Exchange and Mass Transport Flashcards
Alveoli Adaptations
- many alveoli (increase surface area)
- squamous epithelium walls (short diffusion path)
- folded walls (increase surface area)
- ventilation/blood circulation (maintains concentration gradient)
- narrow capillaries compress red blood cells (short diffusion path)
Explain why multicellular organisms require gas exchange systems
- large volume of living cells
- high metabolic requirements
- small surface area to volume ratio
- large diffusion path
Reasons mammalian lungs are within the body
- air alone is not dense enough to protect delicate structures
- reduces water loss to maintain moist gas exchange surface
Give adaptations of airways
- ciliated epithelium (goblet cells produce mucus) traps dust and antigens which cilia move upwards for removal
- smooth muscles constrict to protect alveoli from dust and particulates
Ventilation
Movement of air into and out of lungs
Describe the process of inspiration in terms of pressure changes in the thoracic cavity
- external intercostal muscles contract and internal relax
- diaphragm contracts and flattens
- pressure decreases
- volume increases as lungs fill
Describe the process of expiration in terms of pressure changes in thoracic cavity
- internal intercostal muscles contract and external relax
- diaphragm relaxes and moves up
- pressure increases
- volume decreases as lungs empty
Pulmonary Ventilation Rate
PVR = tidal volume x breathing rate
tidal volume - volume of air entering lungs with each breath at rest
ventilation rate - number of breaths per minute
Reason insects require specialised gas exchange systems
- small surface area to volume ratio
- very active so high metabolic requirements
Describe adaptations for gas exchange in insects
- tracheoles have thin walls (short diffusion path)
- tracheoles HIGHLY branched (short diffusion path/large surface area)
- tracheae tubes are full of air (fast diffusion)
- fluid in the end of tracheoles that moves into tissues during exercise (so faster diffusion to gas exchange surface)
- can move body by muscles to move air (maintain steep concentration gradient for oxygen)
Describe ventilation in larger insects
- contract abdominal muscles
- compresses internal tracheal system
- pressure changes cause movement of air in and out
Explain how insects are adapted for high activity
- end of tracheoles are filled with water
- major activity leads to build up of lactate in cells from anaerobic respiration
- water is drawn into cells by osmosis
- forces air into end of tracheoles via spiracles
Adaptations of insects to reduce water loss
- small surface area to volume ratio
- waterproof cuticle
- spiracle is sunken to trap moisture and prevent evaporation
- spiracles closed most of the time/open periodically
Suggest why gas exchange surfaces are kept moist
- to allow gases to dissolve
- gases only cross cell-surface membranes if dissolved in aqueous solution
Describe a double circulatory system
- blood circulates in two loops passing through the heart twice in each full circuit
- one loop consists of the heart and lungs and the other of the heart and rest of the body
Explain why mammals have a double circulatory system
- blood pressure is reduced at the lungs
- so blood returns to the heart to boost the pressure before travelling to rest of the body
- high pressure allows oxygen and nutrients to be delivered to muscles quickly
- necessary due to the high metabolic requirements of mammals
Describe and explain the importance of ventilation in fish
- open mouth to let water in and close to force water through gills in one direction
- allows for more efficient gas exchange
- important due to low oxygen concentration in water
Describe adaptations of fish for gas exchange
- MANY gill filaments (increase surface area)
- lamellae at right angles to filaments (further increasing surface area)
- walls of lamellae are thin (short diffusion path)
- counter current flow (maintains steep concentration gradient)
- ventilation and blood circulation (maintain steep concentration gradient)
Explain counter current flow in fish
- blood and water flow in opposite directions
- blood always passing water with HIGHER O2 concentration
- maintains a high concentration gradient across WHOLE length of lamellae (without it equilibrium is reached halfway across lamellae)
Explain why small organisms do not require gas exchange systems
- large surface area to volume ratio
- can obtain enough oxygen through cell-surface membrane
Explain why water is always lost from gas exchange surfaces of terrestrial organisms
- all gas exchange surfaces have to be moist
- water moves down the water potential gradient and evaporates
Function of atrioventricular valves
- prevent backflow of blood into atria when ventricles contract
- ensure blood moves out of aorta and pulmonary artery
Function of semilunar valves
- prevent backflow of blood into ventricles
- when pressure in aorta/pulmonary artery exceeds ventricles
Function of pocket valves in veins
- ensures blood flows towards the heart
- when skeletal muscles contract and compress veins
Describe and explain features of blood vessels
- fibrous outer layer resists pressure changes
- muscle layer contracts to control blood flow
- elastic layer maintains CONSTANT blood pressure and reduce pressure surges by stretching and recoiling
- squamous endothelium layer is smooth to reduce friction and thin to allow diffusion
Describe how capillaries are adapted to their function
- thin (short diffusion path)
- branched (large surface area)
- narrow lumen so red blood cells are compressed against wall (short diffusion path of oxygen)
- spaces between lining allow white blood cells to enter tissues to treat infection
Tissue fluid
Watery fluid containing mineral salts, glucose, urea, small proteins, amino acids and white blood cells
Explain why hydrostatic pressure is lower and water potential is more negative at venous end of capillary
- lower hydrostatic pressure since venous end has wider lumen so less resistance / loss of fluid
- water potential is more negative since water leaves but large proteins are too large to leave capillary so protein concentration is high
Explain the formation of tissue fluid
- created by ultrafiltration
- high hydrostatic pressure from arteriole forces water with dissolved substances out of blood plasma
REJECT blood plasma/ tissue fluid out
Explain how tissue fluid is returned to the blood
- low hydrostatic pressure at venous end of capillary causes tissue fluid to flow back into the capillary
- down the water potential gradient by osmosis (due to proteins in vessel)
- EXCESS tissue fluid returned via lymphatic system
Describe the formation of lymph and suggest how it is moved around the body
- filtration of blood plasma normally exceeds reabsorption resulting in EXCESS tissue fluid
- increase in hydrostatic pressure in interstitial spaces forced fluid into lymphatic capillaries (to prevent build up)
- returned to the circulatory system near the vena cava
- moved by hydrostatic pressure and muscular contractions
Atrial Systole
- contraction of atrial walls
- ventricles relax and blood flows into them
Ventricular Systole
- contraction of ventricles (AV valves close)
- ventricular pressure exceeds aorta and pulmonary artery (SL valves open)
Atrial-Ventricular Diastole
- blood enters atria and ventricles from pulmonary vein and vena cava
- pressure in atria exceeds ventricles (AV valves open)
- ventricles are relaxed so pressure in lower than in aorta and pulmonary artery (SL valves close)
Cardiac Output
- volume of blood pumped by one ventricle in one minute
= heart rate x stroke volume (volume of blood pumped out by each beat)
Suggest what causes the typical lub-tub sound of the heartbeat
- lub refers to AV valve closing
- dub refers to SL valve closing
Haemoglobin
- red protein responsible for transporting oxygen
- quaternary structure
- consists of four polypeptide chains each with a haem group that contains ferrous (Fe2+) ion which can bind to one oxygen molecule
- each haemoglobin carries 4 oxygen molecules
Affect on oxygen affinity in high concentration of :
a) oxygen
b) carbon dioxide
c) carbon monoxide
a) increases
b) decreases
c) increases - binds too strongly so oxygen cannot dissociate to supply cells
Explain sigmoidal curve
- binding of first oxygen has allosteric effect causing a change in shape of haemoglobin
- increases affinity of haemoglobin for next oxygen
- smaller increase in partial pressure required for attachment of next oxygen so curve gets steeper
- effect is known as positive cooperativity
- curve flattens out because fewer binding sites are available for attachment of final oxygen
Explain a shift of the right on oxygen affinity curve
- lower oxygen affinity AT LOW PP
- unloading of oxygen MORE READILY at tissues
- more oxygen in tissues
- greater rate of respiration for high metabolic activity etc
Explain a shift of the left on oxygen affinity curve
- greater affinity to oxygen AT LOW PP
- useful in low oxygen environments as haemoglobin is fully SATURATED
- tissues are fully supplied with oxygen
Bohr effect
Greater concentration of carbon dioxide means haemoglobin has lower oxygen affinity
Explain how carbon dioxide changes oxygen affinity
- carbon dioxide dissolved in plasma as carbonic acid
- blood have a lower pH
- causes haemoglobin to denature so its tertiary structure changes shape
- oxygen binds less strongly
Adaptations of leaves for gas exchange
- leaves are thin so short distance for gas exchange
- air spaces in spongy mesophyll so gases can readily diffuse
- palisade cells give a large surface area for faster diffusion
- many stomata and spread out to allow diffusion of gases in and out of cell
Describe adaptations of xerophytes for limiting water loss
- thick cuticle to increase diffusion distance
- waxy cuticle to reduce evaporation
- rolling leaves/ hairs / stomata in sunken pits to trap moist air to decrease water potential gradient
- spines to reduce surface area to volume ratio
Xerophytes
Plants that are adapted to living in areas where water is in short supply
Explain how transpiration occurs
- water evaporate from surface of mesophyll cells to form water vapour
- water vapour diffuses through leaf tissue and collects at air spaces surrounding stoma
- water potential of air spaces next to stomata is higher than surrounding atmosphere
- water molecules diffuse out into the surrounding air
- down water potential gradient
Explain how water moves up xylem vessels
- transpiration occurs where water evaporates from mesophyll cells
- lower water potential of leaf tissue
- H bonds form between water molecules known as cohesion
- water forms continuous column down xylem
- when water evaporates more molecules of water are drawn up by transpiration pull
- adhesion of water to sides of xylem vessel so it is under tension due to negative pressure (cohesion-tension theory)
Evidence of cohesion-tension theory in xylem vessels
- diameter of trees are reduces during the day when transpiration rate is highest (tension)
- broken xylem vessels allows air to enter and water does not leak out (tension) and cannot draw up water as continuous column of water is broken (cohesion)
Suggest why transpiration is a passive process
- does not require metabolic energy to take place so water is not actively transported
- energy is supplied by the sun
Explain how a potometer is prepared
- leafy shoot is cut under water to prevent air entering xylem
- potometer is filled with water and leafy shoot is fitted under water
- air bubble is introduced in capillary tube
Suggest why potometer have a reservoir attached
Tap of reservoir can be opened to push air bubble back to start of scale to reset potometer
Describe how increasing light intensity affects transpiration rate of plant
Increases as more stomata open due to photosynthesis
Describe how increasing temperature affects transpiration rate of plant
Increases as water molecules have more kinetic energy so more evaporation takes place
Describe how increasing humidity affects transpiration rate of plant
Decreases due to reduced water potential gradient
Describe how wind affects transpiration rate of plant
Increases as wind displaces air containing water vapour so maintains a steep water potential gradient
Structure of Xylem
- long, continuous tubes with no end wall
- dead cells
- cellulose walls contain lignin (forms rings around vessel) so impermeable to water + prevents collapse under tension
Structure of Phloem
- made up of sieve tube elements (actively transports solutes) associated with companion cells (provide every for active transport)
- living cells
- non continuous
Translocation
Process by which organic molecules and some mineral ions are transported from one part of a plant to another
Suggest why phloem vessels are closer to the outside of the stem rather than xylem vessels
- phloem cells are living so can grow back if damaged
- xylem vessels are dead so cannot be repaired and
water cannot travel up plant if damaged
Suggest ways organic substances are used at sinks
- respiration
- growth
- storage as starch
Suggest why it is an advantage to transport sucrose over glucose in phloem
Sucrose is a non-reducing sugar so less reactive which means it is less likely to be used during transport
Explain why phloem tissue is in close association with xylem vessels
- water flows into phloem by osmosis
- down water potential gradient from xylem
- hydrostatic pressure moves organic substances along phloem
Translocation
Movement of organic molecules and some mineral ions in the phloem from one part of a plant to another
Compare structure of sieve tube elements to companion cells
- less cytoplasm
- fewer organelles
- larger vacuole
- no nucleus or ribosomes
- contains sieve plate
Evidence for transport in phloem
- ringing experiment where phloem bark is removed to show organic molecules cannot pass below region of removal so death of tissues and swelling
- radioactively labelled 14C organic molecules show up in phloem when section of stem is autoradiographed
- sap removed by aphid contains organic molecules and microscopy shows piercing mouthparts in phloem cells
Describe and explain how organic substances are transported in plants
- sucrose diffuses by facilitated diffusion into companion cells from photosynthesising cells
- H+ actively transported from companion cells into spaces in cells wall using ATP
- then facilitated diffusion through carrier proteins into sieve tube elements taking sucrose with them (co-transport)
- lower water potential in sieve tube so water flows in from xylem by osmosis
- hydrostatic pressure moves organic molecules along
- hydrostatic gradient maintained as sucrose is actively transported into respiring cells (sink)
Suggest why ventilation rate of lab rats increases when carbon dioxide is pumped their chamber
- increase volume of air entering their lungs per minute
- to provide the same amount of oxygen in the same amount of time
Role of tendons in heart
Prevent valves from inverting
Suggest advantage of change in oxygen affinity of haemoglobin for oxygen
Ensures rapid uptake of oxygen at lungs and release at tissues
Suggest why it is an advantage that sieve cells have fewer organelles than companion cells
- larger cytoplasm
- easier flow of sugars (less resistance)
Adaptations of xylem vessel
- hollow tubes with no end cell wall to allow easy passage of water
- lignified wall gives strength to support plant and prevent collapse under transpiration pull
Partial Pressure
Contribution of one gas in a mixture to the total pressure exerted by a gas mixture
Explain why smaller organisms have higher metabolic requirements compared to larger organisms
- greater surface area to volume ratio
- heat lost at a faster rate
- more oxygen required for respiration
Explain why cold-blooded organisms are able to exist at much smaller sizes than warm-blooded organisms
- do not have to produce heat to maintain body temperature
- less energy lost as heat
- can have greater surface area to volume ratio without significantly greater metabolic requirement
Suggest what creates hydrostatic pressure
increase in VOLUME
