Rate of photosynthesis

How can it be measured?

By a photosynthometer. Volume of oxygen produced in a given time period is collected and measured. It can used to investigate the effects of light intensity/wavelegth, carbon dioxide conc, temp

How is the O2 volume collected?

In the capillary tube and can be drawn alongside the scale by means of the syringe, and the length of the bubble measured. Length is proportional to volume

How will the results be valid?

All variables other than the independent variable are kept constant, the plant is given time to adjust to the new condition, three measurements at least with the mean calculated

How to keep temp/light intensity and CO2 conc constant?

Temp = heat filter

Light = LED bulb

CO2 conc = sodium hydrogen carbonate

What are the optimum conditions or photosynthesis in a plant?

High light intensity, temp around 25 degrees, CO2 conc of 0.4%

Why do graphs measuring the rate of photosynthesis level off?

Another factor limits the rate

What can affect CO2 conc in photosynthesis?

Carbon fixation = less or more CO2 entering Calvin cycle

How does temp affect rate of photosynthesis?

Increases as the temp increases, as the substrate molecules have sufficient energy for more frequent successful collisions. Decreases rapidly at 40 degrees as enzymes denature

Why is 0.4% the optimum CO2 conc for photosynthesis?

Above 0.4% stomata close

Why does the rate of photosynthesis double for every 10 degree rise in temp between 0 and 25 degrees?

Enzymes in calvin cycle - increase in their kinetic energy. Speeds up the LIS. Q10 coefficient doubles rate

Above 25 degrees why does the rate of photosynthesis level off then fall?

Enzymes begin to denature, transpiration increases so more water loss leads to stomata closing and less CO2 for photosynthesis, photorespiration can occur (rubisco also catalyses addition of oxygen - competition for rubisco active site between O2 and CO2 onto RuBP)

What happens as light intensity decreases?

Less products from LDR (ATP and NADPH). Less GP converted to TP and RuBP. High levels of GP and lower levels of TP and RuBP

What happens at low CO2 levels?

Less RuBP is converted to GP and TP. Therefore, there is an increase in RuBP but a decrease in GP and TP

What is the compensation point?

Where photosynthesis rate and respiration rate match exactly. CO2 is used up at exactly the same rate it is produced

What is a limiting factor?

Factor that determines the limit at sub-optimal levels

How ca you measure the effect of CO2 conc on the rate of photosynthesis?

Measure O2 production, oxygen produced is collected in a stated time

How can you get a more accurate measure of the rate of photosynthesis?

Use a colorimeter, measure the time taken to reach an absorbance value