1
Q
What are the earliest living organisms?
A
Heterotrophs, survive on nutrients from the environment
2
Q
Autotrophs
A
- These are organisms that get organic nutrients from CO2 and H2S
- Chemoautotroph: energy from inorganic molecules
- Photoautotrophs: use radiant energy (light) to make organic compounds
3
Q
What is the basic and overall formula for photosynthesis
A
- Basic: CO2 + H2O -> (CH2O) + O2
- Overall: 6 CO2 + 12 H2O -> C6H12O6 (glucose) + 6 H2O + 6 O2
4
Q
What does photosynthesis do
A
- Converts sunlight energy into chemical energy stored in carbs
- Takes place in the chloroplast in eukaryotes
5
Q
Describe the structure of the chloroplast
A
- A double membrane with an outer membrane (porins) and an inner membrane (light-absorbing pigments)
6
Q
What are thylakoids?
A
- It is the inner membrane of a chloroplast
-Flattened sacs arranged in stacks (grana) - It is where light reactions occur
7
Q
What are the two stages of photosynthesis?
A
- Light-dependent reactions (sunlight is absorbed = ATP & NADPH)
- Light-independent reactions (Calvin cycle, energy from ATP and NADPH = carbohydrates from CO2)
8
Q
What happens to e- in light-dependent reactions in photosynthesis
A
- e- are transferred from H2O to NADP+ = O2 and NAPDH
9
Q
What is the overall reaction of aerobic respiration
A
- C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + ATP
- Reverse of photosynthesis
- Main stages; glycolysis, TCA cycle and ETC
10
Q
How are photosynthesis and aerobic respiration complementary?
A
- Photosynthesis converts sunlight into chemical energy stored in glucose
- Aerobic respiration breaks down glucose to release energy as ATP
11
Q
What happens when photons are absorbed by chlorophyll?
A
- e- move from the ground state to an excited state
12
Q
What are the structures that makeup the chlorophyll?
A
- A polyphyrin ring that is a conjugated system (alternating single (ø) and double bonds (π))
- The chlorophyll also has a hydrophobic tail embedded in the membrane
13
Q
What accessory pigments are found alongside chlorophylls?
A
- Carotenoids, they absorb light in the blue-green region therefore reflecting light in the red-orange-yellow region.
14
Q
What are chromoplasts and their function?
A
- They are a type of plastid that is responsible for the colour of fruits and flowers
- Ripe fruits change colour bcos chloroplasts => chromoplasts
- Eg: carotene for carrots and lycopene for tomatoes
15
Q
What is a photosynthetic unit composed of?
A
- Lots of chlorophyll molecules with a reaction-center chlorophyll (transfers e- to e- acceptor) and antenna pigments for light absorption
16
Q
The two photosystems involved in photosynthesis
A
- Photosystem II (PSII): P680 (wavelength is stronger), boosts e- from below water energy level to a midpoint in the energy gradient
- Photosystem I (PSI): P700, boosts e- to a level above NADP+
17
Q
What is the Z scheme in photosynthesis?
A
- The flow of e- from H2O to NADP+ through PSII and PSI
18
Q
What is the operation of PSII
A
- Uses absorbed light to split water molecules (photolysis) = e-, H+ and O2
19
Q
Explain the steps involved in the PSII operation
A
- Antenna pigments absorb a photon of light at LHCII which transfers the energy to the inner antenna molecules of PSII
- P680* is excited (higher-energy state) and donates an e- to a primary e- acceptor (Pheo) =P680+ and Pheo-
- Pheo- passes e- to plastoquinone (PQ) reducing it to PQH2, plastoquinol
- P680+ goes through photolysis by splitting 2 H2O => 4H+ (kept in thylakoid lumen) 4e- and O2 (waste product)
20
Q
Explain the steps involved from PSII to PSI
A
- O2 forms 2 PQH2
- The PQH2 diffuses through the thylakoid membrane and binds cyt b6f, H+ are released in the thylakoid lumen
- e- from cyt b6f are passed to plastocyanin which passes the e- to P700+ (excited)
21
Q
What is the end product of PSI operations?
A
- NADPH is reduced to NADP+, catalyzed by ferredoxin-NADP+ reductase
22
Q
What is the overview of PSII and PSI?
A
- PSII capture light to split (oxidized) H2O to O2, produces e-and H+ as well
- PSI re-energizes e- and transfers them to NADP+ (reduced) to NADPH
- for every 8H+ (2 H2O is oxidized to O2 and 2 NADP+ is reduced to 2 NADPH)
23
Q
What is non-cyclic phosphorylation
A
- The movement of e- in a linear path = ATP and NADPH
- Cyclic phosphorylation (PSII to PSI) gives more ATP for carb synthesis
24
Q
What is the Calvin cycle?
A
- A cycle of reactions in photosynthesis that fixes CO2 to produce carbohydrates (C3 pathway)
- CO2 + ribulose bisphosphate = 6C molecule that sprites = 2 3-phosphoglycerate PGA molecules
- Catalyzed by Rubisco
25
Explain the steps of the Calvin cycle
- CO2 **(1C)** + ribulose 1,5- bisphosphate (RuBP) **(5C)** = a **6C** molecule that splits into 2 molecules of 3-phosphoglycerate **(3C)**
- 2 PGA molecules is phosphorylated (ATP )to bisphosphoglycerate (BGP) **(3C)**
- BGP is reduced to (GAP) **glyceraldehyde 3-phosphate) (3C)** with e- from NADPH
- 1 GAP leaves the cycle to form a **carbohydrate** (sucrose, glucose etc)
- The remaining GAP molecules + ATP regenerate **RuBP** to restart the cycle
26
How many carbon molecules are needed to produce one **glucose** molecule
- **Six** CO2
- for every **6 CO2, 12 G3P** is produced
27
What happens to G3P molecules in the **plant cell**
- Synthesizes **sucrose** in the cytosol and **starch** in the chloroplast
28
What is **photorespiration**?
- a process that results in the **uptake** of O2 and **release** of CO2 => loss of fixed carbon
29
What is the C4 pathway
- A **carbon fixation process** where CO2 is fixed with **phosphoenolpyruvate (PEP)** into a 4C compound **oxaloacetate or malate**
30
What are CAM plants and how do they fix CO2?
- They fix CO2 ar **night** using **PEP carboxylase**, storing it as malate for use during the day
31
What is photodynamic therapy?
- A medical treatment using light to activate pigments that produce oxygen radicals, targeting diseased cells
- Most common **photosensitizing agent = Aminolevulinic acid (ALA)**
32
ATP synthase structure in chloroplasts
- **CF1** (head): projects **outward** to the stroma (H+ gradient)
- **CF0** (base): H+ move through to get to **lumen**
BIOL-3221
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