3.3 organisms exchange substances with their environment Flashcards
smaller organisms = ___ SA
larger
how does volume of an organisms increase with size
as the size of an organism increases, its volume increases faster than its surface area.
features of specialised exchange surfaces
- large sa:v ratio which increases rate of exchange
- very thin memrane so short diffusion pathway, materials cross exchange surface rapidly
- selectively permeable to allow selected materials to cross
- movement of environmental medium. e.g. air to maintain a diffusion gradient
- transport system to ensure the movement of the internal medium e.g blood. in order to maintain a diffusion gradient
how is body shape changed to adapt to gas exchange
- flattened shape so short diffusion pathway
- specialised exchange surfaces with large SA:V ratio
how to calculate area of spherical item
πr²
how to calculate surface area of a spherical item
2πrh + 2πr²
relationship between sa:v ratio and metabolic rate
smaller organisms have a higher basal metabolic rate per unit of body mass
high metabolic rate = more materials exchanged
route taken by oxygen as it moves from the outside into the cytoplasm of a respiring cell
spiracles -> trachea -> tracheoles -> tips
gas exchange in single celled organisms
- small therefore large sa:v ratio
- oxygen absorbed by diffusion across body surface.
- carbon dioxide from respiration diffuses out of body surface
- no additonal barriers to the diffusion of gases
what is the tracheal system
network of air filled tubes which become progressively narrower and reach most cells, and so a transport system for oxygen and carbon dioxide isn’t necessary
what are spiracles
openings in insects, valves may open and close. gas enters and leave trachea through this
when open, water vapour can evapourate from the insect, so insects keep spiracles closed to prevent water loss
tracheae vs tracheoles
tracheae: internal network of tubes, supported by rings of chitin to prevent collapsing
tracheoles: tracheae is divided further into these blind ending, narrow and project into/between cells. some tracheoles modified to form air sacs around organs. oxygen bought directly from tracheoles to respiring cells. extend throughout all body tissues as there is a short diffusion pathway from the tracheoles to any body cell
tips of tracheoles
branched = large sa
one cell thick walls
permeable
fluid filled = moist
relationship between diffusion and factors that affect diffusion
diffusion ∝ (surface area x difference in concentration/ length of diffusion path )
three ways gas moves in and out of the tracheal system
- along a diffusion gradient
- mass transport
- ends of tracheoles are filled with water
how do gases move out of tracheal system along a diffusion gradient
- when cells are respiring, oxygen used up so concentration towards ends of tracheoles falls
- creates a diffusion gradient; causes oxygen to diffuse from atmosphere along the tracheae and tracheoles to the cells
- carbon dioxide produced by cells during respiration
- creates a diffusion gradient in the opposite direction.
- causes carbon dioxide to diffuse along tracheoles and tracheae from cells to atmosphere.
how do gases move out of tracheal system by mass transport
- contractions of muscles in insects can squeeze trachea, enabling mass movement of air in and out.
- speeds up exchange of respiratory gases
how do gases move out of tracheoles system by ends of water filled tracheoles
- during major activity, muscle cells resipire anerobically
- produces lactate: soluble and lowers water potential of muscle cells
- therefore water moves from tracheoles into cells by osmosis
- decrease in volume of water in tracheoles and draws air further in them
- final diffusion pathway is in gas rather than liquid, so diffusion is more rapid.
structure of gills
- made up of filaments
- these are stacked up
- at right angles to the filaments are the gill lamellae, which increase the surface area for the gills
- water taken in through the mouth and forced over gills
explain the counter current flow
- lamellae consists of a single layer of flattened cells that cover a vast network of capillaries
- capillary system within lamellae ensures that the blood flow is in opposite direction to flow of water
- this ensures concentration gradient is maintained along the length of the capillary
why is a counter current flow system needed
if the water and blood flowed in the same direction, the diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of the available oxygen would be absorbed by the blood
structure of a leaf
waxy cuticle
upper epidermis - tightly packed cells
palisade mesophyll - layer of elongated cells containing chloroplasts
spongy mesophyll - contains an extensive network of air spaces
guard cells - pair of cells that control the opening and closing of stomata
stomata - small pores (short diffusion pathway) on underside of leaf which allows air to enter
lower epidermis - tightly packed cells
stomata
- each stoma surrounded by pair of guard cells
- these cells can open and close the stomatal pore
- important cause organisms lose water via evapouration so the stomata closes at times when water loss would be excessive
limiting water loss in terrestrial insects
- small sa:v ratio, minimises area over which water is lost
- waterproof chitin covered by waxy cuticle
- spiracles can be closed to reduce water loss. this conflicts with the need for oxygen so occurs largely whilst the insect is at rest
limiting water loss in xerophytic plants
- dont have small sa:v cause photosynthesis requires a large sa for capture of light
- waterproof coverings
- ability to close stomata when needed
- certain plants with a restricted supply of water have also evolved a range of other adaptations to limit water loss through transpiration, these plants are called xerophytes
what are xerophytes
plants that are adapted to living in areas where water is in short supply
how have leaves modified to limit water loss
- thick cuticle: waxy cuticle but 10% water loss can still occur. thicker the cuticle = less evapouration
- rolling up of leaves: traps a region of still air within the rolled leaf and this region becomes saturated with water vapour so has a very high water potential, no water potential gradient between inside and outside of leaf and therefore no water loss.
- hairy leaves: thick layer of hairs on leaves, moist air next to leaf surface, water potential gradient between inside and outside of leaf is reduced and therefore less water lost by evapouration
stomata in pits and grooves: trap still most air next to leaf and reduce water potential gradient.
reduced sa:v ratio: smaller sa:v ratio, slower rate of diffusion. leaves that are small and roughly circular in cross-section can reduce rate of water loss considerably.
components of the human gas exchange system
lungs
trachea
bronchi
bronchioles
alveoli
the lungs
- pair of lobed structures
- made up of highly branched bronchioles, which end in tiny air sacs called alveoli
trachea
- flexible airway
- supported by rings of cartilage
- cartilage prevents trachea collapsing as the air pressure inside falls when breathing in
- tracheal walls made up of muscle, lined with ciliated epithelium and goblet cells
bronchi
- two divisions of the trachea, each leading to one lung
- similar in structure to trachea and also produce mucus to trap dirt particles and have cilia that move the mucus towards the throat
- larger bronchi supported by cartilage
bronchioles
- series of branching subdivisions of the bronchi
- walls made up of muscle lined with epithelial cells
- muscle allows them to constrict so they can control the flow of air in and out the alveoli
alveoli
- minute air sacs
- diameter of between 100µm and 300µm at the end of the bronchioles
- between alveoli there are some collagen and elastic fibres
- alveoli lined with epithelium
- elastic fibres allow alveoli to stretch as they fill the air when breathing in.
- then they spring back during breathing out in order to expel the carbon dioxide rich air.
- alveolar membrane = gas exchange surface
essential features of alveolar epithelium as a gas exchange surface
- large sa = many alveoli and pulmonary capillaries in lungs
- thin alveolar and capillary walls, one cell thick, short diffusion distance.
- distance between alveolar air and rbc is reduced as rbc are flattened against capillary walls
- moist walls = gases dissolve in the moisture helping them to pass across gas exchange surface.
- permeable walls = allow gases to pass through.
- extensive blood supply = ensuring oxygen rich blood taken away from lungs and carbon dioxide rich blood is taken to lungs.
- large diffusion gradient -
blood flow through capillaries maintains concentration gradient, breathing maintains high oxygen concentration in alveoli compared to capillaries so oxygen moves from alveoli to blood. - rbc slowed as they pass through pulmonary capillaries, allowing more time for diffusion
route taken by oxygen as it moves from air outside a mammal to the cytoplasm of the rbc
mouth - buccal cavity - trachea - bronchus - bronchioles - alveolar duct - alveolus - squamous epithelial cell - capillary endothelial cell - blood plasma - rbc cell membrane
inspiration vs expiration
inspiration = active process and requires energy
expiration = passive process but requires a little energy
ventilation at rest: inspiration
- diaphragm muscles contract: flattens so increases volume of thorax
- external intercostal muscles contract
- rib cage moves upwards and outwards: increasing volume of thorax
- volume of thorax increases
- pressure of thorax decreases
- atmospheric air pressure is greater than pulmonary pressure so air is forced into lungs
ventilation at rest: expiration
- diaphragm muscles relax: volume of thorax decreases
- external intercostal muscles relax
- rib cage moves down and in: decreases volume of thorax
- volume of thorax decreases
- pressure of thorax increases
- pulmonary pressure is greater than that of the atmosphere so air leaves the lungs
pulmonary ventilation rate equation
PVR = tidal volume x number of breaths per minute
site of gas exchange in mammals
epithelium of alveoli
risk factors for lung disease
smoking
exposure to pollutants
genetic makeup
infections
occupation
obesity
function of digestive system
to hydrolyse large, insoluble biological molecules into small soluble molecules so that they can be absorbed across the cell membrane
carbohydrate digestion
- require more than one enzyme to completely hydrolyse them into monosaccharides: amylases and disaccharidases
where is amylase produced
mouth and pancreas
amylases’ role in carbohydrate digestion
- hydrolyses alternate glycosidic bond of starch molecule to produce disaccharide (maltose)
- maltose then hydrolysed further into 2 alpha glucose molecules by a disaccharide called maltase
where is maltase produced
lining of ileum
disaccharidases’ role in digestion of carbohydrates
- sucrose and lactose (disaccharides) are hydrolysed by sucrase and lactase (membrane bound enzymes) into monosaccharides
lipid digestion
- digested by lipase and bile salts
lipase’s role in lipid digestion
- can hydrolyse ester bond in triglycerides to form monoglycerides and fatty acids
where is lipase produced
pancreas
bile salts’ role in lipid digesiton
- produced in liver and can emulsify lipids to form tiny droplets, micelles
- increases surface area for lipase to act on
two types of lipid digestion
chemical
physical
physical lipid digestion
- lipids coated in bile salts and creates emulsion
- many small droplets of lipids provides a larger surface area to enable the faster hydrolysis action by lipase
chemical digestion of lipids
lipase hydrolyses lipids into fatty acids and monoglycerides
what are micelles
water soluble vesicles formed of fatty acids, monoglycerides (both products of hydrolysis of lipids) and bile salts
role of micelles in digestion
- deliver fatty acids, monoglycerides and glycerol to epithelial cells of ileum for absorption
digestion of proteins
can be hydrolysed by 3 enzymes
- endopeptidases
- exopeptidases
- membrane bound dipeptidases
co transport mechanisms for the absorption of amino acids and of monosaccharides
- sodium ions actively transported out of epithelial cells lining ileum, into blood, by sodium-potassium pump. creating a conc. gradient of sodium (higher conc Na in lumen than epithelial cell)
- na ions and glucose move by facilitated diffusion into epithelial cell from lumen via a co-transporter protein
- creating a conc. gradient of glucose - higher conc. of glucose in epithelial cell than blood
- glucose moves out of cell into blood by facilitated diffusion through a protein channel.
role of micelles in lipid absorption
- lipids digested into fatty acids and monoglycerides by action of lipase and bile salts: forms micelles
- when micelles encounter ileum epithelial cells they can simply diffuse across the cell surface membrane to enter the cells of epithelial cells (due to non-polar nature of monoglycerides and fatty acids)
- once in the cell, these will be modified back into triglycerides inside of the ER and golgi apparatus
what is haemoglobin
- globular protein with a quaternary structure.
- readily combines with oxygen to transport it around the body
structure of haemoglobin
- primary structure: sequence of amino acids in 4 polypeptide chains
- secondary structure: each polypeptide chain is coiled into a helix
- tertiary structure: each polypeptide chain is folded into a precise shape (to help it carry oxygen)
- quaternary structure: 4 polypeptides, each associated with a haem group (contains ferrous ion). each ferrous ion can combine with a single oxygen molecule making a total of 4 O2 molecules that can be carried by a single haemoglobin molecule in humans
role of haemoglobin
- to transport oxygen
how must haemoglobin be efficient at transporting oxygen
- it must readily associate with oxygen at the surface where gas exchange takes place
- readily dissociate from oxygen at those tissues requiring it
loading/ association of haemoglobin
binding of oxygen to haemoglobin
unloading/ dissociation of haemoglobin
oxygen detaches/unbinds from oxygen
loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve
- oxygen is loaded in regions with a high partial pressure of oxygen e.g alveoli, and is unloaded in regions of low partial pressure of oxygen (e.g respiring tissues).
- shown in curve
cooperative nature of oxygen binding
- cooperative nature of oxygen binding to haemoglobin is due to the haemoglobin changing shape when first oxygen binds.
- makes it easier for further oxygens to bind
what is the bohr effect
when a high co2 concentration causes the oxyhaemoglobin to shift to the right
how does the bohr effect affect affinity
- affinity for oxygen decreases because co2 changes haemoglobin’s shape
- low partial pressure of carbon dioxide in alveoli. curve shifts left, increasing affinity and therefore uploads more oxygen
- high partial pressure of carbon dioxide at respiring tissues. curve shifts right, decreases affinity and unloads more oxygen
what happens when the oxygen dissociation curve shifts right
- unloads more oxygen, low affinity
what happens when oxygen dissociation curve shifts left
- uploads more oxygen, high affinity
animals, affinity and haemoglobin
- many animals are adapted to their environment by possessing different types of haemoglobin with different oxygen transport properties
cardiac output equation
cardiac output = stroke volume x heart rate
atrial diastole
- atrial walls contract
- atrial volume decreases
- atrial pressure increases
- pressure in atrium> pressure in ventricle, so AV valves open
- semi lunar valves closed
- blood forced into ventricles
ventricular systole
- ventricular walls contract
- ventricular volume decreases
- ventricular pressure increases
- pressure in ventricles> pressure in atrium
- AV valves close = prevents backflow
- semi lunar valves close
- blood forced into arteries and out of heart
diastole
- ventricles and atria both relaxed
- pressure in ventricles drop below that of aorta and pulmonary artery, forcing semi lunar valves to close
- atria fills with blood via vena cava and pulmonary vein
- process repeats
general pattern of blood circulation in a mammal
- double circulatory system
- blood passes through the heart twice on a complete circuit of the body
- oxygenated blood leaves the heart through the aorta to the rest of the body
- oxygen is given to respiring tissue, then deoxygenated blood enters heart via vena cava
- blood leaves to the lungs via pulmonary artery, becomes oxygenated then enters the left side of the heart via the pulmonary vein
- ready to pump blood out through aorta
- renal artery takes blood to the kidneys,
- leaves by the renal vein.
- coronary arteries take oxygenated blood to heart cells
structure of artery
- layer of collagen around outside
- thick wall made of muscle and elastic fibres
- endothelium
- small lumen
structure of a vein
- layer of collagen around the outside
- small wall made of muscle and elastic fibres
- endothelium
- very large lumen
structure of capillary
- wall of endothelium
- one cell thick
- very large lumen
order of blood vessel types that blood passes through once it leaves heart
- arteries
- arterioles
- capillaries
- venules
- veins
function of arteries
carry high pressure blood away from heart
function of arterioles
control blood flow from arteries to capillaries
function of capillaries
exchange surface (links arterioles to venules)
function of venules
connects capillary bed to veins
function of veins
carries low pressure blood towards heart
structure of capillaries
- small diameter (lumen); forces blood to travel slowly, allows diffusion to occur
- branch between cells to allow short diffusion distance
- single cell thick (a layer of endothelial cells); reduces diffusion distance for oxygen and carbon dioxide between blood and tissues of body
how much of the blood is made up of plasma
55%
why is plasma a transporter
- its composed of 95% water and as water is a good solvent, many substances can dissolve in it which allows them to be transported around the body
how does exchange of substances between cells and blood occur
- via tissue fluid
- e.g carbon dioxide produced in aerobic respiration will leave the cell, dissolve in the tissue fluid surrounding it and then diffuse into the capillary
formation of tissue fluid
- when blood is at the ‘arterial’ end of the capillary, the hydrostatic pressure is great enough to push molecules out of the capillary
- proteins remain in the blood, increased protein content creates a water potential between the capillary and tissue fluid
- overall movement of water is out from capillaries -> tissue fluid
- at ‘venule’ end of capillary, less fluid is pushed out of the capillary as pressure within the capillary is reduced.
- water potential gradient between capillary and tissue fluid remains the same as arteriole end so water flows back into capillary from the tissue fluid
- overall more fluid, leaves the capillary than what returns, which leaves tissue fluid behind to bathe cells
- if blood pressure is high, pressure at arteriole end is greater
- this pushes more fluid out capillary and fluid accumulates around the tissue (called an oedema)
