Biology for UPSC

Biology is a discipline of science concerned with living organisms and their physiological processes both at the molecular and macro level. Biology helps us comprehend the living world and how the various species (including humans) function, evolve and interact. It encompasses diverse fields, including botany, zoology, genetics, evolution, physiology, microbiology, molecular biology, etc., and is concerned with all physicochemical aspects of life. Advances in the fields of biology have improved people's quality of life.

Properties of Life

All living organisms have certain key traits or functions, which are being described here. 

• Order: Organisms are highly organised structures made up of one or more cells.
  • Unicellular organisms:A unicellular organism depends upon just one cell for all of its functions. Examples: bacteria, yeast, etc. 
  • Multicellular organisms:A multicellular organism has cells specialized to perform different functions that collectively support the organism. Examples: plants, animals, etc. 
• Sensitivity or Response to Stimuli: Organisms react to various stimuli. 
  • For example, plants can bend toward a source of light or respond to touch.
  • Bacteriacan respond to chemicals (chemotaxis) and light (phototaxis) through movement.
• Reproduction: Reproduction is the process of the development of offspring. There are two basic types of reproduction: sexual and asexual.
  • Sexual Reproduction: An organism's genetic information is combined from each of its parents during sexual reproduction. 
  • Asexual Reproduction: In asexual reproduction, one parent copies itself to produce genetically identical offspring. 
  • Many multicellular organisms create specialised reproductive cells and organs.
• Adaptation: All living organisms must be adapted to their environment. This is a consequence of evolution by natural selection, which operates in every lineage of reproducing organisms.
• Growth and Development: Organisms grow and develop according to specific instructions coded for by their genes that direct cellular growth and development. 
• Regulation: Organisms are complex, requiring various regulatory mechanisms to regulate internal processes such as nutrient transport, stimulus-response, and so on.
• Homeostasis: Homeostasis is a process that allows organisms to keep internal conditions within a restricted range almost consistently, despite outside changes.
• Energy Processing: All organisms rely on a source of energy for their metabolic functions. 
  • Some organisms absorb energy from the Sun and transform it into chemical energy in food and others use chemical energy from molecules they take in.

Levels of Organisation of Living Things

Living things are highly organised and structured, with a hierarchy ranging from small to large. 

• Cell and Cell organelles: Cells are the basic building blocks of all living things.
  • Organelles: Cells contain aggregates of macromolecules (carbohydrates, lipids, proteins, nucleic acids, etc.)surrounded by membranes that perform specialised functions, called organelles.
  • Types of cells: Cells are either prokaryotic (lack organelles including a true nucleus)or eukaryotic (have membrane-bound organelles including a nucleus). 
  • Constituents of cell: A cell is generally composed of a cell membrane, nucleus, and cytoplasm.
• Tissues: In most multicellular organisms, cells that perform the same function, join to form tissues.
  • For example, muscle tissue, connective tissue, and nervous tissue. 
• Organs: Organs are groups of tissues that have a common function. For example: Stomach, Heart, Brain, etc.
  • Several organs make up an organ system (such as the digestive system, circulatory system, or nervous system).
• Organism: Several organ systems functioning together form an organism (for example, a human).

Molecular Biology

Molecular biology studies biological processes at the molecular level, including interactions among molecules such as DNA, RNA, and proteins, as well as the way they are regulated.

• Proteins: Proteins are the building blocks of organisms and are critical to most of the work done by cells.
  • They are required for the structure, function, and regulation of the organisms.
  • Amino acids are the monomers that make up proteins.
• DNA: DNA is the genetic material passed down from parents to offspring in almost all life on Earth except RNA viruses.
  • Most DNA is located in the cell nucleus.
  • Generally, DNA is arranged in two strands, twisted around each other to form a right-handed helix, also known as a double helix.
  • Nucleotides are the DNA's building blocks, consisting of deoxyribose (5-carbon sugar), a phosphate group, and a nitrogenous base - adenine (A), Thymine (T), cytosine (C), and guanine (G).
• RNA: Ribonucleic acid is present in all living cells. 
  • RNA is a polymer of nucleotides and is most often single-stranded. 
  • RNA contains uracil (U) in place of Thymine as one of the bases. 
  • Types of RNA based on their function: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), all of which are involved in protein creation from DNA code.
  • mRNA contains the genetic code, used for protein synthesis.

Central Dogma

The central dogma describes the flow of genetic information in cells from DNA to mRNA to protein, stating that genes dictate mRNA sequences, which then specify protein sequences.

• Replication: DNA replication is the process by which a cell copies its DNA before division.
• Transcription: It is the process of transcribing mRNA from DNA.
• Translation: It is the process by which the genetic information contained in the mRNA is read and translated into the string of amino acid chains of proteins. 
• Sites: Both replication and transcription occur within the nucleus whereas; translation occurs on ribosomes (free or attached to the Endoplasmic reticulum). 

Human Diseases

Human disease is a deviation of a person's natural state that disrupts or changes vital functioning. Diseases are often classified as communicable or noncommunicable. 

• Communicable diseases: Communicable diseases are illnesses that can be transmitted to others through contact with contaminated surfaces, bodily fluids, blood products, insect bites, or through the air and are caused by bacteria, viruses, protozoa, etc. 
  • Diseases caused by bacteria:Leprosy (Mycobacterium leprae), Tuberculosis (Mycobacterium tuberculae), Typhoid (Salmonella typhi), etc.
  • Diseases caused by Viruses: Viruses are responsible for causing many diseases, including Ebola (caused by the Ebola virus), Genital herpes (herpes simplex virus), Influenza (influenza virus), Measles (Rubeola virus), Nipah Virus,Monkeypox (Monkeypox virus), and Covid-19(SARS-CoV-2 virus).
  • Diseases caused by protozoa: Diseases caused by protozoa are Malaria (caused by Plasmodium sp.), Kala-Azar (caused by Leishmania donovani), and amoebiasis(caused by Entamoeba histolytica).
  • Diseases caused by Fungi: Diseases caused by fungi are Candida (Candida auris), Aspergillosis (Mold Aspergillus), Athlete’s foot (fungi (dermatophytes), Blastomycosis (Blastomyces dermatitidis), etc. 
• Non-communicable diseases: Non-communicable diseases, also called chronic diseases, are long-term conditions caused by a mix of genetic, physiological, environmental, and behavioural variables.
  • The most common types of NCDs include cardiovascular illnesses (such as heart attacks and strokes), malignancies, chronic respiratory diseases (such as chronic obstructive pulmonary disease and asthma), and diabetes.
  • Noncommunicable diseases (NCDs) kill 41 million people each year, accounting for 74% of all deaths worldwide.

Immunity

Immunity is the body's ability to protect itself against all forms of foreign bodies, such as bacteria, viruses, and poisonous substances that enter the body. Immunity is exhibited by the immune system which is a complex network of lymphoid organs such as bone marrow, thymus, spleen, etc, and specialised cells.

• Types of immunity: 
  • Innate Immunity: It is also called natural or native immunity, consisting of mechanisms that exist before infection and are capable of rapid responses to microbes.
  • Adaptive Immunity: Acquired or adaptive immunity is the immunity that is developed by the host in its body after exposure to an antigen or after the transfer of antibodies or lymphocytes from an immune donor.
    • Acquired Immunity is of two types: Active immunity (induced by natural exposure to a pathogen or by vaccination) and Passive immunity (achieved by transfer of immune products, such as antibodies). 

Vaccines

Vaccines are injections (shots), liquids, pills, or nasal sprays that one takes to instruct the immune system to recognise and protect against hazardous pathogens. There are several types of vaccines. 

• Inactivated vaccines: These vaccinations include a dead version of the bacterium that causes the disease. 
  • Examples: Polio vaccine, the Hepatitis A vaccine, and the Rabies vaccine.
• Live-attenuated vaccines: Live vaccinations include a weakened (or attenuated) version of the germ that causes the disease. They stimulate a powerful and long-lasting immunological response. 
  • Examples: Measles, mumps, rubella (MMR combined vaccine), and Rotavirus vaccine.
• mRNA vaccines: They produce proteins to elicit an immunological response. They do not contain a live virus, thus there is no risk of disease transmission to the person receiving the vaccination.
  • Example: Pfizer-BioNTech and ModernaCOVID-19 vaccines.
• Subunit, recombinant, polysaccharide, and conjugate vaccines: These vaccines use specific components of the germ, such as protein, sugar, or capsid (a coating that surrounds the germ).
  • Example: Hepatitis B vaccine.
• Toxoid vaccines: Toxoid vaccinations include a toxin (harmful substance) produced by the germ that causes the sickness. They develop immunity to the components of the germ that cause the disease rather than the germ itself.
  • Example: Diphtheria and Tetanus.
• Viral vector vaccines: Viral vector vaccines use a modified version of a different virus as a vector (including influenza, measles virus, and adenovirus) to deliver protection.
  • Example: Oxford-AstraZeneca COVID-19 vaccine.

Biology for UPSC UPSC PYQs

Question 1: Consider the following statements: (UPSC Prelims 2023)

1. Some microorganisms can grow in environments with temperature above the boiling point of water.
2. Some microorganisms can grow in environments with temperature below the freezing point of water.
3. Some microorganisms can grow in a highly acidic environment with a pH below 3.

How many of the above statements are correct?

1. Only one
2. Only two
3. All three
4. None

Answer: (c)

Question 2: Which one of the following statements best describes the role of B cells and T cells in the human body? (UPSC Prelims 2022)

1. They protect the body from environmental allergens.
2. They alleviate the body's pain and inflammation.
3. They act as immunosuppressants in the body.
4. They protect the body from the diseases caused by pathogens.

Answer: (d)

Question 3: With reference to recent developments regarding ‘Recombinant Vector Vaccines’, consider the following statements: (UPSC Prelims 2021)

1. Genetic engineering is applied in the development of these vaccines.
2. Bacteria and viruses are used as vectors.

Which of the statements given above is/are correct?

1. 1 only
2. 2 only
3. Both 1 and 2
4. Neither 1 nor 2

Answer: (c)

Question 4: Which of the following diseases can be transmitted from one person to another through tattooing? (UPSC Prelims 2013)

1. Chikungunya
2. Hepatitis B
3. HIV-AIDS

Select the correct answer using the codes given below:

1. 1 only
2. 2 and 3 only
3. 1 and 3 only
4. 1, 2 and 3

Answer: (b)

Biology for UPSC FAQs

Q1. What are the branches of biology?

Ans. Biology encompasses diverse fields, including botany, marine biology, medicine, microbiology, molecular biology, physiology, and zoology.

Q2. What is the difference between communicable and non-communicable diseases?

Ans. Communicable diseases are often transmitted from person to person.On the other hand, non-communicable diseases are not typically spread from one person to another.

Q3. What is Central dogma?

Ans. The central dogma of molecular biology is a theory stating that genetic information flows only in one direction, from DNA to RNA, to protein, or RNA directly to protein.

Q4. What is the difference between prokaryotes and eukaryotes?

Ans. Eukaryotic cells have a distinct nucleus containing the cell's genetic material, while prokaryotic cells don't have a nucleus and have free-floating genetic material instead.