8. 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. Autotrophs 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 C and CAM plants, mesophyll cells are located between the upper and lower epidermis; in C 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

thylakoid

Answer 7

A flattened, membranous sac inside a chloroplast. Thylakoids 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. Chlorophyll a participates directly in the light reactions, which convert solar energy to chemical energy.

Question 9

photosynthesis net formula

Answer 9

6 CO2 + 6 H2O + light energy -> C6H12O6 + 6 O2

Question 10

light reactions

Answer 10

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 11

Calvin cycle

Answer 11

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

Question 12

NADP+

Answer 12

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

Question 13

photophosphorylation

Answer 13

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 14

carbon fixation

Answer 14

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 15

wavelength

Answer 15

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

Question 16

electromagnetic spectrum

Answer 16

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

Question 17

visible light

Answer 17

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

Question 18

photon

Answer 18

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

Question 19

spectrophotometer

Answer 19

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

Question 20

absorption spectrum

Answer 20

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

Question 21

chlorophyll a

Answer 21

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

Question 22

chlorophyll b

Answer 22

An accessory photosynthetic pigment that transfers energy to chlorophyll a.

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, carotenoids 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 of photosystems, 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

action spectrum

Answer 26

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

Question 27

light-harvesting complex

Answer 27

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 28

primary electron receptor

Answer 28

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 29

pigment

Answer 29

substances that absorb visible light

Question 30

photosystem II (PS II)

Answer 30

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 (best at absorbing light at 680 nm) at its reaction center. Functions first in the light reactions, but named in order of discovery.

Question 31

photosystem I (PS I)

Answer 31

One of two light-capturing units 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 32

linear electron flow

Answer 32

A route of electron flow during the light reactions of photosynthesis that involves both photosystems (II and I) and produces ATP, NADPH, and O2. The net electron flow is from H2O to NADPH. Review pages 164 to 165 in the textbook.

Question 33

glyceraldehyde 3-phosphate

Answer 33

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

Question 34

rubisco

Answer 34

Ribulose bisphosphate (RuBP) carboxylase, the enzyme that catalyzes the first step of the Calvin cycle (the addition of CO2 to RuBP).

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

photorespiration

Answer 36

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 37

C4 plants

Answer 37

A plant in which the Calvin cycle is preceded by reactions that incorporate CO4 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle.

Question 38

CAM plants

Answer 38

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