ORGANISMS EXCHANGE SUBSTANCES WITH THEIR ENVIRONMENT TOPIC 3 (Exchange- Chapter 6) Flashcards
1
Q
What is the surface area of a sphere :
A
4 x pi x r^2
2
Q
What is the volume of a sphere ?
A
4/3 x pi x r^3
3
Q
In microscopic organisms (like amoeba), the organism can exchange all the substances it needs directly through the cell membrane. What are the 2 reasons?
A
1) Microscopic organisms have a relatively low rate of respiration , not very active organisms
2) The surface area of the cell membrane of an amoeba is relatively large, compared to volume of the cell. SA:V ratio
4
Q
How do you calculate the surface area to volume ratio ?
A
SA:V = surface area / volume
5
Q
How do you calculate volume ?
A
Length x width x height
6
Q
How to calculate surface area?
A
Area of a face x number of faces
7
Q
What type of SA:V ratio do small animals have, and what does this mean?
A
Small animals have a large SA:Vol ratio. This means very small animals can exchange gases with environment using their external surface
8
Q
What is the happens to diffusion in large surface area: volume ratios ?
A
Organisms like the tapeworm, which have a large surface area to volume ratio, can use the process of diffusion efficiently (to sustain life). It is able to take all of the oxygen that it needs across the body surface by diffusion. Diffusion is sufficient to supply their cells with enough oxygen to allow them to continue to carry out aerobic respiration and to generate ATP.
9
Q
What type of SA:V ratio do large organisms have, and what does this mean?
A
Larger organisms, like humans, have a smaller surface area to volume ratio, so cannot use diffusion alone to survive.
This is because diffusion over this greater distance will not occur fast enough to meet the demands of the cells of the body
10
Q
Larger organisms have evolved 2 specialised systems to compensate :
A
1) Specialised gas exchange with a very large SA. e.g. gills in fish, lungs in mammals
2) They have a specialised transport system to carry molecules around their body. E.g. blood
11
Q
What three things to gas exchange surfaces have ?
A
1) Large SA
2) short diffusion pathway (Thin)
3) Steep concentration gradient
12
Q
How do you calculate the rate of diffusion ?
A
Rate of diffusion = surface area x concentration gradient / diffusion pathway distance
13
Q
Gas exchange in single-celled organisms + insects
A
14
Q
Info about terrestrial insects (land-born animal /insect) :
A
- insects have an exoskeleton made of hard, fibrous material for protection and a lipid layer to prevent water loss
- insects do not have lungs, and instead have a tracheal system
15
Q
What does limiting water loss insects mean ?
A
Organisms that live on land have to balance being able to exchange gases with reducing the amount of water loss
16
Q
What does water have to do with insects (in limiting water loss) ?
A
Water evaporates off the surface of terrestrial insects, and the adaptations of gas exchange surfaces provide ideal conditions for evaporation
17
Q
What are the insect adaptations to reduce water loss?
A
1) Insects have a small surface area to volume ratio where water can evaporate from
2) Insects have a waterproof exoskeleton
3) Spiracles, where gases enter + water can evaporate from, can open and close to reduce water loss
18
Q
Gas exchange in insects involves a tracheal system.
What are spiracles and what do they do?
A
Spiracles are round, valve like opening, running along the length of the abdomen (on the surface of the exoskeleton).
Spiracles allow gases: oxygen + carbon dioxide to diffuse into the body of the insect (gases also diffuse out via spiracles).
The trachea attach to these openings
19
Q
What is the trachea, and what do they have?
A
The trachea is a network of internal tubes, are wider tubes, they extend down and alone the insect’s body.
The walls of trachea are reinforced with spirals of chitin. This chitin prevents the trachea from collapsing (e.g. when insects move).
The trachea tubes have rings within them to strengthen the tubes and to keep them open.
20
Q
What are the tracheoles, and what do they do?
A
The trachea branch into smaller tubes, deeper into the abdomen of the insect called tracheoles.
These extend throughout all of the body tissues, so the diffusion pathway is very short, so oxygen from the air is brought directly to respiring tissues, Oxygen is needed for aerobic respiration, producing CO2.
The huge number of tracheoles provides a very large surface area for gas exchange. This allows insects to maintain a very rapid rate of aerobic respiration. E.g. during flight.
21
Q
How do insects achieve efficient gas exchange ?
A
- Diffusion gradient
- Mass transport
- The ends of the tracheoles are full of water
22
Q
How does an insect’s diffusion gradient achieve gas exchange ?
A
The concentration of oxygen decreases (CO2 increases), at the ends of the tracheoles because it is used up in respiration.
This creates a diffusion gradient so oxygen diffuses from the air into the tracheole, a diffusion gradient for CO2 works in the opposite direction.
23
Q
How does an insect’s mass transport achieve efficient gas exchange ?
A
Muscles contract (when insects contract + relax their abdominal muscles) to squeeze the trachea.
Allows mass movements of air in + out so gas exchange is faster.
24
Q
The ends of the tracheoles are full of water in an insect, how does this achieve efficient gas exchange ?
A
- When the insect is in flight (if the activity is strenuous (a lot), the muscle cells around the tracheoles will start to respire anaerobically, producing lactate.
- [This is soluble], so lowers the water potential of the cells, therefore water moves from the tracheoles into the muscle cells by osmosis [from an area of high water potential to an area of low water potential down the water potential gradient]
- This decreases the volume of water in the ends of the tracheoles and as a result, more air from the atmosphere draws in, this leads to greater water evaporation
25
What is the significance of more air from the atmosphere being drawn in , into the tracheoles?
But how do this cause a potential problem ?
Means the final part of the diffusion pathway of gas, not liquid. This means diffusion happens faster (in gas, than liquid).
Causes a potential problem : increases the amount of evaporation
26
Why are insects small ?
The tracheal system limits the size of insects
~> gas exchange relies upon diffusion, so the pathway needs to be short
27
What are insect’s adaptations for efficient diffusion ?
1. Large number of fine tracheoles - large surface area
2. Walls of tracheoles are thin + short distance
3. Use of oxygen and production of carbon dioxide sets up steep diffusion gradient
28
Gas exchange in fish
29
Why do fish require a gas exchange surface : in the gills ?
Fish are waterproof, and have a small surface area to volume ratio.
Fish obtain oxygen from the water, but there is 30 times less O2 in water than air, so they have a special adaptation to maintain the concentration gradient to enable diffusion to occur
30
What is Fick’s law equation (how to calculate rate of diffusion ) ?
Rate of diffusion = SA x difference in concentration / length of diffusion path
31
How many layers of gills do fishes have on both sides of their head
4 layers of gills
32
What are gills made up of ?
Stacks of gill filaments
33
What is are gill filaments ?
These are stacked in a pile and supported by a bone or cartilage gill bar /arch
34
What is gill lamellae?
Each filament is covered in gill lamellae
Lamellae are positioned at right angles to the filament, creating a large surface area : this is the site of gas exchange
35
What happens when fish open their mouth ?
Water rushes in and over the gills and then out through a hole in the sides of the head
36
Where does diffusion only happen in fish ?
In the lamellae
37
What are the 3 adaptations for efficient gas exchange in fish ?
1) Large surface area to volume ratio created by many gill filaments covered in many gill lamellae
2) Short diffusion distance due to a capillary network in every lamellae and very thin gill lamellae
3) Maintaining concentration gradient ~> countercurrent flow mechanism
38
What is the counter current exchange principle ?
- this is when water flows over the gills in the opposite direction to the flow of blood in the capillaries
39
What does counter current flow ensure, that makes diffusion occur?
It ensures equilibrium is never reached , ensuring that a diffusion gradient is maintained across the entire length of the gill lamellae ; so diffusion occurs.
There is a diffusion gradient favouring the diffusion of oxygen from water into the blood all the way across the gill lamellae. Almost all the oxygen from the water diffuses into the blood
40
What is parallel flow, why is it bad ?
Blood and water move in the same direction, equilibrium is reached, so no diffusion.
There is a diffusion gradient favouring the diffusion gradient of oxygen from water to blood for only part of the way across the gill lamellae.
Only 50% of the oxygen from the water diffuses into the blood.
41
Why can’t fish breathe air ?
- they lack structural support ; they would collapse
- Use in air results in too much water loss by evaporation
42
Gas exchange in leaf of a plant
43
Why is a leaf similar to an insect?
Both have a short diffusion pathway + rapid diffusion
44
How is a leaf adapted to achieve efficient gas exchange ?
- large surface area
- diffusion distances are small
- concentration gradient
45
How does a leaf having a large surface area achieve efficient gas exchange ?
-Large surface area ~> many mesophyll cells (keep moist to aid diffusion - gases can dissolve into the water layer )
46
How does the diffusion distances in a leaf (they are small) achieve efficient gas exchange ?
Leaves are thin - so CO2 and O2 molecules only have to travel from an air space across a single cell wall to get to the cytoplasm in the cell
47
How does a leaf having a concentration gradient achieve efficient gas exchange ?
Concentration gradient is maintained by constant diffusion of O2 + CO2 in and out of the cells (through the stomata)
48
How does a leaf achieve gas exchange in the stomata ?
Stomata : small openings that allow O2 + CO2 in and out of the cell
(O2 diffuses out of the stomata, CO2 diffuses into the stomata)
Surrounded by 2 guard cells, controlling the opening +closing
This controls diffusion of gasses + water vapour
They have a thicker inner wall, thinner outer wall
49
How does the stomata reduce water loss by evaporation ?
Stomata close at night when photosynthesis wouldn’t be occurring
50
How does stomata open + close ?
When cells absorb water, the cell wall expands and becomes turgid. The thinner outer wall bends more than the thicker, inner wall, so stomata will open.
51
What are the 3 factors which influence the stomata to open ?
1) Light intensity
2) Water availability
3) CO2 concentration
52
How do insects limit water loss ?
-small surface area, less SA to lose water from
- waterproof covering -chitin outer skeleton has a waterproof cuticle
- spiracles can close
53
What causes a problem for water loss, and what is the solution ?
- large SA needed for photosynthesis, causes problem for water loss
Solution :
1) waterproof : waxy cuticle
2) Stomata can close
3) Xerophytes
54
What are xerophytes ?
A plant which is able to survive in an environment with little availability of water or moisture
55
What is an example of a xerophyte ?
Marram grass : found at sand dunes
56
What are the 5 adaptations to reduce water loss in xerophytes ?
1) Thick waxy cuticle
2) Reduced SA:V ratio
3) Hairy leaves
4) Sunken stomata
5) Rolled leaves
57
How does a thick waxy cuticle reduce water loss in xerophytes ?
Impermeable to water.
Reduces evaporation.
Increase in diffusion + distance/ slower rate of diffusion
58
How does a reduced SA:V ratio in xerophytes reduce water loss?
E.g. Pine needles.
Pine trees live in conditions where water is inaccessible due to freezing temperatures, so have a small, rounded leaves / needles
So reduces SA:V ratio
59
How does having ‘hairy leaves’ in xerophytes reduce water loss?
E.g Trichomes
The hairs trap a layer of saturated air. This means the water potential gradient between inside + outside of the leaves is reduced, so less water loss by evaporation
60
How does having a sunken stomata in xerophytes reduce water loss ?
The pits above the stomata become saturated.
Air is trapped reducing air movement. Increasing the water vapour around the stomata reduces the water potential gradient, so slows down water loss.
61
How do rolled leaves in xerophytes reduce water loss?
Keeps the stomata on the inside + reduces the area exposed to the air - the rolling traps still air within the leaf, so increases water vapour inside the roll.
This means there isn’t a water potential gradient between inside + outside of the leaf : so no water is lost
62
Structure of human gas exchange system
63
What is the passage of air through respiratory system ?
Nasal captivity ~> trachea ~> bronchus (bronchi) ~> bronchiole ~> alveoli
64
Air entering nasal captivity is filtered by what ?
Hairs, warmed by contact with tissues + moistened by mucus from goblet cells
65
Air passes down the trachea, held open by water ?
C-shaped rings of cartilage
66
What does cartilage do to the trachea ?
Supports the trachea, to keep it open
67
Why is the cartilage C-shaped ?
So you can move your neck, without snapping your trachea
68
What is the trachea lined with ?
Ciliated epithelium
69
What does the trachea divide into, and so on?
Divides into the L/R bronchus, into bronchioles and end in the alveoli : site of gas exchange
70
2 reasons why humans need to absorb large volumes of oxygen from the lungs ?
1. Humans are large
2. Humans have a higher metabolic rate/ high body temp.
71
Explain how the cells lining the trachea + bronchus protect the alveoli from damage ?
- The Goblet cells produce mucus that traps particles of dirt + bacteria in the air breathed in
The cilia on these cells move this debris up the trachea and into the stomach
72
What is the trachea ?
The airway that leads from the mouth and nose to the bronchi.
The trachea is lined with mucus - secreting Goblet cells + cilia. (Cilia sweeps microorganisms away from the lungs)
73
What are the lungs ?
Humans have 2 lungs, both central part of the respiratory system : where gas exchange takes place
74
What is a bronchi?
The L + R bronchi are at bottom of trachea + are similar in structure.
The bronchi leads to the bronchioles.
75
What are the bronchioles ?
Narrow tubes carrying air from bronchi to alveoli. So narrow, so have no supporting cartilage, so can collapse
76
What are alveoli ?
The main site of gas exchange in lungs.
Traps air sacs, have many structural adaptations to enable efficient gas exchange. E.g. thin walls
77
What is a capillary network ?
Extensive network of capillaries surrounding the alveoli + are exchange surface between lungs + blood.
During gas exchange, O2 diffuses from alveoli into capillaries, CO2 diffuses other way and is exhaled.
78
During inhalation, what happens to the pressure and volume ?
Chest cavity increases in volume , lowering pressure in lungs to draw in fresh air
79
What does a decrease in pressure lead to (for lungs ) ?
Leads to a tendency for lungs to collapse. Cartilage keeps trachea + bronchi open, but alveoli lack this structural support.
80
What is lung surfactant , and why is it important ? (How does it maintain the structure of alveoli ?)
Is a phospholipid that coats the surface of the lungs. Without it, the watery lining of the alveoli would create a surface tension, causing them (alveoli ) to collapse.
81
How are the airways in the lungs kept clear?
- walls of trachea + bronchus contain goblet cells, which secrete mucus made of mucin. This traps micro-organisms and debris, helping to keep the airways clear.
- The walls also contain ciliated epithelial cells, which are covered on one surface with cilia
~> these beat regularly to move with micro-organisms + dust particles along with the mucus. Contain many mitochondria, providing energy for beating cilia.
82
What are the gas exchange tissues in the lungs ?
- ciliated epithelium
- goblet cells found scattered through ciliated epithelium in the trachea
- the alveoli have a lining of thin + squamous (thin, flat cells, look like fish gills) epithelium, that allow for gas exchange.
~> The squamous epithelium forms the structure of the alveolar wall and so is very thin + permeable for easy diffusion of gases
83
The mechanism of breathing
84
The ____ the volume, the ____ the pressure
The larger the volume, the lower the pressure
85
When your breathe what happens to your ribs ?
Ribs go up + out
86
What happens to the diaphragm when muscles contract + relax ?
Diaphragm is flat when muscles contract, they are curved when relaxed
87
What does the external intercostal muscles contraction lead to ?
Inspiration
88
What does the internal intercostal muscles contraction lead to ?
Expiration
89
What is ventilation?
The movement of air in (inspiration) and out (expiration) of the lungs as a result of muscular activity
90
What do the external intercostal do in inspiration and expiration ?
Inspiration : contract
Expiration : relax
91
What do the internal intercostal do in inspiration and expiration ?
Inspiration : relax
Expiration : contract
92
How do the ribs move in inspiration and expiration ?
Inspiration : up + out
Expiration : down + in
93
How does the diaphragm move in inspiration and expiration ?
Inspiration : contracts + flattens
Expiration : relaxes + moves up (curves)
94
What happens to the thorax volume in inspiration and expiration ?
Inspiration : increases
Expiration : decreases
95
What happens to the thorax pressure in inspiration and expiration ?
Inspiration : decreases
Expiration: increases
96
What happens to the air in inspiration and expiration ?
Inspiration : enters as atmospheric pressure exceeds lungs pressure
Expiration : leaves as lung pressure exceeds atmospheric pressure
97
What happens to the pressure on alveoli when increasing the volume of thorax ?
Decreases pressure in alveoli below atmospheric pressure.
Air is forced in until alveolar pressure = atmospheric pressure
98
What happens to the pressure on alveoli when decreasing the volume of thorax ?
Causes air pressure in the alveoli to rise above atmospheric pressure.
Air is squeezed out until alveolar pressure = atmospheric pressure
99
What are the stages of inspiration?
1) External intercostal muscles contract
2) This pulls the ribs up + out
3) Diaphragm muscles contract
4) Thorax volume increases
5) Increased thorax volume reduces pressure in lungs
6) Atmospheric pressure is greater than pulmonary pressure
7) Air forced into the lungs
100
What are the stages of expiration ?
1) Internal intercostal muscles contract
2) This pulls the ribs down + in
3) Diaphragm muscles relaxes and bends
4) This decreases the thorax volume
5) This increases the pressure in the lungs
6) Atmospheric pressure is smaller than lung pressure
7) Air forced out of lungs
101
What is pulmonary ventilation ?
The total volume of air that is moved into the lungs during one minute
102
What is tidal volume ?
Volume of air normally taken in at each breath (when body is at rest)
103
What is ventilation rate ?
The number of breaths per minute
104
How do you calculate ventilation ?
Pulmonary ventilation ( dm^3 min-1) = tidal volume (dm^3) x ventilation rate (min-1)
105
Two ways changes in the contraction of diaphragm muscle affects pulmonary ventilation (4 marks )
- contracting more rapidly increases the ventilation rate
- contracting more/ for longer increases lung volume / tidal volume
106
What happens in gas exchange in the alveoli ?
- lots of air sacs (alveoli ) surrounded by capillaries (blood vessels)
- Alveoli fully of highly oxygenated air
107
Alveoli is full of highly oxygenated air, what does this mean , how does oxygen and Carbon dioxide diffuse between the alveoli and epithelial cell ?
Oxygen diffuses from the alveoli across the epithelium, and into the blood, moving from a higher to lower concentration.
Carbon dioxide diffuses from the blood, into the capillaries and into the alveolus, moving from a higher to lower concentration
108
What does inhaling do to the oxygen molecules in the alveolus ?
Inhaling increases the concentration of oxygen molecules in an alveolus.
When you inhale, the concentration of oxygen inside each alveolus is higher than in deoxygenated blood
109
What does deoxygenated blood have low levels and high levels of ?
Deoxygenated blood from the body is low in O2 but has high levels of CO2.
~> concentration of CO2 in deoxygenated blood is higher than in oxygenated blood
110
What are red blood cells compressed against , and what does this do to the diffusion distance ?
Red blood cells are compressed against a capillary wall/stuck to epithelial cell, so diffusion distance is shorter : efficient gas exchange
111
How do red blood cells help with blood flow?
Red blood cells are flexible, helping with blood flow
112
What are the 4 alveoli adaptations for gas exchange ?
1) Large surface area
~> alveoli : there are 300 million in each human lung
2) Short diffusion pathway
~> one cell thick : epithelium cells are very thin to minimise diffusion distance
3) Diffusion gradient
~> each alveolus has its own blood supply.
Each alveolus is surrounded by a network of capillaries to remove exchanged gases, therefore maintaining a concentration gradient.
4) Alveolar lining is kept moist (by fluid from the cytoplasm)
~> allowing gases to dissolve + diffuse
113
Enzymes + digestion
114
During digestion, what happens to the large biological molecules ?
They are hydrolysed into smaller molecules that can be absorbed across the cell membrane
115
What are the two types of digestion (and the definitions) ?
- physical : food is broken down into smaller pieces by structures like the teeth and muscle. Increases surface area.
- chemical : the hydrolysis of larger, insoluble molecules into smaller, soluble ones, carried out by enzymes
116
What are the 2 enzymes in carbohydrates ? (Requires more than one enzyme to hydrolyse carbohydrates into a monosaccharide )
Amylase and membrane-bound disaccharides
117
How does the enzyme amylase work in digestion ?
1) Food is chewed into smaller pieces and coated in saliva, saliva contains salivary amylase.
Amylase is produced by the pancreas + salivary glands. It hydrolyses polysaccharides into the disaccharide maltose by hydrolysing the glycosidic bonds.
(Salts in the saliva maintain the correct pH)
2) Stomach acid denatures the salivary amylase.
3) Upon entering the small intestine, the stomach acid is neutralised. Secretions from the pancreas contains pancreatic amylase which contains the hydrolysis of starch to maltose.
118
How do the enzyme :membrane-bound disaccharides work in digestion ?
The epithelial lining of the ileum (small intestine) produces maltose.
This is a membrane -bound disaccharide that hydrolysed the maltose into alpha-glucose.
119
Within the duodenum + ileum, this is where there are the membrane-bound disaccharides. What are they ?
- sucrase + lactase are membrane-bound enzymes that hydrolyse sucrose + lactose into monosaccharides
- sucrose (fruits) is hydrolysed by sucrase to produce glucose and fructose
- lactose (from daily products) is hydrolysed by lactase to produce glucose and galactose
120
How are lipids digested/hydrolysed ? (What is lipids enzyme) ?
Hydrolysed by the enzyme lipase and the action of bile salts
121
Where is lipase produced ?
In the pancreas
122
How can lipase form the monoglycerides and fatty acids ?
It can hydrolyse the ester bonds in triglycerides to form the monoglycerides and fatty acids
123
Where are bile salts produced ?
In the liver
124
What can bile salts do, and what do they form ? What is the process ?
They emulsify lipids to form tiny droplets : micelles
This process is called emulsification (in duodenum). It increases the surface area for lipase to act on.
125
What are proteins ?
Are large polymer molecules that can be hydrolysed by 3 enzymes
126
What are the 3 enzymes in proteins ?
Endopeptidases, exopeptidases and (membrane-bound) dipeptidases
127
What are endopeptidases, and what is an example of one ?
They hydrolyse peptide bonds between specific amino acids in the middle of a polymer chain/ polypeptide
(forming a series of peptide molecules)
Example : pepsin
128
What are exopeptidases ?
Hydrolyse peptide bonds between amino acids at the end of a polymer chain/polypeptide
(releasing dipeptides + single amino acids)
129
What are dipeptidases ?
Hydrolyse peptide bonds between two amino acids of a dipeptide
130
Where does protein digestion start, and when is it fully digested ?
Starts in the stomach, continues in the duodenum and is fully digested in the ileum.
131
Absorption of digestion products
132
What 2 stages are involved in lipid digestion ?
1) Physical (emulsification + Michelle formation)
2) Chemical (lipase)
133
What happens in the physical stage of lipid digestion ?
-lipids are coated in bile salts to create an emulsion
- many small droplets of lipids provides a larger surface area to enable the faster hydrolysis action by lipase
134
What happens in the chemical stage of lipid digestion ?
Lipase hydrolyses lipids into glycerol + fatty acids (some monoglycerides)
135
What are micelles?
Vesicles containing fatty acids, glycerol, monoglycerides and bile salts
136
What do micelles deliver, and where to ?
Micelles deliver fatty acids, glycerol and monoglycerides to the epithelial cells of the ileum for absorption
137
How do micelles help with lipid absorption ?
- they make the fatty acids more soluble in water
- they carry the fatty acids to epithelial cells of the ileum
- they help maintain a higher concentration of fatty acids compared to the epithelial cells of the ileum
138
Fatty acids are then released from the micelle, but how do they enter the epithelial cell?
By simple diffusion
139
Why do fatty acids enter by simple diffusion ?
They are non -polar (lipid soluble)
~> so they can dissolve + diffuse through the phospholipid bilayer
140
Where does most absorption take place ?
In the small + large intestines
141
What is the difference between the ileum +duodenum ?
Ileum = for absorption, duodenum = for secretion
In mammals, the products of digestion are absorbed across the lining of the ileum
142
What is the ileum wall covered in ? What does this do to absorption ?
Villi, which has thin walls surrounded by a network of capillaries
and epithelial cells have even smaller microvilli
These features maximise absorption by increasing the surface area, decreasing the diffusion distance and maintaining a concentration gradient
143
What does microvilli/ villi do ?
They increase surface area
144
What does this mean by each villi having an extensive capillary network ?
The absorbed food is transported away quickly, maintaining the concentration gradient.
145
What does a good blood supply do from the extensive capillary network ?
Maintains a steep concentration gradient
146
If you need to absorb anything in the cell membrane, what do the molecules have to be ?
Soluble
147
Are molecules in monoglycerides and triglycerides soluble or insoluble ?
Monoglycerides = soluble
Triglycerides = insoluble, so are formed in SER
148
Describe how digested lipids are absorbed and then transported to the ileum and lymphatic system (detailed version )
- lipids are digested into monoglycerides and fatty acids by the action of lipase and bile salts
- monoglycerides and fatty acids associate with bile salts forming micelles
- when the micelles encounter the ileum epithelial, due to the non-polar nature of fatty acids and monoglycerides, they can simply diffuse across the cell surface membrane to enter the cells of the epithelial cells
- once inside the epithelial cells, the SER + Golgi apparatus recombined monoglycerides and fatty acids back into triglycerides
- the Golgi apparatus combines the triglycerides with cholesterol and lipoproteins to from chylomicrons (particles adapted for transport of lipids)
- vesicles containing the triglycerides/chylomicron are released + move towards the cell membrane.
Chylomicrons move out of the epithelial cells by exocytosis where they enter the lymphatic capillaries called lacteals (found in the centre of each villi )
149
Describe how digested lipids are absorbed and then transport to the ileum and lymphatic system (exam question- simple) ?
1. Micelles are made of bile salts, fatty acids and monoglycerides
2. Micelles carry the fatty acids to the epithelial cells of the ileum
3. Fatty acids are absorbed into the cells of the ileum by simple diffusion
4. Triglycerides or chylomicrons are formed
5. Vesicles are removed by exocytosis
150
Describe the importance of micelles in absorbing lipids into the epithelial cells of the ileum (3)
- micelles are made of bile salts, fatty acids and monoglycerides
- micelles make fatty acids more soluble in water
- micelles carry fatty acids to the epithelial cells of the ileum
- the fatty acids are released from the micelle and are absorbed into the cell by simple diffusion
151
When lipids are digested, they first form smaller droplets + then micelles are formed. Explain the advantage of the 2 stages ?
- lipid droplets increase surface areas for lipase
- this speeds up hydrolysis/digestion
- the micelles bring the fatty acids, monoglycerides + bile salts to the epithelial cell
152
How are Golgi apparatus involved in the absorption of lipids? (3)
- they modify triglycerides
- they combine proteins with triglycerides to form chylomicrons
- they are packaged into vesicles
153
What must happen in order for glucose + amino acids to be absorbed from the lumen to the gut ?
And why is active transport + co - transport required ?
There must be a higher concentration in the lumen compared to the epithelial cell (for facilitated diffusion)
BUT,
There is usually more in the epithelial cells , that is why active transport + co-transport are required
