Chapter 10 Photosynthesis

Question 1

Chloroplast

Answer 1

An organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water

Question 2

Photosynthesis

Answer 2

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 3

Autotrophs

Answer 3

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 4

Heterotrophs

Answer 4

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

Question 5

Photoautotroph

Answer 5

An organism that harnesses light energy to drive the synthesis of organic compounds from carbon dioxide

Question 6

Mesophyll

Answer 6

Leaf cells specialized for photosynthesis. In C3 and CAM plants, 3 mesophyll cells are located between the upper
and lower epidermis; in C4 plants, they are located between the bundle-sheath cells and the epidermis

Question 7

Stoma (Plural Stomata)

Answer 7

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 8

Stroma

Answer 8

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 9

Thylakoid

Answer 9

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 10

Chlorophyll

Answer 10

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 11

Light reaction

Answer 11

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 12

Calvin cycle

Answer 12

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 13

NADP+

Answer 13

The oxidized form of nicotinamide adenine dinucleotide phosphate, an electron carrier that can accept electrons, becoming NADPH. NADPH temporarily stores energized electrons produced during the light reactions.

Question 14

NADPH

Answer 14

The reduced form of nicotinamide adenine dinucleotide phosphate; temporarily stores energized electrons produced during the light reactions. NADPH acts as “reducing power” that can be passed along to an electron acceptor, reducing it

Question 15

Photophosphorylation

Answer 15

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 16

Carbon fixation

Answer 16

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 17

Wavelength

Answer 17

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

Question 18

electromagnetic spectrum

Answer 18

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

Question 19

visible light

Answer 19

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 20

Photons

Answer 20

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

Question 21

Spectrophotometer

Answer 21

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

Question 22

Absorption spectrum

Answer 22

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

Question 23

Chlorophyll a

Answer 23

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

Question 24

Chlorophyll b

Answer 24

An accessory photosynthetic pigment that transfers energy to chlorophyll a

Question 25

Action spectrum

Answer 25

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

Question 26

Carotenoids

Answer 26

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 27

Photosystem

Answer 27

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 sur- rounded by numerous light-harvesting com- plexes. There are two types of photosystems, I and II; they absorb light best at different wavelengths

Question 28

Reaction-center complex

Answer 28

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 29

light-harvesting complex

Answer 29

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 30

primary electron acceptor

Answer 30

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 31

Photosystem I

Answer 31

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 32

Photosystem II

Answer 32

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 33

Linear electron flow

Answer 33

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 34

Cyclic electron flow

Answer 34

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 35

Glyceraldehyde 3-phosphate (G3P)

Answer 35

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

Question 36

Rubsico

Answer 36

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 37

C3 plants

Answer 37

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 38

Photorespiration

Answer 38

metabolic pathway that consumes oxygen and ATP, releases carbon dioxide, and decreases photosynthetic out- put. 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 39

C4 plants

Answer 39

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 40

Bundle-Sheath cells

Answer 40

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

Question 41

PEP carboxylase

Answer 41

An enzyme that adds CO to 2 phosphoenolpyruvate (PEP) to form oxaloacetate in mesophyll cells of C4 plants. It acts prior to photosynthesis

Question 42

Crassulacean acid meta

Answer 42

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 43

CAM plants

Answer 43

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