AP Biology Vocabulary & Roots: Ch. 10
1. absorption spectrum-The range of a pigment’s ability to absorb various wavelengths of light;
also a graph of such a range.
2. action spectrum-A graph that profiles the relative effectiveness of different wavelengths of
radiation in driving a particular process.
3. ATP (adenosine triphosphate)- 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.
4. atom-The smallest unit of matter that retains the properties of an element.
5. autotroph-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.
6. bundle-sheath cell- in C4 plants, a type of photosynthetic cell arranged into tightly packed
sheaths around the veins of A leaf.
7. C3 plant-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.
8. C4 plant- 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.
9. Calvin cycle- 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.
10. CAM plant-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.
11. carbon fixation-The initial incorporation of carbon from CO2 into an organic compound by an
autotrophic organism (a plant, another photosynthetic organism, or a chemoautotrophic prokaryote).
12. carotenoid-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.
13. chlorophyll-A green pigment located 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.
14. chlorophyll a- A photosynthetic pigment that participates directly in the light reactions, which
convert solar energy to chemical energy.
15. chlorophyll b-An accessory photosynthetic pigment that transfers energy to chlorophyll a.
16. crassulacean acid metabolism (CAM)-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.
17. cyclic electron flow-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.
18. electromagnetic spectrum-The entire spectrum of electromagnetic radiation ranging in
wavelength from less than a nanometer to more than a kilometer.
19. glyceraldehyde-3-phosphate (G3P)-A three-carbon carbohydrate that is the direct product of
the Calvin cycle; it is also an intermediate in glycolysis.
20. heterotroph-An organism that obtains organic food molecules by eating other organisms or
substances derived from them.
21. leaf-The main photosynthetic organ of vascular plants.
1
22. light reactions-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.
23. light-harvesting complex-A complex of proteins associated with pigment molecules (including
chlorophyll a, chlorophyll b, and carotenoids) that captures light energy and transfers it to reactioncenter pigments in a photosystem.
24. linear electron flow-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+.
25. mesophyll-The ground tissue of a leaf, sandwiched between the upper and lower epidermis and
specialized for photosynthesis.
26. mesophyll cell-In C4 plants, a type of loosely arranged photosynthetic cell located between the
bundle sheath and the leaf surface.
27. NADP+ (Nicotinamide adenine dinucleotide phosphate)- An electron acceptor that, as NADPH,
temporarily stores energized electrons produced during the light reactions.
28. PEP carboxylase-An enzyme that adds CO2 to phosphoenolpyruvate (PEP) to form
oxaloacetate in C4 plants. It acts prior to photosynthesis.
29. photoautotroph-An organism that harnesses light energy to drive the synthesis of organic
compounds from carbon dioxide.
30. photon-A quantum, or discrete quantity, of light energy that behaves as if it were a particle.
31. photophosphorylation-The process of generating ATP from ADP and phosphate by means of a
proton-motive force generated across the thylakoid membrane of the chloroplast or the membrane
of certain prokaryotes during the light reactions of photosynthesis.
32. photorespiration-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.
33. photosynthesis-The conversion of light energy to chemical energy that is stored in sugars or
other organic compounds; occurs in plants, algae, and certain prokaryotes.
34. photosystem-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.
35. photosystem I (PS I)-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.
36. photosystem II (PS II)-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.
37. primary electron acceptor-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.
38. producer-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).
2
39. reaction-center complex-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.
40. rubisco (Ribulose bisphosphate (RuBP) carboxylase)- the enzyme that catalyzes the first step of
the Calvin cycle (the addition of CO2 to RuBP).
41. spectrophotometer-An instrument that measures the proportions of light of different
wavelengths absorbed and transmitted by a pigment solution.
42. stoma(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.
43. stroma-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.
44. thylakoid-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.
45. visible light-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.
46. wavelength-The distance between crests of waves, such as those of the electromagnetic
spectrum.
Word Roots
auto- = self; -troph = food (autotroph: an organism that obtains organic food molecules without
eating other organisms)
chloro- = green; -phyll = leaf (chlorophyll: photosynthetic pigment in chloroplasts)
electro- = electricity; magnet- = magnetic (electromagnetic spectrum: the entire spectrum of
radiation)
hetero- = other (heterotroph: an organism that obtains organic food molecules by eating other
organisms or their by-products)
meso- = middle (mesophyll: the green tissue in the middle, inside of a leaf)
photo- = light (photosystem: cluster of pigment molecules)
3