Patterns in Nature Topic 10: Photosynthesis: Biochemistry

1. Patterns in NatureTopic 10: Photosynthesis: Biochemistry Part of the Patterns in Nature Module Biology in Focus, Preliminary Course Glenda Childrawi and Stephanie Hollis

2. DOT Points • Distinguish between autotrophs and heterotrophs in terms of nutrient requirements • Identify the materials required for photosynthesis and its role in ecosystems • Identify the general word equation for photosynthesis and outline this as a summary of a chain of biochemical reactions colourbox.com

3. Introduction All living organisms need to obtain nutrients in the form of organic substances such as glucose as well as inorganic nutrients such as minerals and water. loupiote.com

4. Introduction Animals are heterotrophs and need to eat food to obtain these nutrients. Plants on the other hand are autotrophs which absorb the inorganic nutrients from the soil but are able to manufacture their own organic nutrients. honglimmp.com

5. Introduction These nutrients are used in two main ways: • As essential building blocks from which cells and tissues are made • As a source of stored energy that can be converted to ATP, the energy essential for cell functioning. We’re going to first look at the specialised structures of plants macronutrients.net

6. Photosynthesis Photosynthesis is the process by which all green plants and some unicellular organisms make food. Carbon dioxide, water, chlorophyll and light are all essential for the chemical process of photosynthesis to occur in cells. organicsoul.com

7. Photosynthesis Photosynthesis is the initial pathway by which energy enters all ecosystems. Organisms that photosynthesise are producers. Producers form the basis of all food webs providing glucose for all living things either directly or indirectly. stephsnature.com

8. Photosynthesis Photosynthesis is often represented by the general equations shown below. This process is not one chemical reaction, its actually a series of many chemical reactions. Word equation Balanced Chemical Equation exportsolutions.com.au

9. Photosynthesis Photosynthesis takes place in two stages. Each stage is not a single chemical reaction, it’s a series or chain of reactions: • Light Phase (photolysis): involves the splitting of water using the energy of light (photo=light, lysis=splitting) • Light independent phase (carbon fixing stage): involves using carbon dioxide to make sugar. No light is used in this stage Each step is controlled by a different enzyme (a chemical catalyst that speeds up reactions in living cells)

10. The Light Phase-Photolysis Radiant energy from the sun is captured by chlorophyll in the thylakoids in the grana of chloroplasts. The energy is sufficient to excite an electron to a higher energy level, where it will break away from the chlorophyll molecule. This series of reactions is occurring in each chlorophyll molecule in every chloroplast exposed to light and there are thousands of these molecules. stephaniel2012biology.wikispaces.com cellssixthgrade.wikispaces.com

11. The Light Phase-Photolysis An excited electron can follow one of two pathways: • It may be used to split water (H₂O) into a hydrogen (H₂) component and an oxygen atom (O). all-water.org

12. The Light Phase-Photolysis The oxygen atom combines with an oxygen atom from another chlorophyll molecule to form a oxygen gas (O₂) which is then released by the plant. The hydrogen atoms will go on to be used in the next phase, the light independent reaction. exportsolutions.com.au

13. The Light Phase-Photolysis Or • It may be used to form ATP, a high energy compound that provides the cell with the energy it needs for functioning exportsolutions.com.au

14. The Light Independent Phase-Carbon Fixing This phase uses carbon dioxide, but requires no chlorophyll and no light. Hydrogen atoms from the light reaction are carried to the stroma to begin this phase. westsidercd.org

15. The Light Independent Phase-Carbon Fixing The hydrogen atoms go through a series of enzyme-controlled reactions where they are combined with carbon dioxide to form a sugar molecule (glucose). This cyclic series of reactions is known as the Calvin Cycle, named after Melvin Calvin who discovered it. msu.edu

16. The Light Independent Phase-Carbon Fixing The ATP produces in the light reaction provides the necessary energy for the light independent reaction to take place. The energy from ATP is incorporated into the new sugar compounds that are formed. zymesllc.com

17. The Light Independent Phase-Carbon Fixing The glucose end product of photosynthesis is converted to starch, the form in which food is most commonly stored in plants. Chloroplasts usually have large starch grains stored in the stroma, evidence that photosynthesis has occurred. sciencefairprojects-ideas.com

18. Overview Photosynthesis takes place immediately following the light phase and so both phases occur during daylight. There is no photosynthesis at night. worldswithwords.wordpress.com

19. Activity -Hand out copies of ‘Requirements for Photosynthesis’ (Teacher Resource CD Prelim Bio in Focus) -Hand out Figures 3.9 and 3.10 from Prelim Bio in Focus text pages 137-138 and discuss

20. Homework Students to complete: -Dot Point Question 3.2.1, 3.3.1 and 3.3.2 from handout last lesson