photosynthesis - Shore Regional High School

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PHOTOSYNTHESIS

Energy and Life

Living things depend on Energy

We need energy to play soccer, go fishing and even sleep. On a cellular level, we also need energy for active transport, growth and repair, and reproduction of cells.

AUTOTROPHS & HETEROTROPHS

Autotrophs: organisms that are able to produce their own food

What are some examples?

Heterotrophs: organisms that are Not able to produce their own food

Most autotrophs use PHOTOSYSTHESIS to produce their own food

WHAT IS PHOTOSYNTHESIS

inputs

PHOTOSYSTHESIS- THE BIG PICTURE outputs inpu

ENERGY IN THE CELL

Energy comes in many forms

Biochemical energy is stored in

CARBS AND LIPIDS

Cells metabolize these compounds in a form it can use called ATP

ATP is the energy currency of the cell the only energy the cell recognizes

1 MOLECULE OF C

6

H

12

O

6

= 90x the chemical energy of ATP

ATP AND ADP

Adenosine---p-----p +energy from glucose+ p

ADP

Adenosine diphosphate

ADP adenosine + ribose sugar+2 phosphate groups

Adenosine----p----p------p

ATP

Lots of energy (originally from glucose is stored in this bond

Adenosine triphosphate

ATP adenosine+ ribose sugar +3 phosphate groups

Energy stored in ATP is released when ATP is converted to ADP and a phosphate group. When the bond is broken energy is released ATP is like a fully charged battery------ ADP like a battery not fully charged

SITE OF PHOTOSYNTHESIS

In addition to O

2 and H

2

O photosynthesis also requires a pigment

What is the PIGMENT found in chloroplasts that is responsible for trapping light energy? ANSWER chlorophyll

There are two types of chlorophyll a (light green) and b (dark green)

Plants also contain other light-absorbing pigments, such as xanthophylls, anthocyanins, and carotenoids (these are referred to as accessory pigments) we know that leaves contain these pigments because of the color of the leaves in the fall

These pigments do not absorb light well in the green region of the light spectrum which is why most plants are green

Co

2

+ water

SITE OF PHOTOSYNTHESIS

sun chloroplast energy

Sugar and oxygen

When chlorophyll absorbs light, the following occurs

Energy(light)is directly transferred to the electrons in the chlorophyll molecule

When transferred the energy level in the electron is raised (electrons get

excited)

Excited electrons have HIGH ENERGY and must have a special chemical carrier called “NADPH”

Electron chauffeur

STRUCTURE OF A CHLOROPLAST

Draw a chloroplast

Thylakoid

: bag-like photosynthetic membranes

Grana : stacked thylakoids

(grannum) single stack

Stroma : fluid inside the chloroplast but OUTSIDE the thylakoid membrane

PHOTOSYNTHESIS AS A BIOCHEMICAL PATHWAY

PHOTOSYNTHESIS IS A BIOCHEMICAL PATHWAY

Photosynthesis is broken down into 2 stages

1. Light dependent reactions

2 Light independent reactions (Calvin Cycle)

Light dependent reactions

Take place in the thylakoid membranes

Occurs only in light light independent reactions

Take place in the stroma

Occurs only in the absence of light

PHOTOSYNTHESIS AS A BIOCHEMICAL PATHWAY

H2O inputs

Light energy

LIGHT DEPENDENT REACTIONS

LIGHT DEPENDENT REACTIONS

TAKE PLACE WHERE? Chloroplast in the thykaloid

REQUIRE WHAT? Sunlight, and water H2O outputs

ATP

- NADPH

O2

LIGHT DEPENDENT REACTIONS PH II

Photosystem II (PH II) Inside the thykaloid

Discovered AFTER PH I, but in the photosynthetic process

Pigments absorb light

Energy from the light “excite” electrons, increasing their energy

Excited electrons passed through the electron transport chain

The electron is passed from one molecule to another as it decreases an energy level or step, the energy given off from the electron decreasing an energy level is used to form ATP

This is the ETC

LIGHT DEPENDENT REACTIONS- PH II

Photosystem II (PH II)

One major problem with PH II is that the electrons are lost

How does PH II replenish the electrons?

By splitting the H2O molecule

Into H+ H+ ions

These ions will then be pumped back into the thylakoid reenergized by light and be carried by NADPH back to the electron transfer chain

A by-product of this reaction is O

2 which is then released into the atmosphere by the plants for organisms to breathe

LIGHT DEPENDENT REACTIONS– PH I

Photosystem l (PH I)

High energy electrons move through the PH II to photosystem I

Energy from these electrons transports H+ ions from the stroma to the inner thylakoid

Pigments in PH I use energy from light to reenergize the electrons. These reenergized electrons are picked up by NADP+ to form NADPH (the high

energy chauffeur) REMEMBER?

So what is NADPH’s role in photosynthesis?

IT IS THE HIGH ENERGY ELECTRON CARRIER

LIGHT DEPENDENT REACTIONS– PH I

Hydrogen ion movement

As a result of the H+ ions released during the splitting of H2O and electron transport, the inside of the thylakoid membrane becomes (+) changed while the outside is (-) charged

This difference in charges provides the energy to make ATP

ATP synthase:

LIGHT INDEPENDENT REACTIONS

Light independent reactions

Take place where?

--

Require what?

Also called the Calvin Cycle of “Dark Reactions” inputs outputs

Products of light dependent rxn’s

--

LIGHT INDEPENDENT REACTIONS

Calvin cycle

6 CO

2 molecules enter the cycle from the atmosphere

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