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What are the three ideal conditions for photosynthesis to occur?

  • High light intensity at a certain wavelengtj
  • Temperature around 25 degrees
  • Carbon dioxide at 0.4 %


Why would you need high light intensity of a certain wavelength?

  • Light helps to provide the energy for LDR - higher the intensity of light , more energy it provides
  • Only certain wavelength are used for photosynthesis
  • Only photosynthetic pigments (chlorophyll a and chlorophyll b and carotene) only absorb red and blye light in sunlight ) green light is refelected - they look green


Why would you need temperature around 25 degrees?

  • Photosynthesis involes an enzyme(e.g ATP synthase and rubsico)
  • If temperature falls, below 10 degrees, enzymes become inactive.
  • If temperature is above 45 degrees they may start to denature


Why is carbon dioxide at 0.4%?

  • Carbon dioxide makes up 0.04% of gases in atmosphere
  • Increasing it to 0.4%- higher rate of photosynthesis
  • (any higher, stomata start to close)


Effect of water on photosynthesis

  • They need a constant supply of water
  • Too little -photosynthesis has to stop
  • Too much -becomes waterlogged (reducing uptake of magnesium and minerals -need to make chlorophyll


What are the limiting factors of photosynthesis?

  • Carbon dioxide
  • Light
  • Temperature
  • (Water doesn't have much effect)


What is a limiting factor in a sunny day?

Carbon dioxide


What is a limiting factor at night?

Light  intensity


Whats happening at points A and B in graph of light intensity?

  • Between points A and B, rate of photosynthesis is limited by light intensity
  • As light intensity increases, rate of photosynthesis increases
  • Point B is satruation point
  • This means increasing light intensity more makes no difference, graph levels off
  • Limting factor is carbon dioxide and temperature


What is happening at both lines for temperature?

  • Both graphs level off when light intensity is no longer a limiting  factor
  • Graph at 25 degrees levels off at a higher point than one at 15 degrees
  •  Showing 15 degrees is a limiting factor


What is happening at both of the lines?

  • Both graphs level off when light intensity is no longer a limiting factor
  • At 0.4% CO2 levels off at a higher point than 0.04% 
  • This shows that 0.04% is a limiting factor

(Temp isn't a limiting factor since it is the same)


What happens as light intensity increases?

More chlorophyll molecules are excited in LDR

Leading to a greater production NADPH and ATP

Products used in LIR to produce more glucose

Leading to a faster growth?


What happens when light intensity increases above the limit?

It will damage chloroplasts and cause cells to overheat


How to prevent high light intensity?

Have greenhouse with white-wash panes in summer

this cuts down light intensity


What happens as carbon dioxide concentration increases?

Increases the rate of carboxylation of RuBP increases

GP , TP and glucose are made at a faster rate leading to a faster growth


What happens when carbon dioxide concentration increases above 0.4%?

Leads to stomata closing

reducing the uptake of carbon dioxide by the plant


What happens as temperature increases?

Enzyme and substrates involed in LIR gain more kinetic energy

Leading to more successful collisions and faster formation of enzyme-subtrate complex

Rate of conversion of RuBP to GP to TP increases

Glucose made at a faster rate

Leading to faster growth


What happens to temperature increasing with respiration?

It increases the rate of respiration as well

Point at which the two rates are the same is called conpensation point 

Optimum temperatue for photosynthesis is lower than optiumum temperature of respiration


What happens when rate of respiratione exceed the rate of photosynthesis?

Plant is using ATP faster than it can make it

Growth rate is reduced

At high temperature , enzyme denature and increase rate of transpiration causing plant to wilt and close stomata (reduce uptake of CO2)


How do farmers keep balance?

  • Heating greenhouse in spring using oil-fried stoves will increase the temperature and carbon dioxide concentration in greenhouse


What is the problem of plants in the winter?

Light intensity is a limiting factor

Plants respire more than they can photosynthesise

Farmers lose money


How to manage carbon dioxide concentration?

Carbon dioxide is added to the air

e.g by burning a small amount of propane in a carbon dioxide generator


How to manage light?

  • Light can get through the glass
  • Lamps can provide light at night-time


How to manage temperature?

  • Glasshouses can trap heat energy from the sunlight which warms the air
  • Heaters and cooling systems can be used to keep a constant optimum temperature
  • Air circulation systems make sure the temperature is even throughout the greenhouse


Exam Qs Example 1

What is shown in this graph?

  • With greenhouse
  • Adde carbon dioxide concentration , plant growth was faster (line is steeper) and aervage the plants were larger than 8 weeks than they were in controlm (30 only to 15 cm with control)
  • More carbon dioxide usesd to produce glucose by photosynthesis
  • More carbon dioxide more glucose meaning they can respire more
  • More ATP for DNA Replication , cell division and protein synthesis - cell growth


Exam Qs 

Example 2

  • At the start of the graph
  • Greater lighter intensity the greater the plant growth
  • At 200 micrmoles of light at the bottom graph flattens out showing carbon dioxide or temp is limiting
  • At 250 micromoles graph flattens out
  • The difference of graph could be that wood fire increases the temp more than electric heater because its increasing carbon con than electric heatr doesn't release carbon dioxide