Ch 8- Photosynthesis
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Animation Quiz - Calvin Cycle
Photosynthesis
Visualizing Electron Transport
Where do plants get the energy they need to produce
food?
• What type of organism makes their own food?
• What type of organism obtains energy from foods they
consume?
• ATP (adenosine triphosphate)- basic energy source of all
cells, chemical compound that cells use to store and
release energy
– Adenine, 5- carbon sugar called ribose, and three phosphate
groups
• ADP (adenosine diphosphatte)- chemical
compound similar to ATP, but has two
phosphate groups
– Key for storing energy
• How is the energy that is stored in ATP
released?
– Chemical bond between second and third
phosphate group is broken
• Because of the characteristics of ATP, it is an
exceptional source of energy
Sec 2- Photosynthesis: An Overview
• Photosynthesis- series of reactions that uses
light energy from sun to convert water and
carbon dioxide into sugars and oxygen
• 6 CO₂ + 6 H₂O→ C₆H₁₂O₆+ 6 O₂
• Plants use the sugars to produce complex
carbohydrates- starches
• In addition to water and carbon dioxide, it
requires light and chlorophyll, molecule in
chloroplasts
• Plants gather the sun’s energy with light absorbing
molecules called pigments
• Several types of pigments which include; chlorophyll
a, chlorophyll b, carotenoids, xanothophylls
• Chlorophyll- principal light absorbing pigment
– Chlorophyll a and chlorophyll b
– Absorbs light very well in certain regions of visible
spectrum, green light is reflected
• Carotene- red and orange pigments, absorbs light
• Chlorophyll b is an accessory pigment that assists in
capturing light
• Carotenoids are also a accessory pigment that
absorbs colors the chlorophylls do not
Sec 3- Reactions in Photosynthesis
• Photosynthesis takes place in chloroplasts
• Thylakoids- sac-like photosynthetic membranes inside
chloroplasts
– Arrange in stacks known as grana
– Proteins in thylakoids organize chlorophyll into
photosystems – 2 types of photosystems
– 2 types of reactions in photosystems- light dependent
reactions and light independent reactions= Calvin cycle
– Light dependent reactions-thylakoid membranes
– Calvin cycle= stroma, a region outside thylakoid
membranes
Electron Carriers
• Sunlight excites electrons in chlorophyll= great
deal of energy
• Electron carriers transport high energy electrons
from chlorophyll to other molecules
• NADPᶧ- carrier molecule that accepts and holds 2
high energy electrons along with hydrogen ion
– Converts NADPᶧ into NADPH
– Allows energy of sunlight to be trapped in chemical
form
• High energy electrons used to build molecules for
cell
Light Dependent Reactions
• Requires light
• Converts ADP and NADPᶧ into ATP and NADPH and
produces oxygen
• Steps of light dependent reaction
– Light is absorbed by electrons in photosystem II Are electrons
ever used up? Where do the electrons come from?
– High energy electrons move through electron transport chain to
photosystem I
– Photosystem I reenergizes electrons released. Electrons are
used to form NADPH
– Positively charged hydrogen ions fill up thylakoid membrane
– Hydrogen ions pass through ATP synthase, ADP is converted into
ATP
Calvin Cycle
• Plants use energy that ATP and NADPH contain to build high energy
compounds
• Does not require light, known as light- independent reactions
• Steps of Calvin cycle
– CO₂ enters the cycle, 6 carbon dioxide molecules combined with six 5
carbon molecules to form twelve 3- carbon molecules
– ATP and NADPH are used to convert twelve carbon molecules into
higher energy forms
– Two 3 carbon molecules removed from cycle to form sugars, lipids,
amino acids
– 10 remaining 3- carbon molecules converted into six 5- carbon
molecules- used in next cycle
• Plants use sugars to build cellulose
Factors Affecting Photosynthesis
• Factors include water, temperature, and
intensity of light
• How are plants found in Arizona different from
plants in Kansas?
• Photosynthesis functions best between 0° and
35° C
• Increasing the light intensity increase the rate
of photosynthesis, the level of intensity varies
among plants