3B Gas exchage

• How are gas exchange surfaces adapted to perform their function?

  1. Large surface area
  2. Thin layer of epithelial cells providing a short diffusion pathway across the gas exchange surface
• How do single celled organisms perform gaseous exchange?

  Through diffusion through their cell surface membranes .
• How does a fish perform gaseous exchange

  Through the gills
• What are the structure of gills and how are they adapted for efficient gaseous exchange?

  Each gill is made of lots of thin plates called gill filamentrs which give a large surface area for gaseous exchange. Gill filaments are filled with lamellae which increase the surface area even more and have capillaries which speed up the rate of diffusion between the water and blood as there's a smaller diffusion distance

  
• How does the counter current system work in fish?

  Blood flows through the lamellae in one direction and water flows over them in the opposite direction. The counter current system allows a high concentration of oxygen inside the water to flow next to blood which has a lower concentration gradient meaning a steep concentration gradient can be maintained between the water and blood meaning that more oxygen can diffuse.

  
• Why must it be counter current in fish?

  Because if the water and blood was flowing in the same direction, equilibrium would be reached and no oxygen can diffuse and no steep concentration gradient can be maintained
• Describe gas exchange in plants

  The palisade mesophyll is the site of photosynthesis, where lots of oxygen is produced and carbon dioxide is used up. This creates a concentration gradient. Therefore, oxygen will travel through the air spaces in the spongy mesophyll and diffuse out of the stomata created by guard cells. Carbon dioxide will diffuse in through the stomata.
• Gas exchange in insects involves a tracheal system. What are the 3 key structures called?

  1. Trachea
  2. Tracheoles
  3. Spiracles
• Describe gas exchange in insects


  Terrestrial insects have microscopic air-filled pipes called tracheae which they use for gas exchange. Air moves into the tracheae thorugh pores on the surface called spiracles. Oxygen travels down the concentration gradient towards the cells. The tracheae branch off into smaller tracheoles which have thin permeable walls and go to individual cells. CO2 moves down its conc gradient towards the spiracles to be released into the atmosphere.
• How do insects control water loss?


  Insects close their spiracles using muscles. They also have a waterproof waxy cuticle all over their body and tiny hairs (Pilli) which trap moisture and reduces evaporation
• How do plants limit water loss?


  Keep their stomata open during the day and to allow gaseous exchange. Water enters the guard cells, making them turgid, which opens the stomatal pore. If the plant starts to get dehyrdated, guard cells lose water and become flaccid which closes the pore
• What are the adaptations of xerophytes?


  Sunken stomata to trap water vapour and reducing the conc gradient of water between the leaf and air

  Layer of hairs on the epidermis to trap water vapour around the stomata

  Curled leaves with the stomata inside, protecting them from wind

  Reduced no of stomata

  Thicker waxy waterproof cuticle to reduce evaporation
• What is the structure of the human gas exchange system?


  :

  
• What are the lungs?

  A pair of lobed structure s made up of a series of highly branched tubules called bronchioles which end in tiny sacs called alveoli
• What is the trachea?


  The trachea is a flexible airway that is supported by rings of

  cartilage. The cartilage prevents the trachea collapsing as the

  air pressure inside falls when breathing in. The tracheal walls

  are made up of muscle, lined with ciliated epithelium and

  goblet cells.
• What is the Bronchi?


  The bronchi are two divisions of the trachea, each leading to

  one lung. They are similar in structure to the trachea and, like

  the trachea, they also produce mucus to trap dirt particles and

  have cilia that move the dirt-laden mucus towards the throat. The

  larger bronchi are supported by cartilage, although the amount of

  cartilage is reduced as the bronchi get smaller.
• What are the bronchioles?


  The bronchi are two divisions of the trachea, each leading to

  one lung. They are similar in structure to the trachea and, like

  the trachea, they also produce mucus to trap dirt particles and

  have cilia that move the dirt-laden mucus towards the throat. The

  larger bronchi are supported by cartilage, although the amount of

  cartilage is reduced as the bronchi get smaller.
• What are alveoli?


  The alveoli are minute air-sacs, with a diameter of between

  100 µm and 300 µm, at the end of the bronchioles. Between the

  alveoli there are some collagen and elastic fibres. The alveoli are

  lined with epithelium. The elastic fibres allow the alveoli to stretch

  as they fill with air when breathing in. They then spring back

  during breathing out in order to expel the carbon dioxide-rich air.

  The alveolar membrane is the gas-exchange surface.
• Explain the process of inspiration

  • The external intercostal muscles contract, while the internal

  intercostal muscles relax.

  • The ribs are pulled upwards and outwards, increasing the volume

  of the thorax.

  • The diaphragm muscles contract, causing it to flatten, which also

  increases the volume of the thorax.

  • The increased volume of the thorax results in reduction of pressure

  in the lungs.

  • Atmospheric pressure is now greater than pulmonary pressure, and

  so air is forced into the lungs .
• Explain the process of Expiration


  • The internal intercostal musdes contract, while the external

  intercostal muscles relax.

  • The ribs move downwards and inwards, decreasing the volume of

  the thorax.

  • The diaphragm muscles relax and so it is pushed up again by the

  contents of the abdomen that were compressed during inspiration.

  The volume of the thorax is therefore further decreased.

  • The decreased volwne of th e thorax increases the pressure in the lungs.

  • The pulmonary pressure is now greater than that of the

  atmosphere, and so air is forced out of the lungs
• What is ventillation

  Consists of inspiration and expiration and is controlled by the movements of the diaphragm, internal and external intercostal muscles as well as the ribcage
• Describe the structure of Alveloi structure

  The wall of the alveolus is made from a single layer of thin, flat cells called alveolar epithelium.

  A) Alveolar epithelium

  B) Capillary endothelium

  C) Blood capillary

  
• Gas exchange in the alveoli

  Oxygen diffuses out of the alveoli, across the alveolar epithelium and the capillary endothelium, and into a compound called haemoglobin in the blood. Carbon dioxide diffuses into the alveoli from the blood

  
• What are the factors that affect the rate of diffusion in alveoli?

  A thin exchange surface - Alveolar epithelium is only once cell thick meaning there's a short exchange surface

  A large surface area - Millions of alveoli meaning there's a large surface area for gas exchange

  Steep concentration gradient of oxygen and carbon dioxide between the alveoli and the capillaries which increases the rate of diffusion