Biology chapter 8

Autotrophs

“self-feeders” : sustain themselves without eating anything derived from other living beings
produce their own organic molecules from CO₂ and other inorganic raw materials obtained from the environment
the ultimate sources of organic compounds for all nonautotrophic organisms
Ex: plants, multicellular algae, unicellular protists, cyanobacteria, purple sulfur bacteria

Heterotrophs

unable to make their own food; live on compounds produced by other organisms
consumers of the biosphere
Ex: animals, decomposers, most fungi, many prokaryotes

Where in the chloroplast do the light reactions take place?

Thylakoid membrane

Where in the chloroplast does the calvin cycle occur?

The stroma

What occurs in the light reactions stage of photosythesis?

Water is split, providing a source of electrons and protons and giving off O₂ as a by-product
Light absorbed by chlorophyll drives a transfer of the electrons and hydrogen ions from water to an acceptor called NADP⁺ where they are temporarily stored
Light reactions use solar power to reduce NADP⁺ to NADPH by adding a pair of electrons along with an H⁺
Light reactions also generate ATP, using chemiosmosis to power the addition of a phosphate group to ADP, a process called photophosphorylation

What occurs in the Calvin Cycle?

Incorporates CO₂ from the air into organic molecules already present in the chloroplast.
Carbon fixation: initial incorporation of carbon into organic compounds
Reduces the fixed carbon electrons in the light reactions
Requires chemical energy in the form of ATP generated by the light reactions to convert CO₂ to carbohydrate

Relationship between Light Reaction and Calvin Cycle?

The light reactions convert solar energy to the chemical energy of ATP and NADPH.
ATP and NADPH are needed in the Calvin cycle
Calvin cycle provides NADP+ and ADP back to the light reactions to be reused.

Absorption spectrum

the range of a pigment’s ability to absorb various wavelengths of light

Action spectrum

graph that profiles the relative effectiveness of different wavelengths of radiation in driving photosynthesis

What wavelengths of light maximize photosynthesis?

Blue: ~450nm
Red: ~680nm

What is the name of the chlorophyll at the reaction center of PS II?

P680

Why is it necessary that P680+ be the strongest oxidizing agent?

it needs to pull electrons from the oxygen atom in water, which does not want to be oxidized

What is the source of O2 in the atmosphere?

The splitting of water

What happens as electrons fall from photosystem II to photosystem I?

the cytochrome complex uses the energy to pump hydrogen ions

What molecule is produced in chemiosmosis due to the proton gradient?

ATP

In photosystem I, NADP+ reductase catalyzes the transfer of the excited electron and H+ to NADP+ to form what?

NADPH

Photophosphorylation is most similar to what process in cellular respiration?

Oxidative Phosphorylation

What source of energy excites the electron in photosystem II?

Light

Where do the electrons come from that replace the excited electrons in photosystem II?

Water

Where do electrons come from that replace the excited electrons in photosystem I?

PS II

Where do electrons have the highest potential energy?

End of PS I

Which wavelengths of light are best for supporting plant growth?

Red & Blue; chlorophyll pigments absorb those specific wavelengths

Why are plants green

Pigments in the plants absorb most colors, except green. Green is reflected, thus our eyes see that color

What carbohydrate produced directly from the Calvin cycle?

The three-carbon compound glyceraldehyde 3-phosphate (G3P)

It will take how many turns of the Calvin Cycle to net one G3P?

3 turns

What enzyme is responsible for carbon fixation in the Calvin Cycle? (Also possibly the most abundant protein on Earth)

Rubisco

In the reduction stage what molecule donates electrons to be the source of the reducing power?

NADPH

How much ATP and NADPH are required to produce one G3P?

9 molecules of ATP; 6 molecules of NADPH

Main purpose of the calvin cycle?

To fix CO₂ into organic sugars. This will be used to power cellular respiration and build plant matter.

Where does the CO₂ that the Calvin cycle fixes come from?

from the atmosphere

Photorespiration

metabolic process in which the plant consumes oxygen and ATP, releases carbon dioxide, and decreases photosynthetic output.

When does photorespiration occur?

when C₃ plants close their stomata on hot dry days; the plants produce less sugar because of declining levels of CO₂ within the air spaces of the leaf

What happens in photorespiration

Rubisco is capable of easily binding O₂ in place of CO₂.
As CO₂ becomes scarce and O₂ builds up, rubisco adds O₂ RuBP instead of CO₂
The product splits and a 2-carbon compound leaves the chloroplast
Peroxisomes and mitochondria split this compound, releasing CO₂

Example of CAM

Cactus

Example of C4

Corn

Example of C3

Apple Tree

Why does CO₂ vary within a year?

Seasonal changes in photosynthesis and respiration drive annual CO₂ cycles.
Spring/Summer: plants grow and photosynthesize ore, absorbing CO₂ from the atmosphere, so atmospheric CO₂ decreases.
Fall/Winter: plant growth slows and decomposition and respiration release CO₂, while less photosynthesis occurs, so atmospheric CO₂ increases.

Why is the total CO₂ concentration increasing over time?

Respiration is always happening
Human activities: burning fossil fuels & deforestation add extra CO₂ to the atmosphere

Equation for Cellular Respiration

C₆H₁₂O₆ + 6 O₂ —> 6 CO₂ + 6 H₂O + energy (ATP + heat)
Exergonic

Equation for photosynthesis

6 CO₂ + 6 H₂O + light energy —> C₆H₁₂O₆ + 6 O₂
Endergonic