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The Correct Answer is Option 3

Key Points What are Immunoglobulins?

• Immunoglobulins (Ig) or antibodies are proteins produced by B cells in response to antigens (foreign substances like viruses or bacteria).
• There are five major classes: IgG, IgA, IgM, IgE, and IgD, each with different roles.

Why IgM is the First?

• IgM is the first antibody produced during the primary immune response (initial exposure to an antigen).
• It is a pentamer (5 antibody units), making it highly effective at agglutination and activating complement proteins.
• It provides early defense before other antibodies like IgG are produced in larger amounts.

 Why the other options are incorrect?

• 1) IgA – Found mainly in mucosal areas (e.g., saliva, tears, breast milk), not first in systemic response.
• 2) IgG – Most abundant in the blood and produced in secondary response, not the first.
• 4) IgE – Involved in allergic reactions and defense against parasites, not the initial response to infection.

Conclusion:

IgM is the first class of immunoglobulin to be produced in response to a new infection, acting as the body’s first line of antibody defense.

So, the correct answer is: Option 3.

The Correct Answer is Option 1

Key Points

What are Biological Membranes?

• Biological membranes are semi-permeable barriers that surround cells and organelles.
• They regulate the movement of substances in and out of cells and provide structural support and communication platforms.

Composition of Biological Membranes:

• Made up of lipids and proteins in varying combinations.
• The main structure is a phospholipid bilayer with embedded proteins.
• The exact composition is specific to the species, cell type, and organelle.

Components:

• Lipids: Provide fluidity and form the basic structural framework.
• Proteins: Serve as channels, receptors, enzymes, and transporters.
• Some membranes also contain carbohydrates attached to proteins and lipids (forming glycoproteins and glycolipids).

Why the other options are incorrect?

• 2) Lipids only – Incorrect; proteins are essential components.
• 3) Proteins only – Also incorrect; lipids form the main structure.
• 4) None of the above – Clearly wrong; the membrane has both lipids and proteins.

Conclusion:

Biological membranes are composed of lipids and proteins in combinations that vary by species, cell type, and organelle.

So, the correct answer is: Option 1.

The Correct Answer is Option 2

Key Points What is a Nonsense Codon?

• A nonsense codon, also known as a stop codon, signals the termination of protein synthesis during translation.
• It does not code for any amino acid.
• The three nonsense (stop) codons are:
• UAA
• UAG
• UGA

Codon Meanings:

 Why Option 1 (AUG) is incorrect:

• AUG is a start codon, not a nonsense codon.
• It initiates translation and also codes for the amino acid Methionine.

Conclusion:

Among the given options, only UAA is a nonsense codon that signals the end of translation.

So, the correct answer is: Option 2.

The Correct Answer is Option 3

Key Points What are Endangered Species?

• Endangered species are organisms that are at serious risk of extinction in the near future.
• This classification is based on rapid declines in population size, habitat, or breeding success.
• The IUCN Red List (International Union for Conservation of Nature) identifies and monitors such species globally.

IUCN Red List Categories (in increasing order of threat):

1. Least Concern
2. Near Threatened
3. Vulnerable
4. Endangered
5. Critically Endangered
6. Extinct in the Wild
7. Extinct

Why the other options are incorrect?

• 1) Rare – Species that exist in low numbers or isolated areas, but not necessarily threatened.
• 2) Vulnerable – At risk, but not as severely as endangered species.
• 4) Extinct – Species that no longer exist anywhere on Earth.

Conclusion:

Species that are currently facing a high risk of extinction in the near future are classified as Endangered.

So, the correct answer is: Option 3.

The Correct Answer is Option 2

Key Points

What are Kharif Crops?

• Kharif crops are sown at the beginning of the monsoon (June–July) and harvested in September–October.
• They require hot and humid weather and plenty of rainfall.

Examples of Kharif Crops:

• Rice
• Maize
• Cotton
• Soybean
• Sugarcane
• Millets

 Why the other options are incorrect?

• 1) Barley – A Rabi crop, sown in winter and harvested in spring.
• 3) Gram – Also a Rabi crop.
• 4) Wheat – A major Rabi crop, not Kharif.

Conclusion:

Among the given options, Sugarcane is the Kharif crop as it is typically planted during the rainy season and harvested after a long growing period.

So, the correct answer is: Option 2.

The Correct Answer is Option 2

Key Points What is Xylem?

• Xylem is a type of vascular tissue in plants.
• Its main function is to transport water and dissolved minerals from the roots to the rest of the plant (upward movement).
• It also provides mechanical support to the plant.

Function of Xylem:

• Transports water and minerals absorbed from the soil.
• Movement is unidirectional (from roots to leaves).
• Includes four types of cells:
• Tracheids
• Vessel elements
• Xylem fibers
• Xylem parenchyma

Why the other options are incorrect?

• 1) Transport of foods – Done by phloem, not xylem.
• 3) Transport of oxygen and other gases – Gases mainly diffuse through stomata and intercellular spaces, not via xylem.
• 4) Transport of essential amino acids – Also part of phloem transport, not xylem.

Conclusion:

Xylem is responsible for the transport of water and dissolved minerals from the roots to other parts of the plant.

So, the correct answer is: Option 2.

The Correct Answer is Option 3

Key Points

Who was AP de Candolle?

• Augustin Pyramus de Candolle was a prominent Swiss botanist.
• He is recognized for being among the first to use anatomical features, especially vascular tissue characteristics, in the classification of plants.
• His work helped shift plant classification from purely morphological (external appearance) to a more scientific and internal structural basis.

Contribution:

• He introduced the concept of using internal tissue systems, such as xylem and phloem, for distinguishing between major plant groups like:
• Vascular (tracheophytes)
• Non-vascular (bryophytes)

Why the other options are incorrect?

• 1) Engler and Prantl – Known for a phylogenetic system of classification, but not the first to use vascular tissues.
• 2) Bentham and Hooker – Created a natural system of classification, focusing mainly on morphological traits.
• 4) More than one of the above – Incorrect; AP de Candolle was the first.

Conclusion:

AP de Candolle was the first botanist to use the characteristics of vascular tissues in the scientific classification of plants, making him the correct answer.

So, the correct answer is: Option 3.

The Correct Answer is Option 2

Key Points

 Structure of a Mango Fruit:

A mango is a drupe (a type of fleshy fruit) and has three main layers of the pericarp (fruit wall):

1. Epicarp – The outer skin of the mango (not eaten).
2. Mesocarp – The thick, fleshy, juicy part that we eat. ✅
3. Endocarp – The hard, stony inner layer that surrounds the seed (the mango stone).

Mesocarp in Mango:

• The edible part of the mango.
• Rich in vitamins, fiber, and sugar.
• Soft, sweet, and aromatic.

The Correct Answer is Option 2

Key Points What is Ozone Day?

• Ozone Day, officially known as the International Day for the Preservation of the Ozone Layer, is celebrated to raise awareness about the importance of the ozone layer and efforts to protect it.

Why 16^th September?

• The United Nations General Assembly designated 16^th September as World Ozone Day to commemorate the signing of the Montreal Protocol in 1987.
• The Montreal Protocol is a global agreement to phase out substances that deplete the ozone layer.

Why the other options are incorrect?

• 1) 5^th June – World Environment Day
• 3) 21^st April – Not associated with ozone day
• 4) 5^th December – World Soil Day, not related to ozone

Conclusion:

Ozone Day is celebrated on 16^th September to mark the signing of the Montreal Protocol and raise awareness about ozone layer protection.

So, the correct answer is: Option 2

The Correct Answer is Option 4

Key Points What is Mycorrhizal Association?

• A mycorrhizal association is a symbiotic relationship between fungi and plant roots.
• The fungus colonizes the plant root system and extends into the soil, increasing the plant’s access to nutrients and water.

Advantages to the Plant:

• Increased mineral absorption (especially phosphorus and other micronutrients)
• Enhanced water uptake
• Protection against soil-borne pathogens and diseases
• Improved soil structure and stress tolerance

Why the other options are incorrect?

• 1) & 2) – Repetition and vague; “food” is not directly provided to the plant by the fungus.
• 3) – Combines incorrect options (A and B).
• 4) – Gives the correct and specific advantages gained by the plant in a mycorrhizal relationship.

Conclusion:

In a mycorrhizal association, the plant gains increased mineral absorption and protection from diseases, making this a vital mutualistic relationship in plant ecology.

So, the correct answer is: Option 4.