BIO + chem OAT Test Prep Day 4

Photosynthesis!!!

Heterotrophs

Obtain energy by consuming food

Autotrophs

Make their own food

• because of photosynthesis

• Plants are photoautotrophs

Cellular respiration ~ a review

• Give me the formula for cellular respiration

• What kind of reaction is it? (endergonic, exergonic, spontaneous, nonspontaneous)

Exergonic

Spontaneous

Photsynthesis

• Give me the formula for photosynthesis

• What kind of reaction is it? (endergonic, exergonic, spontaneous, nonspontaneous)

What is carbon fixation

Carbon Fixation: Incorporating an inorganic carbon (CO2 ) into an organic molecule like glucose,

Leaf Anatomy

• Give me the layers of the tissue (there are 5)

• Epidermis

• Palisade Mesophyll

• Spongy Mesophyll

• Stomata

• Guard Cells

Epidermis (plant cell)

• Function

Provides protection and prevents water loss

Palisade Mesophyll

Many chloroplasts, major site of photosynthesis

Spongy Mesophyll

Loose arrangement allows for gas exchange

Stomata

Pores for gas exchange

Guard Cells:

Regulate opening/closing of stomata

Chloroplast Structures

• Outside

• Fluid inside

• Membranes that undergo reaction

• Inside the membranes that do reactions

Outer + Inner membrane:

Stroma:

Thylakoid:

Lumen

Membranes (plants)

Outer + Inner membrane:

Each made of phospholipid bilayers

Stroma

Stroma: Fluid within chloroplast, site of Calvin cycle

Thylakoid

Thylakoid: Membranes within the stroma, site of light-dependent reactions. A “stack” of thylakoids is called a granum

Lumen

Lumen: Inside of the thylakoid, accumulates H+ ions (↑acidity)

Granum

Stack of thylakoids

Light dependent Reactions in plants

• Where do they occur

• What do they need

• What do they create

• What are these reactions?

Light dependent reactions

• Take place in thylakoid

• Need light energy

• Provide ATP and NADPH for light independent reactions

• Consist of:

  • Non-cyclic photophosphorylation

  • Cyclic photophosphorylation

Light independent Reactions in plants

Where do they occur

What do they need

What do they create

What are these reactions?

• Take place in stroma

• Don’t directly use light energy

• Fix carbon in order to form glucose

• Consists of:

  • Calvin cycle

What are photosystems?

• What are the examples of photosystems?

• What kind of molecules are in photosystems?

• What kind of lights do these systems reflect and absorb?

• Protein complexes containing pigments such as chlorophyll and carotenoids

• Chlorophyll absorbs blue and red light, reflects green light

What structure do photosystems have?

• What are the two types of photosystem

• What is a reaction center in the photosystem?

• Has porphyrin ring with magnesium at the center

• Reaction center: chlorophyll pair in the center converts light energy to chemical energy, otherwise, they would just bounce around in the photosystem chlorophylls

• Two types of photosystems:

  • PS II (P680)

  • PS I (P700)

Non-Cyclic Phosphorylation

• What kind of reaction is it (light dependent or independent)?

Light Dependent

Non-Cyclic Phosphorylation Steps 1 - 6

1. Photolysis: light energy used to split water; electrons (e-) passed to PS II, protons (H+) remain in lumen

2. Electrons in reaction center excited by light energy; passed to electron acceptor (EA) and enter the first electron transport chain (ETC)

3. Electrons undergo a series of redox reactions in the first ETC, protons are pumped from stroma to lumen

4. Electrons reach reaction center of PS I, where they are re-energized with light and passed to another EA, entering the second ETC

5. The second electron transport chain leads to NADP+ reductase, which reduces NADP+ to NADPH

6. Protons accumulate in the lumen to form an electrochemical gradient; ATP synthase uses proton flow to produce ATP

Cyclic Phosphorylation Steps

Photosystem I passes electrons back to the first ETC, making a loop between the two; results in ATP production but no NADPH productions

Keep pumping H+ and breaking down H20

Calvin Cycle:

• What kind or reaction is it (light, no light)

• Where does it occur

• What does it do

• Light independent

• Do not directly use light

• Fix carbon in order to form glucose

Steps of the Calvin Cycle

Stage 1: Carbon fixation:

Stage 2: Reduction:

Stage 3: Regeneration:

Stage 4: Carbohydrate synthesis:

stage 1 of the calvin cycle

Stage 1: Carbon fixation: RuBisCo combines CO2 and 5-carbon RuBP, forming a 6-carbon compound that quickly splits into two 3-carbon PGA molecules

Stage 2 of the Calvin cycle

Stage 2: Reduction: PGA phosphorylated by ATP

and reduced by NADPH to form G3P

Stage 3 of the calvin cycle

Stage 3: Regeneration: Most G3P is converted back to RuBP

Stage 4 of the calvin cycle

Stage 4: Carbohydrate synthesis: Some G3P is

used to make glucose

Photorespiration

• RuBisCo can also react with O2

• Results in production of PGA and phosphoglycolate (2-carbon molecule)

• Phosphoglycolate must be shuttled through peroxisome and mitochondria for conversion into PGA

• This wastes energy and fixed carbons - net benefit of photosynthesis is lost!

• Hot and dry conditions encourage stomata closure, leading to oxygen accumulation and increased photorespiration

• Also known as C2 photosynthesis

C2 Photosynthesis

• RuBisCo can also react with O2

• Results in production of PGA and phosphoglycolate (2-carbon molecule)

• Phosphoglycolate must be shuttled through peroxisome and mitochondria for conversion into PGA

• This wastes energy and fixed carbons - net benefit of photosynthesis is lost!

• Hot and dry conditions encourage stomata closure, leading to oxygen accumulation and increased photorespiration

• Also known as Photorespiration

C3 Photosynthesis

• Fixation of CO2 to form 3-carbon molecule (PGA)

• ~90% of plants do this

• Hot and dry conditions encourage stomata closure and increase photorespiration (C2 photosynthesis)

C4 Photosynthesis

• Purpose

● C4 and CAM photosynthesis are evolutionary adaptations that aim to reduce photorespiration in plants inhabiting tough environments

C4 photosynthesis

1. PEP carboxylase fixes CO2 to three-carbon PEP molecule, producing four-carbon oxaloacetate, which is then converted to malate

—-Mesophylll———————

2. Malate transferred to bundle sheath cells: ↓[O2] (WAY LESS O2)

3. Malate decarboxylated to form CO2 and pyruvate

4. CO2 fixed by RuBisCo to undergo Calvin cycle, pyruvate shuttled back to mesophyll and converted back to PEP

CORN EXAMPLE

C4 Photosynthesis Structures (4) also, name the two main areas.

Bundle Sheath cells and mesophylls

CAM Photosynthesis (Crassuacean Acid Metabolism)

1. Stomata closed during the day to prevent transpiration (water evaporation)

2. Stomata open at night, CO2 converted to malate (like in C4 ) and stored in vacuoles

3. During day malate is decarboxylated to release CO2 for photosynthesis, while pyruvate that is converted back to PEP

EX PINEAPPLE

• Phosphoglycolate

Produced when Rubisco interacts O2, formed alongside PGA.

HAS TO BE BROKEN DOWN EVENTUALLY INTO PGA. BUT to do so it has to go to the peroxisome or mitochondria. HUGE ENERGY LOSS

How many Calvin cycle cycles does it take to make one glucose?

6

Alkali Metals

Low ionization energy (super easy to remove an electron from them)

• Very reactive with water