How Cells Capture Energy

Vocabulary

absorption spectrum

graph that shows how different pigments absorb light

action spectrum

graph that shows how the rate of photosynthesis is affected by different wavelengths of light

adenosine diphosphate (ADP)

reduced form of the biological unit of energy, ATP. ADP has one less phosphate group than ATP.

adenosine triphosphate (ATP)

biological unit of energy that consists of an adenosine (an adenine group and a ribose sugar) and three phosphate groups

bundle-sheath cell

cell in which the Calvin cycle takes place in C4 plants around the veins of the leaves

C3 plant

plant that undergoes the typical metabolic pathways that fix carbon into three-carbon molecules

C4 plant

plant that uses an alternate metabolic pathway in which carbon is fixed into four-carbon molecules

CAM plant

plant that uses an alternate metabolic pathway in which carbon is fixed into organic acids at night and passed on to the Calvin cycle during the day

chemiosmosis

movement of ions across a semipermeable membrane down their electrochemical gradient, which results in a charge that can be used as a source of energy

chemoautotroph

organism that uses chemicals to produce carbon compounds for itself to use as energy

chlorophyll

green pigment used in photosynthesis

chloroplast

membrane-bound organelle found in plants and some other organisms that captures energy from light and converts it into chemical energy

cytochrome complex

enzyme in the thylakoid membrane that forms part of the electron transport chain that moves electrons from photosystem II to photosystem I

glucose

six-carbon sugar that is the product of reactions following the Calvin cycle

granum (plural, grana)

stack of thylakoid sacs where the light reactions of photosynthesis take place

mesophyll cell

cell in a leaf that contains chloroplasts, where photosynthesis takes place, or where carbon fixation occurs in C4 plants

NADP+

oxidized form of NADPH, which is primarily used as an electron carrier in the Calvin cycle

NADPH

reduced form of NADP+ that serves as an electron carrier in the Calvin cycle. The H at the end denotes that the molecule contains an extra hydrogen atom along with two high-energy electrons as compared to NADP+.

nitrogen fixation

taking in nitrogen from the atmosphere and converting it into ammonia

oxaloacetate

product of the carbon-fixation reaction in C4 photosynthesis

photoautotroph

organism that makes its own food using light energy

photorespiration

uptake of O2 and release of CO2 driven by light, which consumes energy and decreases the output from photosynthesis

photosynthesis

process by which autotrophs convert light energy into chemical energy that is stored in organic compounds, such as sugars

photosystem I

second light-capturing complex found in the thylakoid membrane of a chloroplast that converts light energy into chemical energy

photosystem II

first light-capturing complex found in the thylakoid membrane of a chloroplast that converts light energy into chemical energy

plasmodesma (plural, plasmodesmata)

structure with many uses, such as functioning as a small channel between mesophyll cells and bundle-sheath cells through which molecules pass between carbon fixation in the mesophyll cells and the Calvin cycle in the bundle-sheath cells. This channel extends through the cell wall of a plant cell and directly connects the cytoplasm of adjacent plant cells.

pyruvate

molecule that is produced after CO2 is passed on to the Calvin cycle in C4 photosynthesis, which regenerates PEP

rubisco

enzyme that adds one carbon to a five-carbon sugar called ribulose bisphosphate (RuBP) during carbon fixation

stoma (plural, stomata)

small opening mostly found on the undersides of leaves that allows for gas exchange between the plant and the external environment

stroma

fluid inside chloroplasts that contains bundles of membrane-bound sacs called thylakoids