BIOLOGY
CONCEPTS & CONNECTIONS
Fourth Edition
Neil A. Campbell • Jane B. Reece • Lawrence G. Mitchell • Martha R. Taylor
CHAPTER 7
Photosynthesis:
Using Light to Make Food
Modules 7.1 – 7.5
From PowerPoint® Lectures for Biology: Concepts & Connections
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Life in the Sun
• Light is central to the life of a plant
• Photosynthesis is the most important chemical
process on Earth
– It provides food for
virtually all organisms
• Plant cells convert light
into chemical signals
that affect a plant’s
life cycle
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• Light can influence the architecture of a plant
– Plants that get adequate light are often bushy,
with deep green leaves
– Without enough light, plants
become tall and spindly with
small pale leaves
• Too much sunlight can
damage a plant
– Chloroplasts and carotenoids
help to prevent such damage
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AN OVERVIEW OF PHOTOSYNTHESIS
• Photosynthesis is the process by which
autotrophic organisms use light energy to make
sugar and oxygen gas from carbon dioxide and
water
Carbon
dioxide
Water
Glucose
PHOTOSYNTHESIS
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Oxygen
gas
7.1 Autotrophs are the producers of the biosphere
• Plants, some protists, and some bacteria are
photosynthetic autotrophs
– They are the ultimate producers of food
consumed by virtually all organisms
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• On land, plants such as oak trees and cacti are
the predominant producers
Figure 7.1A
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Figure 7.1B
• In aquatic environments, algae and
photosynthetic bacteria are the main food
producers
Figure 7.1C
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Figure 7.1D
7.2 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 chlorophyll
– Chlorophyll is the green pigment that captures
light for photosynthesis
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• The location and structure of chloroplasts
Chloroplast
LEAF CROSS SECTION
MESOPHYLL CELL
LEAF
Mesophyll
CHLOROPLAST
Intermembrane space
Outer
membrane
Granum
Grana
Stroma
Figure 7.2
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Inner
membrane
Stroma
Thylakoid
Thylakoid
compartment
7.3 Plants produce O2 gas by splitting water
• The O2 liberated by photosynthesis is made
from the oxygen in water
Figure 7.3A
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Experiment 1
Not
labeled
Experiment 2
Labeled
Figure 7.3B
Reactants:
Products:
Figure 7.3C
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7.4 Photosynthesis is a redox process, as is cellular
respiration
• Water molecules are split apart and electrons
and H+ ions are removed, leaving O2 gas
– These electrons and H+ ions are transferred to
CO2, producing sugar
Reduction
Oxidation
Figure 7.4A
Oxidation
Figure 7.4B
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Reduction
7.5 Overview: Photosynthesis occurs in two stages
linked by ATP and NADPH
• The complete process of photosynthesis
consists of two linked sets of reactions:
– the light reactions and the Calvin cycle
• The light reactions convert light energy to
chemical energy and produce O2
• The Calvin cycle assembles sugar molecules
from CO2 using the energy-carrying products of
the light reactions
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• An overview of photosynthesis
H2O
CO2
Chloroplast
Light
NADP+
ADP
+ P
LIGHT
REACTIONS
(in grana)
CALVIN
CYCLE
(in stroma)
ATP
NADPH
O2
Figure 7.5
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Sugar