3A: Exchange Flashcards
1
Q
When substances enter or leave an organism what do they go through?
A
The plasma membrane (phospholipid bilayer)
2
Q
What is an exchange surface?
- What do they always include?
A
Any surface across which substances are transferred is called an exchange surface.
- They always include a cellular membrane
3
Q
What is a negative of being a multicellular organism?
A
The distance between the exterior and interior environments are too great for substances to simply diffuse
- This means that multicellular organisms have had to evolve increasingly more intricate systems for exchanging substances with their environment
4
Q
Give some examples of exchange surfaces in animals (5)
A
- Alveoli (lungs)
- Capillaries
- Villi (small intestine)
- Synapses
- Large intestine
5
Q
What substances are exchanged across exchange surfaces?
A
- Oxygen
- Carbon Dioxide
- Water
- Glucose
- Fatty acids
- Amino acids
- Vitamins
- Minerals
- Urea
- Heat
6
Q
(Apart from heat) substances can be exchanged in 2 ways, what are they?
A
- Passively (no metabolic energy required) by diffusion and osmosis
- Actively (metabolic energy required) by active transport
7
Q
How do you calculate SA : V?
A
SA/V = _ : 1
8
Q
What are the 5 common traits of exchange surfaces?
A
- Large SA:V
- Very thin so diffusion can occur across a short distance
- Selectively permeable - control which substances enter/ exit
- Movement of environment to the medium
- A transport system to move internal medium
9
Q
Give 2 examples of animal exchange surfaces
A
- Vili
2. Alveoli
10
Q
Give an example of an exchange surface in a plant
A
Root hair cell
11
Q
What advantages do unicellular organisms have involving exchange surfaces?
A
- Substances are able to diffuse across the cell membrane due to the small distance between interior and exterior environments
- High SA:V
12
Q
In insects, the increase in surface area required for gas exchange conflicts with what?
A
Conflicts with conserving water.
= because water will evaporate from it
13
Q
What are the features of an insects (tracheal) gas exchange system?
A
- Tracheae
- Tracheoles
- Spiracles
14
Q
Describe the tracheae in insects
A
- Internal network of tubes
- Supported and strengthened by rings to prevent them from collapsing
- Divide into smaller dead- end tubes called tracheoles
15
Q
Describe the tracheoles in insects
A
- Dead-end tubes
- Extend throughout all the body tissues of the insect
- Short diffusion pathway from a tracheole to any body cell
16
Q
Describe how gases move in and out of an insect along a diffusion gradient
A
- Cell respiration uses O₂ up and so its conc. decreases towards the end of the tracheoles
- This creates a diffusion gradient that causes oxygen to diffuse from the tracheae and the tracheoles into cells
- Cell respiration produces CO₂
- This creates a diffusion gradient in the opposite direction: CO₂ diffuses from the cells to the tracheoles and tracheae
- Diffusion in the air is faster than in water, gases are exchanged quickly by this method
17
Q
Describe how gases move in and out of an insect using mass transport
A
The contraction of muscles in insects can squeeze the trachea enabling mass movements of air in and out.
- This further speeds up the exchange of respiratory gases
18
Q
What are the 3 methods insects use to exchange gases?
A
- Mass transport
- Diffusion gradient
- Ends of the tracheoles being filled with water
19
Q
Describe how the ends of the tracheoles being filled with water enables insects to exchange gases (oxygen debt)
A
- During periods of major activity, the muscle cells around the tracheoles respire and carry out some anaerobic respiration.
- Produces lactic acid = insoluble and lowers WP in cells
- The water at the ends of the tracheoles decreases in volume (as it is drawn into the cells) which leaves more room for oxygen (which is also drawn into the cells)
- Means that the final diffusion pathway is in a gas rather than a liquid phase = diffusion is more rapid
- This increases the rate at which air is moved in the tracheoles but leads to greater water evaporation
20
Q
In insects, gases enter/ exit tracheae through tiny pores - what are these called?
A
Spiracles
21
Q
How can the spiracles in an insect be opened and closed?
A
By a valve
22
Q
Describe what happens to water vapour when the spiracles are open
A
Water vapour can evaporate from the insect
23
Q
Most of the time insects keep their spiracles closed, why do they do this?
A
To prevent water loss.
- They periodically open their spiracles to allow gas exchange.
24
Q
What are some limitations of the tracheal system in insects
A
- It relies mostly on diffusion to exchange gases between the environment and the cells
- For diffusion to be effective the pathway needs to be short = which is why insects are small
- As a result the length of the diffusion pathway limits the size the insect can be.
25
What does the diffusion pathway need to be like to make diffusion effective?
The pathway must be short. This is why insects are small
26
Describe the outer covering of a fish
Waterproof and therefore gas proof
27
What is the SA:V of fish like?
Because they are relatively large they have a small SA:V
28
What do gills consist of?
Gill filaments
29
Describe the gill filaments
Stacked up in a pile (like the pages in a book)
30
Where are the gill lamellae in relation to the filaments?
At right angles to the filaments
31
What do the gill lamellae do to the SA of the gills?
They increase the SA of the gills
32
Describe the movement of water through a fish
Water is taken in through the mouth and forced over the gills and out through an opening on each side of the body.
33
What can the flow of water over the gill lamellae and the flow of blood be described as?
A countercurrent flow
| - They flow in opposite directions
34
What is the countercurrent flow important for?
It is important for ensuring that the maximum possible gas exchange is achieved.
35
What would gas exchange (in fish) be like if blood and water flowed in the same direction?
Far less gas exchange would take place if blood and water flowed in the same direction
36
What is the countercurrent exchange principle?
Blood and water flow over the gill lamellae in opposite directions
37
What does the countercurrent flow mean for oxygenated blood?
Blood near 100% O2 saturation meets water at 100% O2 saturation
= Oxygen diffuses from the water to the blood
38
What does the countercurrent flow mean for deoxygenated blood?
- Blood with 0% O₂ saturation meets water with an O₂ saturation of near 0%
= Diffusion of O₂ from the water to blood takes place
39
Countercurrent flow results in a diffusion gradient of __1__being maintained across the entire __2__of the __3__
1- oxygen
2- width
3- gill lamellae
40
Countercurrent flow results in a diffusion gradient of which substance?
Oxygen
41
What does the countercurrent flow mean for the diffusion of oxygen? What does this result in?
- A diffusion gradient is maintained across the entire gill lamellae
- As a result around 80% of the oxygen available in the water is absorbed by the fish
42
What would concurrent (parallel) flow mean for the diffusion of oxygen? What would this result in?
- A diffusion gradient is maintained for only half of the distance across the gill lamellae
- Only 50% of the oxygen from the water diffuses into the blood
43
What does the volumes and types of gases that are being exchanged by plants depend on?
The balance between the rates of photosynthesis and respiration.
44
Describe the trachea
- A flexible tube supported by many cartilaginous rings.
- Rings allow the trachea to stay open when inhalation causes the air pressure in the tube decreased.
- The trachea wall is made up of muscle and lined with ciliated epithelial cells and goblet cells
45
- Where are goblet cells found?
| - What are their function?
- In the tracheal wall
| - They produce mucus
46
- Where are the ciliated epithelial cells found?
| - What are their function?
- In the tracheal wall
| - They waft the mucus up out of the lungs
47
Describe the lungs
- A pair of lobed structures
| - Made up from a series of highly branched tubes (bronchioles)
48
What is the function of mucus (in the trachea)?
- Traps dirt and particles etc. and stops them from entering the lungs
49
Describe the bronchioles
- Within the structure of the lungs
- Heavily branched to carry air to all the parts of the lungs
- Their walls are made up of muscles which allows them to regulate the flow of air into and out of the alveoli by contraction of the pipes
50
Describe the alveoli
- Minute air sacs which measure 100- 300μm across
- Positioned at the ends of the bronchioles
- Can stretch to pull air in (collagen and elastic fibres help to do this) and spring back to expel co2
51
Describe 6 key adaptations for gas exchange at the alveoli
| how they have evolved to function
1. Red blood cells are slowed as they pass through the narrow capillaries, increasing time for diffusion
2. Red blood cells are flattened against the capillary walls reducing diffusion pathway
3. Both alveoli + capillaries have very thin walls
4. Alveoli + capillaries have a massive shred surface area
5. Breathing movements keep the lungs ventilated, replacing the external medium
6. The flow of blood maintains the conc. gradients for exchange
52
List the features of the human respiratory system (in order of air coming in)
```
Larynx
Trachea
Bronchi
Bronchioles
Alveoli --> capillaries
```
53
What is the space around the lungs called?
The pleural space
54
What are the membranes around the lungs called?
The pleural membranes
55
What is the thorax?
Chest area
| - Inside it is called the thoracic cavity
56
Describe inspiration (breathing in)
- The external intercostal muscles contract, while the internal intercostal muscle relax
- The ribs are pulled upwards and outwards = increases the volume of the thorax
- Diaphragm muscles contract, it flattens = increases the volume of the thorax
- Increased vol of thorax = lower pressure in the lungs
- Atmospheric pressure is now greater than the pressure inside the lungs --> so the air is then forced into the lungs
57
Describe expiration
- The internal intercostal muscles relax, while the intercostal muscle contract
- The ribs are pulled downwards and inwards = decreases the volume of the thorax
- Diaphragm muscles relax, so its pushed up again by the contents of the abdomen that were compressed during inspiration. The vol of the thorax is further decreased
- Decreased vol of thorax = higher pressure in the lungs
- Pulmonary pressure is now greater than the atmospheric pressure --> so the air is forced out of the lungs
58
How can the relationship between internal and external extra coastal muscles be described?
Antagonistic
59
Why are the lungs located inside the body?
- Air is not dense enough to support and protect these delicate structures
- Water loss could not be regulated, so the body would lose a lot of water and dry out
- Pollutants and pathogens could
60
What is the function of the ribcage?
To protect the lungs
| - Can be moved by the (intercostal) muscles between them
61
State 2 reasons why humans need to absorb large volumes of oxygen from the lungs.
Any 2 from:
- Humans are large/ have a large volume of cells
- Humans have a high metabolic rate
- Humans have a high body temp
62
How do the cells lining the trachea and bronchus protect the alveoli from damage?
- Goblet cells produce mucus
- Ciliated epithelial cells waft the mucus up the trachea (to prevent it settling in the lungs) and into the stomach
- This mucus traps particles of dirt and pathogens in the air breathed in.
- Because the dirt/ pathogens could damage the alveoli
63
Describe what muscles are used in normal breathing.
How is this different to more strenuous conditions?
During normal breathing, the recoil of the elastic tissue in the lungs is the main cause of air being forced out.
Only in more strenuous conditions such as exercise do the various muscles play a major role
64
What is pulmonary ventilation rate?
The total volume of air that is moved into the lungs during 1 minute
65
What is the tidal volume?
What is this usually?
The volume of air normally taken in at each breath when the body is at rest
Usually around = 0.5dm³
66
What is the ventilation (breathing) rate?
What is this normally?
The number of breaths taken in 1 minute
Normally 12-20 breaths in a healthy adult
67
How do you calculate pulmonary ventilation rate?
PVR = tidal volume x breathing rate
68
What is the unit for pulmonary ventilation rate?
dm³ min-1
69
What is the unit for tidal volume?
dm³
70
What is the unit for breathing rate?
min-1
71
What are 5 adaptions of xerophytic plants?
1. Shallow + wide roots (for desert like conditions)
2. Thick cuticle
3. Rolling up of leaves
4. Hairy leaves
5. Stomata in pits/ grooves
72
What are the (7) key features of the digestive system
- Salivary glands
- Oesophagus
- Stomach
- Pancreas
- Ileum
- Large intestine
- Rectum
73
Describe the features of the structure of the leaf of a dicotyledonous plant
(From top to bottom)
- Waxy cuticle
- Upper epidermis
- Palisade mesophyll
- Spongy mesophyll
- Lower epidermis (with guard cells and stomata)
- Waxy cuticle
74
Describe the waxy cuticle's function in plant leaves
Stops water from leaving the leaf (made from lipids)
75
What is the function of the upper epidermis in plant leaves?
Protection
76
What is the function of the palisade mesophyll in plant leaves?
Primary location of photosynthesis
77
What is the function of the spongy mesophyll in plant leaves?
- Allows gases to circulate
| - Increases the surface area
78
What is the function of the lower epidermis in plant leaves?
Adaptation = high conc. of stomata
79
Describe the stomata and their function in plant leaves
- Minute pore, surrounded by 2 guard cells (on either side)
- The guard cells can:
swell open + allow gas exchange while water is available
OR
close when water is short in supply
80
In xerophytic plants, what is the function of their rolled-up leaves?
- Protects the lower epidermis from the outside
- Helps trap a region of still air within the rolled leaf
- This region becomes saturated with water vapor so it has a very high water potential
- There is no water potential gradient between the inside + outside if the leaf so no water loss
81
What is the similarity in stomata location between xerophytic plants and dicotyledonous plants?
Most plants have their stomata largely, or entirely on their lower epidermis
82
Give an example of a xerophytic plant that has rolled up leaves.
The Marram grass
83
In xerophytic plants, how do their rolled up leaves limit water loss?
- The leaves trap a region of still air within the rolled leaf
- This means that the region becomes highly saturated with water = so it has a very high water potential
- This means that there is no water gradient between inside and outside of the leaf
= no water loss
84
In xerophytic plants, what is the function of hairy leaves?
- A thick layer of hairs on leaves, especially on the lower epidermis, traps still moist air next to the leaf surface
- The water potential gradient between the inside and outside of the leaves is reduced
- Therefore less water is lost by evaporation
85
In xerophytic plants, why is it especially important that a thick layer of hairs is on the lower epidermis?
- Because the lower epidermis contains the stomata and guard cells, which is how gases enter and exit the leaf
- Meaning that it is more important the moist still air is concentrated around the stomata because only through there can oxygen enter
86
In xerophytic plants, what is the function of the stomata being in pits/ grooves?
These trap still moist air next to the leaf and reduce the water potential gradient = reducing water loss
87
Give an example of a xerophytic plant that has hairy leaves
One type of Heather plant
88
In xerophytic plants, what is the function of a reduced SA:V ratio of the leaves?
- The smaller the SA: V = the slower the rate of diffusion
- By having leaves that are small + roughly circular (in cross section) rather than being broad + flat the rate of water loss can be considerably reduced.
89
Define xerophyte
A species of plant that has adaptations to survive in an environment with little liquid water, such as a desert or an ice- or snow-covered region
90
Give 2 examples of xerophytic plants
Cacti + Marram grass
91
What is the reduction in SA in xerophytic plant leaves balanced against?
The reduction in SA is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant
92
Give an example of a xerophytic plant leaf that has a reduced surface area.
- What does this limit & why?
Pine needles
| - The reduced SA considerably reduces water loss because a smaller SA = a slower diffusion rate
93
Insects and plants face the same problems when it comes to living on land. What is the main problem they share?
- Efficient gas exchange requires a thin, permeable surface with a large area
- On land these features can lead to a considerable loss of water by evaporation
94
State 1 modification to reduce water loss that is shared by plants and insects.
- Waterproof covering of the body
| - Ability to close the openings of the gas exchange system (stomata/ spiracles)
95
Insects limit water loss by having a small SA:V. Why is this not a feasible way of limiting water loss in plants?
Plants photosynthesise and therefore need a large SA to capture light
96
What is digestion?
The breaking down of large biological molecules found in food, by hydrolysis, to allow them to be absorbed by digestive exchange surfaces
97
What is the function of the Salivary glands?
To secrete saliva which helps to lubricate food but also contains amylase (breaks down starch)
98
What is the function of the Oesophagus?
It is a smooth tube which transports food to the stomach
99
What is the function of the Stomach?
Stores and digests foods, especially proteins. Low pH = optimum for proteases
100
What is the role of the pancreas in digestion
It is a large gland that secretes pancreatic juice just after the stomach. This juice contains enzymes that break down the lipids, proteins and carbs in food
101
What does the pancreas contain?
It contains proteases, lipases and amylase
102
What is peristalsis?
The process by which food moves through the digestive system, involving muscle contraction. (see diagram)
103
What is the function of the ileum?
- Secretes many digestive enzymes
| - Has a massive SA due to epithelial cells covered in villi
104
What is the scientific name for the small intestine?
The ileum
105
What is the function of the large intestine?
It absorbs water
106
Why is the large intestine essential?
It is essential in reclaiming the water that is secreted by the many digestive glands
107
What is the function of the rectum?
Faeces are stored here prior to periodic egestion
108
Describe stage 1 of carbohydrate digestion
- Where does it occur?
- What is hydrolysed?
- What is it hydrolysed by?
- What is released?
- Digestion of carbohydrates begins in the mouth
- Here the saliva is mixed with the food through chewing
- Starch starts to be hydrolysed by salivary amylase into maltose
- The salivary amylase also contains mineral salts that maintain a neutral pH
109
Describe stage 2 of carbohydrate digestion
- Where does it occur?
- What are the conditions like?
- The food is swallowed and enters the stomach, where the conditions are acidic
- The acid denatures the amylase which stops further hydrolysis of the starch
110
Describe stage 3 of carbohydrate digestion
- After a time the food is passed from the stomach to the ileum
- The pancreas secretes pancreatic juice which is mixed with the food
- The pancreatic juice contains pancreatic amylase, this continues the hydrolysis of starch into maltose
- The intestinal wall and pancreas both produce alkaline salts keep the pH neutral so the amylase can function
111
What bonds do lipases break when digesting lipids?
The ester bonds
112
What is released when lipids are digested?
ONE monoglyceride and TWO fatty acids
113
What is a monoglyceride?
A glycerol head bonded to a single fatty acid tail
114
Describe stage 4 of carbohydrate digestion
- Muscles in the intestine wall push the food along to the ileum
- The ileums epithelial lining produces the enzyme called maltase
- Maltase breaks down the maltose from starch breakdown into alpha glucose
115
What is maltase?
| - Where is it produced?
- Maltase is a disaccharidase
- It is produced by the epithelial lining of the ileum
- Maltase is NOT released into the lumen of the ileum but instead is part of the cell-surface membranes of the epithelial cells that line the ileum.
116
What is maltase referred to as?
It is referred to as a membrane bound disaccharidase
117
What is the membrane-bound disaccharidase that hydrolyses sucrose?
What does this produce?
Sucrase
- It hydrolyses the single glycosidic bond in the sucrose molecule
- This produces two monosaccharides glucose and fructose
118
What is the membrane-bound disaccharidase that hydrolyses lactose?
What does this produce?
Lactase
- It hydrolyses the single glycosidic in the lactose molecule
- This produces the two monosaccharides glucose and galactose
119
What is the enzyme that hydrolyses lipids called?
Lipases
120
Where are lipases produced?
In the pancreas
121
What bond do lipases hydrolyse?
They break the ester bond found in triglycerides
122
What does the hydrolysation of a triglyceride produce?
Fatty acids and one monoglyceride
123
What are lipids first split up into?
- By what?
- What is this process called?
Lipids are first spilt up into micelles (tiny droplets) by bile salts
- This process is called emulsification
124
Where are bile salts produced?
In the liver
125
Why are lipids emulsified?
Lipids are emulsified into micelles because it increases the surface area of the lipid to accelerate the effect of digestive enzymes (lipases)
126
What is the group of enzymes that break down proteins called?
Peptidases
127
What are peptidases also known as?
Proteases
128
What are the 3 types of peptidases?
- Endopeptidases
- Exopeptidases
- Dipeptidases
129
What is the function of endopeptidases?
Endopeptidases hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules
130
What is the function of exopeptidases?
- Exopeptidases hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases
- In this way the progressively release dipeptides and single amino acids
131
What is the function of dipeptidases?
Dipeptidases hydrolyse the peptide bond between the two amino acids of a dipeptide
--> Dipeptidases are membrane bound, and are part of the cell- surface membrane of the epithelial cells lining the ileum
132
List 2 structures that produce amylase
Salivary glands and pancreas
133
Suggest why the stomach doesn't have villi or microvilli
- Villi and microvilli increase surface area to speed up the absorption of soluble molecules. - As the food in the stomach has not yet been hydrolysed into soluble molecules they cannot be absorbed and so villi and microvilli are unnecessary
134
Name the final product of starch digestion in the gut
Alpha glucose
135
List 3 enzymes produced by the epithelium of the ileum
Maltase
Sucrase
Lactase
136
Describe the structure of villi
Thin walls lined with epithelial cells on the other side of which is a rich network of blood capillaries
137
Describe what the wall of the ileum is like
The wall of ileum is folded and possessed finger like projections, about 1mm long, called villi. These have micro villi = large SA
138
How do villi increase the efficiency of absorption? (5 ways)
- They increase the SA for diffusion
- Thin walled --> reduces the diffusion pathway
- They are well supplied with blood vessels = blood can carry away absorbed molecules and maintain a diffusion gradient
- Contain muscles so they can move
- The epithelial cells lining the villi possess microvilli.
139
How does the fact that villi have muscles mean they increase the efficiency of absorption?
- Contain muscle so they can move
- This helps to maintain diffusion gradient because their movement mixes the contents of the ileum
- This ensures that, as the products of digestion are absorbed from the food adjacent to the villi, new material rich in the products of digestion replaces it
140
How does the fact that the epithelial cells lining the villi have microvilli increase the efficiency of absorption
The microvilli are finger-like projections of the cells surface membrane that further increase the SA for absorption.
141
What are the cells that line the villi called?
Epithelial cells
142
What is a lacteal?
- A tiny lymphatic vessel
- Absorbs fatty acids + glycerol
- Found at the centre of each villus
143
What does the blood capillary in the villi absorb?
It absorbs glucose and amino acids
144
Once monoglycerides + fatty acids are formed during digestion what do they remain in association with?
Once formed in digestion monoglycerides + fatty acids remain in association with the bile salts that initially emulsified the lipid droplet
145
What happens relating to micelles during the absorption of lipids?
- Micelles are brought into contact with the ileum wall by peristalsis moving substances around the ileum.
- After this the micelles break down releasing the monoglycerides + fatty acids.
146
What about monoglycerides + fatty acids means that they can easily diffuse across the cell membrane of the epithelial cells?
The fact that they are non- polar molecules means that they can easily diffuse across the epithelial cells membrane
147
What happens to the monoglycerides + fatty acids once they are inside the epithelial cells?
(Part of the absorption of triglycerides)
Once inside the epithelial cells, monoglycerides + fatty acids are transported to the (smooth) endoplasmic reticulum where they are recombined to form triglycerides.
148
What process begins in the smooth ER and continues in the Golgi apparatus?
(Part of the absorption of triglycerides)
Starting in the smooth ER and continuing in the Golgi apparatus, the triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons
149
What do chylomicrons transport?
Triglycerides (and other lipids)
150
How do the chylomicrons move out of the epithelial cells?
| Part of the absorption of triglycerides
Chylomicrons move out of the epithelial cells by exocytosis
151
What do the chylomicrons enter after leaving the epithelial cells?
(Part of the absorption of triglycerides)
Next, they enter the lacteals that are found at the center of each villus
152
What is exocytosis?
The process of leaving a cell via diffusion
153
What happens after the chylomicrons enter the lacteals?
- 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 capillaries from there they diffuse into cells
154
How do stomata open? (4 stages)
| What is this triggered by?
1. Triggered by blue light
2. The intake of K+ ions and sugar (and output of H+ ions) increases the solute potential in the guard cells
3. As a result the water potential is decreased + so water enters the cell via osmosis
4. This makes the cell turgid which causes the cells to bend away from each other and the stomata pore to open
