2016 Ch 10: Photosynthesis

Chapter 10: Photosynthesis From Topic 2.9 Essential idea: Photosynthesis uses the energy in sunlight to produce the chemical energy needed for life. Nature of science: Experimental design—controlling relevant variables in photosynthesis experiments is essential (3.1). Understandings: Photosynthesis is the production of carbon compounds in cells using light energy. Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours. Oxygen is produced in photosynthesis from the photolysis of water. Energy is needed to produce carbohydrates and other carbon compounds from carbon dioxide. Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis. Applications and skills: Application: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis. Skill: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis. Skill: Separation of photosynthetic pigments by chromatograph (Practical 4). Skill: Design of experiments to investigate the effect of limiting factors on photosynthesis. Guidance: Water free of dissolved carbon dioxide for photosynthesis experiments can be produced by boiling and cooling water. Students should know that visible light has wavelengths between 400 and 700 nanometres, but they are not expected to recall the wavelengths of specific colours of light. Paper chromatography can be used to separate photosynthetic pigments but thin layer chromatography gives better results. From Topic 8.3 Essential idea: Light energy is converted into chemical energy. Nature of science: Developments in scientific research follow improvements in apparatus—sources of 14C and autoradiography enabled Calvin to elucidate the pathways of carbon fixation (1.8). Understandings: The structure of the chloroplast is adapted to its function in photosynthesis. Light-dependent reactions take place in the intermembrane space of the thylakoids. Reduced NADP and ATP are produced in the light-dependent reactions. Absorption of light by photosystems generates excited electrons. Photolysis of water generates electrons for use in the light- dependent reactions. Transfer of excited electrons occurs between carriers in thylakoid membranes. Excited electrons from Photosystem II are used to contribute to generate a proton gradient. ATP synthase in thylakoids generates ATP using the proton gradient. Excited electrons from Photosystem I are used to reduce NADP. Light-independent reactions take place in the stroma. In the light-independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate. Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP. Triose phosphate is used to regenerate RuBP and produce carbohydrates. Ribulose bisphosphate is reformed using ATP.

Chapter 10: Photosynthesis From Topic 8.3 Applications and skills: Application: Calvin’s experiment to elucidate the carboxylation of RuBP. Skill: Annotation of a diagram to indicate the adaptations of a chloroplast to its function. Aim 6: Hill/s method demonstrating electron transfer in chloroplasts by observing DCPIP reduction, immobilization of a culture of an alga such as Scenedesmus in alginate beads and measurement of the rate of photosynthesis by monitoring their effect on hydrogencarbonate indicator are all possible experiments. Utilization: The Global Artificial Photosynthesis (GAP) project aims to create an artificial “leaf” within the next decade. An electronic version of the leaf that creates oxygen and hydrogen from water and sunlight has already been invented and will be developed for use in the next decade. From Topic 9.1 Understandings: Transpiration is the inevitable consequence of gas exchange in the leaf. Applications and skills: Application: Adaptations of plants in deserts and in saline soils for water conservation.

Ecology Review Plants, algae and other autotrophs are the producers in the ecosystem. Autotrophs synthesize organic molecules from inorganic raw materials. Heterotrophs acquire organic molecules from compounds made by other organisms. (consumers, decomposers)

Review of Plant Cell Structure

Site of Photosynthesis Site of photosynthesis is in the chloroplast. Chloroplasts are found mainly in the mesophyll of the leaf, in the palisade layer.

Structure and Function of Chloroplast Folded Thylakoid membranes Separate Areas (compartments) Lumen for Proton Accumulation Fluid Stroma

Guard Cells Stomata: little openings in the leaf controlled by guard cells - let’s in CO 2 but also let’s out water How do guard cells work?

Chlorophyll Chlorophyll: a green pigment in the chloroplast that absorbs light Two types of chlorophyll: -Chlorophyll a: best absorbs light at violet-blue and red -Chlorophyll b: best absorbs light at blue and orange

Overview of Photosynthesis Transforms solar energy into chemical energy. CO 2 and H 2 O into Glucose CO 2 is carbon source and light is energy source.

Two Stages of Photosynthesis Light Dependent Reactions (Light Reactions) Products Oxygen NADPH ATP Light Independent Reactions (Dark Reactions or Calvin Cycle) Products: Glucose ml

Light Reactions (Non-Cyclic e- Flow) Light Reactions: the “photo” part of photosynthesis; requires light to make it happen -Similar to how the ETC of Cellular Respiration works

Light Reactions (Non-Cyclic e- Flow) Light Reactions: use solar energy to produce ATP and NADPH for the light-independent reactions (aka Calvin Cycle) -ATP is used for chemical energy -NADPH is used for reducing power

Light Reactions (Cyclic e- Flow) Produces only ATP; no NADPH is produced Occurs when [ATP] is gets low for Calvin Cycle to continue Involves only Fd, Pc, and PS 1 in cyclic pattern

Light Independent Reactions (Calvin Cycle) Light-Independent Reactions: uses ATP and NADPH to convert CO 2 to sugar There are 3 parts: 1)Carbon Fixation 2)Reduction 3)Regeneration of CO 2 acceptor (RuBP)

Summary of Photosynthesis Light Reactions Products NADPH ATP Oxygen Dark Reaction Products Glucose

Action Spectrum of Photosynthesis Which wavelength of light best drives photosynthesis?

Intro to Other Types of Carbon Fixation

Angiosperms: Flowering Plants Two basic division: 1) Monocots: “one leaf” 2) Dicots: “two leaves”

Alternatives to Carbon Fixation C3: basic photosynthesis that forms a 3-Carbond compound as its 1 st product; includes both dicots and monocots such as rice, wheat & soybean C4: forms a 4-Carbon compound as its 1 st product; include agriculturally important monocots…sugar cane and corn CAM: include many succulents, cacti, and pineapple

C 4 Structure C4: two distinct types of photosynthetic cells: 1) Mesophyll cells: CO 2 incorporation occurs here 2) Bundle-sheath cells: Calvin cycle occurs here Specifically useful for hot regions with a lot of sunlight

C 3 vs C 4 Structure

CAM Structure CAM: open their stomata at night and closes them during the day to prevent water loss Useful in arid environments and found in succulent plants Carbon fixation occurs in the same cell but occurs at different times

Carbon Fixation Comparisons Compare the three types of carbon fixation. What do they have in common? What differences do they have?

Limiting Factors Light Intensity: increases up to a certain point Temperature: has an optimal temp; too cold or hot is no good. Concentration of CO 2: increases to a certain point Why?