You all have heard a lot about bacteria. Do you think that bacteria also know how to swim, walk, hangout and chill with their friends?
Yes, is it interesting? Now you also must be wondering how is it possible? Yes, it is possible because they have the cell appendages like cilia and flagella, helping them to move, swim or adhere to a surface. Fimbriae and pili even help bacteria to make sexual contact with each other by forming bridge like connections.
You know, being so small in size, their life expectancy becomes very low but thanks to the protective covering they have. Yes, the cell wall and cell membrane. They make a strong shield around them to fight off all the enemies.
Now let's know some more interesting things like this, which enable them to survive better in their habitats.
Table of Contents
It is the outer covering which protects the cytoplasm. A bacterial cell is protected by three outer coverings adhered together as a single unit. They are as follows:
Glycocalyx is an outermost layer of the bacterial cells. It normally protects the cell and helps in adhesion also. It normally differs in thickness and composition. It can have the following compositions:
The glycocalyx is in the form of loose gelatinous sheath here. It normally protects the cells from leakage of materials like water and nutrients.
The glycocalyx is thick and tough here. It is made up of polysaccharides and proteins. It protects the cell against desiccation, antibiotics and viral attack. Gelatinous glycocalyx glues together the bacterial cells to form colonies. It provides virulence also.
It is the middle layer of the cell envelope of a prokaryote which is sandwiched between the glycocalyx and cell membrane. Cell wall in bacteria is made up of peptidoglycan which contains polymers of modified sugars (such as N-acetylglucosamine and N-acetyl muramic acid) cross linked with some short peptides. Teichoic acid is also a component of the cell wall in some bacteria. Mycoplasma lacks a cell wall. Cell wall composition varies in gram negative and gram positive bacteria. Cell wall maintains shape and provides support and strength to the majority of the prokaryotic cells such as bacteria. It prevents the bacteria from bursting.
Cell membrane is the innermost layer of the cell envelope. The membranes are quasi (partly) fluid in nature. It is selectively permeable to some molecules present on either side of it. Most of the bacterial cell membrane lacks sterols like-cholesterol. In some bacteria, pentacyclic molecules can be present in cell membranes termed hopanoids. They help to stabilise the molecular structure of membranes. It is made up of lipoprotein and has membrane proteins (integral and peripheral) incorporated for movement of molecules. The ‘fluid mosaic model’ is used to explain the exact structure of the cell membrane. Cell membrane controls the movement of molecules into and out of the cell. In prokaryotes, the cell membrane acts as a respiratory membrane since it contains respiratory enzymes. It infolds to form specialised structures called mesosomes.
Cell membrane has following invaginations in bacteria:
Mesosomes are formed by the infoldings of the plasma membrane. They bear respiratory enzymes. They are formed of vesicles, lamellae and tubules.
They are of two types as follows:
They are seen associated with the chromosomes or cell wall of dividing cells. It is commonly involved in the cell wall formation, chromosome replication, and distribution of chromosomes to daughter cells.
They are not seen associated with the nucleoid. It possesses respiratory enzymes.
The main functions of mesosomes are as follows:
These are the membranous extensions containing pigment molecules such as bacteriochlorophyll. These are abundantly found in cyanobacteria or blue green algae. Their main role is photosynthesis. They may be of different shapes like lamellar, tubular or vesicular in shape.
Q1. Which of these bacteria lack a cell wall?
Solution: Cell wall maintains the shape and provides support and strength to the majority of the prokaryotic cells such as bacteria. It prevents the bacteria from bursting. Mycoplasma lacks a cell wall. Hence option c is correct.
Q2. Mesosome is derived from ____________.
Solution: Mesosomes are formed by the infoldings of the plasma membrane. They bear respiratory enzymes. They are formed of vesicles, lamellae and tubules. Hence option d is correct.
Q3. Which of these bacteria have chromatophores?
Solution: Chromatophores are the membranous extensions containing pigment molecules such as bacteriochlorophyll. These are abundantly found in cyanobacteria or blue green algae. Their main role is photosynthesis. Hence option d is correct.
Q4. The cell wall of Eubacteria is made up of _________________.
Solution: Cell wall in bacteria is made up of peptidoglycan which contains polymers of modified sugars (such as N-acetylglucosamine and N-acetyl muramic acid) cross linked with some short peptides. Hence the correct option is a.
Q5. What is the main role of the cell wall in prokaryotic cells?
Solution: In prokaryotic cells, the cell wall protects the cells against changes in osmotic pressure and allows it to maintain its shape.
Question1. Name the type of bacteria whose chromatophores are more complex and extensive?
Answer: Photosynthetic bacteria have more complex and extensive chromatophores because of their internal membrane systems.
Question2. Do you think the composition of cell membranes is the same in prokaryotes and eukaryotes?
Answer: Both prokaryotic and eukaryotic cells have a plasma membrane, It is made up of lipoproteins and has membrane proteins (integral and peripheral) incorporated for movement of molecules. The same ‘fluid mosaic model’ is used to explain the structure of cell membranes in both prokaryotes and eukaryotes.
Question3. Bacteria cause diseases, then why can't we just wipe them out from the Earth?
Answer: Bacteria are believed to have existed on Earth for over 3 thousand million years whereas Early man emerged 250 thousand years ago only. They perform various functions. They are involved in nutrient recycling and a part of the detritus food chain. They help in fermentation also.
Question4. Are mesosomes similar to mitochondria?
Answer: Mitochondria are the powerhouse of the cell. They are present in eukaryotic cells. Mesosomes are the invaginations of the plasma membrane present in prokaryotic cells. They are also involved in cellular respiration. They can be considered analogous to cristae in the mitochondria. Cristae are finger-like projections and help mainly the eukaryotic cells to undergo cellular respiration.
|The Living World||Biological Classification||Plant Kingdom|
|Animal Kingdom||Morphology of Flowering Plants||Anatomy of Flowering Plants|
|Structural Organization in Animals||Cells: The Unit of Life||Biomolecules|
|Cell Cycle and Division||Transport in Plants||Mineral Nutrition|
|Photosynthesis in Higher Plants||Respiration in Plants||Plant Growth and Development|
|Digestion and Absorption||Breathing and Exchange of Gases||Body Fluids and Circulation|
|Excretory Products and their Elimination||Locomotion and Movement||Neural Control and Coordination|
|Chemical Coordination and Integration|
Important Biology Concepts Pages
Aerobic and Anaerobic Respiration
NCERT Solutions Important Biology Concepts
Sexual Reproduction in Flowering Plants
NEET Important Pages
NEET 2022 Eligibility Criteria
CUCET Important Pages
CUCET 2022 Examination Details
CUCET 2022 Eligibility Criteria