Download Nutrition and Gas Exchange

YUMMY!!! Sigh, I wish
it’s time for dinner
already. I am so
hungry! Hmmm, I
wonder what we are
having tonight!?
WOW!!! What a
pretty
flower!!!!!
Hey! I wonder if
plants need to eat
too!? If they do,
then how do they
get their food?
Of course we eat!!! And we
are able to make our own
food. That is why we are
called AUTOTROPHS! Hmmm,
I thought you learned all
about this already!!! Do you
remember how we can make
our own food???
Things needed:
• Light
• Carbon dioxide
• Water
• Chlorophyll
Things produced:
• Carbohydrates
(which can be used
to form fats and
proteins)
• Oxygen
Photosynthesis
• As one can see, plants need to obtain
carbon dioxide in order to carry out
photosynthesis
• They also release oxygen as a by-product
• The process by which plants exchange
oxygen and carbon dioxide is called
___________
Gas Exchange
• Plants exchange gases by diffusion
• Where does gas exchange occur in plants?
Internal Structure of Leaf
Gas Exchange
• Gas exchange mainly occurs in the leaves
• How do gases diffuse into and out of the
leaves?
Stomata
Stomata
Gas Exchange
• Gas exchange can also take place in the
stems and roots
• Herbaceous plants – diffusion through
stomata on stem surface
• Woody plants - stomata when young
- lenticels when matured
Lenticels
• Gases cannot penetrate the protective
cork layer
• Lenticels are loosely-packed masses of
cells in the bark of a woody plant, visible
on the surface of a stem as raised spots,
through which gas exchange occurs
Lenticels
Lenticels
Gas Exchange in Roots
• The epidermis is usually just one cell
thick. Root epidermal cells lack a thick
cuticle which would interfere with water
uptake. Moreover, there is no stomata
present as the cell membrane is very thin
and therefore gases can directly diffuse
into and out of the cells
Adaptation of Leaves
to Photosynthesis
Adaptation of Leaves
The leaf is thin
Decreases diffusion
distance for gases
Adaptation of Leaves
Numerous stomata
on lower epidermis
Allows rapid
gaseous exchange
with the
atmosphere
Adaptation of Leaves
Guard cells control
the size of stomata
In presence of light,
stomata open
widely to allow the
diffusion of carbon
dioxide and oxygen
Guard Cells
• When turgor develops
within the two guard
cells, the outer walls
bulge out and force the
inner walls into a
crescent shape. This
opens the stomata.
When the guard cells
lose turgor, the elastic
inner walls regain their
original shape and the
stomata closes
Adaptation of Leaves
Spongy mesophyll
cells are loosely
packed with numerous
large air spaces
Allows rapid diffusion
and free circulation of
gases throughout the
leaf
Adaptation of Leaves
Most cells in the leaves
are surrounded by a layer
of water
Allows gases to dissolve
and diffuse into and out of
the cells
Gas Exchange
Carbon
Dioxide
Oxygen
Oxygen
Carbon
Dioxide
Photosynthesis
Respiration
What will be the net gas
exchange between the leaf
and its surrounding air?
Rate of Gas Exchange
The rate of gas exchange is different throughout
the day due to a change in light intensity
What is going on here?
Light Intensity
• Night – plants carry out RESPIRATION and
release CARBON DIOXIDE
Light Intensity
Light Intensity
• Night – plants carry out RESPIRATION and
release CARBON DIOXIDE
• Early morning – PHOTOSYNTHESIS begins to
take place as light intensity increases
Rate of photosynthesis < Rate of respiration
Net release of CARBON DIOXIDE
Light Intensity
Light Intensity
• Around 6:00 a.m. – light intensity increases
even more
Rate of photosynthesis = Rate of respiration
Release of CO2 = Uptake of CO2
That is, there is NO net gas exchange
This is referred to as the COMPENSATION POINT
Light Intensity
Light Intensity
• Afternoon – light intensity further increases
Rate of photosynthesis > Rate of respiration
Net uptake of CARBON DIOXIDE
Net uptake of carbon dioxide reaches a
maximum in early afternoon
Light Intensity
Light Intensity
• Evening – light intensity begins to decrease
At a certain time period, there will again be a
net release of CARBON DIOXIDE when plants
only carry out RESPIRATION at night
Light Intensity
Similarly, we can study
the relationship between
light intensity and the
exchange of OXYGEN
Critical Thinking 8.1 (p. 11)
Question
1. Does a plant release or absorb oxygen at night?
Ans: A plant absorbs oxygen at night
Critical Thinking 8.1 (p. 11)
Question
2. When the light intensity gradually increases in
the morning, will there be any changes in the
exchange of oxygen? Why?
Ans: The rate of oxygen uptake would gradually
decrease and the rate of oxygen release would
gradually increase. It is because photosynthesis
begins to occur when light intensity gradually
increases in the morning
Critical Thinking 8.1 (p. 11)
Questions
3. Why is there a compensation point?
Ans: Compensation point refers to the light
intensity at which there is no net gas exchange
4. What will happen to the exchange of oxygen
when the light intensity further increases?
Ans: The rate of oxygen release would
increase as light intensity increases
Critical Thinking 8.1 (p. 11)
Question
5. Draw a graph to show the relationship
between light intensity and the exchange of
oxygen of a plant.
Critical Thinking 8.1 (p. 11)
INVESTIGATION #1
Studying the effect of light intensity
on gas exchange in leaves using
hydrogencarbonate indicator
Introduction to Investigation
• In this investigation, you will study the effect of
light intensity on gas exchange in leaves
• Green leaves will be put into different light
intensities, and the level of carbon dioxide will
be estimated by using hydrogencarbonate
indicator solution
• Note: Increase in CO2 – Orange to Yellow
Decrease in CO2 – Orange to Purple
Procedure
Please refer to pages 7 and 8 in your textbook
A
B
C
D
Results Table
Colour of hydrogencarbonate
indicator solution after one hour
Tube A
Tube B
Tube C
Tube D
INVESTIGATION #2
Studying the effect of light
intensity on the gas exchange
of a plant using a data logger
Introduction to Investigation
• In this investigation, you will study the effect of
light intensity on the gas exchange of a water
plant using a data logger
• Gas exchange in plants is affected by both the
rates of respiration and photosynthesis
• You can measure the rate of oxygen released by a
water plant by measuring the change in pressure
in an enclosed set-up
• A data logger and a low-pressure sensor
can be used
Procedure
Please refer to pages 8 and 9 in your textbook
Results Table
Distance between
the lamp and the
conical flask (cm)
20
50
80
110
Initial
pressure
Final
pressure
Change
in pressure
per minute
Discussion
1. What is the purpose of putting a water trough
between the conical flask and the lamp?
Ans: It is used to reduce the heating effect
of the lamp. The result obtained is mainly
due to the influence of the light intensity
Discussion
2. What is the purpose of using dilute sodium
hydrogencarbonate solution in the conical
flask?
Ans: It provides carbon dioxide for the
plant to carry out photosynthesis
Discussion
3. What is the relationship between the light
intensity and the distance between the
conical flask and the table lamp?
Ans: The shorter the distance between the
lamp and the conical flask, the stronger is
the light intensity
Discussion
4. What is the relationship between the
pressure in the conical flask and the light
intensity in this experiment?
Ans: The stronger the light intensity, the
faster is the increase in pressure detected
in the conical flask. The reason is that the
rate of photosynthesis increases with light
intensity, and the rate of oxygen release
also increases
Photosynthesis
Oxygen
Synthesis of Fats
carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
fatty acids
glycerol
Combine to form fats and oils for construction
of cell membranes and as a food storage
Synthesis of Proteins
carbon dioxide and water
photosynthesis
carbohydrates (e.g. glucose)
mineral salts from soil
(e.g. NO3-, SO42-)
amino acids
join together to become
protein molecules
Mineral Requirements in Plants
• In order to synthesize amino acids (i.e. proteins),
plants must absorb minerals through the roots
• Minerals that are required in large quantities:
nitrogen, phosphorus, potassium, magnesium,
sulphur and calcium
• Other minerals are also required but in a lesser
amount: copper, zinc and iron
• A constant supply of minerals is necessary for the
healthy development of a plant
INVESTIGATION #3
Investigating the effects of minerals
on plant growth using potted plants
Introduction to Investigation
• In this experiment, you will investigate the
effects of different minerals on plant growth
• Some of the plants will be watered with a
solution lacking certain essential minerals, such
as nitrogen and magnesium
• How will a lack of minerals affect the growth of a
plant?
Procedure
Please refer to pages 12 and 13 in your textbook
A
B
C
Discussion
1. Why do we use seedlings of similar size?
Ans: It is because seedlings of different size may differ
in nutrient requirements, making it difficult to compare
the results
2. What differences in appearance of seedlings between
pots A and B can you find at the end of the experiment?
Ans: Seedlings in pot A grow healthy, but those in pot B
show poor growth and small, yellowing of leaves
Discussion
3. What differences in appearance of seedlings between
pots A and C can you find?
Ans: The seedlings in pot A grow healthy, but those in
pot C also show poor growth and yellowing of leaves
4. Why do we use sand but not garden soil in the pots?
Ans: As garden soil may contain different minerals
that plants need, accurate result of the effects of
different minerals on plant growth may not be
obtained
Discussion
5. What conclusion can you make from this experiment?
Ans: Both nitrogen and magnesium are important to
plant growth. Insufficient supply of these minerals
would affect plant development
Note to Experiment
• A solution containing ALL the minerals that are
required by a plant is called a complete
culture solution
• A solution which lacks certain essential
minerals for plant growth is called a deficient
culture solution
• Water cultures can be set up for the
investigation of the effects of minerals on
plant growth
Hi! It’s me again. Hmmm, there
are a few things that I still don’t
understand. You mean, in
addition to carbon dioxide, water
and sunlight, plants also need to
take in…arrr…what are those
things called again?
Oh…MINERALS…in order to grow
healthily? Can someone PLEASE
tell me how are these minerals
important to plants? And what
will happen if the plants do not
take in these minerals?
Nitrogen
• Nitrogen is needed for the synthesis of amino
acid (which are the building blocks for
proteins)
Structure of Amino Acid
Proteins in Plants
Proteins are important for the synthesis of
various plant structures:
• Cell membrane
Cell Membrane
Proteins in Plants
Proteins are important for the synthesis of
various plant structures:
• Cell membrane
• Cytoplasm
Cytoplasm
• Reaction
catalyst
• In various
structures of
the cell
Proteins in Plants
•
•
•
•
Proteins are important for the synthesis of
various plant structures:
Cell membrane
Cytoplasm
Enzyme
Hormone
Plant Hormones
• Chemicals made in one part of the plant that
move to another part of the plant where, at
very low concentrations, they regulate growth
and/or development
• Many different types of hormones
• e.g. promotion of growth, promotion of cell
division, etc.
Other Functions of Nitrogen
• DNA (in making the
nitrogenous base)
• Chlorophyll
Nitrogen in Soil
• Usable forms of nitrogen include nitrate (NO3-)
and ammonium (NH4+)
• Nitrate is the more common form of nitrogen
that is absorbed be plants from soil
• However, most of the nitrogen in soil is NOT
present as nitrate nor as ammonium
• Nitrogen in soil must therefore be converted
to the usable forms by soil microorganisms
Nitrogen Deficiency
A deficiency in nitrogen will result in:
• Small and weak plants
• Stunted growth
• Yellowish leaves (Chlorosis)
Nitrogen Deficiency
Magnesium
• Most of the magnesium in the soil exists in
forms which are not directly available to
plants
• Magnesium is taken up by plants as
magnesium ions (Mg2+)
• Magnesium is an essential component of
chlorophyll
Magnesium in Chlorophyll
Magnesium
• Most of the magnesium in the soil exists in
forms which are not directly available to
plants
• Magnesium is taken up by plants as
magnesium ions (Mg2+)
• Magnesium is an essential component of
chlorophyll
• Magnesium also plays a role in enzymes
activation, protein synthesis, etc.
Magnesium Deficiency
A deficiency in magnesium will result in:
• Chlorosis
• Growth can be reduced also
Magnesium Deficiency
Minerals
Soil
Plant
Minerals in soil are taken up by plants, and can
be released back into the soil by decomposition
Minerals
• Crops take up minerals from soil
• When crops are harvested, minerals are
removed from soil
• Soil can also be washed away by rain water
• If there is a lack of minerals in soil, the
production of crops might be affected
• How can farmers prevent the depletion of
minerals in soil?
Fertilizers
• Fertilizers are added to soil to replace the loss
of minerals
• Two kinds of fertilizers can be used:
- Natural fertilizers
- Chemical fertilizers
Natural Fertilizers
• Organic fertilizers
• Made from organic substances, such as
manure (animal wastes) and dead bodies of
plants and animals
• Organic compounds in it are decomposed by
the bacteria in soil to form mineral salts
Chemical Fertilizers
• “Man-made” fertilizers
• Made with inorganic compounds
• Can result in pollution of the environment,
such as algal bloom
Comparison between natural
and chemical fertilizers
Natural fertilizers
Chemical fertilizers
Contain humus which can
improve soil texture
No humus so cannot improve
soil texture
Humus
• Humus is the organic portion of soil, brown or
black in color, consisting of partially or wholly
decayed plant and animal matter that
provides nutrients to plants and increases the
ability of soil to retain water
Comparison between natural
and chemical fertilizers
Natural fertilizers
Chemical fertilizers
Contain humus which can
improve soil texture
No humus so cannot improve
soil texture
Less soluble in water so less
likely to be washed away
Very soluble in water so more
likely to be washed away
Comparison between natural
and chemical fertilizers
Natural fertilizers
Chemical fertilizers
Much cheaper
Very expensive
Less soluble in water so more
difficult to be absorbed
Very soluble in water so
easier to be absorbed
Time is needed for the
decomposition to complete
before nutrients are available
to plants
More readily to be used by
the plants