Biology Chapter 7

autotroph

"self-feeders"; make their own food and are the ultimate source of organic molecules for other organisms.

Light, carbon dioxide, and water.

7.1 What do "self-feeding" photoautotrophs require from the environment to make their own food?

6, 18, 12. Glucose is a highly reduced molecule, storing lots of potential energy in its electrons. The more energy a molecule stores, the more energy and reducing power required to produce that molecule.

7.10 To synthesize one glucose molecule, the Calvin cycle uses ___ CO2, ___ ATP, and ___ NADPH. Explain why this high number of ATP and NADPH molecules is consistent with the value of glucose as an energy source.

Because of their initial fixing of carbon, both C4 and CAM plants can supply rubisco with CO2. When a C3 plant closes its stomata, CO2 levels drop and O2 rises, making it more likely that rubisco will add O2 to RuBP.

7.11 Why would you expect photorespiration on a hot, dry day to occur less in C4 and CAM plants than in C3 plants?

Photosynthesis is the ultimate source of the food for almost all organisms and the oxygen they need for cellular respiration.

7.12 Explain this statement: No process is more important to the welfare of life on Earth than photosynthesis.

CO2 enters leaves through stomata, and H2O enters the roots and is carried to leaves through veins.

7.2 How do the reactant molecules of photosynthesis reach the chloroplasts in leaves?

Mostly from CO2 in the air, which provides both the carbon and oxygen in carbohydrate. Water supplies only the hydrogen.

7.3 Photosynthesis produces billions of tons of carbohydrate a year. Where does most of the mass of this huge amount of organic matter come from?

Photosynthesis.

7.4 Which redox process, photosynthesis or cellular respiration, is endergonic?

ATP... NADPH

7.5 For chloroplasts to produce sugar from carbon dioxide in the dark, they would need to be supplied with _______ and _______ .

Green, because it is mostly transmitted and reflected - not absorbed - by photosynthetic pigments.

7.6 What color of light is least effective at driving photosynthesis? Explain.

In the chloroplasts, light-excited electron from the reaction-center chlorophyll molecules is trapped by a primary electron acceptor rather than giving up its energy as heat and light.

7.7 Compared with a solution of isolated chlorophyll, why do intact chloroplasts release less heat and fluorescence when illuminated?

One photon excites an electron from photosystem II, which is then passed down an electron transport chain to photosystem I. A second photon excites an electron from photosystem I, which is then used in the reduction of NADP+ to NADPH.

7.8 Looking at the model of light reactions in Figure 7.8, explain why two photons of light are required in the movement of electrons from water in NADPH.

The Calvin cycle, which uses the NADPH and ATP, occurs in the stroma.

7.9 What is the advantage of the light reactions producing NADPH and ATP on the stroma side of the thylakoid membrane?

photon

A fixed quantity of light energy. The shorter the wavelength of light, the greater the energy of a photon.

chlorophyll

A green, light-absorbing pigment in the chloroplasts that plays a central role in converting solar energy to chemical energy.

photosystem

A light capturing unit of a chloroplast's thylakoid membrane, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes.

C4 plant

A plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, which then supplies CO2 for the Calvin cycle.

CAM plant

A plant that uses an adaption for photosynthesis in arid conditions in which carbon dioxide entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed.

C3 plant

A plant that uses the Calvin cycle for the initial steps that incorporate CO2 into organic material, forming a three-carbon compound as the first stable intermediate.

photosynthesis

A process in which plants use solar energy to convert CO2 and H2O to sugars and other organic molecules, and release O2 as a by-product.

NADP+

An electron acceptor that, as NADPH, temporarily stores energized electrons produced during light reactions.

photoautotroph

An organism that obtains energy from sunlight and carbon and CO2 by photosynthesis

photorespiration

In a plant cell, a metabolic pathway that consumes oxygen, releases CO2, and decreases photosynthetic output. Photorespiration generally occurs on hot, dry days, when stomata close, O2 accumulates in the leaf, and rubisco fixes O2 rather than CO2. Photorespiration produce no sugar molecules or ATP.

light reactions

Occur in the thylakoids; the first of two stages in photosynthesis; the steps in which solar energy is absorbed and converted to the chemical energy of ATP and NADPH, releasing O2 in the process.

Calvin cycle

Occurs in the stroma of the chloroplast; the second of two stages of photosynthesis; a series of chemical reactions using the carbon in CO2 and the ATP and NADPH produced by the light reactions to make the energy-rich sugar molecule G3P.

thylakoids

Suspended in the stroma; a system of interconnected membranous sacs which enclose another internal compartment called the thylakoid space.

wavelength

The distance between crests of adjacent waves, such as those of the electromagnetic spectrum.

electromagnetic spectrum

The entire spectrum of electromagnetic radiation ranging in wavelength from less than a nanometer to more than a kilometer.

mesophyll

The green tissue in the interior of a leaf where chloroplasts are concentrated.

carbon fixation

The incorporation of carbon from atmospheric CO2 into an organic compund. During photosynthesis in a C3 plant, carbon is fixed into a three-carbon sugar as it enters the Calvin cycle. In C4 and CAM plants, carbon is first fixed into a four-carbon sugar.

photophosphorylation

The production of ATP by chemiosmosis during the light reactions of photosynthesis.

stroma

Thick fluid in an envelope of 2 membranes enclosing an inner compartment.

stomata

Tiny pores where carbon dioxide enters the leaf and oxygen exits.

heterotroph

cannot make their own food, but must consume plants or animals or decompose organic material