Sparrow serves the ecosystem of the earth. Sparrows mostly prefer seeds of millet, thistle, weed and sunflower seed. However, they also eat fruits and berries. During this process, sparrows spread seeds to places away from the fruit tree. This is important for germination of the seeds, because if the seeds fall close to the parent plant, they would have to compete for nutrition with the mature plant. This would reduce the chance of germination of the seed as well as growth of the plant once the seed germinated. By spreading seeds, sparrows help the survival of many plants that are the producers in an ecosystem.
Although primarily seed-eaters, sparrows also feed on small insects and worms such as caterpillars, beetles and aphids. Some of these creatures destroy certain plants. Sparrows keep their population in check; otherwise, the insects would have eaten certain plant species to extinction. Here also sparrows play an important role in preserving the ecosystem.
Most birds of prey, such as eagles and falcons, eat other smaller birds. Snakes, which are also secondary consumers, are known to eat sparrows. For example, sharp-shinned hawks prefer sparrows for food.. Hence by providing food for the secondary consumers, sparrows play an important role in their survival and in preserving the ecosystem.
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Biosphere is a term used to describe the parts of the earth and the thin layer of air above its surface that supports life. It is limited to the waters of the earth, a fraction of its crust and the lower regions of the atmosphere. It is also the part where solar energy is used to bring about photosynthesis and other chemical and physical charges. 
It is a broad natural assemblage of plants and animals shaped by common patterns of vegetations and climate. Some examples of biomes are forest biomes, desert biomes, grass land biomes or tundra biomes etc. 
The biotic factor concerns the organic variable affecting an ecosystem. For example, the changing population of elephants and its effect on the African Savana.
The living components of biosphere such as plants, animals etc. are called biotic components. The non-living components of biosphere such as water, air, stones, etc. are called abiotic components. 
Habitat is defined as a localized environment in which an organism lives and which provides for all or almost all of its needs. 
The term food pyramid is used to describe the quantities of materials that pass from one kind of eater to another. The word pyramid is used because the amount of energy associated with the food material becomes smaller at every link or upward step.
All food chains begin with green plants because they are the only living things that can produce their own food. Green plants produce food by the process of photosynthesis.
Animals living in trees are called arboreal such as monkey.
Plants that grow on other plants using them only for support are called epiphytes. They have no roots in the soil. Epiphytes do not parasitize the plants they grow on.
Camouflage is the disguise used by animals to hide from their enemies. Men also use camouflage, particularly in wars. Most animals use camouflage to hide from predators or other animals that prey on them. Camouflaging is done by adopting matching colour to the surroundings, so that one looks like a part of it.
An animal which obtains food by hunting other animals is called a predator. 
It is an opposite process of hibernation. Some animals go under the ground during the dry season of summer. In zoology it is a state of inactivity and reduced metabolic activity that occurs during the dry season in species such as lungfish and snails. 
Animals and plants which live on the bottom of the sea or lake are called benthos. 
Very small plants and animals living in water are called planktons. They are an important source of food for larger water animals.
Parasites are those animals or plants which live on the living plants and in the bodies of living animals. Parasites that live inside the host such as liver flukes and tapeworms are called entroparasites; those that live on exterior, such as fleas and lice are called ectoparasites. They are harmful for the host.
The living beings that feed on dead or decayed organic matter are called saprophytes. Most saprophytes are fungi and bacteria which contain no chlorophyll. Many other animals eat dead plants and animal matter. They are useful scavengers and in sewage farms and refuse dumps break down organic matter into nutrients and easily assimilable by green plants. 
When food chains are interconnected in an ecosystem they are called food webs. Sometimes one type of plant or animal is eaten by more than one kind of animal. In this way, two or more than two food chains get interconnected and form a food web. The more complex food web shows a greater variety of relationships. 
In ecology, a sequence showing feeding relationship between organisms in particular ecosystem is known as food chain. Each organism depends on the next lowest member of the chain for its food. For example, grass is eaten by a deer and deer is eaten by a lion. Other examples of food chains are algae-duck-otter and flower-butterfly-lizard-snake-peacock.
Living beings which eat both plants and animals are called omnivores. Omnivores have digestive adaptions intermediate between those of herbivores and carnivores. They can digest variety of food stuffs. Human beings are omnivorous, because they eat meat, fish, vegetables and fruits. Other omnivorous animals are rats, pigs, bear and certain birds. 
The livings being which eat other animals are called carnivores such as lion bear, cat, dog, wolf, weasel etc. Carnivores have special teeth for tearing and chewing flesh. In other words all flesh eating animals are carnivores. They also produce special enzymes for digesting meat. 
Apart from animals, there are some plants that capture insects for food. They are called carnivorous plants. Since they cannot prepare their own protein, they get it by eating worms and insects. Venus fly trap, pitcher plant, sundew plant etc. are some examples of carnivorous plants. Similarly a plant called ‘Indian pipe’ is found in the hills of Shimla also eats insects. 
Living beings which consume only plants are called herbivores. We sometimes call them vegetarians. Well-known herbivores are rabbits, deer, cows, sparrows, squirrels and honeybees. They have specially designed teeth and produce special enzymes to digest plant matter.
The four elements of an ecosystem are: (a) The non-living environment, (b) Producers (green plants), (c) Consumers and (d) Decomposers. The non-living environment of an ecosystem includes sunlight, water, oxygen, minerals, dead plants and animal matter. The producers of an ecosystem are green plants. Animals, both herbivorous and carnivorous are the consumers of an ecosystem. Decomposers are bacteria, fungi and insects that decompose dead plants and animals.
The ability of nature to remain unchanged is called the balance of nature or ecological balance. The whole earth is an ecosystem, a system of give and take among plants, animals and their surroundings. In theory the ecosystem is a closed cycle but in practice the ecosystem is seldom in a state of balance. Gradual readjustment to the composition of a balanced community is continuously taking place. Man is often responsible for causing sudden ecological imbalance through activities like deforestation, polluting the atmosphere, destroying habitats, seas, lake and by rapid industrialization or sometimes through the out break of new disease. 
Ecosystem is a functional unit consisting of interacting organisms and all aspects of the environment in any area. It contains both the non-living (abiotic) and living (biotic) components.
Ecology is the branch of science that is concerned with the relationships of life forms with each other and with their surroundings. The word ecology was coined in 1866 by Ernst Haeckel. It is derived from two ancient Greek words meaning “study of the home”. The word ecology comes from the Greek word Oikos meaning ‘household’.