Science Exam - Grade 9 T4

EARTH'S SPHERES

geosphere

All of Earth’s rock, including the core, crust, and mantle.

hydrosphere

All of Earth’s water, like lakes, rivers, oceans, rain, and snow.

biosphere

All living things on Earth, including animals, plants, and humans.

atmosphere

All gases around Earth, such as oxygen, nitrogen, water vapour, and wind.

Interaction of spheres

They constantly exchange matter and energy — for example, plants (biosphere) take in CO_2 (atmosphere) and grow in soil (geosphere) using water (hydrosphere).

CARBON CYCLE

carbon cycle

The movement of carbon through Earth’s spheres — biosphere, atmosphere, hydrosphere, and geosphere.

Importance of Carbon

Carbon is a key element in all living things and helps store and release energy.

Carbon source

Anything that releases more carbon into the atmosphere than it absorbs.

Examples of carbon sources

Burning fossil fuels, respiration, volcanic eruptions, and decomposition.

How is carbon stored in Earth's spheres?

Atmosphere: carbon dioxide gas

Hydrosphere: dissolved carbon in oceans

Geosphere: carbon in fossil fuels and rocks

Biosphere: carbon in plants and animals

Role of photosynthesis in the carbon cycle

Plants take in CO_2 from the atmosphere and use sunlight to make glucose and oxygen.

Role of respiration in the carbon cycle?

Animals and plants release CO_2 back into the atmosphere by breaking down glucose for energy.

Decomposition contribution to the carbon cycle

Dead plants and animals release carbon into soil or the atmosphere.

Oceans contribution to the carbon cycle

Oceans take in CO_2 from the atmosphere.

How do photosynthesis and respiration work together in the carbon cycle?

They move carbon between the biosphere and atmosphere, keeping the carbon cycle balanced.

Carbon cycle importance

Carbon keeps life going, but extra CO_2 from humans can trap too much heat, causing global warming.

GREENHOUSE EFFECT & CLIMATE CHANGE

Greenhouse effect

The process where gases like CO_2 trap heat near Earth’s surface, keeping the planet warm.

Name some greenhouse gases.

Carbon dioxide (CO2), methane (CH4), water vapour, nitrous oxide (N_2O).

Greenhouse effect importance

It keeps Earth warm enough to support life.

Causes of enhanced greenhouse effect

Human activities like burning fossil fuels and deforestation add extra CO_2 to the atmosphere, trapping more heat.

Global warming

The rise in Earth’s average temperature caused by increased greenhouse gases.

Climate change

The long-term changes in temperature, rainfall, and weather patterns caused by global warming.

Connection between global warming and climate change

Global warming causes climate change by heating the planet and altering climate patterns.

How does excess carbon affect the carbon cycle?

It increases CO_2 in the atmosphere, warming the planet and upsetting the natural balance.

COMBUSTION

Combustion

A rapid chemical reaction between a fuel and oxygen that releases heat, light, CO_2, and water.

Write the combustion equation.

Carbon (fuel) + Oxygen
ightarrow Carbon Dioxide + Energy

Common fuels that undergo combustion

Coal, petrol, and natural gas.

Examples of combustion

Cars and planes (transport), gas stoves and heaters (homes), power plants (electricity), and campfires.

How does combustion release CO_2?

Burning carbon-based fuels reacts with oxygen, forming carbon dioxide gas.

Consequences of increased CO_2

Global warming, ocean acidification, melting ice caps, rising sea levels, and loss of biodiversity.

CULTURAL BURNING / FIRESTICK FARMING

Cultural burning

A traditional Indigenous practice of using small, controlled fires to manage and care for the land.

How does cultural burning work?

Cool, slow fires clear dry grass and undergrowth without harming large trees, improving soil and habitats.

Timing importance of cultural burning

Different seasons produce different results — Indigenous knowledge guides when and where to burn.

Environmental advantages of cultural burning

Reduces large wildfires, improves soil quality, promotes biodiversity, and reduces greenhouse gas emissions.

Social benefits of cultural burning

Connects Indigenous people to Country, passes down knowledge, and strengthens community relationships.

firestick farming compared to modern fire management

Firestick farming: small, regular, low-intensity fires that encourage biodiversity

Modern fire managment: A fire safety and land management approach that uses prescribed burns, fuel reduction, and community planning to prevent unwanted fires.

Why do some plants and animals need fire?

Some native plants need fire to release seeds or regrow, and animals depend on new growth for food and shelter.

Why is cultural burning important for climate change?

It prevents massive wildfires, reducing CO_2 emissions and helping the land store more carbon.

CARBON CAPTURE

Carbon capture

A way to reduce CO_2 in the atmosphere to help slow climate change.

Natural methods of carbon capture

Trees, soil, and oceans absorb carbon.

human-made methods of carbon capture

Technologies capture CO_2 from power plants or directly from the air and store it underground or use it in industry.

Why does carbon capture matter?

Less CO_2 in the air helps reduce global warming, protects ecosystems, and keeps the carbon cycle balanced.

carbon sink

Carbon sinks are natural or artificial reservoirs that absorb more carbon dioxide from the atmosphere than they release.

How do forests act as carbon sinks?

Trees and plants absorb carbon dioxide through photosynthesis, storing the carbon in their wood, leaves, and roots.

How do oceans act as carbon sinks?

Oceans absorb about 30\% of the carbon dioxide released into the atmosphere through physical and biological processes.

How does soil act as a carbon sink?

Soil stores carbon through the decomposition of organic matter.

What are Blue-Carbon ecosystems?

Coastal ecosystems like mangroves, salt marshes, and seagrasses that are highly effective at storing carbon.

What are artificial carbon sinks using carbon capture technologies?

Man-made technologies that capture carbon dioxide from the atmosphere or industrial sources and store it underground or in other secure locations.

What are artificial carbon sinks using reforestation and afforestation projects?

Planting new trees and restoring forests to create new natural carbon sinks.

Why are carbon sinks important?

They help balance the carbon cycle, mitigate climate change by reducing greenhouse gases, protect ecosystems, and are vital for climate regulation.