Photosynthesis

Question 1

Photosynthesis

Answer 1

The conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes

Question 2

Autotroph

Answer 2

An organism that obtains organic food molecules without eating other organisms or substances derived from other organisms. They use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones

Question 3

Heterotroph

Answer 3

An organism that obtains organic food molecules by eating other organisms or substances derived from them

Question 4

Mesophyll

Answer 4

Leaf cells specialized for photosynthesis. In C3 and CAM plants, these cells are located between the upper and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis

Question 5

Stoma

Answer 5

A microscopic pore surrounded by guard cells in the epidermis of leaves and stems that allows gas exchange between the environment and the interior of the plant

Question 6

Stroma

Answer 6

The dense fluid within the chloroplast surrounding the thylakoid membrane and containing ribosomes and DNA; involved in the synthesis of organic molecules from carbon dioxide and water

Question 7

Thylakoids

Answer 7

A flattened, membranous sac inside a chloroplast. They often exist in stacks called grana that are interconnected; their membranes contain molecular “machinery” used to convert light energy to chemical energy

Question 8

Chlorophyll

Answer 8

A green pigment located in membranes within the chloroplasts of plants and algae and in the membranes of certain prokaryotes. The a version participates directly in the light reactions, which convert solar energy to chemical energy

Question 9

Light Reaction

Answer 9

The first of two major stages in photosynthesis (preceding the Calvin cycle). These reactions, which occur on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes, convert solar energy to the chemical energy of ATP and NADPH, releasing oxygen in the process

Question 10

Calvin Cycle

Answer 10

The second of two major stages in photosynthesis (following the light reactions), involving fixation of atmospheric CO2 and reduction of the fixed carbon into carbohydrates

Question 11

NADP+

Answer 11

Nicotinamide adenine dinucleotide phosphate, an electron acceptor that, as NADPH, temporarily stores energized electrons produced during light reactions

Question 12

Photophosphorylation

Answer 12

The process of generating ATP from ADP and phosphate by means of chemiosmosis, using a proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane of certain prokaryotes during the light reactions of photosynthesis

Question 13

Carbon Fixation

Answer 13

The initial incorporation of carbon from CO2 into an organic compound by an autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote)

Question 14

Wavelength

Answer 14

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

Question 15

Electromagnetic Spectrum

Answer 15

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

Question 16

Visible Light

Answer 16

That portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from about 380nm to about 750nm

Question 17

Photons

Answer 17

A quantum, or discrete quantity, of light energy that behaves as if it were a particle

Question 18

Spectrophotometer

Answer 18

An instrument that measures the proportions of light of different wavelengths absorbed and transmitted by a pigment solution

Question 19

Absorption Spectrum

Answer 19

The range of a pigment’s ability to absorb various wavelengths of light; also a graph of such a range

Question 20

Chlorophyll A

Answer 20

A photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy

Question 21

Chlorophyll B

Answer 21

An accessory photosynthetic pigment that transfers energy to chlorophyll a

Question 22

Action Spectrum

Answer 22

A graph that profiles the relative effectiveness of different wavelengths of radiation in driving a particular process

Question 23

Carotenoid

Answer 23

An accessory pigment, either yellow or orange, in the chloroplasts of plants and in some prokaryotes. By absorbing wavelengths of light that chlorophyll cannot, these broaden the spectrum of colors that can drive photosynthesis

Question 24

Photosystem

Answer 24

A light-capturing unit located in the thylakoid membrane of the chloroplast or in the membrane of some prokaryotes, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes. There are two types, I and II; they absorb light best at different wavelengths

Question 25

Reaction-Center Complex

Answer 25

A complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor. Located centrally in a photosystem, this complex triggers the light reactions of photosynthesis. Excited by light energy, the pair of chlorophylls donates an electron to the primary electron acceptor, which passes an electron to an electron transport chain

Question 26

Light-Harvesting Complex

Answer 26

A complex of proteins associated with pigment molecules (including chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reaction-center pigments in a photosystem

Question 27

Primary Electron Acceptor

Answer 27

In the thylakoid membrane of a chloroplast or in the membrane of some prokaryotes a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molecules and that accepts an electron from them

Question 28

Photosystem II (PS II)

Answer 28

One of two light-capturing units in a chloroplast’s thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P680 chlorophyll a at its reaction center

Question 29

Photosystem I (PS I)

Answer 29

A light-capturing unit in a chloroplast’s thylakoid membrane or in the membrane of some prokaryotes; it has two molecules of P700 chlorophyll a at its reaction center

Question 30

Linear Electron Flow

Answer 30

A route of electron flow during the light reactions of photosynthesis that involves both photosystems (I and II) and produces ATP, NADPH, and O2. The net electron flow is from H2O to NADP+

Question 31

Cyclic Electron Flow

Answer 31

A route of electron flow during the light reactions of photosynthesis that involves only one photosystem and that produces ATP but not NADPH or O2

Question 32

Glyceraldehyde 3-Phosphate (G3P)

Answer 32

A three-carbon carbohydrate that is the direct product of the Calvin cycle; it is also an intermediate in glycolysis

Question 33

Rubisco

Answer 33

Ribulose bisphosphate (RuBP) carboxylase-oxygenase, the enzyme that normally catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP). When excess O2 is present or CO2 levels are low, rubisco can bind oxygen, resulting in photorespiration

Question 34

Photorespiration

Answer 34

A metabolic pathway that consumes oxygen and ATP, releases carbon dioxide, and decreases photosynthetic output. Photorespiration generally occurs on hot, dry, bright days, when stomata close and the O2/CO2 ratio in the leaf increases, favoring the binding of O2, rather than CO2 by rubisco

Question 35

C3 Plants

Answer 35

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

Question 36

C4 Plants

Answer 36

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

Question 37

Bundle-Sheath Cells

Answer 37

In C4 plants, a type of photosynthetic cell arranged into tightly packed sheaths around the veins of a leaf

Question 38

PEP Carboxylase

Answer 38

An enzyme that adds CO2 to phosphoenolpyruvate (PEP) to form oxaloacetate in mesophyll cells of C4 plants. It acts prior to photosynthesis

Question 39

Crassulacean Acid Metabolism (CAM)

Answer 39

An adaptation for photosynthesis in arid conditions, first discovered in the family Crassulaceae. In this process, a plant takes up CO2 and incorporates it into a variety of organic acids at night; during the day, CO2 is released from organic acids for use in the Calvin cycle

Question 40

CAM Plants

Answer 40

A plant that uses crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. In this process, CO2 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