Lesson 6
Understanding Plant Physiology
Next Generation Science/Common Core Standards Addressed!
 HS‐LS1‐3. Plan and conduct an investigation to provide
evidence that feedback mechanisms maintain homeostasis.
[Clarification Statement: Examples of investigations could
include heart rate response to exercise, stomate response to
moisture and temperature, and root development in response
to water levels.] [Assessment Boundary: Assessment does not
include the cellular processes involved in the feedback
mechanism.]
 HS‐LS1‐5. Use a model to illustrate how photosynthesis
transforms light energy into stored chemical energy.
[Clarification Statement: Emphasis is on illustrating inputs and
outputs of matter and the transfer and transformation of
energy in photosynthesis by plants and other
photosynthesizing organisms. Examples of models could
include diagrams, chemical equations, and conceptual
models.] [Assessment Boundary: Assessment does not include
specific biochemical steps.]
Bell Work
Describe cellular respiration.
When these things are combined,
what is produced as a result?
What are the ingredients needed
for photosynthesis to take place?
Why are photosynthesis and
Respiration important to humans?
Here is a glass of water. How
can I add carbon dioxide to it?
Vocabulary
Cellular respiration
Chlorophyll
Chloroplast
Mitochondria
Photosynthesis
Transpiration
How Does Photosynthesis Work?
 Photosynthesis is the process by which a
plant turns the light energy from the sun
into chemical energy in the form of sugar
(glucose)
 It is a complex series of chemical reactions
that happens within the plant cells
 It is the original source of all important
fuels including oil, coal, wood, and natural
gas
 It is also the source of all foods
Most cells that carry on
photosynthesis have organelles
called chloroplasts
They contain a pigment known as
chlorophyll
Chlorophylls are usually green
because they absorb the red and blue
wavelengths of light and reflect the
green wavelengths
The pigment is responsible for
trapping the sunlight for
photosynthesis to occur
In photosynthesis, carbon dioxide and
water are the raw materials
They are used to form glucose and
oxygen
The formula for photosynthesis is:
6 CO2 + 12 H2O
O2
Carbon dioxide
Water
C6H12O6 + 6 H2O + 6
Glucose
Water
Oxygen
Photosynthesis continued
Notice that water is both a raw material and a
product
This is because there are two steps involved in
photosynthesis: the light and dark reactions
Any excess water is removed through the stomata
of the leaves by a process called transpiration
In the light reaction, light energy is converted
to chemical energy and water is split into
hydrogen and oxygen atoms
In the dark reaction, carbohydrates are
formed from carbon dioxide and hydrogen
atoms
Both processes occur within the chloroplast
Structure of a Chloroplast
 A chloroplast contains
stacks of membranes
called grana which
store the chlorophyll
 Surrounding the grana
are regions called
stroma
 The light reaction
takes place in the
grana while the dark
reaction occurs in the
stroma
Chloroplast
Factors that Affect Photosynthesis
Photosynthesis is affected by six
factors:
 1. Light quality – the best type of light should provide
wavelengths in the blue and red range; This range is
what works best with chlorophyll
 2. Light intensity – some plants need more light, others
less; generally, the brighter the light, the more efficient
the photosynthesis
 3. Light duration – the longer the day, the more
photosynthesis takes place; Some plants need more
light and some less
4. Carbon dioxide concentration –
usually an increase in the amount
of carbon dioxide in the
atmosphere can double the rate of
photosynthesis
5. Temperature – the higher the
temperatures the more
photosynthesis occurs; Of course
excessive temperatures will
decrease the rate too
6. Water availability – plants
lacking water will close their
stomata and decrease
photosynthetic activity
How Does Respiration Work?
 In many ways,
cellular
respiration is
the opposite of
photosynthesis
:
Photosynthesis
Respiration
Produces food
Uses food for
energy
Occurs in cells that Occurs in all cells
contain
chloroplasts
Oxygen released
 Comparison of Water used
Photosynthesis Carbon dioxide
& Respiration
used
Occurs in sunlight
Oxygen used
Water produced
Carbon dioxide
produced
Occurs in dark &
light
In respiration, plants start with
glucose which is broken down in
the presence of oxygen
Water and carbon dioxide are
released along with all the
energy within the bonds
This is the formula for
respiration:
C6H12O6 + 6 H2O + 6 O2 6 CO2 + 12 H2O
Glucose
Water
Oxygen Carbon dioxide Water
Factors Affecting Respiration
Respiration occurs in
structures called
mitochondria and are
affected by five factors:
1. Temperature – as
temperature increases, so
does the respiration rate
2. Oxygen concentration –
low concentrations of
oxygen will decrease the
respiration rate
Mitochondrion
3. Soil Conditions – compacted or
waterlogged soils exclude air, and therefore
oxygen; Respiration is inhibited under these
conditions
4. Light – in low light, photosynthesis is
reduced and therefore the rate of respiration
is reduced because of a decrease in available
glucose
5. Growth rate & metabolic activity – when
plants reach their full development, the rate
of photosynthesis and respiration have
reached their maximum; Age and availability
of glucose affect respiration
How Are Photosynthesis &
Respiration Important to
Humans?
 Photosynthesis and respiration are two of the
most important chemical reactions to human
beings
 All of our food and nutrition comes either directly of
indirectly from photosynthesis
 All of our heat and electricity comes either directly
or indirectly from by-products of photosynthesis in
plants
 All of the oxygen we breathe comes from the
photosynthesis reactions
 Transpiration puts thousands of tons of water into
the air, cooling our environment and encouraging
rainfall.
Summary
 What is photosynthesis?
 What are the two raw materials needed for
photosynthesis? What are the products?
 Where in a cell does photosynthesis take
place?
 Can humans produce food?Why or why
not?
 Where do the light and dark reactions
occur in a chloroplast?
 What is respiration?
Summary Continued
What are the raw materials needed for
respiration? What are the products?
Where in a cell does respiration occur?
How is respiration the opposite of
photosynthesis?
Why are these two processes necessary
for humans?
What factors affect the rate of
photosynthesis and respiration?
The End!