Junior Secondary Science - Unit 7: Living Things and Air - Comprehensive Notes

Unit 7: Living Things and Air

7.1 Air

  • Air is a mixture of gases:
    • Nitrogen (78%)
    • Oxygen (21%)
    • Carbon dioxide (0.04%)
    • Noble gases (about 0.9%)
    • Water vapor and other gases
  • Tests for specific gases:
    • Oxygen: relights a glowing splint.
    • Carbon dioxide:
      • Turns hydrogencarbonate indicator from red to yellow.
      • Turns limewater from colorless to milky.
    • Water: Turns dry cobalt chloride paper from blue to pink.
    • Nitrogen: No simple test.
  • Properties and uses of gases:
    • Oxygen:
      • Supports burning.
      • Used with fuel gas for cutting and welding metals.
      • Used to help patients with breathing difficulties.
    • Carbon dioxide:
      • Does not support burning.
      • Denser than air.
      • Sublimates at -78 °C.
      • Used in fire extinguishers.
      • Used for stage fog effects.
      • Used to keep frozen foods cold.
    • Nitrogen:
      • Unreactive.
      • Very low boiling point (-196 °C).
      • Used in food packaging.
      • Used in the storage of living cells or tissues.
      • Used to freeze foods rapidly

7.2 Photosynthesis

  • Plants produce their own food through photosynthesis, primarily in their leaves.
  • Green leaf cells contain chloroplasts, which contain chlorophyll that absorbs light energy.
  • Light energy is converted to chemical energy during photosynthesis, converting carbon dioxide and water into glucose, with oxygen as a byproduct.
  • Word equation for photosynthesis:
    • Carbon dioxide + Water --(Light Energy & Chlorophyll)--> Food (Glucose) + Oxygen
  • Chemical equation for photosynthesis:
    • 6CO2 + 6H2O \rightarrow C6H{12}O6 + 6O2
  • Reactants and Products:
    • Reactants: Carbon dioxide and water.
    • Products: Glucose (food) and oxygen.
  • Immediate use or storage of glucose:
    • Glucose can be used immediately for energy or stored as starch.
  • Testing for Starch:
    • Iodine solution turns from brown to blue-black in the presence of starch.
  • Steps for testing starch in a leaf:
    1. Boil the leaf in water: Destroys cell membranes to allow alcohol and iodine to enter.
    2. Put the leaf into hot alcohol: Dissolves chlorophyll for better observation of color change.
    3. Wash the leaf in hot water: Removes remaining alcohol and softens the leaf.
    4. Add iodine solution to the leaf: Tests for starch.
  • Necessary factors for photosynthesis: Light, chlorophyll, carbon dioxide, and water.
  • Destarching plants:
    • Plants must be destarched by placing them in the dark for at least 24 hours before experiments.
  • Control Set-up:
    • A control set-up is identical to the experimental set-up except that the factor under investigation is absent.
  • Soda lime absorbs carbon dioxide.
  • Energy transfer: Light energy is converted to chemical energy in food, which is then transferred from plants to animals through feeding.
  • Food Chains:
    • Feeding relationships are represented by food chains (e.g., grass → rabbit → fox).
  • Producers and Consumers:
    • Plants are the producers; animals are the consumers.
  • Importance of Photosynthesis:
    • Provides energy by converting light to chemical energy.
    • Supplies oxygen.

7.3 Respiration

  • Living things release energy by breaking down food through respiration.
  • Chemical energy is converted to other forms to support body activities.
  • Oxygen is typically needed, and carbon dioxide and water are produced.
  • Word equation of respiration:
    • Food (Glucose) + Oxygen --> Carbon Dioxide + Water
  • Chemical equation of respiration:
    • C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O

7.4 Gas Exchange in Plants

  • Hydrogencarbonate indicator shows different colors based on carbon dioxide levels:
    • Lower than normal: Purple
    • Normal (about 0.04%): Red
    • Higher than normal: Yellow
  • Net gas exchange depends on the rates of photosynthesis and respiration:
    • Under light conditions:
      • Photosynthesis rate > respiration rate.
      • Net uptake of carbon dioxide.
      • Net release of oxygen.
    • Under dark conditions:
      • Only respiration occurs.
      • Net uptake of oxygen.
      • Net release of carbon dioxide.
  • Gas exchange occurs through stomata on leaves.

7.5 Gas Exchange in Animals

  • Comparison of inhaled and exhaled air:
    • Exhaled air contains less oxygen.
    • Exhaled air contains more carbon dioxide.
    • Exhaled air contains more water vapor.
    • Exhaled air has a higher temperature.
  • Main parts of the human breathing system: Nostrils, nasal cavity, trachea, bronchi, bronchioles, air sacs, lungs, diaphragm, intercostal muscle, rib.
  • Path of air flow:
    • Inhalation: Nostrils → Nasal cavity → Trachea → Bronchi → Bronchioles → Air sacs
    • Exhalation: Air sacs → Bronchioles → Bronchi → Trachea → Nasal cavity→ Nostrils
  • Gas exchange occurs at air sacs, which are covered with capillaries.
  • The lungs are protected by the rib cage (ribs, backbone, sternum).
  • Intercostal muscles and diaphragm facilitate breathing.
  • Gas exchange process in air sacs:
    1. Inhaled air enters the air sac.
    2. Oxygen diffuses from the air sac into the blood in capillaries.
    3. Blood carries oxygen to body cells for respiration.
    4. Blood carries carbon dioxide from body cells to the air sac.
    5. Carbon dioxide diffuses from the blood into the air sac.
    6. Carbon dioxide is removed during exhalation.

7.6 Harmful Effects of Smoking

  • Tar and chemicals in cigarette smoke reduce gas exchange efficiency:
    • Tar deposits cover air sac surfaces.
    • Carbon monoxide reduces oxygen-carrying ability.
    • Chemicals break down air sac walls, reducing surface area.
  • Nicotine is addictive.
  • Smoking causes diseases like stroke, lung cancer, and heart diseases.

7.7 Balance of Oxygen and Carbon Dioxide in Nature

  • Respiration and photosynthesis maintain balance:
    • Photosynthesis consumes carbon dioxide and produces oxygen.
    • Respiration consumes oxygen and produces carbon dioxide.
  • Human activities disrupt balance:
    • Burning fossil fuels and deforestation increase carbon dioxide levels.
  • Greenhouse effect:
    • Gases like carbon dioxide trap thermal energy, warming the Earth.
    • These gases are called greenhouse gases.
  • The greenhouse effect and global warming:
    • The greenhouse effect keeps Earth at a suitable temperature.
    • Increased carbon dioxide enhances the greenhouse effect, causing global warming.
  • Consequences of climate change:
    • Loss of habitats in polar regions.
    • Sea-level rise and flooding.
    • Unusual weather patterns (typhoons, heat waves, droughts).
    • Extinction of species unable to adapt.

7.8 Air Quality

  • Major air pollutants: Sulphur dioxide, nitrogen oxides, ozone, carbon monoxide, and suspended particulates.
  • Sources: Burning fossil fuels in power stations, factories, and cars.
  • Effects of pollutants:
    • Eyes: Irritation (sulphur dioxide, nitrogen oxides, ozone).
    • Brain: Dizziness and headaches (carbon monoxide).
    • Breathing system: Irritation, worsened bronchitis and asthma (sulphur dioxide, nitrogen oxides, ozone, particulates).
  • Air Quality Health Index (AQHI): Informs the public about health risks and precautionary measures.
  • Monitoring stations: Measure pollutant levels in different districts.