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Lecture 2

AN100 Lecture Notes - Lecture 2: Guard Cell, Cytosol, Leghemoglobin

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Amalia Philips

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CO2- glucose is the process of photosynthesis
You need co2, light, and h20 to make glucose, o2 and h20
ATP and NADPH are the energy intermediates
Green plants, cyanobacteria, and algae are the only ones that do go through
Mesophyll is the tissue on the leaf of the plant and it has cells- chloroplast. This is where
photosynthesis takes place. For photosynthesis to happen, water is taken from the roots to
the leaves through small veins and then co2 is taken through the leaves. O2 is released
through the stomata.
The third membrane of the chloroplast is the thylakoid membrane (in the center of the
cell). That’s where the chlorophyll is. In the membrane there’s these fluid filled things
called thylakoids that enclose the thylakoid lumen. The thylakoids stacked on top of each
other form a granum. In between the inner membrane and the thylakoid membrane is a
fluid filled thing called the stroma.
The light reactions occur in the thylakoid membrane and they produce ATP, NADPH and
The Calvin cycle uses co2, ATP, and NADPH
There is life that doesn’t have access to light (corral)
Bacteria could undergo photosynthesis w/o splitting O2
Fe atoms are deep in the ocean (red sediment) it had the O2, and it rose into the
Shorter the wavelength the higher the energy
Photosynthesis happens at 425nm and 675nm (visible light)
It doesn’t work at the higher energy part of the spectrum; it is just too harsh to capture the
Energy is weaker when it goes into water
Electricity penetrates water because water molecules are charged.
Living organisms respond to what we call visible light.
The higher the energy of electromagnetic radiation, the worse it penetrates water.
The first photosynthetic organisms evolved in an aqueous environment.
Mitochondria and Chloroplasts have 2 outer membranes- it was engulfed by another cell
(evolved from bacteria)
There are 3 types of chlorophyll pigments- chlorophyll a&b (absorbs red and blue), and
carotenoids (absorbs blue and green).
Carotenoids have 2 spots where their electrons can jump. It expresses orange, yellow and
red usually on flowers and fruits.
In leaves, chlorophyll usually masks the carotenoid and so that’s why they are green
Chloroplasts absorbs the light energy and goes to the excited state
Chlorophyll absorbs blue and red light and we see green
The Emerson enhancement effect- able to absorbs red light twice
In the light reactions- capturing the light and converting it to sugar
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There are 2 photosystems in the thylakoid membrane. The electrons are transported
linearly from photosystem II to photosystem I. This is called noncyclic electron flow and
NADPH is made.
Z scheme- high energy e go through the electron transport chain, pump H+ ions across
membrane in chlorophyll, goes through e transport again and reduces 2NADP+
There are 2 photosystems because you need 2 photons of visible light to move the
electrons to the desired energy level
It needs 2 jumps to use the e from O2
Water splitting clock- oxidation of water, split H2O to release O2
ATP synthase- H+ diffuse through and they make ATP form ADP and P
We have electrons and ATP now
Water is split- that’s where the o2 is formed. 2 H2 are taken from the stroma and 2 H2
come from water. NADPH is from the H+ and 2 electrons. The H+ gradient that is made
is in the lumen- creates the ATP synthase production
Chemiosmosis in chloroplast- ATP synthase across an ion gradient- produces less ATP-
water to more NADPH- non Cyclic photophosphorylation
Cyclic photophosphorylation- make lots of ATP and no NADPH
Products- ATP, NADPH, O2
Used- Water and light energy
NADPH and ATP aren’t made in equal amounts
Non- cyclic makes equals amounts of ATP and NADPH (Light reactions)
Cyclic- makes more ATP (Calvin Cycle)- it just stays in photosystem I and makes a
circle that creates a H+ gradient in the lumen to produce lots of ATP
The pigments in the light harvesting complex can can undergo resonance energy transfer
and just let the electron go down the line. When P680 gets excited it can go through
resonance energy transfer so it releases its high energy electron and becomes P680+.
The light harvesting complex is also known as the antenna bc it absorbs energy like a
funnel down to P680.
Rubisco- enzyme that takes co2 from atmosphere and transforms it to the organic
You need 6 NADPH and 9 ATP to make 1 molecule of glucose- Dark reactions
Some photons captured by light harvesting complexes produce ATP but not NADPH
Glucose production requires more ATP than NADPH
Both are related by cause and effect
Calvin Cycle
Phase I: Carbon fixation- co2 is taken from atmosphere and is made into an organic
molecule via rubisco
Phase II: ATP is used for energy to reduce NADPH to NADP, carbohydrate production
Phase III: Regeneration of RuBP- 10 G3P molecules are used for this and ATP
Photorespiration- RuBP is added to o2 instead of CO2 to make 1 G3P and
phophoglcolate which gets phosphorylzed to make an organic molecule ad co2. This
occurs when o2 levels are high around plants- very wasteful bc it releases co2, limiting
plant growth
There wasn’t any oxygen on this earth when things were evolving- that’s why it still
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It’s a protected mechanism- energy can be dissipated through co2
C3 plant- RuBP and Co2 produce the 2 G3P molecules. They have 3 carbons that’s why
they are called C3 (wheat, corn and oak).
C4 plants
Instead of making G3P, these plants a 4 carbon molecule (oxaloacetate)
These plants have a system that limits photorespiration. The mesophyll surrounds the
bundle-sheath cells where the Calvin cycle happens. Co2 enters the stomata and oxalate
gets produced. The enzyme PEP, unlike rubisco, it doesn’t recognize o2 so when o2 is
high and co2 is low, it continues to fix co2.
C4 plants- grass family- Calvin cycle happens in bundle sheath cells- where dark
reactions occur
Coating of mesophyll cells- block bundle sheath from being exposed to high o2
C3 plants outcompete c4 plant when it rains a lot bc c4 has to put energy into it
C4 plants- dry climates
C4 plants can store Co2 in their mesophyll and bundle and change it to oxalate and close
their stomata
C4 plants can do good in the drought bc they don’t need water- stored co2
CAM plants store co2 as malate during the night and releases co2 in the morning to start
the Calvin cycle
They go through light and dark reactions
The leaves of the CAM plants taste sour in the morning
Etc and chemi in chloroplasts and mitochondria
o Where the e comes from and where they end up
o E come from water molecule and end up on NADPH--- chloroplasts
o E come from breaking down from organic molecule and end up on h20---
Plant Structure
Alternation of Generations
Gametes get fertilized and turns into a zygote and then it goes through meiosis
Seeds have dormant embryos and when they germinate it produces a seedling.
Sexual reproduction in plants has 2 multicellular stages- gametophyte produces gametes
(relatively small) and sporophytes produce spores (relatively big).
Seeds are dispersed and wait till it’s a good time to germinate
Monocots and Dicots- 2 groups flowering plants go in
Cotyledons- number of seed leaves present on the embryo
5 multiples of flower parts- di
3 multiples of flower parts- mono
netted leaf- di
parallel line on leaf- mono
Sugar cane is a monocot and it isn’t always a c4 plant
Plant Anatomy
Meristems- the only part of the plant where cell division occurs, where new tissue is
being made (tissues)
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