Organisms Exhange Substances With Their Environment (topic 3) Flashcards
Describe the relationship between the size and structure of an organism and
its surface area to volume ratio (SA:V)
Describe the relationship between the size and structure of an organism and
its surface area to volume ratio (SA:V)
● As size increases, SA:V tends to decrease
● More thin / flat / folded / elongated structures increase SA:V
How is SA:V calculated? Use an example
Divide surface area (size length x side width x number of sides) by volume (length x width x depth)
Suggest an advantage of calculating SA:mass for organisms instead of SA:V
Easier / quicker to find / more accurate because irregular shapes
What is metabolic rate? Suggest how it can be measured
● Metabolic rate = amount of energy used up by an organism within a given period of time
● Often measured by oxygen uptake → as used in aerobic respiration to make ATP for energy release
Explain the relationship between SA:V and metabolic rate
As SA:V increases (smaller organisms), metabolic rate increases because:
● Rate of heat loss per unit body mass increases
● So organisms need a higher rate of respiration
● To release enough heat to maintain a constant body temperature ie. replace lost heat
Explain the adaptations that facilitate exchange as SA:V reduces in larger
organisms
- Changes to body shape (eg. long / thin)
● Increases SA:V and overcomes (reduces) long diffusion distance / pathway - Development of systems, such as a specialised surface / organ for gaseous exchange e.g. lungs:
● Increases (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
● Maintain a concentration gradient for diffusion eg. by ventilation / good blood supply
Explain how the body surface of a single-celled organism is adapted for gas
exchange
● Thin, flat shape and large surface area to volume ratio
● Short diffusion distance to all parts of cell → rapid diffusion eg. of O2 / CO2
Describe the tracheal system of an insect
- Spiracles = pores on surface that can open / close to allow diffusion
- Tracheae = large tubes full of air that allow diffusion
- Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
Explain how an insect’s tracheal system is adapted for gas exchange
● Tracheoles have thin walls
○ So short diffusion distance to cells
● High numbers of highly branched tracheoles
○ So short diffusion distance to cells
○ So large surface area
● Tracheae provide tubes full of air
○ So fast diffusion
● Contraction of abdominal muscles (abdominal
pumping) changes pressure in body, causing air to
move in / out
○ Maintains concentration gradient for diffusion
● Fluid in end of tracheoles drawn into tissues by
osmosis during exercise (lactate produced in
anaerobic respiration lowers ψ of cells)
○ Diffusion is faster through air (rather than
fluid) to gas exchange surface
Explain structural and functional compromises in terrestrial insects that
allow efficient gas exchange while limiting water loss
● Thick waxy cuticle / exoskeleton → Increases diffusion distance so less water loss (evaporation)
● Spiracles can open to allow gas exchange AND close to reduce water loss (evaporation)
● Hairs around spiracles → trap moist air, reducing ψ gradient so less water loss (evaporation)
Explain how the gills of fish are adapted for gas exchange
● Gills made of many filaments covered with many lamellae
○ Increase surface area for diffusion
● Thin lamellae wall / epithelium
○ So short diffusion distance between water / blood
● Lamellae have a large number of capillaries
○ Remove O2 and bring CO2 quickly so maintains
concentration gradien
Counter current flow:
- Blood and water flow in opposite directions through/over lamellae
- So oxygen concentration always higher in water (than blood near)
- So maintains a concentration gradient of O2 between water and blood
- For diffusion along whole length of lamella
If parallel flow, equilibrium would be reached so oxygen wouldn’t diffuse into blood along the whole gill plate.
Explain how the leaves of dicotyledonous plants are adapted for gas
exchange
● Many stomata (high density)→ large surface area for gas exchange (when opened by guard cells)
● Spongy mesophyll contains air spaces → large surface area for gases to diffuse through
● Thin → short diffusion distance
Xerophyte
plant adapted to live in very dry conditions eg. Cacti and marram grass
Explain structural and functional compromises in xerophytic plants that
allow efficient gas exchange while limiting water loss
● Thicker waxy cuticle
○ Increases diffusion distance so less evaporation
● Sunken stomata in pits / rolled leaves / hairs
○ ‘Trap’ water vapour / protect stomata from wind
○ So reduced water potential gradient between leaf / air
○ So less evaporation
● Spines / needles
○ Reduces surface area to volume ratio
Describe the gross structure of the human gas exchange system
Lungs
Trachea -> bronchi-> bronchioles-> alveoli (air sacs) and capiallary network
Explain the essential features of the alveolar epithelium that make it
adapted as a surface for gas exchange
● Flattened cells / 1 cell maintains maintains concentration gradient
Describe how gas exchange occurs in the lungs
thick → short diffusion distance
● Folded → large surface area
● Permeable → allows diffusion of O2 / CO2
● Moist → gases can dissolve for diffusion
● Good blood supply from large network of capillaries
Describe how gas exchange occurs in the lungs
● Oxygen diffuses from alveolar air space into blood down its concentration gradient
● Across alveolar epithelium then across capillary endothelium
Explain the importance of ventilation
● Brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
● Maintaining concentration gradients
Explain how humans breathe in and out (ventilation) - inspiration
Inspiration (breathing in)
1. Diaphragm muscles contract → flattens
2. External intercostal muscles contract, internal
intercostal muscles relax (antagonistic)→
ribcage pulled up / out
3. Increasing volume and decreasing pressure
(below atmospheric) in thoracic cavity
4. Air moves into lungs down pressure gradient
Explain how humans breathe in and out (ventilation - expiration
Expiration (breathing out)
1. Diaphragm relaxes → moves upwards
2. External intercostal muscles relax, internal
intercostal muscles may contract → ribcage
moves down / in
3. Decreasing volume and increasing pressure
(above atmospheric) in thoracic cavity
4. Air moves out of lungs down pressure gradient
Suggest why expiration is normally passive at rest
● Internal intercostal muscles do not normally need to contract
● Expiration aided by elastic recoil in alveoli
Suggest how different lung diseases reduce the rate of gas exchange
● Thickened alveolar tissue (eg. fibrosis)→ increases diffusion distance
● Alveolar wall breakdown → reduces surface area
● Reduce lung elasticity → lungs expand / recoil less → reduces concentration gradients of O2 / CO2
Suggest how different lung diseases affect ventilation
● Reduce lung elasticity (eg. fibrosis - build-up of scar tissue)→ lungs expand / recoil less
○ Reducing volume of air in each breath (tidal volume)
○ Reducing maximum volume of air breathed out in one breath (forced vital capacity)
● Narrow airways / reduce airflow in & out of lungs (eg. asthma - inflamed bronchi)
○ Reducing maximum volume of air breathed out in 1 second (forced expiratory volume)
● Reduced rate of gas exchange → increased ventilation rate to compensate for reduced oxygen in blood
