Biology Chapter 10

Front 1

absorption spectrum

Back 1

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

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action spectrum

Back 2

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

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ATP (adenosine triphosphate)

Back 3

a-den´-o-sen tri fos´-fat) An adenine-containing nucleoside triphosphate that releases free energy when its phosphate bonds are hydrolyzed. This energy is used to drive endergonic reactions in cells.

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atom

Back 4

The smallest unit of matter that retains the properties of an element.

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autotroph

Back 5

(ot´-o-trof) 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 the oxidation of inorganic substances to make organic molecules from inorganic ones.

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bundle-sheath cell

Back 6

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

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C3 plant

Back 7

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.

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C4 plant

Back 8

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.

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Calvin cycle

Back 9

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.

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CAM plant

Back 10

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.

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carbon fixation

Back 11

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

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carotenoid

Back 12

(kuh-rot´-uh-noyd´) 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.

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chlorophyll a

Back 13

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

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chlorophyll b

Back 14

An accessory photosynthetic pigment that transfers energy to chlorophyll a.

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crassulacean acid metabolism (CAM)

Back 15

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.

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cyclic electron flow

Back 16

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

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electromagnetic spectrum

Back 17

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

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glyceraldehyde-3-phosphate (G3P)

Back 18

(glis´-er-al´-de-hid) A three-carbon carbohydrate that is the direct product of the Calvin cycle; it is also an intermediate in glycolysis.

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heterotroph

Back 19

(het´-er-o-trof) An organism that obtains organic food molecules by eating other organisms or substances derived from them.

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leaf

Back 20

The main photosynthetic organ of vascular plants.

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light reactions

Back 21

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.

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light-harvesting complex

Back 22

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.

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linear electron flow

Back 23

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+.

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mesophyll

Back 24

(mez´-o-fil) The ground tissue of a leaf, sandwiched between the upper and lower epidermis and specialized for photosynthesis.

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mesophyll cell

Back 25

In C4 plants, a type of loosely arranged photosynthetic cell located between the bundle sheath and the leaf surface.

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NADP+

Back 26

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

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PEP carboxylase

Back 27

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

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photoautotroph

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(fo'-to-ot'-o-trof) An organism that harnesses light energy to drive the synthesis of organic compounds from carbon dioxide.

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photon

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(fo´-ton) A quantum, or discrete quantity, of light energy that behaves as if it were a particle.

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photorespiration

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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 oxygen concentration in the leaf exceeds that of carbon dioxide.

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photosynthesis

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(fo'-to-sin'-thi-sis) The conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes.

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photosystem

Back 32

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.

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photosystem I (PS I)

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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.

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photosystem II (PS II)

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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.

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primary electron acceptor

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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.

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producer

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An organism that produces organic compounds from CO2 by harnessing light energy (in photosynthesis) or by oxidizing inorganic chemicals (in chemosynthetic reactions carried out by some prokaryotes).

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reaction-center complex

Back 37

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.

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rubisco

Back 38

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

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spectrophotometer

Back 39

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

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stoma

Back 40

(sto´-muh) (plural, stomata) 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.

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stroma

Back 41

(stro´-muh) Within the chloroplast, the dense fluid of the chloroplast surrounding the thylakoid membrane; involved in the synthesis of organic molecules from carbon dioxide and water.

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thylakoid

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(thi´-luh-koyd) A flattened membranous sac inside a chloroplast. Thylakoids exist in an interconnected system in the chloroplast and contain the molecular “machinery” used to convert light energy to chemical energy.

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visible light

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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.

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wavelength

Back 44

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