Science 7 Hardest Questions All Units

1. A food chain has 4 consumer levels. If producers capture 10,000 units of energy, how much energy reaches the tertiary consumer?

100 units

10 units

1 unit

1,000 units

In a food chain, energy transfer between levels is inefficient, typically following the 10% rule, where only about 10% of the energy from one trophic level is passed to the next. Starting with 10,000 units of energy captured by producers, the primary consumers would receive 1,000 units (10% of 10,000). Secondary consumers would then receive 100 units (10% of 1,000), and finally, tertiary consumers would only get 10 units (10% of 100). Thus, the energy that reaches the tertiary consumer is 10 units.

Explanation

In a food chain, energy transfer between levels is inefficient, typically following the 10% rule, where only about 10% of the energy from one trophic level is passed to the next. Starting with 10,000 units of energy captured by producers, the primary consumers would receive 1,000 units (10% of 10,000). Secondary consumers would then receive 100 units (10% of 1,000), and finally, tertiary consumers would only get 10 units (10% of 100). Thus, the energy that reaches the tertiary consumer is 10 units.

2. A plant is placed in a solution where the water concentration outside the root cells is LOWER than inside. Which direction will water move, and what process causes this?

Water moves into the root via diffusion

Water moves out of the root via osmosis

Water moves into the root via active transport

Water moves out of the root via transpiration

When a plant root is placed in a solution with lower water concentration outside than inside, water moves out of the root cells. This movement occurs through osmosis, a passive process where water molecules move from an area of higher concentration (inside the root) to an area of lower concentration (outside the root) across a semipermeable membrane. The goal of this process is to equalize the water concentration on both sides of the membrane, resulting in water loss from the root cells.

Explanation

When a plant root is placed in a solution with lower water concentration outside than inside, water moves out of the root cells. This movement occurs through osmosis, a passive process where water molecules move from an area of higher concentration (inside the root) to an area of lower concentration (outside the root) across a semipermeable membrane. The goal of this process is to equalize the water concentration on both sides of the membrane, resulting in water loss from the root cells.

3. A bimetallic strip in a thermostat bends when heated. Which heat transfer principle and structural concept BEST explains why this controls a heating system?

Radiation causes the strip to emit infrared waves that trigger the furnace

Thermal expansion causes the strip to bend and open or close an electrical switch

Convection moves hot air across the strip, increasing its kinetic energy permanently

Conduction transfers heat to the furnace directly through the strip

A bimetallic strip consists of two different metals bonded together, each with distinct thermal expansion coefficients. When the temperature rises, one metal expands more than the other, causing the strip to bend. This bending action can either open or close an electrical switch, thereby controlling the heating system. This principle of thermal expansion is fundamental in regulating temperature, as it allows the thermostat to respond effectively to changes in heat, ensuring that the heating system operates within desired limits.

Explanation

A bimetallic strip consists of two different metals bonded together, each with distinct thermal expansion coefficients. When the temperature rises, one metal expands more than the other, causing the strip to bend. This bending action can either open or close an electrical switch, thereby controlling the heating system. This principle of thermal expansion is fundamental in regulating temperature, as it allows the thermostat to respond effectively to changes in heat, ensuring that the heating system operates within desired limits.

4. A bridge beam bends downward under a heavy load. Which combination of internal forces is acting on the beam at the same time?

Tension on top, compression on bottom

Shear on top, tension on bottom

Compression on top, tension on bottom

Compression on both top and bottom equally

When a bridge beam bends downward under a heavy load, the top section of the beam experiences compression due to the downward force, while the bottom section undergoes tension as it stretches to accommodate the bending. This combination of internal forces allows the beam to maintain structural integrity while supporting the load, with the top fibers being pushed together and the bottom fibers being pulled apart. This behavior is characteristic of materials under bending stress.

Explanation

When a bridge beam bends downward under a heavy load, the top section of the beam experiences compression due to the downward force, while the bottom section undergoes tension as it stretches to accommodate the bending. This combination of internal forces allows the beam to maintain structural integrity while supporting the load, with the top fibers being pushed together and the bottom fibers being pulled apart. This behavior is characteristic of materials under bending stress.

5. An earthquake measures magnitude 6 on the Richter scale. How many times stronger is it than a magnitude 4 earthquake?

2 times stronger

10 times stronger

20 times stronger

100 times stronger

The Richter scale is logarithmic, meaning each whole number increase on the scale represents a tenfold increase in measured amplitude and approximately 31.6 times more energy release. Therefore, a magnitude 6 earthquake is 10 times stronger in amplitude than a magnitude 5 earthquake, and since a magnitude 4 earthquake is two steps lower, the difference is 10 x 10 = 100 times stronger in terms of energy release. This exponential nature of the scale explains why a magnitude 6 earthquake is significantly more powerful than a magnitude 4 earthquake.

Explanation

The Richter scale is logarithmic, meaning each whole number increase on the scale represents a tenfold increase in measured amplitude and approximately 31.6 times more energy release. Therefore, a magnitude 6 earthquake is 10 times stronger in amplitude than a magnitude 5 earthquake, and since a magnitude 4 earthquake is two steps lower, the difference is 10 x 10 = 100 times stronger in terms of energy release. This exponential nature of the scale explains why a magnitude 6 earthquake is significantly more powerful than a magnitude 4 earthquake.

6. Which sequence correctly describes how a sedimentary rock could eventually become a metamorphic rock and then return to sedimentary rock?

Heat + pressure → metamorphic → cooling → sedimentary

Heat + pressure → metamorphic → weathering, erosion, compaction → sedimentary

Melting → igneous → heat + pressure → sedimentary

Compaction → sedimentary → cooling → metamorphic

Sedimentary rocks can transform into metamorphic rocks through the application of heat and pressure, which alters their mineral structure and texture. Once metamorphic rocks are exposed to surface conditions, they undergo weathering and erosion, breaking down into smaller particles. These particles can then be transported and eventually compacted together to form new sedimentary rocks, completing the rock cycle. This sequence illustrates the dynamic nature of geological processes and how rocks can transition between different forms over time.

Explanation

Sedimentary rocks can transform into metamorphic rocks through the application of heat and pressure, which alters their mineral structure and texture. Once metamorphic rocks are exposed to surface conditions, they undergo weathering and erosion, breaking down into smaller particles. These particles can then be transported and eventually compacted together to form new sedimentary rocks, completing the rock cycle. This sequence illustrates the dynamic nature of geological processes and how rocks can transition between different forms over time.

7. A farmer grows only corn on a large field year after year and uses chemical fertilizers to boost yield. Which combination of problems is MOST likely to result?

High biodiversity, improved soil health, and reduced pest resistance

Low biodiversity, soil damage from excess fertilizer, and increased pest resistance

Monoculture benefits soil through crop rotation and reduces unintended consequences

Biological control naturally balances pests, making fertilizers unnecessary

Growing only corn year after year leads to low biodiversity as the same crop depletes specific nutrients from the soil, reducing its health. The continuous use of chemical fertilizers can cause soil degradation and damage its structure, making it less fertile over time. Additionally, a monoculture environment can create conditions that favor certain pests, leading to increased pest resistance as they adapt to the chemical treatments used, ultimately resulting in a cycle of dependency on more chemicals to control them.

Explanation

Growing only corn year after year leads to low biodiversity as the same crop depletes specific nutrients from the soil, reducing its health. The continuous use of chemical fertilizers can cause soil degradation and damage its structure, making it less fertile over time. Additionally, a monoculture environment can create conditions that favor certain pests, leading to increased pest resistance as they adapt to the chemical treatments used, ultimately resulting in a cycle of dependency on more chemicals to control them.

8. Two oceanic tectonic plates collide. Which sequence of events BEST describes what happens next?

Both plates fold upward forming mountains at a divergent boundary

The denser oceanic plate subducts under the other, potentially forming a volcanic arc

The plates slide past each other causing transform faults and mountain building

New crust forms between the plates as they move apart at a convergent boundary

When two oceanic tectonic plates collide, the denser plate typically subducts beneath the other due to its greater mass. This subduction process leads to intense geological activity, including the formation of a trench and volcanic arcs on the overriding plate. As the subducted plate melts and interacts with the mantle, magma rises to the surface, creating volcanoes. This sequence of events is a key characteristic of convergent plate boundaries, where one plate is forced down into the mantle, resulting in significant geological features and phenomena.

Explanation

When two oceanic tectonic plates collide, the denser plate typically subducts beneath the other due to its greater mass. This subduction process leads to intense geological activity, including the formation of a trench and volcanic arcs on the overriding plate. As the subducted plate melts and interacts with the mantle, magma rises to the surface, creating volcanoes. This sequence of events is a key characteristic of convergent plate boundaries, where one plate is forced down into the mantle, resulting in significant geological features and phenomena.