botany 121 final | sean ryan

phloem

- transports sugars and other organic substances

- composed of different types of cells: sieve tube members

sugar sources

mostly mature leaves

sugar sinks

roots, young leaves, flowers, fruits, seeds

pressure-flow hypothesis

1. sugars are produced inside leaves (photosynthesis)

2. sugar is transported into companion cells via active transport or polymer trap mechanism (phloem loading)

3. water moves passively into sieve tube member from xylem by osmosis

4. high turgor pressure causes pressure-flow

5. sugar is actively in a new place

polymer trap mechanism

1. sucrose accumulates inside leaf mesophyll cells

2. transported into companion cells via diffusion

3. sucrose is polymerized into a heavier sugar

4. heavier sugar is unable to diffuse back, concentration builds up, diffuses into size tube members

translocation

- phloem

- energetically demanding process

- minerals, amino acids, hormones

- up or down

maple trees

- sugar made in the summer is moved to the roots and xylem

- leaves fall off in the autumn

- sugar water throughout the tree prevents

freezing

- sugar moves upward when new leaves are made in the spring.

photosynthesis

- produces sugars and oxygen

- 6CO2 + 6H2O + light → C6H12O6 + 6O2

photosystems

- assemblages of chlorophyll and other pigments closely bound to proteins, enzymes, and electron carriers necessary for chemical reactions

ATP

- adenosine triphosphate

- molecule that powers reactions in cells

- universal currency of biological energy

- ATP stores potential energy in chemical bond

NADPH

- electron carrier that provides high-energy electrons for photosynthesis

- NADP+= low energy state = oxidized

- NADPH = high energy state (contains 2 electrons) = reduced

chlorophyll

- most important pigment involved in photosynthesis

- embedded in thylakoid membrane of chloroplasts

- captures light energy, transfers electrons into photosynthesis

first set of photosynthetic reactions

IN: water, light, NADP+, ADP

OUT: oxygen, H+, NADPH, ATP

first set of photosynthesis reactions

- ATP syntheses uses H+ concentration gradient to synthesize

photosynthesis two main reactions

- light dependent reactions= happen in thylakoid

- light independent reactions = Calvin cycle, happen in the stroma

carbon fixation

the conversion of inorganic carbon (CO2) into more complex, reduced molecules like carbohydrates

Rubisco

- most common enzyme on earth

- makes up 10-25% of leaf protein

- fixes carbon out of the atmosphere

- attaches CO2 to Rubisco, a 5 carbon molecule that is the precursor of glucose

calvin cycle

IN: CO2, Rubisco, ATP, NADPH

OUT: 3-carbon sugar, Rubisco, ADP, NADP+

photorespiration

- when Rubisco fixes O2 instead of CO2

- Rubisco is an inefficient enzyme

- moar likely in warm and dry climates

PEP carboxylase

- can fix CO2 without binding to O2

- used in C4 and CAM photosynthesis

C4 photosynthesis

- statically separates the sites of carbon fixation and sugar production

- in dry, warm environments

- C4 plants have the advantage in conserving water and preventing photorespiration

CAM photosynthesis

- stomates are opened at night and carbon dioxide is fixed to malic acid, which is stored in vacuoles.

- during the day, malic acid decomposes to release carbon dioxide.

- most popular in desert environments

cellular respiration

- release of energy from glucose molecules broken down into individual carbon dioxide molecules

- kinda reserve of photosynthesis

cellular respiration equation

C6H12O6 + 6O2 --(enzymes)--> 6CO2 + 6H2O + ATP

3 stages of cellular respiration

glycolysis, krebs cycle, electron transport chain

glycolysis

#1

- splitting glucose into two pyretic acid molecules

- in the cytoplasm, get out net of 2 ATP

- IN: glucose, ATP, NAD+ OUT: pyruvate, ATP, NADH

citric acid (krebs) cycle

#2

- happens in mitochondria

- produces net of 2 ATP

electron transport system

- in mitochondria

- oxygen is the final electron acceptor

- net get of 38 ATP (ideally)

fermentation

- occurs when oxygen isn't available in cells (anaerobic respiration)

- two types: alcohol fermentation and lactic acid fermentation

alcohol fermentation

produces ethanol

lactic acid fermentation

produces lactate