Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Lesson 10.1
Gas Exchange in Plants
Contents
Introduction
1
Learning Objectives
2
Warm Up
2
Learn about It!
Gas Exchange
General Principles for E cient Gas Exchange
Gas Exchange in Plants
Gas Exchange in Leaves
The Stomata
General Mechanism of Stomatal Function
Role of Potassium Ions in Stomatal Opening
Stomatal Gas Exchange
Role of Abscisic Acid (ABA) in Stomatal Closing
Gas Exchange in Roots and Stems
Root Hairs
Lenticels
4
4
4
6
7
8
8
9
11
12
14
15
16
Key Points
17
Check Your Understanding
19
Challenge Yourself
20
Photo Credits
21
Bibliography
21
Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Lesson 10.1
Gas Exchange in Plants
Introduction
Can you identify the green structures found in the picture above? No, they are not pairs of
beans or peas. They are also neither eyes nor copies of green Mike in the Disney animated
movie, Monsters, Inc. But if you identify them as stomata, then, you are right. The photo
gives a view of a leaf specimen viewed under the microscope, which shows the stomata as
these green bean-like structures surrounding a tiny central hole. Most probably, you have
already seen them in your junior years in high school and learned their roles in plant
maintenance and survival.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
By this time, you already know that living organisms, including plants, obtain the energy
they need from specific biochemical processes. One of these processes is respiration,
which allows animals to acquire the gases they need from the atmosphere. Like animals
and other organisms, plants do “breathe,” but not in the same manner as animals. This
requirement is when stomata come into play. Stomata are essential leaf structures that
allow plants to “breathe.” The question now is, “how?”
To answer the “how” question, you must know the general principles that govern efficient
gas exchange to understand fully how plants and animals respire. Then, as you progress
through the lesson, you will learn the mechanism by which stomata work to allow for plant
respiration. You will also discover other “breathing” structures in plants.
Learning Objectives
In this lesson, you should be able to do the
following:
●
Identify the factors that affect
DepEd Competency
Compare and contrast the process of
gas exchange in plants and animals
(STEM_BIO11/12 -IVa-h-1).
gas exchange efficiency.
●
Discuss the mechanism of
stomatal opening and closing.
●
Identify other plant structures
that facilitate gas exchange.
●
Explain how plants make their
gas exchange efficient.
Warm Up
Leaf in Hot and Cold Water
10 minutes
The leaves of plants are occasionally subjected to changing temperatures. This trend affects
how leaf structures react, thereby affecting plant respiration. In this activity, you will
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
investigate how temperature affects one of the essential leaf structures needed by plants
for “breathing.”
Materials
●
2 transparent glass cups (or beaker, if available)
●
hot water
●
cold water
●
2 leaves of the same plant (preferably of the same size)
Procedure
1. Prepare set-ups of hot and cold water in separate beakers or cups. Make sure they
have the same amount of water.
2. Submerge a leaf into each glass containing water of different temperatures. Refer to
Fig. 10.1.1. as a guide.
Fig. 10.1.1. Leaves submerged in hot and cold water
3. Wait for one minute and observe bubble formation in your set-ups. Notice the part of
the leaf where these bubbles form.
4. Let the beaker with cold water sit for another five minutes. Observe if any bubbles
are forming on the leaf surface.
5. Discuss with the group the implications of your observations. Be ready to share your
ideas in class.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Guide Questions
1. Which temperature allowed for the bubble formation?
2. Which side of the leaf did the bubbles form?
3. What structure of leaf can be associated with the formation of bubbles in the set-up?
How does this relate to the location and number of this structure in the leaf?
4. How does temperature affect the opening and closing of the stomata concerning the
bubble formation on the leaf?
5. Based on the activity, which time of the day (day and night) do you think the stomata
open and close?
Learn about It!
Gas Exchange
All living organisms obtain their energy by metabolizing certain compounds. Metabolism is a
collection of all life-sustaining biochemical processes. One primary biological function that
involves complex reactions is respiration. Respiration releases chemical energy stored in
glucose molecules, and it requires oxygen and releases carbon dioxide as a by-product. The
gas exchange facilitates the movement of these gases across cells and between cells and
the external environment. In the warm-up activity, the bubbles generated under the leaf
showed the flow of gas molecules from the leaf tissue to its environment.
General Principles for Efficient Gas Exchange
Organisms have various means to obtain the gases they need, but the underlying
mechanism that governs gas exchange is diffusion. Diffusion is the movement of molecules
down their concentration gradient, allowing them to move from an area with high
concentration to one with lower concentration. In living organisms, diffusion requires that
the surfaces across which gas exchange occurs must be moist.
The rate of gas exchange by diffusion or how fast molecules move across moist
membranes is primarily affected by four factors discussed in Fick’s law. This law, developed
by Adolf Fick in 1855, describes the main factors that affect the diffusion rate, which
consequently affects the efficiency of gas exchange. Recall from a previous lesson that
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
when the diffusion rate is high, the effectiveness of gas exchange increases, allowing
organisms to generate more energy.
Table 10.1.1. Factors affecting the diffusion rate according to Fick’s law
Factor
Relationship
with Diffusion
Description
Surface Area of
the Membrane
Direct
A greater membrane surface area can
accommodate more molecules for diffusion,
which increases the diffusion rate.
Concentration
Gradient
Direct
The concentration gradient occurs when a
difference in the concentration of molecules is
present between two areas. This difference allows
for the downhill movement of molecules. The
larger the difference in concentration (or the
steeper the gradient), the faster the particles
move.
Thickness of the
Membrane
Inverse
A thicker membrane reduces the diffusion rate,
whereas a thinner membrane increases the rate
at which the particles diffuse.
Inverse
Particles that move over a large distance have a
lower diffusion rate than those moving over a
shorter distance.
Distance of
Diffusion
Based on the factors that affect diffusion, when do
we say that the gas exchange in living systems is
e cient?
Different organisms have different cell sizes and structures that affect gas exchange
efficiency. Unicellular organisms do not have any specialized respiratory organs. Because
of their small size, thin cell membrane, and constant contact with their environment,
gases diffuse into their cells through the membrane itself with the short distance covered.
This feature makes the gas exchange more efficient. By contrast, multicellular organisms
are larger, which relatively decreases the diffusion rate. However, if they are thin and flat
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
(regardless of size), their body’s outer surface is sufficient to make gas exchange efficient.
Large multicellular organisms need to have specialized respiratory organs to improve the
gas exchange efficiency in their bodies. Thus, the effectiveness of gas exchange increases
with a large surface area for diffusion, high concentration gradient, thin membrane through
which gases move, and short distance over which diffusion occurs.
What makes the gas exchange in plants different
from the gas exchange in other organisms?
Gas Exchange in Plants
In the strictest sense, plants do not breathe because breathing is the mechanical inhalation
and exhalation of gases through a respiratory organ. It is just an analogy used to say that
gas exchange occurs in plants. They absorb carbon dioxide for photosynthesis and release
oxygen as its by-product. It may seem that oxygen is a waste product of plants, but they also
need oxygen to survive. Unlike animals and humans, plants do not have specialized
respiratory organs, like lungs and gills, that allow them to breathe. Instead, gas exchange in
plants occurs not only in one organ—it happens in their leaves through stomata, stems
through lenticels, and roots through root hairs.
Stomata in leaves (left), lenticels in stems (center), and root hairs (right) are structures in
plants that facilitate gas exchange.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Gas Exchange in Leaves
The leaves of plants have a very vital role in carbohydrate synthesis and utilization through
photosynthesis and respiration. Since these two processes require gases, leaf structure is
well adapted for gas exchange. Its lower epidermis has two features that allow for the flow
of gases: the spongy mesophyll, which is loosely packed to facilitate gas exchange in the
leaf tissue, and stomata (singular, stoma or stomate), which allow for the entry and exit of
gases to and from the leaf. Fig. 10.1.2. shows the location and structure of stomata and
spongy mesophyll. While both leaf structures are essential for gas exchange, we will focus
on the structure and function of stomata related to the mechanism of gas exchange.
Fig. 10.1.2. The spongy mesophyll and stomata are structures that facilitate the gas
exchange in leaves.
How do stomata determine when to open and close
for gas exchange?
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
The Stomata
On the outer layer of the leaf, particularly on the lower epidermis, are microscopic holes
called stomata, which regulate the gas exchange and loss of water by opening and closing.
Each stoma is surrounded by two bean-shaped guard cells that are attached at both ends.
The thick and elastic lateral edges of these cells do not touch each other to allow them to
expand and contract as they regulate the aperture or opening of the stoma. Guard cells are
also bordered by epidermal cells called subsidiary cells. The stoma, a pair of guard cells,
and the subsidiary cells comprise the stomatal complex, as illustrated in Fig. 10.1.3.
Fig. 10.1.3. A stomatal complex consists of a stoma, two guard cells, and several
surrounding subsidiary cells.
General Mechanism of Stomatal Function
Generally, the stoma opens during the day because of two external factors: light and warm
temperature. By contrast, it closes during the night due to the low temperature and absence
of light. However, stomatal opening and closing are primarily determined by how well the
plant is hydrated. The change in the turgor pressure (pressure caused by water) of guard
cells causes them to swell or shrink. Fig. 10.1.4. illustrates the structure of the stoma and
guard cells when the turgidity is high and low.
1. When guard cells take up water through osmosis, their turgidity increases, causing
them to expand while keeping both of their ends attached. Consequently, the
stoma opens.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
2. When guard cells lose water, their turgidity decreases, causing them to shrink and
become flaccid. The inner walls of the guard cells touch each other resulting in the
closing of the stoma.
Fig. 10.1.4. Stoma opens when turgor pressure in guard cells increases and closes when the
pressure decreases.
Role of Potassium Ions in Stomatal Opening
Water does not just move into the guard cells of stomata to regulate the turgor pressure.
Potassium ions (K+) have a critical role in this movement of water. From the plant’s xylem,
water molecules move into the palisade and spongy cell layers of leaves and then into the
subsidiary cells. The following events take place as blue light triggers stomatal opening.
1. Blue light reception. When light strikes the leaf during the daytime, photosynthesis
begins, and the stomatal opening is triggered, specifically by blue light. The guard
cell photoreceptor protein, called phototropin, acts as a blue light receptor.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
2. H+-ATPase activity. Upon exposure to blue light, the H+-exporting ATPase in the
plasma membrane of guard cells becomes activated and pumps out hydrogen ions
(H+), making the guard cells hyperpolarized or more negative.
3. Potassium ion uptake. The hyperpolarization of the membrane of guard cells
results in the uptake of K+ from the surrounding subsidiary cells through potassium
ion channels.
4. Decrease in water potential. The increase in the K+ concentration of guard cells
results in a decrease in their water potential. Water potential is the measure of
water molecules’ tendency to move from a hypotonic solution (more water, less
solute
concentration)
to
a
hypertonic
solution
(less water, higher solute
concentration). Consequently, water molecules stored in the subsidiary cells enter
the guard cells by osmosis.
5. Stomatal opening. The movement of water increases the turgor pressure and
shape of guard cells, resulting in stomatal opening. Fig. 10.1.5. summarizes the
process of stomatal opening.
Fig. 10.1.5. The mechanism of the stomatal opening through blue light reception
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Stomatal Gas Exchange
Once the stomata of leaves are open, the intercellular free spaces around the spongy
mesophyll become in contact with the gases from the environment. The concentration and
pressure of carbon dioxide outside the leaf are higher than within these free spaces.
In comparison, the concentration and pressure of oxygen inside the leaf are greater
than in the environment.
The principle of diffusion dictates that the movement of particles is down their
concentration gradient. Thus, oxygen gas, including water vapor, will exit the leaf, and
carbon dioxide will enter through stomata. This exchange of gases—carbon dioxide in and
oxygen out—primarily occurs during the light-dependent phase of photosynthesis.
However, in respiration, plants also need oxygen. If plants need oxygen, then why do they
release it? Not all of the oxygen produced in photosynthesis is expelled because some are
used for respiration. Also, when sufficient light is present, the rate of photosynthesis
exceeds that of respiration. Thus, they absorb carbon dioxide more than they emit. This
feature results in a net increase in oxygen production and carbon dioxide usage. Therefore,
overall, plants take in carbon dioxide and give out oxygen. This exchange of gases will
continue to occur as long as the stomata of leaves remain open.
Did You Know?
Not all plants open their stomata during the day and close them at
night. Recall from a previous lesson that plants can be classified as
C3, C4, or CAM species according to their carbon fixation pathways.
Most C3 and C4 plants open their stomata during the day and close
them at night. On the other hand, CAM (Crassulacean Acid
Metabolism) plants, as an adaptation to extremely hot conditions,
prevent excessive water loss by closing their stomata during the
day and opening them at night. Cacti are an example of plants that
perform CAM photosynthesis.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Pineapples are another example of a CAM plant.
Role of Abscisic Acid (ABA) in Stomatal Closing
Stomata are light-mediated structures. Without light input, guard cells start to contract,
leading to the closing of stomata. However, stomatal closing does not just happen as the
day turns into night. An inhibitor for the uptake of K+, particularly the abscisic acid (ABA), is
required. Studies have linked the accumulation of ABA and CO2 in guard cells in the dark as
a critical player in stomatal closure.
1. CO2 accumulation. In the absence of light, the rate of respiration becomes relatively
higher, which results in the accumulation of CO2 in the leaf tissue. Water also
becomes available for reaction with CO2 to produce carbonic acid (H2CO3).
2. ABA accumulation. The decrease in the pH (increase in acidity) of the cell due to the
accumulation of H2CO3 activates ABA.
3. Ca2+ release from vacuoles and K+ uptake inhibition. The accumulation of ABA in
guard cells stimulates the release of calcium ions (Ca2+) from internal stores, such as
the vacuoles and endoplasmic reticulum, and by opening Ca2+ channels in the
membrane. Consequently, Ca2+ concentration in the cytosol increases. Also, ABA
inhibits further K+ uptake by the cell.
4. Membrane depolarization. Ca2+ movement outside of the cell results in plasma
membrane depolarization (less negative), which causes K+ and other solutes to
move out of the guard cells and back into the subsidiary cells.
5. Stomatal closure. The water potential inside guard cells increases. The
movement of water back into the subsidiary cells means that guard cells will lose
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
turgidity, shrink, and close the stoma. Fig. 10.1.6. provides a summary of the
mechanism of ABA-mediated stomatal closing.
Fig. 10.1.6. The mechanism of ABA-mediated stomatal closing
As a general rule, the absence of light closes the stomata during the night. Thus,
light-dependent reactions are also not possible. While these structures and reactions are
affected by the absence of light, gas exchange and respiration in plants continue to occur
even at night. You may wonder how gas exchange and respiration occur even when the
stomata are closed. In the dark, most plants close their stomata, but not so entirely that
oxygen cannot diffuse into the leaf. The tiny gap left between the guard cells is big enough
to allow the small gas molecules to pass through. Since the overall rate of photosynthesis
slows down at night and respiration remains fairly constant, there is a net increase in
oxygen uptake and a net increase in carbon dioxide production. Consequently, the release
of carbon dioxide and the uptake of oxygen is relatively greater at night.
Why do you think the stomata need to close and
cannot remain open even when they are vital for
gas exchange?
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Did You Know?
An open stoma not only allows gas exchange, but it also provides
an opening through which harmful pathogens, like bacterial cells,
can invade the leaf. However, guard cells have receptors for
pathogen-associated molecular patterns (PAMPs) that can
detect molecules associated with pathogens. When they recognize
these PAMPs, the abscisic acid (ABA) mediates the stoma’s closure
to prevent pathogens from entering the leaf. This mechanism is
called innate immunity or the immediate prevention of foreign
bodies’ spread throughout the body of an organism. This
mechanism also resembles the innate immune responses in
animals, such as the skin and specific blood cells.
Gas Exchange in Roots and
Stems
The stomata in leaves are the main
structures that allow gas exchange in
plants. However, cellular respiration takes
place
in
all
plant
cells.
Since
the
metabolism and gas transport from leaves
to different plant organs is slower than
that of other organisms, plants need to
have additional structures to help them
efficiently obtain the gases from the
atmosphere.
Young
plants,
including
those with green stems, have stomata
embedded in their stems, whereas woody
plants have their lenticels. Roots also play
a role in gas exchange, specifically via
their root hairs.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Root Hairs
Aside from absorbing water from the soil, the roots also permit the exchange of gases
through its root hair. Root hairs are single-celled extensions of the root epidermis. This
structure gives the root hairs the permeance for water, minerals, and oxygen. Fig. 10.1.7.
illustrates the structure of root hairs.
Through diffusion, oxygen molecules from the spaces between soil particles diffuse into the
thin membrane of the root hairs. These molecules then reach all the cells of the root where
they are utilized for respiration, while the carbon dioxide produced goes out through the
same root hair.
Fig. 10.1.8. Pneumatophores function for gas exchange and are usually found in plants that
thrive in swamps or mangrove communities. Shown in this photo are the pneumatophores
that stick up from the substrate. These roots come from the mangrove tree shown.
In cases where a plant’s habitat becomes flooded or over watered for an extended period,
the plant may die because too much water displaces the gases in the soil, making oxygen
unavailable to the roots. Pneumatophores, modified aerial roots that are specialized for
gas exchange, are well adapted to this condition. They are also called “breathing tubes”
because of their role in gas exchange in a water-logged condition. They are usually found in
hydrophytic plants whose roots are submerged underwater, like those of the mangrove
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
species. The pneumatophores of these hydrophytes (i.e., plants that are completely or
partially submerged in water) tend to protrude themselves above the surface of the water
or water-logged substrate where they can be properly aerated. A sample picture of
pneumatophores is shown in Fig. 10.1.8.
Lenticels
Mature woody stems are impervious to gases and water because they are sheathed with
dead cells covered with a waxy waterproof and airproof substance called suberin. However,
these layers of dead cells are perforated by non-suberized pores called lenticels. Lenticels
(from the Latin word lenticella, small window) are raised porous tissues consisting of cells
with large intercellular spaces in the periderm of plants with woody stems. They are usually
round, oval, or elongated in structure. These porous tissues are filled in with
complementary cells from the meristematic or dividing tissue of the cork cambium during
the secondary growth of woody stems. Fig. 10.1.9. shows an illustrated and actual structure
of lenticels found on a tree.
Lenticels are analogous to stomata as they permit the exchange of vital gases, such as CO2,
O2, and water vapor, between the environment and the internal tissue spaces in stems. But
unlike stomata, lenticels remain open both day and night as they do not have guard cells to
regulate their aperture.
Fig. 10.1.9. The cells that fill in and surround the lenticels (left) and the structure of lenticels
on a tree trunk (right)
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Based on the gross structure of leaves and the
principles governing gas exchange, how do you
think do plants make their gas exchange e cient?
Key Points
__________________________________________________________________________________________
●
Diffusion is the movement of particles from regions of higher concentration to
regions of lower concentration. It is the fundamental mechanism that governs gas
exchange in organisms.
●
Gas exchange in living systems occurs via diffusion across a moist membrane. It
provides a means for the movement of gases between the cells and their
environment.
●
The rate of diffusion affects the efficiency of gas exchange. This rate is
influenced by four main factors described by Fick’s law.
○
The concentration gradient and surface area of the respiratory membrane
have a direct relationship with the diffusion rate. By contrast, membrane
thickness and the distance covered by particles have an inverse
relationship with the diffusion rate.
●
Gas exchange in plants mainly occurs in epidermal openings called stomata. Each
stoma is flanked by guard cells that regulate its aperture.
●
The mechanism of stomatal opening and closing is triggered by blue light and
mediated by potassium ions and abscisic acid. The figure on the next page
summarizes this mechanism.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
●
Once the stomata open, the concentration gradient between the environment and
the leaf will facilitate the movement of gases.
●
While some oxygen molecules generated in photosynthesis are used in
respiration, photosynthesis occurs at a relatively higher rate than respiration. This
event brings a net increase in oxygen production and a net increase in carbon
dioxide usage. Thus, overall, plants take in carbon dioxide and give out oxygen.
●
At night when stomata are closed, a tiny gap is left between the guard cells,
enough for oxygen to diffuse into the leaf.
●
Since all plant cells perform respiration, and the gas transport into other plant
organs is relatively slower than in other organisms, additional structures such as
lenticels and root hairs supplement the gas exchange in plants.
__________________________________________________________________________________________
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Check Your Understanding
A. Identify the correct term being described in each of the following
items.
1. This plant hormone prevents the potassium ion uptake by guard cells.
2. These microscopic openings in the lower epidermis of leaves permit gas exchange.
3. These openings in woody stems are filled with complementary cells from the cork
cambium.
4. This mechanism governing gas exchange involves the movement of particles down
their concentration gradient.
5. This is the measure of the tendency of water molecules to move from areas with
lesser solutes to areas with more solutes.
B. Determine the accuracy of each of the following statements. Write
true if the statement is correct and false if otherwise.
1. Lenticels do not close, unlike the stomata.
2. Blue light triggers the activation of H+-ATPase.
3. The loss of water in guard cells causes them to open the stoma.
4. The abscisic acid is activated by a decrease in the pH level of guard cells.
5. When guard cells take up water, their turgor pressure decreases.
6. The respiration rate during the day is lower than the photosynthetic rate.
7. During the night, the overall production of oxygen and the consumption of carbon
dioxide is relatively higher.
8. When the surface area of a respiratory membrane is smaller, the rate of gas
exchange increases.
9. When the plasma membrane of guard cells becomes depolarized, potassium ions
move out of the guard cells.
10. The increase K+ concentration in the guard cells leads to the movement of water
from the guard cells into the subsidiary cells.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
C. Determine how plants compensate for the following factors and
possible problematic situations to improve the efficiency of their gas
exchange.
1. the limited surface area of the leaves
2. slow transport of gases to plant parts
3. all plant cells respire and need oxygen
4. extreme heat causing too much transpiration
5. stomata being light-mediated and close at night
Challenge Yourself
Answer the following questions concisely.
1. Stomata open during the day to allow for gas exchange and close at night to
conserve water. If the gas exchange can take place both day and night, and
transpiration occurs mostly during the day when the temperature is relatively higher,
then why is it important for plants to open their stomata during the day despite
these conditions?
2. Leaves are essential in gas exchange in plants. However, some plants, such as the
deciduous trees, shed their leaves as the winter approaches. How do they manage
gas exchange and respiration?
3. Although the opening of stomata is essential for the uptake of gases, it also exposes
the plants to water loss through transpiration. Plants in deserts are at risk of losing
more water because of extreme heat. How do you think do they manage the opening
and closing of their stomata?
4. What could possibly happen if the stomata would not close?
5. It is often stated in elementary science books that plants take in carbon dioxide and
give out oxygen, when in fact, they also take in oxygen. When discussing respiration,
it is often explained that only animals and humans respire and that plants do not. Do
you think it is incorrect to not discuss with grade school students that plants also
respire and need oxygen? Provide possible implications for your answer.
10.1. Gas Exchange in Plants
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
Photo Credits
Cuticle of leaf under microscope by Tyanna is licensed under CC BY-SA 4.0 via Wikimedia
Commons.
Hirschfeldia incana roots2 (14445249597) by Harry Rose from South West Rocks, Australia is
licensed under CC BY 2.0 via Wikimedia Commons.
Hazel (Corylus avellana) lenticels by Rosser 1954 is licensed under CC BY-SA 4.0 via
Wikimedia Commons.
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Unit 10: Plant and Animal Organ Systems and Processes: Gas Exchange
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