7. Living Things and Air

7. Living Things and Air

• Air is a mixture of gases, including nitrogen (78%), oxygen (21%), noble gases (0.9%), water vapor (0.07%), and carbon dioxide (0.03%).
• The layer of air surrounding Earth is the atmosphere.
• Testing for oxygen: a glowing splint will relight in the presence of oxygen, and a burning splint will burn more brightly.
• Testing for carbon dioxide: Carbon dioxide turns a hydrogencarbonate indicator from red to yellow, and it turns limewater from colorless to milky.
• Testing for water vapor and nitrogen/noble gases: both turn dry cobalt chloride paper from blue to pink. There are no simple tests for nitrogen and noble gases. They are unreactive.

Daily Applications of Gases in Air

• Oxygen: used in breathing difficulties, mixes with gas fuel for cutting metals.
• Carbon Dioxide: used in fire extinguishers, dry ice is solid carbon dioxide that produces a fog effect.
• Nitrogen: used to fill food packages to prevent food from going bad, and liquid nitrogen is used to store living cells and tissues.
• Noble Gases: Argon is used to fill light bulbs, helium fills balloons and airships, and neon fills advertising lights.

7.2 Photosynthesis

• Plants make their own food through photosynthesis.
• Raw materials: water (from soil) and carbon dioxide (from air). Energy source: light energy. Chlorophyll absorbs light energy.
• Process: light energy is converted to chemical energy, which is used to make glucose, the food for the plant. Glucose can be stored as starch for later use.
• By-product: oxygen (released into the air).
• Word equation: carbon dioxide + water → glucose + oxygen.
• Chemical equation: 6CO2 + 6H2O → C6H12O6 + 6O2
• Testing for starch in leaves: place a leaf in boiling water to destroy cell membranes, then place it in hot alcohol to remove chloroplasts, and then wash the leaf in hot water, finally add iodine solution to the leaf. This will turn blue-black if starch is present.

7.3 Respiration

• Food is the energy source for all living things.
• Chemical energy in the food is converted, through a process called respiration, into useful forms of energy in the body.
• Respiration occurs in body cells.
• Glucose and oxygen are used in respiration.
• Products: carbon dioxide and water, energy is released.
• Word Equation: glucose + oxygen → carbon dioxide + water + energy
• Chemical Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

7.4 Gas Exchange in Plants and Animals

• Photosynthesis and respiration involve gas exchange in both plants and animals.
• During the day, plants take in carbon dioxide and release oxygen (photosynthesis rate is higher than respiration rate).
• At night, only respiration occurs (plants take in oxygen and release carbon dioxide).
• Stomata (microscopic pores) in leaves control gas exchange in plants.
• Animals (including humans) exchange gases through their respiratory systems (lungs in mammals).

7.5 Balance of Carbon Dioxide and Oxygen in Nature

• Photosynthesis and respiration maintain the balance of carbon dioxide and oxygen in nature.
• Human activities (e.g., burning fossil fuels) can disrupt this balance.
• Greenhouse gases (e.g., carbon dioxide) trap heat from the sun, causing global warming, which can lead to several potential harmful effects like melting ice in polar regions, flooding in low-lying areas, and changes in weather patterns.

7.6 Air Quality

• Burning fossil fuels and industrial processes release harmful air pollutants.
• Examples of harmful air pollutants and their effects: carbon monoxide (reduces oxygen content in blood), sulfur dioxide (irritates respiratory system), hydrogen oxide (irritates respiratory system), and suspended particulates (cause respiratory diseases).
• Air quality is measured using the Air Quality Health Index (AQHI). Higher AQHI scores indicate poorer air quality.