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Compare and Contrast Process in Plants and
Animals: Gas Exchange
by CHED on June 17, 2017
lesson duration of 25 minutes
under General Biology 2
generated on June 17, 2017 at 08:24 am
Tags: Compare and Contrast Process in Plants and Animals: Gas Exchange
K-12 Teacher's Resource Community
Generated: Jun 17,2017 04:24 PM
Compare and Contrast Process in Plants and Animals: Gas Exchange
( 1 hour
and 25 mins )
Written By: CHED on July 18, 2016
Subjects: General Biology 2
Tags: Compare and Contrast Process in Plants and Animals: Gas Exchange
Content Standard
The learners demonstrate an understanding of:
1. Plant and Animal Organ Systems and their Functions
2. Feedback Mechanisms
Performance Standard
The learners shall be able to:
develop a presentation (e.g. role-playing, dramatization and other forms of multimedia) to show how an organism
maintains homeostasis through the interaction of the various organ systems in the body
Learning Competencies
Compare and contrast the following processes in plants and animals: reproduction, development, nutrition, gas
exchange, transport/circulation, regulation of body fluids, chemical and nervous control, immune systems, and sensory
and motor mechanisms
Introduction 5 mins
Communicating Learning Objectives
1. Present the topic outline for Gas Exchange:
I. Basic principles influencing gas exchange
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II. Structures for gas exchange in plants and animals
III. Breathing mechanisms in vertebrates
IV. The Human respiratory system
V. Coordination of gas exchange and circulation
VI. Control of respiration in vertebrates
VII. Respiratory adaptations to extreme conditions
VIII.Respiratory problems and on public health
2. Cite the specific learning objectives for this topic.
Motivation 10 mins
Questions on Gas Exchange
1. Ask the students what else do organisms need to acquire from the environment aside from nutrition? Why?
Suggested response: oxygen – needed for cellular respiration, in the process of extracting chemical energy from food
(with the exception of anaerobic organisms)
2. What gas is considered a metabolic waste product of cellular metabolism? How does it leave the organism’s body?
Suggested response: carbon dioxide – it diffuses out of the respiratory surface of the organism
3. Ask the students to cite the structures in plants and animals that allow for gas exchange.
Suggested responses: please refer to respiratory structures cited in the lecture
4. Let the students enumerate some respiratory problems encountered by humans.
Suggested responses: asthma, emphysema, lung cancer, pneumonia
Instruction 10 mins
Lecture on Gas Exchange
1. Define gas exchange:
I. Gas exchange is the uptake of molecular oxygen from the environment and the discharge of carbon dioxide to the
II. It is often called respiratory exchange or respiration but it should not be confused with cellular respiration.
III. Oxygen is needed in tissues for aerobic cellular respiration to occur and extract ATP from food.
IV. Carbon dioxide must be released to prevent physiological pH in tissues from being very acidic. In plants however,
the carbon dioxide that is released as a by-product of cellular respiration may again be taken up for the process of
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2. State some basic principles influencing gas exchange:
I. The respiratory surface or organ is the part of an animal’s body where gases are exchanged with the environment.
To allow for gas exchange, it must be moist, large enough, and protected from dessication.
II. Respiratory systems rely on the diffusion of gases down pressure gradients.
A. Partial pressures for each gas in the atmosphere can be computed; for example, the partial pressure of oxygen is
160 mm Hg.
B. Fick’s Law states that the amount of diffusion of a gas across a membrane is proportional to the surface area and
the difference in partial pressure between the two sides and inversely proportional to the thickness of the membrane.
III. Surface-to-volume ratio
A. As an animal grows, the surface area increases at a lesser rate than its volume, making diffusion of gases into the
interior more difficult
B. Animals must have a body design that keeps internal cells close to the surface (e.g. flatworms) or must have a
system to move the gases inward.
IV. Ventilation
A. It refers to the movement of the respiratory medium (air or water) over the respiratory surface.
B. Bony fish moves the gill covers (operculum) for water carrying oxygen to flow across the gill.
C. Humans move the muscles of the thorax to expand and contract the chest cavity and move air in and out of the
V. Respiratory Pigments or Proteins
A. Adaptations of animals for gas exchange include respiratory pigments that bind and transport gases.
B. The respiratory pigment of vertebrates is hemoglobin while that of invertebrates (e.g. arthropods and molluscs) is
C. Blood cannot carry sufficient oxygen and carbon dioxide in dissolved form to meet the body’s requirements;
hemoglobin helps enhance its capacity.
3. Describe structures for gas exchange in plants:
I. Stomates in leaves
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II. Lenticels in stems
III. Root hairs in aerial roots
IV. Pneumatophores or the lateral roots of mangroves
4. Describe respiratory surfaces or organs in invertebrates:
I. Cell surface or cell membrane – especially used in unicellular organisms
II. Integumentary exchange – refers to the general body surface or skin used by animals with high surface-to-volume
ratio; e.g. flatworm and earthworm. Amphibians also use their skin in addition to lungs as gas exchange surface
III. External Gills – used by invertebrates that live in aquatic habitats; gills are highly folded, thin- walled, vascularized
epidermis that project outward from the body; e.g. crayfish, lobster, sea star, nudibranch
IV. Tracheal system in arthropods – utilizes fine air-conducting tubules to provide gaseous exchange at the cellular
level; it is not dependent on a circulatory system; e.g. insects, spiders
5. Describe respiratory surfaces in vertebrates:
I. External Gills – thin, vascularized epidermis that project from the body surface of a few amphibians; e.g. larval
II. Internal Gills – rows of slits or pockets in adult fishes positioned at the back of the mouth such that water that enters
the mouth can flow over them as it exits just behind the head.
A. Water flows over the gills and blood circulates through them in OPPOSITE DIRECTIONS.
B. This mechanism, called countercurrent flow, is highly efficient in extracting oxygen from water, whose oxygen
content is lower than air.
III. Lungs – internal respiratory surfaces shaped as a cavity or sac; lungs provide a membrane for gaseous exchange;
since they are not in direct contact with all other parts of the body, lungs require a circulatory
A. Air moves by bulk flow into and out of the lung.
B. Gases diffuse across the inner respiratory surfaces of the lungs.
C. Pulmonary circulation allows the diffusion of dissolved gases across lung capillaries
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D. In body tissues, oxygen diffuses from blood ? interstitial fluid ? cells; the pathway of carbon dioxide is in reverse
E. All lungs receive deoxygenated blood from the heart and return oxygenated blood to the heart
6. Compare breathing mechanisms in vertebrates:
I. Amphibians ventilate their lungs by positive pressure breathing which forces air down the trachea.
II. Birds use a system of air sacs as blower to keep air flowing through the lungs in one direction only, preventing the
mixing of incoming and outgoing air.
III. Mammals ventilate their lungs by negative pressure breathing which pulls air into the lungs when the volume of the
lungs expands as the rib muscles and diaphragm contract. However, the incoming and outgoing air mix, decreasing
the efficiency of ventilation.
7. Describe the human respiratory system:
I. Air enters or leaves the respiratory system through nasal cavities where air is filtered by hair and cilia, warmed by
blood vessels, and moistened with mucus.
8. Discuss the coordination of gas exchange and circulation:
I. Oxygen Transport
A. Oxygen diffuses down a pressure gradient from the lungs into the blood plasma ? red blood cells ? binds to
hemoglobin (4 molecules per hemoglobin to form oxyhemoglobin).
B. Hemoglobin gives up its oxygen in tissues where partial pressure of oxygen is low, blood is warmer, partial pressure
of carbon dioxide is higher, and pH is lower; these four conditions occur in tissues with high metabolism.
II. Carbon Dioxide Transport
A. Carbon dioxide diffuses down its partial pressure gradient from the tissues into the blood plasma and red blood cells
? air in alveoli.
B. Seven percent is dissolved in plasma, 23% binds with hemoglobin to form carbaminohemoglobin, and 70% is in
bicarbonate form.
C. Bicarbonate and carbonic acid formation is enhanced by the enzyme carbonic anhydrase, which is located in the
red blood cells.
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III. Coordination of air flow with blood flow:
A. Gas exchange in the alveoli is most efficient when air flow equals the rate of blood flow.
B. Local controls within the lungs correct imbalances in air and blood flow by constricting or dilating both bronchioles
and arterioles.
9. Explain the control of respiration in vertebrates:
I. The nervous system controls oxygen and carbon dioxide levels for the entire body by regulating the rate and depth
of breathing.
II. The brain monitors the pH of the cerebrospinal fluid through sensors (reflecting carbon dioxide concentration in the
III. Secondary control is exerted by sensors in the aorta and carotid arteries that monitor blood levels of oxygen as well
as carbon dioxide (via blood pH).
10. Describe some respiratory adaptations to extreme conditions such as low-oxygen environments:
I. Animals that inhabit high altitudes have larger hearts and lungs, and hemoglobin with a high affinity for binding
II. Many diving animals have unusually high hematocrits (ratio of the volume of packed red blood cells to the volume of
whole blood) and also muscles with high amounts of myoglobin (an oxygen-binding protein found in muscle cells)
11. Cite some respiratory problems and impact on public health:
I. In a respiratory disorder like asthma, the muscles around bronchioles contract more than usual, increasing
resistance to airflow.
II. Emphysema is an abnormal condition of the lungs marked by decreased respiratory function; associated with
smoking or chronic bronchitis or old age.
III. Smoking tobacco products is one of the leading global causes of death and is strongly linked to cancer,
cardiovascular disease, stroke, and emphysema.
IV. Pneumonia is an infectious disease involving inflammation and fluid buildup in the lungs.
Practice 40 mins
Cross Section of Species
1. As an alternative to a pure lecture discussion, questions related to the different structures for gas exchange in plants
and animals may be asked. As each respiratory structure is discussed, reference to an overhead transparency or
visual is suggested.
2. Ask the students to observe and draw the following either from a microscopic examination or through the use of
visual aids: (a) monocot leaf cross section e.g. Zea mays; (b) dicot leaf cross section e.g. Ixora sp. Label the upper
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and lower epidermis, mesophyll, and vascular bundles.
3. Describe how air can enter the leaf. If the following are available (microscopes, slides, coverslips, scalpel or blade),
prepare thin sections of the upper and lower epidermal surfaces of Rhoeo spathacea. Examine the stomata under the
microscope for both the upper and lower epidermis. Which side contains more stomates? Draw the leaf epidermis
showing the stoma. Label the stomatal pore, guard cells, and subsidiary or accessory cells.
4. Draw an insect tracheal system from a visual aid. The large tracheae are reinforced by thickened spiral rings of
cuticle called taenidia while the smaller tracheae have annular rings. Label the large tracheae, taenidia, smaller
tracheae, and annular rings. As an alternative, dissect a cockroach and locate the tracheal system. Under the
dissecting microscope, these appear as silvery white tubes throughout the insect’s body.
5. Pith and dissect a toad. Examine the external nares and the oral cavity. Locate the epiglottis which leads to the
glottis. Observe the lungs in the chest cavity. What do you call the numerous branches and the air sacs found in the
lungs? Draw a diagrammatic representation of the respiratory system of the toad. Label the external nares, pharynx,
epiglottis, glottis, larynx, trachea, bronchi, and lungs.
Enrichment 10 mins
Conceptual Questions
1. Why is the position of lung tissues within the body an advantage for terrestrial animals?
2. After a heavy rain, earthworms come to the surface. How would you explain this behavior in terms of an
earthworm’s requirements for gas exchange?
3. How does an increase in the carbon dioxide concentration in the blood affect the pH of the cerebrospinal fluid?
Teacher Tip: Answer to Question 3: An increase in blood carbon dioxide concentration causes an increase in
the rate of carbon dioxide diffusion into the cerebrospinal fluid, where the carbon dioxide combines with
water to form carbonic acid. Dissociation of carbonic acid releases hydrogen ions, decreasing the pH of the
cerebrospinal fluid (Reece et al., 2011).
Evaluation 10 mins
1. Which of the following is not a structure for gas exchange in plants?
A. Stomates
B. Lenticels
C. Aerial root hairs
D. Flowers
E. Pneumatophores
2. Which of the following respiratory systems is not closely associated with a blood supply?
A. The lungs of a vertebrate
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B. The tracheal system of an insect
C. The gills of a fish
D. The skin of an earthworm
3. When you hold your breath, which of the following gas changes in the blood first leads to the urge to breathe?
A. Rising oxygen
B. Falling oxygen
C. Rising carbon dioxide
D. Falling carbon dioxide
E. Rising carbon dioxide and falling oxygen
4. The driving force for diffusion of oxygen across the cells of a respiratory organ is:
A. The difference in partial pressure of oxygen in the environment and in the blood.
B. The humidity.
C. The partial pressure of carbon dioxide in the blood.
D. The temperature.
E. All of the above.
5. The process of bringing oxygenated water or air into contact with a gas-exchange surface is:
A. Respiration
B. Ventilation
C. Inspiration
D. Resuscitation
E. Exhalation
6. The group of vertebrates that relies on gas exchange across the skin as well as at the lungs to maintain sufficient
blood oxygen levels is:
A. The fishes
B. The reptiles
C. The amphibians
D. The birds
E. The mammals
7. In negative pressure filling, air moves into the lungs when
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A. The volume of the thoracic cavity increases
B. The pressure in the thoracic cavity decreases
C. Air is forced down the trachea by muscular contractions of the mouth and pharynx
D. All of the above
E. A and B only
8. Which of the following factors does not alter the rate of breathing by influencing the respiratory centers of the brain?
A. Carbon dioxide partial pressures in the blood
B. Oxygen partial pressures in the blood
C. Blood pH
D. Blood glucose levels
E. Hydrogen ion concentration in the blood
9. With rare exceptions, the majority of oxygen is transported in the blood of vertebrates
A. By binding to plasma proteins
B. By binding to hemoglobin in erythrocytes
C. As a component of large organic molecules that are broken down by the cells
D. As dissolved gas in the cytoplasm of erythrocytes
E. By binding to myoglobin
10. Which of the following is brought about by infection and involves inflammation and fluid buildup in the lungs?
A. Emphysema
B. Pneumonia
C. Asthma
D. Coughing
E. Sneezing
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1. Explain the underlying mechanism in the opening and closing of a stomate.
2. How does oxygen get to the different parts of the plant?
3. Explain countercurrent flow. How does it help make the fish gill the most efficient respiratory organ?
4. Compare the avian and mammalian lungs in terms of structure and respiratory function.
5. Discuss the special adaptations for life at high altitudes.
6. In what form does most of the carbon dioxide travel in the blood? How and where is this molecule produced?
7. How does the brain control inspiration and expiration? How do peripheral and central chemoreceptors influence the
brain’s control of breathing?
8. What respiratory problems can arise from habitual smoking? Explain how these problems may develop due to
1. (POOR
(POOR)) – disorganized drawing with many errors in the labeling of cell layers in the root cross sections and in the
tracing of the apoplast and symplast routes.
(SATISFACTORY)) – acceptable drawing with some errors in the labeling of cell layers in the root cross sections and
in the tracing of the apoplast and symplast routes.
3. (VERY GOOD) – clear drawing with minimal error in the labeling of cell layers in the root cross sections and in the
tracing of the apoplast and symplast routes.
(EXCELLENT)) – clear drawing with correct labels for the cell layers in the root cross sections; and accurate tracing
of the apoplast and symplast routes.
1. (POOR)
(POOR) – 74% and below
2. (FAIR
(FAIR)) – 75 TO 79% correct
(SATISFACTORY)) – 80 to 84% correct
4. (VERY
SATISFACTORY) – 85 to 89% correct
(OUTSTANDING)) – 90 to 100% correct
Download Teaching Guide Book 0 mins
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