Chapter 8 Photosynthesis

THE BASICS OF PHOTOSYNTHESIS

• Photosynthesis

– is used by plants, algae (protists), and some bacteria

– uses the energyfrom sunlight to convert water and carbon dioxide into high-energy carbohydrates(glucose and starch)

– oxygen is a waste product!!!

The Simplified Equation for Photosynthesis

6 O2

6 H2O C6H12O6 6 O2

A Photosynthesis Road Map

• The initial incorporation of carbon from the atmosphere into organic compounds is called carbon fixation.

– This lowers the concentration of carbon dioxide in the atmosphere.

– Deforestation reduces the ability of the biosphere to absorb carbon by reducing the amount of photosynthetic plant life.

Chloroplasts: Sites of Photosynthesis

• Chloroplasts are

– the site of photosynthesis

– found mostly in the interior cells of leaves.

• Inside chloroplasts are interconnected, membranous sacs called thylakoids, which are suspended in a thick fluid called stroma.

• Thylakoids are concentrated in stacks called grana.

• Stomata are tiny pores in leaves where carbon dioxide enters and oxygen exits.

Light and Pigments

How do plants capture the energy from sunlight?

• They use light absorbing molecules called pigments found in chloroplasts.

• the main pigment of plants is chlorophyll, and it is found in the thylakoid membrane of a chloroplast.

• when these pigments absorb light they also absorb the light’s energy which raises the energy level of the electrons in the chlorophyll molecules

• these high energy electrons then go on to “power” photosynthesis.

A Photosynthesis Road Map

• Photosynthesis occurs in two multistep stages:

1. the light reactionsconvert solar energy to chemical energy

2. the Calvin cycle uses the products of the light reactions to make sugar from carbon dioxide.

A Photosynthesis Road Map

Light Reactions

Chlorophyll absorbs solar energy and is

then converted to ATP from ADP and NADPH

from NADP+ and gives off O2 gas as a

by-product.

WAIT!!!! BUT, WHAT IS NADP+ and NADPH??????

NADP+ (Light Reactions)

• NADP+ (nicotinamide adenine dinucleotide phosphate) is an electron carrier molecule.

• When sunlight excites electrons in the chlorophyll, the electrons gain a lot of energy!!!

• These electrons then require a special electron carrier molecule which is NADP+.

– Think of theses electrons as hot coals from a campfire, you wouldn’t pick them up with your hands to move them from one place to the next, instead you would use a pan, or a carrier to transport them.

NADP+ (Light Reactions)

• This electron carrier molecule accepts a pair (2) high energy electrons and transfers them along with most of their energy to another molecule.

• This process is called electron transport.

• NADP+ is a carrier molecule that can carry 2 high energy electrons plus a hydrogen ion (H+) to form NADPH!!!

NADP+ 2e- + H+ NADPH

Figure 7.3-1

Light

H2O

O2

Chloroplast

Lightreactions

NADPH

ATP

– –

The Calvin Cycle

Welcome to the Dark Side……

A Photosynthesis Road Map

Calvin Cycle

• Uses the products of the light reactions (ATP and NADPH) to power the production of sugar from CO2.

• Enzymes that drive the CC are in the stroma.

• DOES NOT REQUIRE LIGHT directly!!!

Figure 7.3-2

Calvincycle

CO2

NADP+

ADPP

Sugar

Light

H2O

O2

Chloroplast

Lightreactions

NADPH

ATP

– –

3 Factors That Affect the Rate of Photosynthesis

• Water Supply

• Shortage of water can slow or stop photosynthesis

• Temperature

• Photosynthesis depends on enzymes that function best between 0°C and 35°C

• Light Intensity

• Increasing light intensity increases the rate at which photosynthesis occurs, to a point.

Post Lecture Questions!

In plants, photosynthesis takes place inside the

a) thylakoids.

b) chloroplasts.

c) photosystems.

d) chlorophyll.

Post Lecture Questions!

NADPH is produced in light-dependent reactions and carries energy in the form of

a) ATP

b) high-energy electrons

c) low-energy electrons

d) ADP

Post Lecture Questions!

What is another name for the Calvin cycle?

a) light-dependent reactions

b) light-independent reactions

c) electron transport chain

d) photosynthesis

Post Lecture Questions!

Which of the following factors does NOT directly affect photosynthesis?

a) wind

b) water supply

c) temperature

d) light intensity