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 3rd P group

2. Releasing Energy

• ATP (w/3 P groups)

a) Cells easily break (NRG releasing) and reform (NRG

storing) 3rd 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 1st; 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 (CO2) + 6 (H2O) C6H12O6 + 6 (O2)

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) O2 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 (CO2)

molecules into 1 high-NRG sugar

Summary Of Photosynthesis

8.3 (p. 240) Factors Affecting Photosynthesis

1. H20 shortage: may slow or stop photo (desert plant have

waxy leaf coating to slow loss)

2. Temperature: best range 0-35 0C for photosynthetic enzymes

3. Light Intensity: high intensity best up to a point→plant will

reach max photo rate

Light-dependent reactions

Photosynthesis

Light-independent reactions

(Calvin Cycle)

H2O

Stroma

ATP NADPH CO2

Thylakoid membranes

Energy from

Sunlight

Chloroplast

ATP O2 NADPH

NADP High

Energy Sugars

ADP + P

Includes

Uses

To produce

To produce

Takes place in Takes place in

of the

Uses