Water Cycle

Water Cycle

This Grade 7 worksheet is based on a very interesting and important topics, ’Water Cycle ‘ of  Grade 7 Science syllabus. Using it, students will be able to understand the concepts of the cyclic process that water goes through in its various physical forms. There are few topics in science wherein we need to understand and memorize. When it comes to learning through memorization, solving worksheets can be productive. This science worksheet includes colorful diagrams other than fill-in-blanks, and definitions of specific terms.

For tutors this worksheet acts as an “Assessment Tool” which allows them to measure how well students have understood the topic.

Cycles of Nature

Nature recycles its goods in the very best of the ways. There are four main cycles:

1. Carbon cycle
2. Photosynthesis
3. Nitrogen cycle
4. Water cycle

The forest cover that is green plants and even under sea vegetation absorbs the carbon from CO₂ and releases oxygen and then the carbon moves through food chains, where organisms get and eventually become nutrients including herbivores, carnivores and finally, decomposers. Through living organisms that is through respiration, carbon is released back into the atmosphere (where organisms use oxygen to burn food for energy absorb nutrients and release carbon dioxide as exhaled product).

When an animal dies and its carcass starts’ decomposing in the soil, carbon in it converts into fossil fuels over long periods of time and then also re-enter the atmosphere by combustion.

The nitrogen cycle is mainly carried out by bacteria, fungi and blue-green algae which fix the nitrogen from the air into useable compounds of nitrogen. These nitrogen-fixers generally reside in the soil or on the roots of plants. Like leguminous plants like green peas, beans, alfalfa, clover, lupines etc.

Rhizobia are bacteria that are found in the soil that form root nodules by settling in the roots of legumes. After nodule formation they fix nitrogen gas (N₂) from the atmosphere turning it into usable form of nitrogen. 

How nitrogen becomes available to living things and gets back to nature?

The nitrogen compounds these nitrogen fixing organisms fix is released into the soil and become available when they die, and then these fixed nitrogen move up the food chains. Nitrogen comes back into cycle when dead plants

and animals decompose, and when animals excrete. The excreted matter converts into nitrates after complex bacteria acts on it. Various compounds of nitrogen then cycle from the earth to plants to bacteria and back to the earth again and again without getting back to the air. But, sometimes denitrifying also happens ( denitrifying means to remove nitrogen or a nitrogen compound from a substance) bacteria and fungi usually break down nitrogen compounds and release nitrogen back into the atmosphere.

Check Point

Fill in the blanks –

1.  One of the biggest store houses of ………… is the atmosphere, which is about 0.038% ……………. ………….
2. Through ………………..…., plants take in CO2, water and sunlight to create sugars for energy, and oxygen gas emerges as a by-product.
3. The ……………… is about 78 per cent in the atmosphere.
4. The …………… ……………. is mainly carried out by bacteria, fungi and blue-green algae which fix the nitrogen from the air into nitrogen compounds.
5. The amount of water vapor in the air is called the ………………. …………. and for any given temperature there is a set amount of water that the air can hold.

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