Chapter 5: Photosynthesis

light-dependent reactions

chlorophyll absorbs energy from sunlight and then converts it into chemical energy with the use of water takes place in thylakoid membrane

photostems

clusters, organized by chlorophyll and other pigments

chlorophyll a

A photosynthetic pigment that participates directly in the light reactions, which convert solar energy to chemical energy. green is reflected making plants appear green

electromagnetic spectrum

All of the frequencies or wavelengths of electromagnetic radiation

chlorophyll b

An accessory photosynthetic pigment that transfers energy to chlorophyll a.

Chloroplast

An organelle found in plant and algae cells where photosynthesis occurs have a double membrane

Autotroph

An organism that makes its own food plants, bacteria, algae

Why are carnivores, such as lions, dependent on photosynthesis to survive?

Because lions eat animals that eat plants

Wavelength

Horizontal distance between the crests or between the troughs of two adjacent waves

5.2 The Light-Dependent Reactions of Photosynthesis

In the first part of photosynthesis, the light-dependent reaction, pigment molecules absorb energy from sunlight. The most common and abundant pigment is chlorophyll a. A photon strikes photosystem II to initiate photosynthesis. Energy travels through the electron transport chain, which pumps hydrogen ions into the thylakoid space. This forms an electrochemical gradient. The ions flow through ATP synthase from the thylakoid space into the stroma in a process called chemiosmosis to form molecules of ATP, which are used for the formation of sugar molecules in the second stage of photosynthesis. Photosystem I absorbs a second photon, which results in the formation of an NADPH molecule, another energy carrier for the Calvin cycle reactions.

Which part of the Calvin cycle would be affected if the cell couldn't produce the enzyme RUBisCO

None of the cycle could take place because RuBisCO is essential and fixing carbon dioxide. Specifically RuBisCO catalyzes the reaction between carbon dioxide and RU BP at the start of the cycle

Explain the reciprocal nature of the net chemical reactions for photosynthesis and respiration

Photosynthesis takes the energy of sunlight and combines water and carbon dioxide to produce sugar and oxygen as a waste product. The reactions of respiration take sugar and consume oxygen to break it down into carbon dioxide and water, releasing energy. Thus, the reactance of photosynthesis are the products of respiration, and vice versa.

Describe the pathway of energy in light dependent reactions

The energy is present initially as light. A photon of light hits chlorophyll, causing an electron to be energized. The free electron travels through the electron transport chain, and the energy of the electron is used to pump hydrogen ions into the thylakoid space, transferring the energy into the electrochemical gradients. The energy of the electrochemical gradients is used to power ATP synthase. And the energy is transferred into a bond in the ATP molecule. In addition, energy from another photon can be used to create a high energy bond in the molecule NADP H

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).

5.1 Overview of Photosynthesis

The process of photosynthesis transformed life on earth. By harnessing energy from the sun, photosynthesis allowed living things to access enormous amounts of energy. Because of photosynthesis, living things gained access to sufficient energy, allowing them to evolve new structures and achieve the biodiversity that is evident today. Only certain organisms, called autotrophs, can perform photosynthesis; they require the presence of chlorophyll, a specialized pigment that can absorb light and convert light energy into chemical energy. Photosynthesis uses carbon dioxide and water to assemble carbohydrate molecules (usually glucose) and releases oxygen into the air. Eukaryotic autotrophs, such as plants and algae, have organelles called chloroplasts in which photosynthesis takes place.

5.3 The Calvin Cycle

Using the energy carriers formed in the first stage of photosynthesis, the Calvin cycle reactions fix CO2 from the environment to build carbohydrate molecules. An enzyme, RuBisCO, catalyzes the fixation reaction, by combining CO2 with RuBP. The resulting six-carbon compound is broken down into two three-carbon compounds, and the energy in ATP and NADPH is used to convert these molecules into G3P. One of the three-carbon molecules of G3P leaves the cycle to become a part of a carbohydrate molecule. The remaining G3P molecules stay in the cycle to be formed back into RuBP, which is ready to react with more CO2. Photosynthesis forms a balanced energy cycle with the process of cellular respiration. Plants are capable of both photosynthesis and cellular respiration, since they contain both chloroplasts and mitochondria.

Which statement about thylakoids in eukaryotes is not correct? a. Thylakoids are assembled into stacks. b. Thylakoids exist as a maze of folded membranes. c. The space surrounding thylakoids is called stroma. d. Thylakoids contain chlorophyll.

b. Thylakoids exist as a maze of folded membranes.

What is the energy of a photon first used to do in photosynthesis? a. split a water molecule b. energize an electron c. produce ATP d. synthesize glucose

b. energize an electron

From where does a heterotroph directly obtain its energy? a. the sun b. the sun and eating other organisms c. eating other organisms d. simple chemicals in the environment

c. eating other organisms

What two products result from photosynthesis? a. water and carbon dioxide b. water and oxygen c. glucose and oxygen d. glucose and carbon dioxide

c. glucose and oxygen

Where in plant cells does the Calvin cycle take place? a. thylakoid membrane b. thylakoid space c. stroma d. granum

c. stroma

Which statement correctly describes carbon fixation? a. the conversion of CO2 to an organic compound b. the use of RUBISCO to form 3-PGA c. the production of carbohydrate molecules from G3P d. the formation of RuBP from G3P molecules e. the use of ATP and NADPH to reduce CO2

c. the production of carbohydrate molecules from G3P

Stroma

fluid portion of the chloroplast; outside of the thylakoids

photosynthesis in prokaryotes

lack membrane-bound organelles so the plasma membrane has infoldings for chlorophyll attachment and photosynthesis

Calvin Cycle

light-independent reactions of photosynthesis in which energy from ATP and NADPH is used to build high-energy compounds such as sugar

Heterotroph

organism that obtains energy from the foods it consumes; also called a consumer

Granum

stack of thylakoids

absorption of light

the process by which matter absorbs radiative energy

photautotrophs

uses sunlight and carbon from co2 to synthesize chemical energy in forms of carbohydrates

Photosynthesis equation

6CO2 + 6H2O ------> C6H12O6 + 6O2

Photon

A particle of electromagnetic radiation with no mass that carries a quantum of energy

Chlorophyll

Green pigment in plants that absorbs light energy used to carry out photosynthesis

pigment

Light-absorbing molecule

Stomata

Small openings on the underside of a leaf through which oxygen and carbon dioxide can move

mesophyll

Spongy tissue in the interior of the leaf where most chloroplasts are found

absorption spectrum

The range of a pigment's ability to absorb various wavelengths of light.

What is the overall purpose of the light reactions in photosynthesis?

To convert solar energy into chemical energy that cells can use to do work

Thykaloid

a membrane system found within chloroplasts that contains the components for photosynthesis

Which molecule absorbs the energy of a photon in photosynthesis? a. ATP b. glucose c. chlorophyll d. water

a. ATP

Plants produce oxygen when they photosynthesize. Where does the oxygen come from? a. splitting water molecules b. ATP synthesis c. the electron transport chain d. chlorophyll

a. splitting water molecules

What is the molecule that leaves the Calvin cycle to be converted into glucose? a. ADP b. G3P c. RuBP d. 3-PGA

b. G3P

Which color(s) of light does chlorophyll a reflect? a. red and blue b. green c. red d. blue

b. green