Chapter 8 Photosynthesis 2011.pdf

Chapter 8 Photosynthesis
8.1 Energy and Life

I. Chemical Energy & ATP
• NRG: ability to do work
a) Many forms of NRG: heat; electricity
b) Chemical bonds store NRG = released w/breakdown
• Candle: wax + O2 = CO2 + H2O (heat/light released)
c) All life obtains, then uses NRG (for cell activities)
• ATP (Adenosine Triphosphate): basic NRG source for cells
• Adenine (N) + Ribose + 3P groups

1. Storing Energy
• ADP (Adenosine Diphosphate):
a) Adenine (N) + Ribose + 2P groups
b) Like a rechargeable battery
c) Available NRG stored by adding 3 rd P group

2. Releasing Energy
• ATP (w/3 P groups)
a) Cells easily break (NRG releasing) and reform (NRG
storing) 3 rd P bond for cellular work
b) Ready to be used, full battery, available NRG

3. Using Biochemical Energy
a) Active Transport: uses ATP to move molecules
• Cell proteins pump Na + /K + in & out to contract muscles
b) Protein synthesis
c) ATP: usable NRG; hard to store; small amts in cell
d) Glucose: un-usable form; 90x the NRG of 1 ATP
e) Cells regenerate ATP from ADP w/NRG in food
w/respiration

II. Heterotrophs & Autotrophs
• Photosynthesis: Sun NRG converted to chemical NRG
stored in bonds of carbs
1. Autotroph: use light NRG to make own food (for ATP)
• Ex: Plants, algae, some bacteria
2. Heterotroph: Consumed food NRG to make ATP
• Ex: herbivores/carnivores/decomposers

8.2 Photosynthesis: An Overview
I. Chlorophyll and Chloroplasts
1. Light: wavelengths seen as visible spectrum colors

2. Pigments: light-absorbing molecules in
autotrophs
• Chlorophyll a & Chlorophyll b most important
a) Absorbs blue & red regions of visible spectrum best
b) Green NOT absorb but reflect so plants appear green!
c) Cold destroys chlorophyll 1 st ; others (carotene) visible
w/fall

3. Chloroplast: photosynthetic organelle
• Thylakoids: saclike photosynthetic membranes
a) Arranged in stacks called grana
b) Contain chlorophyll, protein & pigments
• Stroma: outer fluid portion

4. Energy Collection:
• Chlorophyll absorbs light and transfers NRG to own electron
molecules
• These high-energy electrons fuel photosynthesis

II. High Energy Electrons (e - ):
• Highly reactive and need special carrier molecule
a) NADP + = nicotinamide adenine dinucleotide phosphate
b) NADP + + 2 e - + H + NADPH
c) NADPH: traps sun NRG into chemical form
d) NADPH: carry e - produced by light absorption to chem rxn in
cell (used to build carbs)

III.Overview of Photosynthesis:
• Uses sunlight NRG to convert carbon dioxide and water (reactants) to
sugar and oxygen (products)
a) 6 (CO 2 ) + 6 (H 2 O) C 6 H 12 O 6 + 6 (O 2 )
b) Carbon dioxide + Water Sugars + Oxygen
c) Plants use sugar for NRG and growth

Photosynthesis—2 Steps
1) Light-Dependent Reaction
a) Requires light
b) Occurs in thylakoid membranes
c) Uses energy from light to produce ATP & NADPH:
• Light ATP + NADPH
d) O 2 is a by-product

2) Light-Independent Reaction (called Calvin Cycle)
a) Occurs in stroma
b) Does NOT require light
c) Uses ATP & NADPH (from light-dependent) to convert 6 (CO 2 )
molecules into 1 high-NRG sugar

Summary Of Photosynthesis

8.3 (p. 240) Factors Affecting Photosynthesis
1. H 2 0 shortage: may slow or stop photo (desert plant have
waxy leaf coating to slow loss)
2. Temperature: best range 0-35 0 C for photosynthetic enzymes
3. Light Intensity: high intensity best up to a point→plant will
reach max photo rate

Photosynthesis
Light-dependent
reactions
Uses
Takes place in
Includes
Takes place in
Light-independent
reactions
(Calvin Cycle)
H2O
Energy
from
Sunlight
ATP NADPH CO2
To produce
Thylakoid
membranes
Stroma
To produce
ATP
NADPH
O2
of the
ADP
+ P
NADP
High
Energy
Sugars
Chloroplast