Environmental Pollution

Concept:
The International Union for Conservation of Nature (IUCN) classifies species into different categories according to their risk of extinction. These categories are published in the IUCN Red List, which serves as a global inventory of the conservation status of plant and animal species. The classification helps scientists and conservationists determine the level of threat faced by species and prioritize conservation measures.
Step 1: Understanding the category ``Extinct''.
A species is considered Extinct (EX) when there is no reasonable doubt that the last individual of that species has died. This conclusion is usually made after:

• Extensive surveys in the species' known habitats
• Searches conducted at appropriate times of day and year
• Long periods without any confirmed sightings

Once these investigations fail to find any surviving individuals, the species is declared extinct.
Step 2: Other important IUCN conservation categories.

• Endangered (EN): Species facing a very high risk of extinction in the near future.
• Vulnerable (VU): Species facing a high risk of extinction in the medium-term future.
• Near Threatened (NT): Species that are close to qualifying for a threatened category.

These categories indicate different levels of conservation concern but still imply that the species exists in the wild.
Step 3: Identifying the correct category.
Since the question refers to a species whose last individual has died, the correct classification according to the IUCN Red List is: Final Answer:

Concept: Ecological pyramids represent the relationship between different trophic levels in an ecosystem. The three main ecological pyramids are:
• Pyramid of Numbers
• Pyramid of Biomass
• Pyramid of Energy Among these, the Pyramid of Energy is always upright because energy flow in an ecosystem is unidirectional and decreases at each successive trophic level according to the 10% law of energy transfer.

Step 1: Understand energy flow in an ecosystem. Energy enters the ecosystem through producers (plants) via photosynthesis and then passes to consumers through food chains.

Step 2: Energy loss at each trophic level. At each trophic level, a large portion of energy is lost as heat through metabolic activities. Only about 10% of the energy is transferred to the next trophic level.

Step 3: Implication for ecological pyramids. Because energy continuously decreases from producers to top consumers, the energy pyramid can never be inverted. Hence, it always remains upright.

Step 1: Understanding the Concept:
The International Union for Conservation of Nature (IUCN) classifies species into different categories based on their conservation status, population size, and risk of global extinction.

Step 2: Key Formula or Approach:
Recall the specific definitions for the various IUCN Red List categories to identify the one that precisely matches the given description.

Step 3: Detailed Explanation:
An 'Extinct' species is defined as a taxon when there is no reasonable doubt that the last individual has died, or when exhaustive surveys in its known or expected habitat have failed to record an individual.
An 'Endangered' species is one that is facing a very high risk of extinction in the wild in the near future.
A 'Vulnerable' species is one that is considered to be at a high risk of unnatural (human-caused) extinction without further human intervention.
A 'Near threatened' species is one that has been evaluated but does not currently qualify for the Endangered or Vulnerable status, though it is close to qualifying or is likely to qualify in the near future.
Based on the exact definition provided in the question, the correct term is 'Extinct'.

Step 4: Final Answer:
The correct term is Extinct, which corresponds to option (A).

Concept:
In ecology, interactions between species can have positive, negative, or neutral effects. These interactions are classified based on how each organism is affected.

Step 1: Understanding types of interactions

• Mutualism: Both species benefit (+, +)
• Commensalism: One benefits, the other is unaffected (+, 0)
• Parasitism: One benefits, the other is harmed (+, --)
• Amensalism: One is harmed, the other is unaffected (0, --)

Step 2: Identifying the correct interaction
The question specifies that one species is harmed while the other is unaffected. This perfectly matches the definition of amensalism. Conclusion:
Therefore, the correct term is amensalism.