Plant Final

Chlorophyll A

• Universal pigment of all photosynthetic organisms

• Responsible for transferring light energy to electrons

• Also hydrolysis

Chlorophyll B

• Accessory pigment

• Widens range of light absorbed

• Passes energy to chlorophyll A

Carotenoids

• anti-oxident/protective against photodamage

• Always present in the leaves - yellow

Anthocyanins

• Accessory pigment

• Absorbs UV light and acts like sunscreen

• Produced based on the amount of sugars and phosphates present in the leaves → produced more in fall

Phytochrome

• Photoreceptor pigment

• Senses the length of days and regulates leaf out/leaf fall

• Literally changes shape

Photodamage/photoinhibition

• damage which affects the performance of a photosystem

• Regulated with D1 protein which acts as a signifier of damage and can be repaired

Leaf Fall

• Plant pulls in nutrients from leaves → causing a color change

• Enzymes break down chlorophyll (protease, chlorophyll reductase)

• Abscission zone - layer of cells in the stalk of the leaves which die 

  • ethylene stimulates production of a digestive enzyme

• Buds are protected by scales

  • filled with sugars which acts as antifreeze

• Contributing factors: temperature, storms, drought, predation

• Evergreen leaves don’t fall because they are built to be long lasting and take so many nutrients/materials

Leaf out

• Success depends on how many nutrients were stored over the summer

• Phytochrome - acts like a timer of how long the days are/times leaf out

• Maple tapping - sugars move in the tree and can be harvested

Photosynthesis

• Conversion of light energy into sugars

• Mystery for a long time 

  • people lowkey thought that plants ate dirt but eventually it was proven that hydrolysis was happening

• Chloroplasts

  • Stroma - internal matrix, carbon fixation here

  • Thylakoid - pigments found here

• When light energy is absorbed:

  • Florescence - energy → heat + light

  • Resonance - pass energy back and forth

  • Transfer - energy passed to an electron acceptor 

Light reactions

• Happens in the thylakoid membrane

• H20 → Photosystem 2 → ETC → Photosystem 1

• The ETC creates a H+ concentration gradient which powers ATP synthase

• Photosystem 1 creates NADPH

• Non-cyclical reactions create equal amounts of NADPH and ATP

• Photosystem 1 can send electrons back through the ETC to create more ATP in cyclical reactions

Carbon Fixation Reactions

• Converts ATP + NADPH into sugars

• Calvin cycle (regeneration)

• Carbon Fixation

  • RuBP + 3CO2 → 6 PGA

• Reduction

  • 6 PGA + ATP, NADPH → 6 PGAL

• Regeneration

  • 6 PGAL + ATP → 3 RuBP

• RUBISCO is used tto fix carbon in these reactions

The problem with photosynthesis

• RUBISCO is not specific to carbon, it can also fix oxygen which is called photorespiration

• If this happens then the plant has to spend energy to recover the RuBP

• Photorespiration is most common in hot and dry places

• C3 photosynthesis - the calvin cycle- happens in all plants

C4 photosynthesis

• C4 plants have thick bundle sheath cells which surround vascular veins and are packed with chloroplasts

  • This creates a spatial separation of O2 and RUBISCO

• An enzyme called PEP carboxylase fixes carbon from outside the barrier and brings it in where it can follow the normal pathway

• Costs more than C3 but has less waterloss and photorespiration

CAM photosynthesis

• PEP carboxylase fixes CO2 at night and stores it as malic acid in vacuoles 

  • This creates a temporal separation of RUBISCO and O2

• CAM plants are often succulents

• Sugar production is limited by how much CO2 plants can store