Biology, 8: Gas exchange and respiration

• Animals need to exchange gas to supply oxygen for respiration in cells and remove CO2
• Gases are exchanged at the surface by diffusion

  Gas exchange surfaces adapt to maximise rate of diffusion
• How are gas exchange surfaces adapted for diffusion?

  Large surface area

  Short distance to diffuse- thin cells

  Good blood supply

  Good ventilation to deliver more oxygen and remove carbon dioxide more rapidly
• Describe ventilation:

  • When air enters nose, it is moistened and warmed
  • Air passes over larynx, where we make sound
  • Air travels down trachea to the kungs
  • Air enters the lungs through the bronchi
  • Goblet cells secrete mucus, trapping microorganisms and dusts
  • Cilia sweeps mucus to oesophagus where it can be swallowed
  • Alveoli is covered in capillary where gas exchange occurs
  • Movement across this is ventilation
• The alveoli is the site of gas exchange and respiratory surface
• How is the alveoli adapt for diffusion?

  Thin, permeable wall

  Moist lining so gas dissolves before diffusing

  Large surface afea

  High concentration gradient
• The gas exchange in alveoli is a passive process, happens randomly but direction occurs due to concentration gradient
• Inspiration and expiration happens due to change in volume of the thorax

  Change in volume causes pressure changes, and enter to enter or leave the lung
• The ribs surrounding thorax is joined by intercostal muslces

  Internal intercostal muscle and diaphragm works together for lungs to ventilate/breathe
• Below the lungs is the diaphragm

  The diaphragm is a domed sheet of tough tissue, surrounded by muscles attached to the thorax
• In gentle breathing, only the diaphragm ed

  In deep breathing, ribs and intercostal muscles become involved
• When we breathe in, oxygen is taken into the blood

  Carbon dioxide and water vapour exit as we breathe out

  Other gases we breathe in and out are almost unchanged, just warmer
• Carbon dioxide increases in expired air, this is due to

  • Oxygen decreasing, as it is removed by respiring cells
  • Carbon dioxide increases, as it is produced from respiration and diffuses into alveoli
  • Water vapour conc increases, as it evaporates from the moist lining of alveoli into expired air due to warmth of the body
• Rate and depth of breathing increases due to muscles contracting and respiring fasters, making CO2 more rapidly

  CO2 is acidic, and dissolves in water-based solutions (plasma and cytoplasm)

  Change in pH can affect enzymes, therefore CO2 must quickly be removed
• Increase in CO2 is due to increase physical activity detected as blood flows part receptors in brain

  Receptors send impulse to the lungs, causing increase in rate and depth of breathing to remove CO2 as fast as possible
• Tobacco has chemicals that can damage cells

  Chronic obstructive pulmonary disease is a combination of bronchitis, emphysema, lung cancer, and CHD
• Carbon monoxide takes place of haemoglobin, preventing body from absorbing as much oxygen as possible
• Nicotine is addictive, and narrows the blood vessels which increases blood pressure and risk of CHD
• Tar is sticky, and coats trachea, bronchi, and bronchiole

  It leads to cell damage, and a decrease in rate of gas exchange, cancer of the lung/mouth/throat
• Cellular respiration is the release of energy from chemical bonds in food molecules

  It takes place in every living cells that carry out cellular respiration
• In human cells, energy is used for:

  • Contraction of muscle cells
  • New chemical bonds during synthesis of new protein molecules
  • Produce new chemicals needed for cell division for cell growth
  • Active transport of molecules across cell membrane
  • Movement of nerve impulses along nerve cells
  • Maintenance of constant core body temperature
• Glucose is the nutrient molecule broken down in respiration

  If glucose is short in supply, other molecules may be used instead from breakdown of fats or proteins
• Respiration is a series of reaction, controlled by enzymes

  Any changes affecting enzymes will affect respiration
• Aerobic respiration uses oxygen to release energy from glucose in chemical reaction in cells

  Water and carbon dioxide is produced as waste products
• What is the equation for aerobic respiration?

  C6H12O6 + 6O2 -> 6CO2 + 6H2O (+energy)

  Glucose + oxygen -> Carbon dioxide + water
• In aerobic respiration:

  • Oxygen comes from air
  • Carbon dioxide produced is released into the air
  • Water is either used in body or excreted through the kidney
• During aerobic respiration, many chemical bonds in glucose are broken

  This releases a lot of energy for each mole of glucose used
• Anaerobic respiration supplies energy when there is not enough oxygen available for aerobic respiration

  E.g. Diving animals or muscle cells during vigorous exercise
• Anaerobic respiration is often referred to as fermentation

  It releases energy from glucose molecules without ne3 for oxygen
• In anaerobic respiration, glucose molecule is partly broken down, so less energy is released per mole compared to aerobic respiration
• What is the equation for anaerobic respiration in muscle cells equation?

  C6H12O6 -> 2C3H6O3

  Glucose -> lactic acid (+ energy)
• Even when muscle cells are anaerobically respiring, aerobic respiration is also taking place and using available oxygen

  When aerobic respiration cannot supply all the energy needed, additional energy comes from anaerobic respiration
• During anaerobic respiration, concentration of lactic acid builds up in cells and blood

  When expertise is finished and there is sufficient oxygen again, fast heart rate is maintained to transport lactic acid to muscle and liver cells
• Fast breathing continues to supply additional oxygen for breaking down lactic acid

  Lactic acid is converted in muscle and liver cells back to glucose for use in aerobic respiration or to be broken down back into CO2 or H2O
• Oxygen debt is when additional oxygen is ne3ed after exercise

  Need to breathe more deeply is excess post-excercise oxygen consumption
• Yeast can break down glucose without oxygen as well
• What is the equation for anaerobic respiration in yeast cells?

  C6H12O6 -> 2C2H5OH + 2CO2

  Glucose -> Ethanol + carbon dioxide
• Anaerobic respiration in used is utilised when brewing beer and wine

  Ethanol is formed when sugars in barley/grape is broken down
• Yeast is also used in bread making, CO2 released forms bubbles making bread light and spongy