Topic 3 - Organisms exchange substances with their environment Flashcards
(79 cards)
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 decreases
- More thin,flat,elongated,folded structures have increased SA:V
2
Q
How is SA:V calculated
A
Divide surface area by volume
3
Q
Advantage of calculating SA:mass for organisms instead of SA:V
A
easier/quicker to find - more accurate due to irregular shapes
4
Q
What is metabolic rate - how is it measured
A
- Amount of energy used by an organisms within a certain amount of time
- Measured by oxygen uptake -> used in aerobic respiration to make ATP for energy release
5
Q
Explain relationship between SA:V and metabolic rate
A
- As SA:V increases (smaller organisms) - metabolic rate also increases
-> rate of heat loss per unit mass increases
-> organisms need a higher rate of respiration
-> to release enough head to maintain constant body temperature
6
Q
Explain adaptations that facilitate exchange as SA:V decreases in larger organisms
A
1 - changes in body shape (longer/thinner)
-> increases SA:V and reduces long diffusion distance
2 - development of systems like specialised surface/organ for gas exchange
-> increases internal SA:V and reduces long diffusion distance - maintains concentration gradient for diffusion by ventilation
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
- Shorter diffusion distance to all parts of cell → rapid diffusion eg. of O2 / CO2
8
Q
Describe insect tracheal system
A
1 - spiracles = pores on surface that open/close to allow diffusion
2 - tracheae = large tubes full of air to allow diffusion
3 - tracheoles = smaller branches from tracheae - permeable to allow gas exchange with cells
9
Q
How is insect tracheal system adapted to gas exchange
A
- Tracheoles have thin walls -> short diffusion distance to cells
- Tracheae provide tubes full of air -> faster diffusion
- Contraction of abdominal muscles (abdominal pumping) - changes pressure in body causing air to move in and out -> maintains concentration gradient for diffusion
- High numbers of highly branched tracheoles -> shorter diffusion distance and larger surface area
- Fluid in tracheole ends are drawn into tissues by osmosis during exercise (lactate produced in anaerobic respiration decreases water potential of cells) -> as fluid is removed, air fills tracheoles - rate of diffusion to gas exchange surfaces increases as diffusion is faster through air
10
Q
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 open to allow gas exchange and can close to reduce water loss (evaporation)
- Hairs around spiracles -> traps moist air, reduces water potential gradient so less water loss (evaporation)
11
Q
How are gills adapted to gas exchange
A
- Gills are made of many filaments which are covered with many lamellae -> increases surface area for diffusion
- Thin lamellae wall/epithelium -> short diffusion distance between water and blood
- Lamellae have large number of capillaries -> removes oxygen and brings carbon dioxide quickly to maintain concentration gradient
12
Q
Explain counter current flow
A
- Blood and water flow in opposite directions through/over lamellae
- Oxygen concentration always higher in water than blood nearby
- Maintains concentration gradient of oxygen between water and blood
- For diffusion long whole length of lamellae
- If parallel flow -> equilibrium would be reached so oxygen wouldnt diffuse into blood along whole gill plate
13
Q
How are leaves of dicotyledonous plants are adapted for gas exchange
A
- Many stomata -> larger surface area for gas exchange when opened by guard cells
- Spongy mesophyll contains air spaces -> larger surface area for gases to diffuse through
- Thin -> short diffusion distance
14
Q
Structural and functional compromises in xerophytic plants that allow efficient gas exchange while limiting water loss
A
- Xerophyte = plant adapted to live in very dry conditions
- Thicker waxy cuticle -> increases diffusion distance so less evaporation
- Sunken stomata in pits/hairs -> traps water vapour and protects stomata from wind - reduced water potential gradient between leaf and air - less evaporation
- Spines/needles -> reduces surface area to volume ratio
15
Q
Features of alveolar epithelium which adapts it for gas exchange
A
- Flattened cells/1 cell thick -> shorter diffusion distance
- Folded -> increases surface area
- Permeable -> allows diffusion of oxygen and carbon dioxide
- Moist -> gases can dissolve for diffusion
- Good blood supply from large network of capillaries -> maintains concentration gradient
16
Q
How does gas exchange occur in the lung
A
- Oxygen diffuses from alveolar air space into blood down a concentration gradient
- Across alveolar epithelium then across capillary endothelium
- Carbon dioxide = opposite
17
Q
Importance of ventilation
A
- Brings in air containing high concentration of oxygen - removes air with low concentration of oxygen
- Maintains concentration gradients
18
Q
How do humans breathe in (inspiration)
A
1 - diaphragm muscles contract and flatten
2 - external intercostal muscles contract - internal intercostal muscles relax - ribcage pulled up and out
3 - increases volume and decreases pressure in thoracic cavity
4 - air moves into longs down a pressure gradient
19
Q
How do humans breathe out (expiration)
A
1 - Diaphragm muscles relax and move up
2 - External intercostal muscles relax, internal intercostal muscles contract - ribcage moves down and in
3 - Decreases volume and increases pressure in thoracic cavity
4 - Air moves out of lungs down pressure gradient
20
Q
Why is expiration normally passive at rest
A
- Internal intercostal muscles don’t normally need to contract
- Expiration aided by elastic recoil in alveoli
21
Q
Suggest how different lung diseases reduce rate of gas exchange
A
- Thickened alveolar tissue (fibrosis) -> increases diffusion distance
- Alveolar wall breakdown -> decreases surface area
- Decreased lung elasticity -> lungs expand/recoil less - decreases gas concentration gradients
22
Q
Suggest how different lung diseases affect ventilation
A
- Decreased lung elasticity -> lungs expand/recoil less -> decreases volume of air in each breath (tidal volume) - decreases max volume of air breathed out in 1 second (forced expiratory volume)
- Narrow airways/reduced airflow in and out of lungs (asthma or inflamed bronchi) - reduces max 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
23
Q
Why do people with lung disease experience fatigue
A
Cells receive less oxygen -> rate of aerobic respiration decreases -> less ATP made
24
Q
Suggest how to 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
24
Suggest how to evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors
- 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?
25
Difference between correlations and causal relationships
- Correlation = change in one variable reflected by change in another -> identified on scatter diagram
- Causation = change in one variable causes change in another
- Correlation does not mean causation - other factors may be involved
26
What happens in digestion
- Larger insoluble biological molecules are hydrolysed into smaller soluble molecules
- That are small enough to be absorbed across cell membranes into blood
27
Digestion of starch in mammals
- Amylase (produced in salivary glands/pancreas) hydrolyses starch into maltose
- Membrane bound maltase (attached to cells lining ileum) -> hydrolyses maltose to glucose
- Hydrolysis of glycosidic bond
28
Digestion of disaccharides in mammals
-Membrane bound disaccharidases hydrolyse disaccharides into 2 monosaccharides
-> Maltase - maltose -> glucose + glucose
-> Sucrase - sucrose -> fructose + glucose
-> Lactase - lactose -> galactose + glucose
- Hydrolysis of glycosidic bonds
28
Digestion of lipids in mammals - action of bile salts
- Bile salts (produced in liver) emulsify lipids, forming smaller lipid droplets
- Increases surface area of lipids for increased/faster lipase activity
- Lipase (made in pancreas) hydrolyses lipids (triglycerides) into monoglycerides and fatty acids
- Hydrolysis of ester bond
29
Digestion of proteins in mammals
- Endopeptidases -> hydrolyse internal peptide bonds within polypeptide into smaller peptides - more ends/surface area for exopeptidases
- Exopeptidases -> hydrolyses terminal peptide bonds at ends of polypeptide into single amino acids
- Membrane bound dipeptidases - hydrolyse peptide bonds between dipeptide into 2 amino acids
- Hydrolysis of peptide bond
30
Why are membrane bound enzymes important in digestion
- Membrane bound enzymes are found on cell membranes of epithelial cells lining ileum
- Hydrolyses molecules at site of absorption -> maintains concentration gradients for absorption
31
Pathway for absorption of products of digestion in mammals
Lumen (inside) of ileum -> cells lining ileum (small intestine) -> blood
32
Absorption of amino acids and monosaccharides in mammals - co transport
1 - Sodium ions actively transported from epithelial cells lining ileum into blood through sodium potassium pump
- creates concentration gradient of sodium ions (higher in lumen than epithelial cells)
2 - Sodium ions enter epithelial cells down a concentration gradient with monosaccharides/amino acids against a concentration gradient - by a cotransporter protein
3 - Monosaccharide/amino acid moves down concentration gradient into blood by facilitated diffusion
33
Describe the absorption of lipids by a mammal, including the role of micelles
- Bile salts combine with monoglycerides & fatty acids to form micelles
-> micelles make monoglycerides & fatty acids more soluble in water
-> micelles carry monoglycerides & fatty acids to cells lining ileum where they break down to release them
-> maintains high concentration of monoglycerides & fatty acids near cells lining ileum
monoglycerides/fatty acids absorbed into epithelial cell by diffusion (lipid soluble)
- Triglycerides reformed in epithelial cells and aggregate into globules
- Globules are coated with proteins - forming chylomicrons which are packaged into vesicles
- Vesicles move to cell membrane and fuse with it - releases chylomicrons by exocytosis - chylomicrons enter lymphatic vessels and eventually return to blood circulation
34
Describe role of RBC & haemoglobin in oxygen transport
- RBC contain lots of HB -> no nucleus and biconcave shape so more space for HB -> higher surface area to volume ratio & shorter diffusion distance
- HB associates/bind to oxygen at gas exchange surfaces (lungs) -> partial pressure of oxygen is high
- Forms oxyhaemoglobin which transports oxygen -> each can carry 4 oxygen molecules, one at each haem group
- HB dissociates from/unloads oxygen near cells where partial pressure of oxygen is low
35
Structure of haemoglobin
- Protein with quaternary structure
4 polypeptide chains
- Each chain contains haem group -> containing an iron ion
(Group of chemically similar molecules found in many organisms)
36
Loading, transport & unloading of oxygen in relation to oxyhaemoglobin dissociation curve
- Areas with low PO2 (respiring tissues)
-> HB has low affinity for oxygen -> oxygen readily unloads with HB so % saturation is lower
- Areas with high PO2 (gas exchange surfaces)
-> HB has high affinity for oxygen -> oxygen readily loads with HB so % saturation is higher
37
Describe evidence for cooperative nature of oxygen binding
- At low PO2 -> as oxygen increases there is a little/slow increase in % saturation of HB with oxygen -> when first oxygen is binding
- At high PO2 -> as oxygen increases there is a big/fast increase in % saturation of HB with oxygen -> shows it is easier for oxygen to bind
37
How does cooperative nature of oxygen binding result in an S shaped (sigmoid) oxyhaemoglobin curve
- Binding of first oxygen changes tertiary/quaternary structure of haemoglobin
- Uncovers haem group binding sites -> makes further binding of oxygen easier
38
Explain effect of CO2 concentration on dissociation of oxyhaemoglobin
- Increasing blood CO2 (eg - due to increased respiration)
- Lowers blood pH (more acidic)
- Reduces HB affinity for oxygen -> quaternary structure slightly changes
- More & faster unloading of oxygen to respiring cells at a given PO2
38
What is the Bohr effect
Effect of carbon dioxide concentration on dissociation of oxyhaemoglobin -> curve shifts to right
39
Describe evidence for Bohr effect
At a given PO2, the saturation of HB with oxygen is lower
40
General pattern of blood circulation in mammals
- Closed double circulatory system -> blood passes through heart twice for every circuit around the body
1 - deoxygenated blood in right side of heart is pumped to lungs - oxygenated blood returns to left side
2 - oxygenated blood in left side of heart is pumped to rest of body - deoxygenated blood returns to right side
40
Advantage of Bohr effect
More dissociation of oxygen -> faster aerobic respiration/less anaerobic respiration - more ATP produced
41
Explain why different types of haemoglobin can have different oxygen transport properties
- Different types of HB are made of polypeptide chains that have slightly different amino acid sequences
- Results in different tertiary/quaternary structure
- So have different affinities for oxygen
42
Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties
- Curve shifts left -> HB has higher affinity for oxygen
-> more oxygen associates with HB more readily - at gas exchange surfaces where PO2 is lower
-> eg - organisms in low oxygen environments (high altitude/underground)
- Curve shifts right -> HB has lower affinity for oxygen
-> more oxygen dissociates with HB more readily - at respiring tissues where more oxygen is needed
-> eg - where there are high rates of respiration/metabolic rate
43
Name blood vessels entering and leaving heart and lungs
- Vena cava -> transports deoxygenated blood from body cells to heart
- Pulmonary artery -> transports deoxygenated blood from heart to lungs
- Pulmonary vein -> transports oxygenated blood from lungs to heart
- Aorta -> transports oxygenated blood from heart to body cells
44
Importance of double circulatory system
- Prevents mixing of oxygenated and deoxygenated blood -> blood pumped to body is fully saturated with oxygen for aerobic respiration
- Blood can be pumped to body at high pressure -> substances are taken/removed from body cells quickly and efficiently
45
Name blood vessels entering and leaving kidneys
- Renal arteries -> oxygenated blood into kidneys
- Renal veins -> deoxygenated blood from kidneys to vena cava
46
Name blood vessel that carries oxygenated blood to heart muscle
- Coronary arteries -> located on surface of heart - branches from aorta
47
Why is the wall of the left ventricle thicker than the right ventricle
- Thicker muscle to contract with greater force
- Generates higher pressure to pump blood around the entire body
48
Explain pressure & volume changes & associated valve movements during cardiac cycle that maintains unidirectional flow of blood
- DIASTOLE
-> atria & ventricles relax - volume increases - pressure decreases
-> semilunar valves shut when pressure in arteries exceeds pressure in ventricles
-> atrioventricular valves open when pressure in atria exceeds pressure in ventricles
-> blood fills atria through veins & flows passively into ventricles
- ATRIAL SYSTOLE
-> atria contracts - volume decreases - pressure increases
-> atrioventricular valves open when pressure in atria exceeds pressure in ventricles
-> blood pushed into ventricles
- VENTRICULAR SYSTOLE
-> ventricles contract - volume decreases - pressure increases
-> atrioventricular valves shut when pressure in ventricles exceeds pressure in atria
-> semilunar valves open when pressure in ventricles exceeds pressure in arteries
-> blood pushed through arteries out of the heart
49
How to interpret graphs showing pressure/volume changes during cardiac cycle
- SL valves closed - pressure in artery higher than in ventricles - prevents backflow of blood from artery to ventricles
- SL valves open - when pressure in ventricle higher than in artery - blood flows from ventricle to artery
- AV valves closed - pressure in ventricles higher than atrium - prevents backflow of blood from ventricles to atrium
- AV valves open - when pressure in atrium higher than in ventricle - blood flows from atrium to ventricle
50
Equation for cardiac output
Cardiac output = stroke volume (volume pumped in each beat) x heart rate (beats per min)
51
How can heart rate be calculated from cardiac cycle data
Heart rate = 60/length of one cardiac cycle
52
How does structure of arteries relate to their function
- Function = carry blood away from heart at high pressure
- Thick smooth muscle tissue -> can contract & control blood flow & pressure
- Thick elastic tissue -> can stretch as ventricles contract/recoil as ventricles relax -> reduces pressure surges - maintains high pressures
- Thick wall -> withstand high pressure and stop bursting
- Smooth/folded endothelium - reduces friction and can stretch
- Narrow lumen -> increases and maintains high pressure
53
How does structure of arterioles relate to their function
- Function = direct blood to different capillaries/tissues
- Thicker smooth muscle layer than arteries - contracts to narrow lumen (vasoconstriction) -> reduces blood flow to capillaries - relaxes to widen lumen (vasodilation) -> increases blood flow to capillaries
- Thicker elastic layer -> pressure surges are lower (further from heart/ventricles)
54
How does structure of veins relate to their function
- Function = carries blood back to heart at low pressure
- Wider lumen than arteries -> less resistance to blood flow
- Very little elastic and muscle tissue -> blood pressure is lower
- Valves -> prevents backflow of blood
55
How does structure of capillaries relate to their function
- Function = allows efficient exchange of substances between blood and tissue fluid
- Wall is a thin layer of endothelial cells -> reduces diffusion distance
- Capillary bed is a large network of branched capillaries -> increases surface area for diffusion
- Small diameter/narrow lumen -> reduces blood flow rate so more time for diffusion
- Pores in end walls between cells -> allows larger substances to pass through
56
Explain tissue fluid formation
- At the arteriole end of capillaries
1 - higher blood/hydrostatic pressure inside capillaries (due to ventricular contraction) than tissue fluid (creates net outward force)
2 - forces water (& dissolved substances) out of capillaries
3 - large plasma proteins remain in capillaries
57
Explain return of tissue fluid to circulatory system
- At venule end of capillaries
1 - hydrostatic pressure decreases as fluid leaves capillary (due to friction)
2 - due to water loss - increasing concentration of plasma proteins decreases water potential of capillary below that of tissue fluid
3 - water enters capillaries from tissue fluid by osmosis down a water potential gradient
4 - excess water taken up by lymph capillaries - returned to circulatory system through veins
58
Suggest and explain causes of excess tissue fluid accumulation
- Low concentration of protein in blood plasma
-> water potential in capillary not as low - water potential gradient decreases
-> more tissue fluid formed at arteriole end - less water absorbed at venule end by osmosis
-> lymph system may not be able to drain excess fast enough
- High blood pressure (eg. caused by high salt concentration) → high hydrostatic pressure
-> Increases outward pressure from arteriole end AND reduces inward pressure at venule end
-> more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
-> Lymph system may not be able to drain excess fast enough
59
How are xylem tissues adapted
- Cells are joint with no end walls, forming a long continuous tube so water can flow as a continuous column
- Cells contain no cytoplasm/nucleus so easier water flow with no obstruction
- Thick cell walls with lignin to provide support and withstand tension
- Pits in side walls to allow lateral water movement
59
What is a risk factor - examples for cardiovascular disease
- Aspect of a person’s lifestyle or substances in a person’s body/environment
- Which are shown to be linked to increased rate of disease
Eg - age, smoking, lack of exercise, genes
59
Describe function of xylem tissue
Transports water and mineral ions through the stem up the plant to leaves
60
How can potometer be used to measure transpiration rate
- Potometer estimates transpiration rate by measuring water uptake
- Record air bubble position and distance moved in a certain time
- Calculate volume of water uptake - radius of tube and multiply by distance moved by bubble
- Water uptake -> divide volume by time taken
60
Cohesion tension theory - xylem
- Water is lost from leaf by transpiration so water evaporates from mesophyll cells into air spaces and water vapour diffuses through open stomata -> reduces water potential in leaf so water drawn out of xylem down a water potential gradient
- Creates tension in xylem - hydrogen bonds allow cohesion between water molecules so water is pulled up in a continuous column and by adheres to xylem walls
- Water enters roots by osmosis
61
Describe how to set up a potometer
1 - Cut a shoot underwater at a slant -> prevent air entering xylem
2 - Assemble potometer with capillary tube end submerged in a beaker of water
3 - Insert shoot underwater
4 - Ensure apparatus is watertight / airtight
5 - Dry leaves and allow time for shoot to acclimatise
6 - Shut tap to reservoir
7 - Form an air bubble - quickly remove end of capillary tube from water
62
Describe how a potometer can be used to investigate the effect of a named environmental variable on the rate of transpiration
- Carry out the above, change one variable at a time (wind, humidity, light or temperature)
- Eg. set up a fan OR spray water in a plastic bag and wrap around the plant OR change distance of a light source OR change temperature of room - whilst keeping all other variables constant
63
Environmental factors affecting transpiration rate
- LIGHT INTENSITY -> increases rate - stomata opens in light to allow CO2 for photosynthesis, more water evaporates, stomata closes when dark so low transpiration
- HUMIDITY -> decreases rate - more water in air so higher water potential - decreases water potential from leaf to air so water evaporates slower
- WIND SPEED -> increases rate - wind blows away water molecules from around stomata - decreases water potential of air surrounding stomata - increases water potential gradient so water evaporates faster
- TEMPERATURE -> increases rate - water molecules gain kinetic energy as temperature increases so water evaporates faster
63
Limitations of using a potometer to measure transpiration rate
- Rate of water uptake may not be the same as transpiration rate as water is used for turgidity and also in photosynthesis and is produced in respiration
- Rate of movement through shoot in potometer may not be the same as that through the shoot of a whole plant -> because shoot in potometer has no roots but plants do, and xylem is very narrow
64
Function of phloem tissue
Transports organic substances (sucrose and amino acids)
65
How are phloem tissues adapted
- Sieve tube elements -> no nucleus/few organelles - maximises space for easier flow of substances - end walls between cells are perforated
- Companion cells -> many mitochondria - high rate of respiration to make ATP for active transport of sucrose
66
What is translocation
Movement of assimilates/solutes such as sucrose - from source cells (leaves) to sink cells (roots) by mass flow
67
Mass flow hypothesis - translocation
- At source, sucrose is actively transported into phloem sieve tubes/cells by companion cells
- Lowers water potential in sieve tubes so water from xylem can enter by osmosis
- Increases hydrostatic pressure in sieve tubes at source - creates a pressure gradient
- Mass flow occurs - movement from source to sink
- At sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs
68
Tracer experiments to investigate transport in plants
- Leaf supplied with radioactive tracer - CO2 containing radioactive isotope 14C
- Radioactive carbon incorporated into organic substances during photosynthesis which moves around plant by translocation
- Movement is tracked by autoradiography or geiger counter
69
Ringing experiments to investigate transport in plants
- Remove/kill phloem by removing a ring of bark
- Bulge forms on source side of ring
- Fluid from bulge has a higher concentration of sugars than below which shows sugar is transported in phloem
- Tissues below ring die as they cannot receive organic substances
70
Evaluating evidence for/against mass flow hypothesis
- Can movement be due to another factor such as gravity
- Is movement from high to low pressure
- Is movement from source to sink
- Is respiration and active transport involved
- Is the phloem involved
