PhotosynthesisChapter 8 (pages 200-219)

Where energy comes from•Plants and some other types of organisms

use light energy from the to produce food

▫Autotrophs: organisms that make their own food Use the sun’s energy to help make their

food▫Heterotrophs: organisms that do not

make their own food Where does their energy come from?

ATP•Adenosine Triphosphate

▫Definition: One of the principal chemical compounds that cells use to store and release energy

▫Composed of: 5-carbon sugar (ribose) Adenine Three phosphate groups

adenine

ribose 3 phosphate groups

ADP•Adenosine Diphosphate

▫Looks almost like ATP, but only two phosphate groups

▫When a cell has energy available to store, tacks on that extra phosphate group to ADP ATP

Storing vs. Releasing Energy •To store energy add on a phosphate

group

•To release energy remove a phosphate group

Using ATP• Active transport• Cell movement

• Responding the chemical signals• Protein synthesis

• Nucleic Acid synthesis

ATP is not good for storing energy glucose contains 90x the chemical energy that one ATP molecule has. Regenerate ATP from ADP by using energy in foods like glucose

The Scientists of Photosynthesis•Van Helmont: found plants gain mass

from water•Priestley: plants release oxygen•Ingenhousz: plants produce oxygen in

sunlight, not in dark•Mayer: proposed plants convert light into

chemical energy•Calvin: traced chemical path that carbon

follows to form glucose (Calvin Cycle) we will get to this later

Photosynthesis •Photosynthesis

the use of energy from sunlight to convert water and carbon dioxide into high-energy carbohydrates – sugar and starches – and oxygen as a waste product

Light and Pigments•In addition to H2O and CO2, light and

chlorophyll needed▫Where’s chlorophyll found? In chloroplasts!

•Plants gather sun’s energy with light-absorbing molecules called pigments▫Principal pigment in plants chlorophyll▫Two types: chlorophyll a and chlorophyll

b Absorb light in blue and red region of

visible light spectrum When light is absorbed, energy levels of

electrons rise

Inside a Chloroplast

Thylakoid

Stroma

Granum

Sac-like structure; Contains the

photosynthetic pigments, reaction

centers for LDR, and the electron transport

chain

Stack of thylakoids

The inner fluid of the chloroplast between the

grana which contains various enzymes and

where the Calvin Cycle occurs

Electron Carriers•Sunlight excites electrons – hold energy

▫Would you want to transport the electron yourself or have something else transport it?

•Carrier needed to transport excited electron▫Carrier known as = electron transport

chain▫Actual Transporter = NADP+

Holds 2 high energy electrons Holds H+NADP

+e-

e-

- H+

Light Dependent Reactions

Pigments absorb light in photosystem II electrons excited passed to ETC thylakoid membrane replaces electrons with H2O H+, O, electrons

Excited electrons move through ETC to photosystem I energy fuels ETC to move H+ from stroma to inner thylakoid space

Pigments in photosystem I use light energy to reenergize electrons NADP+ picks up electrons and H+ NADPH

When electrons are passed from chlorophyll to NADP+, more H+ ions are pumped across the membrane difference in charges provides energy to make ATP

ATP synthase allows H+ ions to pass through ATP synthase rotates As it rotates, grabs ADP and bonds it to Phosphate group ATP!

Calvin Cycle•Also known as the light independent

reactions (or dark reactions)▫No light required for them to start

•Occur in the stroma of the chloroplast•Use products of LDR as their reactants

NADPH, ATP•Give the products NADP+, ADP, high

energy sugars•Multiple steps!

Calvin Cycle•Multiple steps take CO2 and convert into

multi-carbon containing molecules ▫Step 1: 6 CO2 and 6, 5-Carbon Molecules

12, 3-Carbon Molecules▫Step 2:

ATP ADP (energy storage for LDR) NADPH NADP+ (electron carrier for LDR)

▫Step 2: 12, 3-Carbon Molecules 2 fall off to make sugar (remember 6 carbons are in a monosaccharide)

▫Step 3: 10 3-Carbon Molecules 6, 5-Carbon Molecules ATP ADP

Calvin Cycle

GLUCOSE

Quick reviewLDR LIR

Reactants ADP, NADP+, H2O

ATP, NADPH, CO2

Products OXYGEN GLUCOSE

Location Thylakoid Membrane Stroma

Factors that alter photosynthesis•Water availability

▫Which scientist figured this out? Van Helmont!

•Intensity of light▫Which scientists figured this out?

Ingenhousz!•Temperature

▫What temperature do enzymes function best? 98.6 degrees