Chapter 7 - The Principles of Exchange and Transport Flashcards
1
Q
Knowledge check 1
Which inorganic ion do plants need to absorb to make amino acids?
A
Nitrate (and sulfate) ions
2
Q
Knowledge check 2
Calculate the surface area-to-volume ratio of a cuboid body of dimension 1 x 2 x 3.
A
Surface area = 22
Volume = 6
So the surface area-to-volume ratio is 22:6 or 11:3.
3
Q
Knowledge check 3
Give three reasons why humans need a specialised gas exchange surface (i.e. lungs).
A
- Humans are terrestrial (with an impermeable body surface)
- They are large (small surface area-to-volume ratio)
- They have a high metabolic rate (large demand for oxygen)
4
Q
What is gas exchange?
A
The process by which oxygen reaches cells and carbon dioxide is removed from them.
5
Q
What is respiration?
A
The release of energy from food to synthesise ATP in all living cells.
6
Q
What is an absorptive surface?
A
An absorptive surface allows the uptake of soluble substances - for example, products of digestion in the ileum or water and ions by root hairs.
7
Q
What is a gas exchange surface?
A
- A gas exchange surface allows oxygen to move through in one direction and carbon dioxide in the opposite direction.
- It is sometimes referred to as a respiratory surface because the respiratory gases, oxygen and carbon dioxide, are involved.
8
Q
Living cells require certain substances from their environment in order to …
A
Maintain their metabolic processes
9
Q
Living cells require certain substances from their environment to maintain their metabolic processes, and need to remove …
A
The toxic by-products of metabolism.
10
Q
Living cells require certain substances from their environment to maintain their metabolic processes, and need to remove the toxic by-products of metabolism.
Animal tissues obtain …
A
- Oxygen from the air (or from water if they are aquatic)
- Glucose, fatty acids and amino acids from ingested food
- Water
11
Q
Living cells require certain substances from their environment to maintain their metabolic processes, and need to remove the toxic by-products of metabolism.
Animal tissues remove …
A
- Carbon dioxide
2. Nitrogenous waste (e.g. urea)
12
Q
Living cells require certain substances from their environment to maintain their metabolic processes, and need to remove the toxic by-products of metabolism.
Plant tissues obtain …
A
- Oxygen from the air, especially at night
- Carbon dioxide from the air during the day
- Inorganic ions (e.g. nitrate ions to provide nitrogen for amino acid synthesis and phosphate for the synthesis of phospholipids) from the soil solution
- Water
13
Q
Living cells require certain substances from their environment to maintain their metabolic processes, and need to remove the toxic by-products of metabolism.
Plant tissues remove …
A
- Either carbon dioxide or oxygen, depending on the time of day.
14
Q
Surface area definition
A
Surface area is the total number of cells in direct contact with the surrounding environment.
15
Q
Volume definition
A
Volume is the total three-dimensional space occupied by metabolically active tissues.
16
Q
What are some of the methods of increasing the area of an absorptive/exchange surface?
A
- Evagination (outfolding) of the surface
- Invagination (infolding) of the surface
- Flattening of the organism
17
Q
Small organisms have a large …
A
Surface area-to-volume ratio
18
Q
Large organisms have a small …
A
Surface area-to-volume ratio
19
Q
As an organism’s size increases, it’s surface area …
A
Increases less than its volume
20
Q
As an organism’s size increase, it’s surface area increases less than its volume. Why is this?
A
This is because many cells are not in direct contact with the surrounding environment
21
Q
Why do mammals and flowering plants possess impermeable body surfaces?
A
To prevent water loss by evaporation
22
Q
Volume of metabolically active tissue influences …
A
The demand for metabolites
23
Q
Surface area influences …
A
The rate of supply of metabolites to tissues
24
Q
An organism requires a specialised absorptive surface it if is …
A
- Terrestrial (with an impermeable surface)
- Large (with a small surface area-to-volume ratio)
- Has a high metabolic rate
25
The external surface of a small organism can be used as ...
A gas exchange surface
26
The external surface area of a small organism can be used as a gas exchange surface. Why?
Because the relatively large surface area is able to supply sufficient oxygen to the relatively small volume
27
Give an example of a small organism which uses its external body surface as a gas exchange surface
An earthworm
28
Why do large organisms require a specialised exchange surface to aid passive and active transport?
* A larger organism has a small surface area compared with its large volume, i.e. a small surface area-to-volume ratio.
* The relatively large volume creates a demand for metabolites that the relatively small surface area is unable to supply.
* Therefore, large organisms need specialised permeable surfaces whereby the absorption or exchange area is increased to satisfy the needs of the organisms.
29
The rate at which an organism requires substances depends on ...
It's metabolic rate
30
Cells in living organisms need to be able to obtain essential substances from their surroundings and also be able to remove waste or toxic products. In unicellular organisms this exchange takes place through ...
The cell surface membrane
31
What are some of the features of exchange surfaces that aid passive and active transport into and out of organisms?
1. Increasing the surface area of the exchange surface
2. Thin separating surface
3. Large concentration gradients
32
Other than increasing the surface area-to-volume ratio, what does having a flattened shape achieve?
Decreases the distance over which substances have to diffuse to reach any cell in the organism.
33
Name five examples of efficient absorptive surfaces in flowering plants and mammals
```
Leaf mesophyll
Root hairs
Alveoli
Capillaries
Red blood cells
```
34
Leaf mesophyll is an example of an efficient absorptive surface in flowering plants. Describe and explain the structure and function of leaf mesophyll which makes it an efficient absorptive surface.
Structure
• The leaf is a flattened structure (it's thinness ensures a short diffusion distance) with a tightly packed upper palisade mesophyll layer and a loosely packed lower spongy mesophyll layer.
Function
• The wide expanse of palisade tissue is efficient at trapping light.
• The loose arrangement of the spongy layer provides an air space system through the leaf and creates a huge surface for gas exchange.
35
Root hairs are an example of an efficient absorptive surface in flowering plants. Describe and explain the structure and function of root hairs which make them an efficient absorptive surface.
Structure
• Tubular extensions of the epidermal cells of the young root.
Function
• Increase greatly the surface area of the root for the uptake of oxygen, water and ions.
36
Alveoli are an example of an efficient absorptive surface in mammals. Describe and explain the structure and function of alveoli which make them an efficient absorptive surface.
Structure
• Small (diameter 0.2 mm) sacs, occurring in clusters and in vast numbers within the mammalian lung.
• In human lungs there are 700 million, providing a total surface area of 70 m^2.
Function
• The huge, moist surface area provides for efficient gas exchange.
• Alveolar walls are thin (0.1-1.0 micrometers), so the diffusion distance is short.
37
Capillaries are an example of an efficient absorptive surface in mammals. Describe and explain the structure and function of capillaries which make them an efficient absorptive surface.
Structure
• Small (average diameter 8 micrometers), thin-walled blood vessels, with a total length of 100 000 km and surface area of 1000m^2 in the human body.
Function
• Extensive networks throughout the body represent a huge surface area for exchange of molecules between blood and body tissues.
• The number and distribution of capillaries are such that no cell is further away than 50 micrometers from a capillary.
38
Red blood cells are an example of an efficient absorptive surface in mammals. Describe and explain the structure and function of red blood cells which make them an efficient absorptive surface.
Structure
• Small (diameter around 8 micrometers), flexible biconcave discs, flattened and depressed in the centre, with a dumbbell-shaped cross-section.
Function
• The biconcave disc shape greatly increases the surface area-to-volume ratio for efficient uptake of oxygen.
• The thinness of the cell, particularly where it is depressed in the centre, allows oxygen to diffuse to all the haemoglobin packed into the cell.
39
Knowledge check 4
| Which two features of red blood cells provide them with a large surface area-to-volume ratio?
They are especially small and have a biconcave disc (flattened) shape.
40
What are the two gas exchange surfaces in mammals?
1. Between air in the alveoli and blood in the pulmonary capillaries within lungs.
2. Between blood in the systemic capillaries and cells in body tissues.
41
Give an example of an absorptive surface in mammals.
The mucosal layer in the ileum
42
Why does diffusion occur?
* The molecules in gases and liquids move constantly and at random.
* If there is a difference in concentration of molecules within an area, a net movement of the molecules occur, resulting in the molecules becoming evenly distributed.
43
Draw a diagram of a top view and side view (cross-section) of a flatworm
Textbook page 121
44
Sketch a graph showing the relationship between surface area-to-volume ratio and cube size/side length
Textbook page 120
| Student Guide AS Unit 2 page 7
45
Draw a diagram of a terminal bronchiole
Textbook page 127
Student Guide AS Unit 2 page 9
Diagram should include:
• A terminal bronchiole (Terminal bronchioles are last generation of conducting airways. Respiratory bronchioles can be identified by the presence of some alveoli along their walls. The respiratory bronchiole splits into a number of alveolar ducts, which terminate in alveolar sacs and individual alveoli).
* Alveolar ducts
* Alveoli
* Capillary network present on the surface of the alveoli
* Capillary network connected to a branch of the pulmonary artery (blue = deoxygenated blood) and to a branch of the pulmonary vein (red = oxygenated blood)
46
Draw a cross-section through a root and draw an individual root hair cell
Textbook page 122
Student Guide AS Unit 2 page 13 figure 6
Diagram should show a cross-section of a root, displaying root hairs extending from the epidermis layer.
Individual root hair cell should contain a vacuole, nucleus, cell wall, cell surface membrane and cytoplasm. The root hair extension should be surrounded by soil particles, air spaces and a soil solution. Movement of O2 should be into the root hair (from the air space) and movement of CO2 should be out of the root hair (into the air space). The root hair cell should be labelled as part of the epidermis layer.
47
Draw a diagram of a top view and side view (cross-section) of a red blood cell
Textbook page 122
48
Diffusion (gas exchange) can take place across surfaces as long as ...
The surface is:
• Moist, since gases must dissolve in water before diffusing into tissue cells
• Permeable to the substance(s) in question (e.g. oxygen and carbon dioxide)
49
Transport of substances in larger organisms occurs by ...
Mass flow
50
Mass flow is brought about by ...
A pressure difference
51
Draw a diagram illustrating the mass flow of molecules
Student Guide AS Unit 2 page 10 figure 3
52
Draw a diagram illustrating the diffusion of molecules
Student Guide AS Unit 2 page 9 figure 2
53
Diffusion stops when ...
The molecules have dispersed from an area of high concentration and are evenly dispersed.
54
What is the main difference between mass flow and diffusion?
In mass flow all molecules are swept along in the same direction, whereas in diffusion the molecules move at random in all directions.
55
Give some examples of mass flow systems in flowering plants and mammals
Flowering plants
• Xylem system
• Phloem system
Mammals
• Breathing (ventilation) system
• Blood circulatory system
56
Different mass flow systems have ...
Different means of generating a pressure difference.
57
What is the method of generating a pressure difference in the xylem system of flowering plants?
Water evaporating from the leaf creates a tension (negative pressure) in the leaf xylem that pulls water up through the xylem as part of the transpiration stream.
58
What is the function of the xylem system of flowering plants?
One-way transport of water and inorganic ions (minerals) from roots to leaves in a flowering plant.
59
What is the method of generating a pressure difference in the phloem system of flowering plants?
Energy expenditure is involved in moving the sucrose into the phloem. ATP is used to move sucrose from the companion cell to the phloem sieve tube.
60
What is the function of the phloem system of flowering plants?
Transport of sucrose (translocation) to roots (for storage of carbohydrate) and to growing regions (to provide energy for growth).
Two-way flow of organic solutes in a flowering plant.
61
What is the method of generating a pressure difference in the breathing (ventilation) system of mammals?
Pressures in the thorax are alternately decreased, causing air to enter the lungs (inducing inhalation), and increased, causing air to be expelled from the lungs (inducing exhalation).
62
What is the function of the breathing (ventilation) system of mammals?
Ventilation of the mammalian lungs, whereby fresh air (rich in O2 and low in CO2) is drawn in and stale air (rich in CO2 and low in O2) is forced out, ensuring that diffusion of respiratory gases can occur (by maintaining the concentration gradient between the alveoli and capillaries)
63
What is the method of generating a pressure difference in the blood circulatory system of mammals?
High pressure is generated by the pumping of the muscular heart.
64
What is the function of the blood circulatory system of mammals?
Circulation of blood carrying oxygen, glucose, amino acids, fats, carbon dioxide, urea etc. in a mammal.
65
Knowledge check 5
| How are gases moved across exchange surfaces?
Diffusion
66
Knowledge check 6
| List the features of a good transport system.
A good transport system has a pump (or equivalent), vessels and a fluid to transport materials around the body. It also has exchange surfaces to load substances into the transport system and to remove them where required.
67
Knowledge check 7
| Explain how thinness helps gaseous exchange and means that a transport system is not necessary.
It increases the surface area-to-volume ratio (more oxygen is absorbed relative to the amount required) and means that all tissues are close to the absorbing surface.
68
Give an example of an overlap between the principles of exchange and the principles of transport.
The flattening of an organism/cell
* Increases its surface area, therefore increasing its surface area-to-volume ratio, therefore increasing its effectiveness in terms of absorption (which may eliminate the need for a specialised exchange surface).
* However, it also decreases the diffusion path, as more cells are in direct contact with the surrounding environment (which may eliminate the need for a specialised internal transport system).
69
Why does a flatworm have no need for an internal transport system?
1. It is thin (short diffusion distance for respiratory gases).
2. It's digestive system branches throughout its body so that food is absorbed in close proximity to all tissues.
70
Gas exchange across an exchange surface relies on the process of ...
Diffusion
71
What law summarises the relationship between factors affecting the rate of diffusion?
Fick's law
72
State Fick's law
Rate of diffusion ∝ Surface area X Difference in concentration
—————————————————–
Length of diffusion pathway (thickness of membrane)
73
Fick's law shows that gas exchange is increased where:
1. The exchange surface has a large surface area.
2. There is a big difference in the concentration of gases on each side of the surface.
3. The exchange surface is thin, with a short diffusion distance.
74
Rate of diffusion ∝ Surface area X Difference in concentration
—————————————————–
Length of diffusion pathway (thickness of membrane)
Fick's law shows that gas exchange is increase where:
• The exchange surface has a large surface area.
• There is a big difference in the concentration of gases on each side of the surface.
• The exchange surface is thin, with a short diffusion distance.
The higher the ______ ______ of the organism, the greater the need for these principles to be met
Metabolic rate
75
In Fick's law, the barrier to diffusion is often referred to as a ...
Membrane
76
The term membrane includes ...
Both the cell surface membrane and the epithelium membrane, i.e. the layer of cells covering an organ.
77
What are the two processes in flowering plants that involve gas exchange?
Respiration
| Photosynthesis
78
Where and when does respiration take place in a flowering plant?
In all tissues, all the time
79
Where and when does photosynthesis take place in a flowering plant?
Only in green tissues (i.e. those containing chlorophyll), and only during the daylight hours.
80
The rate of photosynthesis in a flowering plant largely depends on ...
The light intensity
81
The maximum rate of photosynthesis occurs when ...
The light intensity is highest
82
At what time during the day is light intensity the highest?
At midday
83
At what time(s) during the day will light intensity be low?
During dawn and dusk
84
When the light intensity is high (during midday) the rate of photosynthesis greatly (blank) the rate of respiration.
Exceeds
85
During midday, there is a net production of ...
Oxygen
86
When the rate of photosynthesis exceeds the rate of respiration there is a net production of ...
Oxygen
87
At a specific low light intensity (during dawn and dusk) the rate of photosynthesis (blank) the rate of respiration
Equals
88
What happens when the rate of photosynthesis equals the rate of respiration?
The net exchange of oxygen is zero
89
When the rate of respiration exceeds the rate of photosynthesis there is a net production of ...
Carbon dioxide
90
What is a compensation point?
Compensation points - light intensity at which the rate of respiration = rate of photosynthesis
Therefore, the rate of oxygen production (in photosynthesis) is balanced by the rate of oxygen consumption (in respiration).
91
The roots of plants use energy in processes such as ...
1. Cell division (growth)
| 2. The active transport of ions from the soil solution
92
Knowledge check 8
| Suggest why plants have a lower metabolic rate than animals.
Plants lack muscle tissue, i.e. they do not move from place to place.
93
In the growth region of plant roots, the epidermal cells possess ...
Root hairs
94
In soil that is not waterlogged, root hairs are surrounded by ___ ______ between the particles of soil
Air spaces
95
Diffusion of respiratory gases into root hair cells occur through ...
The cell wall and cell surface membrane of the root hair extension.
96
In stems, especially those of woody plants, the most active cells are those ...
Under the surface
97
The outer covering of the stem of a flowering plant is ...
Waterproofed
98
Why is the outer covering of the stem of a flowering plant waterproofed?
To reduce water loss to the air
99
How does oxygen and carbon dioxide diffuse in and out of the stem of a flowering plant?
Although the stem's outer covering is waterproofed to reduce water loss to the air (and so is impermeable to gases) there are small pores to allow oxygen in and carbon dioxide out.
100
Plants lack specialised respiratory surfaces and yet can be very large. Why is this?
This is because they lack tissues with a high energy demand and so have low respiration rates.
101
What is the major photosynthetic organ in a flowering plant?
The leaf
102
The leaf is the major photosynthetic organ in a flowering plant. Why does the leaf need a specialised gas exchange surface?
* A high rate of photosynthesis is generated.
| * The concentration of carbon dioxide in air is low (400 parts per million or 0.04%)
103
Outline the steps and processes which occur during photosynthetic gas exchange in the leaves of flowering plants.
1. The leaf epidermis, particularly the lower epidermis, possesses guard cells that control the opening and closure of stomata.
2. The stomata open during the hours of daylight.
3. When open, air, containing carbon dioxide, diffuses into and out of the leaf mesophyll.
4. Carbon dioxide diffuses through an air space system provided by the spongy mesophyll.
5. Having diffused through the air space system, carbon dioxide is absorbed by mesophyll cells (spongy mesophyll cells and palisade mesophyll cells) (in which carbon dioxide concentration is low as it is used in photosynthesis).
6. It is the moist mesophyll surface that represents the gas exchange surface.
7. Oxygen produced in photosynthesis diffuses out of mesophyll cells into the air space and then out through open stomata. Some oxygen is, of course, used up in respiration.
104
What are the advantages to the leaf in being broad and thin?
```
Broad = Large surface area for the exchange of gases
Thin = Short diffusion distance for gases
```
105
The cell surface membrane of mesophyll cells is ..
Moist
106
Identify the (photosynthetic) gas exchange surfaces in the leaf.
The cell surface membranes of mesophyll cells (spongy mesophyll cells and palisade mesophyll cells)
107
Knowledge check 9
| List three features of leaves that facilitate gas exchange.
* Leaves have an air space system.
* They are thin (and broad).
* They have stomata that connect to the atmosphere.
108
There is much (blank) oxygen dissolved in water than there is oxygen in air.
Less
109
Knowledge check 10
| Why do floating water plants only have stomata on the upper surface of their leaves?
They allow air to enter from the atmosphere;
Carbon dioxide for photosynthesis;
And oxygen, which may diffuse down to the roots through an extensive air-space system, for respiration. Both oxygen and carbon dioxide are more plentiful in air than dissolved in water.
110
Aquatic flowering plants are called ...
Hydrophytes
111
What are hydrophytes?
Aquatic flowering plants
112
There is much less oxygen dissolved in water than there is oxygen in air, so the stems and leaves of aquatic flowering plants (hydrophytes) have ...
Adaptations to facilitate the uptake and movement of oxygen and carbon dioxide.
113
Draw a diagram of the stem of a hydrophytic plant
Describe the structure and function of the stem of a hydrophytic plant
Normal plant stem = Textbook page 138
Hydrophytic plant stem = Student Guide AS Unit 2 page 14
Diagram should include:
• Epidermis
• Cortex
• Vascular bundles, consisting of phloem (outermost) and xylem (innermost)
• Air spaces - easier for oxygen to diffuse to all tissues, including root. (i.e. Oxygen which enters from stomata on the upper surface of leaf will diffuse down to the roots through an extensive air-space system within the stem).
114
Draw a diagram of a leaf of a hydrophytic plant
Describe the structure and function of the leaf of a hydrophytic plant
Student guide AS Unit 2 page 14
Diagram should include:
• Stoma on upper epidermis - allows gas exchange without the leaf becoming flooded; transpirational loss of water not a problem.
• Air spaces - easier for diffusion of gases and aids the flotation of the leaf.
115
Gas exchange in the cells of mammals occurs by ...
Diffusion
116
How is the concentration gradient of respiratory gases induced/maintained in a respiring cell?
In cells respiring aerobically, oxygen is used and carbon dioxide is produced. This affects the concentration gradients and so oxygen diffuses into the cell and carbon dioxide diffuses out.
117
Draw a diagram showing gaseous exchange in a respiring animal cell.
Student Guide AS Unit 2 page 15
```
Diagram should include:
• Cell surface membrane
• Nucleus
• Cytoplasm
• Mitochondria
• Arrows showing O2 entering and CO2 leaving
• Inside cell:
- high CO2 concentration
- low O2 concentration
• Outside cell:
- low CO2 concentration
- high O2 concentration
```
Mitochondrion - Site of aerobic respiration: uses oxygen and produces carbon dioxide.
118
The movement of oxygen to cells, and of carbon dioxide out, involves four stages in mammals (humans). What are these four stages?
* Diffusion of gases between respiring cells and blood
* Transport of gases in blood
* Diffusion of gases across the gas exchange surface between alveolar air and blood
* Ventilation of the lungs with fresh air
119
In mammals, there are two mass flow systems involved in the movement of respiratory gases (oxygen and carbon dioxide). What are these two mass flow systems?
* Breathing (ventilation) system
| * Blood circulatory system
120
In mammals, there are two mass flow systems involved in the movement of respiratory gases (oxygen and carbon dioxide). These two mass flow systems are known as the breathing (ventilation) system and the blood circulatory system. However, movement of respiratory gases at the two interfaces relies on ...
Diffusion
121
Give an account of the structure of the lungs
1. Air is breathed through the nostrils or mouth, and enters or leaves the lungs via the trachea.
2. The lungs are situated within the thorax (also known as the thoracic cavity).
3. The trachea branches into two bronchi (singular bronchus) which further branch into a series of ever-finer bronchioles forming a bronchial tree.
4. Each terminal bronchiole leads to a cluster of alveoli, with an alveolar duct connecting with each alveolus.
5. Each individual alveolus is tightly wrapped in blood capillaries and it is here that gas exchange takes place
122
Draw a diagram of the structure of the lung system
Textbook page 127
Student Guide AS Unit 2 page 16
```
Diagram should include:
• Nostril
• Mouth
• Oesophagus
• Larynx
• Trachea
• Ring of cartilage
• Rib section
• Left lung
• Pleural membranes
• Pleural fluid
• Right bronchus
• Bronchiole
• Heart/ Space occupied by heart
• External intercostal muscles
• Internal intercostal muscles
• Muscular part of diaphragm
• Diaphragm
```
```
Small diagram:
• Terminal bronchiole
• Branch of pulmonary artery (blue)
• Branch of pulmonary vein (red)
• Alveoli
• Capillary network/ capillary
```
Smaller diagram:
• Capillary
• Arrows showing movement of O2 and CO2 between alveolus and capillary
123
What is breathing?
Breathing refers to the movements of the ribs and diaphragm that cause air to enter and leave (ventilate) the lungs and alveoli.
124
Changing the volume of the thoracic cavity changes ...
The air pressure inside the lungs.
125
Air will always move from a region of high pressure to ...
A region of low pressure
126
When air moves into the lungs this is known as ...
Inhalation (or inspiration)
127
When air moves out of the lungs this is known as ...
Exhalation (or expiration)
128
Give an account of the mechanism of inhalation during normal breathing.
* Inspiration (or inhalation) - describes the process of breathing in.
* The external intercostal muscles contract (as the internal intercostal muscles relax) and the ribs are pulled upwards and outwards.
* Simultaneously, the diaphragm muscle contracts, causing the diaphragm to flatten from its domed shape.
* Both these actions increase the volume of the thorax, which in turn reduces the pressure around the lungs.
* The pressure differential between the atmosphere and the lungs causes air to enter the lungs until a pressure equilibrium is achieved.
129
Give an account of the mechanism of exhalation during normal breathing.
* Expiration (or exhalation) - describes the process of breathing out (expiration is really inspiration in reverse).
* The external intercostal muscles relax (as the internal intercostal muscles contract) causing the ribs to move downwards and inwards.
* The relaxation of the diaphragm muscles causes it to return to its domed position.
* The return of the ribs and the diaphragm to their original positions causes the volume of the thorax to reduce, consequently increasing the pressure around the lungs.
* With the thorax now having a higher pressure than the atmosphere, air is forced out of the lungs.
130
What is forced exhalation?
During forced exhalation, the volume of the thoracic cavity is further reduced by the contraction of the internal intercostal muscles depressing the rib cage.
131
Give two examples of when forced exhalation may occur
During hard exercise
| Coughing
132
Knowledge check 11
| Explain the advantage of ventilating the lungs.
Ventilation of the lungs replenishes oxygen-rich air in the alveoli, thus increasing the oxygen diffusion gradient into the blood. It also replaces air that has a high carbon dioxide concentration with air that has a low carbon dioxide concentration, thus increasing the carbon dioxide diffusion gradient out of the blood.
133
The alveoli of the lungs exhibit all the features of an efficient gas exchange surface. Name these features.
```
Permeable
Moist
Large surface area
Thin walls
Close to transport systems
```
134
Knowledge check 12
| Explain this statement 'inhalation is an active process but exhalation is usually passive'.
Inhalation depends on the contraction of muscles of the diaphragm and the external intercostal muscles of the ribcage, while exhalation normally involves only the relaxation of these muscles.
135
Alveoli consist of ...
A single layer of squamous epithelial cells.
Surfactant secreting epithelial cells (septal cells).
Macrophages (phagocytic cell derived from monocyte.)
Alveolar air space.
Moist inner alveolar surface.
136
Gases can diffuse across the moist, permeable walls of the alveoli. Diffusion of gases between the alveoli and the blood is rapid because ...
1. Concentration gradients are maintained by ventilation of the lungs and blood flow through pulmonary capillaries.
2. The alveoli and pulmonary capillaries have very large surface areas.
3. The walls of both alveoli and capillaries are thin and therefore the diffusion distance is very short.
137
Draw a diagram of the structure of an alveolus and its associated capillaries
Student Guide AS Unit 2 page 18
Textbook page 127
Diagram should include
• Alveolar air space
• Alveolar duct
• Arrows showing movement of inhaled air and exhaled air
• Moist alveolar surface
• Surfactant-secreting epithelial cells (septal cells)
• Alveolus
• Macrophage (phagocytic cell derived from monocyte)
• Blood capillary, endothelial cells line capillary (which are squamous epithelium)
• Red blood cell(s)
• Epithelial cells of alveolus are squamous epithelium
• Supporting connective tissue
• Diffusion barrier (alveolar wall)
• Arrows showing movement of gases (O2 and CO2) between alveolar air space and blood capillary
138
There is a short diffusion distance between the alveolar air space and the blood capillary because ...
The alveoli and capillary walls are thin (one cell thick).
| They consist of squamous (pavement) epithelium.
139
Why are alveoli situated deep inside the body?
Since the alveolar surface is situated deep inside the body, evaporation of water from its moist surface is reduced to a minimum.
140
What is lung surfactant?
Lung surfactant is a mixture of lipid and protein. The detergent-like substance reduces surface tension in the fluid coating the alveoli, without which the alveoli would collapse due to cohesive force between the water molecules lining the air sacs.
141
What are monocytes?
A type of white blood cell.
142
What is the function of macrophages within alveolar wall?
Protect the lungs from a broad spectrum of microbes and particles by ingesting them through phagocytosis.
143
The alveolar walls contain ...
Elastic fibres
144
What is the function of elastic fibres within the alveolar wall?
The elastic recoil of the alveoli, helping to force air out during exhalation.
145
Knowledge check 13
Babies born prematurely are often deficient in surfactant, causing a condition called 'respiratory distress syndrome'. From what you know about the role of surfactant, describe and explain the symptoms of this syndrome.
The alveoli collapse and are difficult to expand, making breathing difficult and reducing the efficiency of gas exchange. Blood oxygen levels fall and carbon dioxide levels increase.
146
What is tar?
The collective name given to thousands of toxic substances present in tobacco smoke.
147
What does COPD stand for?
Chronic Obstructive Pulmonary Disease
148
Chronic obstructive pulmonary disease (COPD) is a combination of ...
Chronic bronchitis
| Emphysema
149
What are the symptoms of chronic bronchitis?
Phlegm production
Coughing
Breathlessness
Increased susceptibility to infection
150
What diseases are associated with smoking?
Chronic obstructive pulmonary disease (COPD)
- Chronic bronchitis
- Emphysema
Lung cancer
151
What affect does tar have on the respiratory system?
* Tar brings about an inflammatory response in which airways narrow and excessive amounts of mucus are produced.
* Furthermore, tar paralyses the cilia that sweep mucus and bacteria away from the lungs, so pathogens and mucus build up.
* This leads to phlegm production, coughing and breathlessness - symptoms of chronic bronchitis
* Inability to clear mucus and bacteria results in an increased susceptibility to chest infections, including pneunomia.
152
Give an example of a chest infection
Pneunomia
153
What affect does smoke inhalation have on the respiratory system?
* The inflammatory response to smoke inhalation leads to a breakdown of alveolar walls.
* This reduces the surface area available for gas exchange so it becomes difficult to get enough oxygen.
* There is also a loss of elastic fibres in the alveolar walls.
* Therefore, exhalation becomes more difficult because the ability of alveoli (and lungs) to recoil following inhalation is reduced.
* Air in damaged alveoli cannot be effectively expelled during expiration, leaving a layer of residual air in the alveoli that prevents fresh inhaled air reaching the gas exchange surfaces.
* Emphysema is developed.
154
What is emphysema?
* In emphysema, the inflammatory response to smoke inhalation leads to a breakdown of alveolar walls.
* This reduces the surface area available for gas exchange so it becomes difficult to get enough oxygen.
* There is also a loss of elastic fibres in the alveolar walls.
* Therefore, exhalation becomes more difficult because the ability of alveoli (and lungs) to recoil following inhalation is reduced.
* Air in damaged alveoli cannot be effectively expelled during expiration, leaving a layer of residual air in the alveoli that prevents fresh inhaled air reaching the gas exchange surfaces.
155
What are carcinogens?
Substances that can induce cancer
156
Tobacco smoke contains many ...
Carcinogens
157
What affect do carcinogens have on the respiratory system?
* Carcinogens can damage DNA in the cells lining the bronchial tubes.
* Cells with DNA damage may divide in a modified and uncontrolled way, producing a mass of unspecialised cells known as a tumour.
* Once the tumour reaches a certain size, it can block the airways and/or damage large sections of the lungs.
* A cancerous or malignant tumour may spread to invade other tissues.
158
Give an example of a carcinogen in tobacco smoke
Tar
159
Knowledge check 14
| Explain why a person with emphysema would have difficulty undertaking strenuous activity.
Emphysema reduces the efficiency of breathing (reduced recoil of alveoli due to loss of elasticity) and gas exchange (reduced surface area of alveoli). The overall result is that oxygen uptake is reduced greatly, so that less is available for the production of ATP in respiration - hence the difficulty in undertaking strenuous activity.
160
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
Draw two diagrams of simple respirometers
Textbook page 129
```
Test tube/ glass container
Tap
Airtight bung
Metal gauze
Living material/organism (e.g. Blowfly larvae or woodlice)
Potassium hydroxide (KOH) or water
Capillary tubing
Calibrated scale in mm or mm^3
Coloured bead of liquid OR dye
```
Textbook page 130
```
Living material
Airtight bung
Glass container
Sealed glass tube
Calibrated scale in mm or mm^3
Potassium hydroxide (KOH) or water (with initial potassium hydroxide/water level labelled)
Levelling arm
- Flexible rubber tubing
- Glass tube
```
161
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
Give two examples of living material which can be used in this type of investigation
Blowfly larvae
| Woodlice
162
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
How can oxygen uptake be calculated?
1. Oxygen uptake in living organisms can be calculated by adding potassium hydroxide (KOH) to the respirometer.
2. When the respirometer is set up, the living organisms respire taking in oxygen from within the system.
3. The carbon dioxide produced is absorbed by the potassium hydroxide.
4. The consequent reduction in pressure cause the liquid/dye in the respirometer to move in the direction of the biological material.
5. The distance (volume) moved represents the oxygen used in respiration.
163
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
Normally respirometers are calibrated so it is possible to calculate ...
The initial and final levels of potassium hydroxide
OR
The initial and final levels of dye/ (coloured) liquid
164
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
How can carbon dioxide production be calculated?
1. This can be calculated by repeating the process for calculating oxygen consumption but replacing the KOH with water.
2. The respirometer needs to be left for the same length of time and in the same conditions as that for measuring oxygen uptake.
3. This time the CO2 produced is not absorbed.
4. If there is no change in the movement of the liquid in the manometer or calibrated scale, then the volume of carbon dioxide produced is the same as the volume of oxygen absorbed.
5. If the liquid moves away from the living material, there is more carbon dioxide produced than oxygen taken in.
6. If the liquid moves closer to the living material there is less carbon dioxide produced than oxygen taken in.
7. Volume of carbon dioxide produced = Volume of oxygen consumed in initial test (with presence of KOH) +/- Difference in gas volume in second test (with water, no KOH)
165
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
- Calculating carbon dioxide production
If the liquid moves away from the living material, there is ...
More carbon dioxide produced than oxygen taken in
166
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
- Calculating carbon dioxide production
If the liquid moves closer to the living material, there is ...
Less carbon dioxide produced than oxygen taken in
167
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
- Calculating carbon dioxide production
If the position of the liquid does not change ...
The volume of carbon dioxide produced is equal to the volume of oxygen absorbed
168
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
What is a manometer?
An instrument for measuring the pressure acting on a column of fluid, consisting of a U-shaped tube of liquid in which a difference in the pressures acting in the two arms of the tube causes the liquid to reach different heights in the two arms.
169
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
- Calculating carbon dioxide production
If there is less carbon dioxide produced than oxygen taken in, the liquid moves closer to the living material. Why is this?
The carbon dioxide produced does not fully compensate for the pressure reduction caused by the oxygen uptake.
170
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
What is the role of a thermobarometer?
Compensates for changes in temperature and pressure
171
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
What are the controlled variables in this type of investigation?
1. Where possible, use the same apparatus for calculating oxygen uptake (with KOH) and for calculating carbon dioxide production (with water).
2. Use the same living organisms (this ensures that factors such as age and metabolic rate of the living material are controlled as far as possible).
3. Temperature can be controlled by placing the respirometers in a thermostatically controlled water bath for both parts of the investigation.
4. The apparatus must be left for the same amount of time and in the same conditions for both tests.
172
Practical Work - Use of a respirometer to calculate oxygen uptake and carbon dioxide production
Why is temperature a controlled variable in this investigation?
1. It will affect the respiration rate (and hence oxygen intake and carbon dioxide production).
2. Can cause changes in gas volume due to expansion or contraction of gases within the system.
173
What is urea?
Nitrogenous waste product from protein metabolism
174
Cells in living organisms need to be able to obtain essential substances (such as oxygen and glucose for respiration, or nitrate ions in plants to provide the nitrogen needed for amino acid synthesis) from their surroundings and also be able to remove waste or toxic products (such as carbon dioxide from respiration, or urea in many animals as a waste product of protein metabolism). In unicellular organisms this exchange takes place through (blank).
The cell surface membrane
175
Cells in living organisms need to be able to obtain essential substances (such as oxygen and glucose for respiration, or nitrate ions in plants to provide the nitrogen needed for amino acid synthesis) from their surroundings and also be able to remove waste or toxic products (such as carbon dioxide from respiration, or urea in many animals as a waste product of protein metabolism). In unicellular organisms this exchange takes place through the cell surface membrane. Multicellular organisms often have (blank) that take in or remove materials.
Specialised exchange surfaces
176
Cells in living organisms need to be able to obtain essential substances (such as oxygen and glucose for respiration, or nitrate ions in plants to provide the nitrogen needed for amino acid synthesis) from their surroundings and also be able to remove waste or toxic products (such as carbon dioxide from respiration, or urea in many animals as a waste product of protein metabolism). In unicellular organisms this exchange takes place through the cell surface membrane. Multicellular organisms often have specialised exchange surfaces that take in or remove materials. In the more complex organisms, there is a (blank) that links the specialised exchange surface to the cells throughout the organism.
Transport system
177
What is the role of a transport system?
Links the specialised exchange surface to the cells throughout the organism
178
What are the two types of specialised exchange surfaces?
External exchange surfaces
Internal exchange surfaces
(External/internal relative to the body surface)
179
Give an example of an external exchange surface
The folded external membranes of the external gills of young tadpoles
180
Give two examples of internal exchange surfaces
Fish gills
| Alveoli
181
The presence of root hair extensions on root hair cells facilitates ...
Gas exchange and uptake of mineral ions with the surrounding soil environment (due to the increased surface area).
182
What are some of the adaptations of red blood cells?
1. Biconcave shape of a red blood cell increases its surface area to volume ratio for oxygen uptake.
2. The cell has no nucleus and is tightly packed with haemoglobin.
3. The shape ensures the diffusion distance to any haemoglobin molecule in the cell is very short.
183
To maximise the rate of exchange, gas exchange (respiratory) surfaces:
1. Have a large surface area.
2. Have a moist surface into which the respiratory gases dissolve.
3. Have diffusion gradients for both oxygen and carbon dioxide.
4. Must also be permeable to oxygen and carbon dioxide.
5. Have a short diffusion path - this is aided by exchange surfaces being very thin.
184
What cell type in plants does not carry out photosynthesis?
Root hair cells
185
For a plant to grow ...
The production of carbohydrate in photosynthesis must exceed the loss of carbohydrate as a respiratory substrate.
186
For a plant to grow, the production of carbohydrate in photosynthesis must exceed the loss of carbohydrate as a respiratory substrate. In effect this means that over a period of time (for example, a 24 hour cycle) the net intake of carbon dioxide must (blank) the net production of carbon dioxide.
Exceed
187
Draw a graph showing the relationship between the volume of carbon dioxide taken in/given out (in cubic centimetres per hour) over a 24 hour period in a plant
Textbook page 124
188
What are some of the leaf adaptations for gas exchange?
1. Most leaves are usually thin.
- This ensures that the overall surface area to volume ratio is high but also that there is a short diffusion distance, with no cell being too far from an exchange surface.
2. The large and moist gas exchange surfaces of the spongy mesophyll cells
- The cell surface membranes of spongy mesophyll are the gas exchange surface (i.e. form the metabolic contact with the air spaces within the spongy mesophyll)
- Loose arrangement of cells creates air spaces and ensures that there is a large surface area across which gases can diffuse.
- Due to their positioning within the leaf, the gases involved in photosynthesis and respiration can easily diffuse between the cells of the spongy mesophyll and the palisade cells.
3. The intercellular air spaces of the spongy mesophyll
- Facilitates diffusion within the leaf.
4. Stomata (singular stoma) are pores in the leaf surface that allow gases to diffuse in and out of the leaf easily.
- The opening and closure of a stoma is controlled by two guard cells that can change shape.
- Depending on the degree of turgor (and shape) of the guard cells, a stomatal aperture (pore) may be present or not.
- Stomata are open when the guard cells are turgid and closed when they are not.
189
Guard cells, unlike other epidermal cells, contain ...
Chloroplasts
190
Stomata are open when the guard cells are ...
Turgid
191
When the guard cells are turgid, the stomata are ...
Open
192
Stomata are closed when the guard cells are ...
Flaccid
194
Most water loss from leaves (transpiration) is during the ...
Day, when it is usually warmer
195
Most water loss from leaves (transpiration) is during the day, when it is usually warmer. Why can't the stomata close to reduce water loss?
The stomata are unable to close then without significantly compromising the rate of photosynthesis (and growth).
196
What is the gas exchange surface in mammals?
The alveolar wall
197
Apart from the thin alveolar and capillary walls, how else is the diffusion distance reduced?
The red blood cells have to squeeze their way through the narrow capillaries, ensuring that they are in contact with the endothelial wall, which further reduces the diffusion pathway.
The capillaries sit tight against the alveolar walls, reducing the diffusion pathway.
198
Mammals have a _________ ______ respiratory system
Pulmonary (lung)
199
Alveoli have a rich blood supply. Describe the structure of the capillary network surrounding each alveolus.
The contact surface area between the alveoli and the blood is maximised by the degree of proliferation of capillaries around each alveolus, to the extent that there is almost a continuous layer of blood surrounding each alveolus
200
The diagram on page 127 of the textbook shows the structure of the respiratory tree (system) of a mammalian (human). What is the main function of the structures present (other than the alveoli)?
The other structures (apart from alveoli) shown in the diagram are concerned with ensuring that the alveoli are well ventilated.
201
When the guard cells are flaccid the stomata are ...
Closed
202
The lungs are naturally ...
Elastic
203
The natural elasticity of the lungs produces __ ______ _____ during exhalation
An elastic recoil
204
The natural elasticity of the lungs produces an elastic recoil during exhalation which ...
Helps force air out of the lungs.
205
Often by the time emphysema is diagnosed, the individual's lungs are ...
Irreversibly damaged
206
Past Paper Question - June 2018 AS2 Q1
Q1 A variety of substances are required by living organisms in order to function.
Identify the substances described below:
• reduces surface tension in the moisture layer in the alveoli.
_________________________________________________________________
• directly converts fibrinogen to fibrin. _________________________________________________________________
• waterproof component of the Casparian strip in the endodermis. _________________________________________________________________
• an oxygen store in red muscle. _________________________________________________________________
• carbohydrate transported by the phloem.
_________________________________________________________________ [5]
Surfactant;
| thrombin;
suberin;
myoglobin;
sucrose; [5]
207
Past Paper Question - June 2018 AS2 Q3 a)
Q3 Fick’s Law shows how three factors affect the rate of diffusion:
diffusion rate ∝ surface area × difference in concentration
——————————————————
thickness of membrane
a) Compare and contrast one factor from Fick’s Law as it relates to the gas exchange organs in plants and mammals. In your answer make reference to the structures involved.
Compare _______________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________
Contrast ________________________________________________________
_________________________________________________________________
_________________________________________________________________
_________________________________________________________________ [2]
Q3 a) Any one pair:
• both have a large surface area;
• in plants provided by the spongy mesophyll of the leaf, in mammals millions of lobed alveoli
or
• both have large concentration gradients;
• maintained in plants by respiration/photosynthesis in mesophyll layer
and in mammals by close blood supply/ventilation
or
• both have thin membranes (to provide a short diffusion pathway);
• for example one layer of squamous epithelium in alveoli/plants a few
cell layers in leaf [2]
208
Past Paper Question - June 2018 AS2 Q3 b)i)
Q3 b) Below is a partially drawn graph showing the net carbon dioxide intake by a plant over the first 12 hours of a 24-hour period.
i) Complete the graph to show the expected carbon dioxide intake for 12-24 hours. [2]
(Go do this past paper question)
Q3 b)i) Graph drawn in an approximate mirror image of first 12 hours;
reaching compensation point at approximately 18 hours and dropping
to approximately same point below the x-axis; [2]
209
Past Paper Question - June 2018 AS2 Q3 b)ii)
Q3 b) Below is a partially drawn graph showing the net carbon dioxide intake by a plant over the first 12 hours of a 24-hour period.
ii) Describe and explain the carbon dioxide intake shown for 0-12 hours. [4]
(Go do this past paper question)
Q3 b)ii) Any two pairs:
• From 0–4 hours (0–6 hours) carbon dioxide is given out (negative
intake) by the plant;
• the plant is in darkness/low light so only respiration occurring/
respiration exceeds photosynthesis;
or
• At 6 hours CO2 intake is 0/no net intake or output of CO2;
• where rates of photosynthesis and respiration are equal;
or
• From 6–12 hours, CO2 intake increases;
• light intensity increases, so photosynthesis exceeds respiration; [2]
210
Past Paper Question - June 2018 AS2 Q3 b)iii)
Q3 b) Below is a partially drawn graph showing the net carbon dioxide intake by a plant over the first 12 hours of a 24-hour period.
i) Complete the graph to show the expected carbon dioxide intake for 12-24 hours. [2]
iii) Shade on the graph the area which represents a net gain in glucose. Explain your answer. [2]
(Go do this past paper question)
Q3 b)i) Graph drawn in an approximate mirror image of first 12 hours;
reaching compensation point at approximately 18 hours and dropping
to approximately same point below the x-axis; [2]
iii) Shade part of graph above dotted line and under solid line; production of glucose in photosynthesis must exceed the loss of glucose in respiration; [2]
211
Past Paper Question - June 2018 AS2 Q3 b)ii)
Q3 b) Below is a partially drawn graph showing the net carbon dioxide intake by a plant over the first 12 hours of a 24-hour period.
ii) Describe and explain the carbon dioxide intake shown for 0-12 hours. [4]
(Go do this past paper question)
Q3 b)ii) Any two pairs:
• From 0–4 hours (0–6 hours) carbon dioxide is given out (negative
intake) by the plant;
• the plant is in darkness/low light so only respiration occurring/
respiration exceeds photosynthesis;
or
• At 6 hours CO2 intake is 0/no net intake or output of CO2;
• where rates of photosynthesis and respiration are equal;
or
• From 6–12 hours, CO2 intake increases;
• light intensity increases, so photosynthesis exceeds respiration; [2]
212
Past Paper Question - June 2018 AS2 Q3 b)iii)
Q3 b) Below is a partially drawn graph showing the net carbon dioxide intake by a plant over the first 12 hours of a 24-hour period.
i) Complete the graph to show the expected carbon dioxide intake for 12-24 hours. [2]
iii) Shade on the graph the area which represents a net gain in glucose. Explain your answer. [2]
(Go do this past paper question)
Q3 b)i) Graph drawn in an approximate mirror image of first 12 hours;
reaching compensation point at approximately 18 hours and dropping
to approximately same point below the x-axis; [2]
iii) Shade part of graph above dotted line and under solid line; production of glucose in photosynthesis must exceed the loss of glucose in respiration; [2]
