Chapter 6- Photosynthesis

Question 1

what is photosynthesis?

Answer 1

is the use of light energy to convert carbon from CO2
gas into an organic form. Oxygen, generated from the oxidation of H2O during the process, is released
as a by-product

Question 2

what are autotrophs?

Answer 2

Organisms that make required organic (food) molecules from
inorganic sources such as CO2 and water; self-feeding

Question 3

what are heterotrophs?

Answer 3

Consumers and decomposers which need a source of organic
(food) molecules to survive

Question 4

what are photoautotrophs?

Answer 4

Autotrophs that use light as the energy source to make organic
molecules by photosynthesis; primary producers of the earth

Question 5

what do photosynthetic organisms do?

Answer 5

• Convert sunlight energy into chemical energy
• Use energy to assemble complex organic molecules from inorganic raw materials
• The organic molecules are then used as energy sources
  (but also used as energy source by other organisms)

Question 6

what are the two stages of photosynthesis?

Answer 6

1. Light reactions: light energy absorbed by pigment molecules is transformed into ATP and NADPH; O2 that is produced as a result of the oxidation of water is released as a by-product.
2. Calvin cycle: NADPH and ATP produced during the light reactions
   provide energy and reducing power to fix carbon from CO2 and
   convert it into carbohydrates

Question 7

what type of reaction is photosynthesis?

Answer 7

redox reaction

Question 8

where does photosynthesis take place?

Answer 8

photosynthesis takes place in chloroplasts

Question 9

what two membranes surround the chloroplast?

Answer 9

outer and inner membranes
* Separated by intermembrane space

Question 10

The main aqueous compartment is called the _____________

Answer 10

stroma; this is where carbohydrate synthesis takes place

Question 11

explain thylakoid membranes.

Answer 11

• Location of photosynthetic pigments and electron transport chain
• A complex of flattened, closed sacs
• Stacks of membranes called grana
• Tubular lamellae connect the grana

Question 12

what is the soluble compartment enclosed by thylakoids called?

Answer 12

thylakoid lumen

Question 13

what is the electromagnetic spectrum?

Answer 13

The range of wavelengths of electromagnetic radiation

Question 14

The Sun converts matter to energy, releasing it as _____________

Answer 14

electromagnetic radiation

Question 15

what is light ?

Answer 15

Light is defined as the portion of electromagnetic spectrum that humans can detect with their eyes
* Light behaves like a wave and like particles of energy (photons),
and thus can be understood as a wave of photons.

Question 16

Visible light has wavelengths between how much nm

Answer 16

700 nm (red light) and 400 nm (blue light)

Question 17

The photon can be what ?

Answer 17

• reflected
• transmitted
• absorbed

Question 18

the energy of the photon is transferred to what?

Answer 18

electron within a molecule

Question 19

what are pigments?

Answer 19

molecules that absorb photons of specific wavelengths

Question 20

Critical light absorption feature

Answer 20

a region where carbon atoms are covalently bonded to each other with alternating single and double bonds
(conjugated system)

Question 21

what does a pigment’s color mean?

Answer 21

A pigment’s colour is the result of photons of light it does not absorb.

Question 22

what is a major photosynthetic pigment ?

Answer 22

Chlorophyll

Question 23

what are the three fates of an excited-state electron?

Answer 23

1. Excited electron returns to its ground state, releasing
   energy as heat or as light of a longer wavelength
   (fluorescence)
2. Energy from excited electron in one pigment molecule is transferred to a neighbouring pigment molecule
   * Transfer excites second pigment, returning first pigment to its ground state
3. Excited-state electron itself is transferred to nearby
   electron-accepting molecule

Question 24

what are accessory pigments?

Answer 24

Chlorophyll b and carotenoids; Donate excitation energy to chlorophyll a via inductive resonance

Question 25

what type of chlorophyll can be oxidized?

Answer 25

Some Chlorophyll a molecules can be oxidized and donate excited state electrons to primary electron acceptor

Question 26

The amount of light of different wavelengths that is absorbed by a pigment is its __________________

Answer 26

absorption spectrum

Question 27

The effectiveness of light of each wavelength in driving photosynthesis produces a graph called _______________-

Answer 27

action spectrum of photosynthesis

Question 28

Explain the Engelmann’s Experiment (1883).

Answer 28

* Theodor Engelmann used a glass prism to break light into a spectrum of colours—cast across a microscope slide with a strand of algae and aerobic bacteria. * Bacteria grew best where algae released oxygen in greatest quantity —in areas of blue, violet, and red light. * Engelmann constructed an action spectrum for wavelengths of light, showing the effects of each colour on photosynthesis.

Question 29

what are the two major components of a photosystem?

Answer 29

Antenna complex and Reaction Center

Question 30

what is the purpose of Antenna complex?

Answer 30

* Absorbs light energy: - Chlorophyll a and b - Carotenoids * Energy transferred to Reaction Center chlorophyll a molecules via inductive resonance

Question 31

What is the purpose of the reaction center?

Answer 31

* Pair of special chlorophyll a molecules of reaction center are bound by proteins: * P680 in PSII * P700 in PSI

Question 32

what is the Primary electron acceptor?

Answer 32

Pheophytin in PSII

Question 33

what is photosystem I?

Answer 33

Specialized chlorophyll a molecules in the reaction centre are called P700

Question 34

what is photosystem II ?

Answer 34

Special chlorophyll a molecules in the reaction centre are called P680 (P = pigment; 680 denotes wavelength of max absorbance for the reaction centre)

Question 35

what is pheophytin ?

Answer 35

compound that serves as the first electron carrier intermediate in the electron transfer pathway of Photosystem II in plants

Question 36

what is plastoquinone?

Answer 36

the electron “hole”

Question 37

what does the cytochrome complex do?

Answer 37

transfers electrons to plastocyanin (PC)

Question 38

what is the iron-sulfur protein?

Answer 38

ferredoxin

Question 39

Proton-motive force

Answer 39

established across thylakoid membrane used to synthesize ATP by chemiosmosis and ATP Synthase

Question 40

Absorption of light energy by PS II allows ____________

Answer 40

electrons pulled from water to enter the photosynthetic ETC

Question 41

A second input of light energy by PS I produces ________

Answer 41

electron donor molecules capable of reducing NADP+

Question 42

what is the calvin cycle?

Answer 42

- The Calvin cycle is a metabolic pathway that reduces CO2 and converts it into organic substances. It is an anabolic, endergonic process. *NADPH provides electrons and hydrogen *ATP provides additional energy

Question 43

Carbon fixation

Answer 43

involves capturing CO2 molecules with the key enzyme Rubisco

Question 44

three phases of the calvin cycle?

Answer 44

1. fixation 2. Reduction 3. Regeneration

Question 45

What is fixation?

Answer 45

CO2 added to RuBP to produce two 3PGA molecules (3- phosphoglycerate) molecules  catalyzed by Rubisco

Question 46

what is reduction?

Answer 46

NADPH and ATP used to convert 3PGA into G3P, a higher energy molecule used to build sugars Calvin Cycle

Question 47

what is regeneration?

Answer 47

Remaining G3P molecules are used to regenerate the starting material RuBP

Question 48

what is rubisco?

Answer 48

Most abundant protein on Earth - Provides the source of organic molecules for most of the world’s organisms * Represents 50% or more of the total protein in leaves of higher plants

Question 49

what is rubisco composed of?

Answer 49

* 8 Large Subunits (LSU) * chloroplast genome * 8 Small Subunits (SSU) * nuclear genome

Question 50

photorespiration...?

Answer 50

The oxygenase activity results in a net loss of carbon. Because oxygenase activity consumes O2 and releases CO2, the metabolic pathway it leads to

Question 51

Rubisco Oxygenase Activity

Answer 51

* O2 acts as a competitive inhibitor of Rubisco’s carboxylase activity - Ancient enzyme, originally evolved when very little O2 in the atmosphere

Question 52

algae actively pump what?

Answer 52

bicarbonite anion, the most abundant form of inorganic carbon dissolved in water

Question 53

what does stomata do?

Answer 53

regulate gas exchange

Question 54

C4 Photosynthesis

Answer 54

* Some plants have evolved the C4 pathway to increase the concentration of CO2 relative to O2 near Rubisco so that photorespiration is minimized * In the C4 cycle, CO2 is combined with a 3-carbon molecule, phosphoenolpyruvate (PEP), to produce a 4- carbon intermediate * The Calvin cycle is called the C3 cycle because a 3- carbon intermediate is produced first (3PGA)

Question 55

what binds CO2 in C4 photosynthesis?

Answer 55

enzyme PEP carboxylase

Question 56

mesophyll cells

Answer 56

- first pathway CO2 is captured by PEP carboxylase in mesophyll cells close to the surface of leaves, since PEP carboxylase is not affected by high O2 concentrations

Question 57

bundle sheath cells

Answer 57

- second pathway * The 4-carbon intermediate is then transported to bundle sheath cells deeper in the leaf where CO2 is released * There, O2 is less abundant and CO2 is more concentrated, so Rubisco’s oxygenase activity is minimized (less photorespiration)