The term environment means the surroundings of an organism. It includes both living and non-living components. Man and other living organisms are surrounded by non-living components such as land, air, atmosphere, water, and by living components like plants and animals. The environment also includes the pollutants and other factors that adversely affect our life. Thus, environment is the sum total of all the forces, materials and influences around us at a given point of time and place.

Both the statements are correct.

Ecosystems can be small or large and are placed in nature side by side. There is an exchange of materials and energy within the ecosystem as well as between adjoining ecosystems. They are all interconnected and hence, interrelated. The vast network of all interconnected ecosystems constitutes the Biosphere. It is that part of the earth's terrestrial system-including air, land, and water-in which life develops and where life process in turn get transformed. It is the life zone of the earth.

Statement 1 is correct. A natural ecosystem is an assemblage of plants and animals which functions as a unit and is capable of maintaining its identity such as forest, grassland, an estuary, human intervention is an example of a natural ecosystem. A natural ecosystem is totally dependent on solar energy. There are two main categories of ecosystems. Hence, statement 2 is incorrect.

Terrestrial ecosystem: Ecosystems found on land e.g. forest, grasslands, deserts, tundra.

Aquatic ecosystem: Plants and animal communities found in water bodies. These can be further classified into two sub groups.

• Fresh water ecosystems, such as rivers, lakes and ponds.
• Marine ecosystems, such as oceans, estuary.

Biotic communities are dynamic in nature and change over a period of time. The process by which communities of plant and animal species in an area are replaced or changed into another over a period of time is known as ecological succession. Both the biotic and abiotic components are involved in this change. This change is brought about both by the activities of the communities as well as by the physical environment in that particular area.

The physical environment often influences the nature, direction, rate and optimal limit of changes. During succession both the plant and animal communities undergo change. There are two types of successions:

1. Primary succession
2. Secondary succession

Pairs 2 and 3 are correctly matched. Succession that occurs on land where moisture content is low for e.g. on bare rock is known as xerarch. Succession that takes place in a water body, like ponds or lake is called hydrarch.

Pair 1 is incorrectly matched. The entire sequence of communities in a given area, succeeding each other, during the course of succession is termed sere. Each transitional community that is formed and replaced during succession is called a stage in succession or a seral community.

A niche is the unique functional role or place of a species in an ecosystem. It is a description of all biological, physical and chemical factors that a species needs to survive, stay healthy nd reproductive.

A niche is unique for s species, which means no two species have exact indetical niches. Niche plays an important role in conservation or organisms.

Types of Niche:

1. Habitat niche - where it lives
2. Food niche - what it eats or decomposes & what species it competes with
3. Reproductive niche - how and when it reproduces.
4. Physical & chemical niche - temperature, land shape, land slope, humidity & other requirement.

Statement 1 is correct. The energy enters into the ecosystem in the form of solar radiation and is converted into food (plant biomass) by the producers. The plant converts solar energy into protoplasm by photosynthesis.

Food stored by the plants and their biomass (matter) is the chemical form of energy. From the producers this chemical form of energy passes through various trophic levels in the food chain. This process of transfer of energy through various trophic levels of the food chain is known as flow of energy.

There is a loss of some energy in the form of unusable heat at each trophic level so that energy level decreases from the first trophic level upwards.

Statement 2 is incorrect. Energy never flows in the reverse direction that is from carnivores to herbivores to producers.

Amensalism is a negative association between two species in which one species harms or restricts the other species without itself being adversely affected or harmed by the presence of the other species. Organisms that secrete antibiotics and the species that get inhibited by the antibiotics are examples of amensalism. For example the bread mould fungi Pencillium produce penicillin an antibiotic substance which inhibits the growth of a variety of bacteria. Pencillium benefits apparently by having greater availability of food when the competition because of the bacteria is removed.