we cannot see anything, less than 100 microns.
We use an instrument called, a light or compound microscope, to magnify the image of the cell.
In a simple sense, a microscope, acts like a magnifying glass.
A 10 X magnifying glass, will magnify an image, ten times.
A 40 X magnifying glass, will magnify an image, forty times.
A light microscope, in a laboratory, is a device with many lenses, and mechanical components.
It is a more advanced, and sophisticated instrument, than the one, used by Robert Hooke.
Different microscopes, have different magnification capacity.
A microscope, which has, a magnifying capacity, of 2000 X, magnifies an object 2000 times.
For example, a cell of size 10 microns, will be seen as, 20000 microns or 20 millimeters.
This is good enough, to see the cell, and some of its components.
But, it is not good enough, to see all the internal components, of a cell in detail.
Electron Microscope.
An electron microscope, uses a beam of electrons, to get an image of an object.
It has, a magnifying capacity, of 200 thousand X.
With this, we are now able to study, the components of a cell, in molecular detail.
Cell metabolism.
Though a cell is very small, a lot of activity takes place in it.
It is more complex, and fascinating, than a modern factory.
Many things, which happen within the cell, are organic chemical reactions.
The process of chemical digestion, and its related reactions, are called metabolism.
Cell Metabolism, is a total of all the chemical reactions in the cell.
Two key chemical reactions, are glycolysis and photosynthesis.
The break down of sugars, and release of energy is called glycolysis.
The process of using sun's energy to build sugars is called photosynthesis.
Cell Chemistry.
There is a lot of common chemistry, which happen in all cells.
It is surprising and interesting to know, that carbon, hydrogen, oxygen and nitrogen, constitute most of the cell.
These four elements account for, 99% of a body's atoms.
Hydrogen and oxygen, is present as H 2 O, or water.
Water is the best, and most abundant solvent in the body.
Most other substances, are dissolved in water.
Water contributes to, 60% of our body weight.
It is also involved, in most of the chemical reactions.
Carbohydrates.
Carbohydrates are compounds of Carbon, Hydrogen and Oxygen.
Sugar is a carbohydrate.
Sugars provide living things, with energy.
It also acts as substances, used for structure.
The simplest of sugars, is called glucose.
It has the formula, C 6, H 12, O 6.
This is the sugar, created by photosynthesis, with the sun's energy.
This is the sugar, that is broken down in glycolysis, which releases energy.
Amino acids.
Amino acids have a, carboxyl group,C O O, and an N H 2 group.
Amino acids are used, widely in cells to build proteins.
Proteins.
Proteins are basically, a long chain of amino acids.
In Proteins, these long chains of amino acids, are twisted around like a knot.
Proteins are important part of an organism.
They participate in virtually, every process, within cells.
Enzymes.
Chemical reactions sometimes, require a catalyst to make, the reaction happen.
Enzymes are proteins, which help complex reaction, that happen in cells.
Lipids.
Lipids are, fat cells used by the body.
Their main function, is to store energy.
They also act, as structural components of cell membranes.
Organism and the cell.
The cell, is the basic unit, of an organism.
An organism has many cells.
Is an organism, just a collection of many cells?
No, it is much more than that.
An organism, is a system of organs, which work in a coordinated way.
A human body, is an example of an organism.
Like any other organism, it comprises of cells.
In a simple way, a cell is like a plastic bag, containing a fluid, with a central nucleus or head quarters.
The cell cannot exist by itself.
It requires a mechanism, to supply substances to it, and take away substances from it.
The blood system plays this role.
Blood flows, in thin tubes called capillaries, which reaches all the hundred trillion cells in the body.
Blood carries, oxygen and nutrition to the cells.
Blood takes away, carbon dioxide and waste from the cell.
The lung takes in, oxygen and gives it to the blood.
The lung takes out, the carbon dioxide from the blood, which we breathe out.
The digestive system creates, nutrients and gives it to the blood.
The kidneys filter out the waste, from the blood, for disposal.
This is the way, all the cells in the body are inter related, and contribute to the functionality, of the whole organism.
There are many such functionalities, in the human body.
For example, the nerve system, the respiratory system, the digestive system, etc.,
all contribute to the working, of the organism.
Components of a cell.
A cell has 3 prominent components.
Cell Membrane.
Nucleus.
Cytoplasm.
Cell Membrane.
The cell membrane, is also called as, the plasma membrane.
The cell membrane is the skin, which holds, all the other components, of the cell inside it.
It also acts as a gateway, to the other parts of the organism.
It protects the contents of the cell, from the environment outside the cell.
The cell, however has a need to interact, with its environment.
It needs oxygen, and nutrition from the environment.
It needs to give out, carbon dioxide and waste to the environment.
The cells acts as, a selective gateway for this process.
The cell membrane, is said to be, selectively permeable.
The process by which, it allows substances to move in and out, is called diffusion and osmosis.
Diffusion is a process, by which a substance, is dissolved in water, spreads out to be, uniformally present.
Osmosis is a process, by which solvent molecules move through, a semi permeable membrane, to a region of higher concentration.
These processes selectively allows, oxygen and nutrition molecules, to enter the membrane.
It allows carbon dioxide and waste material, to exit the cell, through the membrane.
The cell membrane allows, the cell to operate as an independent unit,
at the same time selectively interact with the organism.
Nucleus.
The cell nucleus, is like the brain of the cell.
It is a head quarters, from which instructions are issued, to the rest of the cell.
The nucleus has its own, skin or membrane.
It is like a tiny bag, inside the cell.
The nucleus contains chromosomes.
For example, the human nucleus contains, 23 pairs of chromosomes.
Each Chromosome, is made up of, thousands of genes.
These genes are called, the D N A.
The genes of the D N A, is what makes us or any other organism.
The D N A, is an organic compound called, di nucleic acid.
Genes are possibly the, most fascinating part of an organism.
They contain all the, knowledge and information required, to build the organism.
This is how, a living organism grows, from a single cell, to the size of any organism, human being or elephant.
When a cell divides, the chromosomes inside the nucleus, is replicated in the new cell.
It is a remarkable fact that, all the hundred trillion cells, in our body have exactly, the same set of 23 pairs of chromosomes.
The genes, in the chromosomes, acts like a blueprint to produce, other substances inside the cell.
Genes have encoded information for this.
The chromosome, is a long chain of genes, a pair of which, is twisted in a double helix form.
This is like, two snakes coiled around each other.
Gene expression is the process, by which the information in gene is decoded, to form other molecules, like a protein molecule.
The D N A works along, with another molecule called R N A.
The R N A, is the selective copy, of part of the D N A.
R N A, stands for Ribo Nucleic acid.
We know that, the cells in our body, could specialise in different functions.
Though all of them, have the same chromosomes, different genes can express themselves, in different cells.
This is how, the same cell builds, a muscle, bone, kidney, liver, eyes, brain etc.
That is, the genes are selectively expressed, in each type of functional cell.
That's the fascinating aspect of genes, which are contained in the pocket, smaller than a pin head.
Cytoplasm.
The gel like material, within the cell is called the cytoplasm.
Cytoplasm has fatty acid, sugar, and amino acid molecules, dissolved in it.
These are required for, the working of the cell.
The enzymes in it, break down larger molecules, for use by the organelles.
For example, it breaks down Glucose, to be used by the mitochondria.
Many tiny organs, are present inside the cell, in the cytoplasm.
They are called organelles.
Some of the prominent organelles contained in the cytoplasm are,
Cytoskeleton.
Mitochondria.
Centrioles.
Endoplasmic Reticulum.
Ribosomes.
Golgi complex.
Vacuoles.
Lysosomes.
Cytoskeleton.
Cytoskeleton, is a cellular scaffolding or skeleton, that criss crosses the cytoplasm.
It gives a structure to the cell.
It holds the organelles in place.
It also acts like a high way, for movement of molecules, within the cell.
Mitochondria.
A mitochondria, is like the power plant of the cell.
It is the source of energy for the cell.
It uses organic compounds, derived from nutrients, to produce A T P.
A T P, stands for, adenosine triphosphate.
The mitochondria, is the place, where oxygen is combined, with food molecules.
This way, the food is digested, and energy released.
There might be, more than one, mitochondria in a cell.
This depends upon, what is the energy needs, from the cell.
For example, a muscle cell, which expends a lot of energy, contains thousands of mitochondria.
Nerve cells have only a few.
Centrioles.
Centrioles are, rod like structures, made of short microtubules.
Centrioles, play a important role in cellular division.
Endoplasmic Reticulum.
This has two important functions.
Transporting molecules, such as proteins, from one place in the cell, to another place in the cell.
Helping, in the Synthesis of, proteins and lipids.
Ribosomes.
Ribosomes, are small organelles, where proteins are synthesised.
Ribosomes interacts with, R N A molecules, to produce chains of amino acids.
Proteins, are long chains, of amino acids.
Ribosomes, are protein factories, of the cell.
Golgi complex.
Golgi complex modifies, sorts, and packages, different substances in the cell.
It gathers simple molecules, and combines them, to make complex molecules.
It acts like a post office.
It packages and labels items, and sends them, to specific parts of a cell.
Vacuoles.
Vacuoles, are organelles that have, secretory, excretory and storage functions.
Lysosomes.
They are little digestion machines.
When a cell, absorbs some food, they release enzymes.
These powerful enzymes, break down or digest in the cell.
The lysosomes, break down harmful, cell products and waste materials.
They also digest invading bacteria.
Sometimes, lysosomes breakdown the parent cell itself, when the parent cell is ready to die.
Animal cells and plant cells.
There is a simple and important difference, between animals and plants.
Plants, produce their own food.
Animals, cannot produce their own food.
They depend on, plants and other animals, for their food.
All the components, we have discussed are common, to both animal and plant cells.
Plant cell, has some special organelles, to help produce their own food, and some other specialized functionality.
Three organs are prominently different in plant cells.
Cell Wall.
Vacuole.
Plastid.
Cell wall.
A cell wall, is a rigid layer, outside the cell membrane.
It surrounds the membrane.
It contains, cellulose and proteins.
The cell wall provides, structural support and protection.
Plants do not have bones.
Plants have other ways, of becoming structurally stable.
The cells walls, in a plant provide, shape and structural support.
The Cell's walls have tiny pores, to allow water and nutrients, to flow in and out of the cell.
Vacuole.
Plant cells, have a central vacuole, which is much larger than an animal cell.
It can occupy 30 to 90%, of the cell volume.
It is a storage place, for the liquid called sap.
Cell sap is basically water, in which some salts, and other substances, are dissolved.
When a plant droops, it means the vacuoles, have lost its water.
It also stores, other substances like the pigments, which give flowers their colour.
Plastids.
Plastids, are found only in plant cells.
The types of plastids are
Leucoplasts.
Chromoplasts.
Chloroplasts.
Leucoplasts.
They occur in regions, not exposed to sunlight, like in roots.
They are mainly involved, in storage of food.
Chromoplasts.
They contain pigments, which are green, yellow, red and orange in colour.
Chloroplasts.
Chloroplasts are the centre, for production of food.
Chloroplasts have chlorophyll, which is green in colour.
This is what gives plants, there green colour.
Chloroplasts are involved, in photosynthesis.
They harvest light energy from the sun, and manufacture organic food molecule.
Sugar and starches are examples, of the food that they produce.
They use water and carbon dioxide, and release oxygen.
Plants are a source of food for all animals, including human beings.
Chloroplasts, play a central role, in producing this food.