Transcript Photosynthesis - Fort Bend ISD

Photosynthesis
Chapter 8
Autotrophs vs. Heterotrophs
 Autotrophs: Plants and some other types of
organisms that use light energy from SUNLIGHT
to make their own food. These organisms
undergo photosynthesis!!
 – EX: Trees, grass, algae, plants
 Heterotrophs: Organisms that CANNOT use
the sun’s energy to make food– they obtain
energy from the foods they consume
 – EX: Deer, rabbits, bear, fish, insects, etc…
The Photosynthesis Equation
 Photosynthesis uses the energy of sunlight to




convert water and carbon dioxide into high
energy sugars and oxygen
6CO2 + 6H2O + light→C6H12O6 + 6O2
(carbon dioxide + water + light → sugars +
oxygen)
Plants then use the sugars to produce complex
carbohydrates such as starches
Plants obtain CO2 from the air or water in which
they grow
Photosynthesis
Light Energy
Chloroplast
CO2 + H2O
Sugars + O2
Inside a Chloroplast
 Chloroplast= Filled with chlorophyll and are
where photosynthesis takes place in plants and
other photosynthetic eukaryotes
 – Thylakoids= saclike photosynthetic membranes
arranged into stacks known as grana. Area where
light-dependent reactions take place
 – Photosystems= clusters of chlorophyll and other
pigments that are organized by the thylakoids
 – Stroma= Area outside the thylakoid membranes
where light- independent reactions
Light-dependent Reactions
Figure 8-5 Chlorophyll Light Absorption
Section 8-2
Absorption of Light by
Chlorophyll a and Chlorophyll b
Chlorophyll b
Chlorophyll a
V
B
G
YO
R
Electron Carriers
 Electron Transport= The transfer of a pair of high
energy electrons & their energy to another molecule
 Electron Carriers= The “bucket” or carrier that moves
electrons and their energy from molecule to the next
 EX: NADP+: Accepts and holds a pair of high-energy electrons
and an H+ ion, converting NADP+ into NADPH turning energy
from the sun into chemical energy .
 An analogy would be a pan carrying hot coals like the
NADP+ carries two electrons and a H+ ion.
ATP Formation
Adenosine Triphosphate (ATP)
Adenine
Ribose
3 Phosphate groups
ADP and ATP (Electron Carriers)
ATP
ADP
Energy
Energy
Adenosine diphosphate (ADP) + Phosphate
Partially
charged
battery
Adenosine triphosphate (ATP)
Fully
charged
battery
Light-Dependent Reactions
 Light-Dependent Reactions: Use energy
from sunlight to produce the energy
carriers ATP and NADPH and oxygen.
 – Reactions occur within the thylakoid
membranes of chloroplasts
Light-dependent Reactions
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Figure 8-10 Light-Dependent Reactions
Section 8-3
Photosystem II
Hydrogen
Ion Movement
Chloroplast
ATP synthase
Inner
Thylakoid
Space
Thylakoid
Membrane
Stroma
Electron
Transport Chain
Photosystem I
ATP Formation
Photosynthesis
Steps in Photosynthesis
 Photosynthesis: Has five major steps that occur
within the thylakoid membrane of the chloroplast
 – 1. Photosystem II: Light absorbed by photosystem
II is used to break up water molecules into energized
electrons, hydrogen ions (H+) and oxygen.
 – 2. Electron Transport Chain: High-energy
electrons from photosystem II move through the
electron transport chain into photosystem I.
Steps in Photosynthesis
 – 3. Photosystem I: Electrons released by
photosystem II are energized again in
photosystem I. Enzymes in the membrane
use these electrons to make NADPH/
 – 4. Hydrogen Ion Movement: The inside of
the thylakoid membrane is charged with H+
ions. This causes the outside of the thylakoid
membrane to be negatively charged and the
inside of the membrane to be positively
charged.
Steps in Photosynthesis
 – 5. ATP Formation: As hydrogen ions pass through
ATP synthase, their energy is used to convert ADP
into ATP. As it rotates ATP synthase (enzyme) binds
ADP and P+ group to create ATP. Because of this,
light-dependent transport produces high energy
electron AND ATP.
 SUMMARY:
 Light dependent reactions use water, ADP and
NADP+ to produce oxygen, ATP and NADPH
(Water, ADP, NADP+ Oxygen, ATP, NADPH)
 ATP and NADPH then provide energy to build energy
containing sugars from low-energy compounds.
Light-independent Reactions
 Calvin Cycle: Energy stored in the ATP
and NADPH formed during
photosynthesis, is used to build highenergy sugars that can be stored for a
long period of time.
 – Does not require light and is called light
independent reaction
 – Takes place in the stroma of the
chloroplasts
Calvin Cycle
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Steps in the Calvin Cycle
 The Calvin Cycle has four major steps:
 – 1. C02 Enters the Cycle: 6 CO2 molecules are
combined with six 5- carbon molecules to produce
three 12-carbon molecules
 – 2. Energy Input: Energy from ATP and electrons
from NADPH convert the twelve 3-carbon molecules
into higher-energy forms
 – 3. 6-Carbon Sugar Produced: two 3-carbon
molecules are removed to produce sugars, lipids,
amino acids, and other compounds
Steps in the Calvin Cycle
 – 4. 5-Carbon Molecules Regenerated: the
10 remaining 3-carbon molecules are
converted back into six 5-carbon molecules,
which are used to start the next cycle : )
Figure 8-11 Calvin Cycle
Section 8-3
CO2 Enters the Cycle
Energy Input
ChloropIast
5-Carbon
Molecules
Regenerated
6-Carbon Sugar
Produced
Sugars and other compounds
Concept Map
Section 8-3
Photosynthesis
includes
Lightdependent
reactions
Calvin cycle
use
take place in
Energy from
sunlight
Thylakoid
membranes
to produce
ATP
NADPH
O2
takes place in
Stroma
uses
ATP
NADPH
of
to produce
Chloroplasts
High-energy
sugars
Figure 8-7 Photosynthesis: An Overview
Section 8-3
Light
Chloroplast
CO2
Chloroplast
NADP+
ADP + P
LightDependent
Reactions
Calvin
Cycle
ATP
NADPH
O2
Sugars
Factors Affect Photosynthesis

Various Factors Affect the Rate of
Photosynthesis.
 Some of these factors are:
1. Amount of available water
 – EX: Plants in dry areas have waxy leaves to prevent
water loss
2. Temperature
 – EX: Enzymes work best between 0° and 35°C. Temps
above or below this range may slow down photosynthesis
or stop it entirely
3. Light Intensity
 1. EX: The higher the intensity the higher the rate of
photosynthesis. There is a maximum limit however. This
varies from plant to plant