Important Facts About Cells
What are Living Being made up of (Cells)?
Classification of Cells
Prokaryotic Cell versus Eukaryotic Cell
Structure Of A Cell
Plasma Membrane (Cell Membrane)
Effects of Concentration of Solution
Hypotonic Solution
Isotonic Solution
Hypertonic Solution
OSMOSIS
Cell Wall
Nucleus
Cytoplasm
Cell Organelles
Endoplasmic Reticulum
Golgi Apparatus
Functions of Golgi Apparatus
Lysosomes
Mitochondria
Plastids
Vacuoles
Our earth is inhabited by different kinds of Living Organisms, who look very different from each other. These living organisms are archaebacteria, eubacteria, protista, fungi, plants, animals and many more who are still undiscovered either extinct or are in some places on this Earth along with the cosmic timeline.
Important Facts About Cells
- Smallest cellular organelle - ribosome.
- Largest cellular organelle:
- In Plants - Plastid.
- In Animals - Mitochondria.
- Largest cell Structure - Nucleus.
- The thin protoplasmic projections connecting two adjacent plants - Plasmodesmata.
- The connecting layer between two adjacent plant cells - Middle lamella.
- The membrane of the vacuole in the plant cell is called tonoplast.
- Mitochondria and plastics can replicate themselves (they both have DNA and ribosomes).
- Viruses are neither prokaryotic or eukaryotic.
- Viruses are molecular organisms.
- In an eukaryotic cell, the cell organelles have membranous coverings. Mitochondria, chloroplasts and other plastids and nucleus have two membranes around them whereas Golgi apparatus, cytoplasmic single reticulum, vacuoles and lysosomes have single membrane.
- In prokaryotic cells, DNA is not enclosed in a nuclear membrane and thus known as nucleoid.
- In prokaryotic cells, ribosomes are present but are of smaller size.
| Cells | Robert Hooke | 1665 |
| Nucleus | Robert Brown | 1831 |
| Protoplasm | Purkinji | 1839 |
| Cell Theory | Schleiden and Schwann | 1838-1839 |
What are Living Beings made up of (Cells)?
If we look in the past of our human civilization's history, we can see that before we got to know about cells people did not know what they and their surroundings made up of. They don't have a clue about the microscopic world that we can see now, though they knew how to cure some bacterial infection or viral flu. Wonder how they knew it. Could it be that our human civilization has a strong hidden scientific historical background of its own. Well I am not gonna discuss this mysterious topic any further because it's not the sole purpose of writing this article. If you are interested in human history and ancient science in various fields, you can research and surf on the world wide web, Good Luck.
After the discovery of the cell, our vision to see the surroundings and particularly our body changed a lot. Various successive researches in this field have discovered a lot more information to the realm that we do not know till that time. Now we have a better approach towards our surroundings.
Various diseases due to bacteria, viruses and other microorganisms can be cured at their level due to our understanding of their realm. Now we also have some branches like microbiology of which students study and graduate and can also pursue for higher levels like PhD. Sure enough this field has grown a lot.
"Cells are defined as the smallest unit of structure and function of all organisms except viruses." The most important and fundamental level in the organization of the living world is the cellular level. Cells are the fundamental structural and functional units of living organisms and are the basic unit of life.
Cells in the present world have evolved a lot and can mainly be classified as unicellular and multicellular cells and the respective organisms are known as unicellular organisms and multicellular organisms. Unicellular organisms have the ability of self replication and multicellular organisms have the method of reproduction (asexual reproduction and sexual reproduction).
Unicellular Organisms are those organisms which have only one cell. Their lifespan is not long. Amoeba, Paramecium, Bacteria are some of its examples.
Multicellular Organisms are those organisms which are made up of more than one cell. Their lifespan is long. Animals, Mammals fall under this category.
The human body is composed of more than 200 different kinds of cells, each specialized to carry out different kinds of functions such as memory, sight, movement and digestion.
Classification Of Cells
All the living organisms on this Earth can be classified into two categories as given below:
- Non Cellular Organisms.
- Cellular Organisms.
Non Cellular Organisms are those which do not have any perfect cell and machinery in their body. These include specially Viruses.
Viruses lack any membrane and hence do not show characteristics of life until they enter a living body (i.e prokaryotic cell or eukaryotic cell) to use its cell machinery to reproduce.
Cellular Organisms contains either one or many cells in their body and they are further classified as:
- Prokaryotes.
- Eukaryotes.
Prokaryotes have primitive and incomplete cells while on the other hand Eukaryotes have advanced and complete cells.
Prokaryotic Cell versus Eukaryotic Cell
| Size of a cell is generally small (1-10 mm). | Size of a cell is generally large (5-100 mm). |
| Nuclear region or nucleoid is not surrounded by a nuclear membrane. | Nuclear material is surrounded by a nuclear membrane. |
| It contains single chromosome. | It contains more than one chromosomes. |
| Nucleolus is absent. | Nucleolus is present. |
| Membrane bound cell organelles are absent. | Membrane bound cell organelles such as mitochondria, plastids, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, etc., are present. |
| Cell division takes place by fission or budding (no mitosis). | Cell division occurs by mitotic or meiotic cell division. |
Structure Of A Cell
After a lot of successive evolution of primordial cells, now in our present world there are a variety of cells with complex machinery systems to regulate its nutrition and basic needs for growth.
But one thing is for sure, that though their shape, size and activities vary, all cells have following three major functional regions:
- The cell membrane or plasma membrane and cell wall.
- The Nucleus.
- The Cytoplasm.
The outer boundary of a cell is the plasma membrane. Cytoplasm lies inside it. Various cell organelles and inclusions are suspended in the cytoplasm. You can say this as the rough blueprint of a cell.
Some organelles and nuclei can be easily seen under a light microscope. The other organelles can be seen under an electron microscope only.
Plasma Membrane (Cell Membrane)
It is the outermost covering of a cell which separates the inner contents of the cell from the outer non required materials or contents. The plasma membrane allows only the selective organics, chemical species or molecules (cellular materials) to pass through them. So, it is also known as selective permeable membrane.
Effects Of Concentration of Solution
If a cell is put in a solution of sugar, salt, etc, there are three situations that may occur i.e., the cell may swell up, remain unchanged (same) or it will shrink.
Hypotonic Solution
If the solution has higher concentration than the cell (inside of the cell or other side of the plasma membrane), the cell will swell up because of osmosis.
Isotonic Solution
If the concentration of the solution is same as the concentration inside the cell, the cell will neither swell up nor shrink, it will remain in its original state or same state (unchanged).
Hypertonic Solution
If the concentration of the solution is lesser than the concentration inside the cell, then the cell will shrink (if we consider the first case i.e., Hypo-tonic Solution, then the phenomena in this case will be called reverse osmosis).
OSMOSIS
The spontaneous movement of water through a semipermeable membrane or plasma membrane from a region of higher concentration to a region of lower concentration is known as osmosis.
Cell Wall
It is present only in the plant cell. The cell wall was mainly composed of cellulose. It gives rigidity to the cell.
The phenomenon of losing water in hyper-tonic solution via a plant cell is known as plasmolysis.
Nucleus
Nucleus is the center of the cell and can be seen easily through a light microscope. Nucleus has a double layer covering called the nuclear membrane. The nuclear membrane has pores through which the fluid substance i.e Cytoplasm goes inside or outside of Nucleus.
- Nucleus contains chromosomes.
- Chromosomes contain the information for inheritance of features from their parents for the next generation in the form of DNA (deoxyribo nucleic acid).
- Chromosomes are composed of DNA and proteins.
- Functional segment of DNA is the gene.
Nucleus plays a very crucial role in cellular reproduction, the process by which a single cell divides and organizes into two new cells. Nucleus determines the structure and the way in which the cell will develop.
Cytoplasm
The part of the cell which occurs between the plasma membrane and nuclear envelope is called cytoplasm. Or simply inside the plasma membrane all the organelles and other parts of the cell have emerged into something and that thing is cytoplasm. Cytoplasm consists of an aqueous ground substance, the cytosol, containing a variety of cell organelles and some other inclusions such as insoluble wastes, starch, glycogen, lipid, some other storage products, etc.
Now let’s see some functions of cytoplasm:
- Cytoplasm acts as a store of vital chemicals such as amino acids, glucose, vitamins, ions, etc.
- Cytoplasm is the site of certain metabolic pathways, such as glycolysis. Synthesis of fatty acids, nucleotides, and some amino acids also take place in the cytosol.
- Living cytoplasm is always in a state of movement.
Cell Organelles
Cell Organelles are like factories of cells. Cell organelles are very essential for cell because they perform important functions that include making new material or useful chemical species and disposal of waste materials.
Here are list of some organelles, for example:
- Endoplasmic Reticulum.
- Golgi Apparatus.
- Lysosomes.
- Mitochondria.
- Plastids.
- Vacuoles.
Endoplasmic Reticulum
The endoplasmic reticulum is a large network of membrane bound tubes and sheets. It looks like a round bag.
There are two types of Endoplasmic Reticulum (ER):
- Rough ER.
- Smooth ER.
Rough ER is seen as rough under a microscope because it has an organelle called ribosome. Ribosomes are the sites of protein manufacture in the cell.
Smooth ER are the sites of fat (lipid) manufacturers in the cell. Smooth ER plays a crucial role in detoxifying many drugs and poisons.
Some of these proteins and lipids help to make plasma membranes or cell membranes. This process is known as membrane bio-genesis.
Golgi Apparatus
It consists of a system of membrane-bound vesicles arranged approximately parallel to each other in stacks called cisterns. Its membrane also has some connections with the membrane of endoplasmic reticulum and therefore, constitute another portion of the complex cellular membrane system.
Functions
- Storage, modification and packaging into vesicles.
- It is also involved in the manufacture of lysosomes.
Lysosomes
It is the waste disposal system of cells. If any foreign material (such as bacteria, virus, etc.) enters or any part of the cell is damaged, lysosomes digest all of them and throw them outside. Lysosomes are able to do this because they have some powerful digestive enzymes.
Lysosomes are also known as the suicide bag. The reason behind this scary name is that when a cell is destroyed or not in work (abandoned), the lysosomes may burst and digest their own cell.
Mitochondria
Mitochondria is known as the powerhouse of the cell. For every sightliest function, energy is needed. If you consider the cell as a whole clan and Nucleus as the chief of the clan, then Mitochondria would be the top sect clan elder. This is just a visualization. Mitochondria produces the energy in the form of ATP (adenosine triphosphate). ATP is the energy currency of the cell. It has its own genetic material (DNA and ribosomes).
Plastids
Plastids are present only in the plant cells. Plastids contain the pigment chlorophyll known as chloroplast. It is important in photosynthesis in plants. It also contains yellow or orange pigments.
There are two types of Plastids:
- Chromoplast (colored).
- Leucoplast (white or colorless).
Leucoplasts are primarily organelles which store starch, oil, and proteins. Plastids also have their own genetic material (DNA and ribosomes).
Vacuoles
These are present in plant cells and cover most of the volume (50% - 70%). The vacuoles are not present in animal cells (if present, they are too small).
Some points to ponder about Vacuoles:
- It is the storage sack of plant cells.
- It also provides turgidity and rigidity.
- In unicellular organisms like Amoeba, the food is engulfed and stored in vacuoles.
- In multicellular organisms, vacuoles also play crucial roles such as expelling excess water and waste material from the cell.
Que: What is the difference between Plant Cell and Animal Cell?
| Plant cells are bigger. | Animal cells are smaller. |
| Plastids are present. | Plastids are absent. |
| A modified plant cell has a big vacuole covering 50% to 70% of the total volume of the cell body. | An animal cell has very small vacuole or null. |
| Plant cell does not have a centriole. | Animal cells have centrioles. |
| Plant cell does not have a modified Golgi Apparatus. | Animal cell has a well developed Golgi Apparatus. |
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