Exchange

• what are stomata?

  Pores, usually found in the lower epidermis of a leaf, through which gases such as oxygen and carbon dioxide diffuse
• during the day stomata is:

  open
• which process(es) occur in the stomata during the day?

  photosynthesis and respiration
• during the night, the stomata is:

  closed
• which process(es) occur in the stomata during the night?

  respiration
• what is transpiration?

  evaporation of water through stomata down a water potential gradient
• factors that increase the rate of transpiration

  -increasing temperatures

  -increasing wind

  -decrease humidity
• what is cohesion?

  a positively charged hydrogen atom of one water molecule is attracted to a negatively charged oxygen atom from another molecule, forming a hydrogen bond
• what is the cohesion-tension theory of water transport in the xylem?

  -loss of water by transpiration decreases the water potential in mesophyll cells

  -this pulls water up the xylem, which puts it under tension

  -inside the column, water molecules adhere to the walls, and are stuck together by hydrogen bonds
• what is a xerophyte?

  plants adapted to survive in habitats with limited water supply
• adaptations of the leaves of xerophyte that help reduce water loss:

  -thick, waxy cuticle

  -stomata in sunken pits

  -leaves which are curled

  -leaves covered in hair
• what does a potometer measure the rate of?

  water uptake
• what are the limitations of using a potometer to measure transpiration?

  -it assumes that all the plant's water will be transpired

  -the plant's roots are removed
• pathway of air into the lungs:

  • trachea
  • bronchi
  • bronchioles
  • alveoli
• describe how we breath in:

  • diaphragm and external intercostal muscles contract
  • this causes the volume of the thorax to increase and the pressure in the thorax to decrease
  • as a result air is forced into the lungs
• describe how we breath out:

  • diaphragm and external intercostal muscles relax
  • this causes the volume of the thorax to decrease and the pressure in the thorax to increase
  • as a result air is forced out of the lungs
• describe the structure of the alveoli:

  tiny air sacs with a one-cell thick layer of epithelial
• describe the structure of capillaries:

  blood vessels with a one cell thick layer of endothelial cells
• how are alveoli adapted for efficient gas exchange?

  • alveolar epithelium is one cell thick which creates a short diffusion pathway for gas exchange
  • the lungs contain a large number of alveoli which provides a large surface area for gas exchange
  • there is a steep concentration gradient for oxygen and carbon dioxide
• How is a steep concentration gradient of oxygen and carbon dioxide maintained between the alveoli and capillaries?

  • there is constant ventilation
  • there is a good blood supply
• structure of the gills:

  • gill arch
  • gill filaments
  • lamellae
• what is the main gas exchange site for fish?

  lamellae
• Which parts of the gill contain blood vessels?

  • gill filaments
  • gill arch
  • lamellae
• In the blood, oxygen concentration is low and carbon dioxide concentration is high.What process, occurring in body tissues, results in these relative concentrations of oxygen and carbon dioxide in the blood?

  respiration
• what adaptations do the gills have for efficient gas exchange?

  • a short diffusion pathway
  • a large surface area
  • counter-current flow
• features of the lamellae to create a short diffusion pathway:

  • a network of capillaries in each lamella which brings blood close to the surface
  • surface of the lamella is made up of just a single layer of flattened cells
• how does a short diffusion pathway help for efficient gas exchange in the gills?

  there is a very short diffusion pathway in the lamellae between the fish's blood and the water
• how is a large surface area achieve in fish gills?

  • the more gill filaments present on the gill arch, the larger the surface area for diffusion
  • the more lamellae present on the gill filament, the larger the surface area for diffusion
• in general, the fish with a higher gill surface area: body mass ratio comes from habitats where the oxygen concentration is...

  low
• what is counter-current flow?

  when two substances flow in opposite directions
• How does counter-current flow enable efficient gas exchange in fish?

  maintains steep concentration gradients for carbon dioxide and oxygen across the lamella
• The insect gas exchange system contains three important structures:

  • spiracles
  • tracheae
  • tracheoles
• what is the function of the spiracles?

  allow air to flow in and out of the insect
• to prevent the tracheae and tracheoles from collapsing, the tubes are supported by spirals of chitin around the outside
• what is the main site of gas exchange in insects?

  tracheae
• In insects, the tracheae branch off into smaller tubes called tracheoles, which extend into the insect’s muscle tissue.
• On the insect’s body surface, tracheae end in tiny openings called spiracles
• what is the fluid at the end of each tracheole called?

  tracheal fluid
• differences between the trachea in a human and the tracheae in an insect:

  • the human trachea has a much bigger diameter and length than an insect tracheae
  • humans have one trachea, insects have many tracheae
  • a human trachea branches into bronchi, an insect trachea branches into tracheoles
  • a human trachea is supported by cartilage, an insect trachea is supported by chitin
• The oxygen concentration in the insect tissues is lower than the oxygen concentration in the air.