Photosynthesis Answer Key

Photosynthesis Light Absorption Define photosynthesis Photosynthesis is the process by which cells use light energy to synthesise organic compounds from ………………………………………………………………………………………………………………………………………………….......... inorganic molecules ………………………………………………………………………………………………………………………………………………….......... Identify the range of wavelengths absorbed via photosynthesis Photosynthesis uses the visible spectrum (white light), which ranges from 400 nm (violet) to 700 nm (red) ………………………………………………………………………………………………………………………………………………….......... State the main photosynthetic pigment in plants and identify where they are found Chlorophyll (a) is the main photosynthetic pigment and it is found in chloroplasts in plants ………………………………………………………………………………………………………………………………………………….......... Outline the difference in absorption of red, green and blue light by plants Plants predominantly absorb red and blue light, but reflect green light ………………………………………………………………………………………………………………………………………………….......... Draw the action spectrum and absorption spectrum and provide a comparison between the two Absorption Spectrum Rate of Photosynthesis Amount of light absorbed Action Spectrum 400 nm 700 nm 400 nm 700 nm The range of wavelengths used by a plant for photosynthesis Action Spectrum: …………………………………………………………………………………………………………………………….. (red and blue is used for a high photosynthetic rate, green is not used) ………………………………………………………………………………………………………………………………………………….......... The range of wavelengths absorbed by a plant (each pigment has its own spectrum) Absorption Spectrum: ……………………………………………………………………………………………………………………… (for chlorophyll a: red and blue are absorbed, green is reflected) ………………………………………………………………………………………………………………………………………………….......... Photosynthetic Action Complete the following diagram outlining the key components of photosynthesis LIGHT DEPENDENT REACTIONS Light energy Water Chlorophyll Chemical energy e– Oxygen gas Hydrogen NADPH Carbon dioxide gas LIGHT INDEPENDENT REACTIONS ATP Carbon fixation Carbon compounds Summarise the key events of the two stages of photosynthesis Light Dependent Reactions: Light is absorbed by chlorophyll, which triggers the production of ATP (via photophosphorylation) ………………………………………………………………………………………………………………………………………………….......... Light is also responsible for the photolysis of water, which produces hydrogen (carried by NADPH) ………………………………………………………………………………………………………………………………………………….......... The photolysis of water also produces oxygen gas as a by-product ………………………………………………………………………………………………………………………………………………….......... Light Independent Reactions: The products of the light dependent reaction (NADPH and ATP) are used in the light independent reactions ………………………………………………………………………………………………………………………………………………….......... These reactions fix carbon (from carbon dioxide) to form organic molecules (such as carbohydrates) ………………………………………………………………………………………………………………………………………………….......... Outline how photosynthetic pigments can be separated via chromatography Pigments are dissolved in a fluid (mobile phase) …………………………………………………………………………………………………………………………………………… Fluid is then passed through a static material (stationary phase) …………………………………………………………………………………………………………………………………………… Different pigments pass through the static material at different speeds, becoming separated …………………………………………………………………………………………………………………………………………… A retardation factor (Rf) can be assigned to each pigment (to allow for identification) …………………………………………………………………………………………………………………………………………… Measuring Photosynthesis Outline the law of limiting factors A reaction will only proceed as fast as the component nearest its minimum value (rate-limiting factor) ………………………………………………………………………………………………………………………………………………….......... List three conditions by which photosynthesis can be detected and suggest how they can be measured Oxygen uptake - measure by pressure change (data logger) or displacement of syringe cap 1. …………………………………………………………………………………………………………………………………………………... …………………………………………………………………………………………………………………………………………………... Carbon dioxide production - measure by a change in pH if plant is in solution 2. …………………………………………………………………………………………………………………………………………………... (carbon dioxide dissolves in water to form carbonic acid = decreases pH) …………………………………………………………………………………………………………………………………………………... Change in biomass - measure by a change in weight 3. …………………………………………………………………………………………………………………………………………………... (plant sample must first be dessicated to account for change in mass due to water) …………………………………………………………………………………………………………………………………………………... Temperature Rate of Photosynthesis Rate of Photosynthesis Rate of Photosynthesis Explain the effect of different factors on the rate of photosynthesis Light Intensity CO2 Concentration Temperature affects enzyme activity (photosynthesis controlled by enzymes) Temperature: …………………………………………………………………………………………………………………………………. Activity initially increases as a rise in kinetic energy results in more frequent collisions ………………………………………………………………………………………………………………………………………………….......... Above a certain temperature, activity decreases as enzymes become denatured ………………………………………………………………………………………………………………………………………………….......... Increasing light levels results in more photoactivation of chlorophyll (= increased activity) Light Intensity: ……………………………………………………………………………………………………………………………….. At a certain intensity, all chlorophyll are photoactivated and so activity plateaus ………………………………………………………………………………………………………………………………………………….......... (i.e. plant is saturated with light) ………………………………………………………………………………………………………………………………………………….......... Carbon dioxide is fixed (via the enzyme Rubisco) to form organic compounds CO2 Concentration: ……….………………………………………………………………………………………………………………… Activity increases at higher concentrations as there are more frequent collisions ………………………………………………………………………………………………………………………………………………….......... Above a certain level activity will plateau as all enzyme active sites are occupied …………………………………………………………………………………………………………………………………………………..........