Picture Guide to Chapter 8

Photosynthesis

8-1 Energy and Life

Objectives• Explain where plants get the

energy they need to produce food

• Describe the role of ATP in cellular activities

Q: Where does energy come from?

A: Our food, but originally the energy in food comes from the sun

Autotrophs• Make their own food

Heterotrophs• Cannot make their own food

Chemical Energy and ATP

• The principal chemical compounds that cells use to store and release energy is called ATP adenosine triphosphate

Storing Energy• ATP stores energy in the third

phosphate

• ATP is like a fully charged battery

Releasing EnergyQ: How is the energy in ATP released?

A: Break bond between the second and 3rd phosphates

ADP

2

ATP Formation - Using Biomechanical Energy

• Active Transport

• Movement of organelles throughout cell

• Synthesis of proteins and nucleic acids

• Produce light– Blink of firefly caused by an enzyme

powered by ATP

ATP Availability

• Most cells only have enough ATP for a few seconds of activity

• Why?– Not good at storing energy over the long term– Glucose stores 90 times the chemical energy

of ATP– Cells generate ATP from ADP as needed by

using the energy in foods like glucose

Photosynthesis• The process in which plants use

the energy of sunlight to convert water and carbon dioxide into high energy carbohydrates – sugars and starches – and oxygen as a waste product

Photosynthesis

The Photosynthesis Equation

CO2 + H2O +C6H12O6 O2light

(Carbon Dioxide) (Water) (Sun) (Glucose) (Oxygen)

Chlorophyll• The plants principal pigment,

absorbs light energy in the blue-violet and red spectrum of visible light

Absorption of Light byChlorophyll a and Chlorophyll bAbsorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

Because light is a form of energy…

• Anything that absorbs light also absorbs the energy from that light

• When chlorophyll absorbs light, much of the energy is transferred to electrons in the chlorophyll molecule, raising the energy level of these electrons

• These high-energy electrons make photosynthesis work

8-3 The Reactions of Photosynthesis

Thylakoids• Sac-like photosynthetic

membranes arranged in stacks

Grana• Stacks of thylakoids

Stroma• The region outside the thylakoid

Scientists describe the reactions of photosynthesis in two parts

1. Light – dependent reactions (takes place in the thylakoid membranes)

2. Light – independent reactions (takes place in stroma)

Carrier Molecule• Compound that can accept a pair

of high energy electrons and transfer them along with most of their energy to another molecule

• Ex.) NADP+

Q: What does this do?• NADP+ NADPH

A: this traps sunlight in chemical form

Light Dependent Reactions

• Uses energy from light to produce

1. Oxygen gas

2. ATP

3. NADPH

Fig. 8-10

The Calvin Cycle• The ATP and NADPH formed by the light-

dependent reactions contain an abundance of chemical energy, but they are not stable enough to store that energy for more than a few minutes.

• The Calvin cycle uses ATP and NADPH from light – dependent reactions to produce high energy sugars

The Calvin Cycle• These reactions don’t require

light, therefore these reactions are called

• Light – independent reactions

Fig 8.11

Factors Affecting Photosynthesis

• Not enough water

• Temperature

• Light intensity