Ch. 8 Photosynthesis Study Guide Slideshow

Define photosynthesis

a process whereby energy within light is captured and used to synthesize glucose and other organic molecules

T/F Nearly all organisms depend on photosynthesis either directly or indirectly

true

What are the two stages of photosynthesis?

light reactions and the calvin cycle

What happens in the first stage of photosynthesis?

light energy is absorbed by chlorophyll and converted to ATP and NADPH

What happens in the 2nd stage of photosynthesis?

ATP and NADPH are used to drive the synthesis of carbohydrates

Photosynthesis Equation?

CO2+H2O+light energy—> C6H12O6+O2+H2O

In the photosynthesis equation, what is reduced?

CO2

In the photosynthesis equation, what is oxidized?

H2O

Is photosynthesis a endergonic or exergonic rxn?

endergonic, requires an addition of free energy and does not proceed spontaneously

What type of energy drives an endergonic reaction with a free energy change of +685 kcal/mol?

energy from light

Which process is responsible for powering the biosphere?

photosynthesis

define biosphere

regions on the Earth and atmosphere where living organisms exist

What is the biosphere largely driven by?

The photosynthetic power of photosynthetic plants, algae, and cyanobacteria

What is the energy cycle?

a process whereby cells use organic molecules for energy and plants replenish those molecules using photosynthesis

What byproduct do plants produce during photosynthesis?

oxygen

How do heterotrophs sustain life?

must eat food(organic molecules from their environment) to sustain life

examples of heterotrophs

bacteria, protists, fungi, animals

How do autotrophs sustain life?

make organic molecules from inorganic sources

example of an autotroph

photoautotroph

How do photoautotrophs sustain life?

use light as an energy source to make organic molecules

examples of photoautotrophs

plants, algae, cyanobacteria

• an important energy cycle between photosynthesis and cellular respiration

• photosynthesis is a process in which light, CO2, and H2O are used to produce O2 and organic molecules

• the organic molecules are broken down to CO2 and H2O via cellular respiration to supply energy in the form of ATP

• for aerobic respiration, O2 is reduced to H2O

What is the chloroplast?

organelle in plants and algae that carries out photosynthesis

What is chlorophyll?

green pigment

Where does the majority of photosynthesis occur?

internally in leaves, in the mesophyll

What is the mesophyll?

the inner tissue of a leaf

What must mesophyll cells receive?

light, water, and carbon dioxide

How do carbon dioxide and oxygen move in and out of a leaf during photosynthesis?

carbon dioxide enters and oxygen exits leaves through pores called stomata

• leaves are composed of layers of cells

• the epidermal cells are on the outer surfaces w/ mesophyll cells in between

• the mesophyll cells contain chloroplasts and are the primary sites of photosynthesis in most plants

What separates the outer and inner membrane of a chloroplast?

intermembrane space

What is the third membrane in a chloroplast called and what does it contain?

the thylakoid membrane, and it contains pigment molecules

What structures are formed by the thylakoid membrane?

thylakoids

What do thylakoids enclose?

the thylakoid lumen

What is a granum?

a stack of thylakoids

What are thylakoids?

flattened fluid-filled tubules

What is the stroma?

fluid-filled region between the thylakoid and inner membrane

• CO2 enters the leaf via stomata

• product of photosynthesis O2 exits via stomata

Where do light reactions take place?

thylakoid membranes

What do light rxns produce?

ATP, NADPH, O2

Is the calvin cycle a light dependent or independent rxn?

light independent

Where does the Calvin cycle take place?

the stroma

The calvin cycle uses ATP and NADPH to do what?

incorporate CO2 into carbohydrate

The calvin cycle in the stroma uses CO2, ATP, and NADPH to do what?

make carbohydrates

During photosynthesis, where is energy in the form of light transferred from?

the sun to a pigment molecule in a plant

Why is light essential?

to support life on Earth

What type of radiation is light?

electromagnetic radiation

How does light travel?

light travels as waves

What is the range of wavelengths in light?

short to long wavelengths

Define wavelengths

distance between the peaks in a wave pattern

What does the electromagnetic spectrum encompass?

all possible wavelengths of electromagnetic radiation

• bottom portion of this figure emphasizes visible light

• light in the visible portion of the electromagnetic spectrum drives photosynthesis

How does light behave besides traveling as waves?

as particles called photons

Define photons

massless particles traveling in a wavelength pattern and moving at the speed of light

What type of wavelength radiation carries more energy?

shorter wavelength radiation

How do molecules interact with the energy of visible light?

molecules can absorb the energy of visible light in a way that does not cause damage

What do pigments do with light energy?

pigments absorb some light energy and reflect others

Why are leaves green?

leaves are green because they absorb red and violet wavelengths and reflect green wavelengths

What happens to electrons during light absorption?

Absorption boosts electrons to higher energy levels.

What determines the wavelength of light that a pigment absorbs?

the amount of energy needed to boost an electron to a higher orbital

How do different pigments benefit plants?

allows plants to absorb light at many different wavelengths

What happens to an electron after it absorbs energy?

it is in an excited state and usually unstable

How does an electron release energy?

as heat or light

What can happen to excited electrons in pigments?

can be transferred to another molecule or "captured"

What do different pigment molecules in plants absorb?

the light energy used in photosynthesis

What do chlorophylls a and b contain?

a porphyrin ring

What is bound to the porphyrin ring in chlorophyll?

a magnesium ion

What are carotenoids and where are they commonly found?

another pigment in chloroplasts and are often the major pigments in flowers and fruit

What does an absorption spectrum plot?

a pigment’s light absorption as a function of the light's wavelength

In which parts of the spectrum do chlorophylls absorb light strongly and what do they reflect?

chlorophylls absorb light strongly in the red and violet parts of the spectrum and reflect green

Which wavelengths of light do carotenoids absorb and reflect?

carotenoids absorb blue and blue-green visible light and reflect yellow and red

What does an action spectrum plot?

the rate of photosynthesis as a function of the wavelength of light

How do different pigments benefit plants in terms of light absorption?

different pigments allow plants to absorb light at many different wavelength

With which wavelengths do the highest rates of photosynthesis in green plants correlate?

the wavelengths that are strongly absorbed by chlorophylls and carotenoids

• these absorption spectra show the absorption of light by chlorophyll a, b, and b-carotene

• shows the action spectrum of photosynthesis depicting the relative rate of photosynthesis in green plants at different wavelengths of light

What can captured light energy be transferred to, and what does it produce

other molecules to produce energy-intermediate molecules for cellular work

What do the thylakoid membranes of chloroplasts contain?

two distinct complexes of molecules, Photosystem I (PSI) and Photosystem II (PSII)

Which photosystem was discovered first?

Photosystem I (PSI) was discovered first

Which photosystem is involved in the first step of photosynthesis?

Photosystem II (PSII)

What happens when light excites pigment molecules?

t happens in both PSII and PSI

What is the initial step in photosynthesis?

light exciting electrons in pigment molecules within the light-harvesting complex of photosystem 2

Where is energy transferred in Photosystem II?

the P680 pigment molecule

What does Photosystem II do to water molecules?

oxidizes water, generating O₂ and H⁺

Where do electrons go after exiting PSII?

electrons exit PSII and enter an electron transport chain

What is the energy from the electrons used for in the electron transport chain?

used to make an H⁺ electrochemical gradient

Primary role of photosystem 1?

to make NADPH

What happens when light hits the light-harvesting complex of PSI(photosystem 1)?

a high-energy electron is removed from the P700 pigment molecule and transferred to a primary electron acceptor

What role does ferredoxin play in Photosystem I?

accepts two high-energy electrons and transfers electrons to NADP⁺ reductase

How is NADPH produced in Photosystem I?

electrons are transferred to NADP⁺, which also accepts an H⁺ to produce NADPH

What is linear electron flow in Photosystem I?

the movement of electrons linearly from PSII to PSI to reduce NADP⁺ to NADPH

the movement of electrons from photosystem 2 to photosystem 1 to NADPH is called linear flow

How is ATP synthesis in chloroplasts achieved?

by a chemiosmotic mechanism called photophosphorylation

What drives the synthesis of ATP in chloroplasts?

the flow of H⁺ from the thylakoid lumen into the stroma via ATP synthase

How is the H⁺ gradient generated in chloroplasts?

• Increase of H⁺ in the thylakoid lumen by the splitting of water

• Increase of H⁺ by the electron transport chain (ETC) pumping H⁺ into the lumen

• Increase of H⁺ in the stroma from the formation of NADPH

How is oxygen (O₂) produced in the thylakoid lumen?

by the oxidation of H₂O by PSII

What happens to the electrons from the oxidation of H₂O?

they are transferred to P680⁺ molecules

How is NADPH produced in the stroma?

high-energy electrons that start in PSII and are boosted in PSI

What is the chemical reaction for the production of NADPH?

NADP⁺ + 2 electrons + H⁺ → NADPH

How is ATP produced in the stroma?

by ATP synthase using the H⁺ electrochemical gradient

In noncyclic electron flow, where do electrons begin and where do they eventually transfer to?

electrons begin at PSII and eventually transfer to NADPH, following a linear process

What does noncyclic electron flow produce?

both ATP and NADPH in equal amounts