Chapter 4 - Photosynthesis Flashcards
heterotrophs
organisms (like humans) that obtain chemical energy from the food they eat
autotrophs
make their own food
photoautotrophs
like plants, capture solar energy and convert it to chemical energy by photosynthesis
photosynthesis releases:
oxygen (necessary for cellular respiration)
photosynthesis removes ____ from the air. without this:
carbon dioxide; co2 would accumulate in the atmosphere and trap heat (greenhouse effect)
glucose provides plants with ___ ___
fixed carbon
____ ___ occurs when inorganic carbon is incorporated into an organic molecule
carbon fixation
Where does photosynthesis store solar energy?
in the carbon bonds of organic glucose molecules
true or false: photosynthesis is exergonic and spontaneous
false - has a positive Gibbs free energy, so it is non-spontaneous and endergonic
photosynthesis and cellular respiration are:
essentially opposite reactions
How are photosynthesis and cellular respiration similar?
They both utilize a series of redox reactions, also have electron transport chains that create an electrochemical gradient with protons which allows for ATP synthesis by chemiosmosis
Leaf anatomy from top to bottom of leaf
- Upper epidermic
- Palisade mesophyll
- Spongy mesophyll
- Lower epidermis containing guard cells and stomata
Epidermis tissue is found:
on roots, stems, leaves, flowers, fruits, and seeds
Epidermis tissue function
protects structures from injury, water loss, and infection
Which type of cells conducts most photosynthesis?
palisade mesophyll cells
Describe palisade mesophyll cells structure
contain many chloroplasts and are well organized as a single layer below the upper epidermis
Which cells conduct some photosynthesis?
Spongy mesophyll cells
Why do spongy mesophyll cells not do as much photosynthesis?
they have few chloroplasts and do not receive as much light because they are found toward the bottom of the leaf
Primary role of spongy mesophyll cells:
facilitating the movement of gases within the leaf. this relates to their structure: the gaps between spongy mesophyll cells allows this gas exchange to occur
stomata
pores mainly found in the bottoms of leaves. site of atmospheric gas exchange
guard cells
surround stomata and control whether they are open or closed
chloroplasts
dual membrane organelles found in plants and photosynthetic algae, they make ATP and have their own DNA
____ are photosynthetic organisms that do not have a chloroplast
cyanobacteria
plastid
double-membranes cytoplasmic organelles found within plant cells
example of plastid in plant cell
chloroplast
function of plastids
store molecules, like pigments and starch
stroma
fluid that fills area inside inner membrane
Where does the Calvin cycle occur?
stroma of chloroplast
thylakoids
phospholipid bilayer structured organelle suspended within the stroma
Where do light dependent reactions occur?
Thylakoids
Stack of thylakoids is called:
granum
Junction between two grana is called
lamella
Thylakoid lumen
interior of the thylakoid where H+ accumulates
What is the ATP from the light dependent reactions used for?
used to power the Calvin cycle, which makes glucose
Each photosystem has a special pair of chlorophyll molecules located in the ___ of the protein, called:
center; reaction center
Reaction center in Photosystem I:
P700 - absorbs 700nm wavelengths best
Reaction center in photosystem II:
P680 - absorbs 680nm wavelengths best
First step of non-cyclic photophosphorylation
Photosystem II splits a water molecule to release 2 protons, 2 electrons, 1/2 O2
When photons reach photosystem II, they will ____ electrons at the ___ ___. This forces electrons to:
excite; reaction center; go to a higher energy level and be passed to primary electron acceptor
Excited electrons are passed down the ___ in the _____. The energy released from these electrons is used to:
electron transport chain; thylakoid membrane; pump protons from the stroma into the thylakoid lumen
What creates an electrochemical gradient in the thylakoid lumen?
water splitting and proton pumps
Excited electrons from Photosystem II are eventually passed onto:
Photosystem I
Electrons from Photosystem I travel down a short _____ and eventually reduces ____ to form ____
electron transport chain; NADP+; NADPH
Cyclic photophosphorylation
cell recycles electrons through photosystem I, as opposed to using them too reduce NADP+
Purpose of cyclic photophosphorylation
continue to bring more H+ into thylakoid lumen to make more ATP while NADPH is low
Calvin Cycle is also known as:
dark reactions or light independent reactions
What is the purpose of the calvin cycle?
fixes inorganic carbon dioxide into organic glucose sugars
Calvin cycle occurs in the:
stroma
Calvin cycle needs __ carbon dioxide molecules to synthesize 1 glucose
6
First stage of calvin cycle is called ____ ____. What happens during this stage?
carbon fixation; CO2 combines with ribulose-1,5-bisphosphate (RuBP) which has 5 carbons. This is catalyzed by rubisco. Splits into 2 PGA molecules (phosphoglycerate)
Where is rubisco found?
Wherever plants are photosynthesizing (most common protein in the world)
What happens when CO2 combines with RuBP?
molecule is unstable so it splits into 2 PGA molecules (each 3 carbons)
Second stage of calvin cycle
Where reduction takes place; ATP from light dependent reactions will phosphorylate PGA. NADPH reduces this intermediate to make G3P
True or false: all G3P made during calvin cycle is used to generate sugars
False - some of it is used to regenerate RuBP. This requires ATP from light dependent reactions
3rd stage of calvin cycle
Regeneration
Overall calvin cycle reaction:
6 CO₂ + 18 ATP + 12 NADPH + H⁺ → 18 ADP + 18 Pᵢ +12 NADP⁺ + 1 glucose
How many ATP is needed to convert G3P to RuBP
6 ATP to convert 10 out of 12 G3P
How many G3P enter 4th stage of calvin cycle (carbohydrate synthesis)
2 G3P
