topic 3A: exchange and transport systems

Question 1

Describe the relationship between the size and structure of an organism and
its surface area to volume ratio (SA:V)

Answer 1

-As size increases, SA:V tends to decrease
-More thin/flat/folded/elongated structures increase SA:V

Question 2

suggest an advantage of calculating SA: mass or organisms instead of SA:V

Answer 2

easier and quicker to find and more accurate because irregular shapes

Question 3

what is metabolic rate and suggest how it can be measured

Answer 3

-metabolic rate = amount of energy used up by an organism within a given period of time
-this is often measured by oxygen uptake and as used in aerobic respiration to make ATP for energy release

Question 4

explain the relationship between SA:V and metabolic rate

Answer 4

-as SA:V increases (smaller organisms), the metabolic rate increases because:
-the 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

Question 5

explain the adaptations that facilitate exchange as SA:V reduces in larger organisms

Answer 5

1. changes to BODY SHAPE (e.g. long/ thin)
   -increases SA:V and overcomes (Reduces) long diffusion pathway
2. development of SYSTEMS, such as a specialized surface or organ for gaseous exchange e.g. lungs:
   -INCREASES (internal) SA:V and overcomes long diffusion pathway
   -maintains a CONCENTRATION GRADIENT for diffusion e.g. by ventilation/ good blood supply

Question 6

explain how the body surface of a single celled organism is adapted for gas exchange

Answer 6

-thin, flat shape and large surface area to volume ratio
-short diffusion distance to all parts of cell, rapid diffusion e.g. of O2 / CO2

Question 7

describe the tracheal system of an insect

Answer 7

-spiracles: pores on surface that can open and close to allow diffusion
-traccheae: large tubes full of air that allow diffusion
-tracheoles: smaller branches from tracheae, permeable to allow gas exchange with cells

Question 8

explain how an insects tracheal system is adapted for gas exchange

Answer 8

1. TRACHEOLES have THIN WALLS
   -so SHORT DIFFUSION DISTANCE to cells
2. HIGH NUMBERS of highly BRANCHED TRACHEOLES
   -so SHORT DIFFUSION DSTANCE to cells
   -so LARGE SURFACE AREA
3. TRACHEAE provides tubes full of AIR
   -so FAST DIFFUSION
4. CONTRACTION of abdominal MUSCLES (abdominal pumping) changes PRESSURE in body, causing air to MOVE IN AND OUT
   -maintains concentration gradient for diffusion
5. FLUID in end of tracheoles drawn into TISSUES by osmosis during EXCERCISE (lactate produced in anaerobic respiration lowers water potential of cells)
   -as fluid is removed, air fills tracheoles
   -so rate of diffusion to gas exchange surface increases as DIFFUSION is FASTER through AIR

Question 9

explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss

Answer 9

-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 water potential gradient so less water loss (evaporation)

Question 10

explain how the gills of fish are adapted for gas exchange

Answer 10

1. gills made of MANY FILAMENTS covered with MANY LAMELLAE
   -INCREASE SURFACE AREA for diffusion
2. THIN lamellae wall/ epithelium
   -so SHORT DIFFUSION DISTANCE between water or blood
   -lamellae have a LARGE NUMBER of CAPILLARIES
   -remove O2 and bring CO2 quickly so maintains CONCENTRATION GRADIENT

Question 11

counter current flow

Answer 11

1. blood and water flow in OPPOSITE DIRECTIONS through the lamellae
2. so OXYGEN CONCENRATION always HIGHER in WATER than blood
3. so maintains a CONCENTRATION GRADIENT of oxygen between water and blood
4. for DIFFUSION along WHOLE LENGTH OF LAMELLAE

Question 12

what happens if it was parallel flow?

Answer 12

if parallel flow, EQUILIBRIUM would be reached so oxygen wouldnt diffuse into blood along the whole gill plate

Question 13

explain how the leaves of dicotledonous plants are adapted for gas exchange

Answer 13

-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

Question 14

explain structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss

Answer 14

xerophyte: plant adapted to live in very DRY conditions e.g. cacti and marram grass

1. THICKER WAXY cuticle
   -INCREASES DIFFUSION DISTANCE so less evaporation
2. 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
3. SPINES/ NEEDLES
   -reduces SURFACE AREA TO VOLUME RATIO

Question 15

explain the essential features of the alveolar epithelium that make it adapted as a surface for gas exchange

Answer 15

1. FLATTENED cells/ 1 CELL THICK so a SHORT DIFFUSION DISTANCE
2. FOLDED creates a LARGE SURFACE AREA
3. PERMEABLE so allows DIFFUSION of oxygen and carbon dioxide
4. MOIST so gases can dissolve for diffusion
5. good blood supply from large network of CAPILLARIES so maintains CONCENTRATION GRADIENT

Question 16

describe how gas exchange occurs in the lungs

Answer 16

-oxygen DIFFUSES from alveolar air space into blood down its CONCENTRATION GRADIENT
-across ALVEOLAR EPITHELIUM then across CAPILARRY ENDOTHELIUM

Question 17

explain the importance of ventillation

Answer 17

-brings in air containing HIGHER CONCENTRATION OF OXYGEN and removes air with lower concentration of oxgen, maintaining CONCENTRATION GRADIENTS

Question 18

explain how humans breathe in - INSPIRATION

Answer 18

1. DIAPHRAGM muscles CONTACT and FLATTENS
2. EXTERNAL intercostal muscles CONTRACT, internal intercostal muscles relax (antagonistic) and the ribcage pulled up and out
3. INCREASING VOLUME and DECREASING PRESSURE (below atmospheric) in thoracic cavity
4. air moves into lungs DOWN PRESSURE GRADIENT

Question 19

explain how humans breathe out - EXPIRATION

Answer 19

1. DIAPHRAGM RELAXES and moves UPWARDS
2. EXTERNAL intercostal muscles RELAX, INTERNAL intercostal muscles MAY CONTRACT and the ribcage moves DOWN and IN
3. DECREASING VOLUME and INCREASING PRESSURE (Above atmospheric) in thoracic cavity
4. air moves out of lungs DOWN PRESSURE GRADIENT

Question 20

suggest why expiration is normally passive at rest

Answer 20

-internal intercostal muscles do NOT normally need to contract
-expiration aided by ELASTIC RECOIL in alveoli

Question 21

suggest how different lung diseases reduce the rate of gas exchange

Answer 21

-THICKENED alveolar tissue (e.g. fibrosis) increases the diffusion pathway
-alveolar wall BREAKDOWN and REDUCES SURFACE AREA
-reduce lung ELASTICITY and lungs EXPAND and RECOIL less so reduces the concentration gradients of oxygen and carbon dioxide

Question 22

suggest how different lung diseases affect ventilation

Answer 22

1. REDUCE lung ELASTICITY (e.g. fibrosis - build up of scar tissue), so lungs expand and recoil less
   -reducing VOLUME OF AIR in EACH BREATH (tidal volume)
   -reducing MAXIMUM VOLUME of air breathed out in one BREATH (forced vital capacity)
2. NARROW AIRWAYS/ REDUCE AIRFLOW in and out of lungs (e.g. asthma - inflamed bronchi)
   -reducing MAXIMUM VOLUME of air breathed out in 1 second (forced expiratory volume)
3. reduced rate of gas exchange, so increased VENTILATION RATE to compensate for reduced oxygen in blood

Question 23

suggest why people with lung disease experience fatigue

Answer 23

-cells recieve less oxygen so the rate of aerobic respiration reduced so less ATP is made

Question 24

suggest how you can analyse and interpret data to the effects of pollution, smoking and other risk factors on the incidence of lung disease

Answer 24

1. describe OVERALL trend e.g. POSITIVE AND NEGATIVE CORRELATION between risk factor and incidence of disease
2. MANIPULATIVE DATA → eg. calculate PERCENTAGE CHANGE
3. Interpret STANDARD DEVIATIONS: OVERLAP suggests differences in means are likely to be due to chance
4. Use STATISTICAL TESTS → identify whether DIFFERENCE / CORRELATION is SIGNIFICANT or due to CHANCE
   -CORRELATION COEFFICIENT → examining an ASSOCIATION between 2 sets of data
   -STUDENTS TEST → comparing MEANS of 2 sets of data
   -CHI- SQUARED TEST → for CATEGORICAL data

Question 25

Suggest how you can evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors

Answer 25

1. Analyse and interpret data as above and identify what does and doesn’t support statement 2. Evaluate METHOD of collecting data ○ SAMPLE SIZE → large enough to be REPRESENTATIVE of population? ○ Participant DIVERSITY e.g. age, sex, ethnicity and health status → representative of population? ○ CONTROL GROUPS → used to enable comparison? ○ CONTROL VARIABLES e.g. health, previous medications → valid? ○ DURATION of study → long enough to show long-term effects? 3. Evaluate CONTEXT → has a broad generalisation been made from a specific set of data? 4. Other risk factors that could have affected results?

Question 26

Explain the difference between correlations and causal relationships

Answer 26

-CORRELATION = change in one variable REFLECTED by a change in another - identified on a scatter diagram -CAUSTAION = change in one variable CAUSES a change in another variable -CORRELATION DOES NOT MEAN CAUSATION → may be OTHER FACTORS involved