Stanford Achievement Science Concepts Flashcards

A student places a metal spoon in a cup of hot soup. After a few minutes, the handle of the spoon becomes warm. Which of the following best explains this phenomenon?

Answer: Heat from the soup is transferred through the spoon by conduction.

Conduction is the transfer of heat through direct contact. The hot soup transfers thermal energy to the spoon's molecules, which then vibrate and transfer that energy along the length of the spoon to the handle.

A scientist is testing the effect of different amounts of fertilizer on the height of tomato plants. Each plant is given the same amount of water and sunlight. What is the independent variable in this experiment?

Answer: The amount of fertilizer used.

The independent variable is the factor that the scientist intentionally changes or manipulates to observe its effect. In this case, the scientist is changing the amount of fertilizer to see how it affects plant height.

In a forest ecosystem, which of the following is an example of a producer?

Answer: An oak tree making its own food using sunlight.

Producers are organisms that create their own food, usually through photosynthesis. An oak tree uses sunlight, water, and carbon dioxide to produce its own energy, making it a producer at the base of the food web.

Which of the following is a primary requirement for the process of photosynthesis to occur?

Answer: Carbon Dioxide

Photosynthesis is the process where plants use sunlight, water, and carbon dioxide to create their own food (glucose) and release oxygen as a byproduct. Therefore, carbon dioxide is a necessary reactant, or input, for the process to begin.

After a rainstorm, a puddle of water on the sidewalk disappears over a few hours on a sunny day. This process is known as:

Answer: Evaporation

Evaporation is the stage of the water cycle where liquid water turns into water vapor (a gas) and rises into the atmosphere. The sun's heat provides the energy for this process to occur, causing the puddle to 'disappear'.

Which of the following is an example of physical weathering?

Answer: Water freezing in the crack of a rock and splitting it apart.

Physical (or mechanical) weathering is the process of breaking down rocks into smaller pieces without changing their chemical composition. When water freezes, it expands, exerting force on the rock and causing it to crack and break apart.