Our Environment

Trophic levels are the different steps or levels in a food chain, showing who eats whom.

Example of a food chain: grass → goat → human

- 1st trophic level: grass (producers)
- 2nd trophic level: goat (primary consumer)
- 3rd trophic level: human (secondary consumer)

So, each step in the food chain is a trophic level.

Decomposers such as bacteria and fungi break down dead plants, dead animals, and waste products into simpler inorganic substances.

Their role is important because they:
- return nutrients to the soil,
- help plants use these nutrients again,
- prevent the accumulation of dead remains and garbage,
- maintain the natural replenishment of the soil.

Some substances are biodegradable because microorganisms like bacteria and fungi can break them down into simpler substances. Others are non-biodegradable because they cannot be broken down by these biological processes, so they persist in the environment for a long time.

Any two ways biodegradable substances would affect the environment are:
- They are broken down by microorganisms and become part of the soil again.
- They help in the recycling of nutrients and natural replenishment of soil.

They may also cause pollution if dumped in large amounts before decomposing, but their main effect is that they do not persist for long.

Any two ways non-biodegradable substances would affect the environment are:
- They persist for a long time and accumulate in the environment.
- They may harm living organisms and disturb the ecosystem.

They can also enter food chains and cause biological magnification.

Ozone is a molecule made of three oxygen atoms, written as O₃. It is harmful near the ground, but in the higher atmosphere it forms a protective layer.

It affects ecosystems by absorbing ultraviolet (UV) radiation from the Sun and protecting living organisms from its harmful effects. Without this protection, UV rays can damage organisms and even cause skin cancer in human beings.

Two ways to reduce the problem of waste disposal are:
- Segregate waste into biodegradable and non-biodegradable waste so that it can be treated properly.
- Reduce waste generation by using less disposable material, reusing items, and avoiding unnecessary packaging.

Other acceptable methods include recycling paper, plastic, glass and metal, and composting kitchen waste.

All the items in (a) are biodegradable: grass, flowers and leather can be broken down by microorganisms.

So the correct option is (a).