Topic 3 Flashcards
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
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 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
2. 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 0, / co,
Describe the tracheal system of an insect
Spiracles = pores on surface that can open / close to allow diffusion
2. Trachede = large tubes full of air that allow diffusion
3. Tracheoles = smaller branches from trachee, 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 u of cells)
• As fluid is removed, air fills tracheoles
• So rate of diffusion to gas exchange surface increases as diffusion is faster through air
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 y gradient so less water loss (evaporation)
Suggest an advantage of calculating SA:mass for organisms instead of SA:V
Easier / quicker to find / more accurate because irregular shapes
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 O, and bring CO, quickly so maintains concentration gradient
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 O, between water and blood
4. For diffusion along whole length of lamellae
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
Explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss
Xerophyte = plant adapted to live in very dry conditions
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
Explain the essential features of the alveolar epithelium that make it adapted as a surface for gas exchange
• Flattened cells / 1 cell thick → short diffusion distance
Folded → large surface area
Permeable → allows diffusion of 0, / Co,
Moist → gases can dissolve for diffusion
Good blood supply from large network of capillaries → maintains concentration gradient
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 (breathing in)
- Diaphragm muscles contract → flattens
- External intercostal muscles contract, internal intercostal muscles relax (antagonistic) - ribcage pulled up / out
- Increasing volume and decreasing pressure (below atmospheric) in thoracic cavity
- Air moves into lungs down pressure gradient
Expiration (breathing out)
- Diaphragm relaxes → moves upwards
- External intercostal muscles relax, internal intercostal muscles may contract - ribcage moves down / in
- Decreasing volume and increasing pressure (above atmospheric) in thoracic cavity
- 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 0, / CO,
Suggest why people with lung disease experience fatigue
Cells receive less oxygen → rate of aerobic respiration reduced → less ATP made
Suggest how you can analyse and interpret data to the effects of pollution, smoking and other risk factors on the incidence of lung disease
Describe overall trend - eg. positive / negative correlation between risk factor and incidence of disease
• Manipulate data → eg. calculate percentage change
Interpret standard deviations → overlap suggests differences in means are likely to be due to chance
Use statistical tests → identify whether difference / correlation is significant or due to chance
• Correlation coefficient → examining an association between 2 sets of data
• Student’s t test → comparing means of 2 sets of data
Chi-squared test → for categorical data
Explain the difference between correlations and causal relationships
Correlation = change in one variable reflected by a change in another - identified on a scatter diagram
Causation = change in one variable causes a change in another variable
Correlation does not mean causation → may be other factors involved
