Topic 2 Flashcards

1
Q

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

A

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

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2
Q

How is SA:V calculated?

A

Divide surface area (size length x side width x number of sides) by volume (length x width x depth)

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3
Q

Suggest an advantage of calculating SA:mass for organisms instead of SA:V

A

Easier / quicker to find / more accurate because irregular shapes

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4
Q

What is metabolic rate? Suggest how it can be measured

A

● 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

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5
Q

Explain the relationship between SA:V and metabolic rate

A

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

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6
Q

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

A
  1. Changes to body shape (eg. long / thin)

● Increases SA:V and overcomes (reduces) long diffusion distance / pathway

  1. 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

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7
Q

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

A

● Thin, flat shape and large surface area to volume ratio
● Short diffusion distance to all parts of cell → rapid diffusion eg. of O2 / CO2

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8
Q

Describe the tracheal system of an insect

A
  1. Spiracles = pores on surface that can open / close to allow diffusion
  2. Tracheae = large tubes full of air that allow diffusion
  3. Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
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9
Q

Explain how an insect’s tracheal system is adapted for gas exchange

A

● 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

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10
Q

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

A

● 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)

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11
Q

Explain how the gills of fish are adapted for gas exchange

A

● 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 gradient

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12
Q

Counter current flow:

A
  1. Blood and water flow in opposite directions through/over lamellae
  2. So oxygen concentration always higher in water (than blood near)
  3. So maintains a concentration gradient of O2 between water and blood
  4. For diffusion along whole length of lamellae
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13
Q

Parallel flow:

A

If parallel flow, equilibrium would be reached so oxygen wouldn’t diffuse into blood along the whole gill plate.

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14
Q

Explain how the leaves of dicotyledonous plants are adapted for gas
exchange

A

● 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

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15
Q

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

A

● 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

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16
Q

Xerophyte

A

Xerophyte = plant adapted to live in very dry conditions eg. Cacti and marram grass

17
Q

Describe the gross structure of the human gas exchange system

A

Trachea
Bronchi
Bronchioles
Alveoli (air sacs)
Capillary network surrounding alveoli

18
Q

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

A

● Flattened cells / 1 cell 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 →
maintains concentration gradient

19
Q

Describe how gas exchange occurs in the lungs

A

● Oxygen diffuses from alveolar air space into blood down its concentration gradient
● Across alveolar epithelium then across capillary endothelium
Carbon dioxide opposite

20
Q

Explain the importance of ventilation

A

● Brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
● Maintaining concentration gradients

21
Q

Explain how humans breathe in

A
  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
22
Q

Explain how humans out

A
  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
23
Q

Suggest why expiration is normally passive at rest

A

● Internal intercostal muscles do not normally need to contract
● Expiration aided by elastic recoil in alveoli

24
Q

Suggest how different lung diseases reduce the rate of gas exchange

A

● 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

25
Q

Suggest how different lung diseases affect ventilation

A

● 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

26
Q

Suggest why people with lung disease experience fatigue

A

Cells receive less oxygen → rate of aerobic respiration reduced → less ATP made

27
Q

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

A

● 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

28
Q

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

A

● Analyse and interpret data as above and identify what does and doesn’t support statement
● Evaluate method of collecting data
○ Sample size → large enough to be representative of population?
○ Participant diversity eg. age, sex, ethnicity and health status → representative of population?
○ Control groups → used to enable comparison?
○ Control variables eg. health, previous medications → valid?
○ Duration of study → long enough to show long-term effects?
● Evaluate context → has a broad generalisation been made from a specific set of data?
● Other risk factors that could have affected results?

29
Q

Explain the difference between correlations and causal relationships

A

● 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

30
Q

Explain what happens in digestion

A

● Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
● That are small enough be absorbed across cell membranes into blood

31
Q

Describe the digestion of starch in mammals

A

● Amylase (produced by salivary glands / pancreas) hydrolyses starch to maltose
● Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
● Hydrolysis of glycosidic bond

32
Q

Describe the digestion of disaccharides in mammals

A

● Membrane-bound disaccharidases hydrolyse disaccharides to 2 monosaccharides:
○ Maltase - maltose → glucose + glucose
○ Sucrase - sucrose → fructose + glucose
○ Lactase - lactose → galactose + glucose
● Hydrolysis of glycosidic bond

33
Q

Describe the digestion of lipids in mammals, including action of bile salts

A

● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
● This increases surface area of lipids for increased / faster lipase activity
● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids
● Hydrolysis of ester bond

34
Q

Describe the digestion of proteins by a mammal

A

● Endopeptidases - hydrolyse internal (peptide) bonds
within a polypeptide → smaller peptides
○ So more ends / surface area for exopeptidases
● Exopeptidases - hydrolyse terminal (peptide) bonds at
ends of polypeptide → single amino acids
● Membrane-bound dipeptidases - hydrolyse (peptide)
bond between a dipeptide → 2 amino acids
● Hydrolysis of peptide bond

35
Q

Suggest why membrane-bound enzymes are important in digestion

A

● Membrane-bound enzymes are located on cell membranes of epithelial cells lining ileum
● (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption

36
Q

Describe the pathway for absorption of products of digestion in mammals

A

Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood

37
Q

Describe the absorption of amino acids and monosaccharides in mammals

A

Co-transport:
● Na
+ actively transported from
epithelial cells lining ileum to
blood (by Na
+
/K
+ pump)
● Establishing a conc. gradient
of Na
+
(higher in lumen than
epithelial cell)

● Na
+ enters epithelial cell down
its concentration gradient with
glucose against its
concentration gradient
● Via a co-transporter protein

● Glucose moves down a conc.
gradient into blood via
facilitated diffusion

38
Q

Describe the absorption of lipids by a mammal, including the role of micelles

A

● Micelles contain bile salts, monoglycerides and fatty acids
○ Make monoglycerides and fatty acids (more) soluble in water
○ Carry / release fatty acids and monoglycerides to cell / lining of ileum
○ Maintain high concentration of fatty acids to cell / lining
● Monoglycerides / fatty acids absorbed (into epithelial cell) by diffusion (lipid soluble)
● Triglycerides reformed in (epithelial) cells and aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and leave via exocytosis
○ Enter lymphatic vessels and eventually return to blood circulation