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Bacteria - Definition, Structure, Diagram, Types & Classification

Bacteria - Definition, Structure, Diagram, Types & Classification

Edited By Irshad Anwar | Updated on Jul 02, 2025 05:11 PM IST

Bacteria Definition

Bacteria are unicellular organisms belonging to the prokaryotic group where the organisms lack a few organelles and a true nucleus.

The study of bacterial cells is known as bacteriology. Bacteriology is the subfield of microbiology which involves identification, classification and characterization of various bacterial cells. In our daily life, Bacteria is useful, for example during the formation of curd at that time lactobacillus bacteria forms curd from milk. Bacteria are an important topic in Biology and they carry a weightage of 5-6% in NEET and 4-5% in CBSE and other Paramedical Exams.

This Story also Contains
  1. Bacteria Definition
  2. Bacteria Diagram
  3. Ultrastructure of a Bacteria Cell
  4. Classification of Bacteria
  5. Bacteria Functions
  6. Examples of Bacteria
  7. Surviving conditions of Bacteria
Bacteria - Definition, Structure, Diagram, Types & Classification
Bacteria - Definition, Structure, Diagram, Types & Classification

Bacteria Diagram

The structure of a typical bacterial cell with its various parts is depicted in the bacteria diagram below. The cell wall, cytoplasm, plasmid, and flagella are clearly marked in the diagram.

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Ultrastructure of a Bacteria Cell

Generally, all bacteria have cell walls and cell membranes. The cell membrane is made up of a lipid bilayer which provides fluidity to the cell membrane, And the cell wall is made up of peptidoglycan which provides a rigid structure to the cell.

The cell wall is the thick structure then the cell membrane. The cell membrane covers the cytoplasmic region of the bacterial cell, the cytoplasmic region is reached with DNA, protein, ribosome, vacuoles and storage body.

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Classification of Bacteria

According to Gram staining, Bacteria are divided into Gram-positive Bacteria and Gram-negative bacteria. Gram staining differentiates a bacterium in Gram-positive or Gram-negative nature based on the cell wall composition of that particular bacteria.

Classification of bacteria based on Shape

Type of ClassificationExamples

Bacillus (Rod-shaped)

Escherichia coli (E. coli)

Spirilla or spirochete (Spiral)

Spirillum volutans

Coccus (Sphere)

Streptococcus pneumoniae
Vibrio (Comma-shaped)Vibrio cholerae

Based on gram staining:

  • Gram-positive bacteria

  • Gram-negative bacteria.

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Gram-positive Bacteria characteristics

  • Gram-positive bacteria do not have an outer membrane, while in Gram-negative bacteria outer membrane is present.

  • Gram-positive bacteria appear blue or purple under the microscope.

  • The cell wall is the structure surrounding the cell’s membrane.

  • In Gram-positive bacteria cell walls are made of multiple layers of molecules, less lipid and protein.

  • The cell wall protects the bacteria from killing or any type of damage

  • In Gram-positive bacteria, the peptidoglycan is 20 to 80 nm (nanometer) thick

Gram-negative Bacteria characteristics

  • Gram-negative bacteria are made up of a thinner layer of peptidoglycan.

  • They also have a lipid membrane at the outer region and protect the cell from the surrounding environment.

  • Whereas this peptidoglycan layer is only 2 to 3 nm thick in Gram-negative bacteria.

  • Due to this lipid membrane layer, they are more resistant to antibiotics and other drugs. Although Gram-negative bacteria are more challenging to treat with drugs or chemical compounds.

Bacteria Functions

Bacteria are useful in the following sectors for daily human uses:

  • Fermentative nature

  • Acid production

  • Antibiotics production

  • Metabolites production

  • Bacteria are used as probiotics

  • Helps in curd formation

  • It able to degrade complex nutrients

  • It produces vitamins, amino acid

Examples of Bacteria

Following are some examples of bacteria which are commonly found:

  • Escherichia coli

  • Clostridium botulinum

  • Lactobacillus species

  • Actinobacteria

  • Bacillus stearothermophilus

  • Mycobacterium tuberculosis

  • Salmonella typhi

Surviving conditions of Bacteria

A bacteria which can live in extreme conditions from the human point of view. Extreme conditions include High temperature, Low temperature, High pH, Low pH, High pressure, and High salt concentration. Examples of extremophiles are shown in the below table.

Extreme conditions

Bacteria Name

Examples

High temperature

  • Thermophile

  • Thermus aquatics

High pH condition

  • Alkaliphiles

  • Bacillus, Pseudomonas.

Low temperature

  • Psychrophiles

  • Psychroflexus, Psychrobacter

Low pH

  • Acidophiles

  • Acidithiobacillus ferrooxidans

High pressure

  • Piezophiles

  • Halomonas Salaria

High salt concentration

  • Halophiles

  • Salinibacter

Facts about Bacteria

Based on their effect on humans, bacteria are categorized into beneficial bacteria and harmful bacteria.

  • Beneficial bacteria live on the body surface and it is also known as human microbial flora.

  • Pathogenic bacteria can cause diseases in the human body such as tuberculosis and Syphilis disease caused by mycobacterium tuberculosis and Treponema pallidum respectively.

  • Based on the presence or absence of flagella, Bacteria can be divided into motile bacteria and non-motile bacteria.

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Frequently Asked Questions (FAQs)

1. What are the examples of extremophiles?

Thermus aquaticus, Bacillus, Pseudomonas, Psychroflexus, Psychrobacter, Acidithiobacillus ferrooxidans, Halomonas salaria, Salinibacter are the examples of extremophiles.

2. What is the use of bacteria?

For fermentative process, Use in acid production, For antibiotics production, For metabolites production, Probiotics formation, use in curd formation, Use in production of vitamins, amino acid.

3. What is the meaning of fascinating bacteria?

Fascinating bacteria means bacteria possessed unique characteristics, which are not shown by other normal bacteria.

4. Who is the father of biology?

Aristotle is the father of biology.

5. What do you mean by bacteria?

Bacteria are small in size and single cell organisms which are not seen by the naked eye.

6. What is the role of bacteria in the nitrogen cycle?
Bacteria play crucial roles in the nitrogen cycle. Nitrogen-fixing bacteria convert atmospheric nitrogen into ammonia, which plants can use. Nitrifying bacteria oxidize ammonia to nitrites and then nitrates. Denitrifying bacteria convert nitrates back to atmospheric nitrogen. Some bacteria perform anaerobic ammonium oxidation (anammox). These processes are essential for soil fertility, plant growth, and maintaining the balance of nitrogen in ecosystems.
7. How do bacteria contribute to food production and preservation?
Bacteria contribute to food production and preservation through fermentation processes. They produce lactic acid in foods like yogurt and cheese, enhancing flavor and extending shelf life. Some bacteria produce antimicrobial compounds that inhibit the growth of harmful microorganisms. Understanding these processes has led to the development of probiotics and improved food preservation techniques.
8. How do symbiotic relationships between bacteria and other organisms work?
Symbiotic relationships between bacteria and other organisms involve close, often long-term interactions that can be mutualistic (both benefit), commensal (one benefits, the other is unaffected), or parasitic (one benefits at the expense of the other). Examples include nitrogen-fixing bacteria in plant root nodules (mutualism), gut bacteria in animals (often mutualistic or commensal), and pathogenic bacteria causing diseases (parasitic). These relationships play crucial roles in ecosystem function and organismal health.
9. How do bacteria contribute to the carbon cycle?
Bacteria contribute significantly to the carbon cycle through various processes. As decomposers, they break down organic matter, releasing carbon dioxide. Some bacteria fix carbon dioxide through photosynthesis or chemosynthesis. Methanogens produce methane, a potent greenhouse gas. In oceans, bacteria play a role in the biological carbon pump by decomposing sinking organic matter. Understanding these bacterial roles is crucial for climate change research and carbon cycle modeling.
10. How do bacteria interact with the human immune system?
Bacteria interact with the human immune system in complex ways. Pathogenic bacteria trigger immune responses through various components like lipopolysaccharides or flagellin. The immune system recognizes these pathogen-associated molecular patterns (PAMPs) and initiates inflammatory responses. Some bacteria evade immune detection or suppress immune responses. Commensal bacteria, part of the normal microbiome, help train and modulate the immune system. Understanding these interactions is crucial for developing vaccines, treatments for autoimmune diseases, and managing overall health.
11. What are bacteria and how do they differ from other microorganisms?
Bacteria are single-celled microorganisms that lack a true nucleus and other membrane-bound organelles. They differ from other microorganisms like fungi, protists, and viruses in their cellular structure, size, and genetic material organization. Bacteria have a cell wall, circular DNA, and reproduce by binary fission.
12. What are the main differences between prokaryotic and eukaryotic cells?
The main differences between prokaryotic (bacterial) and eukaryotic cells include: prokaryotes lack a membrane-bound nucleus and other organelles, have circular DNA, and are generally smaller. Eukaryotes have a true nucleus, membrane-bound organelles, linear DNA organized into chromosomes, and are typically larger. Prokaryotes have a cell wall containing peptidoglycan, while eukaryotic cell walls (when present) are made of different materials. These differences affect cellular processes, reproduction methods, and overall complexity.
13. What are the differences between obligate and facultative bacteria?
Obligate bacteria have strict growth requirements and can only survive under specific conditions. For example, obligate aerobes require oxygen, while obligate anaerobes cannot tolerate oxygen. Facultative bacteria, on the other hand, are more adaptable and can survive in various environments. Facultative anaerobes, for instance, can use oxygen when it's available but can also survive without it. This distinction is important for understanding bacterial ecology and designing cultivation methods.
14. What is the significance of bacterial plasmids?
Bacterial plasmids are small, circular DNA molecules separate from the main chromosome. They are significant because they often carry genes that provide advantages to the bacteria, such as antibiotic resistance or the ability to degrade specific compounds. Plasmids can be transferred between bacteria, facilitating rapid adaptation and evolution within bacterial populations.
15. How do bacterial toxins affect host organisms?
Bacterial toxins affect host organisms in various ways. Endotoxins, part of the cell wall of gram-negative bacteria, can trigger strong immune responses. Exotoxins, secreted by bacteria, can have specific effects on host cells, such as disrupting cell membranes, inhibiting protein synthesis, or interfering with nerve function. Some toxins act locally, while others can spread throughout the body. Understanding toxin mechanisms is crucial for developing treatments for bacterial infections and toxin-mediated diseases.
16. What is the difference between gram-positive and gram-negative bacteria?
Gram-positive and gram-negative bacteria differ in their cell wall structure. Gram-positive bacteria have a thick peptidoglycan layer that retains crystal violet stain, appearing purple under a microscope. Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane, which doesn't retain the stain and appears pink. This difference affects their susceptibility to certain antibiotics and environmental stresses.
17. What are the main methods used to classify bacteria?
The main methods used to classify bacteria include morphological characteristics (shape, size, arrangement), biochemical tests (metabolic capabilities), genetic analysis (16S rRNA sequencing), and more recently, whole-genome sequencing. These methods help in identifying and grouping bacteria based on their evolutionary relationships and functional similarities, which is essential for understanding bacterial diversity and ecology.
18. What are the main differences between archaebacteria and eubacteria?
Archaebacteria and eubacteria, both prokaryotes, differ in several key aspects. Archaebacteria have unique cell membrane lipids, different cell wall compositions, and distinct RNA polymerases. They often inhabit extreme environments and have metabolic pathways more similar to eukaryotes. Eubacteria, or "true bacteria," are more diverse and widespread, with cell walls containing peptidoglycan.
19. What are the main shapes of bacteria and how do these shapes relate to their function?
The main shapes of bacteria are cocci (spherical), bacilli (rod-shaped), and spirilla (spiral). These shapes relate to their function by affecting surface area-to-volume ratio, motility, and ability to attach to surfaces. For example, cocci can cluster together for protection, while bacilli are often more motile and can move through environments more easily.
20. How do bacteria obtain nutrients and energy?
Bacteria obtain nutrients and energy through various methods, including photosynthesis (photoautotrophs), chemosynthesis (chemoautotrophs), or by consuming organic matter (heterotrophs). Some bacteria can switch between these methods depending on environmental conditions, showcasing their metabolic diversity and adaptability.
21. How do bacteria contribute to nutrient cycling in ecosystems?
Bacteria play crucial roles in nutrient cycling by decomposing organic matter, fixing nitrogen, and participating in other biogeochemical processes. For example, decomposer bacteria break down dead organisms and waste, releasing nutrients back into the ecosystem. Nitrogen-fixing bacteria convert atmospheric nitrogen into forms that plants can use, essential for soil fertility.
22. What is the role of bacteria in the human microbiome?
Bacteria in the human microbiome play essential roles in digestion, immune system function, and protection against pathogens. They help break down food, produce vitamins, train the immune system, and compete with harmful bacteria. The balance of different bacterial species in our microbiome is crucial for overall health.
23. How do bacteria impact global climate?
Bacteria impact global climate through their roles in carbon and nitrogen cycles. Some bacteria release methane, a potent greenhouse gas, while others help sequester carbon in soils and oceans. Nitrogen-fixing bacteria affect plant growth, indirectly influencing carbon dioxide uptake. Understanding these bacterial processes is crucial for climate change research and mitigation strategies.
24. What is the significance of bacterial flagella?
Bacterial flagella are significant for several reasons. They provide motility, allowing bacteria to move towards nutrients or away from harmful substances. This movement is crucial for colonizing new environments, forming biofilms, and interacting with host organisms. Flagella also play a role in bacterial pathogenesis, as they can help pathogens adhere to host cells. The complex structure and assembly of flagella provide insights into bacterial evolution and have inspired biomimetic technologies.
25. What are the main mechanisms of bacterial pathogenesis?
The main mechanisms of bacterial pathogenesis include adhesion to host cells, invasion of tissues, toxin production, and evasion of host immune responses. Adhesion involves specific interactions between bacterial surface proteins and host cell receptors. Invasion may involve secretion systems that inject proteins into host cells. Toxins can damage host tissues or disrupt cellular functions. Immune evasion strategies include capsule formation, antigenic variation, and interfering with immune signaling pathways.
26. How do bacteria adapt to extreme environments?
Bacteria adapt to extreme environments through various strategies: producing specialized enzymes that function under extreme conditions, altering membrane composition for temperature or pH tolerance, developing protective structures like spores or capsules, and evolving unique metabolic pathways. Some extremophiles have DNA repair mechanisms to cope with high radiation or use solutes to balance osmotic pressure in high-salt environments. These adaptations allow bacteria to thrive in conditions that would be lethal to most other organisms.
27. What are extremophiles and why are they significant in biology?
Extremophiles are bacteria that thrive in extreme environments such as high temperatures, high pressure, or high salinity. They are significant in biology because they expand our understanding of life's limits, provide insights into early Earth conditions, and have potential applications in biotechnology and astrobiology.
28. What are endospores and why are they important?
Endospores are dormant, highly resistant structures produced by some bacteria in response to unfavorable conditions. They are important because they allow bacteria to survive extreme environments, including heat, radiation, and chemical stress. This ability contributes to the persistence of certain bacterial species and can pose challenges in sterilization processes.
29. How do bacteria reproduce and why is this process significant?
Bacteria reproduce through binary fission, a form of asexual reproduction where one cell divides into two identical daughter cells. This process is significant because it allows bacteria to multiply rapidly under favorable conditions, contributing to their adaptability and potential for both beneficial and harmful effects in various environments.
30. How do bacteria communicate with each other?
Bacteria communicate through a process called quorum sensing, where they produce and detect chemical signals called autoinducers. This allows bacteria to coordinate behaviors based on population density, such as forming biofilms, producing virulence factors, or emitting bioluminescence. This communication is crucial for bacterial survival and adaptation in various environments.
31. How do bacteria form biofilms and why are these structures important?
Bacteria form biofilms by adhering to surfaces and secreting a matrix of extracellular polymeric substances. These structures are important because they provide protection from environmental stresses, increase antibiotic resistance, and allow for complex community interactions. Biofilms play roles in both beneficial processes (like wastewater treatment) and harmful ones (like chronic infections).
32. How do bacteria develop antibiotic resistance?
Bacteria develop antibiotic resistance through genetic mutations or by acquiring resistance genes from other bacteria. This can occur through natural selection when exposed to antibiotics, where resistant individuals survive and reproduce. Overuse and misuse of antibiotics accelerate this process, leading to the emergence of "superbugs" that are difficult to treat.
33. What is horizontal gene transfer in bacteria and why is it significant?
Horizontal gene transfer is the process by which bacteria can exchange genetic material with other bacteria, even from different species. This is significant because it allows for rapid adaptation and evolution, including the spread of antibiotic resistance genes. It challenges the traditional view of evolution and has implications for bacterial classification and medical treatments.
34. How do bacteria adapt to different oxygen environments?
Bacteria adapt to different oxygen environments through various metabolic strategies. Aerobic bacteria require oxygen for respiration, while anaerobic bacteria thrive without it. Facultative anaerobes can switch between aerobic and anaerobic metabolism depending on oxygen availability. Some bacteria, like microaerophiles, prefer environments with lower oxygen levels than atmospheric conditions.
35. What are bacteriophages and how do they interact with bacteria?
Bacteriophages, or phages, are viruses that infect bacteria. They interact with bacteria by attaching to specific receptors, injecting their genetic material, and either integrating into the bacterial genome (lysogenic cycle) or replicating and causing cell lysis (lytic cycle). Phages play roles in bacterial evolution, population control, and have potential applications in treating bacterial infections (phage therapy).
36. How do bacteria interact with plants, both beneficially and harmfully?
Bacteria interact with plants in various ways. Beneficial interactions include nitrogen fixation by rhizobia in legume root nodules, promotion of plant growth by producing hormones or solubilizing nutrients, and protection against pathogens. Harmful interactions involve plant pathogens that cause diseases, affecting crop yields and plant health. Understanding these interactions is crucial for agriculture and ecosystem management.
37. What are the main differences between bacterial and eukaryotic gene expression?
The main differences between bacterial and eukaryotic gene expression lie in their organization and regulation. Bacterial genes are often arranged in operons (clusters of related genes), allowing for coordinated expression. They lack introns and undergo coupled transcription and translation. Eukaryotic genes have more complex regulation, including enhancers and silencers, undergo RNA processing (including intron splicing), and have separate transcription and translation processes occurring in different cellular compartments.
38. What is the role of bacteria in bioremediation?
Bacteria play a crucial role in bioremediation, the process of using microorganisms to clean up polluted environments. Certain bacteria can break down or transform pollutants like oil spills, heavy metals, and industrial chemicals into less harmful substances. This ability makes them valuable tools in environmental cleanup efforts. Understanding and harnessing these bacterial capabilities is an active area of research in environmental science and biotechnology.
39. How do bacteria contribute to the production of antibiotics?
Bacteria contribute to antibiotic production in two main ways. First, many antibiotics are naturally produced by certain bacteria (like Streptomyces) as secondary metabolites, often to compete with other microorganisms in their environment. Second, bacteria are used in the industrial production of antibiotics through fermentation processes, where genetically modified bacteria are engineered to produce specific antibiotics more efficiently. Understanding these processes has been crucial in developing new antibiotics and combating antibiotic resistance.
40. What is quorum sensing and how does it affect bacterial behavior?
Quorum sensing is a communication system used by bacteria to coordinate their behavior based on population density. Bacteria produce and detect small signaling molecules called autoinducers. When the concentration of these molecules reaches a certain threshold, it triggers changes in gene expression, leading to coordinated behaviors such as biofilm formation, virulence factor production, or bioluminescence. This system allows bacteria to act as a collective, enhancing their survival and adaptability in various environments.
41. How do bacteria impact soil health and agriculture?
Bacteria play crucial roles in soil health and agriculture. They decompose organic matter, releasing nutrients for plants, and some fix atmospheric nitrogen into forms usable by plants. Certain bacteria promote plant growth by producing hormones or suppressing plant pathogens. They also contribute to soil structure and water retention. In agriculture, understanding and managing soil bacterial communities is essential for sustainable farming practices, including reducing chemical fertilizer use and improving crop yields.
42. How do bacteria respond to environmental stresses?
Bacteria respond to environmental stresses through various mechanisms. These include producing stress proteins (like heat shock proteins), altering gene expression, forming biofilms, entering dormant states (like spore formation), and undergoing genetic mutations. Some bacteria can also produce pigments or change their cell membrane composition to protect against UV radiation or osmotic stress. These responses allow bacteria to survive and adapt to changing conditions.
43. How do bacteria develop resistance to antibiotics?
Bacteria develop antibiotic resistance through several mechanisms: genetic mutations that alter the antibiotic target or increase efflux pump activity, acquisition of resistance genes through horizontal gene transfer, production of enzymes that degrade or modify antibiotics, and changes in cell permeability. Natural selection in the presence of antibiotics favors resistant bacteria. Overuse and misuse of antibiotics accelerate this process, leading to the emergence of multi-drug resistant strains.
44. What is the role of bacteria in food spoilage and how can it be prevented?
Bacteria play a major role in food spoilage by breaking down food components, producing off-flavors, and changing texture. They can also produce toxins that make food unsafe. Prevention methods include proper storage (refrigeration, freezing), preservatives, packaging techniques (vacuum sealing, modified atmosphere packaging), and processing methods (pasteurization, canning). Understanding bacterial growth conditions and using hurdle technology (combining multiple preservation methods) are key strategies in food preservation.
45. How do bacteria contribute to the production of biofuels?
Bacteria contribute to biofuel production in several ways. Some bacteria can ferment plant biomass into ethanol

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Question : Comprehension:
 Read the given passage and answer the questions that follow.

Key factors influencing subway air pollution will include station depth, date of construction, type of ventilation (natural/air conditioning), types of brakes (electromagnetic or conventional brake pads) and wheels (rubber or steel) used on the trains, train frequency and more recently the presence or absence of platform screen-door systems. In particular, much subway particulate matter is sourced from moving train parts such as wheels and brake pads, as well as from the steel rails and power-supply materials, making the particles dominantly iron-containing. To date, there is no clear epidemiological indication of abnormal health effects on underground workers and commuters. New York subway workers have been exposed to such air without significant observed impacts on their health, and no increased risk of lung cancer was found among subway train drivers in the Stockholm subway system. But a note of caution is struck by the observations of scholars who found that employees working on the platforms of Stockholm underground, where PM concentrations were greatest, tended to have higher levels of risk markers for cardiovascular disease than ticket sellers and train drivers. The dominantly ferrous particles are mixed with particles from a range of other sources, including rock ballast from the track, biological aerosols such as bacteria and viruses, and air from the outdoors, and driven through the tunnel system on turbulent air currents generated by the trains themselves and ventilation systems.

Question

What is the tone of the speaker?

Option 1: Serious

Option 2: Pessimistic

Option 3: Joyful

Option 4: Informal

Correct Answer: Serious


Solution : The correct option is the first option.

Explanation:
The tone of the speaker is serious as it discusses various factors influencing subway air pollution, particularly focusing on the sources of particulate matter, health risks for subway workers, and the mix of particles within the subway system.

The language used is factual and analytical, examining the potential health impacts without conclusive evidence and citing observations and studies. There's a sense of concern and caution regarding the potential health risks associated with subway air pollution, which contributes to an overall serious tone in the passage.

Therefore, the correct answer is serious.

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Team Careers360 26 January,2024

Question : Comprehension:

Read the following passage and answer the questions.

All foodstuffs change. Green fruits become ripe and eggs go bad or rotten. It is the enzymes naturally present in each food which bring about the complex chemical changes that lead first to ripening and then to rotting.

How does one control the activity of enzymes, bacteria, yeasts and moulds in food? All of them require air, moisture and a certain temperature, usually somewhere near the body temperature, to be active. Depriving them of one or more of these will suppress them. All microorganisms can be killed by heat sterilisation. This simply means heating the food to high enough temperatures by boiling, deep or shallow frying, roasting, baking and, for milk particularly, pasteurisation. After such sterilisation, if the food is sealed in airtight containers, it can be kept for a long time. A certain water content in food is necessary for microorganisms to be active. Drying in the sun is a simple way of bringing down the moisture level so low that the enzymes and microorganisms cannot flourish.

Some chemicals can suppress undesirable activity. The addition of salt, vinegar, spices and oil or sugar syrup are other ways of preventing foods from going bad. If heating kills, freezing inactivates the enzymes and microorganisms. This is what happens in a refrigerator, in which fruits, vegetables and milk can be kept for fairly long periods. For meat and fish, even colder temperatures, below freezing point, are necessary for preservation. All foods which are kept cold in this way, once taken out and returned to room temperature, are again subject to spoilage and change.

Question:
What action does freezing have on the enzymes?

Option 1: It activates them

Option 2: It kills them

Option 3: It preserves them

Option 4: It inactivates them

Correct Answer: It inactivates them


Solution : The fourth option is the correct choice.

The passage in the third paragraph mentions that freezing inactivates the enzymes and microorganisms. This helps to preserve food.

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Team Careers360 25 January,2024

Question : Comprehension:
Read the given passage and answer the questions that follow.

Key factors influencing subway air pollution will include station depth, date of construction, type of ventilation (natural or air conditioning), types of brakes (electromagnetic or conventional brake pads) and wheels (rubber or steel) used on the trains, train frequency, and more recently, the presence or absence of platform screen-door systems.

In particular, much subway particulate matter is sourced from moving train parts such as wheels and brake pads, as well as from the steel rails and power supply materials, making the particles predominantly iron-containing.

To date, there is no clear epidemiological indication of abnormal health effects on underground workers and commuters. New York subway workers have been exposed to such air without significant observed impacts on their health, and no increased risk of lung cancer was found among subway train drivers in the Stockholm subway system.

But a note of caution is struck by the observations of scholars who found that employees working on the platforms of Stockholm underground, where PM concentrations were greatest, tended to have higher levels of risk markers for cardiovascular disease than ticket sellers and train drivers.

The dominantly ferrous particles are mixed with particles from a range of other sources, including rock ballast from the track, biological aerosols such as bacteria and viruses, and air from the outdoors, and driven through the tunnel system on turbulent air currents generated by the trains themselves and ventilation systems.

Question:
Inferring from the passage, what is the most practical way of reducing the health risk of subway life?

Option 1: Generating ventilation systems.

Option 2: Opting for other transportation modes.

Option 3: Wearing face masks during journey.

Option 4: Reducing subway commutation.

Correct Answer: Generating ventilation systems.


Solution : The correct choice is the first option.

The passage mentions factors influencing subway air pollution. It also discusses the observation that employees working on platforms with higher particulate matter concentrations tend to have higher levels of risk markers for cardiovascular disease. Therefore, improving ventilation systems in the subway environment could be a practical measure to reduce the health risks associated with subway life.

Therefore, generating ventilation system is the most practical way of reducing the health risk of subway life.

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Team Careers360 23 January,2024

Question : Comprehension:

Read the following passage and answer the questions.

All foodstuffs change. Green fruits become ripe and eggs go bad or rotten. It is the enzymes naturally present in each food which bring about the complex chemical changes that lead first to ripening and then to rotting.

How does one control the activity of enzymes, bacteria, yeasts and moulds in food? All of them require air, moisture and a certain temperature, usually somewhere near the body temperature, to be active. Depriving them of one or more of these will suppress them. All microorganisms can be killed by heat sterilisation. This simply means heating the food to high enough temperatures by boiling, deep or shallow frying, roasting, baking and, for milk particularly, pasteurisation. After such sterilisation, if the food is sealed in airtight containers, it can be kept for a long time. A certain water content in food is necessary for microorganisms to be active. Drying in the sun is a simple way of bringing down the moisture level so low that the enzymes and microorganisms cannot flourish.

Some chemicals can suppress undesirable activity. The addition of salt, vinegar, spices and oil or sugar syrup are other ways of preventing foods from going bad. If heating kills, freezing inactivates the enzymes and microorganisms. This is what happens in a refrigerator, in which fruits, vegetables and milk can be kept for fairly long periods. For meat and fish, even colder temperatures, below freezing point, are necessary for preservation. All foods which are kept cold in this way, once taken out and returned to room temperature, are again subject to spoilage and change.

Question:
Which of these is NOT required for the growth of bacteria?

Option 1: Air

Option 2: Optimum temperature

Option 3: Chemicals

Option 4: Moisture

Correct Answer: Chemicals


Solution : The third option is the correct choice.

As stated at the start of the second paragraph, bacteria require air, optimum temperature, and moisture to be active. Thus, bacteria do not require chemicals to be active.

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Team Careers360 25 January,2024

Question : Comprehension:

Read the following passage and answer the questions.

All foodstuffs change. Green fruits become ripe and eggs go bad or rotten. It is the enzymes naturally present in each food which bring about the complex chemical changes that lead first to ripening and then to rotting.

How does one control the activity of enzymes, bacteria, yeasts and moulds in food? All of them require air, moisture and a certain temperature, usually somewhere near the body temperature, to be active. Depriving them of one or more of these will suppress them. All microorganisms can be killed by heat sterilisation. This simply means heating the food to high enough temperatures by boiling, deep or shallow frying, roasting, baking and, for milk particularly, pasteurisation. After such sterilisation, if the food is sealed in airtight containers, it can be kept for a long time. A certain water content in food is necessary for microorganisms to be active. Drying in the sun is a simple way of bringing down the moisture level so low that the enzymes and microorganisms cannot flourish.

Some chemicals can suppress undesirable activity. The addition of salt, vinegar, spices and oil or sugar syrup are other ways of preventing foods from going bad. If heating kills, freezing inactivates the enzymes and microorganisms. This is what happens in a refrigerator, in which fruits, vegetables and milk can be kept for fairly long periods. For meat and fish, even colder temperatures, below freezing point, are necessary for preservation. All foods which are kept cold in this way, once taken out and returned to room temperature, are again subject to spoilage and change.

Question:
The main theme of the passage is:

Option 1: Chemicals in foodstuff

Option 2: Ripening of fruit

Option 3: Production of micro-organisms

Option 4: Preservation of food

Correct Answer: Preservation of food


Solution : The fourth option is correct.

The given passage initially talks about the changes that take place in food articles over time. Then we are introduced to some methods to check the growth of various microorganisms inside food items. And finally, some chemicals, such as salt and vinegar, are also mentioned that help in the preservation of foods. It can be concluded that the primary theme of the passage is the preservation of food.

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Team Careers360 24 January,2024
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