Energy needs of life All life needs a constant input of energy –Heterotrophs (Consume) get their energy from “eating others” –eat food = other organisms = organic molecules make energy through respiration –Autotrophs (Producers) produce their own energy (from “self”) Photo-autotrophs convert energy of sunlight build organic molecules (CHO) from CO 2 make energy & synthesize sugars through photosynthesis

PHOTOSYNTHESIS The process that occurs in the chloroplasts of plant cells in which the sun’s energy is used to make simple sugars (food energy). These sugars are then converted to complex carbohydrates, starches, and stored.

Obtaining raw materials –sunlight leaves = solar collectors –CO 2 stomata = gas exchange –H2O–H2O uptake from roots –nutrients N, P, K, S, Mg, Fe… uptake from roots

The chloroplasts, where photosynthesis occurs, are found within the mesophyll cells in leaves. Two kinds of mesophyll cells in a typical leaf: Palisade- close together, most photosynthesis occurs Spongy- here the cells aren't so close.

Section 23.2 Summary – pages Carbon Dioxide moves in and Oxygen and water move out of a leaf through the stomata, which are located on the top and bottom of the leaf. LEAVES

Section 23.2 Summary – pages Guard cells are tiny cells that surround and control whether the stomata are open or shut. LEAVES The loss of water through the stomata is called transpiration.

Photosynthesis takes place inside the chloroplasts in the leaf of a plant.

There can be from 1 to 50 or more chloroplasts in a single mesophyll cell. The number varies with the plant species, age, and health of the cell.

The pigments (most commonly, chlorophyll) are in the membrane of the thylakoid discs. These are what absorb the sunlight. Photons (light particles) from sunlight hit the pigments, electrons are "knocked" loose, and off they go to energize the complicated process of photosynthesis.

Pigments are organized in the Thylakoid membrane in clusters known as Photosystems (Reaction centers)

Photosynthesis gets energy by absorbing wavelengths of light –chlorophyll a absorbs best in red & violet-blue wavelengths & reflects green –accessory pigments with different structures absorb light of different wavelengths chlorophyll b (absorbs blue and orange), Carotenoids (absorbs blue-violet and blue green) Phycobilins (absorbs blue) Why are plants green?

A Look at Light The spectrum of color ROYGBIV

Photosystems of photosynthesis 2 photosystems in thylakoid membrane –collections of chlorophyll molecules –act as light-gathering molecules –Photosystem II chlorophyll a P 680 = absorbs 680nm wavelength red light –Photosystem I chlorophyll b P 700 = absorbs 700nm wavelength red light reaction center antenna pigments

ETC of Photosynthesis Photosystem IIPhotosystem I chlorophyll a chlorophyll b

PHOTOSYNTHESIS LIGHT-DEPENDENT PHASE (Requires Sunlight) LIGHT-INDEPENDENT PHASE (Does Not Require Sunlight)

LIGHT-DEPENDENT REACTIONS ATP Production- FIRST PHASE The Light-DEPENDENT reactions convert water and energy from sunlight into chemical energy (ATP and NADPH)- which is used later (in light independent)to make food energy….

17 Light Dependent Reaction copyright cmassengale Reactants Products

Light energy is transferred into the electrons within the atoms of the pigment molecules, and the electrons become highly energized.

PS II (with chlorophyll a) absorbs light –excited electrons pass from chlorophyll to “primary electron acceptor”

20 Light Dependent Reaction copyright cmassengale

Once the energized electrons hit the primary electron accepter, they then go through an electron transport chain. Passing from one protein to the next, losing a little bit of energy along the way. (still pretty energized at the end)

The electron transport chain is a series of proteins embedded in the thylakoid membrane.

The energy that is lost goes and bonds a phosphate to ADP (Adenosine Di-phosphate), creating ATP. This process is called Photophosphorylation A little energy is lost at each protein.

Now, Photosystem I comes into play. The electron transport chain terminates with PS I (P 700 ). Here the electrons again become energized by sunlight, passing to yet another electron acceptor. (different from PS II)

STROMA (Fluid interior) From the second electron transport chain in the thylakoid memebrane, the electrons leave and go to the stroma, the fluid in the chloroplasts that surrounds the stacks of thylakoid (grana.

Electrons leave the electron transport chain and enter the stroma by attaching to an electron carrier molecule called NADP.

It is important to replace the lost electrons from the chlorophyll molecules because then the chlorophyll wouldn’t be able to absorb more light energy.

Section 9.2 Summary – pages To replace the lost electrons, molecules of water are split. This reaction is called photolysis.

18 ATP + 12 NADPH ATP

The second phase of photosynthesis is called the Calvin Cycle (Light-Independent phase) LIGHT-DEPENDENT PHASE (Requires Sunlight) LIGHT-INDEPENDENT PHASE (Does Not Require Sunlight) REMEMBER: This is when the chemical energy produced in the first phase is combined with Carbon Dioxide to create sugar.