Class 8 General Science NCERT Based - 1 - Free MCQ Practice Test with solutions,

Kharif crops are sown during the monsoon (June to September), and not in summer. Rice, corn, soybean, groundnut, cotton, etc. are Kharif crops.

Rabi crops are grown in winter. Wheat, chickpea, pea, mustard, flax are examples of Rabi crops.

Apart from this, several pulses and vegetables are grown in the summer season, in many places.

Organic manure is better than chemical fertilizers. While organic manure enhances the water holding capacity of the soil, makes the soil porous and loose, and increases the number of friendly microbes; prolonged use of chemical fertilizers decline the soil fertility and also cause water pollution.

Chemicals are used as pesticides and weedicides as well. 2, 4 D is an example of weedicide. The chemicals present in these increase the chemical content of the soil.

SUGAR and Citric Acid (Lemon Juice) are the main preservatives The product is preserved by lowering the water activity by cooking the fruit (evaporating water) in a very high sugar concentration.

Acid helps by lowering the pH After the jam is ready it is hot-filled to a clean jar, which is sterilized by the heat from the jam. The inversion of the jars helps by sterilizing the lid. Vinegar contains acetic acid, it is perfectly suited to preserve foods. It works because most of the microorganisms responsible for destroying food cannot live in an acetic acid environment.

Preservation is probably the most common reason vinegar is used in food preparation.

The use of mustard oil or vinegar prevents the spoilage of fruits and vegetables because food-spoiling bacteria cannot live in such an environment.

They are used as preservatives for preserving fruits such as raw mango,amla and lemon in the form of their pickles.

Bean and Peas are leguminous plants.

They fix nitrogen in the soil with the help of Rhizobium bacteria present in the root nodules of the plants.

Thus, they fix nitrogen and replenish the deficiency of nitrogen in the soil. Therefore, farmers prefer to grow beans and peas in nitrogen deficient soil.

The processing of loosening and turning the soil is called 'tilling' or 'ploughing' of the soil. It is the most important task in the field of agriculture.

It is very important to loosen the soil because it allows the roots of the plants to penetrate deep into the soil. This provides roots the space to expand under the surface of the earth.

The loosened soil helps in the growth of earthworms and microbes which add humus to the soil and increase the fertility. Loosening and turning the soil brings the nutrients to the top so that the plants can use them.

Rhizobium are a group of Gram-negative soil bacteria that are well known for their symbiotic relationship with various leguminous (soybeans, alfalfa etc). Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae).

To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. In general, they are gram negative, motile, non-sporulating rods.

Lactobacillus is a type of bacteria. There are lots of different species of lactobacillus bacteria. These are "friendly" bacteria that normally live in our digestive, urinary, and genital systems without causing disease.

Lactobacillus is also in some fermented foods like yogurt and in dietary supplements.Lactobacillus is most commonly taken by mouth to treat and prevent diarrhea, including infectious diarrhea and diarrhea linked with using antibiotics.

Some people also take lactobacillus by mouth for general digestion problems, irritable bowel syndrome (IBS), colic in babies, inflammatory bowel disease (IBD), inflammation of the colon, stomach pain, constipation, and many other conditions but there is no good scientific evidence to support many of these uses.

Of the given microorganisms, Spirogyra and Chlamydomonas are examples of algae. Common examples of protozoa are amoeba and paramecium.

Rhizopus (bread mould), Penicillium and Aspergillus are examples of fungi. Microorganisms can be unicellular, like bacteria; some are multicellular, like algae and fungi.

Some microorganisms are dependent on other microorganisms (parasitic), while some are not (free living). Microorganisms like amoeba live alone (solitary) while fungi live in groups (colonial).

The process of conversion of sugar into alcohol is called fermentation. Louis Pasteur discovered fermentation in 1857.

Penicillin was discovered by Alexander Fleming in 1929. It is an antibiotic which destroys the disease causing organisms.

Streptomycin, terramycin and erythromycin are some of the commonly used antibiotics; which are produced from fungi and bacteria.

Vaccine for measles was invented by Edward Jenner in 1798. If dead or inactive microorganisms are injected into the body, then the cells of the body release antibodies according to the microorganisms. This concept is the basis for the production of vaccines. Robert Koch discovered Bacillus anthracis in the year 1876, which is the causative organism of anthrax. Anthrax is a dangerous disease affecting humans and animals.