Science 8 Notes: Water Cycle, Gas Cycles, and Nitrogen Cycle

Vocabulary flashcards covering key terms from the notes on the water cycle, gas cycles, and the nitrogen cycle.

Water cycle (hydrological cycle)

The continuous movement of water through the atmosphere, land, and bodies of water, involving processes such as evaporation, transpiration, condensation, precipitation, infiltration, groundwater, and surface runoff.

Evaporation

Water from oceans, lakes, rivers, or soil changes into water vapor due to heat from the sun.

Transpiration

Plants release water vapor from leaves as water moves to the leaves, powered by sunlight.

Condensation

Water vapor cools and turns into tiny droplets, forming clouds; dust helps; can form ice in cold areas.

Precipitation

Water droplets in the atmosphere fall to Earth as rain, snow, hail, or sleet; in the Philippines, rain is common.

Infiltration

Rainwater soaks into the ground and becomes groundwater, stored in aquifers and retrievable by wells.

Groundwater

Water stored underground in soil and rocks.

Aquifer

An underground layer of rock or soil that holds groundwater.

Surface runoff

Excess water that flows over the land to rivers, lakes, or oceans when the ground cannot absorb more water.

Solar energy

The sun’s energy that drives the water cycle by heating water and powering processes like evaporation.

Atmosphere

The layer of gases surrounding Earth, involved in the water cycle and gas exchanges.

Oxygen-Carbon Dioxide Cycle

The cycle of exchanging oxygen and carbon dioxide between plants and animals through photosynthesis and respiration.

Photosynthesis

Plants use sunlight to convert carbon dioxide and water into glucose and oxygen.

Respiration

Organisms take in oxygen and release carbon dioxide as they convert food to energy.

Stomata

Small openings on leaves through which gas exchange (CO2 in, O2 out) occurs and water vapor exits.

Carbon dioxide (CO2)

A gas released by respiration and burning; used by plants in photosynthesis; a greenhouse gas.

Oxygen (O2)

Gas required by animals for respiration and produced by plants during photosynthesis.

Nitrogen cycle

Biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates through air, soil, and water.

Nitrogen gas (N2)

Major component of Earth’s atmosphere; not directly usable by most plants and animals.

Nitrates (NO3-)

A usable form of nitrogen for plants.

Nitrites (NO2-)

An intermediate form in the process of converting nitrogen into nitrates.

Ammonium (NH4+)

A usable form of nitrogen for plants.

Nitrogen fixation

Bacteria in soil or legumes convert nitrogen gas (N2) into ammonium (NH4+).

Assimilation

Plants absorb nitrates and ammonium from the soil to build proteins and grow.

Ammonification

Bacteria break down dead organisms and waste into ammonium.

Nitrification

Bacteria convert ammonium first to nitrites, then to nitrates.

Denitrification

Bacteria convert nitrates back into nitrogen gas, returning it to the atmosphere.

Global warming

Increase in Earth’s average surface temperature due to greenhouse gases like CO2, largely from human activities.

Deforestation

Removal or clearing of forests, reducing CO2 absorption and contributing to higher atmospheric CO2.

Carbon sequestration

Process of capturing and storing carbon dioxide, for example in forests and soils.