Health, Nature's Harmony, Earth & Cells: Class 8–9 Science Essentials: 18 MCQs with answers

D · Complete physical, mental, and social well-being

Health is broader than not being sick — it includes physical, mental, and social well-being.

C · Interdependence and cycling of materials

These roles form cycles where each organism depends on others, showing interdependence.

D · Liquid water, protective atmosphere, moderate temperature, diverse habitats

Earth has all four key conditions together, which no other known planet has.

B · Cell → tissue → organ → organ system → organism

Cells are the basic unit; similar cells form tissues, tissues form organs, organs form systems, and systems form the organism.

D · Tissue

A tissue is a group of similar cells with a shared function.

D · Break food into simpler molecules that can be absorbed

The digestive system breaks food down so nutrients can be absorbed into the blood.

D · Inside cells

Respiration is a cellular process — energy is released inside cells.

A · True

Earth is the only known planet that supports life because it has liquid water, a protective atmosphere, moderate temperature, and diverse habitats.

B · Not fully healthy because mental and social well-being are missing

Health requires all three dimensions; physical fitness alone does not make someone fully healthy.

D · Effects ripple outward, disturbing the local web of life

Nature works as an interconnected web; removing one part affects the whole system.

D · Xylem, phloem, parenchyma

Xylem, phloem, and parenchyma are plant tissues; epithelial, muscle, and nervous are animal tissues.

D · Epithelial, muscle, nervous

Epithelial, muscle, and nervous tissues are animal tissues; xylem, phloem, and parenchyma are plant tissues.

C · A layer of mucus continuously protects the inner lining

Mucus forms a protective barrier between the acid and the stomach tissue.

B · Both A and R are true, and R correctly explains A

The combination of conditions in R is exactly why Earth can support life, so R explains A.

B · Ulcers can form as acid damages the stomach lining

Without the mucus barrier, acid directly damages the stomach lining, leading to ulcers.

B · Cells starve because nutrients cannot reach them

Cells need absorbed nutrients; if absorption fails, cells cannot get energy even if food is eaten.

C · The decline in animal species may lead to further stunting of plant growth due to disrupted pollination and seed dispersal.

The correct option highlights the crucial role animals play in pollination and seed dispersal, which are essential for healthy plant growth. Disruption of one species can have cascading effects on the entire ecosystem.

B · The digestive system may be breaking down food but failing to absorb nutrients effectively, resulting in energy-starved cells.

The correct option explains that even with a balanced diet, if the digestive system fails to absorb nutrients properly, the cells do not receive the energy they need, leading to fatigue and weakness.