CELL | STRUCTURE,DEFINITION,FUNCTION,DIAGRAM,THEORY
THERE IS A LARGE VARIETY OF ORGANISMS ON THIS EARTH. THEY ARE ALL DISTINCT IN THEIR FORM AND STRUCTURE, YET THEY ALL POSSESS SIMILARITY IN THEIR BASIC STRUCTURE AND FUNCTIONS. JUST AS A BUILDING IS MADE UP OF BRICKS, SIMILARLY, THE BODIES OF ALL PLANTS AND ANIMALS ARE MADE UP OF CELLS. FROM MICROSCOPIC BACTERIA OR AMOEBA TO LARGE ORGANISMS LIKE ELEPHANTS, WHALES OR GIGANTIC TRESS, ALL ARE MADE UP OF THE BASIC UNITS CALLED CELLS.
SOME CELLS EXIST AS UNICELLULAR ORGANISMS WHILE OTHERS ARE A PART OF MULTICELLULAR ORGANISMS. CERTAIN BASIC FUNCTIONS LIKE NUTRITION, RESPIRATION, GROWTH, DEVELOPMENT AND REPRODUCTION ARE PERFORMED BY ALL THE CELLS. THESE FUNCTIONS ARE ESSENTIAL FOR THE SURVIVAL OF THE CELL.
DEFINITION
A CELL CAN BE DEFINED AS THE BASIC STRUCTURAL AND FUNCTIONAL UNIT OF ALL LIVING ORGANISMS.
DISCOVERY OF THE CELL
CELLS ARE THE BASIC STRUCTURE OF ALL LIVING BEINGS, YET THEY REMAINED UNDISCOVERED FOR A LONG TIME. THIS IS BECAUSE THE MAJORITY OF THE CELLS ARE TOO SMALL TO BE SEEN BY THE NAKED EYE. IT WAS ONLY AFTER THE ADVENT OF OPTICAL INSTRUMENTS IN THE SEVENTEENTH CENTURY, THAT THE STUDY OF THE CELL COULD BE POSSIBLE.ROBERT HOOKE WAS THE FIRST SCIENTIST WHO DISCOVERED THIN SLICES OF CORK THROUGH HIS SELF-DESIGNED MICROSCOPE IN 1665.
HE OBSERVED HONEY-COMB LIKE STRUCTURES CONSISTING OF LITTLE COMPARTMENTS. IT WAS LATER EXPLAINED THAT THESE COMPARTMENTS WERE ACTUALLY DEAD CELLS BOUND BY CELL WALL.
CHARACTERISTICS OF CELL
Following are the various essential characteristics of cells:
- Cells provide structure and support to the body of an organism.
- The cell interior is organised into different individual organelles surrounded by a separate membrane.
- The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
- Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
- Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell.
- Lysosomes digest unwanted materials in the cell.
- Endoplasmic reticulum plays a significant role in the internal organisation of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations.
CELL THEORY
Cell Theory was proposed by the German scientists, Theodor Schwann, Matthias Schleiden, and Rudolf Virchow. The cell theory states that:
- All living species on Earth are composed of cells.
- A cell is the basic unit of life.
- All cells arise from pre-existing cells.
A modern version of the cell theory was eventually formulated, and it contains the following postulates:
- Energy flows within the cells.
- Genetic information is passed on from one cell to the other.
- The chemical composition of all the cells is the same.
Functions of Cell
A cell performs these major functions essential for the growth and development of an organism. Important functions of cell are as follows:
Provides Support and Structure
All the organisms are made up of cells. They form the structural basis of all the organisms. The cell wall and the cell membrane are the main components that function to provide support and structure to the organism. For eg., the skin is made up of a large number of cells. Xylem present in the vascular plants is made of cells that provide structural support to the plants.
Facilitate Growth Mitosis
In the process of mitosis, the parent cell divides into the daughter cells. Thus, the cells multiply and facilitate the growth in an organism.
Allows Transport of Substances
Various nutrients are imported by the cells to carry out various chemical processes going on inside the cells. The waste produced by the chemical processes is eliminated from the cells by active and passive transport. Small molecules such as oxygen, carbon dioxide, and ethanol diffuse across the cell membrane along the concentration gradient. This is known as passive transport. The larger molecules diffuse across the cell membrane through active transport where the cells require a lot of energy to transport the substances.
Energy Production
Cells require energy to carry out various chemical processes. This energy is produced by the cells through a process called photosynthesis in plants and respiration in animals.
Aids in Reproduction
A cell aids in reproduction through the processes called mitosis and meiosis. Mitosis is termed as the asexual reproduction where the parent cell divides to form daughter cells. Meiosis causes the daughter cells to be genetically different from the parent cells. Thus, we can understand why cells are known as the structural and functional unit of life. This is because they are responsible for providing structure to the organisms and performs several functions necessary for carrying out life’s processES.
CELL STRUCTURE
CELL MEMBRANE
- The cell membrane supports and protects the cell. It controls the movement of substances in and out of the cells. It separates the cell from the external environment. The cell membrane is present in all the cells.
- The cell membrane is the outer covering of a cell within which all other organelles, such as the cytoplasm and nucleus, are enclosed. It is also referred to as the plasma membrane.
- By structure, it is a porous membrane (with pores) which permit the movement of selective substances in and out of the cell. Besides this, the cell membrane also protects the cellular component from damage and leakage.
- It forms the wall-like structure between two cells as well as between the cell and its surroundings.
- Plants are immobile, so their cell structures are well-adapted to protect them from external factors. The cell wall helps to reinforce this function.
- The cell wall is the most prominent part of the plant’s cell structure. It is made up of cellulose, hemicellulose and pectin.
- The cell wall is present exclusively in plant cells. It protects the plasma membrane and other cellular components. The cell wall is also the outermost layer of plant cells.
- It is a rigid and stiff structure surrounding the cell membrane.
- It provides shape and support to the cells and protects them from mechanical shocks and injuries.
- The cytoplasm is a thick, clear, jelly-like substance present inside the cell membrane.
- Most of the chemical reactions within a cell take place in this cytoplasm.
- The cell organelles such as endoplasmic reticulum, vacuoles, mitochondria, ribosomes, are suspended in this cytoplasm.
- The nucleus contains the hereditary material of the cell, the DNA.
- It sends signals to the cells to grow, mature, divide and die.
- The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell.
- The nucleus protects the DNA and is an integral component of a plant’s cell structure.
The cell structure comprises individual components with specific functions essential to carry out life’s processes. These components include- cell wall, cell membrane, cytoplasm, nucleus, and cell organelles. Read on to explore more insights on cell structure and function.
HOW CELLS WORK
In order to accomplish them, they must have:
- A cell membrane that separates the inside of the cell from the outside. By concentrating the chemical reactions of life inside a small area within a membrane, cells allow the reactions of life to proceed much faster than they otherwise would.
- Genetic material which is capable of passing on traits to the cell’s offspring. In order to reproduce, organisms must ensure that their offspring have all the information that they need to be able to carry out all the functions of life.All modern cells accomplish this using DNA, whose base-pairing properties allow cells to make accurate copies of a cell’s “blueprints” and “operating system.” Some scientists think that the first cells might have used RNA instead.
- Proteins that perform a wide variety of structural, metabolic, and reproductive functions.
- There are countless different functions that cells must perform to obtain energy and reproduce.
- Depending on the cell, examples of these functions can include photosynthesis, breaking down sugar, locomotion, copying its own DNA, allowing certain substances to pass through the cell membrane while keeping others out, etc.
- Proteins are made of amino acids, which are like the “Legos” of biochemistry. Amino acids come in different sizes, different shapes, and with different properties such as polarity, ionic charge, and hydrophobicity.
- By putting amino acids together based on the instructions in their genetic material, cells can create biochemical machinery to perform almost any function.
- Some scientists think that the first cells might have used RNA to accomplish some vital functions, and then moved to much more versatile amino acids to do the job as the result of a mutation.
The different cell types we will discuss below have different ways of accomplishing these functions.
EXAMPLE OF CELLS
Archaebacteria
As mentioned above, archaebacteria are a very old form of prokaryotic cells. Biologists actually put them in their own “domain” of life, separate from other bacteria.
Key ways in which archaebacteria differ from other bacteria include:
- Their cell membranes, which are made of a type of lipid not found in either bacteria or eukaryotic cell membranes.
- Their DNA replication enzymes, which are more similar to those of eukaryotes than those of bacteria, suggesting that bacteria and archae are only distantly related, and archaebacteria may actually be more closely related to us than to modern bacteria.
- Some archaebacteria have the ability to produce methane, which is a metabolic process not found in any bacteria or any eukaryotes.
Archaebacteria’s unique chemical attributes allow them to live in extreme environments, such as superheated water, extremely salty water, and some environments which are toxic to all other life forms.
Scientists became very excited in recent years at the discovery of Lokiarchaeota – a type of archaebacteria which shares many genes with eukaryotes that had never before been found in prokaryotic cells!
It is now thought that Lokiarchaeota may be our closest living relative in the prokaryotic world.
Bacteria
You are most likely familiar with the type of bacteria that can make you sick. Indeed, common pathogens like Streptococcus and Staphylococcus are prokaryotic bacterial cells.
But there are also many types of helpful bacteria – including those that break down dead waste to turn useless materials into fertile soil, and bacteria that live in our own digestive tract and help us digest food.
Bacterial cells can commonly be found living in symbiotic relationships with multicellular organisms like ourselves, in the soil, and anywhere else that’s not too extreme for them to live!
ANIMAL CELL
For this exercise, let’s look at a type of animal cell that is of great importance to you: your own liver cell.
Like all animal cells, it has mitochondria which perform cellular respiration, turning oxygen and sugar into large amounts of ATP to power cellular functions.
It also has the same organelles as most animal cells: a nucleus, endoplasmic reticulum, Golgi apparatus, etc..
But as part of a multicellular organism, your liver cell also expresses unique genes, which give it unique traits and abilities.
Liver cells in particular contain enzymes that break down many toxins, which is what allows the liver to purify your blood and break down dangerous bodily waste.
The liver cell is an excellent example of how multicellular organisms can be more efficient by having different cell types work together.
Your body could not survive without liver cells to break down certain toxins and waste products, but the liver cell itself could not survive without nerve and muscle cells that help you find food, and a digestive tract to break down that food into easily digestible sugars.
And all of these cell types contain the information to make all the other cell types! It’s simply a matter of which genes are switched “on” or “off” during development.
PLANT CELLS
Plant cells are eukaryotic cells that are part of multicellular, photosynthetic organisms.
Plants cells have chloroplast organelles, which contain pigments that absorb photons of light and harvest the energy of those photons.
Chloroplasts have the remarkable ability to turn light energy into cellular fuel, and use this energy to take carbon dioxide from the air and turn it into sugars that can be used by living things as fuel or building material.
In addition to having chloroplasts, plant cells also typically have a cell wall made of a rigid sugars, to enable plant tissues to maintain their upright structures such as leaves, stems, and tree trunks.
Plant cells also have the usual eukaryotic organelles including a nucleus, endoplasmic reticulum, and Golgi apparatus.
Frequently Asked Questions
1. What is a Cell?
2. State the characteristics of cells.
- Cells provide the necessary structural support for an organism.
- The genetic information necessary for reproduction is present within the nucleus.
- Structurally, the cell has cell organelles which are suspended in the cytoplasm.
- Mitochondria is the organelle responsible for fulfilling the cell’s energy requirements.
- Lysosomes digest metabolic wastes and foreign particles in the cell.
- Endoplasmic reticulum synthesises selective molecules and processes them, eventually directing them to their appropriate locations.
3. Highlight the cell structure and its components.
- Cell membrane
- Cell wall
- Cell organelles
- Nucleolus
- Nuclear membrane
- Endoplasmic reticulum
- Golgi Bodies
- Ribosome
- Mitochondria
- Lysosomes
- Chloroplast
- Vacuoles
4. State the types of cells.
Cells are primarily classified into two types, namely
- Prokaryotic cells
- Eukaryotic cells
5. Elaborate Cell Theory.
Cell Theory was proposed by Matthias Schleiden, Theodor Schwann, and Rudolf Virchow, who were German scientists. The cell theory states that:
- All living species on Earth are composed of cells.
- A cell is the basic unit of life.
- All cells arise from pre-existing cells.
6. What is the function of mitochondria in the cells?
7. What are the functions of the cell?
The essential functions of the cell include:
- The cell provides support and structure to the body.
- Facilitates growth by mitosis
- Helps in reproduction
- Provides energy and allows the transport of substances.
8. What is the function of Golgi bodies?
9. Who discovered cell and how?
10. Name the cell organelle that contains hydrolytic enzymes capable of breaking down organic matter.
11. Which cellular structure regulates the entry and exit of molecules to and from the cell?
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Reviewed by CURIOUS FACT
on
April 11, 2021
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