IB 150 EXAM 2025-2026 QUESTIONS
WITH CORRECT ANSWERS
What |is |one |reason |that |organisms |have |to |maintain |homeostasis |(maintaining |a |relatively |
stable |internal |environment |that |differs |from |the |external |environment)? |- |CORRECT |
ANSWER✔✔-Organisms |have |to |perpetually |keep |themselves |out |of |equilibrium |with |the |
environment.
What |can |you |conclude |about |an |organism |that |has |reached |equilibrium |with |its |external |
environment? |- |CORRECT |ANSWER✔✔-The |organism |is |dead.
Which |of |the |cell |shapes |in |the |previous |question |do |you |expect |to |make |up |the |lining |of |your
|respiratory |system. |- |CORRECT |ANSWER✔✔-Sheet
Match |the |following |concepts |to |their |appropriate |relationships |and |functions |with |respect |to |
diffusion: |- |CORRECT |ANSWER✔✔-the |Fick's |Law |equation |→ |models |the |rate |of |diffusion
metabolic |rate |of |organism |→ |determines |(in |part) |P1
each |of |the |four |variables |in |Fick's |Law |→ |affects |the |likelihood |of |respiratory |gas |molecules |
to |move |from |point |A |to |point |B |via |random |motions
Second |Law |of |Thermodynamics |→ |shows |that |the |process |of |diffusion |is |exergonic
surface |area |to |volume |ratio |(SA/V) |→ |explains |the |relationship |between |the |rate |of |supply |to |
the |rate |of |demand |for |respiratory |gases
The |figure |below |shows |the |simplified |diagram |of |the |insect |respiratory |system |that |we |used |
to |model |its |supply |of |oxygen |to |its |cells |via |diffusion.
Why |did |we |have |to |divide |the |entire |length |that |an |oxygen |molecule |has |to |traverse |via |
diffusion |from |the |external |atmosphere |to |inside |the |mitochondria |of |a |body |cell |into |two |
,distances, |and |calculate |the |rate |of |diffusion |separately |for |the |distance |X-Y |and |Y-Z? |- |
CORRECT |ANSWER✔✔-D |differs |for |the |two |distances
In |class, |we |determined |that |the |larger |insect |was |not |able |to |achieve |a |sufficient |rate |of |
diffusion |from |point |X |to |point |Y |in |its |tracheal |satisfy |the |oxygen |demand |of |its |cells |without |
increasing |the |cross-sectional |area |of |its |tracheal |tubes.
The |variables |of |Fick's |Law |that |we |determined |for |our |larger |insect |with |thin |trachea |is |
shown |in |the |table |below:
Assuming |that |the |cells |of |the |insect |require |an |oxygen |supply |of |2.0 |* |10-6 |mL/min |(= |
0.000002), |use |Fick's |Law |to |determine |what |the |cross-sectional |area |(A) |of |this |larger |insect |
has |to |minimally |be |in |µm2 |to |maintain |the |minimal |rate |of |diffusion |of |oxygen |of |2.0 |* |10-6 |
mL/min.
Round |your |answer |to |the |nearest |full |µm2. |- |CORRECT |ANSWER✔✔-110
Amphibians |such |as |frogs |breathe |both |with |their |lungs |and |via |gas |exchange |through |their |
moist |skin. |Which |is |likely |to |be |able |to |derive |a |higher |proportion |(fraction) |of |its |oxygen |
demand |from |gas |exchange |through |their |skin |as |opposed |to |via |its |lungs? |Hint: |consider |
which |concept |you |need |to |consider |to |answer |this |question. |- |CORRECT |ANSWER✔✔-poison |
dart |frog |(one |of |the |smallest |frogs |in |the |world)
Which |concept |did |you |have |to |apply |to |determine |the |answer |to |the |previous |question? |- |
CORRECT |ANSWER✔✔-SA/V
There |are |amphibians |that |are |even |larger |than |bullfrogs. |Which |of |the |following |could |explain
|how |such |a |large |amphibium |could |obtain |a |sufficient |rate |of |diffusion |of |respiratory |gases? |- |
CORRECT |ANSWER✔✔-different |shape |(e.g. |flat |or |ribbon |shaped)
larger |internal |surface |area |of |the |lungs
reduced |metabolic |rate |(reduced |rate |of |cellular |respiration)
Respiratory |surfaces |must |always |stay |moist |(be |covered |by |a |very |thin |film |of |water). |
Diffusion |across |dry |surfaces |is |exceedingly |slow.
,Which |variable |of |Fick's |Law |is |most |likely |responsible |for |this? |- |CORRECT |ANSWER✔✔-D
In |class, |we |oversimplified |the |insect |respiratory |system |a |bit |to |make |our |lives |easier |for |
calculating |Fick's |Law |variables.
For |example, |as |in |any |respiratory |organ, |the |actual |respiratory |surfaces |where |the |tips |of |the |
tracheoles |make |contact |with |individual |cells |of |the |insect |are |moist |and |filled |with |water.
When |the |insect |becomes |active |and |its |muscle |cells |have |a |greater |demand |for |oxygen |as |a |
result, |this |water |gradually |pulls |out |of |the |tracheoles |and |into |the |muscle |cells |again |(see |
figure |above). |What |might |the |benefit |of |this |be |to |the |insect? |- |CORRECT |ANSWER✔✔-
Decreases |the |part |of |the |distance |filled |with |a |medium |that |has |a |lower |diffusion |coefficient |
to |increase |the |diffusion |rate |at |times |of |high |metabolic |demand |for |oxygen.
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Ignoring |surface |area |of |gills, |which |of |the |following |variables |DECREASES |as |a |lugworm |grows |
larger? |- |CORRECT |ANSWER✔✔-SA/V
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Which |variable |does |presence |of |gills |most |affect |in |lugworms? |- |CORRECT |ANSWER✔✔-A
Blue |whales |are |mammals |and |just |like |us |have |lungs |with |alveoli |and |transport |oxygen |in |
blood |via |a |closed |circulatory |system. |However, |in |contrast |to |us, |blue |whales |are |the |biggest |
animals |that |have |ever |lived.
Compared |to |a |human, |the |total |distance |that |oxygen |has |to |diffuse |to |reach |cells |in |blue |
whales |is |blank |, |while |the |distance |of |bulk |flow |for |oxygen |in |blue |whales |is |blank |. |- |
CORRECT |ANSWER✔✔-roughly |the |same,
larger.
, What |is |a |prerequisite |(requirement) |for |counter-current |exchange |to |function? |- |CORRECT |
ANSWER✔✔-unidirectional |flow |of |the |outside |medium |(air |or |water)
bulk |flow |(mass |flow) |of |blood |and |external |medium |(air |or |water)
Mammalian |lungs |with |the |respiratory |surfaces |in |the |shape |of |dead-end |alveoli |require |tidal |
flow |to |ventilate. |Tidal |flow |is |not |conducive |to |counter-current |exchange. |The |next |two |
questions |ask |you |to |explore |why |not.
When |asked |to |demonstrate |why |something |cannot |work, |an |effective |strategy |is |to |model |
the |ineffective |set-up |and |explore |what |the |consequences |would |be. |Below |is |a |diagram |of |
what |our |alveoli |might |look |like, |if |they |were |set-up |to |enable |counter-current |flow |during |
inhalation:
First, |identify |the |concentration |gradient |for |both |inhalation |and |for |exhalation |in |the |
hypothetical |alveoli |above |that |are |plumbed |for |counter-current |exchange |during |inhalation. |- |
CORRECT |ANSWER✔✔-blood |during |exhalation |→ |Phigh
blood |during |inhalation |→ |Plow
air |during |exhalation |→ |Plow
air |during |inhalation |→ |Phigh
Based |on |your |answer |to |the |previous |question, |what |problem |prevents |mammalian |lungs |
from |engaging |in |counter-current |design?
If |mammalian |alveoli |had |respiratory |capillaries |directed |to |engage |in |counter-current |
exchange |during |inhalation |... |- |CORRECT |ANSWER✔✔-the |concentration |gradient |would |
reverse |during |exhalation |and |cause |diffusion |of |oxygen |from |blood |to |the |air.
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Lugworms |create |a |unidirectional |water |current |that |runs |through |their |U-shaped |burrows. |
Why |does |this |allow |lugworms |to |establish |a |countercurrent |oxygen |exchange |in |their |gills? |- |
CORRECT |ANSWER✔✔-Capillaries |in |gills |can |be |consistently |directed |to |run |blood |in |the |
opposite |direction |as |external |water |flow
WITH CORRECT ANSWERS
What |is |one |reason |that |organisms |have |to |maintain |homeostasis |(maintaining |a |relatively |
stable |internal |environment |that |differs |from |the |external |environment)? |- |CORRECT |
ANSWER✔✔-Organisms |have |to |perpetually |keep |themselves |out |of |equilibrium |with |the |
environment.
What |can |you |conclude |about |an |organism |that |has |reached |equilibrium |with |its |external |
environment? |- |CORRECT |ANSWER✔✔-The |organism |is |dead.
Which |of |the |cell |shapes |in |the |previous |question |do |you |expect |to |make |up |the |lining |of |your
|respiratory |system. |- |CORRECT |ANSWER✔✔-Sheet
Match |the |following |concepts |to |their |appropriate |relationships |and |functions |with |respect |to |
diffusion: |- |CORRECT |ANSWER✔✔-the |Fick's |Law |equation |→ |models |the |rate |of |diffusion
metabolic |rate |of |organism |→ |determines |(in |part) |P1
each |of |the |four |variables |in |Fick's |Law |→ |affects |the |likelihood |of |respiratory |gas |molecules |
to |move |from |point |A |to |point |B |via |random |motions
Second |Law |of |Thermodynamics |→ |shows |that |the |process |of |diffusion |is |exergonic
surface |area |to |volume |ratio |(SA/V) |→ |explains |the |relationship |between |the |rate |of |supply |to |
the |rate |of |demand |for |respiratory |gases
The |figure |below |shows |the |simplified |diagram |of |the |insect |respiratory |system |that |we |used |
to |model |its |supply |of |oxygen |to |its |cells |via |diffusion.
Why |did |we |have |to |divide |the |entire |length |that |an |oxygen |molecule |has |to |traverse |via |
diffusion |from |the |external |atmosphere |to |inside |the |mitochondria |of |a |body |cell |into |two |
,distances, |and |calculate |the |rate |of |diffusion |separately |for |the |distance |X-Y |and |Y-Z? |- |
CORRECT |ANSWER✔✔-D |differs |for |the |two |distances
In |class, |we |determined |that |the |larger |insect |was |not |able |to |achieve |a |sufficient |rate |of |
diffusion |from |point |X |to |point |Y |in |its |tracheal |satisfy |the |oxygen |demand |of |its |cells |without |
increasing |the |cross-sectional |area |of |its |tracheal |tubes.
The |variables |of |Fick's |Law |that |we |determined |for |our |larger |insect |with |thin |trachea |is |
shown |in |the |table |below:
Assuming |that |the |cells |of |the |insect |require |an |oxygen |supply |of |2.0 |* |10-6 |mL/min |(= |
0.000002), |use |Fick's |Law |to |determine |what |the |cross-sectional |area |(A) |of |this |larger |insect |
has |to |minimally |be |in |µm2 |to |maintain |the |minimal |rate |of |diffusion |of |oxygen |of |2.0 |* |10-6 |
mL/min.
Round |your |answer |to |the |nearest |full |µm2. |- |CORRECT |ANSWER✔✔-110
Amphibians |such |as |frogs |breathe |both |with |their |lungs |and |via |gas |exchange |through |their |
moist |skin. |Which |is |likely |to |be |able |to |derive |a |higher |proportion |(fraction) |of |its |oxygen |
demand |from |gas |exchange |through |their |skin |as |opposed |to |via |its |lungs? |Hint: |consider |
which |concept |you |need |to |consider |to |answer |this |question. |- |CORRECT |ANSWER✔✔-poison |
dart |frog |(one |of |the |smallest |frogs |in |the |world)
Which |concept |did |you |have |to |apply |to |determine |the |answer |to |the |previous |question? |- |
CORRECT |ANSWER✔✔-SA/V
There |are |amphibians |that |are |even |larger |than |bullfrogs. |Which |of |the |following |could |explain
|how |such |a |large |amphibium |could |obtain |a |sufficient |rate |of |diffusion |of |respiratory |gases? |- |
CORRECT |ANSWER✔✔-different |shape |(e.g. |flat |or |ribbon |shaped)
larger |internal |surface |area |of |the |lungs
reduced |metabolic |rate |(reduced |rate |of |cellular |respiration)
Respiratory |surfaces |must |always |stay |moist |(be |covered |by |a |very |thin |film |of |water). |
Diffusion |across |dry |surfaces |is |exceedingly |slow.
,Which |variable |of |Fick's |Law |is |most |likely |responsible |for |this? |- |CORRECT |ANSWER✔✔-D
In |class, |we |oversimplified |the |insect |respiratory |system |a |bit |to |make |our |lives |easier |for |
calculating |Fick's |Law |variables.
For |example, |as |in |any |respiratory |organ, |the |actual |respiratory |surfaces |where |the |tips |of |the |
tracheoles |make |contact |with |individual |cells |of |the |insect |are |moist |and |filled |with |water.
When |the |insect |becomes |active |and |its |muscle |cells |have |a |greater |demand |for |oxygen |as |a |
result, |this |water |gradually |pulls |out |of |the |tracheoles |and |into |the |muscle |cells |again |(see |
figure |above). |What |might |the |benefit |of |this |be |to |the |insect? |- |CORRECT |ANSWER✔✔-
Decreases |the |part |of |the |distance |filled |with |a |medium |that |has |a |lower |diffusion |coefficient |
to |increase |the |diffusion |rate |at |times |of |high |metabolic |demand |for |oxygen.
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Ignoring |surface |area |of |gills, |which |of |the |following |variables |DECREASES |as |a |lugworm |grows |
larger? |- |CORRECT |ANSWER✔✔-SA/V
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Which |variable |does |presence |of |gills |most |affect |in |lugworms? |- |CORRECT |ANSWER✔✔-A
Blue |whales |are |mammals |and |just |like |us |have |lungs |with |alveoli |and |transport |oxygen |in |
blood |via |a |closed |circulatory |system. |However, |in |contrast |to |us, |blue |whales |are |the |biggest |
animals |that |have |ever |lived.
Compared |to |a |human, |the |total |distance |that |oxygen |has |to |diffuse |to |reach |cells |in |blue |
whales |is |blank |, |while |the |distance |of |bulk |flow |for |oxygen |in |blue |whales |is |blank |. |- |
CORRECT |ANSWER✔✔-roughly |the |same,
larger.
, What |is |a |prerequisite |(requirement) |for |counter-current |exchange |to |function? |- |CORRECT |
ANSWER✔✔-unidirectional |flow |of |the |outside |medium |(air |or |water)
bulk |flow |(mass |flow) |of |blood |and |external |medium |(air |or |water)
Mammalian |lungs |with |the |respiratory |surfaces |in |the |shape |of |dead-end |alveoli |require |tidal |
flow |to |ventilate. |Tidal |flow |is |not |conducive |to |counter-current |exchange. |The |next |two |
questions |ask |you |to |explore |why |not.
When |asked |to |demonstrate |why |something |cannot |work, |an |effective |strategy |is |to |model |
the |ineffective |set-up |and |explore |what |the |consequences |would |be. |Below |is |a |diagram |of |
what |our |alveoli |might |look |like, |if |they |were |set-up |to |enable |counter-current |flow |during |
inhalation:
First, |identify |the |concentration |gradient |for |both |inhalation |and |for |exhalation |in |the |
hypothetical |alveoli |above |that |are |plumbed |for |counter-current |exchange |during |inhalation. |- |
CORRECT |ANSWER✔✔-blood |during |exhalation |→ |Phigh
blood |during |inhalation |→ |Plow
air |during |exhalation |→ |Plow
air |during |inhalation |→ |Phigh
Based |on |your |answer |to |the |previous |question, |what |problem |prevents |mammalian |lungs |
from |engaging |in |counter-current |design?
If |mammalian |alveoli |had |respiratory |capillaries |directed |to |engage |in |counter-current |
exchange |during |inhalation |... |- |CORRECT |ANSWER✔✔-the |concentration |gradient |would |
reverse |during |exhalation |and |cause |diffusion |of |oxygen |from |blood |to |the |air.
There |are |many |different |species |of |marine |annelid |worm. |Some |are |very |small, |only |a |few |
millimeters |in |length. |Others, |such |as |lugworms, |are |much |larger. |Lugworms |live |in |U-shaped |
burrows |that |they |build |in |the |sediment |of |shallow |marine |intertidal |zones.
Lugworms |create |a |unidirectional |water |current |that |runs |through |their |U-shaped |burrows. |
Why |does |this |allow |lugworms |to |establish |a |countercurrent |oxygen |exchange |in |their |gills? |- |
CORRECT |ANSWER✔✔-Capillaries |in |gills |can |be |consistently |directed |to |run |blood |in |the |
opposite |direction |as |external |water |flow
