chap 9 photosynthesis

Energy and Life

• All living things store energy in chemical bonds of certain compounds.
• ATP (Adenosine Triphosphate) consists of adenine, a 5-carbon sugar called ribose, and three phosphate groups.
• The phosphate groups are key to ATP's ability to store and release energy.
• ATP functions like a rechargeable battery, releasing energy when a phosphate group is split off and released.

How Cells Use ATP

• Cells use ATP for carrying out active transport, moving molecules against their concentration gradient.
• ATP provides energy for sodium-potassium pumps in cell membranes to pump sodium ions out and potassium ions into the cell.
• Energy stored in ATP enables cells to move and transfer energy to other molecules for processes like protein synthesis and responses to chemical signals.

Energy Transfer

• ATP is not suitable for storing large amounts of energy over long periods.
• Glucose molecules can store more than 90 times the energy required to produce ATP.
• Heterotrophs obtain energy by consuming other living things, while autotrophs obtain energy from the sun.
• Photosynthesis is the process by which plants convert energy from sunlight into chemical energy stored in carbohydrates.

Photosynthesis

• Chlorophyll, a pigment that absorbs light, is involved in photosynthesis.
• Chlorophyll absorbs light in the blue-violet and red regions of the visible spectrum and reflects green light, making leaves appear green.
• Photosynthesis takes place inside the chloroplast, which is surrounded by two envelope membranes and contains saclike chlorophyll-containing membranes called thylakoids.
• Thylakoids are interconnected and arranged in stacks known as grana.

Process of Photosynthesis

• Light-dependent reactions require direct involvement of light and light-absorbing pigments.
• Light-dependent reactions take place in thylakoid membranes and use energy from sunlight to produce ATP and NADPH.
• Light-independent reactions take place outside thylakoids in the stroma and use ATP and NADPH to build high-energy sugars from carbon dioxide.
• Photosynthesis produces oxygen as a by-product.

Light-Dependent Reactions

• Hydrogen ion movement and ATP formation occur during light-dependent reactions.
• Hydrogen ions build up inside the thylakoid membrane, creating a concentration difference that provides energy for ATP synthase to produce ATP.
• ATP synthase binds ADP and a phosphate group to produce ATP.

Light-Independent Reactions: The Calvin Cycle

• Carbon dioxide enters the Calvin Cycle from the atmosphere.
• An enzyme within the stroma combines CO2 with a 5-carbon sugar called RuBP, producing two molecules of 3-phosphoglycerate.
• Sugar production occurs during the Calvin Cycle, where 3-phosphoglycerate molecules are converted back into RuBP, which combines with new CO2 molecules to begin the next cycle.

Photosynthesis

• Light-dependent reactions trap the energy of sunlight in chemical form, while light-independent reactions use that chemical energy to synthesize stable, high-energy sugars from carbon dioxide and water.
• Factors affecting photosynthesis include temperature, light, and water.
• High light intensity increases the rate of photosynthesis, but after a certain level, the plant reaches its maximum rate.

Photosynthesis under Extreme Conditions

• C4 plants have adapted to extremely bright, hot conditions by using a specialized chemical pathway that allows them to capture very low levels of CO2 and pass it to the Calvin cycle.
• C4 plants, including crops like corn, sugar cane, and sorghum, require extra energy in the form of ATP to function.
• CAM plants, like those in the Crassulaceae family, have a similar adaptation, where CO2 is incorporated into organic acids during photosynthesis.
• CAM plants admit air into leaves only at night, combining CO2 with existing molecules to produce organic acids, which release carbon dioxide inside the leaf during the daytime, enabling carbohydrate production.