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PHOTOSYNTHESIS - PowerPoint PPT Presentation

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PHOTOSYNTHESIS. A utotroph (Producers) Make their own food Photosynthesis Chemosynthesis - Plants - Some bacteria & protists. Heterotroph (Consumers) Energy obtained by eating. Photosynthesis. 6H 2 0 + 6CO 2  C 6 H 12 O 6 + 6O 2. How can plants do it?.

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Make their own food



- Plants

- Some bacteria & protists



Energy obtained by eating


6H20 + 6CO2 C6H12O6 + 6O2

How can plants do it
How can plants do it?

  • Plants contain the green pigment chlorophyll, which takes in sunlight and captures it’s energy, in the chloroplasts.

    • There are two main types of chlorophyll, “chlorophyll a” and “chlorophyll b”

  • When chlorophyll absorbs light, energy is transferred to electrons in the chlorophyll molecule, raising their energy level.

  • These high-energy electrons make photosynthesis work.

Interpreting diagrams

Which wavelengths/ color(s) are absorbed best?

Which wavelengths/ color(s) are reflected?

What is the relationship between reflection of light and the perception of color?

Interpreting Diagrams

Not all plants have green leaves

They still have chlorophyll!!

It is just hidden by other pigments.

Not all plants have green leaves…

Why do leaves change colors
Why do leaves change colors?

  • Chlorophyll breaks down in cold weather as the strength of the sun’s rays weakens.

  • The other colors, that were always there, show through.

How do we know


Method of separating pigments

The solvent moves past the spot that was applied

The pigments will differ in solubility and in the strength of their adsorption to the adsorbent

Some will be carried farther up the plate than others.

How do we know?

Process overview
Process Overview

Two steps:

  • Light Dependent (Light Reactions)

    -> thylakoid

  • Light Independent (Calvin Cycle)

    -> stroma

A closer look
A closer look…….






Light- dependent reactions

Calvin cycle



Light dependent reactions

Light is absorbed by chlorophyll in clusters called photosystems

A flow of e- starts

This provides energy to make ATP & NADPH

Water is split to replace e- and allow the flow to continue & O2 is released

ATP & NADPH go to the stroma to fuel the Calvin Cycle

Light-Dependent Reactions

NADPH photosystems

  • When water is split to replace e- in PS-II, H+ are left over

  • As free e- reach PS-I, two are picked up by NADP+, resulting in NADP-

  • This negative charge attracts H+ ions resulting in NADPH

    NADP+ + 2e- NADP-

    NADP- + H+  NADPH

  • NADPH carries electrons (energy source) as well as hydrogen (to build sugars) to the stroma for the Calvin Cycle.

Chemiosmosis photosystems

  • Mechanism that generates ATP

  • Uses potential energy of an H+ concentration gradient

  • H+ flow across the thylakoid membrane into the stroma through an enzyme membrane protein called ATP synthase

  • This drives the (photo) phosphorylation of ATP

Self assessment l d reactions
Self-Assessment – L.D. Reactions photosystems

  • Where in the chloroplast do the light dependent reactions take place?

  • What happens when a molecule of chlorophyll absorbs light?

  • How is water used during the light dependent reactions? (2 uses) What is the bi-product of using water?

  • What two things does NADPH supply for the Calvin Cycle?

  • What is chemiosmosis? What enzyme is involved in this process? What supplies the energy for this process?

Calvin cycle

1. CO2 enters the stroma photosystems

2. It combines with a

5-C sugar RuBP using the enzyme Rubisco to form a 3-C acid (carbon fixation)

Using energy from ATP & NADPH high energy sugars (G3P) are made for the plant

4. ADP & NADP+ go back to the thylakoid to be “recharged”

Calvin Cycle

In order for the “cycle” to continue, RuBP must be regenerated. 3 “turns” of the Calvin Cycle are needed to generate one G3P molecule. In other words, 3 CO2 molecules are used to make 1 G3P and remake RuBP.

Self assessment calvin cycle
Self-Assessment – Calvin Cycle photosystems

  • What is “waiting” in the stroma to combine with CO2? What enzyme catalyzes this combination?

  • What is the direct result of this combination?

  • What is the general name to describe this conversion of inorganic CO2 into a molecule plants can use for biosynthesis?

  • Why is the Calvin Cycle called a “cycle”? How many “turns” are needed to provide the plants with a molecule of sugar?

Process recap
Process Recap photosystems

The two sets of photosynthetic reactions work together.

  • The light-dependent reactions trap sunlight energy in chemical form (ATP and NADPH).

  • The light-independent reactions use that chemical energy to produce stable, high-energy sugars.

Global impact of photosynthesis
Global Impact of Photosynthesis photosystems

  • Carbon cycle

  • Greenhouse effect

    • Greenhouses gases in atm. prevent some heat from the sun from escaping

    • CO2, methane, H2O vapor are the main GH gases

  • Global warming

    • Excessive levels of GH gases result in more heat being trapped

    • This is not the same thing as ozone depletion

Food energy
Food & Energy photosystems

Food serves as a source of raw materials, or building blocks, for the cells in the body and also as a source of energy.

Animal Cells




Plant Cells

Chemical energy food
Chemical Energy & Food photosystems

  • Cells don't “burn” glucose. Instead, they gradually release the energy from glucose and other food compounds.

  • Cellular (aerboic)respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen.

  • This process occurs in the mitochondria.

Cellular respiration
Cellular Respiration photosystems

Oxygen + Glucose  Carbon Dioxide + Water + ATP

(6O2 + C6H12O6 6CO2 + 6H2O + ATP)

  • Cellular respiration is an aerobic process because it requires oxygen (aerobic respiration)

  • There are three steps in cellular respiration

    • Glycolysis

    • Krebs Cycle (a.k.a. “Citric Acid Cycle”)

    • Electron Transport Chain (ETC)

  • In the absence of oxygen, glycolysis is followed by fermentation. This is called anaerobic respiration.

Overview of cellular respiration
Overview of Cellular Respiration photosystems



Glycolysis photosystems

  • Occurs in the cytoplasm

  • One molecule of glucose (6-C) is split, producing two molecules of pyruvic acid (3-C)

  • The cell uses two molecules of ATP to start the process and when glycolysis is complete 4 gross or 2 net ATP and 2 NADH are produced.





Fermentation photosystems

  • Alcoholic Fermentation:

    • Performed by yeasts and a few other microorganisms

    • pyruvic acid + NADH → alcohol + CO2 + NAD+

  • Lactic Acid Fermentation:

    - in cells, such as muscle cells, the pyruvic acid from

    glycolysis is converted to lactic acid

    - pyruvic acid + NADH → lactic acid + NAD+

    **Fermentation regenerates NAD+ so that glycolysis can continue

Kreb s cycle e t c
Kreb’s Cycle & E.T.C. photosystems

  • In the presence of oxygen, pyruvic acid enters the Kreb cycle where it is further broken down, releasing carbon dioxide.

  • ATP is generated in a series of complex reactions that involves high energy electrons moving through the electron transport chain.

  • Oxygen serves as the final electron acceptor, allowing energy to be released to cells

Kreb s cycle
Kreb’s Cycle photosystems

  • Entering the mitochondria, the pyruvic acids from glycolysis are converted to 2-C acetyl CoA molecules by losing a molecule of CO2

  • The acetyl CoA molecules enter the Krebs cycle in the matrix and join a 4-C acceptor molecule to form citric acid.

  • This molecule is then broken down in a series of reactions releasing CO2and producing the energy molecules ATP, NADH and FADH2

E t c
E.T.C. photosystems

  • Electron carriers NADH and FADH2 drop off electrons and release H+ ions along the inner cristae membrane.

  • The energy from the electron flow pumps (against gradient) the H+ ions across the cristae into the inter-membrane space.

  • The ions that diffuse back across the cristae through ATP synthase providing energy to bind ADP + P to make ATP.

Energy totals
Energy Totals photosystems

  • Glycolysis produces just 2 net ATP molecules per molecule of glucose.

  • Krebs Cycle & the ETC produce up to 36 additional ATP. Two (per glucose) from Krebs & up to 34 from the ETC.

  • The complete breakdown of glucose through cellular respiration, including glycolysis, results in the production of 38 molecules of ATP (net).

Photosynthesis v cellular respiration
Photosynthesis v. Cellular Respiration photosystems

  • Photosynthesis:

  • Respiration:

  • Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back.

  • Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food