Biology Ch. 8 Photosynthesis

8-1 Energy and Life Energy is the ability to do work. Living things get their energy from food. Most energy from food comes from the sun.

Energy and Life, cont. Plants and some other types of organisms are able to use light energy from the sun to make food. These organisms are called AUTOTROPHS. Organisms that obtain energy from consuming other organisms are called HETEROTROPHS.

Adenosine triphosphate (ATP) Energy can be stored in chemical compounds. Chemical fuel for cells is stored as ATP. ATP consists of adenine, ribose (a 5-carbon sugar), and three phosphate groups. ADP is similar to ATP, but has only two phosphate groups.

Adenine Ribose 3 Phosphate groups Section 8-1 Structure of ATP Go to Section:

Energy transfer Cells can store energy by adding a phosphate group to ADP. Energy is released when ATP is converted back to ADP. ATP’s characteristics make it a useful molecule that is the basic energy source for all types of cells.

ADP ATP Energy Adenosine diphosphate (ADP) + PhosphateAdenosine triphosphate (ATP) Partially charged battery Fully charged battery Section 8-1 Comparison of ADP and ATP to a Battery Go to Section: ATP Energy Adenosine diphosphate (ADP) + PhosphateAdenosine triphosphate (ATP) Partially charged battery Fully charged battery Section 8-1 Go to Section:

Energy storage ATP is good for storing small amounts of energy for a short period. Glucose molecules store 90X more energy than ATP. It is more efficient for cells to keep small amounts of ATP on hand. Cells can convert ADP to ATP when needed by using energy stored in carbohydrates like glucose.

8-2 Photosynthesis: An Overview Plants use the energy from sunlight to convert water and carbon dioxide into oxygen and high energy carbohydrates (sugar and starch). Photosynthesis equation: 6 CO H 2 O light  C 6 H 12 O O 2

Chloroplasts and chlorophyll Plants capture the sun’s energy with light- absorbing molecules called PIGMENTS. Chlorophyll is found in the chloroplasts of plants. There are two types of chlorophyll: chlorophyll a and chlorophyll b. When chlorophyll absorbs sunlight, the energy is transferred to electrons in the chlorophyll molecule. These high-energy electrons make photosynthesis work.

Absorption of Light by Chlorophyll a and Chlorophyll b Chlorophyll b Chlorophyll a Chlorophyll Light Absorption Go to Section:

Historical Notes Jan van Helmont (1643) discovered that water was involved in increasing the mass of a plant. Joseph Priestley (1771) discovered that a plant produces the substance in air required for substances to burn. Jan Ingenhousz (1779) determined that light was necessary for plants to produce oxygen. The experiments of these scientists revealed that in the presence of light, plants transform carbon dioxide and water into carbohydrates and release oxygen: PHOTOSYNTHESIS!

Light Energy Chloroplast CO 2 + H 2 OSugars + O 2 Section 8-2 Photosynthesis: Reactants and Products Go to Section:

Reactions of Photosynthesis In plants and other eukaryotes, photosynthesis takes place in chloroplasts. The chloroplasts contain saclike photosynthetic membranes called thylakoids. A stack of thylakoids is called a granum (plural: grana).

Reactions, cont. The process of photosynthesis is broken down into two stages: Light dependent reactions take place in the thylakoid membranes. Splits water to give off oxygen, produces ATP and NADPH. Calvin cycle (light independent reaction) takes place in the stroma, the area outside the thylakoid membranes. Uses ATP and NADPH to make sugar from carbon dioxide.

Chloroplast Light O2O2 Sugars CO 2 Light- Dependent Reactions Calvin Cycle NADPH ATP ADP + P NADP + Chloroplast Section 8-3 Photosynthesis: An Overview Go to Section:

Light-dependent Reactions The light-dependent reactions produce oxygen and convert ADP to ATP, and NADP+ to NADPH. Steps: 1) Pigments absorb light in Photosystem II. Energy from the light is absorbed by electrons, which are then passed on to the electron transport chain. 2) High energy electrons move from Photosystem II to Photosystem I. Energy from the electrons is used by molecules in the electron transport chain to transport H+ ions from the stroma to the inner thylakoid.

Light-dependent reactions, cont. Steps: 3) Pigments add energy from light to the electrons. NADP+ is converted to NADPH. 4) The inside of the thylakoid membrane becomes positively charged due to H+ ions from water, while the outside of the membrane is negatively charged. 5) ATP synthase is an enzyme that helps H+ ions move across the thylakoid membrane. It binds phosphate to ADP to make ATP.

The Calvin Cycle The Calvin cycle uses ATP and NADPH to produce high-energy sugars. The Calvin cycle takes place in the stroma of chloroplasts and does not require light.

Calvin cycle steps 1) Six carbon dioxide molecules enter the cycle from the atmosphere. The carbon dioxide molecules combine with six 5-carbon molecules. The result is twelve 3-carbon molecules. 2) The twelve 3-carbon molecules are changed into higher-energy forms. The energy for this comes from ATP and NADPH. 3) Two of the 3-carbon molecules are converted into two similar 3-carbon molecules. These form 6- carbon sugars. 4) The 10 remaining 3-carbon molecules regroup to form six 5-carbon molecules, which will react with carbon dioxide from the air to restart the cycle.

Calvin cycle, cont. The Calvin cycle uses 6 molecules of carbon dioxide to produce a 6-carbon sugar molecule. The plant uses the sugars for energy, and to make more complex carbohydrates like starches and cellulose. When organisms eat plants, they can use the energy stored in the carbohydrates.

Photosynthesis includes of take place in takes place in uses to produce use Light- dependent reactions Calvin cycle Thylakoid membranes StromaNADPH ATP Energy from sunlight ATPNADPHO2O2 Chloroplasts High-energy sugars Section 8-3 Photosynthesis Concept Map Go to Section:

Factors affecting photosynthesis Availability of water Temperature Light intensity