B11: Gas exchange and respiration

Features:

• large surface area: faster diffusion across the surface

• thin walls: short distance (visible)

• good ventilation with air: diffusion gradient maintained

• good blood supply: maintain high concentration gradient (visible)

Breathing system:

• Ribs: bone that protects internal organs like the lungs

• intercostal muscle: muscles between the rib, controls inhale/exhale movements

• diaphragm: helps change volume of thorax to allow inhaling/exhaling

• trachea: windpipe that connects to lungs

• larynx: voicebox

• bronchi: large tubes, branch off trachea

• bronchioles: smaller tubes connected to alveoli

• alveoli: tiny air sacs where gas exchange takes place

Inhaled vs exhaled air

During gas exchange:

• oxygen enters the blood from alveoli

• CO2 and water vapor leave the blood and into the alveoli

Effects of physical activity on breathing:

• frequency and depth of breathing increases → need more oxygen to respire aerobically

• respiration increases → CO2 in the blood increases (lower blood pH) → brain detects and signals respiratory muscles to increase breaths → helps expel more CO2 from lungs with each breath (deeper breaths increase O2 intake)

Volume and pressure changes in the lungs:

• Diaphragm contracts → increases volume but decreases air pressure

• Diaphragm relaxes → decreases volume but increases air pressure

• Inhalation → intercostal muscles contract

• Exhalation → intercostal muscles relax

Investigating the Differences in Inspired & Expired Air

• When we breathe in, the air is drawn through boiling tube A

• When we breathe out, the air is blown into boiling tube B

• Lime water is clear but becomes cloudy (or milky) when carbon dioxide is bubbled through it

• The lime water in boiling tube A will remain clear, but the limewater in boiling tube B will become cloudy

• This shows us that the percentage of carbon dioxide in exhaled air is higher than in inhaled air

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Uses of energy:

• Muscle contraction

• protein synthesis

• cell division

• growth

• active transport

• generation of nerve impulses

• maintaining body temperature

Aerobic respiration

• the chemical reactions in cells that use oxygen to break down nutrients for energy

  • Glucose + oxygen → carbon dioxide + water

  • C6H12O6 + 6O2 → 6CO2 + 6H2O

Anaerobic respiration

• The chemical reactions in cells that break down nutrient molecules to release energy without using oxygen

  • Incomplete break down of glucose

  • releases a small amount of energy compared to aerobic respiration

• Anaerobic respiration in humans:

  • takes place during rigorous exercise → higher demand for energy

  • produces lactic acid

  • glucose → lactic acid

• Anaerobic respiration in yeast:

  • produces ethanol (alcohol)

  • CO2 produced (gives bear its fizz)

• Oxygen debt in anaerobic respiration

  • Lactic acid builds up in muscles and blood → lowers pH of cells (could cause them to denature) → lactic acid has to be removed

  • lactic acid gets secreted to the blood

    • blood transports it to liver → liver oxidises lactic acid → producing CO2 + H2O

• after rigorous exercise:

  • heavy breathing: O2 needed to remove lactic acid through aerobic respiration

  • increased heart rate: blood pumping to transport lactic acid

  • aerobic respiration of lactic acid in the liver