Gas exchange, B3.1

• What is gas exchange?

  Absorbing one gas, and releasing another. All living organisms do this. (Not viruses)
• What is one example of gas exchange?

  Redwood trees absorb carbon dioxide for photosynthesis, and release the oxygen that is produced in the process.
• What is another example of gas exchange?

  Humans absorb oxygen for cell respiration and release the carbon dioxide that is produced.
• What is the difference between gas exchange in terrestrial and aquatic organisms?

  Terrestrial organisms exchange gases within the air, while aquatic animals exchange gases within water.
• What is diffusion?


  Diffusion is the basis of gas exchange.

  Diffusion is slow, as molecules move randomly. It occurs due to the random movement of particles, and occurs from a high to low concentration.
• What is the significance of surface area in relation to gas exchange?

  A larger surface area allows for a significantly faster rate of diffusion, and therefore gas exchange, compared to a smaller surface area. This is because a larger surface area provides more spaces for diffusion to happen simultaneously.

  Smaller organisms have a larger SA:V ratio, and larger have a smaller SA:V ratio. So larger organisms need specialised gas exchange tissues adapted for increasing the surface area, to optimise gas exchange.
• What are some examples of specialised gas exchange tissues?

  External gills

  Internal gills

  Lungs

  Leaf spongy mesophyll

  Plant stomata
• What is a gas exchange surface?

  A gas exchange surface is a specialised area within an organism where gases are exchanged between the body and the surrounding environment, typically through the process of diffusion.
• What are the four properties of gas exchange surfaces?

  Permeable

  -So that gases that diffuse across freely

  Large surface area

  -To increase rate of diffusion across surface

  Moist

  -To dissolve gases (covered by a film of moisture in terrestrial organisms)

  Thin

  -Usually a single layer of cells, so that the gases have a short distance to diffuse (increasing rate)
• How are concentration gradients maintained on the cellular level?

  Cellular respiration maintains concentration gradients.

  It continuously uses oxygen, so the oxygen concentration will remain lower inside than outside the cell.

  It continuously releases carbon dioxide, so the carbon dioxide concentration will remain higher inside than outside the cell.

  The concentration gradient is therefore maintained.
• How are concentration gradients maintained on the tissue level?

  Flow of blood maintains concentration gradients.

  Constantly circulating through capillaries, blood maintains a concentration gradient between the blood and the tissue.

  The blood has a low concentration of oxygen, and a high concentration of carbon dioxide, due to aerobic respiration.

  The concentration gradient is therefore maintained.
• How are concentration gradients maintained on the organ level?

  Ventilation maintains concentration gradients.

  Ventilation is the process of actively moving air (in lungs) or water (in gills) over the respiratory surface.

  
  

  In lungs, oxygen moves from high concentration in the alveoli to lower concentration in the blood, and carbon dioxide moves the opposite way. Exhalation and inhalation keeps the oxygen concentration high and the carbon dioxide concentration low in the alveoli, while capillaries maintain a high carbon dioxide concentration.

  In gills, water flows over the gill filaments, which supplied the gills with a high oxygen concentration. Blood in the gill capillaries flows in the opposite direction to water. As the capillaries have higher carbon dioxide concentration, the concentration gradient is maintained.
• What is the respiratory system?

  The respiratory system is a network of organs and tissues that enable gas exchange between the body and the environment.
• What is the upper respiratory tract?

  Nose, mouth, pharynx, larynx, passageway where air is warmed and humidified
• What is the lower respiratory tract?

  Trachea, bronchi, bronchioles

  Series of branching tubes that moves air to and from the alveoli of the lungs.

  Trachea- strong tube that contains cartilage rings to prevent collapse and ensure they remain open. Lined with Cilia to sweep out foreign particles

  Bronchi- tubes connecting the trachea to the lungs

  Bronchioles- smaller branches of the bronchi that branch into alveoli. Smooth muscle fibres within their walls, allowing their width to vary.
• What are the lungs?

  Pair of spongy organs that exchange gases between the blood and the air (carbon dioxide and oxygen)

  All mammals use lungs for gas exchange, even marine mammals.

  Air is drawn through the trachea (windpipe) and to the the left and right bronchi (in the lungs).

  The bronchi branch off, forming bronchioles.

  The bronchioles branch off further, into alveolar ducts.

  The alveolar ducts branch further into alveoli.
• What are the respiratory muscles?

  Diaphragm- partition between chest and abdominal cavity

  Intercostals- antagonistic muscles between the rib bones

  - Contract and relax to facilitate breathing
• What are alveoli?


  A pulmonary alveolus has a diameter of 0.2mm to 0.5 mm, with a wall of a single layer of type I pneumocyte cells (0.2 micrometres thick).

  There are about 300 million in a pair of adult lungs.

  Alveoli are surrounded by dense capillary networks. The capillary wall is also one cell layer thick, approximately 0.2 micrometres. The dense network of capillaries that they are surrounded by are known as capillary beds, and the blood flow through a capillary maintains a concentration gradient. It prevents equilibrium from being reached due to the constant flow of blood. They also have a large surface area, due to their round shape and large number of them. This facilitates faster diffusion and gas exchange.

  Some have collagen fibres to strengthen the lung tissue and elastic fibres to help limit inhalation and cause passive exhalation.
• What is a pulmonary surfactant?

  Type II pneumocytes within the alveoli secrete a pulmonary surfactant- a specialised fluid that consists of proteins and phospholipids. The molecules form a monolayer on the surface of the moisture lining on the alveoli, with the hydrophilic tails facing the water and the hydrophobic tails facing the air.

  This reduces surface tension and prevents the water from causing the sides of the alveoli to adhere when air is exhaled from the lungs (expiration), also preventing lung collapse.
• What is ventilation?


  Ventilation is the process of moving air in and out of the lungs. It is essential in maintaining a concentration gradient.

  It occurs through Inspiration (inhalation) and expiration (exhalation)
• What is the relationships between pressure, volume and air movement in and out of the lungs?

  The volume of a fixed amount of gas is inversely proportional to its pressure.

  As the volume of a gas decreases, its pressure increases.

  So, when the chest cavity's volume is lower, its pressure is higher

  Although gas molecules move randomly, the net movement of a gas will be from areas of high pressure to areas of low pressure, due to the higher number of molecules in the high-pressure region.

  This explains the movement of air in and out of the lungs:

  Inspiration- volume of chest cavity increases, causing pressure in the lungs to decrease, drawing air into them.

  Expiration- volume of chest cavity decreases, causing pressure in the lungs to increase, forcing air out of them.
• What occurs during inspiration?

  Diaphragm contracts and moves down, pushing the abdomen out.

  The abdomen is relaxed.

  The external intercostal contracts, pulling the rib cage up and out.

  The internal intercostal is relaxed.

  The volume increases, so pressure decreases in the lungs. Air moves from higher pressures outside the body to lower pressures inside the lungs.
• What occurs during expiration?

  Diaphragm relaxes into an upwards, domed shape

  The abdomen contracts, pushing abdominal organs and the diaphragm upwards- only when expiration is forced!

  The external intercostal is relaxed.

  The internal intercostal contracts, pulling the rib cage up and down.

  The volume decreases, so pressure increases in the lungs. Air moves from a higher pressure inside the lungs to lower pressure outside the body.
• What are the methods of making lung volume measurements?

  Water displacement

  Spirometer
• What are the types of lung volume measurements?

  Ventilation rate

  Tidal volume

  Vital capacity

  Inspiratory reserve volume

  Expiratory reserve volume
• What is a spirometer and a spirogram?

  A spirometer is an apparatus that is used for measuring the volume of air inspired and expired by the lungs. Spirometers can be connected to computers for easy data visualisation- as a spirogram

  A spirogram is a graph that shows the volume and frequency of breaths over time.

  It is a common method of measuring lung function, and is used to aid lung disease diagnosis.
• What is ventilation rate?

  The ventilation rate is the number of inspiration-expiration cycles per minute. The average adult has between 12-20 per minute.

  Ventilation rates are dependent on health, age, sex, height and fitness.
• What is tidal volume?

  The tidal volume is the volume of air moved in and out of the lungs during a normal breath cycle.

  A normal adult tidal volume is approximately 500ml.
• What is vital capacity?

  Vital capacity is the maximum amount of air that a person can exhale from their lungs after taking a maximum breath.

  A normal adult vital capacity is between 3 and 5 litres.
• What is inspiratory reserve volume?

  Inspiratory reserve volume is the amount of air that can be inhaled forcefully after a normal breath.
• What is expiratory reserve volume?

  Expiratory reserve volume is the amount of air that can be exhaled forcefully after a normal breath.
• How is lung capacity measured via water displacement?


  Lung capacity can be measured using water displacement. A container is filled with water, then inverted, as one blows into the tube connected to the container, the same volume of water as the air within their lungs will be displaced.

  This is unsafe to do for extended time periods.
• What is gas exchange in plants?

  Carbon dioxide enters the chloroplasts, while oxygen moves out. This is necessary for photosynthesis.

  Water vapor also moves out of the leaf, during transpiration.
• How is the epidermis adapted?

  Transparent (allows light through for photosynthesis)

  Protective outer layer
• How is the waxy cuticle adapted?

  Wax secreted by the epidermis cells

  Thicker on the upper surfaces of leaves in dry habitats (preventing water loss)

  Reduces water loss

  Prevents desiccation

  Low permeability to gases
• How is the stoma adapted?

  Are pores, not cells

  Allow gas exchange and transpiration
• How are the guard cells adapted?

  Control the opening and closing of stomata

  Close them at night, when no gas exchange is required (no photosynthesis) and under water stress.
• How are the air spaces adapted?

  Maintain concentration gradient

  Facilitate diffusion
• How is the spongy mesophyll adapted?

  Contains air spaces

  Walls have large surface area (for faster diffusion)
• How is the palisade mesophyll adapted?

  Tightly packed with chloroplasts (for photosynthesis)