7th Grade Science (Life Science) practice questions and exam guide

Weather:

1. Short-term atmospheric conditions (temperature, humidity, precipitation) at a place
2. Long-term
3. Same as climate
4. Random

Answer: A — Short-term atmospheric conditions (temperature, humidity, precipitation) at a place

A) Definition. B) Climate. C/D) Each is incorrect.

Pollution types:

1. Air, water, soil, light, noise — each affects ecosystems
2. Just air
3. Random
4. No pollution

Answer: A — Air, water, soil, light, noise — each affects ecosystems

A) Standard. B/C/D) Each is incomplete.

Which is an example of commensalism?

1. A shark and a remora fish, where the remora eats scraps without harming the shark
2. Bees pollinating flowers
3. A tapeworm living in a dog's intestines
4. Two deer competing for the same food

Answer: A — A shark and a remora fish, where the remora eats scraps without harming the shark

Commensalism: one benefits (+), one is unaffected (0). The remora benefits from food scraps; the shark is neither helped nor hurt. (B) mutualism: both benefit; (C) parasitism: one harmed; (D) competition: both potentially lose.

A student writes: 'My trait is determined entirely by my genes.' The MOST accurate correction is:

1. Correct — genes alone control all traits
2. Traits are influenced by genes AND environment; phenotype = genotype + environmental factors
3. Only the environment matters; genes do nothing
4. Genes determine eye color but not other traits

Answer: B — Traits are influenced by genes AND environment; phenotype = genotype + environmental factors

B) The genes-determine-everything view is a common misconception. A/C) opposite extremes; D) overly narrow.

The WAVELENGTH of a wave is:

1. The distance from one crest to the next crest (or trough to trough)
2. The wave's energy
3. The number of cycles per second
4. The wave's loudness

Answer: A — The distance from one crest to the next crest (or trough to trough)

A) Length of one full cycle. B/C/D) different properties.

Which human activity has the LARGEST direct impact on the carbon cycle?

1. Reading books
2. Burning fossil fuels (coal, oil, gas)
3. Sleeping
4. Brushing teeth

Answer: B — Burning fossil fuels (coal, oil, gas)

B) Combustion releases stored geological carbon into the atmosphere. A/C/D) negligible direct impact.

Compared with a gas at LOW temperature, a gas at HIGH temperature has, on average:

1. Slower molecules
2. Faster molecules with higher kinetic energy
3. The same molecular speeds
4. Stationary molecules

Answer: B — Faster molecules with higher kinetic energy

B) Higher T → higher average KE → higher molecular speeds. A/C/D) wrong.

Asexual reproduction is best characterized by:

1. Two parents contributing genes
2. Egg + sperm fertilization
3. One parent producing offspring genetically identical to itself (e.g., binary fission, budding)
4. Random genetic mutation only

Answer: C — One parent producing offspring genetically identical to itself (e.g., binary fission, budding)

C) Single-parent cloning is the definition. A/B) Sexual reproduction. D) Mutations occur but aren't reproduction.

A species best adapted to its environment will tend to:

1. Disappear quickly
2. Reproduce less than others
3. Survive and reproduce more, passing favorable traits to offspring
4. Lose its variation entirely

Answer: C — Survive and reproduce more, passing favorable traits to offspring

C) Differential reproduction is selection's outcome. A/B) Opposite. D) Selection acts on existing variation, doesn't eliminate it.

Decomposers role:

1. Break down dead organisms, return nutrients to soil — bacteria, fungi
2. Only producers
3. Random
4. Have no role

Answer: A — Break down dead organisms, return nutrients to soil — bacteria, fungi

A) Standard. B/C/D) Each is incorrect.

Mitochondria are most directly involved in:

1. Photosynthesis
2. Storing genetic information
3. Protein synthesis
4. Cellular respiration — making ATP from glucose using oxygen

Answer: D — Cellular respiration — making ATP from glucose using oxygen

D) Powerhouse role. A) chloroplasts; C) ribosomes; B) nucleus.

Comparing forelimbs of humans, whales, bats, and cats reveals similar bone structures (humerus, radius, ulna). This is evidence of:

1. Coincidence
2. Common ancestry — homologous structures
3. Convergent evolution only
4. Parents teaching skeletons to their kids

Answer: B — Common ancestry — homologous structures

B) Same underlying skeletal pattern indicates a shared ancestor. A/C) misses homology; D) absurd.

Who discovered cells?

Robert Hooke (1665) — observed cells in cork. Anton van Leeuwenhoek first saw living cells.

Worked example — From a wave diagram: amplitude reads 4 cm, wavelength 2 m, and the source produces 5 complete waves per second. Find amplitude, wavelength, and frequency.

Step 1 — Amplitude = maximum displacement from rest. Read from the diagram: A = 4 cm = 0.04 m. Step 2 — Wavelength (λ) = distance from one crest to the next. Given: λ = 2 m. Step 3 — Frequency (f) = number of complete cycles per second = 5 Hz. (Optional speed: v = f × λ = 5 Hz × 2 m = 10 m/s.) Final: A = 0.04 m, λ = 2 m, f = 5 Hz.

What is an 'ecosystem'?

A community of living things + their non-living environment, interacting together.

What is 'cytoplasm'?

Jelly-like fluid filling the cell where organelles float.

Worked example — Two identical sealed bottles each hold the same gas at the same volume. Bottle A is at 10 °C; bottle B is at 200 °C. Compare the average speed of gas molecules and the pressure on the walls.

Step 1 — Temperature is the average kinetic energy per molecule. Higher T ⇒ higher average KE ⇒ higher average molecular speed. Step 2 — Bottle B (200 °C) molecules move faster than bottle A (10 °C) molecules. Step 3 — Faster molecules collide with the walls more often AND harder, so the pressure in bottle B is higher than in bottle A. Final: Bottle B has faster molecules and higher pressure than bottle A.

Where does photosynthesis happen?

Mostly in plant leaves, in chloroplasts (which contain chlorophyll).