Question 1

Name the hormones controlling moulting and metamorphosis in insects. Describe the hormonal control of moulting and metamorphosis in detail.

Accepted Answer

Moulting and metamorphosis in insects are intricately regulated by a coordinated interplay of several key hormones, primarily Prothoracicotropic Hormone (PTTH), Ecdysone, and Juvenile Hormone (JH), as detailed in the MZOE-005 course material.

**Hormones Controlling Moulting and Metamorphosis**

The primary hormones involved are:
•   **Prothoracicotropic Hormone (PTTH):** A neuropeptide secreted by neurosecretory cells (NSC) in the insect brain.
•   **Ecdysone (Molting Hormone):** A steroid ho

Question 2

Explain the structure and function of Malpighian tubules in insects. Compare the process of osmoregulation in terrestrial and aquatic insects.

Accepted Answer

Insect physiology involves sophisticated mechanisms for waste removal and fluid balance. The Malpighian tubules, in conjunction with the hindgut, form the primary excretory and osmoregulatory system in insects. Their structure facilitates efficient filtration of hemolymph, while their function ensures the removal of nitrogenous waste and the precise regulation of water and ion levels. The challenges of maintaining osmotic balance differ significantly between terrestrial and aquatic environments,

Question 3

Explain mechanism of circulation in insects. Discuss the functions of haemolymph.

Accepted Answer

### a) Mechanism of Circulation in Insects

Insects possess an open circulatory system, meaning their haemolymph (insect blood) does not flow within a closed network of arteries and veins but circulates freely within the body cavity, known as the haemocoel. The primary circulatory organ is the dorsal vessel, a tube extending along the insect's back, which is differentiated into a posterior, pulsatile heart and an anterior, non-pulsatile aorta.

The heart, located in the abdomen, features paired,

Question 4

Discuss various respiratory methods employed by aquatic insects. Explain the impulse transmission process in insects.

Accepted Answer

Insect physiology showcases remarkable adaptations for survival in diverse environments, particularly in aquatic habitats where oxygen acquisition presents unique challenges. Similarly, the rapid and precise control of their bodies relies on an efficient neural impulse transmission system. These two fundamental processes, respiration in aquatic conditions and nerve signal propagation, highlight the complexity and sophistication of insect biological mechanisms, enabling their ecological success.

Question 5

Explain the hormonal link between flight and egg production with suitable examples. Define the following: i). Spermatogenesis ii). Paedogenesis iii). Polyembryony iv). Parthenogenesis v). Sex determination

Accepted Answer

**a). Hormonal Link Between Flight and Egg Production**

The hormonal link between flight and egg production in insects is a classic example of physiological trade-offs, often mediated by Juvenile Hormone (JH). Sustained flight, especially during migration, requires significant energy investment in flight musculature and metabolism, often at the expense of reproductive development. This energetic partitioning is hormonally regulated to ensure that reproduction occurs only when conditions are opt

Question 6

Explain the different indices of acute toxicity i.e. LD50, LC50 and LT50 and significance of these values.

Accepted Answer

Acute toxicity indices are crucial quantitative measures used in toxicology to assess the short-term harmful effects of a substance on a test population. LD50, LC50, and LT50 are standard metrics that quantify the lethality of a toxicant under specific conditions, providing vital information for risk assessment and regulatory purposes.

**LD50 (Lethal Dose 50%)**

LD50 refers to the statistically derived single dose of a substance that is expected to cause death in 50% of the tested animal popul

Question 7

What are organochlorine compounds? Describe their characteristic features and uses. Discuss, why these are considered harmful for the environment?

Accepted Answer

Organochlorine compounds (OCs) are a class of synthetic organic compounds characterized by the presence of at least one chlorine atom covalently bonded to a carbon atom. These compounds are typically derived from hydrocarbons and were widely used as pesticides, particularly insecticides, due to their potent and persistent action.

Their characteristic features include high chemical stability and resistance to degradation by light, heat, and biological processes, leading to environmental persiste

Question 8

What are pyrethroids? How are these different from the pyrethrins? Categorize them based on the cyano group and discuss, their mode of action. Describe the source, active ingredient and uses of neem oil as a safe pesticide.

Accepted Answer

Insecticides are crucial in pest management, with synthetic pyrethroids and natural pyrethrins being significant examples. Understanding their chemical structures, modes of action, and environmental impact is essential for effective and sustainable pest control. Furthermore, botanical pesticides like neem oil offer safer alternatives, leveraging natural compounds for pest suppression. This comprehensive approach considers both synthetic and natural options, highlighting their distinct characteri

MZOE-005 Solved Assignment — January 2025 / July 2025

INSECT PHYSIOLOGY AND TOXICOLOGY | IGNOU Master of Science (Zoology) Programme (MSCZOO)

MZOE-005—January 2025 / July 2025

INSECT PHYSIOLOGY AND TOXICOLOGY

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MZOE-005 Assignment Questions — January 2025

Q1.. Name the hormones controlling moulting and metamorphosis in insects. Describe the hormonal control of moulting and metamorphosis in detail.

Q2.. Explain the structure and function of Malpighian tubules in insects. Compare the process of osmoregulation in terrestrial and aquatic insects.

Q3.. Explain mechanism of circulation in insects. Discuss the functions of haemolymph.

Q4.. Discuss various respiratory methods employed by aquatic insects. Explain the impulse transmission process in insects.

Q5.. Explain the hormonal link between flight and egg production with suitable examples. Define the following: i). Spermatogenesis ii). Paedogenesis iii). Polyembryony iv). Parthenogenesis v). Sex determination

Q6.. Explain the different indices of acute toxicity i.e. LD50, LC50 and LT50 and significance of these values.

Q7.. What are organochlorine compounds? Describe their characteristic features and uses. Discuss, why these are considered harmful for the environment?

Q8.. What are pyrethroids? How are these different from the pyrethrins? Categorize them based on the cyano group and discuss, their mode of action. Describe the source, active ingredient and uses of neem oil as a safe pesticide.

Q9.. How do insect growth regulators (IGRs) function as insecticides? What role do enzyme inhibitors play in the action of pesticides? Explain the different types of hydrolytic processes that help in detoxification of pesticides during extramicrosomal metabolism of pesticides.

Q10.. Define the following terms: i) Biopesticide ii) Nanopesticide iii) Antifeedant iv) Entomopathogenic fungi v) Antidote

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