3.3.1-3.3.3 exchange Flashcards
(186 cards)
1
Q
how does an organism’s size relate to their surface area to volume ratio?
A
the larger the volume, the lower the surface area to volume ratio
2
Q
what substances do organisms need to exchange with their environment and why?
A
- cells need to take in oxygen (for aerobic respiration) and nutrients
- need to excrete waste products like carbon dioxide and urea
- need to stay roughly same temp, so heat needs to be exchanged
3
Q
how might a large organism adapt to compensate for its small SA:V ratio?
A
- changes that increase SA e.g. folding; body parts become larger e.g. elephants ears; elongating shape; developing specialised gas exchange surface
4
Q
why do multicellular organisms require specialised gas exchange surfaces as opposed to single-celled organisms?
A
- their smaller SA:V ratio means its difficult to exchange enough substances to supply a large volume of animal through relatively small outer surface as opposed to a smaller, single-celled organisms
- also, some cells are deep within the body, distance to be crossed by substances is large
5
Q
give examples of specialised gas exchange surfaces
A
lungs of mammals/birds
gills of fish
6
Q
name three features of an efficient gas exchange surface
A
- large SA e.g. folded membranes in mitochondria or root hair of cells
- thin/short distance e.g. wall of capillaries
- steep concentration gradient, maintained by blood supply/ventilation e.g. alveoli
7
Q
what are other characteristics allow efficient exchange of materials across specialised gas exchanges?
A
- selectively permeable membrane to allow selected materials to cross
- movement of environmental medium e.g. air to maintain diffusion gradient
- transport system to ensure movement of internal medium e.g. blood, in order to maintain a diffusion gradient
8
Q
what is Ficks’s law?
A
diffusion ∝ (SA x conc gradient)/ diffusion distance
9
Q
why are specialised exchange surfaces often located WITHIN an organism?
A
b/c being thin they can easily become damaged or dehydrated
10
Q
what does rate of heat loss from an organism depend on?
A
its surface area
- organism with large vol e.g. hippo, has a small SA so its harder to lose heat from its body
11
Q
why do smaller organisms have a higher metabolic rate?
A
- smaller organisms have large SA (relative to their volume), so heat is lost more easily
- means they have high metabolic rates to generate enough heat to stay warm
(high metabolic rates mean they need to consume more calories, more calories means more energy so can generate heat)
12
Q
discuss how organisms with high SA:V ratio adapt to lose less water
A
- they lose more water as it evaporates from their surface
- so some desert mammals have kidney structure adaptations so they produce less urine to compensate
13
Q
discuss how some organisms support their high metabolic rates
A
- small mammals in cold regions need to eat large amounts of high energy foods e.g. seeds and nuts
14
Q
why do large organisms (e.g. elephants and hippos) in hot regions need to adapt and how do they?
A
- they find it hard to keep cool b/c their heat loss is relatively slow
- e.g. elephants have developed large flat ears to increase SA, allowing them to lose more heat
- hippos spend much of day in water - a behavioural adaptation to help them lose heat
15
Q
how do single-celled organisms exchange?
A
- they absorb and release gases by diffusion through their outer surface
- they tend to be small, have large SA and a short diffusion pathway
16
Q
what kind of SA:V ratio do fishes have?
A
- relatively small SA:V ratio
17
Q
why do fishes need a specialised gas exchange surface?
A
- small SA:V ratio
- they have an impermeable membrane so gases can’t diffuse through their skin
- also there’s lower conc of oxygen in water than in air, so they need special adaptions to get enough
18
Q
name and describe the two main features of a fish’s gas transport system
A
gills: located within body, supported by arches, made up of thin plates called gill filaments (multiple projections stacked up in piles) which increase SA for exchange
lamellae: structures on gill filaments which increase SA. Blood and water flow across them in opposite directions (counter-current exchange system)
19
Q
A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange
A
- Large S.A. due to the lamellae
- thin epithelium = short distance between water and blood
- water and blood flow in opposite directions so maintains C.G. along gill
- circulation replaces blood saturated with oxygen
- ventilation replaces water (o2 is removed)
- lamellae has lots of blood capillaries and thin surface of cells to speed up diffusion
20
Q
Explain how the counter-current mechanism in fish gills ensures the maximum amount of the oxygen passes into the blood flowing through the gills (3)
A
- water and blood flow in opposite directions in lamallae (counter-current exchange)
- blood always passes water which has a higher 02 conc.
- so large concentration gradient is maintained across the whole gill
21
Q
Explain why a vein may be described as an organ (1)
A
Made up of different tissues
22
Q
explain the process of gas exchange in fish
A
- fish opens mouth to enable water to flow in, closes its mouth to increase pressure
- water passes over lamellae, and oxygen diffuses into bloodstream from water (they flow in opposite directions i.e. countercurrent system)
- waste carbon dioxide diffuses into water and flows back out of gills
23
Q
how does the countercurrent exchange system maximise oxygen absorbed by the fish?
A
- maintains a steep concentration gradient (equilibrium never reached), as water is always next to blood of a lower oxygen concentration
- so keeps rate of diffusion and enables 80% of available oxygen to be absorbed
24
Q
in relation to fish gills, describe what is meant by countercurrent flow
A
movement of water and blood in opposite directions across gill lamellae
25
outline why countercurrent flow is an efficient means of exchanging gases across gills of fish
- b/c of steady diffusion gradient maintained over whole length of gill lamellae (equilibrium never reached as high O2 conc of water meets high O2 conc of blood)
- therefore more oxygen diffuses from water into the blood
26
what adaptation would a more fast-swimming fish have than a slower one?
- more gill filaments/gill lamellae so larger SA
27
water flow over fish gills is one-way whereas the flow of air in and out of lungs is two-way. Suggest why one-way flow is an advantage to fish
less energy required because flow doesn't have to be reversed (important as water is dense and difficult to move)
28
what would happen if flow of blood and water were the same in the gills of fish? (parallel flow)
- diffusion gradient would only be maintained across part of the length of the gill lamellae and only 50% of available oxygen would be absorbed by the blood (compared to 80% in countercurrent flow)
29
briefly explain gas exchange in insects
- insects don't possess transport system so O2 needs to be transported directly to
respiring tissues
- achieved with the help of spiracles, small openings of tubes, either bigger trachea or smaller tracheoles, which run into the body of an insect and
supply it with the required gases
- gases move in and out through diffusion, mass transport as a
result of muscle contraction and as a result of volume changes in the tracheoles
30
why can't insects use their bodies as an exchange surface?
- they have waterproof chitin exoskeleton and a small SA:V ratio to conserve as much water as possible
31
name and describe the three main features of an insect's gas transport system
spiracles: holes in body's surface which may be opened or closed by a valve for gas or water exchange
tracheae: large tubes extending through all body tissues, supported by rings to prevent collapse
tracheoles: smaller branches dividing off the tracheae
32
explain the process of gas exchange in insects
- trachea containes pores: spiracles. Air moves through spiracles
- oxygen moves into the cell, down a conc gradient (conc of O2 outside cell is higher than inside cell)
- to reach individual cells of insect's body, the trachea branch off into smaller tracheoles
- like oxygen, carbon dioxide also moves down a conc gradient, from inside cell to spiracles. Eventually CO2 released to atmosphere
- rhythmic abdominal movements facilitate the moving in and out of air in the spiracles
33
what system have insects developed for gas exchange?
tracheal system
34
explain different ways in which an insect's tracheal system is adapted for efficient gas exchange
1. tracheoles have thin walls so short diffusion distance to cells
2. highly-branched/large no. of tracheoles so:
- short diffusion distance to cells
- large SA for gas exchange
3. trachea provide tubes full of air so fast diffusion (into insect tissues)
4. fluid in end of tracheoles that moves out (into tissues) during exercise so larger SA (for gas exchange)
5. Body can be moved (by muscles) to move air so maintain diffusion/conc gradient for oxygen/carbon dioxide
35
describe the walls of tracheoles
thin and permeable and go to individual cells
- means oxygen diffuses directly into the respiring cells
(insect's circulatory system doesn't transport O2)
36
why do insects keep their spiracles closed most of the time?
to prevent water loss
37
why insects open their spiracles periodically?
to allow gas exchange
38
explain why there is a conflict in terrestrial insects between gas exchange and conserving water
- gas exchange requires a thin permeable surface with a large area
- conserving water requires thick, waterproof surfaces with a small area
39
explain how the tracheal system limits the size of insects
- b/c it relies on diffusion to bring oxygen to the respiring tissues
- if insects were large it would take too long for oxygen to reach the tissues rapidly enough to supply their needs
40
how does a diffusion gradient facilitate exchange in insects
when cells respire, oxygen is used up and so its conc is lower towards end of tracheoles
- creates diffusion gradient that causes oxygen to diffuse from atmosphere and along trachea and tracheoles
- carbon dioxide produced by cells during respiration, creates diffusion gradient in opposite direction
- so CO2 diffuses along tracheoles and trachea from cells to atmosphere
41
how does a diffusion gradient facilitate exchange in insects
when cells respire, oxygen is used up and so its conc is lower towards end of tracheoles
- creates diffusion gradient that causes oxygen to diffuse from atmosphere and along trachea and tracheoles
- carbon dioxide produced by cells during respiration, creates diffusion gradient in opposite direction
- so CO2 diffuses along tracheoles and trachea from cells to atmosphere
note: diffusion in air much more rapid than in water, respiratory gases are exchanged quickly like this
42
how does mass transport facilitate exchange in insects
- contraction of muscles in insects can squeeze trachea enabling mass movements of air in and out
- further speeds up exchange of respiratory gases
43
how is air brought into tracheoles when insects respire anaerobically?
- when insect is in flight the muscle cells start to respire anaerobically to produce lactate
- lowers water potential of the cells, and so water moves from the tracheoles into the cells by osmosis
- this decreases the water volume in the tracheoles and as a result more air from the atmosphere is draw in
note: this increases rate which air is moved in the tracheoles but leads to greater water evaporation !!!
44
name the process by which carbon dioxide is removed from a single-celled organism
diffusion over the body surface
45
how do dicotyledonous plants exchange gases with their environment?
through stomata
| - stomata are the tiny pores mainly on leaves
46
draw the structure of a leaf
* google search this*
47
state two ways gas exchange in plants is similar to that of insects
- no living cell is far from the external air and so air is a source of oxygen and carbon dioxide (respiratory gases)
- diffusion takes place in the gas phase (air), (which makes it more rapid than if it were in water)
- diffuse air through pores in outer covering (can control opening and closing of these pores)
48
how do gases move in and through a plant?
diffusion b/c there's no specific transport system for gases
49
name and describe three adaptations of a leaf that allow efficient gas exchange
- short diffusion pathway: many stomata so no cell is far from a stomata
- air-spaces throughout mesophyll cells so gases readily come in contact with mesophyll cells and allows gases to move around leaf, facilitating diffusion
- large SA of mesophyll cells for rapid diffusion (leaf also thin and fla to provide short diffusion pathway and large SA:V ratio)
50
how is the diffusion gradient in a leaf maintained?
by mitochondria carrying out respiration and chloroplasts carrying out photosynthesis
51
state two differences between gas exchange in plant leaf and gas exchange in a terrestrial insect
any 2 of the following:
- insects have a smaller SA:V ratio than plants
- insects have special structures (trachea) along which gases can diffuse, plants don't
- insects don't interchange gases between respiration and photosynthesis, plants do
- insects may create mass air flow, plants never do
52
explain the advantage to a plant being able to control the opening and closing of stomata
helps to control water loss by evaporation/transpiration
53
why is it important stomata can open and close?
- to prevent water loss
| - to allow gas exchange (like respiratory gases)
54
where are stomata mainly found?
underside of leaves
55
what three adaptations have insects evolved to reduce water loss?
- small SA:V ratio to minimise area over which water is lost
- waterproof coverings over body surfaces (in insects this is rigid outer skeleton made of chitin with waterproof cuticle)
- spiracles are openings in tracheae at body surface and can be closed to reduce water loss (conflicts w/ need for oxygen so largely occurs when insects are at rest)
56
why can't plants have a small SA: ratio to limit water loss?
this conflicts with photosynthesis
| - photosynthesis requires large leaf SA for capture of light and exchange of gases
57
why can't plants have a small SA: ratio to limit water loss?
this conflicts with photosynthesis
| - photosynthesis requires large leaf SA for capture of light and exchange of gases
58
what are terrestrial plants?
a plant that grows on, in, or from land
59
what are xerophytes?
- plants adapted to living in areas where water is in short supply (w/o these adaptations they'd become desiccated and die)
60
only name the adaptations of xerophytes to limit water loss?
- a thick cuticle
- rolling up leaves
- hairy leaves
- stomata in pits or grooves
- reduced SA:V ratio of leaves
61
how does 'a thick cuticle' limit the water loss in xerophytes?
the thicker the cuticle, the less water can escape by this means (reduces evaporation rate)
62
how does 'rolling up of leaves' limit the water loss in xerophytes?
- in most leaves stomata is in lower epidermis so rolling leaves protects lower epidermis from outside trapping a region of still air within rolled leaf
- region becomes saturated w/ water vapour and so very high water potential
- there's no WP gradient between inside and outside of leaf so no water loss
63
how do 'hairy leaves' limit the water loss in xerophytes?
- thick layer of hairs on leaves, especially lower epidermis, traps still moist air next to leaf surface
- WP gradient between inside and outside of leaves is reduced, so slower diffusion, less water lost from air spaces
- so less water lost by evaporation
64
how does 'stomata in pits or grooves' limit the water loss in xerophytes?
- trap still,moist air next to leaf
- this reduces WP gradient, so slower diffusion, less water lost from air spaces
- hence less water lost by evaporation
65
how does 'a reduced SA:V ratio of leaves' limit the water loss in xerophytes?
- by having leaves small and circular in cross-section instead of broad and flat, the rate of water loss is reduced (less area for water to evaporate from)
- this reduction in SA is balanced against need for sufficient area for photosynthesis to meet requirements of plant
66
insects and plants face same problem when it comes to living on land. What is the main problem they share?
- efficient gas exchange requires thin, permeable surface with large area
- on land these features can lead to considerable loss of water by evaporation
67
state one modification to reduce water loss that is shared by plants and insects
any one of the following:
| waterproof covering of body/ ability to close the openings of gas-exchnage system (stomata and spiracles)
68
state two reasons reasons why humans need to absorb large volumes of oxygen from the lungs
- have a large vol of cells/humans are large
| - have a high body temp/high metabolic rate
69
what specialised surfaces have mammals evolved/developed?
lungs
| - to ensure efficient exchange between air and their blood
70
why are mammalian lungs located inside the body?
- air isn't dense enough to support and protect delicate structures
- body as a whole would lose a lot of water and dry out
71
list in the correct sequence all the structures that air passes through on its journey from the gas exchange surface of the lungs to the nose
alveoli, bronchioles. bronchus, trachea, nose
72
explain how the cells lining the trachea and bronchus protect the alveoli from damage
- cells produce mucus that traps particles of dirt and bacteria in air breathed in
- cilia on these cells move this debris up the trachea and into the stomach
- this dirt/bacteria could damage/cause infection in alveoli
73
describe the structure of the lungs
pair of lobed structures made up series of highly branched tubules - bronchioles - which end in tiny air sacs called alveoli
- surrounded by ribcage which serves to protect them
74
describe the trachea and its function in the mammalian gaseous exchange system
- flexible airway supported by rings of cartilage
- lined by ciliated epithelium cells which move muscus towards the throat to be swallowed - preventing lung infections
- carries air to the bronchi
75
describe the trachea and its function in the mammalian gaseous exchange system
- flexible airway supported by rings of cartilage
- lined by ciliated epithelium cells which move mucus towards the throat to be swallowed - preventing lung infections
- carries air to the bronchi
76
describe the bronchi and their function in the mammalian gas exchange system
- like trachea, supported by rings of cartilage and lined by ciliated epithelium cells
- however, they're narrower and there are two of them (1 for each long)
- allow passage of air into the bronchioles
77
describe the bronchioles and their function in the mammalian gasesous exchange system
- narrower than bronchi
- don't need to be kept open by cartilage, so mostly have only muscle and elastic fibres so that they can contract and relax easily during ventilation
- allow passage of air into the alveoli
78
describe the alveoli and their function in the mammalian gaseous exchange system
- mini air sacs, lined with epithelium cells, site of gas exchange
- walls only one cell thick, covered with network of capillaries, 300 million in each lung, all of which facilitates gas diffusion
79
how is diffusion of gases across alveolar epithelium maintained?
- by air constantly being moved in and out
80
what is ventilation?
- mechanism of breathing
- involves the diaphragm and antagonistic interaction between the external and internal intercostal muscles in bringing about pressure changes in the thoracic cavity
81
what is inspiration/inhalation?
when air pressure of the atmosphere is greater than air pressure in lungs, air is forced into lungs (down pressure gradient)
82
what is expiration/exhalation?
when air pressure in lungs is greater than that of the atmosphere, so air is forced out of the lungs (down pressure gradient)
83
what is the diaphragm?
- sheet of muscle that separates thorax from the abdomen
84
what are the two sets of intercostal muscles and what do their contractions lead to?
- they lie between ribs:
- internal intercostal muscles, their contraction leads to expiration
- external intercostal muscles, their contraction leads to inspiration
85
explain the process of inspiration and the changes that occur throughout the thorax
- external intercostal muscles contract (while internal relax), pulling ribs upwards and outwards, increasing volume of thorax
- diaphragm contracts and flattens, further increases vol of thorax
- increased vol of thorax results in reduction of pressure in lungs
- atmospheric pressure greater than pulmonary pressure, so air is forced into lungs (down pressure gradient)
86
explain the process of expiration and the changes that occur throughout the thorax
- internal intercostal muscles contract (while external relax), pulling ribs downwards and inwards, decreasing volume of thorax
- diaphragm relaxes and domes upwards, vol of thorax decreases
- decreased vol of thorax increases pressure in lungs
- pulmonary pressure greater than that of atmosphere, so air is forced out of lungs (down pressure gradient)
87
what is tidal volume?
- vol of air we breathe in and out during each breath at rest
88
what is breathing rate?
number of breaths we take per minute
89
how to calculate pulmonary ventilation rate?
tidal vol x breathing rate
| - can be measured using a spirometer, a device which records vol changes onto a graph as a person breathes
90
how normal quiet breathing different to what happens during inhalation?
- recoil of elastic tissue is main cause of air being forced out
- only under strenuous conditions (like exercise) do the various muscles play a part
91
name the site of gas exchange in mammals
epithelium of the alveoli
92
why is the diffusion pathway short across the alveoli?
- they have a single layer of epithelial cells
| - the blood capillaries have only a single layer of endothelial cells
93
state and explain why diffusion of gases between the alveoli and blood will be rapid
- RBCs are slowed as they pass through pulmonary capillaries, allowing more time for diffusion
- distance between alveolar air and RBCs is reduced as RBCs are flattened against capillary walls (short DD)
- walls of both alveoli and capillaries are v thin and therefore diffusion distance is short
- alveoli and pulmonary capillaries have large total SA
- breathing movements constantly ventilate lungs and action of heart constantly circulates blood around alveoli- ensures a steep conc gradient of gases to be exchanged is maintained
- blood flow through pulmonary capillaries maintains a conc gradient
94
explain how the following features contribute to the efficiency of gas exchange in alveoli:
a. wall of alveolus is not more than 0.3 micrometres thick
b. there are 300 million alveoli in each lung
c. each alveolus is covered by a dense network of pulmonary blood capillaries
d. each pulmonary capillary is very narrow
a. rate of diffusion is more rapid the shorter the distance across which the gases diffuse
b. there is a v large SA in 600 million alveoli (2 lungs) and this makes diffusion more rapid
c. diffusion more rapid, the greater the conc gradient. pumping blood through capillaries removes oxygen as it diffuses from alveoli into blood. supply of new CO2 as it diffuses out of blood into alveoli helps maintain a conc gradient that would otherwise disappear as concentrations equalised
d. red blood cells are flattened against walls of capillaries to enable them to pass through. this slows them down, increasing time for gas exchange and reducing diffusion pathway, thereby increasing rate of diffusion
95
define digestion
hydrolysis of large, insoluble biological molecules into smaller molecules which can be absorbed across cell membrane
96
name the major parts of the digestive system
oesophagus, stomach, ileum, large intestine, rectum, salivary glands and pancreas
97
what two stages does digestion take place in?
1 physical breakdown
| 2 chemical digestion
98
what happens in physical breakdown?
- large food broken down into smaller pieces by structures like teeth, which provides large SA for chemical digestions
- food churned by muscles in stomach wall which also physically breaks it up
99
what happens in chemical digestion?
- hydrolyses large, insoluble molecules into smaller, soluble ones by means of enzymes
enzymes being: carbohydrases, lipases and proteases
100
what do the following enzymes hydrolyse and into what:
1 carbohydrases ?
2 lipases ?
3 proteases ?
1 hydrolyse carbohydrates into monosaccharides
2 hydrolyse lipids (fats and oils) into glycerol and fatty acids
3 hydrolyse proteins into amino acids
101
describe the role of the oseophagus in the digestive system
carries food from mouth to the stomach
102
describe the role of the stomach in the digestive system
(muscular sac with inner layer that produces enzymes )
| - role is to store and digest food, especially proteins, it has glands that produce enzymes which digest protein
103
describe the role of the ileum in the digestive system
(long muscular tube)
- food further digested in ileum by enzymes it produces and glands that pour secretion into it
- inner walls of ileum folded into villi which gives large SA (villi have microvilli on epithelial cell of each villus which further increases SA)
104
how is ileum adapted for its role?
- inner walls of ileum folded into villi which gives large SA (villi have microvilli on epithelial cell of each villus which further increases SA)
- adapts ileum for its purpose of absorbing products of digestion into bloodstream
105
describe the role of the large intestine in the digestive system
- absorbs water
| - most of water that's absorbed is water from secretions of many digestive glands
106
describe the role of the rectum in the digestive system
- final section of intestines
| - faeces stored here before being removed via anus in process called: egestion
107
describe role of salivary glands in the digestive system
- near mouth
| - pass secretions via duct into mouth, secretions contain amalyse which hydrolyses starch into maltose
108
describe the role of the pancreas in the digestive system
- large gland below stomach
- produces pancreatic juice - this contains proteases, lipases and amalyses (to hydrolyse proteins, lipids and starch respectively)
109
which enzymes are involved in carbohydrate digestion? Where are they found?
- amylase in mouth and pancreas
| - maltase, sucrase, lactase in membrane of small intestine
110
describe the digestion of carbohydrates in mammals including the role of amylase and membrane-bound dissacharides
- amylase in saliva hydrolyses starch in food to maltose (amylase hydrolyses alternate glycosidic bonds), contains mineral salts that maintain neutral PH - optimum pH for salivary enzyme to work
- food swallowed, enters stomach, acidic stomach denatures salivary amylase
- food passed into SI (not all starch digested bc of denatured amylase in stomach), where it mixes w secreted pancreatic juices, juice contains pancreatic amylase which continues hydrolysis of remaining starch to maltose
- muscles in intestine wall push food along ileum; ileum has its own epithelium (outer tisssue) which contains a membrane-bound disacchadrise (maltase enzyme embedded)
- membrane-bound maltase hydrolyses maltose into alpha glucose molecules (which are much more readily absorbed into cells and blood)
111
what does pancreas and intestinal wall produce and why is this helpful in the digestion of carbohydrates?
- alkaline salts
- it maintains neutral pH so amalyase can function
(bc everything coming from through SI from stomach has low pH which will damage cells after stomach)
112
how are sucrose and lactose hydrolysed?
hydrolysed by membrane-bound enzymes in ileum:
- sucrase hydrolyses single glycosidic bond in sucrose molecule, this hydrolysis produces two monosacchardies: glucose and fructose
- lactase hydrolyses single glycosidic bond in the lactose molecule, this hydrolysis produces two monosaccharides: glucose and galactose
113
where are lipases produced and what dp they do?
- pancreas
| - hydrolyse ester bond in triglycerides to form two fatty acids and a monoglyceride
114
where are lipids digested?
the SI
115
what needs to happen before lipids can be digested?
- must be emulsified by bile salts produced by the liver
| - this breaks down large fat molecules into smaller, soluble molecules called micelles, increasing SA
116
how are lipids digested?
- lipases hydrolyse ester bonds in triglyceride to form a monoglyceride (glycerol w/ single fatty acid) and 2 fatty acids
- lipids split into tiny droplets: micelles by bile salts, which are produced by liver (emulsification)
- this increases SA of lipids so action of lipases is sped up
117
explain the importance of bile salts in the digestion of lipids
- lipids are hydrophobic, meaning they collect into droplets in aqeuous environments
- large droplets have a low SA:V ratio, bile salts separate large droplets into smaller droplets called micelles (by emuslification)
- this increases SA:V ratio, providing larger SA for lipases to hydrolyse lipids
118
state the name of the enzymes responsible for hydrolysing lipids, and describe what they do
- lipases
- lipases hydrolyse ester bonds between glycerol and two of the fatty acids in lipids, forming two fatty acids and a monoglyceride
119
describe how digestion products of lipids enter the blood from the ileum lumen
- in the ileum, bile salts in micelles break down, releasing monoglycerides and fatty acids
- these diffuse into epithelial cells, where they travel to endoplasmic reticulum
- here they're recombined into triglycerides and packaged into stuctures called chylomicrons which also contain cholesterol and lipoproteins
- chylomicrons (which contain lipids) are released into capillaries by exocytosis
120
list two structures that produce amylase
- salivary glands
| - pancreas
121
suggest why the stomach doesn't have villi or microvilli
- villi and microvilli increase SA to speed up absorption of soluble molecules, food in stomach hasn't been hydrolysed into soluble molcules they can't be absorbed so villli/microvilli unnecessary
122
name the final product of starch digestion in the gut
alpha glucose
123
list 3 enzymes produced by the epithelium of the ileum
maltase, sucrase and lactase
124
which enzymes are involved in protein digestion? What is their role?
peptidases:
endopeptidases = peptidases that hydrolyse peptide bonds in middle region of proteins
exopeptidases = peptidases hydrolyse peptide bonds at the end of proteins, releasing single AAs and dipeptides
dipeptidases = hydrolyse peptide bonds in dipeptides to single AAs (yield 2 AAs) - lead to AAs being absorbed through cells and into blood
125
how do endopeptidases allow exopeptidases to work more efficiently?
- they hydrolyse peptide bonds in middle region of proteins
- expose more ends (increase SA) of polypeptide chain
- allows more exopeptidases to work simulatenously, increasing rate they hydrolyse proteins for digestion
126
describe and explain the adpatations of the ileum that make it well-suited for absorption of products of digestion
- increase the surface area for diffusion
- thin-walled, reducing diffusion distance
- contain muscles so can move, helps maintain diffusion gradients b/c movement of muscles mixes content of stomach. Ensures as products of digestion absorbed from food, new material is rich in products to replace it
- well supplied w/ blood vessels so blood can carry away absorbed molecules and maintain diffusion gradient
- its epithelial cells have microvilli, which increase SA for absorption
127
what molecules require co-transport?
amino acids and monosaccharides (e.g. glucose)
128
explain how sodium ions are involved in co-transport
- Na+ ions are actively transported out of cell and into lumen, creating diffusion gradient
- nutrients are then taken up into cells along with Na+ ions
129
why do fatty acids and monoglycerides not require co-transport?
- molecules are non-polar so they can easily diffuse across membrane of epithelial cells
130
describe the absorption of triglycerides
- micelles travel to ileum, they break down at the epithelial lining of ileum and release monoglycerides and fatty acids which diffuse across cell-surface membrane into epithelial cells (bc they're non-polar)
- inside epithelial cell, monoglycerides and fatty acids transported to endoplasmic reticulum and continuing in golgi appartus, they're recombined into triglycerides and packaged (in vesicles)
- they associate w/ cholesterol and lipoproteins in structures called chylomicrons, chylomicrons released from epithelial cell by exocytosis
- they enter lymphatic capillaries called lacteals that are found at centre of each villus; chylomicrons travel into blood system and triglycerides in chylomicrons hydrolysed by enzyme in endothelial cells of blood capillaries - from where they diffuse into cells
note: fatty acid then absorbed into cell (used in respiration or stored as fat)
131
what are micelles made up of?
bile salts, fatty acids and monoglycerides
132
describe how digestion products of lipids enter the blood from ileum lumen [ 4 MARKS]
- in ileum, bile salts in micelles break down, releasing monoglycerides and fatty acids
- they diffuse into epithelial cells, where they travel to endoplasmic reticulum
- here they're recombined into triglycerides and packaged into structures called chylomicrons, which also contain cholesterol and lipoproteins
- chylomicrons (which contain lipids) are released into capillaries by exocytosis
133
list three organelles that you would expect to be numerous and/or well developed in an epithelial cell of the ileum, giving a reason for your choice in each case
- ER to re-synthesise triglycerides from monoglycerides and fatty acids
- Golgi apparatus to form chylomicrons from triglycerides, cholesterol and lipoproteins
- mitochondria to provide ATP required for co-transport of glucose and amino acid molceules
134
describe the co-transport mechanisms for the absorption of amino acids and of
monosaccharides
- glucose molecules/AAs absorbed into ileum epithelium and then into blood:
- high Na+ conc in ileum lumen comapred to inside cell, while low glucose conc in lumen compared to inside cell
- protein co-transporter transfer Na+ down its conc gradient and glucose against its conc gradient
135
how are amino acids and/or monosacchardies absorbed into the blood? [1 MARK}
by co-transport with sodium ions
136
Explain how co-transport takes place when cells lining the ileum absorb glucose (3)
- Na+ actively transported from ileum cells to blood
- Maintains diffusion gradient for Na+ to enter cells from gut
- Glucose enters by facilitated diffusion with Na+
137
name three types of adaptations organisms have to increase rate of diffusion across the exchange surface
- maintain steep conc gradient
- short diffusion pathway
- large surface area
138
what organ produces maltase?
small intestine
139
how do single-celled organisms exchange gases?
- by simple diffusion across their body surface
140
what are tracheae?
microscopic air-filled pipes/tubes
141
Describe the ventilation mechanism in fish (in terms of their buccal and operculum cavity)
- buccal cavity of the fish opens and the buccal floor moves downwards
- creates a larger vol in the buccal cavity causing pressure to fall (relative to pressure in external environment)
- water will run in through the fish's mouth making contact with the gill filaments, gas exchange takes place
- buccal cavity closes and the buccal floor rises, causes vol in buccal cavity to fall and pressure to rise (relative to the external environment)
- this will cause the deoxygenated water to flow out through the operculum which opens as the buccal cavity closes
142
3 structures of the small intestine
duodenum (from stomach), jejunum (middle) and ileum (end)
143
how are proteins digested [2 Marks]
- proteins are hydrolysed to amino acids, which can be absorbed in the ileum of the small intestine
- hydrolysed by endopeptidases, exopeptidases and membrane-bound dipeptidases
144
how does the countercurrent flow system mean that gas exchange is more efficient?
- maintains a large conc gradient between water and oxygen
| - maximum amount of oxygen moves from water into the blood
145
what organ produces amylase?
pancreas
146
what organ prodces maltase?
small intestine
147
Maltose is hydrolysed by the enzyme maltase. Explain why maltase catalyses only this reaction. [3 Marks]
- active site of maltase complementary to maltose
- only maltose can bind
- to form an E-S complex
148
Describe how proteins are digested in the human gut [4 Marks]
1. hydrolysis of peptide bonds
2. endopeptidases break/hydrolyse polypeptides into smaller peptide chains (increase SA)
3. exopeptidases remove terminal ends (hydrolysed peptide bonds at end of PP chain)
4. dipeptidases hydrolyse dipeptides into amino acids
149
Describe the ventilation mechanism in fish (in terms of their buccal and operculum cavity)
- buccal cavity of the fish opens and the buccal floor moves downwards
- creates a larger vol in the buccal cavity causing pressure to fall (relative to pressure in external environment)
- water will run in through the fish's mouth making contact with the gill filaments, gas exchange takes place
- buccal cavity closes and the buccal floor rises, causes vol in buccal cavity to fall and pressure to rise (relative to the external environment)
- this will cause the deoxygenated water to flow out through the operculum which opens as the buccal cavity closes
150
3 structures of the small intestine
duodenum, jejunum and ileum
151
how are proteins digested
- proteins are hydrolysed to amino acids, which can be absorbed in the ileum of the small intestine
152
protein digestion begins with what enzyme and why?
- begins with endopeptidases
- action of endopeptidases increases number of ‘ends’ that can be hydrolysed by exopeptidases. This speeds the rate of protein digestion
153
The epithelial cells in the lungs are arranged into structures called alveoli. Explain how the alveoli create a surface for efficient gaseous exchange.
```
1.wall is one cell thick for short(er)
diffusion, distance / pathway ;
2.squamous, cells / epithelium , provide
short diffusion distance / pathway ;
3.elastic so, recoil / expel air / helps
ventilation ;
4.create / maintain, concentration
gradient / described ;
5.large number (of alveoli) provide large(r)
surface area ;
6.small size (of alveoli) provide large(r)
surface area to volume ratio ;
7.(cells secrete) surfactant to maintain
surface area ;
```
154
To improve gaseous exchange, the air in the alveoli is refreshed by ventilation. The air movement created by ventilation can be recorded using a suitable apparatus. Name the apparatus used to record these air movements.
spirometer
155
When the rubber sheet is pulled down the balloons expand. Explain why the balloons expand.
1 volume, inside / of, jar increases ;
2 pressure inside, jar / balloons, decreases ;
3 to below pressure in atmosphere ;
4 (therefore) air, moves / pushed / forced, into, balloons / glass tube ;
156
Explain the meaning of the term tidal volume
volume of air, inhaled / exhaled ;
in, one / each, breath ;
during, steady / regular, breathing ;
157
Explain the meaning of the term vital capacity.
the maximum volume of air ;
| inhaled / exhaled, in one breath ;
158
List three reasons why a large, multicellular animal, such as a mammal, needs a transport system.
low / small, surface area to volume ratio ;
diffusion, too slow / distance too great ;
to supply enough, oxygen / (named) nutrients ;
to prevent, CO2 / (named) waste product, building up ; active ;
159
Explain why cartilage is essential in the trachea.
(provides) strength / support, to keep, it / trachea / airway,
open
OR
(provides) strength / support, to prevent collapse ;
during, inspiration / inhaling / breathing in ;
volume of, chest cavity / thorax / lungs, increases ;
low(er) / negative, pressure in, trachea / thorax / lungs ;
160
The air sacs contain many elastic fibres.
| Explain the role of these elastic fibres during ventilation (2)
to prevent bursting;
recoil;
to return air sac to original size/shape;
to help expel air;
161
Explain how refreshing the air in the air sacs (through ventilation) helps to maintain a steep diffusion gradient.(2)
1 increases partial pressure/concentration, of oxygen;
2 so concentration of oxygen (in the air sac) is higher than that in the blood;
3 decreases, partial pressure/concentration, of carbon dioxide (in air sac);
4 so concentration of CO2 (in the air sac) is lower than that in the blood ;
162
Describe and explain one other way (apart from ventilation) in which a steep diffusion gradient is maintained in the lungs. (2)
- (continuous) blood flow (in the capillaries);
| - to, bring in (more) carbon dioxide / take away (more) oxygen;
163
name the type of epithelium in the walls of the air sacs
squamous
164
the air sacs contain many elastic fibres
| explain the role of these elastic fibres during ventilation
- to prevent bursting
- recoil
- to return air sac to original shape
- to help expel air
165
explain what causes the change in the volume of air during expiration
- intercostal muscles and diaphragm relax
- rib cage moves down
- pressure inside the chest cavity increases
- above external pressure
- air leaves down pressure gradient
- elastic fibres recoil
166
outline how the diaphragm and intercostal muscles cause inspiration
- diaphragm flattens and moves down
- intercostal muscles contract to move ribs up and out
- increase volume in thorax
- reduce pressure inside the thorax
- to below atmospheric pressure
167
describe how the spirometer would be used to measure tidal volume
- not breathing through your nose
- subject breathes regularly
- measure height of waves from trace
- measure at least three waves and calculate the mean
168
describe how you could use a spirometer trace to measure the rate of oxygen uptake
- measure the volume of oxygen used
- measure the volume change
- measure time taken to use up this oxygen
- divide volume by time taken
169
suggest two factors that should be considered when carrying out a risk assessment for an experiment using a spirometer
- check health of volunteer
| - sufficient oxygen in chamber
170
using the mammalian gaseous exchange system as an example, explain how the different cells and tissues enable the effective exchange of gases
- thin squamous epithelium lining the walls of alveoli
- thin endothelium lining the walls of capillary
- elastic fibres for recoil and aiding ventilation
- provides a short diffusion distance
- reduce surface tension and prevent alveoli from collapsing
- diaphragm maintains diffusion gradient
- ciliated epithelium and goblet cells protect alveoli from dust and bacteria
- cartilage holds airway open
- smooth muscle controls the diameter of airway and blood vessel
- erythrocytes
- transport gases to and from exchange surface of alveoli
- neutrophil engulf pathogens
171
explain why a person using the spirometer to measure their vital capacity should wear a nose clip
- to ensure all air breathed comes from chamber
| - makes results more valid
172
state two other precautions that should be taken when using a spirometer to measure vital capacity
- use oxygen
| - disinfect mouthpiece
173
explain why a single-celled organisms does not need a specialised area to carry out gaseous exchange
- large surface area to volume ratio
| - small so demand for oxygen is low
174
explain, using the term surface area to volume ratio, why large, active organisms need a specialised surface for gaseous exchange
- large, active organisms have a higher demand for oxygen and need to remove carbon dioxide
- smaller surface area to volume ration
- surface area is too small so diffusion takes longer to supply needs
175
describe how goblet cells and ciliated cells work together to keep the lung surface clear of dust and other particles
- goblet cells release mucus
- mucus traps dust and other particles
- ciliated cells move the mucus
- to top of trachea and back to the mouth
176
state the function of the smooth muscle fibres
to constrict the bronchus
177
explain why blood capillaries and alveoli are very close together
- short diffusion pathway
- so that diffusion gradient is high
- therefore high rate of gas exchange
178
state the function of elastic fibres in alveoli
recoil
179
state two ways in which breathing may change in order to increase ventilation rate
- increase in tidal volume
| - increase on no. of breaths per minute
180
Explain the advantages of lipid droplet and micelle formation
1. Droplets increase surface areas (for lipase /
enzyme action);
2. (So) faster hydrolysis/digestion (of
triglycerides / lipids);
3. Micelles carry fatty acids and glycerol /
monoglycerides to / through membrane / to
(intestinal epithelial) cell;
181
Explain how the Golgi apparatus is involved in the absorption of lipids
```
Modifies/processes triglycerides;
Combines triglycerides with proteins;
Packaged for release/exocytosis
OR
Forms vesicles;
```
182
describe and explain two features you would expect to find in a cell specialised for absorption
- microvilli for large SA for absorption
| - lots of carrier proteins for facilitated diffusion/active transport
183
describe the role of micelles in the absorption of fats into the cells lining the ileum
- micelles include bile salts and fatty acids
- make fatty acids (more) soluble in water
- carry FAs to lining of ileum
- maintain higher conc of FAs to cell lining ileum
- FAs absorbed by diffusion
184
what does the elastic recoil do?
- maintain rate of blood flow/blood pressure
185
state 2 reasons why humans need ti absorb large volumes of oxygen from the lungs?
- humans have large volumes of cells i.e. they're multicellular
- they have high body temp and metabolic rate (and respiratory rates)
186
explain how cells lining trachea and bronchus protect alveoli fro damage
- cells produce mucus that trap dirt and bacteria in air breathed in
- cilia on cells move debris up trachea and into stomach
- dirt/bacteria could damage/cause infection in alveoli
