Photosynthesis:

1
Chapter 7

• Photosynthesis
• Using Light to Make Food

2
Plant Power for Power Plants

• Plants make 160x109 metric tons of organic
  material per year
• use this in the form of wood and coal for heat,
  light and fuel
• Willow tree plantation used as renewable energy
  source to make electrical energy
• also useful as wildlife habitat, reduce erosion,
  farmers diversify and removes CO2 that leads to
  global warming

3
Autotrophs

• Make their own food in the form of organic
  molecules from inorganic molecules using
  photosynthesis
• plants, protists and photosynthetic bacteria

4
Chloroplasts

• Site of photosynthesis
• Leaves usually have the most chloroplasts
• Green from chlorophyll molecules that capture the
  suns energy
• CO2 brought in and O2 released to environment
  thru the stomata also needs H2O from the roots

5
Leaf Section and Stomata
Opened
Closed
6
Chloroplast Structure

• Double membrane
• Inner membrane filled with stroma
• Within the stroma are thylakoids that are disc
  shaped structures that surround the thylakoid
  space
• increase surface area
• chlorophyll in the membrane
• Thylakoids are concentrated into grana

7
Overall Reaction

• CO2 and H2O are waste in cellular respiration but
  the beginnings of photosynthesis
• Glucose is used by the plant and others and O2 is
  released to environment for cellular respiration
  use
• All done with the energy of the sun

8
Photosynthesis Road Map

• Complex process even though the equation looks
  simple
• 2 stages
• Light reaction
• Calvin Cycle

9
Light Reaction

• Converts solar energy to make ATP and NADPH
• NADPH (reduced form) is similar to NADH
  electron carrier NADP is oxidized form
• get electrons from the splitting of H2O whereas
  NADH gets electrons from food molecules
• DOES NOT make sugar in this step, just energy
  carriers

10
Calvin Cycle

• Also referred to as dark cycle as it does not
  require light
• Makes the sugar from the energy in ATP and NADPH
• high energy electrons from NADPH converts CO2 to
  sugar
• Indirectly dependent on the sun

11
Nature of Sunlight

• Radiation energy and moves in waves
• like a rock in a puddle
• Crest to crest is a wavelength
• short to long is the electromagnetic spectrum
• visible light is only a small part of the
  spectrum
• Colors are generated when wavelength is not
  absorbed
• chlorophyll absorbs all but green so it appears
  green

12
What Colors Are Required for Photosynthesis?

• Took algae and placed it on a slide and placed O2
  sensitive bacteria on them
• Used a prism to split the light into the visible
  spectrum and looked where the bacteria where
  growing
• bacteria in the red-orange and the blue-violet
  lights but not the green-yellow

13
Chloroplasts Pigments

• All are found in the thylakoid membrane
• Chlorophyll a collects blue-violet and red
  light
• participates directly in the light reactions
• Chlorophyll b collects blue and orange light
• not directly involved but passes its energy on to
  chlorophyll a
• broadens the spectrum of light that can be used
• Carotenoids collects blue-green light
• some energy is passed to chlorophyll a
• others protect from excessive energy that may
  hurt the chlorophyll
• carrots have a lot of carotenoids so can protect
  our eyes from bright light
• see in fall foliage colors because chlorophyll
  decreases

14
Fall Foliage
15
Light Energy as Photons

• Light also functions as photons fixed quantity
  of light energy and move as a particle
• Pigment hit by photon and electrons in
  chlorophyll a are excited and move up from the
  ground state and then falls back to ground state
• most of this increase/decrease in energy is given
  off as heat but some is given off as light
• like in a glow stick

16
Part of Chlorophyllresponsible for releasing
electron
17
Photosystems

• Chlorophyll a is part of a photsystem, few 100
  per chloroplast
• Consists of pigments (chlorophyll and
  carotenoids) reaction center which is a special
  chlorophyll a molecule and a primary electron
  acceptor which will generate ATP and NADPH

18
Generation of ATP and NADPH

• 2 photosystems used
• Light activates the H2O splitting photosystem and
  release O2 into the atmosphere
• Electrons move down an ETC and make ATP and
  stimulate the NADPH-generating photosystem
• electrons end up on NADP thru its ETC

19
Summary
20
Light Reactions

• Occur in the thylakoid membrane
• ATP synthesis is similar to that of cellular
  respiration but H are pumped into the thylakoid
  space rather than the intermembrane space
• difference also in source of H - food for
  cellular respiration and light in photosynthesis

21
Calvin Cycle

• Makes sugar from CO2
• Happens in the stroma of the chloroplast by the
  enzyme called Rubisco
• Done without the use of light so also called the
  dark reactions
• Need CO2, ATP and NADPH to create glyceraldehyde
  3-phosphate which is the precursor to sugar and
  other organic molecules

22
Calvin Cycle



Must know things

23
C3 Plants

• Plants like soybeans, oats, wheat, rice, etc.
  need to use CO2 directly out of the atmosphere
• On hot, dry days these plants close the stomata
  to prevent H2O loss but also shut off the intake
  of CO2
• no sugar is made in this situation

24
C4 Plants

• Have an adaptation to be able to make sugar
• corn, sugarcane and sorghum
• Convert CO2 into a 4-C molecule by using a
  special enzyme to get CO2 out of the leaf spaces
  even when stomata are closed and move to Calvin
  cycle
• called the carbon shuttle

25
CAM Plants

• Another adaptation seen in succulent plants
  cacti, aloe, jade and pineapple
• Admit CO2 through stomata but mainly during the
  cooler nights
• Process is similar to C4 plants and CO2 is
  shuttled to Calvin cycle in the day time

26

• In C3, C4 and CAM plants, the sugar is only made
  by the Calvin cycle!!!!
• The CO2 is just delivered by different methods to
  the process

27
Summary

• Convert light into chemical reaction
• Doesnt show how energy moves from producers
  (plants) to consumers (herbivores and animals)
• Helps with gas exchange and also global
  temperatures

28
Greenhouse Heating

• Sun comes thru the greenhouse glass and heats the
  soil that in turn heats the air which raises the
  temperature enough for the plants to grow

29
Greenhouse Effect

• Greenhouse effect also applies to the global
  settings
• Heat is trapped by the greenhouse gasses of CO2,
  H2O vapor, CH4 (methane) and other synthetic gases

30
Global Warming

• CO2 is most important greenhouse gas
• much is stored in plants that end up as long term
  fossil fuel storage and returned to the
  atmosphere by cellular respiration
• increase use of fossil fuels increases the CO2
  emissions which are linked to global warming
• these increased CO2 levels also coincide with the
  cutting down of rain forests that would use the
  CO2 if the trees were still there
• All this leads to an increase in the temperature
  of the Earth