Photosynthesis Chapter 8

ENERGY and LIFE 1. Every living things requires energy (from food) to survive. Autotrophs: make their own food (plants) Heterotrophs: consume their food (animals) 3. Chemical energy = energy stored in molecules

How do cells store energy? 4. ATP - Adenosine triphosphate *Easy for cells to use *Basic energy source for cells; used to power cell processes. Ex: active transport *Cannot store large amounts of energy ADP = Adenosine diphosphate Has only 2 phosphate groups and less energy than ATP

How do cells store energy? Glucose 5. Stores LOTS of energy (90 times more than 1 ATP molecule!!) Can be used to make more ATP 6. Too big! Not as accessible for cell processes

How do cells get ATP and glucose? PHOTOSYNTHESIS 7. Photosynthesis – Plants use energy from sunlight to convert CO2 and H2O into O2 and glucose.

Experiments that help us understand photosynthesis Jan van Helmont (1643) Question: Do plants gain mass (grow) by taking material out of the soil? Answer: Mass of plant comes from water, not soil.

Experiments that help us understand photosynthesis Joseph Priestley (1771) Question: Why does a candle remain burning under a jar when a plant is under the jar? Answer: A plant produces a substance (oxygen) required for burning.

Experiments that help us understand photosynthesis Jan Ingenhouz (1779) Repeated Priestley’s experiment in light and dark. Question: Does light affect the candle burning when a plant is present? Answer: Light is required for plants to produce oxygen.

Experiments that help us understand photosynthesis From these experiments we know: With light, plants transform water and carbon dioxide into carbohydrates and oxygen

How do plants use light? Light is a form of energy 8 a. Pigments - molecules that absorb specific wavelengths of light 8 b. Chlorophyll - green pigment (reflects green, absorbs blue, violet & red light energy) Moves energy to electrons that drive reactions

9. Photosynthesis takes place in the chloroplast of the cell. 10. a. Stroma - space outside the thylakoids b. granum - stack of thylakoids c. grana - plural of granum d. thylakoid - membrane sacs that contain pigments to absorb light energy

Two parts to photosynthesis: 11. a. Light Dependent Reactions USES sunlight and water. PRODUCES oxygen, ATP, and NADPH. Occurs in the thylakoid membranes or grana. b. Light Independent Reactions (Calvin Cycle) USES CO2, ATP and NADPH. PRODUCES sugars. Occurs in the stroma.

How do plants use light? *When chlorophyll absorbs light, it absorbs energy *That energy is transferred to electrons *Those electrons power photosynthesis Electron carriers - molecules that transfer high energy electrons from chlorophyll to other moleucles Example: NADP+ (nicotinamide adenine dinucleotide phosphate) can accept 2 high energy electrons. 2 electrons + NADP+ --> NADPH