exam 2 module 8- Photosynthesis Flashcards
life depends on photosynthesis
a) autotrophs- Producers, such as trees, carry out photosynthesis. They are autotrophs which produce organic compounds (ex., glucose) from inorganic sources (ex., CO2).
b) heterotrophs- organisms that obtain carbon and energy by eating other organisms (consumers).
summary of photosynthesis
a) 6CO2 + 6H2O + light energy C6H12O6 + 6O2
Describe how plants use carbohydrates
Plant cells use about half of the sugar as fuel for their own cellular respiration. A plant also uses glucose molecules as the building blocks of the cellulose wall that surrounds every plant cell. Additionally, plants often combine carbohydrates with other substances to manufacture additional compounds. Examples include amino acids and a host of economically important products, such as rubber, medicine and spices.
Finally, if a plant produces more glucose than it immediately needs, it may store the excess as starch. Carbohydrate-rich tubers and grains, such as potatoes, rice, corn and wheat, are all energy-storing plant organs. Some plants, including sugarcane and sugar beets, store energy as sucrose instead.
sunlight’s role in photosynthesis
Light from the sun provides the energy that drives photosynthesis.
electron magnetic spectrum
range of naturally occurring radiation.
photons
it is discrete packages of energy.
i) wavelength (short – high energy; long – low energy)
sunlight that reaches the earth
i) ultraviolet radiation- has the shortest wavelengths and, therefore, contains the most energy. Its high energy photons cause sunburn and cancer.
ii) visible light (colors)- provides the energy for photosynthesis. We perceive the energy of visible light as colors.
iii) infrared radiation- very little energy per photon, so it is not very useful to organisms.
photosynthetic pigments
a) major pigment – chlorophyl a
b) accessory pigments – chlorophyl b and carotenoid
c) Photosynthetic pigments absorb and reflect light (figure 5.4)
leaf and chloroplast anatomy
a) stomata
b) mesophyll cell
c) chloroplast
i) inner and outer membrane
ii) stroma
iii) grana
iv) thylakoids
v) thylakoid space
photosystems
a) reaction center- special pair of chlorophyll a molecules that actually use the energy in photosynthetic reactions.
b) antenna pigments- additional pigments that capture photon energy and funnel it to the reaction center
c) photosystem I (PSI) and photosystem II (PSII)
overview: two stages of photosynthesis (figure 5.7)
a) light reactions
i) input – H2O, light energy, NADP+, and ADP
ii) output – ATP, NADPH, O2
b) carbon reactions
i) input – ATP, NADPH, CO2
ii) output – sugar, NADP+
, ADP
light reactions - figure 5.8
a) Describe the 6 steps.
(1) Chlorophyll molecules in photosystem II transfer light energy to electrons.
(2) Electrons are stripped from water molecules, releasing oxygen.
(3) The energized electrons pass to photosystem I. Each transfer releases energy that is used to pump protons (H+) into the thylakoid space.
(4) The resulting proton gradient is used to generate ATP.
(5) In photosystem I, the electrons absorb more light energy and (6) are passed to NADP+, creating the energy-rich NADPH.
carbon reactions (Calvin cycle) – figure 5.9
b) Describe the 4 steps.
STEP 1: Carbon Fixation: CO2 combines with RuBP (ribulose bisphosphate) to form an unstable molecule. Rubisco is the enzyme that catalyzes this first reaction.
STEP 2: PGAL Synthesis: The unstable molecule splits to form PGA (phosphoglycerate). With the energy from the ATP and NADPH produced in the light reactions, PGA is converted to PGAL (phosphoglyceraldehyde).
STEP 3: Creation of Glucose: PGAL molecules are combined to form glucose, which is used to form starch and sucrose and other organic molecules.
STEP 4: Additional RuBP: Some of the PGAL is rearranged to form additional RuBP, allowing the Calvin cycle to repeat.
