Kamis, 27 Agustus 2015

#98 Photosynthesis Syllabus 2016-2018

13.1  Photosynthesis as an energy transfer process
13.2  Investigation of limiting factors
13.3  Adaptations for photosynthesis

Photosynthesis is the energy transfer process that  is the basis  of much  of life on Earth. It provides the basis  of most food chains  providing energy directly or indirectly for all other  organisms. In eukaryotes, the process occurs within chloroplasts. Candidates use  their knowledge of plant cells and leaf structure from the section on Cell structure while studying photosynthesis. Various environmental factors influence the rate  at which photosynthesis occurs.

Candidates will be expected to use  the knowledge gained  in this section to solve problems in familiar and unfamiliar contexts.

Learning outcomes

Candidates should  be able to:

13.1  Photosynthesis as an energy transfer process

Light energy absorbed by chloroplast pigments in the light dependent stage of photosynthesis is used to drive reactions of the light independent stage that produce complex organic compounds.

Chromatography is used to identify chloroplast pigments and was  also used to identify the intermediates in the Calvin cycle.

a)   explain that  energy transferred as ATP and reduced NADP from the light dependent stage is used during the light independent stage (Calvin cycle) of photosynthesis to produce complex organic molecules

b)   state the sites of the light dependent and the light independent stages in the chloroplast

c)   describe the role of chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) in light absorption in the grana

d)   interpret absorption and action spectra of chloroplast pigments e)   use  chromatography to separate and identify chloroplast pigments and carry out an investigation to compare the
chloroplast pigments in different plants  (reference should  be made to Rf  values  in identification)

f) describe the light dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (cyclic and non-cyclic photophosphorylation should  be described in outline  only)

g)   outline  the three main stages of the Calvin cycle:

fixation of carbon  dioxide by combination with ribulose bisphosphate (RuBP), a 5C compound, to yield two molecules of GP (PGA), a 3C compound
•   the reduction of GP to triose  phosphate (TP) involving ATP and reduced NADP
•   the regeneration of ribulose  bisphosphate (RuBP) using ATP

h)   describe, in outline,  the conversion of Calvin cycle intermediates to carbohydrates, lipids and amino  acids  and their uses in the plant cell

13.2  Investigation of limiting factors

Environmental factors influence the rate  of photosynthesis. Investigating these shows how they  can

be managed in protected environments used in crop production.

a)   explain the term  limiting factor in relation to photosynthesis

b)   explain the effects of changes in light intensity, carbon  dioxide concentration and temperature on the rate  of photosynthesis

c)   explain how an understanding of limiting factors is used to increase crop yields in protected environments, such  as glasshouses

d)   carry out an investigation to determine the effect of light intensity or light wavelength on the rate  of photosynthesis using a redox indicator (e.g. DCPIP) and a suspension of chloroplasts (the Hill reaction)


e)   carry out investigations on the effects of light intensity, carbon dioxide and temperature on the rate  of photosynthesis using whole  plants,  e.g. aquatic  plants  such  as Elodea and Cabomba

 13.3  Adaptations for photosynthesis

All the stages of photosynthesis occur  in the chloroplast. Some tropical crops  have C4 metabolism and adaptations to maximise carbon  dioxide fixation.

a)   describe the relationship between structure and function  in the chloroplast using diagrams and electron micrographs

b)   explain how the anatomy and physiology  of the leaves of C4 plants,  such  as maize or sorghum, are adapted for high rates of carbon  fixation at high temperatures in terms of:

the spatial separation of initial carbon  fixation from the light dependent stage (biochemical details  of the C4 pathway are required in outline  only)
•   the high optimum temperatures of the enzymes involved