Amanda's Handout Week 2

Week 2 Handout – Photosynthesis

A03: Amanda Rajapaksa [email protected] OH: M 3-4@CLICS /by appt.

Write the overall photosynthesis reaction:

The overall photosynthesis reaction requires ____ quanta of light energy. This light energy is used to generate the NADPH and ATP used in the photosynthesis reaction. Plants obtain energy when light strikes a _________________ in their chloroplast membranes. Excess light absorption creates _______________ which can lead to ____________________. Carotenoids scavenge up free radicals and can help to minimize the damage from excess light energy.

By analyzing the photosynthetic unit size of plants you can measure the _____________. This value will be high in plants grown under ____-light conditions, and low in those grown under ______-light conditions. Some plants are unable to adapt to different light conditions and must be maintained at a specific light condition.

Purple-sulfur bacteria require much less energy to drive their equivalent reaction. The reason for this is that _____ is split instead of water.

Energy-Transduction Reactions:

Light energy absorbed by chlorophyll a molecules in ___________________ is used indirectly to power the synthesis of ATP. Simultaneously, in the interior of the thylakoid, water is split into oxygen gas and hydrogen atoms. The electrons are ultimately accepted by ____________ to produce NADPH.

The light-reaction has two forms; cyclic and non-cyclic photophosphorylation. Under certain conditions, photoexcited electrons take an alternative path called cyclic electron flow, which uses photosystem ______ but not photosystem ____. There is no production of ________ and no release of oxygen, however cyclic flow does generate _______.

Calvin Cycle:

In the carbon-fixation reactions, which occur ___________ of the chloroplast, sugars are synthesized from carbon dioxide and the hydrogen carried by NADPH. This process is powered by the ______ and _______ produced in the energy-transduction reactions. The most important enzyme of the light-independent reactions is ________________.

To fix one molecule of CO2, a net of ____ molecules of ATP and ____ molecules of NADPH are required.

RuBisCO : ribulose-1,5-bisphosphate carboxylase/oxygenase

Carbon fixation by RUBISCO can be enhanced by increasing the ________________ concentration in the compartment containing the enzyme (chloroplast stroma). Some plants have evolved methods of maximizing the efficiency of carbon fixation.

C4 Plants:

C4 plants have maximized their carbon fixation efficiency by making structural changes in their leaf anatomy so that RUBISCO is sequestered where the CO2 level is high (and O2 low). There are two important cell types found in C4 plants: ______________ and ____________ cells. The arrangement of the cells is known as ______________________. Through this arrangement, photorespiration is minimized and CO2 fixation is maximized.

CAM Plants:

Instead of segregating the C4 and C3 pathways in different parts of the leaf, these types of plants use a ________________. At night, CAM plants take in CO2 through _______________. The CO2 joins with PEP to form ________________. This is converted to malic acid, which accumulates in the _____________ of the cells. In the day, the stomata close to ____________ and the malic acid leaves the vacuole and is broken down to release CO 2. The CO2 is taken up and used in the Calvin cycle.

Combustion of Octane: The amount of CO2 given off with each gallon of gas consumed is approximately: ___________.

PS#4: What is the difference between cyclic and noncyclic photophosphorylation in terms of products generated, compounds consumed and energy utilized?

Oxygen?

NADPH?

Proton gradient?

ATP?

Non-cyclic ppp Cyclic ppp

PS#9: Give three reasons why C4 photosynthesis is more efficient at fixing CO2 than is C3 photosynthesis.