Chapter 8 - Photosynthesis · 8.3 Worksheet Light-Dependent Reactions Summary Photosystem II PSII...
Transcript of Chapter 8 - Photosynthesis · 8.3 Worksheet Light-Dependent Reactions Summary Photosystem II PSII...
Chapter 8 - Photosynthesis
8.1 – Energy and Life
All activities performed by a cell require energy (the ability to do work)
Cells must obtain and use energy
ATP
Most energy in a cell is stored and released by adenosine triphosphate (ATP)
Structure
Adenine molecule, ribose (sugar) molecule, and three phosphate groups
Energy is stored and released from the phosphate group bonds
ATP does not store
energy when it is in
the form of ADP
(only 2 phosphates)
ATP stores energy when
it has all three phosphates.
It’s like a fully charged
battery.
Energy is stored when a phosphate group is added to adenosine diphosphate (ADP)
ADP + p + energy ATP
Energy is released when a phosphate group is removed
ATP ADP + p + energy
Energy can be continuously added and released this way
Used to power many functions in cell
Active transport
Movement (muscle cells)
Chemical reactions
ATP does not store energy for long periods of time
Molecules such as sugar (glucose) are produced to store energy
Stored energy is used to produce ATP when needed
How organisms obtain energy
Heterotrophs – organisms that obtain food by eating other organisms (animals, fungi)
Autotrophs – organisms that can make their own food (plants, algae)
Photosynthesis – sunlight energy is used to produce glucose (sugar)
Energy in sunlight is converted into chemical energy
Chemosynthesis – inorganic chemicals are used to produce food
Chapter 8 - Photosynthesis
8.2 – Photosynthesis: An Overview
Light and pigments
Different colors of sunlight (energy) travel at specific wavelengths of light
Pigments – molecules that absorb specific colors of light
Chlorophyll – absorbs all light except green, which is reflected (so, plants appear green)
Carotenoids (Carotene) - an accessory pigment in plants that absorbs all light except for red, orange, or yellow (usually seen in Autumn leaves)
The Chloroplast
Structure
Grana - Stacks of membrane sacks (singular = Granum)
Thylakoid – the membrane sacks of grana
Chlorophyll is located on membrane of thylakoid, where light absorption occurs
Stroma – Internal space surrounding grana
Structure of the chloroplast
Functions of photosynthetic
structures
Chapter 8 - Photosynthesis
8.3 – Photosynthesis
The Process
2 Steps:
1. Light-dependent reactions – uses sunlight to produce two energy carriers: NADPH and ATP
2. Light-independent reactions – uses carbon dioxide (CO2) to produce glucose, using energy from NADPH and ATP (from
step 1)
1. Light-dependent Reactions
Requires sunlight to work
Occurs on the membrane of the thylakoid in the chloroplast
Clusters of chlorophyll, called photosystems, absorb sunlight and excite electrons
Electrons were provided when H2O was broken down to form O2, which is then released as a waste
Electrons are passed along a chain of molecules
Energy from this is used to produce 2 molecules:
NADPH is made from NADP+
ATP is made from ADP
2. Light-independent reactions
Occurs in the stroma (open space) of the chloroplast
Does not require sunlight
Also called the Calvin Cycle
Continuous chain of chemical reactions in
which energy is used to convert CO2 into glucose
CO2 enters cycle and is combined with a 5-carbon sugar
Molecules are then rearranged using energy from the NADPH and ATP made during the light-dependent reactions
By the end of the cycle, some carbon molecules are used to make glucose, while the rest continue the Calvin cycle
Overall Reaction: (you must know this equation!)
(sunlight)
6 CO2 + 6 H2O ----> C6H12O6 + 6 O2
Light-Dependent Reactions:
http://www.youtube.com/watch?v=hj_WKgnL6MI
8.3 Worksheet Light-Dependent Reactions
Summary
Photosystem II PSII absorbs light, which increases electron energy. Electrons are passed to the Electron Transport Chain. Water is broken down to replace the lost electrons. H+ and O2
Electron Transport Chain
Energy from electrons is used by proteins in ETC to pump H+ ions from the stroma into the thylakoid space. Electrons are passed to PSI.
Photosystem I Energy in electrons declined, so light is absorbed again to reenergize electrons. Electrons are passed down another ETC, where NADP+ picks up the electrons and H+ ions to become NADPH.
Hydrogen Ion Movement and ATP Formation
H+ ions were building up in thylakoid space. Concentration (charge gradient) causes H+ ions to diffuse out of thylakoid through ATP synthase, which generates production of ATP.
How does ATP synthase produce ATP?
H+ ions pass though the enzyme, causing ATP synthase to rotate. This produces the energy needed to bind ADP to a phosphate group, to produce ATP.
When sunlight excites electrons in chlorophyll, how do the electrons change?
The electrons take on a great deal of energy, which causes them to move to a higher energy level.
What does the Calvin cycle use to produce sugars?
They use CO2 and energy from ATP and NADPH from the light-dependent reactions to make sugar.