1.3 Exchange of Substances 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
How is SA:V calculated?
Divide surface area (size length x side width x number of sides) by volume (length x width x depth)
Suggest an advantage of calculating SA:mass for organisms instead of SA:V
- Easier / quicker to find / more accurate because irregular shapes
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 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
- 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 (2)
- Thin, flat shape and large surface area to volume ratio
- Short diffusion distance to all parts of cell → rapid diffusion eg. of O2 / CO2
Describe the tracheal system of an insect (3)
- Spiracles = pores on surface that can open / close to allow diffusion
- Tracheae = large tubes full of air that allow diffusion
- Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
Explain how an insect’s tracheal system is adapted for gas exchange (6)
Explain structural and functional compromises in terrestrial insects that allow efficient gas exchange while limiting water loss (3)
- 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)
Explain how the gills of fish are adapted for gas exchange
- The gills are made of many filaments covered with many lamellae - This increases the surface area for diffusion
- Thin lamellae wall / epithelium - so short diffusion distance between water / blood
- Lamellae have a large number of capillaries - This removes O2 and brings CO2 quickly so maintains concentration gradient
Describe the counter current flow of blood in fish
- Blood and water flow in opposite directions through / over lamellae
- So oxygen concentration is always higher in water (than blood near)
- So maintains a concentration gradient of O2 between water and blood
- For diffusion along the whole length of lamellae
If parallel flow, equilivrium would be reached so oxygen wouldn’t diffuse into the blood along the whole gill plate
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
Leaf Cross-Section Diagram:
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 eg. Cacti and marram grass
- 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 three ways in which an insect’s tracheal system is adapted for efficient gas exchange (3)
- Tracheoles have thin walls so short diffusion distance to cells
- Highly branched / large number of tracheoles so short diffusion distance to cells
- Highly branched / large number of tracheoles so large surface area (for gas exchange)
- Tracheae provide tubes full of air so fast diffusion (into insect tissues)
- Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface
- Body can be moved (by muscles) to move air so maintains diffusion /
concentration gradient for oxygen / carbon dioxide
Name the structure through which gases enter and leave the body of an insect (1)
Spiracle
Name the small tubes that carry gases directly to and from the cells of an insect (1)
Tracheole/trachea
Explain the movement of oxygen into the gas exchange system of an insect when it is at rest (3)
- Oxygen used in (aerobic) respiration
- (so) oxygen (concentration) gradient (established)
- (so) oxygen diffuses in
Explain what causes the oxygen concentration in the tracheae to fall when the spiracles are closed (2)
- (oxygen is used in) respiration therefore diffuses (from tracheae) to tissues;
- oxygen unable to enter organism
Describe how the structure of the insect gas exchange system:
- provides cells with sufficient oxygen
- limits water loss
- Explain your answers (5)
- Spiracles (lead) to tracheae (that lead) to tracheoles
- Open spiracles allow diffusion of oxygen from air
- Oxygen diffusion through tracheae/tracheoles
- Tracheoles are highly branched so large surface area (for exchange)
- Tracheole (walls) thin so short diffusion distance (to cells)
- Tracheoles push into cells so short diffusion distance
- Tracheole walls are permeable to oxygen
- Spiracles close (eg.during inactivity) preventing water loss
Describe and explain how the countercurrent system leads to efficient gas exchange across the gills of a fish (3)
- Water and blood flow in opposite directions
- Maintains concentration / diffusion gradient / equilibrium not reached / water always next to blood with a lower concentration of oxygen
- Along whole / length of gill / lamellae
Amoebic gill disease (AGD) is caused by a parasite that lives on the gills of some species of fish. The disease causes the lamellae to become thicker and to fuse together
AGD reduces the efficiency of gas exchange in fish. Give two reasons why (1)
- (Thicker lamellae so) greater / longer diffusion distance / pathway
- (Lamellae fuse so) reduced surface area
Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)
- Many lamellae / filaments so large surface area
- Thin (surface) so short diffusion pathway
an image of a fish gill taken using a scanning electron microscope:
Identify structures labelled F and G (1)
- F = Filament and
- G = (Secondary) lamella(e) / (gill) plate
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange (6)
- Large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient
- Thin epithelium / distance between water and blood
- Water and blood flow in opposite directions / countercurrent
- maintains concentration gradient (along gill) / equilibrium not reached / as water always next to blood with lower concentration of oxygen
- Circulation replaces blood saturated with oxygen
- Ventilation replaces water (as oxygen removed)
The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why (2)
- Mixing of air and water (at surface)
- Air has higher concentration of oxygen than water
- Diffusion into water
Explain what happens in digestion
- Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
- That are small enough be absorbed across cell membranes into blood
Describe the digestion of starch in mammals
- 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
Describe the digestion of disaccharides in mammal
- Membrane-bound disaccharidases hydrolyse disaccharides to 2 monosaccharides
- Maltase - maltose → glucose + glucose
- Sucrase - sucrose → fructose + glucose
- Lactase - lactose → galactose + glucose
Hydrolysis of glycosidic bond
Describe the digestion of lipids in mammals, including action of bile salts
- 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
Describe the digestion of proteins by a mammal
- 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
Suggest why membrane-bound enzymes are important in digestion
- 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
Describe the pathway for absorption of products of digestion in mammals
Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood
Amylase
A digestive enzyme which catalyses starch into maltose
Lipase
Breaks down lipids into monoglycerides and fatty acids
Endopeptidases
Hydrolyses peotide bonds within a protien
Exopeptidases
Hydrolyse peptide bonds at the end of protien molecules
Describe the process of protien digestion in the human gut (4)
- Hydrolysis of peptide bonds
- Endopeptidases break polypeptides into smaller peptide chains
- Exopeptidases remove amino acids at the end of a peptide chain
- Membrane bounds dipeptidases hydrolyse dipeptides into amino acids
Adaptations of the Ileum
- Villi - Increase SA for absorption
- Many microvilli - found on epithelial cells, further increases surface area for diffusion
- Many mitochondria - produce ATP for active transport
- Carrier protiens - Allows for active transport and facilitated diffusion or molecules into epithelial cells
- Large blood capiallry network - Maintains the diffusion gradient and increases the SA for diffusion
- Muscles (Peristalsis) - Helps maintain the diffusion gradient by moving contents through the gut
- Membrane-bound enzymes - Digest dipeptides / disaccharides
Describe the gross structure of the human gas exchange system
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 O2 / CO2
- 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
CO2 = Opposite
Explain the importance of ventilation
- Brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
- Maintaining concentration gradients
Inspiration (breathing in)
Explain how humans breathe in (ventilation)
- 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)
Explain how humans breathe out (ventilation)
- 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
Describe how humans breathe in and out (5)
- Breathing in - Diaphragm (muscles) contract and diaphragm flattens
- External intercostal muscles contract and ribcage pulled up/out
- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric pressure)
- Breathing out - Diaphragm (muscles) relaxes and internal intercostal muscles contract
- (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric pressure)
Describe the absorption of lipids by a mammal, including the role of micelles
- 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
The action of endopeptidases and exopeptidases can increase the rate of protein digestion. Describe how (2)
- Exopeptidases hydrolyse peptide bonds at the ends of a polypeptide/protein AND endopeptidases hydrolyse internal peptide
bonds within a polypeptide/protein - More ‘ends’
- More surface area
Describe the role of enzymes in the digestion of proteins in a mammal (4)
- (Reference to) hydrolysis of peptide bonds
- Endopeptidase act in the middle of protein/polypeptide
- Exopeptidases act at end of protein/polypeptide
- Dipeptidase acts on dipeptide/between two amino acids to produce single amino acids
Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own (2)
- Endopeptidases hydrolyse internal (peptide bonds)
- Exopeptidases remove amino acids/hydrolyse (bonds) at end(s)
- More ends or increase in surface area (for exopeptidases)
The addition of a respiratory inhibitor stops the absorption of amino acids.
Use the diagram to expain why (3)
- No/less ATP produced
- Sodium (ions) not moved (into/out of cell);
- By active transport
- No diffusion gradient for sodium (to move into cell with amino acid)
Describe the role of the enzymes of the digestive system in the complete breakdown of starch (5)
- Amylase
- (Starch) to maltose
- Maltase
- Maltose to glucose
- Hydrolysis
- (Of) glycosidic bond
Describe the processes involved in the absorption of the products of starch digestion (5)
- Glucose moves in with sodium (into epithelial cell)
- Via (carrier / channel) protein
- Sodium removed (from epithelial cell) by active transport / sodium- potassium pump
- Into blood
- Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium concentration gradient
- Glucose moves into blood
- By (facilitated) diffusion
Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (5)
- Micelles contain bile salts and fatty acids/monoglycerides
- Make fatty acids/monoglycerides (more) soluble (in water) | Bring/release/carry fatty acids/monoglycerides to cell/lining (of the iluem)
- Fatty acids/monoglycerides absorbed by diffusion
- Triglycerides (re)formed (in cells)
- Vesicles move to cell membrane
Describe the role of micelles in the absorption of fats into the cells lining the ileum (3)
- Micelles include bile salts and fatty acids
- Make the fatty acids (more) soluble in water
- Bring/release/carry fatty acids to cell/lining (of the ileum)
- Maintain high(er) concentration of fatty acids to cell/lining (of the ileum)
- Fatty acids (absorbed) by diffusion
Explain the advantages of lipid droplet and micelle formation (3)
- Droplets increase surface areas (for lipase / enzyme action)
- (So) faster hydrolysis / digestion
- Micelles carry fatty acids and glycerol / monoglycerides to / through membrane / to (intestinal epithelial) cell
Name structure Q in the diagram above and suggest how it is involved in the absorption of lipids (4)
- Golgi (apparatus)
- Modifies / processes triglycerides
- Combines triglycerides with proteins
- Packaged for release / exocytosis
- Forms vesicles
Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how. (3)
- Sodium ions actively transported from ileum cell to blood
- Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose)
- Glucose enters by facilitated diffusion with sodium ions
Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer (2)
- Single layer of cells - Reduces diffusion distance/pathway
- Permeable - Allows diffusion of oxygen/carbon dioxide
Describe and explain the mechanism that causes lungs to fill with air (3)
- Diaphragm (muscle) contracts and external intercostal muscles contract
- (Causes volume increase and) pressure decrease
- Air moves down a pressure gradient
Describe the pathway taken by an oxygen molecule from an alveolus to the blood (2)
- (Across) alveolar epithelium
- Endothelium / epithelium of capillary
Explain how one feature of an alveolus allows efficient gas exchange to occur (2)
- (The alveolar epithelium) is one cell thick
- Creating a short diffusion pathway / reduces the diffusion distance
Describe the gross structure of the human gas exchange system and how we breathe in and out (6)
- Named structures – trachea, bronchi, bronchioles, alveoli
- Breathing in – diaphragm contracts and external intercostal muscles contract
- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in)
- Breathing out - Diaphragm relaxes and internal intercostal muscles contract
- (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out)
Explain two ways in which the structure of fish gills is adapted for efficient gas exchange (2)
- Many lamella / filaments - large SA
- Thin (surface) so short diffusion pathway
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 O2 / CO2
Describe the role of red blood cells and haemoglobin in oxygen transport
- Red blood cells contain lots of haemoglobin (Hb) - no nucleus, biconcave, high SA:V, short diffusion path
- Hb associates with / binds / loads O2at gas exchange surfaces where partial pressure of O2 (pO2) is high
- This forms oxyhaemoglobin which transports O2 (each can carry 4O2 - one at each Haem group)
- Hb dissociates from / unloads O2 near cells / tissues where pO2
is low
Describe the structure of haemoglobin
- Protein with a quaternary structure
- Made of 4 polypeptide chains
- Each chain contains a Haem group containing an iron ion (Fe 2+)
The haemoglobins are a group of chemically similar molecules found in many different organisms.
Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve
Suggest how different lung diseases affect ventilation
- 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
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
Suggest how you can evaluate the way in which experimental data led to
statutory restrictions on the sources of risk factors
Explain how the cooperative nature of oxygen binding results in an S-shaped (sigmoid) oxyhaemoglobin dissociation curve
- Binding of first oxygen changes tertiary / quaternary structure of haemoglobin
- This uncovers Haem group binding sites, making further binding of oxygens easier
Describe evidence for the cooperative nature of oxygen binding
- A low pO2 as oxygen increases there is little / slow increase in % saturation of Hb with oxygen
- When first oxygen is binding
- At higher pO2
- as oxygen increases there is a big / rapid increase in % saturation of Hb with oxygen
- Showing it has got easier for oxygens to bind
What is the Bohr effect?
Effect of CO2 concentration on dissociation of oxyhaemoglobin → curve shifts to right
Explain effect of CO2 concentration on the dissociation of oxyhaemoglobin
- Increasing blood CO2 eg. due to increased rate of respiration
- Lowers blood pH (more acidic)
Reducing Hb’s affinity for oxygen as - shape / tertiary / quaternary structure changes slightly
- So more / faster unloading of oxygen to respiring cells at a given pO2
- How the curve provides evidence for this:
- at a given pO2 % saturation of Hb is lower
Explain why different types of haemoglobin can have different oxygen transport properties
- Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
- Resulting in different tertiary / quaternary structures / shape → different affinities for oxygen
Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties
Describe and explain the effect of increasing carbon dioxide concentration on the dissociation of oxyhaemoglobin (2)
- Increases/more oxygen dissociation/unloading
- (By) decreasing (blood) pH/increasing acidity
Use information in the graph to explain how the seal’s myoglobin dissociation curve shows the seal is adapted for diving (2)
- High(er) affinity for O2 (than haemoglobin)
- Allows (aerobic) respiration when diving/at low(er) pO2
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse (3)
- The mouse is smaller (Smaller so) larger surface area to volume ratio
- More/faster heat loss (per gram/in relation to body size)
- (Faster rate of) respiration/metabolism releases heat
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind.
Explain why (2)
- Binding of first oxygen changes tertiary / quaternary (structure) of haemoglobin
- Creates / leads to / uncovers second / another binding site
- First oxygen binds (to Hb) causing change in shape;
- (Shape change of Hb) allows more O2 to bind (easily) / greater saturation with O2
Explain the meaning of quaternary structure (1)
- (Molecule contains) more than one polypeptide (chain)
Describe the role of haemoglobin in supplying oxygen to the tissues of the body (2)
- Oxyhaemoglobin formed/ haemoglobin is loaded/ uptakes/associates/binds with oxygen in area of higher ppO2 / in gas exchange surface/lungs/gills
- (oxygen) unloaded/dissociates from/released (in area of lower
ppO2 / in capillaries/to cells/tissues)
Explain the advantage to a person with anaemia of the change shown in the oxygen
dissociation curve (3)
- (Anaemia curve shifted to right) haemoglobin has lower affinity for oxygen / binds less tightly
- releases more oxygen / oxygen is released quicker / oxygen dissociates/ unloads more readily to muscles/tissues/cells;
- For respiration
- High(er) affinity for oxygen / absorbs / loads more oxygen
- At lower partial pressure (of oxygen) / lower pO2
The oxygen dissociation curve of the fetus is to the left of that for its mother. Explain the
advantage of this for the fetus (2)
- Higher affinity / loads more oxygen at low / same / partial pressure / pO2
- (Therefore) oxygen moves from mother / to fetus
After birth, fetal haemoglobin is replaced with adult haemoglobin. Use the graph to suggest the advantage of this to the baby (2)
- Low affinity / oxygen dissociates
- (Oxygen) to respiring tissues / muscles / cells
The haemoglobin in one organism may have a different chemical structure from the
haemoglobin in another organism. Describe how (1)
- Different primary structure / amino acids / different number of polypeptide chains
- Low partial pressure of oxygen in lungs
- (Llama) haemoglobin able to load more oxygen / (llama) haemoglobin saturated (at low / particular partial pressure of oxygen)
- Higher affinity for oxygen
Describe the advantage of the Bohr effect during intense exercise (2)
- Increases disassociation / unloading of oxygen
- For aerobic respiration at the tissues
Define Affinity
- This is the tendacy for a molecule to bind with oxygen
Describe the general pattern of blood circulation in a mammal
- Closed double circulatory system - blood passes through heart twice for every circuit around body:
- Deoxygenated blood in right side of heart pumped to lungs; oxygenated returns to left side
- Oxygenated blood in left side of heart pumped to rest of body; deoxygenated returns to right
Suggest the importance of a double circulatory system
- Prevents mixing of oxygenated / deoxygenated blood
- So blood pumped to body is fully saturated with oxygen for aerobic respiration
- Blood can be pumped to body at a higher pressure (after being lower from lungs)
- Substances taken to / removed from body cells quicker / more efficiently
Draw a diagram to show the general pattern of blood circulation in a mammal, including the names of key blood vessels
Name the blood vessels entering and leaving the heart and lungs
- Vena cava – transports deoxygenated blood from respiring body tissues → heart
- Pulmonary artery – transports deoxygenated blood from heart → lungs
- Pulmonary vein – transports oxygenated blood from lungs → heart
- Aorta – transports oxygenated blood from heart → respiring body tissues
Name the blood vessels entering and leaving the kidneys
- Renal arteries – oxygenated blood → kidneys
- Renal veins – deoxygenated blood to vena cava from kidneys
Name the the blood vessels that carry oxygenated blood to the heart muscle
Coronary arteries - located on surface of the heart, branching from aorta
Label a diagram to show the gross structure of the human heart (inside)
Suggest why the wall of the left ventricle is thicker than that of the right
- Thicker muscle to contract with greater force
- To generate higher pressure to pump blood around entire body
Explain the pressure & volume changes and associated valve movementsduring the cardiac cycle that maintain a unidirectional flow of blood
Explain the pressure & volume changes and associated valve movementsduring the cardiac cycle that maintain a unidirectional flow of blood (Atria Systole)
- Atria contract → volume decreases, pressure increases
- Atrioventricular valves open when pressure in atria exceeds pressure in ventricles
-
Semilunar valves remain shut as pressure in arteries
exceeds pressure in ventricles - So blood pushed into ventricles
Explain the pressure & volume changes and associated valve movementsduring the cardiac cycle that maintain a unidirectional flow of blood (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
- So blood pushed out of heart through arteries
Explain the pressure & volume changes and associated valve movementsduring the cardiac cycle that maintain a 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
So blood fills atria via veins & flows passively to ventricles
Explain how graphs showing pressure or volume changes during the cardiac cycle can be interpreted, eg. to identify when valves are open / closed
Describe the equation for cardiac output
Cardiac output (volume of blood pumped out of heart per min) = stroke volume (volume of blood pumped in each heart beat) x heart rate (number of beats per min)
How can heart rate be calculated from cardiac cycle data?
Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)
Explain how the structure of arteries relates to their function
Function – carry blood away from heart at high pressure
- Thick smooth muscle tissue → can contract and control / maintain blood flow / pressure
- Thick elastic tissue → can stretch as ventricles contract and recoil as ventricles relax, to reduce pressure surges / even out blood pressure / maintain high pressure
- Thick wall → withstand high pressure / stop bursting
- Smooth / folded endothelium → reduces friction / can stretch
- Narrow lumen → increases / maintains high pressure
Explain how the structure of arterioles relates to their function
Function – (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues
- Thicker smooth muscle layer than arteries
- Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries
- Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries
- Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)
What are the function of arterioles ?
Function – (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues
Explain how the structure of veins relates to their function
Function – carry blood back to heart at lower pressure
- Wider lumen than arteries → less resistance to blood flow
- Very little elastic and muscle tissue → blood pressure lower
- Valves → prevent backflow of blood
Explain how the structure of capillaries relates to their function
Function - allow efficient exchange of substances between blood and tissue fluid (exchange surface)
- Wall is a thin (one cell) 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 walls between cells → allow larger substances through
Explain the formation of tissue fluid
- At the arteriole end of capillaries:
- Higher blood / hydrostatic pressure inside capillaries (due to contraction of ventricles) than tissue fluid (so net outward force)
- Forcing water (and dissolved substances) out of capillaries
- Large plasma proteins remain in capillary
Explain the return of tissue fluid to the circulatory system
- At the venule end of capillaries:
- Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
- (Due to water loss) an increasing concentration of plasma proteins lowers water potential in capillary below that of tissue fluid
- Water enters capillaries from tissue fluid by osmosis down a water potential gradient
- Excess water taken up by lymph capillaries and returned to circulatory system through veins
What is a risk factor? Give examples for cardiovascular disease
- An aspect of a person’s lifestyle or substances in a person’s body / environment
- That have been shown to be linked to an increased rate of disease
- Examples - age, diet high in salt or saturated fat, smoking, lack of exercise, genes
- The principles of analysis, interpretation and evaluation of data covered in ‘3.2 gas exchange’ also apply here.
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 is reduced - So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
- High blood pressure (eg. caused by high salt concentration) → high hydrostatic pressure
- Increases outward pressure from arterial end AND reduces inward pressure at venule end
- So 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
- (Overall) outward pressure of 3.2 kPa
- Forces small molecules out of capillary
The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why (1)
Loss of water / loss of fluid / friction (against capillary lining)
High blood pressure leads to an accumulation of tissue fluid. Explain how (3)
- High blood pressure = high hydrostatic pressure
- Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary
- (So) more tissue fluid formed / less tissue fluid is reabsorbed
Allow lymph system not able to drain tissues fast enough
The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why (3)
- Water has left the capillary
- Proteins (in blood) too large to leave capillary
- Increasing / giving higher concentration of blood proteins (and thus wp
Explain the role of the heart in the formation of tissue fluid (2)
- Contraction of ventricle(s) produces high blood / hydrostatic pressure
- (This) forces water (and some dissolved substances) out (of
blood capillaries)
Lymphoedema is a swelling in the legs which may be caused by a blockage in the lymphatic system. Suggest how a blockage in the lymphatic system could cause lymphoedema (1)
Excess tissue fluid cannot be (re)absorbed / builds up
Give one way in which fluid F is different from tissue fluid (1)
- (Blood) plasma
- More / larger proteins / less urea / carbon dioxide / more glucose / amino acids / fatty acids / oxygen / high(hydrostatic) pressure
The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure (1)
Contracts
Do NOT accept pumping
The blood pressure decreases along the length of the capillary. What causes this decrease in pressure? (1)
Loss of fluid
In children, some diets may result in a low concentration of protein in fluid F. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid (3)
- Water potential (in capillary) not as low / is higher / less negative / water potential gradient is reduced
- More tissue fluid formed (at arteriole end)
- Less / no water absorbed (into blood capillary) by osmosis; (into blood capillary)
Explain how fluid leaves the capillary at the arterial end (2)
- hydrostatic pressure / blood pressure / arterial pressure;
- greater than osmotic effect which forces molecules / fluid out
The hydrostatic pressure of the blood at the arteriole end of the capillary helps to form tissue fluid. Explain how (2)
- Hydrostatic pressure higher than osmotic “effect”;
- Forces / squeezes / pushes out / water / small molecules / ions / examples
Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue (4)
- permeable capillary wall / membrane
- single cell thick / thin walls, reduces diffusion distance
- flattened (endothelial) cells, reduces diffusion distance
- fenestrations / pores, allows large molecules through
- small diameter / narrow, gives a large surface area to volume / short diffusion distance
- narrow lumen, reduces flow rate giving more time for diffusion
- red blood cells in contact with wall / pass singly, gives short diffusion distance / more time for diffusion
Explain how tissue fluid is formed and how it may be returned to the circulatory system (6)
- (hydrostatic) pressure of blood high at arterial end
- fluid / water / soluble molecules pass out (reject plasma)
- proteins / large molecules remain
- this lowers the water potential / water potential becomes more negative
- water moves back into venous end of capillary (reject tissue fluid) by osmosis
- lymph system collects any excess tissue fluid which returns to blood /
circulatory system / link with vena cava / returns tissue fluid to vein
In humans, substances move out of the capillaries to form tissue fluid. Describe how this tissue fluid is returned to the circulatory system (3)
- (Hydrostatic) pressure lower in capillary / blood / higher in tissues / tissue fluid
- Water (returns)
- By osmosis
- Water potential lower / more negative in blood / capillary / higher / less negative water potential in tissues / via water potential gradient
- Due to protein (in blood)
- (Returns) via lymph (system / vessels);*
Give the pathway a red blood cell takes when travelling in the human circulatory system from a kidney to the lungs.
Do not include descriptions of pressure changes in the heart or the role of heart valves in your answer (3)
- Renal vein
- Vena cava to right atrium
- Right ventricle to pulmonary artery
Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection (2)
- Only use single lines/do not use sketching (lines)/ensure lines are
continuous/connected - Add labels/annotations/title
- Add magnification/scale (bar)
- Do not use shading/hatching
- Draw all parts to same scale/relative size
Describe two precautions the student should take when clearing away after the dissection (2)
- Carry/wash sharp instruments by holding handle
- Carry/wash sharp instruments by pointing away (from body)/down
- Disinfect instruments/surfaces
- Disinfect hands
Explain how an arteriole can reduce the blood flow into capillaries (2)
- Muscle contracts
- Constricts/narrows arteriole/lumen
Vasoconstriction
Name valve A and chamber B (1)
- (Left) atrioventricular
- Left ventricle
Give two safety precautions that should be followed when dissecting a heart (1)
- Use a sharp scalpel/scissors
- Wash hands/wear gloves
- Disinfect bench/equipment
- Cover any cuts
- Cut away from self/others/on a hard surface
- Safe disposal
Describe the function of xylem tissue
Transports water (and mineral ions) through the stem, up the plant to leaves of plants
Suggest how xylem tissue is adapted for its function
- Cells joined with no end walls forming a long continuous tube → water flows as a continuous column
- Cells contain no cytoplasm / nucleus → easier water flow / no obstructions
- Thick cell walls with lignin → provides support / withstand tension / prevents water loss
- Pits in side walls → allow lateral water movements
Explain the cohesion-tension theory of water transport in the xylem
Describe how to set up a potometer
Describe how a potometer can be used to measure the rate of transpiration
Potometer estimates transpiration rate by measuring water uptake
- Record position of air bubble
- Record distance moved in a certain amount of time (eg. 1 minute)
- Calculate volume of water uptake in a given time:
- Use radius of capillary tube to calculate cross-sectional area of water (πr2)
- Multiply this by distance moved by bubble
- Calculate rate of water uptake - divide volume by time taken
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
- Keep all other variables constant
Suggest limitations in using a potometer to measure rate of transpiration
- Rate of water uptake might not be same as rate of transpiration
- Water used for support / turgidity
- Water used in photosynthesis and produced during respiration
- Rate of movement through shoot in potometer may not be same as
rate of movement through shoot of whole plant - Shoot in potometer has no roots whereas a plant does
- Xylem cells very narrow
Suggest how different environmental variables affect transpiration rate
Describe the function of phloem tissue
Transports organic substances eg. sucrose in plants
Suggest how phloem tissue is adapted for its function
- Sieve tube elements
- No nucleus / few organelles → maximise space for / easier flow of organic substances
- End walls between cells perforated (sieve plate)
- Companion cells
- Many mitochondria → high rate of respiration to make ATP for active transport of solutes
What is translocation?
- Movement of assimilates / solutes such as sucrose
- From source cells (where made, eg. leaves) to sink cells (where used / stored, eg. roots) by mass flow
Explain the mass flow hypothesis for translocation in plants
- At source, sucrose is actively transported into phloem sieve tubes / cells
- By companion cells
- This lowers water potential in sieve tubes so water enters (from xylem) by osmosis
- This increases hydrostatic pressure in sieve tubes (at source) / creates a hydrostatic pressure gradient
- So 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
Describe the use of tracer experiments to investigate transport in plants
- Leaf supplied with a radioactive tracer eg. CO2 containing radioactive isotope 14C
- Radioactive carbon incorporated into organic substances during photosynthesis
- These move around plant by translocation
- Movement tracked using autoradiography or a Geiger counter
Describe the use of ringing experiments to investigate transport in plants
- Remove / kill phloem eg. remove a ring of bark
- Bulge forms on source side of ring
- Fluid from bulge has higher conc. of sugars than below - shows sugar is transported in phloem
- Tissues below ring die as cannot get organic substances
Suggest some points to consider when interpreting evidence from tracer &
ringing experiments and evaluating evidence for / against the mass flow
hypothesis
- Is there evidence to suggest the phloem (as opposed to the xylem) is involved ?
- Is there evidence to suggest respiration / active transport is involved?
- Is there evidence to show movement is from source to sink? What are these in the experiment?
- Is there evidence to suggest movement is from high to low hydrostatic pressure?
- Could movement be due to another factor eg. gravity?
The mass flow hypothesis is used to explain the movement of substances through phloem. Use your understanding of the mass flow hypothesis to explain how pressure is generated inside this phloem tube (3)
- Sucrose actively transported (into phloem)
- Lowering/reducing water potential
- Water moves (into phloem) by osmosis (from xylem)
The student used a sharp scalpel to cut the celery. Describe how she should ensure she handled the scalpel safely during this procedure (2)
- Cut away from body
- Against hard/non-slip/flat surface
The rate of water movement through a shoot in a potometer may not be the same as the rate of water movement through the shoot of a whole plant.
Suggest one reason why (1)
- Plant has roots
- xylem cells very narrow
Describe the mass flow hypothesis for the mechanism of translocation in plants (4)
- In source / leaf sugars (sucrose) actively transported into phloem;
- By companion cells;
- Lowers water potential of sieve cell / tube and water enters by osmosis;
- Increase in hydrostatic pressure causes mass movement (towards sink / root);
- Sugars used / converted in root for respiration for storage
The scientist used the reduction in total leaf area of the experimental plants as an indicator of plant growth. Outline a method by which you could find the area of a plant leaf (1)
Draw around leaf on graph paper and count squares
Describe the cohesion-theory of water transport in the xylem (5)
- Water is lost from leaves beacuse of transpiration / evaporation of water - diffusion from mesophyll cells
- Diffusion through open stomata from leaves
- Lowers water potential of mesophyll / leaf cells
- Water pulled up by xylem (creating tension)
- Water molecules cohere / stick together by hydrogen bonds
- Forming a continuous water column
- Adhesion of water molecules to walls of xylem
Define Transpiration
The evaporation of water from the walls of the spongy mesophyll cells (using solar energy) and diffuses as water vapour through the stomata
Adaptations of capillaries (5)
- Flattened Endothelium - Smooth to reduce friction
- Narrow Lumen - singular movement
- Very small - Reduces rate of flow - more time for diffusion
- Gaps / pores / fenestrations between endothelial cells - Allows movement of large substances
- Thin wall - endothelium one cell thick - flattened cells - Short diffusion pathway - rapid exchange of substances between the blood and tissue fluid
Adaptations of veins (5)
- Endothelium - smooth to reduce friction + short diffusion pathway
- semi-lunar valves - prevents backflow of blood
- Wide lumen - Allows laege volumes of blood to flow
- Wall distends easily - allows veins to accomodate changing volumes of blood
- Thin walls - withstands low pressures / allows surrounding skeletal muscles to squeeze / veins do not have to withstand high pressures
Adaptations of arteries / Arterioles (7)
- Endothelium - smooth to reduce friction
- Thickest muscular wall - enabling the artieries to carry blood at high pressures / to withstand pressure surges
- Narrow lumen - Maintains high pressure
- Elastic fibres / tissues / wall - Expands / stretches under pressure then recoils / springs back to maintain pressure / to smooth the surges
- Collagen fibres - provide strength
- Musce fibres - Maintains high pressure; contracts to reduce diameter of lumen to help divert blood to where needed / to recude blood flow / control blood flow
Tissue fluid is formed from blood at the arteriole end of a capillary bed.
Explain how water from tissue fluid is returned to the circulatory system (4)
- (Plasma) proteins remain
- (Creates) water potential gradient
- Water moves (to blood) by osmosis
- Returns (to blood) by lymphatic system
Phloem pressure is reduced during the hottest part of the day. Use information in the graph above along with your understanding of transpiration and mass flow to explain why (3)
- High (rate of) transpiration/evaporation
- Water lost through stomata
- (Causes) less water movement from xylem to phloem
- Insufficient water potential in phloem to draw water from xylem
Identify the type of blood vessel labelled M in the figure above, Explain your answer (2)
- Vein
- Wide(r) lumen
- a ) Initial and final mass (of beaker and all contents)
- Number of (groups of) xylem vessels
- b ) Prevent evaporation/water loss
- (So) evaporation/water loss/transpiration only from celery
Tissue fluid is formed from blood at the arteriole end of a capillary bed. Explain how water from tissue fluid is returned to the circulatory system (4)
- (Plasma) proteins remain
- (Creates) water potential gradient as it reduces the water potential of the blood
- Water moves (to blood) by osmosis
- Returns (to blood) by lymphatic system
- Aortic/semi-lunar valves is closed
- Because pressure in aorta higher than in ventricle
At Q on the diagram above there is a small increase in pressure and in rate of blood flow in the aorta.
Explain how this happens and its importance (2)
- Elastic recoil (of the aorta wall/tissue)
- Smooths the blood flow
A student correctly plotted the right ventricle pressure on the same grid as the left ventricle pressure in diagram above.
Describe one way in which the student’s curve would be similar to and one way it would be different from the curve shown in the diagram above.
- Peaks/contractions at the same/similar time
- Lower pressure
Phloem pressure falls as (rate of) water movement (in xylem) increases
Phloem pressure is reduced during the hottest part of the day. Use information in the graph above along with your understanding of transpiration and mass flow to explain why (3)
- High (rate of) transpiration/evaporation;
- Water lost through stomata
- (Causes) less water movement from xylem to phloem
- Water evaporates/is transpired (from leaves/ stalk/celery/plant)
- Water potential gradient/lower water potential creates tension/pulls up water
- Hydrogen bonds/cohesion/adhesion maintains column
- Used to compare effect of other treatments / as a baseline
- Shows / Measures effect of substance (X)
Using the diagram and the table above, what can you conclude from treatments D and E about root growth? (3)
- (D shows) substance (X) is not required for (some) root growth / production of roots
- Substance X moves through plant
- (E shows) substance (X) causes / increases / doubles number of roots / root growth
The mass flow hypothesis is used to explain the movement of substances through phloem. Evaluate whether the information from this investigation supports this hypothesis. Do not consider statistical analysis in the answer (4)
Give two reasons why it was important that the student counted the number of stomata in several parts of each piece of leaf tissue (2)
- So it is a representative sample
- To obtain a (reliable) mean
Other than the distribution of stomata, suggest and explain two xerophytic
features the leaves of this plant might have (2)
- Hairs so ‘trap’ water vapour and water potential gradient decreased
- Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased
- Thick (cuticle/waxy) layer so increases diffusion distance
- Waxy layer/cuticle so reduces evaporation/transpiration
- Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased
- Spines/needles so reduces surface area to volume ratio
Suggest two reasons why the rate of water uptake by a plant might not be the same as the rate of transpiration (2)
- Water used for support/turgidity
- Water used in photosynthesis
- Water used in hydrolysis
Using the information provided, explain how two features of the body of the
tubifex worm allow efficient gas exchange (2)
- Thin/small so short diffusion pathway
- Flat/long/small/thin so large surface area to volume ratio/surface area volume
- Water potential higher in worm
- Water leaves by osmosis (and worm dies)
The mean FEV1 value of non-smokers decreases after the age of 30.
Use your knowledge of ventilation to suggest why (1)
Internal intercostal muscle(s) less effective
Describe the processes involved in the transport of sugars in plant stems (5)
- (At source) sucrose is actively (transported) into the phloem/sieve element/tube
- By companion/transfer cells
- Lowers water potential in phloem/sieve element/tube and water enters by osmosis
- Produces) high (hydrostatic) pressure
- Mass flow/transport towards sink/roots/storage tissue
- At sink/roots sugars are removed/unloaded
Explain why oxygen uptake is a measure of metabolic rate in organisms (1)
(Oxygen used in) respiration, which provides energy / ATP
Use your knowledge of transport across membranes to explain the shape of the curve in Figure 1 for uptake of monosaccharides between concentrations
A and B | C and D
- . Movement through carrier proteins
- Facilitated diffusion
- Between A and B
- Rate of uptake proportional to (external) concentration
- Between C and D
- All channel / carrier proteins in use / saturated / limiting
Figure 1 is evidence for monoglycerides being lipid-soluble molecules.
Suggest how (2)
- Rate of uptake is proportional / does not level off (so diffusion occurring)
- (Lipid-soluble molecules) diffuse through / are soluble in phospholipid (bilayer)
What is digestion? (2)
- Hydrolysis (of)
- (Large / insoluble substances) to small(er) / soluble substances
Endocellulases and exocellulases act at different places on cellulose molecules. Suggest why (2)
Endocellulases act in the middle of the cellulose molecule and exocellulases act at the
ends of the cellulose molecule
- Active sites are different shapes
- So different enzyme-substrate complexes (are formed)
- So complementary to different parts of cellulose / substrate
The scientist used the same concentration of endocellulase and exocellulase in the box mixtures. The rate of digestion of cellulose is greatest when both enzymes are present.
Suggest why (2)
- Endocellulase create more ends / increases surface area
- For exocellulase to act on / hydrolyse / digest
