Download factors in photosynthesis

photosynthesis
A summary of what you should
know
Revision of third form photosynthesis
Photosynthesis
What happens to the glucose formed in photosynthesis?
PHOTOSYNTHESIS
CELLULOSE
LIPIDS
GLUCOSE
respiration
ATP
Required to make plant cell walls. It is made
of 100s of glucose molecules bonded
together.
Glucose is chemically converted to fatty acids and
glycerol to make lipids, which are needed to make
plant cell membranes and seed storage oils.
STARCH
Is used by roots and leaves to store excess
glucose in an osmotically inactive form. It is
made of 100s of glucose molecules.
PROTEINS
Using nitrate ions absorbed by plant roots,
glucose is converted first to amino acids
then to protein.
CARBON
DIOXIDE AND
WATER
The carbon dioxide can be used again in
photosynthesis or may diffuse out of the
leaf via the stomata
Factors necessary for photosynthesis
Factors affecting the rate of photosynthesis
The effect of light intensity
on photosynthetic rate
Light
intensity
limiting.
The main external factors affecting
the rate of photosynthesis are:
The rate is limited by another
factor such as carbon dioxide
concentration
carbon dioxide
light intensity
Increasing light intensity increases the energy
entering chlorophyll and thus the amount of ATP
and produced to drive photosynthesis
temperature
light wavelength
Notice how increasing the light intensity
beyond a certain point causes no further
increase in rate of photosynthesis.
Something else is now ‘holding the reaction
back’. Light is no longer the limiting factor.
Photosynthetic sugar production is catalysed by
enzymes. If the temperature is raised too high
the enzymes denature and photosynthesis stops.
Rate of photosynthesis
light intensity
The effect of
temperature on
photosynthetic
rate
Heat energy increases
kinetic energy. More
collisions, with more force,
thus the rate increases
Optimum
Enzyme protein
denatures. They lose
their catalytic ability to
catalyse
photosynthesis
temperature (degrees C)
Factors necessary for photosynthesis
Limiting factors
At low light intensities increasing the temperature has little
effect on the rate of photosynthesis.
Rate of photosynthesis
The effect of temperature
and light
At high light intensities the rate of photosynthesis increases
much more rapidly over the same temperature range.
High light intensity
This is an example of
THE LAW OF LIMITING FACTORS If a
process is influenced by more than 1
factor, the rate will be limited by the
factor nearest its lowest value
Low light intensity
5
10
15
20
temperature (degrees C)
25
25O C and 0.4% CO2
Here is another example of
the law of limiting factors
What 3 factors are limiting in regions A, B, C
respectively?
ANSWERS:
At
A
CO2 limiting
At
B
temperature limiting
At
C
light limiting
Rate of photosynthesis
0
the law of limiting factors.
C
25O C and 0.04% CO2
A
B
15O C and 0.04% CO2
Light intensity
Plant mineral requirements
Plants require small quantities of minerals for healthy growth
Minerals are absorbed by the root hairs, either by diffusion or active
transport, depending on their concentration in the soil – see next topic.
The most important minerals for plants are:
Nitrogen usually as nitrate, nitrite or ammonium ions, NO3- , NO2-, NH4+
Phosphorous often in the form of phosphate ions, PO4- ions.
Potassium in the form of K+ ions.
Magnesium in the form of Mg2+ ions
Iron in the form of Fe2+ ions
Mineral requirements of plants
NO3
PO4-
K+
-
Nitrogen (nitrate ions: Needed
to make proteins and
chlorophyll
Potassium: Helps enzymes in
photosynthesis and respiration
Phosphorous: Required for
photosynthesis and respiration
Deficiency: Poor growth and
leaf yellowing
Deficiency: Yellow leaves with
dead spots
Deficiency: Poor root growth
and purple younger leaves
Mg+
REMEMBER
THESE ARE
REQUIRED
IN IONIC
FORM!
Magnesium is required as part
of the chlorophyll molecule
Deficiency: Yellowing of
leaves and poor growth
Fe2+
Iron is required by the enzymes
that make chlorophyll
Deficiency: Leaf yellowing
WHAT YOU SHOULD
KNOW AT THE END
OF THIS UNIT
The photosynthesis word equation. That light energy is absorbed by chlorophyll in
chloroplasts and used to make sugar from carbon dioxide. Oxygen is a bye-product.
The rate of photosynthesis may by limited by: low temperature, shortage of carbon
dioxide, shortage of light.
The glucose produced in photosynthesis may be converted to insoluble starch. Start does
not attract water by osmosis.
Plant cells use some of the photosynthetic glucose for respiration. In addition, nitrates,
absorbed by the roots, are needed for healthy growth.
Any 1 of light, temperature and carbon dioxide will be limiting the rate of photosynthesis at
any particular time.
The energy from respiration is used to build smaller molecules into larger ones, including:
sugars into starch, sugars into cellulose for cell walls, sugars, nitrates and other nutrients
into amino acids and then proteins. Sugars into lipids for seed storage.
For healthy growth plants need mineral ions including: nitrate for protein synthesis,
phosphate and potassium for photosynthesis and respiration.
Symptoms shown by mineral ion-deficient plants include:
Stunted growth and yellow older leaves if nitrate ions are deficient
Poor root growth and purple younger leaves if phosphate ions are deficient
Yellow leaves with dead spots if potassium ions are deficient.