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• Nitrogen – 78% • Oxygen – 21% • Noble gases (mainly argon) – 0.9% • Water vapour and other gases – 0.07% • Carbon dioxide – 0.03% These components represent the approximate composition of Earth’s atmosphere.

It relights a glowing splint and causes it to burn more brightly. This indicates the presence of oxygen in a sample.

• Turns limewater from colourless to milky • Turns hydrogencarbonate indicator from red to yellow The color change indicates the presence of carbon dioxide.

> 0.0%: Yellow =0.04% Red <0.04% Purple This indicates a high concentration of carbon dioxide.

Turns dry cobalt chloride paper from blue to pink. This indicates the presence of water.

No, there are no simple tests because they are very unreactive. This makes detection challenging.

• Help patients to breathe • Oxygen + Hydrogen burns to cut metal These applications highlight the importance of oxygen in medicine and industry.

• Used in fire extinguishers to put out fire • Solid carbon dioxide (dry ice) produces a fog effect on stage This highlights its use in safety and entertainment.

• Fills food packages to prevent spoilage • Liquid nitrogen (-196ºC) used for storing living cells and tissue This shows its role in food preservation and medical applications.

• Argon: Used to fill light bulbs • Helium: Used to fill balloons and airships • Neon: Used to fill advertising lights These applications demonstrate their utility in various industries.

Carbon dioxide + Water → Glucose + Oxygen This summarizes the process of photosynthesis.

6CO2 + 6H2O → C6H12O6 + 6O2 This shows the molecular transformation during photosynthesis.

to absorb light energy

• Carbon dioxide obtained from the air • Water absorbed from the soil These materials are essential for the photosynthetic process.

Use iodine solution to test for the presence of starch, which changes from brown to blue-black. This indicates that starch has been produced during photosynthesis.

Placing the plant in the dark for at least 48 hours This technique ensures that any detected starch is a result of photosynthesis.

• Chlorophyll • Carbon dioxide • Light • Water Each factor plays a crucial role in the photosynthesis process.

• Helps maintain the balance of oxygen and carbon dioxide • Provides food for living things This illustrates the ecological importance of photosynthesis.

Producer → Consumer → Consumer This shows the flow of energy through an ecosystem.

A process to release energy from food by taking in oxygen to produce energy and carbon dioxide. This occurs in cells and is essential for life.

Glucose + Oxygen → Carbon dioxide + Water This summarizes the process of respiration.

C6H12O6 + 6O2 → 6CO2 + 6H2O This illustrates the molecular transformation during respiration.

• Require oxygen • Produce carbon dioxide Both processes involve energy release.

• Burning is quick, respiration is slow • Burning occurs at high temperatures, respiration occurs at body temperature This highlights the distinct characteristics of the two processes.