Download The Working Cell: Energy from Sunlight

The Working Cell:
Energy from Sunlight
Chapter 8
What process is this?
Photosynthesis uses light energy to
make food
• Photosynthesis is the opposite of cellular
respiration
• Photosynthesis is the process in which
plants and other producers convert the
energy of sunlight into energy stored in
organic molecules
• The cellular organelle in which
photosynthesis takes place…
Chloroplast
• Chloroplasts contain chlorophyll, a
chemical compound that give the
chloroplast a green color
• In most plants leaves contain the most
chloroplasts and are the major site of
photosynthesis
• Leaves have tiny pores, called stomata,
throughout their surface which allow CO2
in and O2 out
• Chloroplasts have an inner and outer membrane
• Inside the inner membrane is a thick fluid called
stroma
• Suspended in the stroma are many disk-shaped
sacs called thylakoids
• A stack of thylakoids is called a grana
Photosynthesis occurs in two stages:
1. The light reactions = convert the energy in
sunlight to chemical energy
2. The Calvin cycle = makes sugar from the
atoms in carbon dioxide, hydrogen ions, and
high-energy electrons
Overview of Photosynthesis
• Electromagnetic energy= a form of energy that exhibits
wavelike behavior as it travels through space
– Visible light, microwaves, X rays
•Wavelength= the shortest distance between equivalent
points on a continuous wave
• Electromagnetic spectrum = range of types of
electromagnetic energy
• The most important segment for life is a narrow
band between 380 to 760nm…visible light
• ROY G BIV
• A particle of electromagnetic radiation is called a
photon
•
•
Pigments= chemical compounds that
determine a substance’s color
When light shines on a material that
contains pigments, three things can
happen:
1. Absorption
2. Transmission (goes through the material)
3. Reflection (bounces back)
•
Why do leaves look green?
• Within the thylakoid membrane,
chlorophyll and other molecules are
arranged in clusters called photosystems
– think solar panel!
• Each photosystem contains a few hundred
pigment molecules, including chlorophyll
a,chlorophyll b, and carotenoids
– Chlorophyll a, the dominant pigment,
absorbs best in the red and blue wavelengths,
and least in the green
• Only chlorophyll a participates directly in
the light reactions but accessory
photosynthetic pigments absorb light and
transfer energy to chlorophyll a.
– Chlorophyll b, with a slightly different
structure than chlorophyll a, has a slightly
different absorption spectrum and funnels the
energy from these wavelengths to chlorophyll
a.
– Carotenoids are pigments that range in color
from pale yellow to deep red
• they are involved in the color changes of leaves in
the fall
• they funnel the energy from other wavelengths to
chlorophyll a.
Carotenoids
Photosynthesis
• Overview:
Chlorophyll absorbs light
↓
Energy transferred to electrons
↓
Energy level of electrons increased (unstable)
↓
Carbohydrates, oxygen
Light
Reactions
• The light reactions involve two
photosystems, photosystem I and
photosystem II, connected by an electron
transport chain
• Photons of light, as well as water
molecules, come into the thylakoid and
strikes photosystem I
• The oxygen is “sliced” off of the water
molecule and is released through the
stomata into the atmosphere
– Called photolysis
• This leaves hydrogen ions and electrons
• The electrons are funneled to the electron
transport chain
• The electrons move from carrier to carrier
within the electron chain
• Each time an electron moves to the next
carrier energy is produced
• When the electrons exit the electron chain
they move to photosystem II
• Photosystem II is called the “NADPH
producing system”
• What is NADPH?
Nicotinamide Adenine Dinucleotide Phosphate
It’s a carrier molecule!!
• What does it carry?
Electrons!!!
• The electrons are carried by NADPH to
the Calvin cycle
• Now, back to the hydrogen ions…
• The ETC produces energy by moving the
electrons from carrier to carrier
• This energy is used to pump hydrogen
ions across the membrane from an area of
low concentration to area of high
concentration
• Potential energy builds up and the
hydrogen ions rush through the ATP
synthase which produces what?
ATP
• The ATP is then used in the Calvin Cycle
The Calvin cycle makes sugar from
carbon dioxide
• The light reactions produce oxygen, a very
important product for life to exist
• But life needs more…organic molecules!
The Calvin cycle
• Carbon enters as CO2
• ATP and NADPH, from the light reactions,
provide energy and electrons that are used to
make the sugar
• The sugar that is produced is called G3P, a
smaller molecule than glucose (three carbons
instead of 6 carbons)
• G3P exits the cycle
• G3P is the raw material that plants use to make
glucose and other organic molecules
Summary of Photosynthesis
• Overall equation for photosynthesis
Sunlight + 6 CO2 + 6 H2O   C6H1206 + 6 O2
• Light reactions
–
–
–
–
take place in thylakoid membrane
use light and water
convert light energy to the ATP and NADPH
product is oxygen
• Calvin cycle
– takes place in the stroma
– Uses ATP and NADPH to convert carbon dioxide to
sugar
Photosynthesis has a global impact
• On a global scale, photosynthesis is the
most important process to the welfare of
life on Earth
• Photosynthetic organisms make about 160
billion metric tons of organic material per
year
• Earth’s atmosphere
• Carbon dioxide traps heat from the sun
and prevents it from escaping back out
into outer space
• The greenhouse effect, keeps the world
climate warm enough for life to exist
• In recent years the amount of CO2 in the
atmosphere has been rising