2.9 Photosynthesis Applications: Understanding: Photosynthesis is the production of carbon compounds in cells using light energy Visible light has a range of wavelengths with violet the shortest wavelength and red the longest Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours Oxygen is produced in photosynthesis from photolysis of water Energy is needed to produce carbohydrates and other carbon compounds Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis Applications: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis Skills: Design of experiments to investigate limiting factors on photosynthesis Separation of photosynthetic pigments by chromatography Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis Nature of science: Experimental design: controlling relevant variables in photosynthesis experiments is essential

Sunlight Glucose Water Oxygen Carbon dioxide

Photosynthesis

Photosynthesis Plants are able to make their own energy using sunlight and simple compounds. Carbon dioxide + water  glucose + oxygen Produces carbon compounds Understanding: Photosynthesis is the production of carbon compounds in cells using light energy

Photosynthesis Light energy converted to chemical energy for photosynthesis Endothermic (energy goes in) Understanding: Oxygen is produced in photosynthesis from photolysis of water Energy is needed to produce carbohydrates and other carbon compounds

Photosynthesis Photolysis splits water to release electrons needed in other stages of photosynthesis Only happens when light present (photo) Understanding: Oxygen is produced in photosynthesis from photolysis of water Energy is needed to produce carbohydrates and other carbon compounds

Effects of Photosynthesis Prokaryotes completed photosynthesis initially 3,500 million years ago Followed by algae and plants Caused an increased oxygen concentration in the atmosphere Applications: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis

Caused by reduction in greenhouse gases Glaciation Caused by reduction in greenhouse gases Applications: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis

Oxidation Dissolved iron in water oxidized causing it to precipitate on the sea bed Caused a distinctive rock formation of iron oxide Banded iron formation Applications: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis

Oxidation Applications: Changes to the Earth’s atmosphere, oceans and rock deposition due to photosynthesis

Wavelengths Red Orange Yellow Green Blue Indigo Violet Light is made up of many wavelengths Some wavelengths are invisible to us Understanding: Visible light has a range of wavelengths with violet the shortest wavelength and red the longest

Wavelengths Too short to see: X-rays, UV rays Too long to see: Infrared Visible light range from 400 to 700 nanometres Understanding: Visible light has a range of wavelengths with violet the shortest wavelength and red the longest

Wavelengths Wavelengths of light detected by human eye also used in photosynthesis They are the most abundant wavelengths on earth so plants have adapted to use these Understanding: Visible light has a range of wavelengths with violet the shortest wavelength and red the longest

Pigments Pigments are substances that absorb light – they appear colored to us If a pigment absorbs all colours, it appears black as it emits no light If it looks white – the object reflects all colours Some pigments only absorb certain wavelengths of light Understanding: Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours

Pigments Gentian flower absorbs all colour except blue So it appears blue The blue wavelength from sunlight is reflected and can pass into our eye. Understanding: Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours

Chlorophyll There are various forms of chlorophyll but they all appear green to us They absorb red and blue light easily Green light is absorbed less effectively so is reflected This is why plants look green! Understanding: Chlorophyll absorbs red and blue light most effectively and reflects green light more than other colours

Spectra Action Shows rate of photosynthesis at each wavelength of light Absorption Percentage of light absorbed at each wavelength for each pigment Skills: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis

Rules for drawing spectra Action Absorption Both Y-axis should be used for rate of photosynthesis – often given as a percentage of the maximum rate (0-100%) Y-axis should be labelled % absorption (0-100%) X axis should have label: wavelength (nm) Scale from 400-700 nm for wavelength Skills: Drawing an absorption spectrum for chlorophyll and an action spectrum for photosynthesis

Chromatography Chloroplasts have many types of chlorophyll and other pigments Because they absorb different wavelengths of light they look different colours to us We can separate these pigments by chromatography Skills: Separation of photosynthetic pigments by chromatography

Limiting Factors What can affect the rate of photosynthesis? Too cold/too hot = slower photosynthesis Even if other variables are there Optimum temperature = faster photosynthesis Less light = plant photosynthesises slowly Even if there is a lot of water and carbon dioxide More light = faster photosynthesis Less carbon dioxide = slower photosynthesis Even if there is a high light intensity More carbon dioxide = faster photosynthesis Understanding: Temperature, light intensity and carbon dioxide concentration are possible limiting factors on the rate of photosynthesis

What can slow the rate of photosynthesis? Limiting Factors What can slow the rate of photosynthesis? Light Intensity Graph: Description: Carbon dioxide Graph: Description: Temperature Graph: Description:

Planning an investigation How ONE factor can affect the rate of photosynthesis. You can choose which one. Hypothesis Variables Equipment Method Risk Assessment What are the different ways you can measure the rate of photosynthesis? Skills: Design of experiments to investigate limiting factors on photosynthesis Nature of science: Experimental design: controlling relevant variables in photosynthesis experiments is essential

Planning an investigation Direct and most accurate Measure uptake of carbon dioxide (carbon dioxide monitor) Measure production of oxygen (volume of bubbles produced in measuring cylinder) Indirect and least accurate Measure production of carbohydrates (measure sections of leaf) Measure the increase in overall mass of plant over time Skills: Design of experiments to investigate limiting factors on photosynthesis Nature of science: Experimental design: controlling relevant variables in photosynthesis experiments is essential