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 C3
and CAM plants, 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 5

stomata

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

light reactions

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
carbohydrate

Question 11

NADP+

Answer 11

Nicotinamide adenine dinucleotide phosphate, an electron acceptor that, as NADPH,
temporarily stores energized electrons produced during the 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 nanometre to more than a kilometre.

Question 16

visible light

Answer 16

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

Question 17

photon

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, carotenoids broaden the spectrum of colours 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-centre 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-centre 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-centre 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-centre 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 centre.

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 centre.

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 photosystem I 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, the enzyme that catalyzes the
first step of the Calvin cycle (the addition of CO2
to RuBP).

Question 34

C3 plant

Answer 34

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 35

photorespiration

Answer 35

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, favouring
the binding of O2
rather than CO2
by rubisco.

Question 36

C4 plant

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 cell

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 plant

Answer 40

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.