Photosynthesis Chapter 8

Autotrophs vs. Heterotrophs Autotrophs: Plants and some other types of organisms that use light energy from SUNLIGHT to make their own food. These organisms undergo photosynthesis!! – EX: Trees, grass, algae, plants Heterotrophs: Organisms that CANNOT use the sun’s energy to make food– they obtain energy from the foods they consume – EX: Deer, rabbits, bear, fish, insects, etc…

The Photosynthesis Equation Photosynthesis uses the energy of sunlight to convert water and carbon dioxide into high energy sugars and oxygen 6CO2 + 6H2O + light→C6H12O6 + 6O2 (carbon dioxide + water + light → sugars + oxygen) Plants then use the sugars to produce complex carbohydrates such as starches Plants obtain CO2 from the air or water in which they grow

Photosynthesis Light Energy Chloroplast CO2 + H2O Sugars + O2

Inside a Chloroplast Chloroplast= Filled with chlorophyll and are where photosynthesis takes place in plants and other photosynthetic eukaryotes – Thylakoids= saclike photosynthetic membranes arranged into stacks known as grana. Area where light-dependent reactions take place – Photosystems= clusters of chlorophyll and other pigments that are organized by the thylakoids – Stroma= Area outside the thylakoid membranes where light- independent reactions

Light-dependent Reactions

Figure 8-5 Chlorophyll Light Absorption Section 8-2 Absorption of Light by Chlorophyll a and Chlorophyll b Chlorophyll b Chlorophyll a V B G Y O R

Electron Carriers Electron Transport= The transfer of a pair of high energy electrons & their energy to another molecule Electron Carriers= The “bucket” or carrier that moves electrons and their energy from molecule to the next EX: NADP+: Accepts and holds a pair of high-energy electrons and an H+ ion, converting NADP+ into NADPH turning energy from the sun into chemical energy . An analogy would be a pan carrying hot coals like the NADP+ carries two electrons and a H+ ion.

ATP Formation

Adenosine Triphosphate (ATP) Adenine Ribose 3 Phosphate groups

ADP and ATP (Electron Carriers) Energy Energy Adenosine triphosphate (ATP) Adenosine diphosphate (ADP) + Phosphate Partially charged battery Fully charged battery

Light-Dependent Reactions Light-Dependent Reactions: Use energy from sunlight to produce the energy carriers ATP and NADPH and oxygen. – Reactions occur within the thylakoid membranes of chloroplasts

Light-dependent Reactions http://highered. mcgraw-hill

Figure 8-10 Light-Dependent Reactions Section 8-3 Hydrogen Ion Movement Photosystem II Chloroplast ATP synthase Inner Thylakoid Space Thylakoid Membrane Stroma Electron Transport Chain Photosystem I ATP Formation

Photosynthesis

Steps in Photosynthesis Photosynthesis: Has five major steps that occur within the thylakoid membrane of the chloroplast – 1. Photosystem II: Light absorbed by photosystem II is used to break up water molecules into energized electrons, hydrogen ions (H+) and oxygen. – 2. Electron Transport Chain: High-energy electrons from photosystem II move through the electron transport chain into photosystem I.

Steps in Photosynthesis – 3. Photosystem I: Electrons released by photosystem II are energized again in photosystem I. Enzymes in the membrane use these electrons to make NADPH/ – 4. Hydrogen Ion Movement: The inside of the thylakoid membrane is charged with H+ ions. This causes the outside of the thylakoid membrane to be negatively charged and the inside of the membrane to be positively charged.

Steps in Photosynthesis – 5. ATP Formation: As hydrogen ions pass through ATP synthase, their energy is used to convert ADP into ATP. As it rotates ATP synthase (enzyme) binds ADP and P+ group to create ATP. Because of this, light-dependent transport produces high energy electron AND ATP. SUMMARY: Light dependent reactions use water, ADP and NADP+ to produce oxygen, ATP and NADPH (Water, ADP, NADP+ Oxygen, ATP, NADPH) ATP and NADPH then provide energy to build energy containing sugars from low-energy compounds.

Light-independent Reactions Calvin Cycle: Energy stored in the ATP and NADPH formed during photosynthesis, is used to build high-energy sugars that can be stored for a long period of time. – Does not require light and is called light independent reaction – Takes place in the stroma of the chloroplasts

Calvin Cycle http://highered. mcgraw-hill

Steps in the Calvin Cycle The Calvin Cycle has four major steps: – 1. C02 Enters the Cycle: 6 CO2 molecules are combined with six 5- carbon molecules to produce three 12-carbon molecules – 2. Energy Input: Energy from ATP and electrons from NADPH convert the twelve 3-carbon molecules into higher-energy forms – 3. 6-Carbon Sugar Produced: two 3-carbon molecules are removed to produce sugars, lipids, amino acids, and other compounds

Steps in the Calvin Cycle – 4. 5-Carbon Molecules Regenerated: the 10 remaining 3-carbon molecules are converted back into six 5-carbon molecules, which are used to start the next cycle : )

Figure 8-11 Calvin Cycle Section 8-3 CO2 Enters the Cycle Energy Input ChloropIast 5-Carbon Molecules Regenerated 6-Carbon Sugar Produced Sugars and other compounds

Concept Map Photosynthesis Light- dependent reactions Calvin cycle Section 8-3 Photosynthesis includes Light- dependent reactions Calvin cycle takes place in uses use take place in Thylakoid membranes Stroma NADPH ATP Energy from sunlight to produce of to produce ATP NADPH O2 Chloroplasts High-energy sugars

Figure 8-7 Photosynthesis: An Overview Section 8-3 Light O2 Sugars CO2 Chloroplast Chloroplast NADP+ ADP + P Light- Dependent Reactions Calvin Cycle ATP NADPH

Factors Affect Photosynthesis Various Factors Affect the Rate of Photosynthesis. Some of these factors are: 1. Amount of available water – EX: Plants in dry areas have waxy leaves to prevent water loss 2. Temperature – EX: Enzymes work best between 0° and 35°C. Temps above or below this range may slow down photosynthesis or stop it entirely 3. Light Intensity 1. EX: The higher the intensity the higher the rate of photosynthesis. There is a maximum limit however. This varies from plant to plant