Transcript photosynthesis - Biology-RHS

PHOTOSYNTHESIS
Chapter 8.2
MAIN IDEA
Light energy is trapped
and converted into
chemical energy
during photosynthesis
Overview of Photosynthesis
• Most autotrophs –including
plants—make organic
compounds, such as
sugars, by a process called
photosynthesis
Photosynthesis occurs in 2 phases
1. Light Reactions
• Light energy is absorbed & then
converted into chemical energy in the
form of ATP and NADPH
2. The Calvin Cycle (Light Independent)
• The ATP and NADPH are used to
make glucose
Phase 1: Light Reactions
• Absorption of light is the first step in
photosynthesis
• Chloroplasts large organelles that
aid in capturing light energy
• The light dependent reactions take
place with the THYLAKOIDS
• Within the THYLAKOIDS are
light-absorbing colored
molecules called PIGMENTS
• Different pigments absorb
different wavelengths of light
• The major light absorbing pigments in
plants are CHLOROPHYLLS
• The most common of the chlorophylls are
a and b
• In general, chlorophyll absorb most
strongly in violet-blue region of the visible
light spectrum
•Why are plants green?
• Plants are green because
they reflect light in the
green region of the
spectrum
• Additional pigments trap light
energy from other areas of the
visible spectrum
• Carotenoids absorb light mainly in
the blue and green regions, while
reflecting most light in the yellow,
orange, and red regions
• CAN YOU NAME ANY
VEGTABLES THAT YOU
EAT THAT CONTAIN
CAROTENOIDS?
Electron Transport
• Electron Transport chain uses 2 photosystems to produce energy-storage
molecules
• Photo-system II  light energy excites
electrons, splits water molecules,
releases electrons, produces oxygen
as a bi-product
• Photo-system I transfers electrons,
produces energy-storage molecule
• Energy-storage molecule is called
NADPH
Phase Two: The Calvin Cycle
• NADPH and ATP provide cells with
large amounts of energy these
molecules are not stable enough to
store chemical energy for long
periods of time
• The Calvin cycle is when energy is
stored in organic molecules such
as glucose
• In the final steps of the Calvin
Cycle, an enzyme called
RUBISCO converts inorganic
carbon dioxide molecules into
organic molecules
• Plants use the sugars formed
during the Calvin cycle both as a
source of energy and as building
blocks for complex carbohydrates,
including cellulose, which provides
structural support for the plant
Alternative Pathways
• Environment in which an organism
lives can impact the organisms’ ability
to carry out photosynthesis
• For example, plants in hot, dry
environments are subject to excessive
water loss and decreased
photosynthetic rate
C4 Plants
• Occurs in plants such as sugarcane &
corn
• These plants fix carbon dioxide into 4carbon compounds instead of 3carbon compounds
• C4 plants keep their stomata (plant cell
pores) closed during hot days, while
the 4-carbon compounds are
transferred to special cells where CO2
enters the Calvin cycle
• This allows for sufficient carbon
dioxide uptake, while simultaneously
minimizing water loss
Stomata
CAM Plants
• Occurs in plants that live in deserts,
salt marshes, other environments
where water is limited
• CAM plants allow carbon dioxide to
enter the leaves only at night, when
the atmosphere is cooler and more
humid
• At night, these plants fix
carbon dioxide into organic
compounds
• During the day, carbon dioxide
is released from these
compounds and enters the
Calvin cycle
BOUNS QUESTIONS (10pts)
ANSWERS DUE FRIDAY! (No late
answers will be accepted)
• List 4 other examples of C4 and
CAM plants. (DO NOT USE THE ONES GIVEN IN
THE NOTES) (YOU MAY HAVE TO USE OTHER SOURCES
TO FIND YOUR ANSWERS)
• Why do trees leaves change
color in the fall?