1. A summary of what you should know
photosynthesis
A summary of what you should know

2. PHOTOSYNTHESIS Check out what you remember. Some could
Revision of third form photosynthesis
Check out what
you remember.
Some could
come up in the GCSE

3. CARBON DIOXIDE AND WATER
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.
STARCH
CELLULOSE
LIPIDS
PROTEINS
CARBON DIOXIDE AND WATER
PHOTOSYNTHESIS
GLUCOSE
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.
respiration
ATP
The carbon dioxide can be used again in photosynthesis or may diffuse out of the leaf via the stomata

4. temperature (degrees C)
PHOTOSYNTHESIS
Factors necessary for photosynthesis
Factors affecting the rate of photosynthesis
The effect of light intensity on photosynthetic rate
The main external factors affecting the rate of photosynthesis are:
The rate is limited by another factor such as carbon dioxide concentration
light wavelength
light intensity
temperature
carbon dioxide
Light intensity limiting.
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
Optimum
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)

5. temperature (degrees C) Rate of 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
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 A B C
ANSWERS:
At A CO2 limiting
15O C and 0.04% CO2
At B temperature limiting
At C light limiting
Light intensity

6. 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:
Nitrogen
Potassium
Magnesium
Iron
Phosphorous
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

7. REMEMBER THESE ARE REQUIRED IN IONIC FORM!
PHOTOSYNTHESIS
Mineral requirements of plants
Nitrogen (nitrate ions: Needed to make proteins and chlorophyll
Deficiency: Poor growth and leaf yellowing
NO3-
Potassium: Helps enzymes in photosynthesis and respiration
Deficiency: Yellow leaves with dead spots K+
Phosphorous: Required for photosynthesis and respiration
Deficiency: Poor root growth and purple younger leaves
PO4-
Magnesium is required as part of the chlorophyll molecule
Deficiency: Yellowing of leaves and poor growth
Mg+
Iron is required by the enzymes that make chlorophyll
Deficiency: Leaf yellowing
Fe2+
REMEMBER THESE ARE REQUIRED IN IONIC FORM!

8. WHAT YOU SHOULD KNOW AT THE END OF THIS UNIT
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.