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NAME:___________________________ OPTION GROUP:__________________

GAS EXCHANGE IN PLANTS &

ANIMALS

WORKBOOK

2 TRLJ. Version 1, 2019

Instructions

Regular revision throughout the year is essential. It’s vital you keep a track of what you understand and what you don’t understand. This booklet is designed

to help you do this. Use the following key to note how well you understand the work after your revision. Put the letter R, A or G in the table. If you place an

R or an A then you should make a note of what you are struggling with and the end of this book under the relevant section and seek help with this.

Key R = Red. I am not confident about my knowledge and understanding A = Amber. I am fairly confident about my knowledge and understanding G = green. I am very confident about my knowledge and understanding

STUDY CHECKLIST AND ASSESSMENT OBJECTIVES


The following points are what you need to know, revise and answer questions on.

Place an R, A or G when you have revised and make notes of what you do not understand.

Adaptations for Gas Exchange In Animals & Plants 1. Can you describe the general principles of gas exchange?

2. Can you describe and list the features of a gas exchange surface and related this to Fick’s law?

3. Can you explain the importance of volume, surface area and surface area to volume ratio to gas exchange?

4. Can you calculate the volume, surface area and surface area to volume ratio for a cube and a sphere?

5. Can you explain the relationship between the volume of an organism and its oxygen requirement?

6. Can you explain the relationship between the surface area of an organism and its supply of oxygen?

7. Can you explain why unicellular organisms like amoeba and multicellular organisms like the earthworm and the flatworm can survive with gas exchange occurring across their body surface?

8. Can you explain why some animals need specialised gas exchange organs?

9. Can you label/describe the gas exchange organ for a fish?

10. Can you label/describe the gas exchange organ for an Insect?

11. Can you label/describe the gas exchange organ for a human?

12. Can you interpret histology images of the human lung?

13. Can you describe and explain the ventilation mechanism in a fish?

14. Can you describe and explain the ventilation mechanism in an insect?

15. Can you describe and explain the ventilation mechanism in a human?

16. Can you describe the relationship between volume and pressure?

17. Can you describe and explain the counter current exchange mechanism in a bony fish?

18. Can you describe and explain the parallel flow mechanism in a cartilaginous fish?

19. Can you describe/explain how amphibian’s carryout gas exchange?

20. Can you label a drawing/histology image of a dicotyledonous leaf?

21. Can you explain how a dicotyledonous leaf is adapted for efficient photosynthesis?

22. Can you explain how a dicotyledonous leaf is adapted for efficient gas exchange?

23. Can you explain the role of stomata in gas exchange and the mechanism by which they open and close?


Assessment Objective Description AO1 Demonstrate knowledge and understanding of scientific ideas, processes, techniques and procedures.

AO2 Apply knowledge and understanding of scientific ideas, processes, techniques and procedures:

• In a theoretical context

• In a practical context

• When handling qualitative data

• When handling quantitative data

AO3 Analyse, interpret and evaluate scientific information, ideas and evidence, including in relation to issues, to:

• Make judgments and reach conclusions

• Develop and refine practical design and procedures


Below is a list of some key words and phrases you will need to learn and understand in this gas exchange

topic.

1. Air space

2. Alveolus

3. Amoeba

4. Angiosperm

5. Bony fish

6. Bronchi

7. Bronchiole

8. Buccal cavity

9. Cartilaginous fish

10. Concentration gradient

11. Counter current flow

12. Cuticle

13. Cuticle

14. Diaphragm

15. Dicotyledonous

16. Diffusion

17. Earthworm

18. Elastic fibers

19. Flatworm

20. Gas exchange surface.

21. Gill arch

22. Gills

23. Guard cells

24. Intercostal muscles

25. Lamellae

26. Light intensity

27. Lower epidermis

28. Malate

29. Operculum

30. Palisade mesophyll cells

31. Parallel flow

32. Phloem

33. Pleural cavity

34. Ribs

35. Spiracle

36. Spongey mesophyll cells

37. Squamous epithelium

38. Stomata

39. Surface area

40. Surface area to volume ration

41. Surfactant

42. Trachea

43. Tracheal system

44. Upper epidermis

45. Vascular bindle

46. Ventilation

47. Xylem

WORD BANK


1.0.1 Concept. Gas exchange is the process by which an organisms takes gasses in

from the atmosphere and releases gasses into the atmosphere. This exchange of

gasses occurs across a gas exchange surface. The gasses that are exchange are

normally carbon dioxide and oxygen, as shown below:

1.0.2 Concept. The gas exchange surface has the following features that make it

ideal for exchanging gases:

1. It is thin.

2. It is permeable to gasses.

3. It has an extensive blood supply of capillaries.

4. It is moist

5. There is a steep diffusion gradient.

6. Large surface Area

Not every gas exchange surface will have all of the above features – this depends on the

particular organism. This will be covered later.

1.0.3 Question Why does the gas exchange surface have to be thin?

Answer Gas exchange occurs by diffusion. Diffusion must occur rapidly and

this can only occur over short distances. So the gas exchange surface

is thin to allow a short distance for diffusion to occur over.

1.0.4 Question Why does the gas exchange surface have to be permeable?

Answer So that gases can pass though the gas exchange surface by diffusion.

1.0.5 Question Why does the gas exchange surface have an extensive blood capillary network?

Answer So that oxygen can enter the blood and be transported around larger animals rapidly.

1.0 THE PRINCIPLES OF GAS EXCHANGE

1.0.1 – 1.0.9 The Gas Exchange Surface and the basic principles of gas exchange

Atmosphere

Inside Organism

O2

CO2

Gas Exchange Surface


1.0.6 Question Why does the gas exchange surface have a steep diffusion gradient?

Answer A steep diffusion gradient ensure that diffusion occurs rapidly.

1.0.7 Question Why does the gas exchange surface have to be moist?

Answer So gasses can dissolve into solution and diffuse through the gas

exchange surface.

1.0.8 Question Why does the gas exchange surface have to have a large surface area?

Answer This is needed to ensure sufficient gasses can be exchange between the organisms and the environment rapidly to meet the metabolic demands of the organism.

1.0.9 Concept Fick’s law is a mathematical expression relating: surface area,

distance and diffusion gradient to the rate of diffusion. The expression is:

The equation tells us that if the Surface area and the diffusion gradient are high and the distance is short then the rate of diffusion will be rapid.

Rate of diffusion is ∝ Surface Area × Diffusion Gradient

Distance

1.0.10 – 1.0.12 Surface Area, Volume and Surface Area to Volume ratio calculations

1.0.10 Concept The volume of an organism is a measure of its size and so its metabolic demand for oxygen to do aerobic respiration.

1.0.11 Concept The surface area of an organism is a measure of how much gas

can be delivered to, or removed, from an organism. 1.0.12 Concept The volume and surface area of a cube and a sphere can be

calculated using the following equations:

Cube Sphere

Volume = Length x width x breath V = L x W x B

Volume = 4/3 x pi x radius cubed V = 4/3 x π x r3

Surface area = 6 x length x width SA = 6 x L x W

Surface area = 4 x pi x radius squared SA = 4 x π x r2

The surface area to volume ratio is calculated by dividing the surface area by the volume


The following table shows the calculations of volume, surface area and surface area to volume ratio for a cube of different sizes:

Size of the cube (cm)

Volume (cm3) Surface Area (cm2)

Surface area to volume ratio

0.5 0.125 1.5 12

1.0 1 6 6

2.0 8 24 3

4.0 64 96 1.5

8.0 512 384 0.75

Closely analyze the values in the table, read the statement below then answer the questions that follow: As the size of the cube doubles:

1. The volume:

2. The surface area:

3. The surface area to volume ratio:


2.0.1 – 2.0.9 How volume, surface area and surface area to volume ratio affects gas exchange

Amoeba

2.0.1 Concept An amoeba is a unicellular, eukaryotic aquatic animal. It is shown

below: 2.0.2 Concept The size of an amoeba depends on the species, but they are typically

a few micrometers in size. Because of its small size, amoeba have a large surface area to volume ratio, a very small volume and a large surface area. The distance to the center of an amoeba is also very short. Because of the features mentioned in this concept, the amoeba is able to survive by having gas exchange occurring across its body surface.

2.0.3 Question How can an amoeba obtain sufficient oxygen across its body surface

in order to survive? Answer 1 Because its volume is very small it has a low metabolic demand for

oxygen. Answer 2 The surface area of the amoeba is sufficiently large to deliver enough

oxygen rapidly into the amoeba to meet the demands for ATP production via aerobic respiration.

Answer 3 Because its volume is small the distance to the center of the amoeba is very short. This means the rate of diffusion will be rapid. The distance to the center is the maximum distance that oxygen will have to diffuse into the amoeba.

2.0 GAS EXCHANGE IN AMOEBA, EARTHWORMS

AND FLATWORMS


Earthworm

2.0.4 Concept An earthworm is a multicellular, eukaryotic terrestrial animal. It is

shown below:

2.0.5 Concept The length of an earthworm is much longer that its width. Because of its narrow width, its volume is relatively small and its surface area is relatively large. Its surface area to volume ratio, therefore, is relatively large. Gas exchange occurs across the body surface of an earthworm.

2.0.6 Question How can an earthworm obtain sufficient oxygen across its body surface in order to survive?

Answer 1 Because it volume is small it has a low metabolic demand for oxygen.

Answer 2 The surface area of the earthworm is sufficiently large to deliver enough oxygen into the earthworm to meets the demands for ATP

production by aerobic respiration.

Answer 3 Earthworms have a circulatory system, with blood vessels just under the surface of the skin. The distance from the surface of the earthworm to the blood vessels is short, so oxygen can diffuse rapidly into the blood vessels. The circulatory system is then used to transport oxygen around the whole earthworm as diffusion would take too long to do this.

Image to show gas exchange in the

earthworm. Note the oxygen and carbon

dioxide entering and leaving the blood

capillaries.


Flatworm

2.0.7 Concept Flatworms are multicellular, eukaryotic aquatic worms of the phylum

Platyhelminthes. An example is shown below:

2.0.8 Concept There are a great variety of different flatworms. Their overall body shape can vary a lot. However, the width of all flatworms is very thin. Their volume can be very small, their surface area large and their surface area to volume ratio also large. They do not have a circulatory system.

2.0.9 Question How can a flatworm obtain sufficient oxygen across its body

surface in order to survive?

Answer 1 Because its volume is very small it has a low metabolic demand for oxygen.

Answer 2 The surface area of the flatworm is sufficiently large to deliver enough oxygen rapidly into the flatworm to meet the demands for ATP production via aerobic respiration.

Answer 3 Because its thin, the distance to the center of the flatworm is very short. This means the rate of diffusion will be rapid. The distance to the center is the maximum distance that oxygen will have to diffuse into the flatworm.


Q1. The images below of simple representations of different organisms.

(a) For each organism, calculate its volume, surface area and surface area to volume ratio.

ACTIVITIES ON SECTION 1 AND 2

Size Volume Surface Area SA/V Ratio

Length of side is 12µm


Diameter is 5µm


Length of side

of one cube is

12µm


Length of side

of one cube is

12µm


Length of side of

one cube is 6µm


Diameter is 2.5µm

Organism A

Organism B

Organism C

Organism D

Organism E

Organism F


(b) Give an account of the role of surface area and volume in the metabolism of an organism and the effect of increasing body size on the relationship between these two factors.

Q2. Small organisms obtain oxygen by diffusion through a permeable and moist body surface. However, their demand for oxygen is determined by their volume and how metabolically active their tissue is. A small singled celled organism, when at rest, is assumed to adopt a cube shape with a side of 12µm long.

(i) Calculate the surface area and volume of this cubed shape organism. Show your workings out.

Surface Area______________________ µm2

Volume______________________ µm3


When at rest, this organism absorbs oxygen at a rate of 0.02µm3 µm-2 min-1, while it consumes oxygen at a rate of 0.01µm3 µm-3 min-1.

(ii) Calculate the total volume of oxygen absorbed and consumed in one minute at rest. Show your workings out.

Oxygen absorbed_________________________ µm3

Oxygen consumed at rest_________________________ µm3

(iii) Explain why this organism must change its shape if it is to become more active.

(iv) Explain why smaller specimens of this species are more active than larger ones.

Q3. The amount of oxygen entering cells changes when their rate of respiration increases. Use Fick’s law to explain how.


Q4


3.0 GAS EXCHANGE IN HUMANS, FISH & INSECTS

3.0.1 Concept Large, multicellular organisms, like humans, fish and insects need specialized gas exchange organs that increase the surface area over which oxygen, and other gasses, can diffuse. This high surface area is needed to allow enough oxygen to enter the organism to meet that high demands for making ATP through aerobic respiration.

3.0.2 Concept The gas exchange organ of the human is the lungs, but the gas exchange surface is the alveoli.

3.0.3 Diagram The gross structure of the human lungs is shown below. You must be able to label this diagram in the exam.

3.0.1 – 3.0.5 The Human lungs – Structure and histology


Histology & tissues of the lungs in t.s section 3.0.4 Histology and tissues of the trachea.

“C” Shaped Cartilage

Lumen of trachea

No cartilage at back of trachea

Relaxed oesophagus

“C” Shaped Cartilage

Expanded oesophagus

Distorted trachea

Ciliated columnar epithelium with goblet cells

Function of the ciliated columnar epithelium and

goblet cells.

The goblet cells produce mucus that traps bacteria

and particulates that enter the trachea. The cilia

will then waft the mucus up and out of the trachea.

This prevents infection and diseases of the lungs

occurring.

Function of “C” shaped cartilage

The cartilage prevents collapse of the trachea

during breathing. The lack of cartilage at the back

of the trachea allows the expanding oesophagus to

distort the trachea to allow passage of food by

peristalsis.

Trachea


3.0.5 Histology and tissues of the bronchus, bronchioles and alveoli.

This image shows the different parts of the

respiratory tree outlining the difference in the

distribution and amount of cartilage support. The

respiratory tree includes the trachea, primary

bronchi, secondary bronchi, tertiary bronchi and then

the bronchioles.

The primary Bronchi

The bronchi has a columnar epithelium (E) with

less goblet cells than found in the trachea.

There is a layer of elastic tissue (LP)

There is a layer of smooth muscle (S) below the

submucosa (M).

The last, outer layer is the cartilage (C). This

forms flattened plates rather than “C” shapes

as in the trachea.

The Bronchiole

The bronchiole has a columnar epithelium (E)

with less goblet cells than found in the trachea.

There is a layer of elastic tissue (LP)

There is a layer of smooth muscle (S) below the

submucosa (M).

The last, outer layer is the cartilage (C). This

forms flattened plates rather than “C” shapes

as in the trachea.


The terminal and respiratory bronchiole

The terminal bronchiole is the last part of the

bronchiole before it forms the respiratory

bronchiole. It is a very narrow tube (typically

less than 1mm in diameter). This image is of a

terminal bronchiole along with the pulmonary

blood vessel and alveoli.

This image shows how the respiratory

bronchiole (RB) forms from the terminal

bronchiole (TB). The terminal bronchiole has

less smooth muscle (SM), no goblet cells but

has cuboidal or columnar epithelium. The

respiratory bronchioles form into the alveoli

ducts which then end in an alveolus. See

image below:

Detail image showing the

relationship between the terminal

bronchiole, respiratory

bronchiole, alveoli duct and

alveoli.


The alveoli

Diagram to show the alveoli at the

end of the respiratory bronchiole.

The alveoli wall

The alveolus wall is composed of squamous epithelium which are very flat so reduces the distance

over which gasses are exchanged. Cells produce surfactant to reduce the surface tension of water

that lines the squamous cells. This prevents the alveoli from sticking together during breathing. The

alveoli are surrounded by an extensive network of capillaries. The wall of the capillaries is made of

endothelial cells. The connective tissue is made up of elastic tissue to allow the alveoli to expand

and retract during breathing. The alveoli are very numerous sac shaped structures to increase their

surface area. The gas exchange surface is made up of the squamous epithelium, the endothelium

and the basement membrane.

Lumen of alveolus

Gas exchange surface


The three images on this page show the

structure of the alveola wall. Image A

and B show the very thin squamous

epithelium along with the surfactant

cells. Also shown in these images are

the blood capillaries that form part of

the alveola wall. Note how thin the

alveola wall is.

Image C shows the alveola macrophage

cell that provides protection from

pathogens.

Squamous epithelial cells

Squamous epithelial cells

Surfactant cell

A

Nucleus of

Squamous

epithelium cell

Surfactant cell

B

C


ACTIVITIES ON SECTION 3 – 3.0.1 TO 3.0.5

Q1 Why does the trachea have ciliated columnar epithelium and goblet cells?

Q2 Why does the trachea and the bronchi have cartilage. Give an account of the structural and distribution differences between the cartilages in the trachea and bronchi.

Q3 Identify the structures labeled in the image below.

A

B

C


Q4 Using Fick’s law only, explain how the human lungs are adapted for gas exchange.

Q5 The three images below, A, B and C are of human lung tissue.

One image is of normal lung tissue and the other two are examples of diseased lung tissue that cause sufferers to experience shortness of breath.

a. Identify the normal lung tissue.

A B

C


b. For the remaining two images, explain the structural features in the tissue that will cause the shortness of breath.


3.0.6 – 3.1.3 The Human lungs – Ventilation & Gas Exchange

3.0.6 Definition Ventilation is the process by which the gas exchange medium is passed over the gas exchange surface. In humans, and other land organisms, the gas exchange medium in the air – it is what contains the gasses that are exchange between the organism and the environment.

3.0.7 Concept Ventilation ensures that a steep diffusion gradient is maintained. This ensures that rapid diffusion of gasses occurs.

3.0.8 Concept Ventilation involves breathing in which is called inspiration and breathing out called expiration. Humans and other mammals use negative pressure breathing. This means air is pulled into the lungs and not pushed into the lungs. See also concept 3.0.9 and 3.1.0.

3.0.9 Concept Ventilation causes volume and pressure changes to occur in the pleural cavity and lungs according the following rule:

• As the volume increases the pressure decreases.

• As the volume decreases the pressure increases. 3.1.0 Concept The volume and pressure changes that occur during ventilation can

be presented on a graph. A typical example is shown below.


3.1.1 Concept Ventilation requires the ribs, intercostal muscles, pleural membrane and the diaphragm to cause volume and pressure. These structures are shown in the images below:

There are 24 ribs in the human ribcage. Between the ribs are three layers of intercostal muscles. Just beneath the ribs is the outer pleural membrane, which is also attached to the diaphragm. An Inner pleural membrane is attached to the lung surface. Between the inner and outer pleural membranes is the pleural cavity. A detailed image of these structures is shown below:

Pleural

cavity

Inner pleural membrane

Outer pleural membrane

Rib


3.1.2 Concept The steps in inspiration and expiration:

Inspiration Expiration

1. The diaphragm contracts and becomes flattened.

The diaphragm relaxes and becomes dome shaped.

2. The external intercostal muscles contract and the rib cage moves up and out.

The external intercostal muscles relax, and the rib cage moves down and in.

3. The ribs pull on the outer pleural membrane pulling it outwards. This causes the pleural cavity to reduce in pressure and the inner pleural membrane is pulled outwards.

The outer and the inner pleural membranes moves inwards. The pressure in the pleural cavity increases.

4. The pulling of the inner pleural membrane causes the lungs to be pulled outwards which causes the alveoli to expand. This causes an increase in the lung volume and a reduction in the pressure in the lungs.

The elastic recoil of the elastic fibers in the lungs causes the lungs to reduce in volume and the pressure to rise.

5. The pressure in the lungs falls below that of the atmosphere and air is drawn in down a pressure gradient.

The pressure in the lungs rises above that of the atmosphere and air is forced out down a pressure gradient.


3.1.3 Concept Gas exchange in the alveoli occurs as shown in the diagram below:


Q1. Describe how gas exchange is facilitated in the lungs of a mammal.

Q2. Outline the sequence of events that leads to the creation of areas of differential pressure during inspiration.

Q3

QUESTIONS ON SECTION 3 – 3.0.6 TO 3.1.3


Q4


Q5.


Q6


Q7


Q8


3.1.4 – 3.1.6 The Fish Gills – Structure and histology

3.1.4 Concept Fish have 8 gills, 4 on each side of the body. They are located in the opercular cavity and are protected from the outside by the opercular flaps (also called the operculum).

3.1.5 Concept A fish gill gas the following structures: gill arch, fill filament, gill

lamellae, gill rakers and a blood supply. Some of these structures are shown in the images below:

Opercular flap Mouth

Opercular flap removed to show the gills

Gill Rakers

Gill Arch

Gill Filaments

Gill Lamellae


3.1.6 Concept The gill filaments extend from the gill arch in pairs. Blood vessels enter and leave the gill filament from the gill arch. These carry and removed blood from the gill lamellae which is the gas exchange surface of the gill.

Gill filament

Gill Lamellae

Electron micrograph of

gill filament and gill

lamellae.

Deoxygenated blood enters the gill filament

via the afferent arteriole

Oxygenated blood leaves the gill

filament via the efferent arteriole

Gill Lamellae

Capillaries in the gill

lamellae showing direction

of blood flow.

Direction of water flow


3.1.7 – 3.2.1 The Fish Gills – Ventilation and gas exchange

3.1.7 Concept Gas exchange in bony fish occurs by the counter current flow mechanism. This involves water flowing over the gill filaments in one direction and the blood in the gill lamellae flowing in the opposite direction.

3.1.8 Concept The counter current flow mechanisms is a very efficient form of gas exchange with 85% of the oxygen in water entering the blood of the fish. The features that make this so efficient are: a shallow but constant diffusion gradient maintained over the whole width of the gill lamellae, this allows diffusion of oxygen to occur over the whole width of the gill lamellae.

100 80 60 40 20

10 30 50 70

Distance along the gill lamellae



3.1.9 Concept Gas exchange in cartilaginous fish occurs by the parallel flow mechanism. This involves water flowing over the gill filaments in the same direction as the flow of blood.

3.2.0 Concept The parallel flow mechanisms is a less efficient form of gas exchange compared with the counter current flow mechanism. Only 50% of the oxygen in water will diffuse into the blood. The features that make this inefficient are: a diffusion gradient that is initially steep but half way along the gill lamellae the gradient reaches an equilibrium, this allows diffusion of oxygen to occur over half of the gill lamellae

100 80 60 20

10 30 50 50


50

100 50 80 60 50 50 50



3.2.1 Concept Fish ventilate their gills as outlined below:

Inspiration

1. The mouth opens

2. The operculum closes

3. The floor of the mouth is lowered

4. The volume in the mouth cavity increases

5. The pressure in the mouth decreases below that of the external pressure.

6. The water flows into the mouth down a pressure gradient

Expiration

1. The mouth closes

2. The operculum opens

3. The floor of the mouth is raised

4. The volume in the mouth cavity decreases

5. The pressure in the mouth increases

6. The water flows out over the gills because the pressure in the mouth cavity is highlker than in the opercular cavity and the outside.


Q1 Explain how the structure of the gill is adapted to gas exchange.

Q2 Identify the structures in the image below

Q3 Explain why the counter current flow mechanism is more efficient then the parallel flow

mechanism.



Q4 The organism below is an amphibian called an axolotl. It has external gills which are similar in

structure to the internal gills found in bony fish. Describe how both bony fish and axolotls are

adapted to increase the efficiency of gas exchange and explain how the structures in the heads of

bony fish enable them to be highly active even when oxygen levels are relatively low but axolotls

are slower moving under these conditions.


Q5


Q6


Q7


3.2.2 – 3.2.3 The insect tracheal system – Structure and histology

3.2.2 Concept Gas exchange in insects occur via the tracheal system. This is a network of tubes than originate at the surface of the insect at opening called the spiracles. The tubes than span inwards towards the center of the insect and end by entering or lying close to the respiring cells of the insect as tracheoles. Tracheoles are the gas exchange surface of the insect. The tracheal system is shown below:

Trachea Spiracle

Tracheole

Drawing of the insect tracheal system.

Tracheal system of a laval form of an insect.


3.2.3 Concept The spiracles have a complex structure, and are not just simples

holes in the exoskeleton of an insect.

Trachea showing the chitin rings. The

chitin rings ensure the trachea does not

collapse.

Trachea system of an insect to show

spiracle (S), tracheoles (T) and trachea (L)

Segment of insect

Spiracle

Laval form of an insect to show

body segments and spiracles.

Spiracle

Segment of larvae


Diagram of a spiracle. The first part is called the atrium, it has hairs that trap dust and water vapor. They also sense the environment and control the opening and closing of the spiracular valve. The spiracular vales are closed most of the time to prevent water loss.

Electron microscope image of the

spiracle.

Electron microscope image of the

spiracle open (A) and closed (B)


3.2.4 Concept Tracheoles end in or near cells that respire. The very end of the tracheoles are the gas exchange surface. When an insect is at rest and so has a lower demand for oxygen there is a lot of fluid in the end of the tracheoles. The excess fluid increases the diffusion distance for oxygen and carbon dioxide. See image below:

3.2.5 Concept When an insect becomes active, e.g. when it is flying its demand for oxygen increases as the aerobic respiration rate will increase. Initially the supply of oxygen does not meet the demand for aerobic respiration, so anaerobic respiration will occur. This produces lactic acid and lowers the water potential of the cell compared to the fluid in the tracheole. This causes the fluid to enter the cell by osmosis. As this occurs all the oxygen dissolved in the fluid is delivered into the cell so that aerobic respiration can occur. The lack of fluid in the tracheole also reduces the diffusion distance for gasses.

3.2.4 – 3.2.5 The insect tracheal system – Gas Exchange

Fluid in which oxygen and

carbon dioxide dissolve and

then diffuse across the

tracheole membrane and

into/out of the cell.

Excess fluid that increases the

diffusion distance

Fluid in which oxygen is

dissolved enter the cell by

osmosis. This delivers oxygen

to the cell and reduces the

diffusion distance.


3.2.6 Concept The insect spiracles are closed to reduce water loss. For ventilation to occur these spiracles must open. The stimulus that causes the spiracles to open is the high carbon dioxide concentration that accumulates in the tracheole system due to aerobic respiration.

3.2.7 Concept An insect has three part to its body: a head, a thorax and an abdomen. Both the thorax and the abdomen have spiracles. To ensure one way flow of air through the tracheal system, air enter through the thoracic spiracles and leaves through the abdominal spiracles. This is summarized in the image below:

3.2.6 – 3.2. The insect tracheal system – Ventilation and spiracle movements

Body segments of an insect


3.2.8 Concept Spiracle movements, pressure changes, volume changes, oxygen and carbon dioxide concentration are graphically shown below during ventilation.

Spiracle movements

Oxygen concentration

Pressure of thorax

Volume of thorax

Open

Closed

Spiracle movements

Carbon dioxide

concentration

Pressure of abdomen

Volume of abdomen

Open

Closed

Inspiration

Expiration



1


2


3


4


5


4.0 GAS EXCHANGE IN PLANTS 4.0.1-4.0.3 Structure of an dicotyledonous leaf

4.0.1 Concept A dicotyledonous leaf has the following structures:

Abaxial (lower) surface of leaf to show midrib, veins and lamina (leaf blade).

Lamina

Microscope image of the cells, regions and structures of the leaf

Adaxial (upper) surface

Abaxial (lower) surface

Waxy cuticle Upper epidermis

Palisade mesophyll

cells

Vascular Bundle

Lower epidermis

Stomata

Phloem Xylem Air space

Spongy mesophyll

cells


4.0.2 Concept Structure of the lower epidermis and stomata:

Drawing of the structure of a dicotyledonous leaf

Adaxial (upper) surface

Abaxial (lower) surface

Vascular Bundle

Xylem

Phloem Air space

Stomata

Lower epidermis

Upper epidermis Waxy cuticle

Palisade mesophyll

cells

Spongy mesophyll

cells

Lower epidermal cell

Stomata

Microscope image of the lower epidermis to show epidermal cells and the stomata

Lower epidermal cell

Stomata

Light Microscope image

Electron Microscope image


4.0.3 Concept Guard cells are plant cells that have an uneven thickening of their

cell wall. The thickest region is called the inner cell wall and is located where the stoma is formed between two guard cells. The rest of the guard cell wall is thin.

Drawing of the lower epidermis to show epidermal cells and the stomata

4.0.4-4.0.6 Opening and closing of the stomata and gas exchange

4.0.4 Concept Stomata re open during the day and closed during the night. During the day gasses must diffuse in and out of the open stomata. Carbon dioxide diffuses in and oxygen will diffuse out along with water vapour.

4.0.5 Concept The stimulus for the stomata to open is light. The light will initiate a number of responses that will lower the water potential of the guard cell to allow water to enter by osmosis and make the guard cells turgid. The responses that lower the water potential of the guard cells are: active transport of potassium ions into the guard cells form the epidermal cells and the conversation of starch to malate. When the guard cells become turgid, they become bent in shape because the inner thicker cell wall is less able to stretch compared to the outer thinner cell wall. This bending will open the stomatal pore. These events are shown in the diagram below:


4.0.6 Concept Stomata closed by the reverse mechanism outlined in concept 4.0.4.

potassium will be pumped out and malate will be converted to starch. This will raise the water potential of the guard cells and cause water to leave the guard cell by osmosis making them plasmolyzed. The guard cells will become straighter in shape causes the stomatal pore to close. This is shown in the image below

K+

K+


4.0.7 Concept The number of stomata per mm2 of leaf can vary depending on the species of plant and its environment in which it lives. Plant that live in very dry condition, called xerophytes, will have less stomata as they will need to reduce their water loss, while plants like mesophytes can have more stomata as they live in conditions where water is not limited to large degree.

4.0.8 Concept Depending on the species of plant stomata can be found on the lower epidermis, the upper epidermis or both. Some species will have a greater number of stomata on the lower epidermis compared to the upper epidermis or have equal number on both upper and lower epidermis.

4.0.9 Concept The number of stomata per mm2 can be calculated by making a replica of the epidermis using clear nail varnish and using a microscope to count the number of stomata in the field of view. The equation to calculate the mean number of stomata is:

4.0.7-4.0.9 Number and distribution of stomata

𝑚𝑒𝑎𝑛 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑡𝑜𝑚𝑎𝑡𝑎 𝑝𝑒𝑟 𝑚𝑚2 𝑚𝑒𝑎𝑛 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑠𝑡𝑜𝑚𝑎𝑡𝑎 𝑝𝑒𝑟 𝑓𝑖𝑒𝑙𝑑 𝑜𝑓 𝑣𝑖𝑒𝑤

𝑎𝑟𝑒𝑎 𝑜𝑓 𝑓𝑖𝑙𝑒𝑑 𝑜𝑓 𝑣𝑖𝑒𝑤 𝑖𝑛 𝑚𝑚2

To calculate the area of the field of view you will need the

calibration values obtained in the cell structure booklet

4.1.0 Significance of leaf structure to gas exchange and photosynthesis

Leaf feature Significance for gas exchange Significance for photosynthesis

Thin Short diffusion distance Light can penetrate the leaf

Transparent cuticle Light can penetrate the palisade mesophyll cells.

Palisade cells are elongated Cells can pack close together so a large number can fit into the leaf

Palisade cells have many chloroplasts

So to absorb as much light as possible.

Chloroplast can move To move so that maximum light can be absorbed.

Air spaces To allow carbon dioxide and oxygen to diffuse between the stomata and the cells.

To allow carbon dioxide to diffuse into the photosynthesizing cells

Stomatal pores Gas exchange into and out of the leaf.


QUESTIONS ON SECTION 4 1


2


3 3


4


5


6

workbook - thiacin.co.uk · 7. can you explain why unicellular organisms like amoeba and...

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