An Overview of Photosynthesis

1. An Overview of Photosynthesis

2. The Big Picture All organisms need energy to carry out essential functions (growth, movement, maintenance, repair, reproduction). The ultimate source of energy is the sun. Energy flows from the sun to autotrophs, then to organisms that eat autotrophs (heterotrophs), and then to organisms that feed on other organisms (heterotrophs).

3. Autotrophs vs. Heterotrophs • Organisms are classified by how they obtain their energy • Autotrophs- organisms that make their own food / use solar energy to power the production of food • (plants, some kinds of protists and bacteria) • Heterotrophs- organisms that must get energy from food instead of directly from sunlight / get energy by eating other organisms or organic wastes • (all animals, all fungi, most protists, many bacteria)

5. Autotrophs: Chemosynthesis vs. Photosynthesis • Photosynthesis- the conversion of light energy from the sun into chemical energy in the form of organic compounds. • 6CO2 + 6H2O + (light energy)  C6H12O6 + 6O2 • Chemosynthesis- the use of energy stored in inorganic molecules (CO2) to produce carbohydrates (organic molecules) / chemicals are used as the energy source rather than sunlight • 6CO2 + 6H2O + (chemical energy-3H2S)  C6H12O6 + 3H2SO4

6. Which Organisms use Photosynthesis?Which Organisms use Chemosynthesis? • Photosynthesis – takes place on land and in shallow waters where sunlight can reach plants and seaweed • Chemosynthesis – takes place around hydrothermal vents and methane seeps in the deep sea where there is no sunlight. It is performed by bacteria living on the sea floor or within animals.

7. Overview of Photosynthesis • 6CO2 + 6H2O + (light energy)  C6H12O6 + 6O2 (Reactants) (Products) • Autotrophs use photosynthesis to produce organic compounds from carbon dioxide and water. • The Two Stages of Photosynthesis: • Light Reactions (Light Dependent Reactions) • Calvin Cycle (Light Independent Reactions)

8. Stage 1: Light Reactions • Series of steps in which: • Light energy is absorbed from the sun and converted into chemical energy (ATP and NADPH) • Water (H2O) is the first reactant used, and O2 is the first byproduct produced. • Chemical energy is temporarily stored as ATP and NADPH (energy carrier molecule)

9. Stage 2: Calvin Cycle • Series of steps in which: • Carbon Dioxide (CO2) is the second reactant used, along with the chemical energy from the light reactions (stored in ATP and NADPH) • Organic compounds (glucose – C6H12O6) are formed.

11. Structure and Function of a Leaf

12. Structure and Function • Upper Epidermis- structure, support, protection • Cuticle- waxy coating, helps prevent water loss • Palisades Layer-where majority of photosynthesis takes place • Chloroplast- site of photosynthesis • Phloem- transports sugars in any direction • Xylem- transports water upward only (roots  shoots) • Guard Cells- specialized cells that border a stoma and regulate gas exchange • Stomata- gas exchange • Vein- transport tissue (vein= xylem + phloem) • Lower Epidermis- structure, support, protection • Spongy Layer- photosynthesis, air exchange • Mesophyll- air exchange and photosynthesis (3 +11)

13. Stomata – please sketch on your lab Guard Cells Stomata