EXCHANGE AND TRANSPORT SYSTEMS

- small animals have a high SA:V (more surface area for diffusion to act on)

- a larger surface area increases heat loss and water loss

- small animals with high metabolic rates and a large SA:V eat high energy foods (e.g. seeds and nuts) and have thick layers of fur or hibernate when the weather is cold

- larger animals with a small SA:V that live in hot regions do not lose heat as easily so may develop physiological or behavioural adaptations such as spending most of the day in water (hippos) or developing large flat ears to increase surface area for heat loss (elephants)

- single celled organisms absorb and release gases by diffusion through their outer surface and have a large SA:V, thin surface and short diffusion pathway

- water (containing oxygen) enters mouth of fish and passes out through gills

- each gill made up of gill filaments = big SA:V

- gill filaments covered in lamellae (increase SA:V even further)

- lamalle have lots of blood capillaries (good blood supply) and thin surface layer (short diffusion pathway) to speed up rate of diffusion

- blood flows through lamellae in one direction and water flows over in the other direction = counter-current system 

- maintains large conc. gradient (conc. of oxygen in water always higher than that of bood, so lots of oxygen diffuses into blood)

- air moves into tracheae (microscopic air-filled pipes) through spiracles

- oxygen travels down conc. gradient towards cells

- tracheae branch off into tracheoles which have thin, permeable walls and go to individual cells, which means oxygen diffuses directly into respiring cells

- carbon dioxide from the cells moves down its conc. gradient towards the spiracles and is released into the atmosphere

- insects use rhythmic abdominal movements to move air in and out of spiracles or to close to spiracls to prevent water loss

- insects have a waterproof, waxy cuticle on body and hairs around spiracles to reduce evaporation

- gas exchange surface at surface of mesophyll cells which have a large SA:V. mesophyll cells inside the leaf so gases move in through pores in the epidermis called the stomata

- stomata open to allow gases to move in and close to prevent water loss. guard cells control the opening and closing of the stomata

- plants adapted for warm/dry/windy habitats where water loss is a problem are called xerophytes which have several adaptations:

- stomata sunk in pits that trap moist air, reducing conc. gradient of water between leaf and air so reduces amount of water diffusing out of leaf 

- layer of hairs on epidermis to trap moist air and waxy, waterproof cuticles

- curled leaves with stomata inside to protect against wind and reduced number of stomata (fewer places for water to escape)

- air enters trachea 

- trachea splits into two bronchi, one bronchus leading to each lung

- each bronchus splits off into bronchioles

- bronchioles end in small air sacs called alveoli

- large no. of alveoli in lungs (large SA:V) with thin cell wall and good blood supply (each alveoli surrounded by network of capillaries)

- oxygen diffuses out of alveoli through the alveolar epithelium, the capillary endothelium and into the haemoglobin 

INSPIRATION

- external intercostal muscles and diaphragm muscles contract

- ribcage moves up and out, diaphragm flattens and volume of thoracic cavity increases

- lung pressure decreases and air flows into lungs (from high atmospheric pressure to low pressure)

EXPIRATION

- external intercostal muscles and diaphragm muscles relax

- ribcage moves down and in, diaphragm contracts and volume of thoracic cavity decreases

- lung pressure increases and air is forced out of lungs down conc. gradient

Tidal volume - volume of air in each normal breath

Ventiliation rate - number of breathes per minute

Forced expiratory volume - maximum volume of air that can be forced out in 1 second

Forced vital capacity - maximum volume of air it is possible to breathe forcefully out of the lungs after manimum inspiration

Residual volume - the amount of air left in the lungs after maximum expiration

Spirometer  - breathing aparatus used to measure all of the above

TB - cells build up wall around TB bacteria in lungs forming small, hard lumps called tubercles

- infected tissues within turbercles die so gasesous exhcnage is damaged and tidal vol. decreases

- causes fibrosis (build up of scar tissue) further reducing tidal vol., meaning less air is inhaled with each breath, so patients have to breathe faster (ventilation rate is increased)

- symptoms: coughing (with blood and mucus), chest pains, fatigue, shortness of breath

Fibrosis - formation of scar tissue due to exposure to asbestos or dust

- scar tissue is thicker and less elastic than lung tissue, meaning lungs are less able to expand so can't hold as much air, so tidal vol. is reduced and venilation rate increased. also causes a reduction in diffusion (slower across a thicker, scarred membrane)

- symptoms: shortness of breath, dry cough, chest pain, fatigue and weakness

Asthma - airways become inflamed and irritated due to allergic reaction with dust or pollen

- during asthma attack, smooth muscle of bronchioles contract and mucus is produced. this causes constriction of airways making it difficult to breathe. air flow is reduced so less oxygen moves into blood 

- symptoms: wheezing, tight chest, shortness of breath. attacks can be relieved by inhalers

Emphysema - inflammation caused by smoking or exposure to air pollution

- inflammation attracts phagocytes which produces an enzyme that breaks down elastin (protein found in walls of alveoli which helps alveoli return to normal shape after ventilation)

- leads to destruction of alveoli which reduces SA:V which reduces rate of diffusion

- symptoms: shortness of breath, wheezing and increased ventilation rate 

- amylase, produded by salivary glands and pancreas (into small inenstine), catalyses the conversion of starch (polysaccharide) into maltose (disaccharide) by hydrolysing the glycosidic bonds in starch

- membrane-bound disaccharidases, attached to cell membranes of epithelial cells in ileum, break down disccharides into monosaccharides via the hyrolysis of glycosidic bonds 

- maltose is broken down by maltase to produce glucose + glucose

- sucrose is broken down by sucrase to produce glucose + fructose

- lactose is broken down by lactase to produce glucose + galactose

- glucose and galactose is then absorbed by active transport with sodium ions via a co-transporter protein

- fructose is then absorbed via facilitated diffusion via a different co-transporter protein

- lipase, secreted by the pancreas (into small intenstine), catalyse the breakdown of lipids into monoglycerides and fatty acids via the hyrdolsis of ester bonds in lipids

- bile salts are produced by the liver which emulsify lipids, causing the lipids to form small droplets

- several small lipid droplets form a bigger SA:V than a large single droplet so there is more area for the enzyme to act on

- once the lipid is broken down, the monoglycerides and fatty acids stick with the bile salts to form micelles

- micelles help to move monoglyerides and fatty acids towards the epithelium. micelles break down and reform which releases the monoglycerides and fatty acids to be absorbed - they are lipid-soluble so can diffuse across the epithelial cell membrane freely. micelles are not absorbed

- broken down by proteases which catalyse the conversion of proteins into amino acids by hydrolysing the peptide bonds between them

- endopeptidases hydrolyse peptide bonds within a protein. examples include trypsin and chymotrypsin (synthesised in the pacreas for the small intestine) and pepsin (released by stomach cells and work only in acidic conditions)

- exopeptidases hydrolyse peptide bonds at the ends of proteins by removing single amino acids. examples include dipeptidases which work specifically on dipeptides by seperating the amino acids that make up a dipeptide by hydrolysing the peptide bond between them (located in cell-surface membrane of epithelial cells in small intenstine)

- haemoglobin is contained in red blood cells and has a large quaternary structure (4 polypeptide chains) each with one haem group containing an iron ion (gives blood its red colour). haemoglobin has a high affinity for oxygen (can carry 4 oxygen molecules at a time) and joins with oxygen to form oxyhaemoglobin

- haemoglobin's affinity for oxygen varies depending on partial pressure of oxygen (measure of oxygen concentration) - oxygen loads onto haemoglobin to form oxyhaemoglobin at a high partial pressure of oxygen (lungs) and oxyhaemoglobin unloads its oxygen at a low partial presure of oxygen (respiring cells)

- dissociation curves show an 'S' shape - when haemoglobin first combines with oxygen, its shape alters in a way that makes it easier for other molecules to join too. but as the haemoglobin starts to become saturated, it gets harder for more oxygen molecules to join 

- haemoglobin gives up its oxygen more readily at higher partial pressures of carbon dioxide. respiring cells produce carbon dioxide which increases the rate of oxygen unloading (the rate at which oxyhaemoglobin dissociates) so dissociation curves shifts right = the Bohr effect

- foetal haemoglobin and myoglobin = higher affinity than (adult) haemoglobin

- circulatory system = heart and blood vessels. heart pumps blood through blood vessels to target organs or to lungs (two circuit system). blood carries respiratory gases, metabolic waste and hormones

- arteries carry blood from the heart to rest of body. walls are thick and mscular and have elastic tissue for stretch and recoil as the heart beats (helps maintain high pressure). the endothelium is folded, allowing artery to stretch. carries oxygenated blood

- arterioles are sub-divisions of arteries. they form a network throughout the body and contract to restrict blood flow or relax to allow full blood flow

- capillaries are sub-divisions of arterioles and facilitate exchange of small molecules (i.e. glucose and oxygen) between cells and blood vessels. they are adapted for efficient diffusion: near cells and one cell thick = short diffusion pathway; large no. of capillaries = increased SA for exchange

- veins take blood back to the heart under low pressure. they have a wider lumen with little elastic tissue. veins contain valves to prevent backflow of blood and carry deoxygenated blood

- made of oxygen, water and nutrients (no red blood cells or big proteins as too large to be pushed out of capillary walls)

- at start of capillary bed at the arterial end, the hydrostatic pressure inside capillaries is greater than in the tissue fluid

- this difference means an overall outward pressure forces fluid out of the capillaries into spaces around cells, forming tissue fluid

- as fluid leaves, the hydrostatic pressure reduces in the capillaries - so hydrostatic pressure is lower at venule end of the capillary bed

- due to fluid loss and increasing conc. of plasma proteins (unable to leave as too big), water potential at venule end is lower than water potential in tissue fluid

- therefore water re-enters capillaries from tissue fluid at venule end via osmosis

- left ventricle of heart has thicker, more muscular walls as it needs to contract powerfully to pump blood all the way round the body

- ventricles have thicker walls than in atria because they have to push blood out of the heart whereas the atria just have to push the blood a short distance into the ventricles

- the atrioventricular valves (AV) valves prevent backflow of blood from ventricles to atria when the ventricles contract

- the semi-lunar (SL) valves prevent backflow of blood from pulmonary artery and aorta to ventricles after the ventricles contract

- the cords attach the atrioventricular valves to the ventricles to stop them being forced up into the atria when the ventricles contract

- the valves only open one way. if there's a high pressure behind it, it's forced open, but if the pressure is in front of the valve, it's forced shut. this ensures blood only flows one way

- ventricles are relaxed. SAN recieves impulse and sends wave of electrical acitivity across the atria, causing the atria to contract simultaneously, pushing blood into the ventricles as the atrioventricular valves are forced open

- the atria relax and the atrioventricular valves are forced shut to prevent backflow as pressure increases in the ventricles. the AVN receivies the electrical impulse from the SAN and, after a short delay (to ensure all blood has left the atria), the AVN stimulates the ventricles to contract simultaneously. the semi-lunar valves open and blood is forced into the aorta and pulmonary artery

- ventricles and atria both relax. high pressure in aorta and pulmonary artery cause semi-lunar valves to shut to prevent backflow of blood. blood returns to the heart and the atria begin to fill again due to high pressure from vena cava and pulmonary vein. pressure in ventricles fall below pressure of atria so atrioventricular valves open and blood passively flows in

- if damage occurs to endothelium, macrophages and lipids form from the blood clump together to form fatty streaks. over time, this builds up and harden to form fibrous plaque = atheroma

- the atheroma partially blocks the lumen of the artery and restricts blood flow, causing blood pressure to increase. lots of atheromas restrict blood flow to the heart muscle which can cause myocardial infarction (heart attack) 

- atheromas increase the risk of aneurysm and thrombosis

- aneurysm: atheroma plaque damage arteries and cause them to narrow (increases blood pressure). when blood travels through a weakened artery at a high pressure, it pushes the inner layer of the artery through the outer elastic layer to form a balloon-like swelling. the aneurysm may burst, causing a haemorrhage

- thrombosis: atheroma plaque can rupture the endothelium of an artery which damages the artery wall and leaves a rough surface. platelets and fibrin accumulate at the site of the damage to form a blood clot. this can cause a blockage and eventually mycocardial infarction

1) high blood cholesterol and poor diet

- high cholesterol = main constituent of fatty deposit that form atheromas. atheromas cause high blood pressure and blood clots which could block flow of blood to heart and cause a myocardial infarction

- poor diet in high saturated fat increases risk of high blood cholesterol/high blood pressure

2) cigarette smoking

- nicotine increases risk of high blood pressure and carbon monoxide combines with haemoglobin (has a higher affinity for it) and reduces the amount of oxygen transported in blood so reduces amount of oxygen for heart musles

- decreases antioxidants in blood so more cell damage in cornonary artery walls -> atheroma

3) high blood pressure

- increases risk of damage and atheromas -> blood clots > myocardial infarction

xylem = dead tissue

water moves up through xylem via transpiration (cohesion and tension)

- water evaporates from leaves at top of xylem from moist cell walls ans accumulates in the spaces between cells in the leaf. when the stomata open it moves out of the lead down the conc. gradient (transpiration)

- creates tension (suction) which pulls more water into the leaf

- water molecules are cohesive so stick together, so when some are pulled into the lead others follow, meaning a whole column of water move upwards

- water enters stem through roots

1) light - more light means more stomata open to let in CO2 for photosynthesis which means more water is produced and more evaporates thus transpiration is more frequent

2) temperature - high temperature means water molecules have more energy so evaporate faster. this increases the conc. gradient between inside of leaf and atmosphere outside of leaf so water diffuses out of leaf faster

3) humidity - low humidity means air around plant is dry, increasing the conc. gradient between the leaf and air so diffusion is quicker

4) wind - winder conditions means more water molecules are blown away from the stomata which increases the conc. gradient so diffusion is quicker

- cut shoot underwater to prevent air from entering xylem and cut at slant to increase surface area available for water uptake

- insert shoot into potometer in water so no air can enter

- keep capillary tube submerged in water. appartatus must be fully submerged and air tight

- dry the leaves and allow time for shoot to acclimatise and then shut the tap

- remove end of capillary tube from the beaker of water until one air bubble has forme, then put end of tube back in water

- record starting position of air bubble and start a stopwatch and record the distance moved by the bubble per hour (rate of air bubble movement = transpiration rate)

mass flow hypothesis

- active transport is used to actively load solutes from companion cells into sieve tubes of the phloem at the source (e.g. leaves)

- this decreases the water potential inside sieve tubes so water enters the tubes via osmosis from xlyem and companion cells

- creates high hydrostatic pressure inside sieve tubes at source 

- at sink end, solutes removed from phloem to be used up

- this increases water potential inside sieve tubes so water also leaves tubes via osmosis, lowering the hydrostatic pressure inside the sieve tubes

- pressure gradient forms from source end to sink end. this pushes solutes along the sieve tubes towards the sink end

- when they reach the sink the solutes wil be used (respiration) or stored (as starch)

- if a ring of bark is removed from a woody stem, a buldge forms above the ring. the flluid from the buldge has a higher conc. of sugars than the fluid from below the ring - this is evidence for the downward flow of sugars

- radioactive tracer (e.g. C14) can be used to track the movement of organic substances in a plant

- radioactive carbon pumped into container surrounding leaf which is then incorporated into organic substances produced by leaf which will be moved around plant via translocation

- audiography can track where tracer has spread. the plant is killed and then is placed on photographic film - this turns black wherever tracer is present 

- pressure in phloem can be investigated using aphids (pierce phloem then their bodies are removed leaving the mouthpiece behind which allows to sap to flow out) - the sap flows out quicker nearer the leaves than further down stem which is evidence of pressure gradient

- if metabolic inhibitor (stops ATP production) is put into phloem, then translocation stops - evidence that active tranport is involved

- sugar travels to many different sinks, not just one with the highest water potential, as the model would suggest

- the sieve plates would create a barrier to mass flow. a lot of pressure would be needed for the solutes to get through at a reasonable rate