Chapter 4: Photosynthesis and the Chloroplast

Question 1

Redox potential of S—H2S couple

Answer 1

-0.25 V

Question 2

Redox potential of O2—H2O couple

Answer 2

+0.816V

Question 3

The polypeptides found within modern-day chloroplasts are encoded by both the _______ and ___________ genomes.

Answer 3

nuclear, chloroplast

Question 4

Give the dimensions of chloroplasts in higher plants

Answer 4

• 2-4 um wide
• 5-10 um long
• numbering 20-40 per cell

Question 5

Shape of chloroplasts of higher plants

Answer 5

lens-shaped

Question 6

non-pigmented precursors of chloroplasts

Answer 6

proplastids

Question 7

Chloroplasts arise by _______ from preexisting chloroplasts

Answer 7

fission

Question 8

The German biologist who identified chloroplasts as the site of photosynthesis in his ingenious experiment

Answer 8

T. Engelmann (1881)

Question 9

The green alga illuminated by the German biologist where he found that actively moving bacteria would collect outside the cell near the site of the large ribbon like chloroplast

Answer 9

Spirogyra

Question 10

Envelope membranes of chloroplast

Answer 10

• inner envelope membrane
• outer envelope membrane

Question 10

Flattened membranous sacs wherein membrane of the chloroplast is organized

Answer 10

thylakoids

Question 11

Thylakoids are arranged into these orderly stacks

Answer 11

granum/grana

Question 12

Space inside a thylakoid sac

Answer 12

lumen

Question 13

Space outside the thylakoid and within the chloroplast envelope

Answer 13

stroma

Question 14

Contains the enzymes responsible for carbohydrate synthesis

Answer 14

stroma

Question 15

Contains the chlorophyll molecules and protein complexes

Answer 15

thylakoid membrane

Question 16

Chloroplast DNA contains about ____________ involved in either gene expression or photosynthesis

Answer 16

60-200 genes

Question 17

One of the galactose-containing glycolipids in thylakoid membranes

Answer 17

Monogalactosyl diacylglycerol

Question 18

Prevailing belief on photosynthesis in 1930

Answer 18

• energy of light was used to split CO₂
• molecular oxygen (O₂) was released
• transfer of carbon atom to a molecule of water to form a unit of carbohydrate (CH₂O)

Question 19

Graduate student from Stanford University who proposed an alternative mechanism for Photosynthetic Metabolism

Answer 19

C. B. van Niel (early 1930s)

Question 20

In the experiment of van Niel, he demonstrated that these organisms were able to reduce CO₂ to carbohydrate using the energy of light without the simultaneous production of molecular O₂

Answer 20

sulfur bacteria

Question 21

van Niel’s proposed reaction for sulfur bacteria

Answer 21

CO₂ + 2 H₂S —light—> (CH₂O) + H₂O + 2 S

Question 22

van Niel’s proposed reaction for all activities

Answer 22

CO₂ + 2 H₂A —light—> (CH₂O) + H₂O + 2 A

Question 23

Reaction for production of a hexose (e.g. glucose)

Answer 23

6 CO₂ + 12 H₂A —light—> C₆H₁₂O₆ + 6 H₂O + 12 A

Question 24

Carbon dioxide in a plant cell is reduced to form hexose in this reaction

Answer 24

6 CO₂ + **12 H₂O** ---light---> C₆H₁₂O₆ + 6 H₂O + **6 O₂**

Question 25

# True or False? Each molecule of oxygen is derived from the breakdown of two molecules of H₂O

Answer 25

True

Question 26

Two scientists from the University of California, Berkeley who established the role of water in the formation of molecular oxygen

Answer 26

- **S**amuel **R**uben (1941) - **M**artin **K**amen (1941)

Question 27

Two series of reactions in photosynthesis

Answer 27

1. **light-dependent reactions** 2. light-independent reactions (**dark reactions**)

Question 28

Stage where energy from sunlight is absorbed and stored as chemical energy in **ATP** and **NADPH**

Answer 28

light-dependent reactions

Question 29

Stage where carbohydrates are synthesized from CO₂ using the energy stored in the ATP and NADPH molecules from the light-dependent reactions

Answer 29

dark reactions

Question 30

# True or False? "Dark reactions" take place much more rapidly when the light-dependent reactions are also occurring

Answer 30

True

Question 31

Light travels in these **packets** or **quanta** of energy that can be thought of as **"particles" of light**

Answer 31

photons

Question 32

The _\_\_\_\_\_\_ the wavelength, the _\_\_\_\_\_ the energy content

Answer 32

shorter, higher

Question 33

One mole of photons of **680 nm wavelength** contains approximately _\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, equivalent to a change in redox potential of approximately _\_\_\_\_

Answer 33

- 42 kcal of energy - 1.8 V

Question 34

The **first step** in any photochemical process

Answer 34

absorption of light

Question 35

When an electron becomes sufficiently energetic to be pushed from an inner to an outer orbital, it is said to have shifted from the ____________ to an _____________

Answer 35

- ground state - excited state

Question 36

How long the excited state of a molecule is expected to last

Answer 36

10^-9 second

Question 37

Compounds that **appear colored** because they only absorb light of particular wavelength(s)

Answer 37

pigments

Question 38

Chloroplasts in leaves absorb these regions most strongly

Answer 38

**blue** and **red** regions

Question 39

Each chlorophyll molecule consists of these two parts

Answer 39

- **porphyrin ring** — functions in light absorption - **hydrophobic phytol chain** — keeps the chlorophyll embedded in the photosynthetic membrane

Question 40

Plot of the **intensity of light absorbed** relative to its wavelength

Answer 40

absorption spectrum

Question 41

Orange and red accessory pigments

Answer 41

carotenoids

Question 42

# Enumerate... Functions of carotenoids

Answer 42

- act as secondary light collectors during photosynthesis - draw excess energy away from excited chlorophyll molecules and dissipate it as heat

Question 43

**Ultrareactive free radical** produced when excess energy not absorbed by carotenoids is transferred to oxygen

Answer 43

singlet oxygen (¹O₂) - can cause **cell death** - can **destroy biological molecules**

Question 44

Plot of the **relative rate/efficiency of photosynthesis** produced by light of various wavelengths

Answer 44

action spectrum ## Footnote - identifies wavelengths effective in bringing about a given physiologic response

Question 45

Two scientists from the California Institute of Technology who determined the **minimum amount of light** needed to produce maximal O₂ production during photosynthesis

Answer 45

- **R**obert **E**merson (1932) - **W**illiam **A**rnold (1932)

Question 46

**Green alga** involved in determination of minimum amount of light needed for O₂ production

Answer 46

*Chlorella*

Question 47

One molecule of oxygen is released during a brief flash of light for every _____________________________

Answer 47

2500 molecules of chlorophyll

Question 48

Emerson showed that a minimum of _________ must be absorbed to produce one molecule of O₂

Answer 48

8 photons