Transcript Photosynthesis

Plant Nutrition and
Photosynthesis
Reading Quiz
•Get out a small sheet of paper and write your name at
the top. Answer the following questions in silence
1) What is the chemical process that plants use to make
energy from sunlight? 6CO2+6H2O+sunlightC6H12O6+6O2
2) What reactants do plants need to do this reaction?
CO2, H2O, and sunlight
3) Why are plants green? Only color they don’t absorb well
4)What is the organelle that absorbs sunlight?
Chloroplasts
ATP: The Energy unit of the Cell
Adenine
NH2
N
O
O
-O
O
-
O
O
O
-
O
N
CH2
N
CH
C
N
O
H
Phosphate groups
C
HC
O
O
C
H
H
H
OH
Ribose
OH
ATP (adenosine triphosphate,三磷酸腺苷）
Cell Energy use in Active Transport
• Energy is released from ATP (-30.54 kJ/mol)
– When the 3rd phosphate bond is broken
Trapping Energy from Sunlight
• The process that uses
the sun’s energy to
make simple sugars is
called photosynthesis
• Bases of all
ecosystems on Earth
6 CO2 + 6 H2O + Light energy 
C6H12O6 + 6 O2
Tissue of a Leaf
•Plant tissue:
•Upper epidermis water proof outer
covering; covered with cuticle
•Palisade mesophyll photosynthetic cells;
lots of chloroplasts
•Spongy mesophyll space for CO2/O2
circulation
•Phloem transport solutes
•Xylem transport water and salts
•Lower epidermis stomata for gas
exchange
Where Does CO2 come from?
•Enters leafs through the stomata
Leaf cross section
Vein
Mesophyll
Stomata
Where does H2O come from?
•Absorbed by roots and pulled up to
the leaves by cohesion and adhesion
(transpiration)
CO2
O2
The Problem with Gas Exchange
• How does CO2 and O2
get in and out of a
plant?
– Stromata under the
leaves
• What else can escape
through a stromata
that the plant needs?
– H2 O
• What problems must
plants in dry, hot
climates deal with?
– The plant needs to
take in CO2 and
release O2, but the
open stromata will
also release H2O
H2O out
Where does Light Energy come from?
• Energy from the sun must
be absorbed by pigments,
light absorbing molecules
(chlorophyll)
• Inside a chloroplasts are
thylakoids and inside their
membranes are pigments
• What wavelength of light do
the pigments not absorb?
– Green; reason why
plants are green
Photosynthesis: 2 Reaction Set
1) Light-dependent
reactions chemical
reactions driven by
light energy absorbed
by pigments
2) Light-independent
reactions chemical
reactions that use ATP
and NADPH to create
sugars out of CO2
H2O
CO2
Light
NADP

ADP
+ P
CALVIN
CYCLE
LIGHT REACTIONS
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
The Light-Dependent reactions
Light
Reflected
Light
Chloroplast
Absorbed
light
Granum
Transmitted
light
Pigments- light absorbing molecules
Chlorophyll main light absorbing pigment
Light-dependent reactions use chlorophyll to trap light
energy. This energy produces ATP, NADPH, and O2
The Light-Dependent reactions
Photolysis
H2O
CO2
Light
NADP

ADP
+ P
CALVIN
CYCLE
LIGHT REACTIONS
ATP
NADPH
Chloroplast
O2
[CH2O]
(sugar)
The Light-Independent reactions
Final Numbers
Light-Dependent
Reactions
Use
Produce
Sunlight
NADPH
H2O
ATP
O2
Light-Independent
Reactions
(Calvin Cycle)
Use
Produce
NADPH
RuBP
(recycled to keep
cycle going)
RuBP
ATP
CO2
PGAL (Which
form sugars)
Photosynthetic Rates
Structure of a Leaf
• If photosynthesis occurs
mostly in the leaf, what
factors must be considered
when designing a leaf?
1) Amount of sun exposure
–
More surface area = more
photosynthesis
2) Movement of CO2 and O2
–
Space for exchange
3) Movement of H2O and
products of photosynthesis
–
Water from the roots and
organic molecules to other
areas
Photosynthetic Rates: Light
• What factors could affect
photosynthetic rate?
–
–
–
–
Light intensity
Amount of CO2 / H2O
Too much O2
Temperature
• Increase Light Intensity
= Higher Photosynthetic
rate
– BUT there is a max. limit;
Why?
•
Limit to how fast enzymes
can work
Photosynthetic Rates: Temperature
•
If just temperature is increased,
rates go up Why?
–
•
Why is there only a small increase
in rate?
–
•
Light-dependent stage is limited by
light intensity
What would be create the best
photosynthetic rate?
–
•
More kinetic energy = faster
enzymatic rates
High temperature and high light
intensity
Why do rates drop after raising
the temperature too high?
–
Enzymes (proteins) denature
Photosynthetic Rates: Limiting Factors
•
Even with high temps
and high light intensity,
what factors must be
considered?
–
–
•
Availability of CO2 and
H2O
Too much O2 (limits
enzymes in high conc.)
Limiting factor the
factor least available or
having the strongest
affect on reactions rates
–
Can be light, temperature,
CO2, H2O, or O2
depending on the situation
Limiting Factors Practice
• What is the limiting factor for :
1) Plants in the rain forest?
–
Light intensity; Rain forests have
plenty of rainfall and humidity but
limited space; plants fight for sunlight
2) Plants in the deserts?
–
Water; Deserts have plenty of sun and
open space but very little rain
3) Plants underwater?
–
CO2/Sunlight; Dissolved CO2 harder
to access and sunlight loses strength as
it passes through water
4) Plants in the arctic?
–
Temp/Sunlight; Cold temperatures
and little direct sunlight limits growth
Limiting Factors on Growth
•
We have plant that gets
plenty of sunlight, water,
and CO2. However it seems
to grow very slowly and
looks unhealthy. Why?
–
–
•
Missing other nutrients
Soil does not contain enough
mineral salts
Mineral salt plant
nutrients needed for
growth and repair
–
–
–
Nitrates
Phosphates
Ions like Mg and K
Mineral Salts
•
Nitrates nitrogen based
compounds like NH3, NO2-, and
NO3- which are used to build
amino acids
–
–
–
•
•
•
Most nitrogen is N2 which is
unusable
Nitrogen fixation by bacteria
make nitrates
Animal urine has urea which is
similar to NH3
Phosphates PO43- which is
used to build DNA and RNA
Magnesium ions Mg2+ which
is used to build chlorophyll
Potassium ions K+ which is
used to make stable cells all
over the plant
Getting Mineral Salts
•
Mineral salts must be present in
the soil for plants to grow. How
can we add mineral salts?
1) NPK fertilizers mix of
material containing NPK ions
which are absorbed by the roots
–
Can wash away and cause algae
blooms rapid growth of algae
in lakes that causes the
ecosystem to crash
2) Humus natural
decomposition of material
(compost) that slowly added
mineral salts to soil
–
Farms can never be sure if
enough of each Ion is present in
compost