Food preservation & nitrogen cycle — Class 8 CBSE Science MCQs with Solutions
Free Class 8 CBSE Science Food preservation & nitrogen cycle MCQs with step-by-step solutions (15 questions). Part of Microorganisms: Friend and Foe. Practise online on Prepizo — no login needed.
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Questions with solutions
Q1 — Food preservation & nitrogen cycle · easy · theory
What are preservatives?
A. Bacteria that convert warm milk into curd
B. Chemicals that check the growth of microorganisms in food ✓ Correct
C. Vitamins added to increase the food value of a dish
D. Insects that carry disease-causing microbes to food
Solution: Preservatives are chemicals added to food to check the growth of microorganisms, so the food does not spoil.
Q2 — Food preservation & nitrogen cycle · easy · theory
Which of these chemicals are commonly used as preservatives in jams and squashes?
A. Penicillin and streptomycin
B. Chlamydomonas and Spirogyra
C. Sodium benzoate and sodium metabisulphite ✓ Correct
D. Lactobacillus and yeast
Solution: The chapter names sodium benzoate and sodium metabisulphite as the preservatives used in jams and squashes.
Q3 — Food preservation & nitrogen cycle · easy · theory
Pasteurisation, the process used to preserve milk, was discovered by:
A. Alexander Fleming
B. Edward Jenner
C. Robert Koch
D. Louis Pasteur ✓ Correct
Solution: Louis Pasteur discovered pasteurisation (he also discovered fermentation).
Q4 — Food preservation & nitrogen cycle · easy · theory
About what fraction of the atmosphere is nitrogen gas?
A. 78% ✓ Correct
B. 21%
C. 0.03%
D. 50%
Solution: The atmosphere is made up of about 78% nitrogen gas.
Q5 — Food preservation & nitrogen cycle · medium · theory
Sugar is chiefly used as a preservative for which of the following?
A. Meat and fish
B. Jams, jellies and squashes ✓ Correct
C. Pickles of raw mango
D. Idli and dosa batter
Solution: Sugar is used to preserve jams, jellies and squashes.
Q6 — Food preservation & nitrogen cycle · medium · theory
Which foods are traditionally preserved by covering them with common (dry) salt?
A. Bread and cakes
B. Jams and jellies
C. Meat and fish ✓ Correct
D. Milk and cheese
Solution: Common salt is used to preserve meat and fish (as well as amla, raw mangoes and tamarind) by checking bacterial growth.
Q7 — Food preservation & nitrogen cycle · medium · theory
During pasteurisation, milk is treated in which way?
A. Boiled continuously for about 30 minutes
B. Frozen at 0 degrees C for one full hour
C. Heated to about 70 degrees C for 15 to 30 seconds and then suddenly chilled ✓ Correct
D. Mixed with salt and left to dry in the sun
Solution: In pasteurisation the milk is heated to about 70 degrees C for 15 to 30 seconds and then suddenly chilled and stored, which prevents microbial growth.
Q8 — Food preservation & nitrogen cycle · medium · theory
The nitrogen-fixing bacterium Rhizobium is found living in:
A. The root nodules of leguminous plants ✓ Correct
B. The leaves of wheat plants
C. Stagnant water in coolers and tyres
D. The human intestine
Solution: Rhizobium lives symbiotically in the root nodules of leguminous plants and fixes atmospheric nitrogen for them.
Q9 — Food preservation & nitrogen cycle · medium · theory
Pickles are preserved in oil and vinegar because:
A. The oil coats the food and adds helpful vitamins to it
B. Bacteria cannot live in such an environment ✓ Correct
C. Vinegar acts as a strong antibiotic
D. They make the pickle taste sweeter
Solution: Bacteria cannot survive in oil and vinegar, so keeping pickles in them prevents spoilage.
Q10 — Food preservation & nitrogen cycle · medium · theory
Nitrogen is an essential constituent of which group of substances in living things?
A. Only fats and oils
B. Common salt and sugar
C. Plastic and glass
D. Proteins, chlorophyll, nucleic acids and vitamins ✓ Correct
Solution: Nitrogen is an essential part of proteins, chlorophyll, nucleic acids and vitamins.
Q11 — Food preservation & nitrogen cycle · medium · theory
Besides certain bacteria and blue-green algae, atmospheric nitrogen can also be fixed by:
A. Refrigeration
B. Lightning ✓ Correct
C. Sunlight acting alone
D. Houseflies
Solution: Nitrogen from the atmosphere can also be fixed by lightning.
Q12 — Food preservation & nitrogen cycle · hard · theory
What is the main reason food is preserved rather than left to spoil?
A. Microbes on spoilt food only change its colour but stay completely harmless
B. Preserved food supplies extra nitrogen that the body needs
C. Some microbes growing on food produce toxic substances that can cause serious illness ✓ Correct
D. Preservation is done mainly to make the food taste sweeter
Solution: Microbes spoiling food can produce toxic substances that cause food poisoning, so preservation stops their growth.
Q13 — Food preservation & nitrogen cycle · hard · theory
Adding a large amount of sugar helps a jam stay good for a long time because the sugar:
A. Reduces the moisture content, which inhibits the growth of bacteria ✓ Correct
B. Kills bacteria by raising the temperature of the jam
C. Adds sodium benzoate to the food
D. Supplies nitrogen that the bacteria cannot use
Solution: Sugar preserves food by reducing its moisture content, and low moisture inhibits bacterial growth.
Q14 — Food preservation & nitrogen cycle · hard · theory
The percentage of nitrogen in the atmosphere stays roughly constant mainly because:
A. Lightning removes nitrogen permanently from the air
B. Certain bacteria convert some nitrogen compounds back into nitrogen gas that returns to the air ✓ Correct
C. Green plants breathe out nitrogen gas during the night
D. Rhizobium releases nitrogen gas from the root nodules
Solution: Certain (denitrifying) bacteria convert some nitrogen compounds back into nitrogen gas that returns to the atmosphere, balancing fixation so the level stays about constant.
Q15 — Food preservation & nitrogen cycle · hard · theory
Which statement correctly compares refrigeration and boiling as ways of dealing with microbes in food?
A. Both refrigeration and boiling kill all microbes instantly
B. Refrigeration only slows down the growth of microbes, while boiling kills many of them ✓ Correct
C. Refrigeration kills microbes but boiling only slows their growth
D. Neither refrigeration nor boiling has any effect on microbes
Solution: Refrigeration (low temperature) only inhibits or slows microbial growth, whereas boiling actually kills many microbes.