photosynthesis

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photosynthesis

• A summary of what you should know
• WITH THANKS TO LRGS

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PHOTOSYNTHESIS
Revision of third form photosynthesis
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PHOTOSYNTHESIS
Photosynthesis
What happens to the glucose formed in
photosynthesis?
Required to make plant cell walls. It is made of
100s of glucose molecules bonded together.
PHOTOSYNTHESIS
Glucose is chemically converted to fatty acids
and glycerol to make lipids, which are needed to
make plant cell membranes and seed storage oils.
Is used by roots and leaves to store excess
glucose in an osmotically inactive form. It is
made of 100s of glucose molecules.
Using nitrate ions absorbed by plant roots,
glucose is converted first to amino acids then to
protein.
The carbon dioxide can be used again in
photosynthesis or may diffuse out of the leaf via
the stomata
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PHOTOSYNTHESIS
Factors necessary for photosynthesis
Factors affecting the rate of photosynthesis
The main external factors affecting the rate of
photosynthesis are
The effect of light intensity on photosynthetic
rate
Increasing light intensity increases the energy
entering chlorophyll and thus the amount of ATP
and produced to drive photosynthesis
light intensity
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.
The effect of temperature on photosynthetic rate
Rate of photosynthesis
Enzyme protein denatures. They lose their
catalytic ability to catalyse photosynthesis
Heat energy increases kinetic energy. More
collisions, with more force, thus the rate
increases
Photosynthetic sugar production is catalysed by
enzymes. If the temperature is raised too high
the enzymes denature and photosynthesis stops.
temperature (degrees C)
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PHOTOSYNTHESIS
Factors necessary for photosynthesis
Limiting factors
At low light intensities increasing the
temperature has little effect on the 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.
Rate of photosynthesis
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
0 5 10
15 20 25
temperature (degrees C)
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?
Rate of photosynthesis
25O C and 0.04 CO2
ANSWERS
At A CO2 limiting
15O C and 0.04 CO2
At B temperature limiting
At C light limiting
Light intensity
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PHOTOSYNTHESIS
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
usually as nitrate, nitrite or ammonium ions,
NO3- , NO2-, NH4
often in the form of phosphate ions, PO4- ions.
in the form of K ions.
in the form of Mg2 ions
in the form of Fe2 ions
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PHOTOSYNTHESIS
Mineral requirements of plants
REMEMBER THESE ARE REQUIRED IN IONIC FORM!
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PHOTOSYNTHESIS
WHAT YOU SHOULD KNOW AT THE END OF THIS UNIT
REVIEW
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.