Biocontrol Biofertilizers

8 MCQs9-step worked example
Source: NCERT Cell: The Unit of LifePYQ coverage: NEET 2020, 2021, 2022, 2023, 2024, 2025Official key: NTA-verifiedLast reviewed: May 2026

Lesson

Biocontrol agents and biofertilizers are two pillars of ecologically sustainable agriculture tested regularly in NEET — not as heavy calculation questions, but as recall and direct-application items where precise organism–function pairing decides the mark.

Biological control (biocontrol) uses living organisms to suppress pest populations without synthetic pesticides. Key agents:

  • Bacillus thuringiensis (Bt) — produces crystal protein (Cry protein) toxic to insect larvae; basis of Bt-cotton. The toxin activates only in the alkaline gut of insects, sparing vertebrates.
  • Trichoderma — a free-living fungus that parasitises pathogenic fungi in the soil (e.g., Fusarium). Used as a biopesticide in root-zone treatment.
  • Nucleopolyhedrovirus (NPV, especially baculoviruses) — species-specific viral biocontrol agents with no negative impact on non-target organisms; narrow host range is the distinguishing advantage.
  • Ladybird beetles and dragonflies — predatory insects controlling aphids and mosquitoes respectively in integrated pest management (IPM).

Biofertilizers are organisms that enrich soil nutrient quality:

  • Rhizobium — symbiotic nitrogen fixer in root nodules of legumes (not free-living).
  • Free-living N₂ fixers — Azospirillum, Azotobacter (soil); Anabaena, Nostoc (cyanobacteria, also fix nitrogen in paddy fields and form associations with Azolla).
  • Mycorrhiza (e.g., Glomus) — fungal symbiont that extends phosphorus absorption from soil into plant roots; also improves drought tolerance.

The common NEET trap here is organism–role mismatch: confusing Rhizobium (symbiotic, legume-specific) with Azotobacter (free-living, non-specific), or misidentifying Trichoderma as a biofertilizer when it is a biocontrol agent.

(Reference: NCERT Class 12 Biology Chapter 9, page 211)

Practice MCQs

Select an option to see the explanation. Wrong answers show why your choice was tempting — and name the exact trap it exploits.

MCQ 1Easy RecallPractice

Which of the following is a free-living nitrogen-fixing bacterium used as a biofertilizer?

MCQ 2Easy RecallPractice

The Cry protein produced by *Bacillus thuringiensis* becomes active in:

MCQ 3Easy RecallPractice

*Mycorrhiza* (e.g., *Glomus*) primarily helps the plant in absorption of:

MCQ 4Direct ApplicationPractice

Which biocontrol agent is species-specific and has no negative impact on non-target organisms, plants, or mammals?

MCQ 5Direct ApplicationPractice

*Azolla* is used as a biofertilizer in rice paddies because it harbours:

MCQ 6Direct ApplicationPractice

In integrated pest management, *Trichoderma* is effective against:

MCQ 7Concept TrapPractice

A farmer wants to improve phosphorus availability for a non-leguminous crop without chemical fertilisers. The most appropriate biofertiliser recommendation is:

MCQ 8Concept TrapPractice

Which of the following correctly pairs the organism with its role?

Worked Example

  1. 1

    Given

    A NEET question asks: "Which of the following is used as a biocontrol agent against plant diseases caused by soil-borne fungi?" Options: (A) *Glomus* (B) *Rhizobium* (C) *Trichoderma* (D) *Anabaena*

  2. 2

    Required

    Identify the organism whose documented biological function is control of pathogenic soil fungi.

  3. 3

    Concept

    Biocontrol = using living organisms to suppress pests/pathogens. Key distinction: *Trichoderma* is a fungal antagonist (kills other fungi); *Glomus* is a mycorrhizal symbiont (helps phosphorus uptake); *Rhizobium* and *Anabaena* are nitrogen fixers.

  4. 4

    Classification rule

    Biocontrol of soil fungi → *Trichoderma* (parasitises *Fusarium*, *Pythium*, etc.) Biofertiliser (P) → *Glomus* Biofertiliser (N, symbiotic with legumes) → *Rhizobium* Biofertiliser (N, cyanobacterium) → *Anabaena*

  5. 5

    Application

    The question specifies "biocontrol agent" + "soil-borne fungi" — both conditions point exclusively to *Trichoderma*.

  6. 6

    Evaluation

    - *Glomus* is a mutualist (helps plants), not an antagonist of pathogenic fungi. - *Rhizobium* and *Anabaena* are nitrogen-fixers with no documented antifungal role. - Only *Trichoderma* parasitises soil-borne pathogenic fungi.

  7. 7

    Final answer

    **(C) *Trichoderma***

  8. 8

    Common trap

    Selecting *Glomus* because it is a soil fungus associated with roots. But *Glomus* is a biofertiliser (enhances P uptake via symbiosis), NOT a biocontrol agent against pathogenic fungi. The organism–function mismatch (*Glomus* ≠ antagonist) is the designed distractor.

  9. 9

    Similar NEET-style question

    "A farmer observes *Fusarium* wilt in his tomato field. Which organism can be applied to the soil as a biological control measure?" (A) *Azotobacter* (B) *Trichoderma* (C) *Glomus* (D) *Nostoc* Answer: (B) — *Trichoderma* parasitises *Fusarium* in soil; others are biofertilisers (N or P), not biocontrol agents. ---

Before solving, remember these

Key Fact

Biocontrol & biofertilizers

Biocontrol: ladybird → aphids; dragonfly → mosquitoes. Bacillus thuringiensis (Bt): toxin against insects. Trichoderma vs fungal pathogens. Biofertilizers: Rhizobium (legumes), Azospirillum, Azotobacter (free-living N fixers), cyanobacteria (Anabaena, Nostoc), mycorrhiza (Glomus — P uptake).

-- NCERT Class 12 Biology, Ch. 9, p. 211

Exam Traps & Common Mistakes

These are the exact patterns that cause wrong answers in NEET. Each trap includes when it triggers and how to avoid it.

Trap

AIDS confirmation vs screening

Category: Similar Terms

ELISA = screening (cheap, sensitive); Western blot = confirmation. CD4+ T cell count tracks disease progression.

When it triggers

Question on which test confirms HIV vs which monitors progression.

How to avoid

ELISA first (screening); Western blot confirms; CD4+ count = monitoring marker (<200/µL = AIDS).

Trap

Active vs passive immunity

Category: Similar Terms

Active: own immune response (vaccination, infection). Passive: pre-formed antibodies received (colostrum, antiserum injection).

When it triggers

Question on immunity type from vaccination, antiserum, mother's milk.

How to avoid

Active = body produces; passive = body receives. Vaccination → active. Mother's milk → passive (IgA).

Past Year Questions

29 questions from NEET 2020, 2021, 2022, 2023, 2024, 2025. Answers verified against NTA official keys.

NEET 2024

Given below are two statements: Statement I : Bt toxins are insect group specific and coded by a gene cry IAc. Statement II : Bt toxin exists as inactive protoxin in B. thuringiensis. However, after ingestion by the insect the inactive protoxin gets converted into active form due to acidic pH of the insect gut. In the light of the above statements, choose the correct answer from the options given below:

1Both Statement I and Statement II are true
2Both Statement I and Statement II are false
3Statement I is true but Statement II is false
4Statement I is false but Statement II is true
NTA Answer: Option 3(final)
NEET 2024

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R: Assertion A : Breast-feeding during initial period of infant growth is recommended by doctors for bringing a healthy baby. Reason R : Colostrum contains several antibodies absolutely essential to develop resistance for the new born baby. In the light of the above statements, choose the most appropriate answer from the options given below:

1Both A and R are correct and R is the correct explanation of A
2Both A and R are correct but R is NOT the correct explanation of A
3A is correct but R is not correct
4A is not correct but R is correct
NTA Answer: Option 1(final)
NEET 2023

Which one of the following is NOT an advantage of inbreeding?

1It exposes harmful recessive genes but are eliminated by selection.
2Elimination of less desirable genes and accumulation of superior genes takes place due to it.
3It decreases the productivity of inbred population, after continuous inbreeding.
4It decreases homozygosity.
NTA Answer: Option 3(final)
NEET 2022

Given below are two statements: Statement I: Autoimmune disorder is a condition where body defense mechanism recognizes its own cells as foreign bodies. Statement II: Rheumatoid arthritis is a condition where body does not attack self cells. In the light of the above statements, choose the most appropriate answer from the options given below:

1Statement I is incorrect but Statement II is correct
2Both Statement I and Statement II are correct
3Both Statement I and Statement II are incorrect
4Statement I is correct but Statement II is incorrect
NTA Answer: Option 4(final)
NEET 2022

Select the incorrect statement with respect to acquired immunity.

1Acquired immunity is non-specific type of defense present at the time of birth.
2Primary response is produced when our body encounters a pathogen for the first time.
3Anamnestic response is elicited on subsequent encounters with the same pathogen.
4Anamnestic response is due to memory of first encounter.
NTA Answer: Option 1(final)
NEET 2020

Match the following columns and select the correct option. 107. ÁŸêŸ Sà ÷Ê ∑§Ê Á◊‹ÊŸ ∑§⁄U ‚„Ë Áfl∑§À¬ ∑§Ê øÿŸ ∑§⁄UÊ – Column - I Column - II Sà ÷ - I Sà ÷ - II (a) Bt cotton (i) Gene therapy (a) ’Ë≈UË ∑§¬Ê‚ (i) ¡ËŸ ÁøÁ∑§à‚Ê (b) Adenosine (ii) Cellular defence (b) ∞«UËŸÊ ‚ËŸ Á«U∞◊ËŸ ¡ (ii) ∑§Ê Á‡Ê∑§Ëÿ ‚È⁄UˇÊÊ deaminase ∑§Ë ∑§◊Ë deficiency (c) •Ê⁄U.∞Ÿ.∞.•Ê߸ (iii) HIV ‚ ∑˝§◊áÊ ∑§Ê ¬ÃÊ (c) RNAi (iii) Detection of HIV ‹ªÊŸÊ infection (d) ¬Ë.‚Ë.•Ê⁄U. (iv) ’ÒÁ‚‹‚ (d) PCR (iv) Bacillus ÕÈÁ⁄ UÁ¡ÁŸÁ‚‚ thuringiensis (a) (b) (c) (d) (a) (b) (c) (d)

1(i) (ii) (iii) (iv) (1) (i) (ii) (iii) (iv)
2(iv) (i) (ii) (iii) (2) (iv) (i) (ii) (iii)
3(iii) (ii) (i) (iv) (3) (iii) (ii) (i) (iv)
4(ii) (iii) (iv) (i) (4) (ii) (iii) (iv) (i)
NTA Answer: Option 2(final)
NEET 2020

ÁŸêŸ ◊ ∑§ÊÒŸ flÊÁ„Ã◊‹ ©¬øÊ⁄U ∑ § Á‹∞ •flÊÿflËÿ •Ê¬ ∑§ 120. Which of the following is put into Anaerobic sludge digester for further sewage treatment ? ‚ ¬ÊÁøòÊ ◊ «UÊ‹Ê ¡ÊÃÊ „Ò?

1Activated sludge (1) ‚ Á∑˝§ÿËà •Ê¬ ∑§
2Primary sludge (2) ¬˝ÊÕÁ◊∑§ •Ê¬ ∑§
3Floating debris (3) ÃÒ⁄Uà „È∞ ∑ͧ«∏ -∑§⁄U∑§≈U
4Effluents of primary treatment (4) ¬˝ÊÕÁ◊∑§ ©¬øÊ⁄U ∑ § ’Á„—dÊfl
NTA Answer: Option 1(final)
NEET 2020

Which of the following statements about inclusion 128. • ÃÁfl¸c≈U ∑§ÊÿÊ ∑ § Áfl ÿ ◊ ÁŸêŸÁ‹Áπà ◊ ‚ ∑§ÊÒŸ ‚Ê ∑§ÕŸ bodies is incorrect ? ª‹Ã „Ò?

1These represent reserve material in (1) ÿ ∑§Ê Á‡Ê∑§ÊŒ˝√ÿ ◊ ÁŸÁøà ¬ŒÊÕ¸ ∑§Ê √ÿÄà ∑§⁄Uà „Ò – cytoplasm.
2ÿ Á∑§‚Ë Á¤ÊÀ‹Ë ‚ ÁÉÊ⁄ U Ÿ„Ë „Ê Ã – (2) They are not bound by any membrane.
3These are involved in ingestion of food (3) ÿ πÊl ∑§áÊÊ ∑ § • ê˝¸„áÊ ◊ ‡ÊÊÁ◊‹ „Ê Ã „Ò – particles.
4ÿ ∑§Ê Á‡Ê∑§ÊŒ˝√ÿ ◊ Sflà òÊ M§¬ ◊ „Ê Ã „Ò – (4) They lie free in the cytoplasm.
NTA Answer: Option 3(final)
NEET 2020

¬˝ÁÃ⁄UˇÊÊ ∑ § ‚ Œ÷¸ ◊ ª‹Ã ∑§ÕŸ ∑§Ê ¬„øÊÁŸ∞– 131. Identify the wrong statement with reference to immunity.

1÷˝ÍáÊ ◊ÊÃÊ ‚ ∑ȧ¿U ¬˝ÁÃ⁄UˇÊË ¬˝Êåà ∑§⁄UÃÊ „Ò, ÿ„ ÁŸÁc∑˝§ÿ (1) Foetus receives some antibodies from ¬˝ÁÃ⁄UˇÊÊ ∑§Ê ©ŒÊ„⁄UáÊ „Ò– mother, it is an example for passive
2¡’ ¬⁄U¬Ê Ë ∑§Ê ‡Ê⁄UË⁄U (¡ËÁflà •ÕflÊ ◊ÎÃ) ¬˝Á០∑ § immunity. ‚ ¬∑¸§ ◊ •ÊÃÊ „Ò •ÊÒ⁄U ©‚∑ § ‡Ê⁄UË⁄U ◊ ¬˝ÁÃ⁄UˇÊË ©à¬ÛÊ (2) When exposed to antigen (living or dead) „Ê Ã „Ò – ß‚ ““‚Á∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ”” ∑§„à „Ò – antibodies are produced in the host’s body. It is called “Active immunity”.
3¡’ ’Ÿ ’ŸÊ∞ ¬˝ÁÃ⁄UˇÊË ¬˝àÿˇÊ M§¬ ‚ ÁŒ∞ ¡Êà „Ò , ß‚ (3) When ready-made antibodies are directly ““ÁŸÁc∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ”” ∑§„à „Ò – given, it is called “Passive immunity”.
4‚Á∑˝§ÿ ¬˝ÁÃ⁄UˇÊÊ ¡ÀŒË „Ê ÃË „Ò •ÊÒ⁄U ¬Íáʸ ¬˝ÁÃÁ∑˝§ÿÊ Œ ÃË (4) Active immunity is quick and gives full „Ò– response.
NTA Answer: Option 4(final)

How NEET usually asks this

Recurring question shapes from past papers. Each pattern shows why wrong options look tempting.

Diseases, immunity, AIDS, cancer, drugs, animal husbandry, microbes

RecallMedium

Common distractors

active vs passive immunity confusion

Vaccination triggers the body to produce its own antibodies (active immunity), but students interpret 'given externally' as passive. Passive immunity (antiserum, colostrum IgA from mother's milk) provides preformed antibodies with no immune response from the recipient. Questions that pair vaccination, antiserum, and colostrum expose students who cannot classify by mechanism rather than by route of administration.

vector vs causative agent confusion

Questions name both the vector (organism that transmits) and the causative agent (organism that causes disease) as answer options. Students who associate 'Anopheles = malaria' select Anopheles as the causative agent rather than recognising it as the vector; Plasmodium is the causative agent. The distinction -- vector transmits, causative agent infects -- is lost when both options are plausible from partial recall.

microbe product pair swap

Match-list questions pair 10 or more microbe names with industrial or household products. Students confuse Lactobacillus (lactic acid fermentation, curd) with Saccharomyces cerevisiae (ethanol, bread), or Aspergillus niger (citric acid) with Clostridium butylicum (butyric acid). Partial recall of one-to-one mappings produces swapped pairs, especially when two products share the same chemical class.

Sources

NCERT refs: Class 12 Biology Chapter 9, p.211

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