Chapter 10 Flashcards
What is photosynthesis?
The process that converts solar energy into chemical energy within chloroplasts.
What does photosynthesis do?
Nourishes almost the entire living world directly or indirectly.
What are autotrophs?
“Self-feeders” that sustain themselves without eating anything derived from other organisms.
What do autotrophs do?
They are the producers of the biosphere; they produce organic molecules from other inorganic molecules.
Are all plants photoautotrophs?
Almost all; photosynthesis also occurs in algae, certain other protists, and some prokaryotes.
What are some examples of photoautotrophs?
Plants, cyanobacteria, multicellular algae, unicellular protists, and purple sulfur bacteria.
What are heterotrophs?
They obtain organic material from other organisms, and are the consumers of the biosphere.
What do heterotrophs do to obtain their food?
Some consume other living things, others (decomposers) eat dead organic materials or feces.
What are fossil fuels made from?
The remains of organisms that died hundreds of millions of years ago, representing ancient stores of the sun’s energy.
What do almost all heterotrophs depend on?
Photoautotrophs; either directly or indirectly for food.
What are chloroplasts?
Organelles that are structurally similar to and likely evolved from photosynthetic bacteria. The structural organization of these organelles allows for the chemical reactions of photosynthesis.
What contains chloroplasts?
Plants and other photosynthetic organisms.
Where does most photosynthesis occur?
In the leaves.
Where are chloroplasts found in?
The cells of the mesophyll, the interior tissue of the leaf.
What are stomata?
Pores that exit the leaf through microscopic openings on the epidermis.
What transports water from the roots and exports sugar to other parts of the plant?
Veins.
What is stroma?
A dense fluid that is surrounded by two membranes.
What are thylakoids?
Connected sacs in the chloroplast that compose a third membrane system. They may be stacked in columns called grana.
What is chlorophyll?
The pigment that gives leaves their green color, resides in the thylakoid membranes.
What is the chemical equation for photosynthesis?
6CO2 + 6H2O → C6H12O6 + 6O2
What can the overall chemical change during photosynthesis be described as?
The reverse of cellular respiration.
What is photolysis?
Photolysis (‘light’ and ‘split’): light energy and catalysts interact to drive the splitting of water molecules into protons (H+), electrons, and oxygen gas
What do all photosynthetic organisms require?
A hydrogen source, but the source can vary among organisms.
Ex. sulfur bacteria uses water and forms yellow globules of sulfur as a waste product.
What does photosynthesis do compared to cellular respiration?
Reverses the direction of electron flow compared to respiration.
What kind of process is photosynthesis?
An endergonic process; the energy boost is provided by light.
What molecule is reduced during photosynthesis and what does it become?
Carbon dioxide; it becomes glucose.
What are the two stages of photosynthesis?
Light reactions and the Calvin cycle.
Where do the light reactions occur?
In the thylakoids.
What are the steps of the light reaction?
Electrons are removed from water and end up as NADPH after going through 2 photosystems, each requiring light to be absorbed. It also makes ATP from ADP by photophosphorylation.
Where does the Calvin cycle take place?
In the stroma.
What does the Calvin cycle do?
Makes sugar from ATP and NADPH generated during the light reactions.
What is carbon fixation?
The first step of the Calvin Cycle.
It involves the enzyme RuBisCO ‘‘fixing’’ CO2 to RuBP, producing two molecules of 3-PGA. Three molecules of CO2 are needed for the Calvin cycle to go through one full turn, producing six 3-PGA molecules. The second step is the reduction of 3-PGA to make G3P.
How does the Calvin cycle make carbohydrates?
Reduces fixed carbon by transferring electrons from NADPH.
How do the two stages of photosynthesis correlate?
The light reactions occur in the thylakoids and release NADPH and ATP to the stroma for use in the Calvin cycle.
What is light?
Electromagnetic energy, also called electromagnetic radiation.
How does light travel?
Electromagnetic energy travels in rhythmic waves.
What is wavelength?
The measure of the distance between crests of electromagnetic waves. It can range from less than a nanometer (gamma rays) to more than a kilometer (radio waves).
What is the electromagnetic spectrum?
The entire range of electromagnetic energy, or radiation.
What is visible light?
Wavelengths 380 nm to 740 nm, drives photosynthesis and produces the colors seen by the human eye.
What are photons?
Discrete particles, each photon has a fixed quantity of energy which is inversely related to the wavelength of light; shorter wavelengths have more energy per photon of light.
What are pigments?
Substances that absorb visible light. Different pigments absorb different wavelengths, and the wavelengths that are absorbed disappear.
What happens to wavelengths that are not absorbed?
They are reflected or transmitted.
Ex. leaves appear green because chlorophyll absorbs violet-blue and red light while reflecting and transmitting green light.
What is a spectrophotometer?
Measures a pigment’s ability to absorb various wavelengths. It sends light through pigments and measures the fraction of light transmitted at each wavelength.
What is the absorption spectrum?
A graph plotting a pigment’s light absorption versus wavelength.
What are the three types of pigments in chloroplasts?
Chlorophyll a
Chlorophyll b
Carotenoids
What is chlorophyll a?
The key light capturing pigment that participates directly in light reactions.
What is chlorophyll b?
An accessory pigment.
What are carotenoids?
A separate group of accessory pigments.
What does the absorption spectrum mean in regards to chlorophyll a?
It indicates that violet-blue and red light will work best for photosynthesis while green is the least effective.
What is the action spectrum?
For photosynthesis, a profile of the relative effectiveness of different wavelengths, confirms the effectiveness of violet blue and red light.
When was the action spectrum first demonstrated?
1883, by Theodor W. Engelmann.
He exposed different segments of a filamentous alga to different wavelengths of light and used the growth of aerobic bacteria as a measure of production.
What do accessory pigments do for photosynthesis?
Broaden the spectrum used for photosynthesis.
What is the difference between chlorophyll a and b?
A slight structural difference.
What two forms of chlorophyll have been discovered?
Chlorophyll d and f; that absorb higher wavelengths of light.
What organism uses chlorophyll f?
Cyanobacterium Chroococcidiopsis thermalis, uses it in place of chlorophyll a in shaded conditions.
What are carotenoids?
Accessory pigments that are yellow or orange because they absorb violet and blue-green light.
They also broaden the spectrum for photosynthesis.
Some of photoprotective.
What does photoprotective mean?
Absorb excessive light that would otherwise damage chlorophyll or react with oxygen.
What happens when a pigment molecule absorbs light?
One of its electrons goes from a ground state to an excited state, which is unstable.
What happens to excited electrons in isolation?
They fall back to the ground state, releasing excess energy as heat or light, an afterglow called fluorescence.
What is a photosystem?
A reaction center complex surrounded by light harvesting complexes.
What is the reaction center complex?
An association of proteins holding a special pair of chlorophyll a molecules and a primary electron acceptor.
What is the light harvesting complex?
Consists of various pigment molecules bound to proteins. They transfer the energy of photons to the chlorophyll a molecules in the reaction center complex.
What is a primary electron acceptor?
In the reaction center complex, accepts excited electrons and is reduced as a result.
What is the solar powered transfer of an electron from a chlorophyll a molecule to the primary electron acceptor?
The first step of the light reactions.
What are the two types of photosystems in the thylakoid membrane?
Photosystem 1 (PSII), also called P700.
Photosystem 2 (PSI), also called P680.
Why is it called P680?
Because the reaction center chlorophyll a is best at absorbing light with a wavelength of 680 nanometers; the same reasoning for P700.
What are the two routes for electron flow during light reactions?
Cyclic and linear.
What is linear electron flow?
The primary pathway, and involves both photosystems and produces ATP and NADPH using light energy.
How many steps in linear electron flow?
8 steps.
What is the first step of linear electron flow?
A photon hits a pigment in a light harvesting complex and its energy is passed among pigment.
What is the second step of electron linear flow?
An excited electron from P680 is transferred to the primary electron acceptor; we refer to the oxidized form as
