Lecture 15: Photosynthesis (Part 1) Flashcards
What is the general process of photosynthesis?
process of using sunlight to produce energy intermediates needed to make carbohydrates from carbon dioxide.
Is fixation and reduction of carbon to form carbohydrates an endergonic or exergonic process?
endergonic
Byproduct of oxygenic photosynthesis?
molecular oxygen
Is the byproduct of anoxygenic photosynthesis the same as oxygenic’s?
No, can be for example S2
Is photosynthesis a regulated process? Why?
Yes, to help promote the efficient use of energy and resources.
What is the balanced equation of oxygenic photosynthesis?
What is the energy imput in the process of photosynthesis?
light energy
What is the light energy transformed to for the energy for photosynthesis?
ATP and NADH
What is the link between photosynthesis and cellular respiration in the environement?
They complete an energy cycle within the Carbon Cycle.
What are the five types of photosynthesizers?
(a) Plants
(b) Multicellular alga
(c) Unicellular protists
(d) Cyanobacteria
(e) Purple sulfur bacteria
What type of organism carry out photosynthesis?
photoautotrophs
- Phototrophs: Energy comes from light .
- Autotrophs: carbon comes from inorganic sources .
(review) What do primary producers produce?
organic compounds
(review) What is the importance of primary production in ecosystems?
play a critical role in sustaining life on Earth by initiating the flow of energy through ecosystems:
organic compounds produced = source of energy and nutrients for the rest of the ecosystem
they convert solar energy into chemical energy in the form of carbohydrates, such as glucose, by using carbon dioxide and water.
carbohydrates = basis of the food chain, providing energy to consumers (herbivores), which are then consumed by other organisms (carnivores and omnivores) in higher trophic levels.
(review) Do all ecosystems rely on photosynthetic primary producers?
No,
for example, in certain deep-sea ecosystems such as hydrothermal vent communities, primary production is fueled by chemosynthesis rather than photosynthesis(sunlight does not reach).
Chemosynthetic bacteria use chemical energy from sources like hydrogen sulfide or methane to produce organic compounds, serving as the base of the food chain in these environments.
What are the two linked sets of reactions that compose photosynthesis?
- Light-Capturing Reactions:
produces energy intermediates and O2 as a byproduct. - Carbon Fixation/Reduction:
produces sugar from CO2 using the energy intermediates.
Which set of reactions makes the organism a phototroph?
Light-Capturing Reactions
Which set of reactions makes the organism a autotroph?
Carbon Fixation/Reduction
Where does the O2 (byproduct of photosynthesis) come from?
from the splitting of water.
Water is the electron donor (reducing agent) of the process.
Electrons of water are used to reduce the carbon atoms of carbon dioxide to produce sugars.
Where does photosynthesis occur? In what organisms?
in the chloroplasts of plants, algae, and other photosynthetic organisms.
What type of organelle is a choloroplast?
- A chloroplast is a type of plastid organelle.
- It is a double membrane-bound organelle
What is the inner membrane of the chloroplast called?
the thylakoid membrane
Do all chloroplasts look the same?
same within the same species and can be different between species
In plants, how many chloroplasts do cells that photosynthesize have?
around 40-50
What are the flattened thylakoid membrane compartments called?
thylakoids
What are stacks of thylakoids called?
grana (singular: granum)
What are the fluid-filled space between the thylakoids and inner membrane called?
stroma
What is the function of the thylakoid membrane? What is it made of?
it is the site of the light reactions
pigments, ETC and enzymes
What is the thylakoid lumen?
Compartment where a proton electrochemical gradient is generated.
What happens in the stroma? What is it composed of?
it the site of carbon fixation
contains the chloroplast genome and ribosomes.
Do cyanobacteria have chloroplasts?
No;
the plasma membrane is folded inward and forms photosynthetic membranes.
These photosynthetic membranes are similar to the thylakoids of chloroplasts.
Photosynthetic membranes
What is the endosymbiont theory of the evolution of the chloroplast?
The endosymbiont theory suggests that chloroplasts evolved from ancient cyanobacteria that were engulfed by ancestral eukaryotic cells. Over time, the cyanobacteria formed a symbiotic relationship with the host cell, eventually evolving into specialized organelles capable of photosynthesis. This theory is supported by evidence such as the presence of double membranes, circular DNA, and independent replication within chloroplasts, similar to prokaryotic cells.
What is the nature of light?
it is a type of electromagnetic radiation
What are the two characteristics of magnetic radiation?
it is both particle-like and wave-like
What type of energy does magnetic radiation carry?
radiant energy
How can light be characterized in its wave form?
by wavelength
How can light be characterized in its particle form?
it exists as photons
What is the relationship between wavelength and energy?
inversely proportional
can be represented by the electromagnetic spectrum:
What is the electromagnetic spectrum?
the range of wavelengths of electromagnetic radiation.
What can happen to a photon as it hits an object?
they may be:
A. Absorbed
B. Transmitted
C. Reflected
What are pigments?
colorful chemical compounds that **absorb **certain wavelengths of light and reflect others.
- Each pigment has a characteristic absorption spectrum.
- Can be measured usinbg a spectrophotometer.
How do pigments work?
They contain certain chemical groups that can absorb light energy of a particular wavelength.
What are the two types of photosynthetic pigments?
A. Chlorophylls
B.Accessory Pigments
What is the absorption spectrum of chlorophylls?
they:
absorb blue and red light
transmit green light
What is the absorption spectrum of carotenoids?
they:
absorb blue and green light
transmit yellow, orange or red light
How do you build an absorption spectrum?
using a spectrophotometer which measures a pigment’s ability to absorb various wavelengths.
it sends a specific wavelength of light through pigments and measures the fraction of light transmitted at each wavelength (converted to absorbance reading).
Which pigment is said to “link life to sunlight?” Why?
chlorophylls
Chlorophyll a acts as the primary photosynthetic pigment in cyanobacteria and all photosynthetic eukaryotes.
Which part of the chlorophyll be pigment structure absorbs light?
The ring structure in the “head” of the molecule
What are the two groups of accessory pigments?
A. Carotenoids (lipids)
B. Phycobilins (hydrophilic; attached to proteins)
Do accessory pigments have the same absorption spectrums than chlorophylls?
no
What are the functions of accessory pigments?
- They expand the range of wavelengths of light caught and that can be used by the organism.
- They also help protect chlorophylls from the harmful effects of high energy radiation (photo-oxidation).
How does variation in the accessory pigments of aquatic phototrophs help them in the ecosystem?
What does the action spectrum show?
the rate of photosynthesis vs. wavelength.
What do the highest levels of photosynthesis on the action spectrum correspond to?
to the absorbance spectrums of the photosynthetic pigments (or chlorophylls)
What do accessory pigments do to photosynthesis?
The accessory pigment increase the range of wavelengths of light that can be used for photosynthesis and increases the overall rate of photosynthesis.
What happens when a pigment absorbs a photon?
In chlorophyll a, what can blue and red photons do as they get absorbed?
They excite electrons to different states:
A. Low-energy red photons raise electrons to state1.
B. Higher-energy blue photons raise electrons to state 2.
What happens when electrons return to their ground states?
- Fluorescence and Heat: Energy is transformed into light and heat. Only approximately 2% of red and blue photons produce fluorescence. The remaining 98% drive photosynthesis.
- Resonance Energy Transfer:Energy is transferred to excite an electron in another adjacent pigment.
Chlorophyll solution fluoresces red under UV. Why not blue?
UV light is not well absorbed by chlorophylls so not a lot of energy is absorbed. Since red light has less energy, it is the only light that can be reflected.
What happens to light energy when electrons are captured?
Light energy is transformed into chemical energy.
