• ATP (adenosine triosphate) is the universal currency of energy used by all living organisms.
• ATP is a nucleotide formed from ADP and a phosphate group (Pi).
• ATP ? ADP + Pi
• ATP molecules are constantly being cycled in both directions.
• carbon dioxide + water (+ Iight energy) ? glucose + oxygen
• The process of photosynthesis takes place completely in the chloroplasts.
• Chloroplasts contain light-absorbing pigments capable of absorbing light at different wavelengths thereby increasing its absorption spectrum.
• The action spectrum is the rate of photosynthesis with different light wavelengths.
• Chlorophyll arranges itself with other pigments and proteins to form photosystems. Within chloroplasts are two different kinds of photosystem, photosystem I (PSI) and photosystem II (PSII).
• Photosynthesis is, in fact, composed of two major steps: light-dependent and light-independent reactions.
• The light-dependent reaction occurs on the thylakoid membranes and involves electrons being passed down the proton complex chain to create a proton gradient.
• The Calvin cycle (light independent reactions) takes place in the stroma and creates glucose.
• The rate of photosynthesis can be limited by temperature, carbon dioxide concentration, and light intensity.
• Commercial greenhouses can use this information to create the optimum conditions for growing plants.

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TEST IT!

1.

Over a 24 hour period carbon dioxide levels above a forest change.

a) Describe these changes using what you know about photosynthesis.

b) The carbon in carbon dioxide becomes carbon in triose phosphate in the light-dependant reaction. How?

2.

a) Photosynthesis takes place in different parts of the chloroplast.

b) Where exactly in the chloroplast does:

i. the light-independent reaction take place?

ii. the light-dependant reaction take place?

b) Chloroplasts contain chlorophyll. Different pigments are able to absorb light at different wavelengths. What is meant by the action spectrum?

3.

The rate of photosynthesis can be limited by a number of factors.

a) How can temperature limit the rate of photosynthesis?

b) On the graph below draw a line to represent how the rate of photosynthesis changes with light intensity.

c) How do commercial growers take advantage of better understanding of limiting factors?

ANSWERS

1.

a) The high concentration of carbon dioxide is linked with the dark as no photosynthesis is occurring. At night plants and other organisms respire. In the day time, plants use more carbon dioxide for photosynthesis and the rate of photosynthesis exceeds that of respiration. There’s also a decrease in carbon dioxide at a height as at the ground level there’re less photosynthesising tissues and more animals.

b) Carbon dioxide combines with ribulose bisphosphate to produce two molecules of glycerate 3-phosphate. These are reduced to triose phosphate which requires reduced NADP and energy from ATP.

2.

a)

i. stroma

ii. thylakoid membranes

b) The action spectrum is the rate of photosynthesis with different light wavelengths.

3.

a) If the temperature becomes too high then the enzymes needed to produce glucose become denatured and so the rate of photosynthesis slows down. If the temperature is too low then the rate of photosynthesis is slower as the molecules in the plant have less energy.

b) The line should rise then reach a plateau.

c) They create conditions in which the temperature is kept at the optimum for the plant they’re cultivating. Carbon dioxide is continuously pumped in and the light intensity is kept constant.