B6 Flashcards
what affects the amount of each material that needs to be exchanged in an organism
size and metabolic rate
e.g. high metabolic rate –> exchanges more materials so requires larger sa/v
things that need to be interchanged between an organism and its environment
respiratory gases; O2, CO2
nutrients; glucose, fatty acids, amino acids, vitamins, minerals
excretory products; urea, CO2
heat
except for heat, how does exchange of substances take place
passively; diffusion + osmosis
actively; active transport
explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake
larger organisms have smaller sa:v
the specialised system overcomes the long diffusion pathway
so faster diffusion
sa:v
how does it change as organisms get larger
small organisms have a large sa:v
- as organisms become larger, their volume increases at a faster rate than their surface area
how have organisms evolved to maximise sa:v (2 features)
flattened shape
- no cell = ever far from surface
specialised exchange surface with large areas
- to increase sa:v
features of a specialised exchanged surface
- problem with thin membranes
large surface area:volume
–> increase rate of exchange
thin
–> diffusion distance is short
selectively permeable
–> allow selected materials to cross
movement of the environmental medium
–> maintain concentration gradient e.g. airflow
movement of the internal medium
–> transport system to maintain concentration gradient e.g. blood flow
*
being thin, specialised exchange surfaces are easily damaged and dehydrated
- they are often located an organisms
- when an exchange surface is located inside the body, the organism needs to have a means of moving the external medium over the surface
e.g. ventilating the lungs in a mammal
gas exchange in single-celled organisms
- single celled organisms are small and therefore have a large surfacearea : volume
- oxygen is absorbed by diffusion across their body surface, which is covered only by a cell-surface membrane
- in the same way, CO2 from respiration diffuses out across their body surface
- where a living cell is surrounded by a cell wall, this is no additional barrier to the diffusion of gases
gas exchange in insects
- water conservation vs efficient gas exchange
- trachea
-tracheoles
- as with all terrestrial organisms, insects have evolved mechanisms to conserve water:
- thick waterproof surface
- small surface area
- the increase in surface area required for gas exchange conflicts with conserving water, because it will evaporate more easily:
- thin, permeable surface
- small surface area
- for gas exchange, insects have evolved a network of tubes called tracheae
- the tracheae are strengthened with rings of chitin to prevent them from collapsing
- the trachea divide into smaller dead-end tubes- tracheoles
- these extend throughout all the body tissues of the insect
- in this way atmospheric air, with the O2 it contains, is brought directly to the respiring tissues, as there is a short diffusion pathway from a tracheole to any body cell
the 3 ways in which respiratory gases move in/out of the tracheal system
*ALONG A DIFFUSION GRADIENT
- when cells = respiring, O2 is used up, so its concentration to the end of the tracheole falls
- this creates a diffusion gradient that causes O2 to diffuse from the atmosphere, along tracheae + tracheoles, to cells
-CO2 is produced by cells during respiration
- this creates a diffusion gradient in the opposite direction
- causes CO2 to diffuse along the tracheoles and trachea from cells to the atmospheree
- as diffusion in air is much more rapid than in water, respiratory gases are exchanged quickly by this method
*MASS TRANSPORT
- the contraction of muscles in insects can squeeze the trachea enabling mass movements of air in/out
[–> body moved by muscles to move air–> maintains conc. gradients for O2/ CO2]
*THE ENDS OF THE TRACHEOLES = FILLED WITH WATER
- during anaerobic respiration, lactate is produced
- this is soluble and lowers the water potential of the muscle cell
-water therefore moves into the cells from the tracheoles by osmosis
- the water in the ends of the tracheoles decreases in volume and, in doing so, draws air into them
- this means that the final diffusion pathway is in gas phase so is more rapid
- this increases the rate at which air is moved into the tracheoles but leads to greater water evaporation
[–> fluid in ends of tracheoles moves out during exercise, so faster diffusion through in air to gas exchange surface]
how to gases enter/ leave tracheae in insects
- tiny pores called spiracles on the body surface
- opened/ closed by a valve
- when spiracles = open, water vapour can evaporate from insect
- for much of the time, insects keep their spiracles closed to prevent this water loss
- periodically they open the spiracles to allow gas exchange
—-> SO H2O DOES NOT CONTINUOUSLY DIFFUSE OUT
limitations of tracheal system
- relies on diffusion to exchange gases between cells
- for diffusion to be effective, the diffusion pathway needs to be short which is why insects are small
- so the length of the diffusion pathway limits the size that insects can attain
adaptations in insect tracheal systems
- tracheoles have thin walls so short diffusion distance to cells
- highly branched/ large number of tracheoles so short diffusion distance to cells
- highly branched so large surface area for gas exchange
- trachea provide tubes of air so fast diffusion into insect tissues
- fluid in the ends of tracheoles move out 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 gradient for O2/ CO2
structure of the gills
- located within the fish body, behind the head
- made of gill filaments
—> filaments = stacked up in a pile - at right angles to filaments = gill lamellae, which increases the surface area of the gills
- water is taken in through the mouth and forced over the gills and out through the operculum on each side of the body
adaptations of gills for efficient gas exchange
many lamellae
–> large surface area
thin surface
–> short diffusion pathway
countercurrent flow
- blood flow and water flow are in opposite directions
- blood always passing water with a higher O2 concentration
- makes diffusion more efficient- ensures equilibrium is not reached
- maintains a diffusion gradient across the entire length of the lamellae
why is the flow of H2O over gills in 1 direction more efficient than in 2 ways, like in human lungs?
- less energy = required
- the flow does not have to be reversed
important as water is less dense than air + difficult to move
outline how the countercurrent flow of blood and water results in efficient gas exchange in fish
- blood flows in opposite direction to water across the gills
- so highly oxygenated water comes into contact with poorly oxygenated blood
- this maintains an oxygen concentration gradient across the whole of the gill plate
- this maximises diffusion
describe and explain how the countercurrent system leads to efficient gas exchange across the gill of a fish
- blood and water travel in opposite directions
- this maintains a steep O2 concentration gradient
- across the whole gill
- so blood always comes into contact with water with a higher O2 concentration
amoetic gill disease 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
why does AGD reduce the efficiency of gas exchange in fish
longer diffusion distance
lower surface area
why does the highly folded structure of the gills increase the efficiency of gas exchange
- increases surface area
over which diffusion takes place
suggest why gill lamellae would not provide an efficient gas exchange surface on land
- the gill may dry out
- preventing oxygen dissolving on the surface of the gills
- they are no longer supported by water/ folds may stick together with surface tension
list similarities and differences between the gas exchange of an insect and an animal
similarities
- large surface area
- moist gas exchange surface
- thin gas exchange surface
- concentration gradient achieved by ventillation
differences
- transport (circulatory) system in mammals but not insects
- the respiratory surface in mammals is alveoli, but in insects it is the junction between tracheoles and respiring tissues
advantages of rolled leaves in decreasing water loss
- water evaporating from the leaf =trapped
- the region within the rolled up leaf = saturated with water vapour
- there is no water potential gradient between the inside and outside of leaf
so water loss decreases
what would happen to evaporation of water from a rolled leaf if it was rolled the other way
- all stomata = on lower epidermis
- air current would decrease water potential immediately outside the leaf
- water potential gradient increases so more water vapour= lost
maram grass- problems obtaining water
rain drains away through sand
windy conditions increase concentration gradient for water loss
why are smaller plant leaves less important in cold climates
- photosynthesis = an enzyme-controlled reaction
- enzymes work less efficiently at low temperatures
- so this limits photosynthesis regardless of s.a. for light capture
plants: photosynthesis and respiration
- during photosynthesis, plant cells take in CO2 and produce O2
- at times the gases produced in one process can be used for the other
- this reduces gas exchange with the external air
–> overall, this means that the volumes and types of gases that are being exchanged by a plant leaf change- this depends on the balance between rates of photosynthesis and respiration - when photosynthesis is not occuring, e.g. in the dark, O2 diffuses into the leaf because it is constantly being used by cells during respiration
–> in the same way, CO2 produced during respiration diffuses out
structure of a plant leaf and gas exchange
- how diffusion takes place
- adaptations
- short diffusion pathway
- diffusion takes place in the gas phase, which males it more rapid than in water
- air spaces inside a leaf have a very large surface area compared with the volume of living tissue
- there is no specific transport system for gases, which simply move in and through the plant by diffusion
- many small pores: stomata, so short diffusion pathway
- numerous air-spaces: throughout the mesophyll so large surface area for gas exchange
- large surface area of mesophyll cells for rapid diffusion
stomata + guard cells
- pores on underside of leaf
- surrounded by guard cells
–> open and close to control the rate of gaseous exchange + control water loss - plants have evolved to balance the conflicting needs of gas exchange and control of water loss
—> do this by closing stomata at times when water loss would be excessive - when the plant has enough water, the guard cells open the stomata
–> this allows CO2 to enter for photosynthesis - however, if the plant is losing water faster than its roots can replace it, guard cells close stomata
- the inner cell wall of the guard cells are thicker than outer cell wall
- lots of water in vacuole pushes the outer wall so it curves, opening stomata
- guard cells = light sensitive
- at night, not enough light to photosynthesise
- no benefit to letting in CO2 while the leaf cannot photosynthesise
—> stomata close in the dark to conserve water
[ can still take in O2 and release CO2 for respiration]
limiting water loss in insects
- balancing efficient gas exchange with minimising water loss
- adaptations to reduce water loss
- the problem for all terrestrial organisms is that water easily evaporates from the surface of their bodies- they can become dehydrated
- efficient gas exchange surfaces require a thin permeable surface with a large area
- these features conflict with the need to conserve water: waterproof, thick, small surface area
adaptations to reduce water loss
- SMALL SA/V: minimise sa for water loss
- WATERPROOF COVERINGS: rigid outer skeleton of chitin + waterproof cuticle
-SPIRACLES: closed to reduce water loss. this conflicts with the need for oxygen so occurs largely when the insect is at rest
- these features mean that insects cannot use their body surface to diffuse respiratory gases in the way a single-celled organism foes
- instead they have an internal network of trachea to carry air-containing oxygen directly to tissues
gas exchange in plant leaf vs terrestrial insects
*similarities
- no living cell = far from external air
- diffusion = in gas phase
- need to avoid excess water loss
- diffuse air through pores in outer covering
—> control opening/ closing
*differences
- insects can create mass air flow
- insects have smaller sa;v
- insects have special structures for gas diffusion i.e. trachea
- insects do not interchange gases between respiration and photosynthesis
limiting water loss in plants
while plants have waterproof coverings, they cannot have a small sa:v
–> this is because they photosynthesise, and photosynthesis requires a large sa for the capture of light and exchange of gases
- to reduce water loss, terrestrial plants have a waterproof covering over parts of the leaves and the ability to close stomata
the majority of water loss occurs through the leaves, they show modifications:
*THICK CUTICLE
the thicker the cuticle, the less water can escape
*ROLLING UP LEAVES
- majority of stomata on lower epidermis
- rolling protects the lower epidermis from outside
- traps a region of still air
- this air becomes saturated with water vapour so has high water potential
- there is no water potential gradient between the inside + outside so no water loss
*HAIRY LEAVES
- thick layer of hair esp on lower epidermis traps moist still air next to the leaf surface
- this reduces the water potential gradient inside + outside to limits water loss
*STOMATA IN PITS/ GROOVES
- trap still moist air next to leaf so reduce water potential gradient
*REDUCED SA:V
- slower rate of diffusion
- small + roughly circular in cross section as opposed to broad and flat
- this reduction in surface area is balanced with the need for a sufficient surface area for photosynthesis to meet the plants requirements
what are xerophytes
plants with access to limited water that have adapted to limit water loss through transpiration
–> warm, dry, windy habitats
why must the volume of O2 that has to be absorbed and the volume of CO2 removed be large in mammals
- they are large organisms with a large volume of living cells
- they maintain a high body temperature which means they have high metabolic and respiratory rates
–> evolved specialised surfaces- lungs to ensure efficient gas exchange between air + blood
the lungs
- why are they inside the body as opposed to out
- where are they inside the body
- what is their structure
- air is not dense enough to support delicate lungs
- the body as a whole would otherwise lose much water and dry out
the lungs are protected by the ribcage.
the ribs can be moved by intercostal muscles
the lungs can be ventilated by a tidal stream of air, ensuring the air within them is constantly replenished
structure
- pair of lobed structures made of highly branched tubles- bronchioles which end in tiny sacs- alveoli
- trachea = flexible airway supported by rings of cartilage. the cartilage prevents the trachea collapsing as air pressure inside them falls when breathing in. the tracheal walls are made of muscle, lined with ciliated epithelium and goblet cells,
- bronchi = two divisions of trachea, each leading to one lung. they are similar in structure to the trachea and also produce mucus to trap dirt particles, and have cilia that move dirt-laden mucus towards the throat. the larger bronchi are supported by cartilage . although the amount of cartilige is reduced as bronchi get smaller
- the bronchioles are series of branching subdivisions of the bronchi. their walls are made of muscle lined with epithelial cells. this muscle allows them to constrict so they can control the flow of air in/ out of the alveoli
- the alveoli are minute air-sacs, at the end of the bronchioles
- between the alveoli there is some collagen and elastic fibres. the alveoli are lined with epithelium. the elastic fibres allow the alveoli to stretch as they fill with air when breathing in. they then spring back during breathing out to expel the CO2 rich air
the alveolar membrane = gas- exchange surface
how do tracheal cells protect alveoli
- the cells produce mucus that traps particles of dirt + bacteria in air breathed in
- the cilia on these cells move this debris up the trachea and into the stomach
- the dirt/ bacteria would cause infection in the alveoli
why is breathing necessary
- to maintain diffusion of gases across the alveolar epithelium
what 3 muscles bring about the pressure changes within the lungs
diaphragm: sheet of muscle that separates thorax from abdomen
intercostal muscles: between the ribs
2 sets
internal: contractions lead to expiration
external: contractions lead to inspiration
2 sets = antagonistic
inspiration + expiration
inspiration
breathing in = an active process
- external intercostal muscles contract. internal intercostal muscles relax
- ribs pulled up and out, increasing voume of thorax
- diaphragm muscles contract, causing it to flattten, increasing thorax volume
- increased thorax volume reduces pressure in the lungs
- atm pressure > pulmonary pressure so air = forced into lungs
expiration
breathing out= passive process
- internal intercostal muscles contract. external intercostal muscles contract
- ribs move downwards and inwards, decreasing thorax volume
- diaphragm muscles relax so is pushed up again by contents of abdomen that were compressed in inspiration
- volume of thorax = further decreased
- decreased thorax volume increases pulmonary pressure
- pulmonary pressure > atm pressure so air = forced out lungs
why is expiration a normally passive process
how does it become an active process
- during normal quiet breathing, the recoil of the elastic tissue in the lungs = main cause of air being forced out
in forced expiration, internal intercostal muscles contract- push the ribcage further than normal
features of efficient exchange surface
thin
partially permeable
large surface area
movement of internal + external medium
–> diffusion alone is not fast enough to maintain adequate transfer of oxygen and carbon dioxide along the trachea, bronchi and bronchioles
- breathing = essentially mass transport
pulmonary ventilation
tidal volume
breathing rate
the total volume of air that is moved into the lungs in 1 minute
pulmonary ventilation rate = tidal volume x breathing rate
(dm^3min^-1 ) (dm^3) (min-1)
tidal volume = vol. air taken in at each breath
breathing rate = number of breaths taken in 1 minute
role of alveoli in gas exchange
- each alveolus = lined with epithelial cell
- around each alveolus is a network of pulmonary capillaries, so narrow that rbc = flattened against the thin capillary endothelium walls in order to squeeze through
- these capillaries have walls that are only a single layer of cells thick
how is diffusion of gases between the aveoli and the blood made more rapid
- rbc = slowed as they pass through the pulmonary capillaries, allowing more time for diffusion
- the distance between the alveolar air and rbc is reduced as the rbc are flattened against the capillary wall
- the alveolar epithelium + capillary endothelium = one cell thick so short diffusion distance
- alveoli and pulmonary capillaries have a very large total surface area
- breathing movements constantly ventilate the lungs
- the action of the heart constantly circulates blood around the alveoli
—–> maintains steep concentration gradient - blood flow through the pulmonary capillaries maintains a concentration gradient
describe movement of CO2 and O2 in capillaries
- O2 diffuses out of the alveolar space, across the alveolar epithelium and the capillary endothelium and into the blood
–> where it binds to haemoglobin in rbc - CO2 diffuses from the blood into the alveolar space and is exhaled
lacteals
lymphatic vessels at the centre of the villi
lumen
cavity of a structure
micelles
emulsified lipid droplets
chylomicrons
the product of triglycerides associating with cholesterol and lipoproteins
exocytosis
movement out of a cell
ileum
the small intestine
colon
the large intestine
enzyme
a biological catalyst produced by a gland
hydrolysis
breakdown of a compound by a chemical reaction with water
assimilate
nutrients in food are taken into the cells of the body
monosaccharide
a class of sugar that cannot be hydrolysed to a simpler sugar
disaccharide
a class of sugar whose molecules contain 2 monosaccharide residues
polysaccharide
a carbohydrate whose molecules consist of a number of sugar molecules bounded together
monomer
a molecule that can be bonded to similar/ identified monomers to form a polymer
lipid
fat
peptide
a compound made from two or more linked amino acids- smaller than proteins
glycosidic bond
links a carbohydrate molecule to another molecule
emulsification
breakdown of fat to smaller molecules to provide larger surface area
what is the human digestive system made of and what is its role
- a long muscular tube and its associated glands
- the glands produce enzymes that hydrolyse large molecules into small molecules ready for absorbtion
- the digestive system is therefore an exchange surface through which food substances are absorbed
what are the major parts of the digestive system
oesophagus: carries food from the mouth to the stomach
stomach: a muscular sac with an inner layer that produces enzymes, its role is to store and digest food, especially proteins. it has glands that produces proteases
ileum: a long muscular tube. food is further digested in the ileum by enzymes that are produced by its walls by glands that pour their secretions into it
–> the inner walls of the ileum are folded into villi, which gives them a large surface area
–> surface area of these villi is further increased by millions of tiny microvilli on the epithelial cell of each villus. this adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream
large intestine: absorbs water. most of the water that is absorbed is water from the secretions of the many digestive glands
rectum: final section of the intestines. the faeces are stored here before periodically being removed via the anus in egestion
*
salivary glands: situated near the mouth, they pass their secretions via a duct in the mouth. these secretions contain amylase, which hydrolyse starch into maltose
the pancreas: a large gland situated below the stomach. it produces pancreatic juice, containing proteases, lipases, amylase
the process of digestion: the main 2 stages
- PHYSICAL BREAKDOWN
- if food = large it is broken down into smaller pieces by the TEETH
- this makes it possible to ingest the food
- it also provides a large surface area for chemical digestion
- food = CHURNED by muscles in the stomach wall, which also physically breaks it up
*
2. CHEMICAL DIGESTION
- chemical digestion hydrolyses large, insoluble molecules into smaller, soluble ones
–> carried out by enzymes by hydrolysis
- enzymes are specific, so more than one enzyme is needed to hydrolyse a large molecule
- typically, one enzyme hydrolyses the molecule into sections and then other enzymes hydrolyse these sections into smaller monomers
- these enzymes are usually produced in different part of the digestive system, and must be added to the food in the correct sequence
enzymes: carbohydrases, lipases, proteases
carbohydrate digestion
- maltose
- sucrose
- lactose
- saliva enters mouth from salivary glands + mixed with food during chewing
- contains salivary amylase, hydrolyses alternate glycosidic bonds in starch to maltose
- also contains MINERAL SALTS help maintain pH around neutral (optimum pH for salivary amylase)
- food = swallowed and enters the stomach (acidic)
- denatures amylase, prevents further starch hydrolysis
- after a time, the food = passed into ileum, mixes with pancreatic juice secretion
- pancreatic juice contains pancreatic amylase, continues hydrolysis starch –> maltose
- ALKALINE SALTS = produced in pancreas and intestinal wall to maintain the pH around neutral so amylase can function
- muscles in the intestine wall push the food along the ileum
- its epithelial lining produces a disaccharide maltase
–> not released into ileum lumen but is part of the cell surface membranes of epithelial cells lining ileum
—–> a membrane-bound disaccharidase - the maltase hydrolyses the maltose from starch breakdown into a-glucose
*
sucrose = found in natural foods esp fruit
lactose = found in milk
each disaccharide = hydrolysed by a membrane bound disaccharidase:
sucrase - single glycosidic bond in sucrose –> glucose + fructose
lactase - single glycosidic bond in lactose –> glucose + galactose
lipid digestion
- hydrolysed by lipases
- lipases = produced in pancreas and hydrolyse the ester bond in triglycerides to form fatty acids and monoglycerides
- lipids = firstly broken up into MICELLE droplets by BILE SALTS, produced in liver
—-> process = EMULSIFICATION, increases surface area of lipids so action of lipase speeds up
also increases triglyc. solublilty in water
protein digestion
- proteins = large complex molecules
- hydrolysed by peptidases (proteases)
endopeptidase: hydrolyses the peptide bonds between the amino acids in the central region of the protein molecule, forming a series of peptide molecukes
exopeptidase: hydrolyses the peptide bonds on the terminal amino acids of the peptide molecules FORMED BY ENDOPEPTIDASES
- in this way they progressively release dipeptides and single amino acids
dipeptidase: hydrolyse the bond between the two amino acids of a dipeptide
- dipeptides = membrane bound = part of the cell-surface membrane of the cells lining the ileum
advantage of lipid droplet and micelle formation
- DROPLETS increase surface area for enzyme action
- so faster hydrolysis/ digestion of lipids
- micelles carry fatty acids and glycerol through membrane –> intestinal epithelial cell
role of golgi apparatus in triglyceride absorbtion
- modifies/ processes triglycerides
- combines triglycerides with proteins –> lipiproteins
- packaged for exocytosis/ forms vesicles
how is the ileum adapted to the function of absorbing the products of digestion
+ in the cells of the ileum
- wall = folded and have finger- like projections - villi
- have thin walls, lined with epithelial cells on the other side of which is a network of blood capillaries
- villi increase surface area of the ileum therefore increase rate of absorbtion
- villi = situated at the interface between the lumen of the intestines and the blood and other tissues inside the body
how they increase rate of absorbtion:
- increase SURFACE AREA for absorbtion
- thin walled, reduing DIFFUSION DISTANCE
- contain muscle so are able to move. this maintains DIFFUSION GRADIENTS because their movement mixes the ileum contents. this ensures that, as the produces of digestion are absorbed from the food adjacent to the villi, new material rich in the products of digestion replaces it
- they are well supplied with blood vessels so that blood can carry away absorbed molecules, maintaining a DIFFUSION GRADIENT
- the epithelial cells lining the villi possess microvilli. these are finger like projections on the cell surface membrane that further increase the SURFACE AREA for absorbtion
*
in the cells:
- ER: resynthesise triglycerides from monoglycerides and fatty acids
- Golgi: to form chylomicrons by combining: triglycerides, cholesterol, lipoproteins
- mitochondria: produce ATP for co-transport
absorbtion of monosaccharides and amino acids
- diffusion
- co-transport
- glucose and amino acids are absorbed by co-transport with the sodium potassium pump
1. Na+ actively transported ileum->blood
2. maintains conc gradient for Na+ to enter, brings glucose
3. glucose enters by facilitated diffusion w/ Na+ ions
absorbtion of triglycerides
- once formed during digestion, monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipid droplets
—> forms micelle droplets - through the movement of material within the lumen of the ileum, the micelles come into contact with the epithelial cells lining the villi of the ileum
- here the micelles break down, releasing the monoglycerides and fatty acids
—-> as these are non-polar molecules, they easily diffuse across the cell-surface membrane into the epithelial cells - once inside the epithelial cells, monoglycerides and fatty acids are transported to the ER where they are recombined –> triglycerides
- starting in the ER and continuing to Golgi, the triglycerides associate with cholesterol and lipoproteins to form chylomicrons
—–> chylomicrons are particles adapted for the transport of lipids - chylomicrons moved out of the epithelial cells by exocytosis
- they enter lymphatic capillaries called lacteals that are found at the centre of each villus
- from here, the chylomicrons pass, via lymphatic vessels, into the blood system
- the triglycerides in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries from where they diffuse into cells
absorbtion of fatty acids
- bile salts play a role in the digestion and absorbtion of fatty acids
- one end of the bile salt molecule = soluble in fat (lipophillic) but not in water (hydrophobic). the other end is lipophobic and hydrophillic
- bile salt molecules therefore arrange themselves with their lipophillic ends in fat droplets, leaving the lipophobic ends sticking out
- in this way, they prevent fat droplets from sticking to each other to form large droplets, leaving only tiny ones (micelles)
- it is in this form that fatty acids reach the epithelial cells of the ileum where they break down, releasing the fatty acid for absorbtion
describe how lipid molecules = absorbed + transported
- micelles = formed by bile salts, fatty acids + monoglycerides
- micelles make fatty acids/ monohlycerides more soluble in water
- release fatty acids and monoglycerides to cell lining of ileum
- fatty acids and monoglycerides = absorbed by diffusion
- triglycerides = reformed in cells
—> chylomicrons form - vesicles move to cell membrane (exocytosis)
describe the tole of the enzymes of the digestive system in the complete breakdown of starch
- in the mouth, salivary amylase, hydrolyses starch to maltose
-in the ileum, pancreatic juice containing pancreatic amylase hydrolyses remaining starch to maltose - the membrane- bound enzyme maltase in the ileum hydrolyses maltose to a-glucpse
- hydrolysis of glycosidic bonds!!!!!!!
where is amylase produced
where is maltase produced
pancreas
ileum
maltose - hydrolysed by the enzyme maltase. explain why maltase catalyses only this reaction
- the active site of maltase is specifically shaped to be complementary to the maltose substrate
- therefore only maltose can bind to maltase
- to form an ENZYME SUBSTRATE COMPLEX
why does large numbers of mitochondria help the epithelial ileum cell absorb the products of digestion
- mitochondria = the site of aerobic respiration/ ATP production
- in active transport of the products of digestion, energy = needed to move the substances against the concentration gradient
describe the role of enzymes in the digestion of proteins in a mammal
- enzymes hydrolyse the peptide bonds in proteins
- endopeptidases act in middle
- exopeptidases act at end
- dipeptidases are membrane bound and act between two amino acids to produce single amino acids
define hydrolysis
a reaction causing the breakdown of molecules by the addition of water to the bonds that hold the molecule together
2 structures that produce amylase
salivary glands, pancreas
why does the stomach not have villi/ microvilli?
- villi/ microvilli speed up the absorbtion of soluble molecules
- food in the stomach has not yet been hydrolysed into soluble molecules that they could absorb, so they could be unnecessary
the final product of starch digestion in the gut
a-glucose
3 enzymes produced by the epithelium of the ileum
maltase, sucrase, lactase
state the difference between villi and mirovilli
- single villi within the small intestine = made up of intestinal epithelial cells
- each of the cells will have multiple hair like projections from the cell- microvilli
describe how the diffusion gradient is maintained across the villus
- the capillary network is closely associated with the villi
- anything absorbed is quickly transported away to continually provide a low concentration of absorbed substances in the capillary
- this maintains a steep concentration gradient
describe the role of lymphatic vessels
to absorb fats from the small intestine
what causes fat gobules to emulsify
associate with bile salts to form an emulsification
allows the fats to be small enough for digestion by lipases into fatty acids and glycerol
what is the role of the golgi apparatus in lipid digestion
- monoglycerides + fatty acids = transported by ER and taken to the golgi where they are recombined to form triglycerides
- modified
- protein added –> lipoproteins
- packaged and transported via exocytosis
what are chylomicrons and what is their role in fat absorbtion
chylomicrons are triglyerides that have associated with cholesterol and lipoproteins
- this forms a structure that enables the triglycerides to leave a cell via exocytosis
explain the advantages of lipid droplet and micelle formation
- droplet formation increases the surface area for lipase action
- so faster hydrolysis/ digestion of triglycerides/ lipids
- micelles carry fatty acids and glycerol throguh the membrane to intestinal epithelial cells
role of golgi in triglyceride absorbtion
- modifies/ processes triglycerides
- combines triglycerides with proteins
- package for exocytosis/ form vesicles
explain the advantage for larger organisms of having a specialised system that facilitates oxygen uptake
larger organisms have smaller sa:v
the specialised system overcomes the long diffusion pathway
–> so faster diffusion
why do mice have a higher metabolic rate than horses
- larger sa:v
- more/ faster heat loss per gram/ in relation to body size
- faster rate of respiration so faster metabolic rate releases heat to replace heat lost
whats the practical advantage of measuring the masses of frogs eggs, tadpoles and adults as opposed to measuring their volumes
- more accurate/ less error
- easier to find mass because irregular shapes
why is O2 uptake a measure of metabolic rate in organisms
- O2 = used in respiration
- which provides energy/ which is a metabolic process
what features of alveolar epithelium make it well adapted as a surface for gas exchange. do not refer to surface area or moisture
- flattened/ single layer of cells
—> reduces diffusion pathway - permeable
—> allows diffusion of O2/ CO2
suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and alveoli
- less CO2 exhaled
- more CO2 remains in lung
- so reduces diffusion gradient between blood and alveoli
- less movement of CO2 out of blood
describe and explain the mechanism that causes the lungs to fill with air
diapgragm contracts
external intercostal muscles contract
volume of lungs increases and pressure decreases
atmospheric pressure greater than pulmonary pressure
air forced into lungs down pressure gradient
suggest and explain one way leaf growth of xerophytic plants would be different from the leaf growth of sunflowers
slower growth
due to smaller number of stomata for gas exchange
using gas exchange in leaves, explain why plants grown in soil with very little water grow only slowly
stomata are closed
less CO2 uptake
less photosynthesis
less glucose production
describe the pathway taken by an oxygen molecule from an alveolus to the blood
across alveolar epithelium across capillary endothelium
explain how one feature of an alveolus allows efficient gas exchange to occur
the ALVEOLAR EPITHELIUM is one cell thick
creating a short diffusion pathway
describe the gross structure of the human gas exchange system and how we breathe in and out
trachea
bronchi
bronchioles
alveoli
lungs
breathing in
- diaphragm contract
- external intercostal muscles contract
- volume lungs increases, pressure decreases below atmospheric
- air forced in down pressure gradient
breathing out
- diaphragm relaxes
- internal intercostal muscles contract
- volume decreases and pressure increases in lungs
- to above atmospheric so air moves out down pressure gradient
explain how an insect’s tracheal system = adapted for efficient gas exchange
- tracheoles have thin walls
—-> short diffusion pathway - tracheoles extend to all cells = highly branched
—-> large surface area and short diffusion pathway - ends ot tracheoles = filled with water that moves out during anaerobic respiration, maintains concentration gradient
- trachea provide tubes of air
—> diffusion = faster in gas phase so fast diffusion into insect tissues
the damselfly larva is a carnivore that actively hunts prey
explain how the presence of gills adapts the damselfly to its way of life compared to other species that do not actively hunt prey and do not have gills
- damselfly larvae has higher metabolic rate/ respiratory rate
- so uses more oxygen per unit time/ mass
explain two ways in which the structure of fish gills is adapted for efficient gas exchange
- many lamellae –> large surface area
- thin surface –> short diffusion pathway
describe the process involved in absorbtion and transport of digested lipid molecules from the ileum into lymph vessels
- micelles = formed by bile salts, fatty acids and monohlycerides
- micelles make fatty acids/ monoglycerides MORE SOLUBLE IN WATER
–> releases fat and monoglycerides to CELL LINING OF THE ILEUM - fatty acids and monoglycerides = absorbed by diffusion
- triglycerides = reformed in cells –> chylomicrons form
- vesicles move to cell membrane via exocytosis
explain the role of ATP hydrolase in the Na K pump
hydrolyses ATP –> ADP + Pi
- releases energy for IONS TO BE MOVED AGAINST THE CONCENTRATION GRADIENT
the movement of Na+ out of a cell allows the absorbtion of glucose into the cell lining the ileum. explain how
concentation gradient of Na + from lumen to epithelial cell
na + moves by facilitated diffusion down conc gradient into cell
brings glucose molecule with it
glucose molecule moves against its concentration gradient
what does lipase hydrolyse in triglycerides
ester bonds
describe the role of micelles in the absorbtion of fats into the cells lining the ileum
micelles include bile salts, fatty acids, monoglycerides
micelles increase the surface area of the lipid droplets and make them soluble in water
carry monoglycerides and fatty acids to cell lining of ileum- releases them to cross membrane by diffusion
describe the role of enzymes in the digestion of protein in a mammal
protease hydrolyses peptide bonds in protein
- endopeptidases - peptide bonds in centre of polypeptide
- exopeptidases hydrolyse peptide bonds at the end of the polypeptide- produce dipeptides/ amino acids
- dipeptidases produce single amino acids
explain how cells lining the ileum absorb glucose by co-transport with sodium ions
- sodium ions = actively transported from ileum cell –> blood
- maintains diffusion gradient for NA + ions to enter and bring glucose with it
- glucose enters by facilitated diffusion with Na+ ions
