krit.club logo

Microbes in Human Welfare - Microbes as Biocontrol Agents and Biofertilizers

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

•

Biocontrol refers to the use of biological methods for controlling plant diseases and pests, reducing reliance on toxic chemical pesticides and weedicides.

•

The organic farming approach focuses on biodiversity; instead of eradicating pests, it keeps them at manageable levels through a complex system of checks and balances.

•

The bacterium BacillusBacillus thuringiensisthuringiensis (BtBt) is used to control butterfly caterpillars. The toxin is released in the alkaline pHpH of the insect's gut, creating pores that cause cell swelling and lysis.

•

Fungus TrichodermaTrichoderma species are free-living fungi very common in the root ecosystems. They are effective biocontrol agents against several plant pathogens.

•

Baculoviruses, particularly those in the genus NucleopolyhedrovirusNucleopolyhedrovirus, are species-specific, narrow-spectrum insecticidal agents. They are excellent for Integrated Pest Management (IPM) programs as they have no negative impact on non-target organisms.

•

Biofertilizers are organisms that enrich the nutrient quality of the soil. The main sources are bacteria, fungi, and cyanobacteria.

•

RhizobiumRhizobium forms symbiotic associations with the root nodules of leguminous plants, fixing atmospheric nitrogen (N2N_2) into organic forms used by the plant.

•

Mycorrhiza is a symbiotic association between fungi (e.g., genus GlomusGlomus) and plants. The fungus absorbs phosphorus (PP) from the soil and provides resistance to root-borne pathogens and salinity/drought tolerance.

•

Cyanobacteria like AnabaenaAnabaena, NostocNostoc, and OscillatoriaOscillatoria are autotrophic microbes that fix atmospheric nitrogen, acting as significant biofertilizers in paddy fields.

📐Formulae

Inactive Protoxin (in Bt)→Alkaline pH of gutActive Toxin\text{Inactive Protoxin (in } Bt\text{)} \xrightarrow{\text{Alkaline } pH \text{ of gut}} \text{Active Toxin}

N2+8e−+8H++16ATP→2NH3+H2+16ADP+16PiN_2 + 8e^- + 8H^+ + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i

Nitrogen Fixation: N2→NH3→NO2−→NO3−\text{Nitrogen Fixation: } N_2 \rightarrow NH_3 \rightarrow NO_2^- \rightarrow NO_3^-

💡Examples

Problem 1:

How does BacillusBacillus thuringiensisthuringiensis kill the larvae of certain insects without affecting other organisms?

Solution:

The BtBt toxin exists as inactive protoxins in the bacterium. Once an insect ingests the BtBt spores, the inactive toxin is converted into an active form due to the alkaline pHpH of the insect's gut. The activated toxin binds to the surface of midgut epithelial cells, creating pores that cause cell swelling and lysis, eventually leading to the death of the insect. Other organisms are unaffected as they lack the specific gut pHpH and receptors.

Explanation:

This demonstrates the specificity of biocontrol agents.

Problem 2:

Identify the benefits a plant derives from a Mycorrhizal association (GlomusGlomus).

Solution:

  1. Absorption of Phosphorus (PP) from the soil. 2. Resistance to root-borne pathogens. 3. Tolerance to salinity and drought. 4. Overall increase in plant growth and development.

Explanation:

The fungal hyphae increase the surface area for absorption, providing nutrients the plant cannot easily access alone.

Microbes as Biocontrol Agents and Biofertilizers Revision - Class 12 Biology CBSE