PhotosynthesiPhotosynthesis!s!

Obtaining NRG Autotrophs

Use NRG from the sun to make organic compounds

Heterotrophs Must get NRG from food instead of directly

from sunlight

ATP=NRG! ATP= adenosine triphosphate

ATP is the molecule that DIRECTLY provides NRG to do cellular work

Chemical NRG from organic molecules is transferred to ATP

ATP ATP is made up of five parts:

The sugar= ribose

The base= adenine

3 phosphate groups

ATP cont. When ATP loses the 3rd phosphate:

NRG is released

This NRG is used by the cell

ADP is left

NRG Conversion

Obtaining NRG PHOTOSYNTHESIS

Converts light NRG from sun into chemical NRG

Series of reactions known as biochemical pathways

Photosyn. Overview The oxygen (O2) and some organic

compounds produced by photosynthesis are used by cells in process called cellular respiration.

Chloroplasts Chloroplasts have double membranes

Outer Membrane Separates chloroplast from

cytoplasm

Thylakoids Inner membranes

Numerous

Grana Stacks of thylakoids

Stroma Fluid-like space

Overview cont. Photosynthesis can be divided into two

stages: LIGHT REACTIONS

Light NRG is converted to chemical NRG

Temporarily stored in ATP and the NRG carrier molecule NADPH (nicotinamide adenine dinucleotide phosphate-oxidase)

CALVIN CYCLE

Organic compounds are formed using CO2 and the chemical NRG stored in ATP and NADPH

Photosynthesis Equation

Capturing Light NRG The light reactions begin with the absorption

of light in chloroplasts Found in cells of plants, some bacteria, and

algae

Capturing Light NRG Light and Pigments

White light from the sun is composed of an array of colors called the visible spectrum

Pigments:

Absorb certain colors of light and reflect or transmit the other colors

Capturing Light NRG Chloroplast Pigments:

Located in the membrane of the thylakoids are several pigments:

1. Chlorophylls: chlorophyll a and chlorophyll b

2. Carotenoids: yellow, orange, and brownish

Light NRG to Chemical NRG

PHOTOSYSTEM: Grouped clusters of a few hundred pigment

molecules in the thylakoid membrane

By absorbing light, pigment molecules in the photosystems (I and II) acquire some of the NRG carried by the light

Steps 1 and 2 In each photosystem, the acquired NRG is

passed quickly to other pigment molecules until it reaches a specific pair of chlorophyll a molecules.

The acquired NRG forces electrons to enter a higher NRG level in the two chlorophyll a molecules of photosystem II

These excited electrons now have NRG to leave the chlorophyll a.

Step 3 The acceptor of these electrons from

photosystem II is called the primary electron receptor, which donates the electrons to the electron transport chain.

Electrons move from molecule to molecule, losing most of the acquired NRG!

The NRG they lose is used to move H+ into the thylakoid

Light Rxn

Step 4 Light is absorbed by photosystem II at the

same time it is absorbed by photosystem I.

Electrons move from chlorophyll a to another primary electron receptor.

Electrons lost from chlorophyll a are replaced by electrons that have passed through the electron transport chain from photosystem II.

Step 5 Electrons are then donated to another chain,

which brings the electrons to the side of the thylakoid membrane that faces the stroma.

In the stroma, the electrons combine with a proton and NADP+. This causes the NADP+ to be reduced to NADPH.

Electron Replacement

Electrons from photosystem II replace electrons that leave photosystem I.

Replacement electrons are provided by the splitting of water molecules

For every two water molecules that are split, four electrons become available

Products? Oxygen produced when water molecules are

split diffuses out of the chloroplast and leaves the plant!

Light to Chemical NRG

Making ATP in Light Reactions: Light reactions produce ATP through

chemiosmosis!

During chemiosmosis, the movement of protons through ATP synthase into the stroma releases NRG, then used to produce ATP.

Carbon Fixation CALVIN CYCLE

The ATP and NADPH produced in the light reactions drive this stage

CARBON FIXATION

CO2 is incorporated into organic compounds, a process called carbon fixation

Carbon Fixation CALVIN CYCLE

Occurs in the stroma

Assisted by enzymes to produce three carbon sugars

Most three carbon sugars (PGAL) generated in the Calvin Cycle are converted to five carbon sugars (RUBP).

Some of the three carbon sugars leave the cycle and are used to make organic compounds that are stored as NRG for later

Calvin Cycle

Factors Affecting Photosynthesis

Light Intensity Rate increases as light intensity increases

More electrons get excited in both photosystems!

Once all electrons are excited, the rate levels off.

Factors Affecting Photosynthesis

Carbon Dioxide Levels

Increasing levels of CO2 also stimulate photosynthesis until the rate levels off.

Factors Affecting Photosynthesis

Temperature As temperature increases, photosynthesis

increases to a maximum and then decreases with further increases in temperature.

Too high of a temperature will denature key enzymes!