MCQ (Solution) - The Invisible Living World: Beyond Our Naked Eye | Science Curiosity Class 8 - New NCERT PDF Download

Answer: Option D
Solution:

• The flask filled with water behaves like a convex lens (thicker in the middle, thinner at edges), bending light rays to converge and thus producing a magnified image of the letters underneath. 
  
  
• This directly connects to the chapter’s explanation that lentil-shaped glass pieces (lenses) make small objects look bigger by refraction.
• Why others are incorrect: 
  A: Absorption reduces brightness, not magnification. 
  B: Air bubbles are incidental and typically distort rather than produce controlled magnification.
  C: Reflection alone does not enlarge images. 

Answer: Option B
Solution:

• Hooke viewed thin slices of cork with a 200–300x microscope and observed a honeycomb-like array of compartments, which he named “cells,” marking the term’s first use in biology.
• This observation was structural, not about living activity in cork (which was dead tissue in his sample).
• Why others are incorrect: 
  A: He did not see live bacteria in cork; Leeuwenhoek later described bacteria. 
  C: Electron microscopes came centuries later. 
  D: The chapter emphasizes both helpful and harmful microbes; Hooke did not make such a sweeping claim.

Answer: Option C
Solution:

• Safranin is a stain that binds to cellular components and increases contrast, allowing structures like the cell wall, cytoplasm, and nucleus to be seen more distinctly under the microscope.
• The protocol then rinses excess stain and adds glycerin for clarity and moisture control.
• Why others are incorrect: A: Staining is for visibility, not sterilization. B: Dehydration is for permanent slides; this is a temporary wet mount. D: Careful lowering of the coverslip minimizes bubbles; stain doesn’t remove them.
  

Answer: Option C
Solution:

• Bacteria possess a nucleoid—DNA not enclosed by a nuclear membrane—unlike plant and animal cells which have a membrane-bound nucleus.
• They may have a cell wall but lack organelles like chloroplasts found in plant cells.
• Why others are incorrect: A: Chloroplasts occur in plant cells, not bacteria. B: All cells have a cell membrane. D: A large central vacuole is characteristic of many plant cells, not bacteria.

Answer: Option A
Solution:

• Onion peel cells (plant) have a cell wall that provides rigidity, support, and compact arrangement; cheek cells (animal) lack a cell wall and are thin/flat for protective lining.
• Both have a nucleus and cytoplasm, but plant cells also show plastids and large vacuoles.
• Why others are incorrect: B: Animal cheek cells lack chloroplasts. C: Plant cells have a membrane-bound nucleus; a nucleoid is bacterial. D: Large vacuoles are a plant cell feature, not animal cheek cells.

Answer: Option B
Solution:

• The chapter states the hierarchy as: Cell → Tissue → Organ → Organ system → Organism, building complexity from basic units to the whole living being.
• This mirrors how similar cells form tissues, tissues combine into organs, organs coordinate in systems.
• Why others are incorrect: A, C, D misorder key steps, breaking the logical progression of biological organization.

Level of Organization

Answer: Option B
Solution:

• Decomposer microbes (bacteria and fungi) break down plant waste into simpler nutrient-rich matter, returning nutrients to the soil and increasing fertility.
• Optimal temperature and moisture accelerate this composting process.
• Why others are incorrect: A: Photosynthesis is done by photosynthetic organisms; composting is decomposition. C: They recycle, not remove all minerals. D: Evaporation alone doesn’t create manure.

Answer: Option D
Solution:

• High osmotic conditions due to salt or sugar inhibit microbial growth by drawing water out of microbial cells, limiting their activity and reproduction.
• This is a traditional preservation strategy referenced in the chapter’s discussion on spoilage resistance.
• Why others are incorrect: 
  A: Light alone isn’t the key factor. 
  B: Daily boiling is not a stated or practical preservation method for pickles/murabbas. 
  C: Chlorophyll is irrelevant to preservation.

Answer: Option B
Solution:

• Yeast respires using sugar, especially in warm conditions, releasing carbon dioxide that forms bubbles, making dough soft and fluffy; a small amount of alcohol is also produced.
• This is the basis of leavening in bread, cakes, and related foods.
• Why others are incorrect: A: Cold inhibits yeast activity; salt doesn’t release oxygen. C: Lactic acid is produced by Lactobacillus (curd/batter), not yeast for rising. D: Glycerin isn’t used here; it is used in slide mounts.

Answer: Option A
Solution:

• Microalgae are photosynthetic and release oxygen, contributing substantially to global oxygen production; examples include Spirulina, Chlorella, and Diatoms.
• They are used as supplements, in water cleaning, and biofuel production; conserving them supports environmental balance.
• Why others are incorrect: B: They are plant-like and often autotrophic. C: They can also live in soil, air, and on trees. D: Many are beneficial and nutritionally valuable.

Answer: Option B
Solution:

• Lactobacillus ferments lactose to lactic acid, curdling milk and imparting sourness; it thrives in warm conditions.
• Other examples: Rhizobium fixes nitrogen in legume root nodules; yeast leavens dough; fungi/bacteria decompose wastes; Spirulina is a nutritious microalga “superfood.”
• Why others are incorrect: A: Rhizobium is beneficial nitrogen fixer. C: Yeast is a fungus used in leavening/fermentation, not nitrogen fixation. D: Spirulina is used for nutrition, not primarily as a decomposer.

Answer: Option A
Solution:

• Within an optimal range, higher temperature increases yeast enzyme activity and fermentation rate, producing more CO₂ that gets trapped in the dough network.
• This principle of “optimal temperature” is common to microbial growth discussed across activities.
• Why others are incorrect: B: Denaturation reduces activity; beyond optimum, yeast activity declines. C: Sugar doesn’t become oxygen. D: Evaporation doesn’t generate fermentation bubbles.

Answer: Option C
Solution:

• The chapter outlines the hierarchy from cells to tissues to organs to organ systems to organism, emphasizing specialization and cooperation in multicellular life.
• Unicellular organisms (e.g., bacteria, protozoa) do perform all life functions within one cell; multicellular organisms distribute functions across specialized cell types.
• Why others are incorrect: A: Plants are cellular. B: Unicellular microbes contradict this claim. D: Bacteria lack chloroplasts and a membrane-bound nucleus.