Unit 2b: Metabolic Processes - Photosynthesis

Question 1

light-dependent reactions

Answer 1

In photosynthesis, the reactions in which light energy is captured and used in production of ATP and NADPH. In plants this involves the action of two linked photosystems.

Question 2

light-independent reactions

Answer 2

In photosynthesis, the reactions of the Calvin cycle in which ATP and NADPH from the light-dependent reactions are used to reduce CO2 and produce organic compounds such as glucose. This involves the process of carbon fixation, or the conversion of inorganic carbon (CO2) to organic carbon (ultimately carbohydrates).

Question 3

carbon fixation

Answer 3

The conversion of CO2 into organic compounds during photosynthesis; the first stage of the dark reactions of photosynthesis, in which carbon dioxide from the air is combined with ribulose 1,5-bisphosphate.

Question 4

chlorophyll

Answer 4

The primary type of light-absorbing pigment in photosynthesis. Chlorophyll a absorbs light in the violet-blue and the red ranges of the visible light spectrum; chlorophyll b is an accessory pigment to chlorophyll a absorbing light in the blue and red-orange ranges. Neither pigment absorbs light in the green range , 500-600 nm.

Question 5

stroma

Answer 5

In plants, a minute opening bordered by guard cells in the epidermis of leaves and stems; water passes out of the plant mainly through the stomata. (pl. stomata)

Question 6

photosystems

Answer 6

An organized complex of chlorophyll, other pigments, and proteins that traps light energy as excited electrons. Plants have two linked photosystems in the thylakiod membrane of chloroplasts. Photosystem II passes an excited electron through an electron transport chain to photosystem I to replace an excited electron passed to NADPH. The electron lost from photosystem II is replaced by the oxidation of water.

Question 7

photon

Answer 7

A particle of light having a discrete amount of energy. The wave concept of light explains the different colours of the spectrum, whereas the particle concept of light explains the energy transfer during photosynthesis.

Question 8

pigments

Answer 8

A molecule that absorbs light.

Question 9

photoelectric effect

Answer 9

The ability of a beam of light to excite electrons, creating an electrical current.

Question 10

absorption spectrum

Answer 10

The relationship of absorbance vs. wavelength for a pigment molecule. This indicate which wavelengths are absorbed maximally by a pigment. For example, chlorophyll a absorbs most strongly in the violet-blue and red regions or the visible light spectrum.

Question 11

action spectrum

Answer 11

A measure of the efficiency of different wavelengths of light for photosynthesis. In plants it corresponds to the absorption spectrum of chlorophylls.

Question 12

carotenoid

Answer 12

Any of a group of accessory pigments found in plants; in addition to absorbing light energy, these pigments act as antioxidants, scavenging potential damaging free radical.

Question 13

phycobiloprotein

Answer 13

A type of accessory pigment found in cyanobacteria and some algae. Complexes of phycobiloprotein are able to absorb light energy in the green range.

Question 14

antenna complex

Answer 14

A complex of hundreds of pigment molecules in a photosystem that collects photons and feeds the light energy to a reaction center.

Question 15

reaction center

Answer 15

A transmembrane protein complex in a photosystem that receives energy from the antenna complex exciting an electron that is passed to an acceptor molecule.

Question 16

1. primary photoevent (Light-Dependent Reactions)

Answer 16

A photon of light is captured by a pigment. This primary photoevent excites an electron within the pigment.

Question 17

2. charge separation (Light-Dependent Reactions)

Answer 17

This excitation energy is transferred to the reaction center, which transfers an energetic electron to an acceptor molecule, initiating electron transport.

Question 18

3. electron transport (Light-Dependent Reactions)

Answer 18

The excited electrons are shuttled along a series of electron carrier molecules embedded within the photosynthetic membrane. Several of them react by transporting protons across the membrane, generating a proton gradient. Eventually the electrons are used to reduce a final acceptor, NADPH.

Question 19

4. chemiosmosis (Light-Dependent Reactions)

Answer 19

The protons that accumulate on one side of the membrane now flow back across the membrane through ATP synthase where chemiosmotic synthesis of ATP takes place, just as it does in aerobic respiration.

Question 20

noncyclic photophosphorylation

Answer 20

The set of light-dependent reactions of two plant photosystems, in which excited electrons are shuttled between the two photosystems, reducing a proton gradient that is used for the chemiosmotic synthesis of ATP. The electrons are used to reduce NADP to NADPH. Lost electrons are replaced by the oxidation of water producing O2.

Question 21

1. energy (Carbon Fixation: The Calvin Cycle)

Answer 21

ATP (provided by cyclic and noncyclic photophosphorylation) drives the endergonic reactions.

Question 22

2. reduction potential (Carbon Fixation: The Calvin Cycle)

Answer 22

NADPH (provided by photosystem I) provides a source of protons and the energetic electrons needed to bind them to carbon atoms. Much of the light energy captured in photosynthesis ends up invested in the energy-rich C-H bonds of sugar.

Question 23

photophosphorylation

Answer 23

The phosphorylation of ADP to ATP using the energy of sunlight in the process of photosynthesis.

Question 24

Calvin cycle

Answer 24

The dark reactions of C3 photosynthesis; also called the Calvin-Benson cycle.

Question 25

C3 photosynthesis

Answer 25

The main cycle of the dark reactions of photosynthesis, in which CO2 binds to ribulose 1,5-bisphosphate (RuBP) to form two 3-carbon phosphoglycerate (PGA) molecules.

Question 26

ribulose 1,5-bisphosphate (RuBP)

Answer 26

In the Calvin cycle, the five-carbon sugar to which CO2 is attached, accomplishing carbon fixation. This reaction is catalyzed by the enzyme rubisco.

Question 27

ribulose bisphosphate carboxylase/oxygenase (rubisco)

Answer 27

The four-subunit enzyme in the chloroplast that catalyzes the carbon fixation reaction joining CO2 to RuBP.

Question 28

photorespiration

Answer 28

Action of the enzyme rubisco, which catalyzes that oxidization of RuBP, releasing CO2; this reverses carbon fixation and can reduce the yield of photosynthesis.

Question 29

CAM plants

Answer 29

Plants that use C4 carbon fixation at night, then use the stored malate to regenerate CO2 during the day to minimize dessication (extreme dryness).

Question 30

crassulacean acid metabolism (CAM)

Answer 30

A mode of carbon dioxide fixation by which CO2 enters open leaf stomata at night and is used in photosynthesis during the day, when stomata are closed to prevent water loss.

Question 31

C4 photosynthesis

Answer 31

A process of CO2 fixation in photosynthesis by which the first product is the 4-carbon oxaloacetate molecule.