Photosynthesis. By the end of this lecture you will be able to: 1.Understand that ENERGY can be transformed from one form to another. 2.Know that energy.

photosynthesis

By the end of this lecture you will be able to:

1. Understand that ENERGY can be transformed from one form to another.2. Know that energy exist in two forms; free energy - available for doing work

or as heat - a form unavailable for doing work.3. Appreciate that the Sun provides most of the energy needed for life on

Earth.4. Explain why photosynthesis is so important to energy and material flow for

life on earth.5. Know why plants tend to be green in appearance.6. Equate the organelle of photosynthesis in eukaryotes with the chloroplast. 7. Describe the organization of the chloroplast.8. Understand that photosynthesis is a two fold process composed of the

light-dependent reactions (i.e., light reactions) and the light independent reactions (i.e. Calvin Cycle or Dark Reactions).

9. Tell where the light reactions and the CO2 fixation reactions occur in the chloroplast.

10. Define chlorophylls giving their basic composition and structure.11. Draw the absorption spectrum of chlorophyll and compare it to the action

spectrum of photosynthesis.12. Define the Reaction Centers and Antennae and describe how it operates.13. Describe cyclic photophosphorylation of photosynthesis.14. Describe noncyclic photophosphorylation of photosynthesis.

LEARNING OBJECTIVES

What is Photosynthesis?

The process of photosynthesis is a chemical reaction.

It is the most important chemical reaction on our planet.

Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water

A process in which light energy is stored in the bonds of glucose for later use

AN OVERVIEW OF PHOTOSYNTHESIS

Carbondioxide

Water Glucose Oxygengas

PHOTOSYNTHESIS

Terminology

Autotrophs - Can make their own food (“Self-feeders”)

Heterotrophs – Can not make their own food

Light-dependent Photosynthesis - Requires light for photosynthetic process to complete

Light-independent Photosynthesis – Does NOT require light for photosynthetic process to complete

• Almost all plants are photosynthetic autotrophs, some bacteria and protists– Autotrophs generate their own organic matter through

photosynthesis– Sunlight energy is transformed to energy stored in the

form of chemical bonds

(a) Mosses, ferns, andflowering plants

(b) Kelp

(c) Euglena (d) Cyanobacteria

THE BASICS OF PHOTOSYNTHESIS

Light Energy Harvested by Plants & Other Photosynthetic Autotrophs

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2

What is the equation for the chemical reaction of photosynthesis?

Six molecules of carbon dioxide react with six molecules of water to form 1 molecule of

glucose and six molecules of oxygen.

Describe PhotosynthesisThe process of changing light energy to

chemical energy Energy stored as sugarOccurs in plants and some algae Plants need light energy, CO2, and H2O Takes place in the chloroplasts, using

chlorophyll, the green pigment in plants

What happens during photosynthesis?Plants capture light energy and use that

energy to make glucose

Sunlight provides the energy needed by chlorophyll to change molecules of carbon dioxide and water into glucose

Oxygen is also released in this reaction

What happens during photosynthesis?Carbon dioxide enters the leaf through

holes called stomata CO2 combines with the stored energy in

the chloroplasts through a chemical reaction to make glucose

The sugar is moved through tubes in the leaf to the roots, stems and fruits of the plants

Some of the sugar is used right away by the plant for energy; some are stored as starch; and some are built into plant tissue

Why is this important to us?

We cannot make our own food (glucose, energy), we must get our food from plants.

Plants are the first step in the food chain. The oxygen released during photosynthesis is

necessary for all living things.

WHY ARE PLANTS GREEN? WHY ARE PLANTS GREEN?

Plant Cells have Green Chloroplasts

The thylakoid membrane of the chloroplast is impregnated with photosynthetic pigments (i.e., chlorophylls, carotenoids).

Chloroplasts absorb light energy and convert it to chemical energy

LightReflected

light

Absorbedlight

Transmittedlight

Chloroplast

THE COLOR OF LIGHT SEEN IS THE COLOR NOT ABSORBED

• The Calvin cycle makes sugar from carbon dioxide– ATP generated by the light

reactions provides the energy for sugar synthesis

– The NADPH produced by the light reactions provides the electrons for the reduction of carbon dioxide to glucose

LightChloroplast

Lightreactions

Calvincycle

NADP

ADP+ P

The light reactions convert solar energy to chemical energyProduce ATP & NADPH

AN OVERVIEW OF PHOTOSYNTHESIS

Chloroplasts: Sites of Photosynthesis

• Photosynthesis– Occurs in chloroplasts, organelles in certain

plants– All green plant parts have chloroplasts and carry

out photosynthesis• The leaves have the most chloroplasts• The green color comes from chlorophyll in the

chloroplasts• The pigments absorb light energy

Photosynthesis occurs in chloroplasts

In most plants, photosynthesis occurs primarily in the leaves, in the chloroplasts

A chloroplast contains: stroma, a fluid grana, stacks of thylakoids

The thylakoids contain chlorophyllChlorophyll is the green pigment that captures

light for photosynthesis

The location and structure of chloroplasts

LEAF CROSS SECTION MESOPHYLL CELL

LEAF

Chloroplast

Mesophyll

CHLOROPLAST Intermembrane space

Outermembrane

Innermembrane

ThylakoidcompartmentThylakoidStroma

Granum

StromaGrana

Chloroplast PigmentsChloroplasts contain several pigments

– Chlorophyll a – Chlorophyll b – Carotenoids

Figure 7.7

Plants produce OPlants produce O22 gas by splitting H gas by splitting H22OO

The O2 liberated by photosynthesis is made from the oxygen in water (H+ and e-)

Review: Photosynthesis uses light energy to make food molecules

A summary of the chemical processes of photosynthesis

Light

Chloroplast

Photosystem IIElectron transport

chains Photosystem I

CALVIN CYCLE Stroma

Electrons

LIGHT REACTIONS CALVIN CYCLE

Cellular respiration

Cellulose

Starch

Other organic compounds

What is Cellular Respiration? The release of chemical energy for use by cells. Once the energy that was in sunlight is changed

into chemical energy by photosynthesis, an organism has to transform the chemical energy into a form that can be used by the organism.

This process is called cellular respiration.

The breakdown of glucose molecules to release energy

Takes place in all living things

Is a step by step process

What is the chemical equation for cellular respiration?

It's not that It's not that easy bein' easy bein' green… but it green… but it is essential for is essential for life on earth!life on earth!