• Option D is correct.
• Ecological balance is a state of dynamic equilibrium within a community of organisms in a habitat or ecosystem. It can happen when the diversity of the living organisms remains relatively stable. Gradual changes do take place but that happens only through natural succession.
• A stable balance in the numbers of each species in an ecosystem occurs through competition and cooperation between different organisms where population remains stable. This balance is brought about by the fact that certain species compete with one another determined by the environment in which they grow. This balance is also attained by the fact that some species depend on others for their food and sustenance.

Option B is the correct answer.
Environment: The environment is the totality of all the external conditions affecting the life, development and
survival of an organism.
Ecosystem: A system formed by interaction of all living organisms with each other and with the physical and chemical factors of the environment where they live.
Ecology: “Ecology is the study of the relationships between living organisms, including humans, and their physical environment; it seeks to understand the vital connections between plants and animals and the world around them.
Biome: Very large area of planet classified by plants and animals living together.
Habitat: The place where an organism such as plan or animal makes his home is called habitat.

• Option C is correct.
• Green chemistry is a science-based philosophy of designing chemicals, products, and processes with the intention of making them less hazardous and more sustainable. It applies to the life cycle of a product, from creation to disposal.
• When put into practice, green chemistry can:
1. Prevent pollution at the source by making safer chemicals.
2. Reduce or eliminate the use of toxic chemicals—which protects workers, consumers, and the environment.
3. Reduce energy and material use, while increasing use of renewable materials.
Examples of green chemistry innovations:
• Some manufacturers use supercritical carbon dioxide or water to remove caffeine from coffee beans. These decaffeination methods are much safer than solvents like benzene, which manufacturers used to use, or methylene chloride, which some manufacturers still use.
• Packing peanuts made from starch are an alternative to polystyrene packing peanuts. Unlike polystyrene, which comes from oil, starch peanuts are made from renewable plant starch. Instead of going into the trash, starch peanuts can be composted after use. Starch is also much less hazardous than styrene.
• Scientists can also copy natural processes to create new innovations, an approach called biomimicry. For example, researchers can study how mussels and barnacles attach to wet rocks in order to develop new, safer adhesives for surgery and other uses.

Option D is correct. Ecocline: A gradation from one ecosystem to another when there is no sharp boundary between the two. It is the joint expression of associated community (coenocline) and complex environmental gradients.
Ecotone: An ecotone is a transition area between two biomes. It is where two communities meet and
integrate. It may be narrow or wide, and it may be local (the zone between a field and forest) or regional (the transition between forest and grassland ecosystems).
Ecotype: In evolutionary ecology, an ecotype, sometimes called ecospecies, describes a genetically
distinct geographic variety, population or race within a species, which is adapted to specific environmental conditions. They typically show morphological differences.
An ecological niche is the role and position a species has in its environment; how it meets its needs for food and shelter, how it survives, and how it reproduces. A species’ niche includes all of its interactions with the biotic and abiotic factors of its environment. No two species have identical niches.

• Option D is correct.
• Energy pyramid concept helps to explain the phenomenon of biological magnification – the tendency for toxic substances to increase in concentration progressively at higher levels of the food chain.
• Biomagnification occurs because certain substances, including some pesticides and heavy metals, are not easily degraded and can accumulate in organisms’ tissues or internal organs. Pregnant women are advised not to eat certain kinds of fish because of the potential for biomagnification of mercury, a heavy metal, in aquatic systems.
• In order for biomagnification to occur, the pollutant must be: long-lived, mobile, soluble in fats, biologically active.

• Option D is correct.
• Standing crop is the amount of biomass or energy present in different trophic levels at any given time. This is another important characteristic of an ecosystem. It can be expressed in terms of
1. biomass
2. number or
3. total energy fixed at each step at each trophic level.

• Option D is correct.
• Amensalism is a biotic interaction where one species is harmed, the other is unaffected. Example: A large tree shades a small plant, retarding the growth of the small plant.
• The small plant has no effect on the large tree. Hence, the correct answer is (A).

• Option B is correct.
• Zabo system is traditional system is practiced in Nagaland.
• The term Zabo means ‘impounding run-off’. When rain falls on terraced hill slopes, the runoff collects in ponds in the middle terrace. The runoff then passes through slopes where there are cattle yards, and finally reaches the paddy fields at the foot of the hills.
• Thus it is through this system that not only the irrigation of paddy fields is brought about, but the fertility of the crop- field is also improved.

• Option C is correct.
• TamiraSES project is being jointly implemented restore Thamirabarani River.
• The Thamirabarani river originates from Agastyarkoodam peak of Pothigai hills in Western Ghats. It is the only perennial river in Tamil Nadu.
• TamiraSES project is jointly implemented by the district administration of Tirunelveli in Tamil Nadu and Bengaluru-based NGO Ashoka Trust for Research in Ecology and the Environment (ATREE).
• The project involves the use of “hyper-local” approach to restore one Thamirabarani river.
• Its objective is to restore the social ecological systems of the Thamirabarani river’s riverscape, covering head-waters, estuaries and surrounding areas to enable the native conditions of the biodiversity to thrive.
• It will restore Thamirabarani as well as all the waterbodies in the riverscape.
• Under the first phase of this project, five social ecological observatories will be set up. These will act as pilots to help the project expand further.
• This phase will be limited to the borders of Tirunelveli district.
• It was launched as an experimental project since it focuses mainly on community engagement instead of the relying solely on technical and nature-based solutions as was done in national and international river restoration projects.

• Option B is correct.
• New IUCN Green status has been launched to focus on recovery efforts to give a fuller picture of threats to plant and animal populations.
• The IUCN Green Status classifies species into nine Species Recovery Categories, indicating the extent to which species are depleted or recovered compared to their historical population levels.
• Each Green Status assessment measures the impact of past conservation on a species, a species’ dependence on continuing support, how much a species stands to gain from conservation action within the next ten years, and the potential for it to recover over the next century.