Adaptions for gas exchange

• What happens when the size of the cell increases?

  when the cell increases in size, diffusion pathways get longer, diffusion from the outer cell surface to the centre is slower.
• what happens if a cell gets too large?

  Diffusion will not meet the cells needs, such as supplying nutrients like oxygen and glucose and waste removed like carbon dioxide and urea.
• how to calculate surface area: volume ratio

  surface area-find area of one side and add all sides up

  volume- length x width x height.
• explain Amoeba's gas exchange

  .extremely large SA:V

  .permeable membrane to allow for diffusion of gasses

  .gas exchange occurs across whole surface

  .specialised gas exchange surfaces not required.

  .Diffusion sufficient enough to meet oxygen requirement needs of the organism.
• explain flatworm gas exchange

  .evolved to have a flattened shape to overcome their increased size problem.

  .This increases SA:V, no cell is far away from the surface, so a short diffusion pathway.

  .exchange gasses directly with the environment via diffusion.

  Diffusion is sufficient enough across the permeable membrane to meet oxygen requirements of the organism.
• explain Earthworm gas exchange

  .Developed tubular shape and restricted to damp environments

  .worms secrete mucus to keep the cells of the body surface moist (allows gasses to dissolve and diffuse)

  .elongated shape provides bigger SA:V than compact organism of similar volume

  .Exchange gasses directly with the environment by diffusion across the moist surface-blood vessels close to the body surface so gasses can diffuse in/out of the blood and then across the cells covering body surface.

  .Blood circulates in the vessels, maintains a concentration gradient for diffusion of oxygen into cells and carbon dioxide out.
• How can respiratory surfaces reach max rate of diffusion?

  -Thin-diffusion pathways short

  -Moist-gasses can dissolve for diffusion

  -Permeable-respiratory gasses can diffuse

  -Large SA:V-relatively greater area for diffusion of gasses
• What are the two holes on the side of an insect?

  the paired holes are called spiracles, and they're on each side of the body. The spiracles lead to a branched system of chitin lined air tubes called tracheae.
• Why can spiracles open and close?

  -Stops water loss- prevents dehydration

  -open to allow gas exchange-oxygen in/CO2 out
• how do insects make sure oxygen is in sufficient supply during periods of activity?

  Movements of the abdomen ventilate the tracheae. Many insects have air sacs off the tracheae to help aid ventilation of the tracheae system.

  Abdomen movements also cause pressure changes, these cause air movements throughout the tracheal system.
• How does gas exchange surface work in insects?


  The tracheae branch repeatedly until they end as very fine, thin walled tracheoles. Oxygen diffuses directly from the end of the tracheoles into the cells, and carbon dioxide out of cells into the tracheoles. Surface of the tracheoles are lined with chitin to allow some flexibility and keeps airways open during body movements.
• what are advantages of the tracheal system?


  1. Oxygen supplied directly to tissues

  2. No respiratory pigment needed

  3. Oxygen diffuses faster in air than blood

  4. Spiracles close to reduce water loss
• what are disadvantages of the tracheal system?

  -Limits the size of the organism

  -In larger organisms, the number and length of tracheal tubes needed would significantly increase the size of the organism's weight/volume, restricting movement.
• What are the problems caused by living in water?


  -Water has a lot less dissolved oxygen than air

  -rate of diffusion is slower in water

  -water is more dense than air so it does not flow as freely.
• what are the features of a cartilaginous fish? (e.g shark)

  -Have a skeleton made of entirely cartilage.

  -nearly all live in sea water

  -just behind head on each side are 5 gill clefts which open at gill slits

  -Water is taken into the mouth and forced through the gill slits when the floor of the buccal cavity is raised

  -Gas exchange involves parallel flow - blood in the capillaries circulate in the same direction as water flowing over the gills
• What are the features of a bony fish? (e.g herring)

  -internal skeleton is made of bone

  - gills are covered with a flap called the operculum

  -Gas exchange involves counter-current flow, blood in the gill capillaries flow in opposite direction as water flowing over the gills.
• head of a bony fish


  4 gills on each side

  
• How does water flow into a fish?

  mouth ( buccal cavity)- opens

  operculum- closes

  floor of buccal cavity-lowers

  volume- increases

  pressure- decreases

  direction of water flow- into buccal cavity
• how does water flow out of a fish?

  mouth (buccal cavity)- closes

  operculum- opens

  buccal floor- raises

  volume- decreases

  pressure- increases

  direction of water flow- out over gills
• structure of gills of bony fish

  each arch has many thin filaments, on these are gill lamellae --> this gives gill filaments large surface area for gas exchange. Blood circulates through lamellae creating a concentration gradient-oxygen diffuses through gill lamellae into capillaries and CO2 diffuses out into water.

  
• what is counter current flow? ( bony fish)

  -blood always meets water at a higher oxygen concentration

  -The gradient for diffusion for oxygen from the water into blood is maintained across the whole length of the gill lamellae

  -so oxygen diffuses into the blood from the water across the whole length gill lamellae

  -counter current flow is more efficient than parallel flow as it results in higher blood oxygen saturation level.

  
• what is parallel flow ( cartilaginous fish)

  -water is taken into the mouth and blood flows through the gill capillaries in the same direction as water

  -gas exchange is very efficient at first due to very steep conc gradient

  -however half way over the gill lamellae, equilibrium is reached and diffusion of oxygen and CO2 is no longer possible.
• what is gas exchange like in amphibian (frogs) larvae (babies)?


  The larvae (tadpoles) live in water and have gills for gas exchange
• what is gas exchange in adult amphibians?


  when inactive (at rest)-diffusion across moist surface (skin)

  when active (e.g mating)-lungs
• describe lung structure of an amphibian


  Lungs have a simple structure with little infolding of the gas exchange tissues
• Rings of cartilage support the trachea, bronchi and bronchioles. Suggest a reason for this cartilage.


  supports all three to prevent airways from collapsing during inspiration when pressure is low
• What are goblet cells?

  produce and secret mucus to trap microorganisms. Cilia will then waft to move the mucus up and out of trachea.
• what are wrong with diseased lung tissue?

  alveoli air sac walls break down, drastically reducing gas exchange surface area.
• how does ventilation of human lungs work? - inspiration (breathing in)


  external intercostal muscles and ribs- muscle contracts moving ribs up and out

  outer pleural membrane- pulled outwards reducing pressure in pleural cavity.

  inner pleural membrane- pulled outwards

  lungs and alveoli- lung surface drawn out, causing alveoli to expand

  pressure in alveoli- lowers atmospheric pressure so air moves in

  diaphragm- contracts + flattens
• how does ventilation of human lungs work? - expiration (breathing out)

  external intercostal muscles and ribs- muscles relax moving ribs down and in

  outer pleural membrane- moves inwards

  inner pleural membrane- moves inwards

  lungs and alveoli- lungs move in, alveoli deflates

  pressure in alveoli- higher than atmospheric pressure so air moves out

  diaphragm- relaxes + moves up
• why are alveoli suitable gas exchange surfaces?

  -large surface area for diffusion of gasses

  -moist-gasses dissolve and diffuse more easily

  -permeable-oxygen and CO2 able to diffuse

  -walls of alveoli one cell thick-short diffusion pathway

  -each alveoli has an extensive capillary network, circulation of blood maintains a gradient for diffusion for 02 and CO2.
• What is surfactant?


  A chemical substance, covering the surface of the alveoli, reduces surface tension and helps keep the alveoli from collapsing when breathing out and prevents them sticking together.
• suggest why cellular demand for oxygen is higher in a mammal compared to a fish of the same size?


  -fish have a lower metabolic rate due to cold blood

  -mammals have a higher body temp than fish

  -mammals have a higher metabolic rate

  -more energy required to support mammal
• what are the adaptations of leaves for gas exchange?

  -Leaf blade is flat and thin-short diffusion pathway

  -Spongy mesophyll layer allows diffusion and circulation of gasses to maintain diffusion gradients.

  -Mesophyll walls are moist to allow diffusing and dissolving of gasses

  -stomata pores allow for gas exchange of O2 and CO2 gases.
• why do plants need both carbon dioxide and oxygen

  -require oxygen to respire to make ATP for energy, so respire day and night

  -in the day the photosynthesise using chloroplasts, which requires carbon dioxide
• What are the adaptations of leaves for photosynthesis?

  -Large SA to absorb as much light as possible

  -Leaves can orientate themselves towards the sunlight

  -Leaves are thin to allow light to penetrate lower layers.

  -Cuticle and epidermis are transparent to allow light to pass to the mesophyll below

  -palisade cells are elongated and densely packed together and contain many chloroplasts

  -chloroplasts can rotate and move within the mesophyll cells to maximise light absorption

  -Intercellular air spaces allow carbon dioxide to diffuse into cells and oxygen and water vapour to diffuse away
• Where in the leaf can the stomata be found?

  Small pores which can be found at the bottom of the lower epidermis of the leaf
• What is the role of the stomata?


  They open to allow for gas exchange in the plant, and control water loss (transpiration) when closed.
• How many guard cells surround each stomata?

  two guard cells!
• What is unusual about guard cells?

  -they are the only epidermal cells that contain chloroplasts

  -they have unevenly thickened cell walls