PHOTOSYNTHEIS
 Converting light energy into chemical
energy stored in organic molecules
carbon
sun
+ water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + sun  C6H12O6 + 6O2
energy
Regents Biology
Energy Needs of Life
 Nutrition

The process by which organisms get food
and break it down so it can be used for
metabolism
 Nutrients

Substances that provide the energy and
material needed for metabolic activity
 Organic: Proteins, carbohydrates, fats, vitamins
 Inorganic: minerals & water
Regents Biology
Energy Needs of Life
 All life needs a constant input of energy

Heterotrophs (Animals)
 get their energy from “eating others”
consumers
 eat food = other organisms = organic molecules
 make energy through respiration

Autotrophs (Plants)
 produce their own energy (from “self”)
producers
 convert energy of sunlight
CO2
 build organic molecules from H2O
 Photosynthesis: solar energy into chemical
energy
Regents Biology
 Photosynthesis

Occurs in plants, algae, certain other
protists, and some prokaryotes
These organisms use light energy to drive the
synthesis of organic molecules from carbon dioxide
and (in most cases) water. They feed not only
themselves, but the entire living world. (a) On
land, plants are the predominant producers of
food. In aquatic environments, photosynthetic
organisms include (b) multicellular algae, such
as this kelp; (c) some unicellular protists, such
as Euglena; (d) the prokaryotes called
cyanobacteria; and (e) other photosynthetic
prokaryotes, such as these purple sulfur
bacteria, which produce sulfur (spherical
globules) (c, d, e: LMs).
(a) Plants
(c) Unicellular protist 10 m
(e) Pruple sulfur
bacteria
Figure 10.2
Regents Biology
(b) Multicellular algae
(d) Cyanobacteria
40 m
1.5 m
Plant Structures
 Roots


leaves
Take in water and minerals
from the soil
Some roots store food
 Leaves



Where photosynthesis takes
place
Absorbs CO2 & sunlight
Usually flat
stem/shoot
 Stem/Shoot


Hold the leaves & allow them
to receive sunlight
Contains vascular tissue
(bundles)
Regents Biology
roots
Plant structure
 Obtaining raw materials

sunlight
 leaves = solar collectors

CO2
 stomates = gas exchange

H2O
 uptake from roots

nutrients
 N, P, K, S, Mg, Fe…
 uptake from roots
Regents Biology
Function of Leaf Structures
 Cuticle



cuticle
waxy coating on epidermis
reduces water loss
protection
 Epidermis



palisade
mesophyll
Protective tissue on outer layer
Usually 1 cell thick
 Palisade mesophyll

Upper epidermis
lower epidermis
high concentration of chloroplasts
Photosynthesis
Regents Biology
Function of Leaf Structures
 Spongy mesophyll



Large air spaces
gas exchange
CO2 in & O2 out
 Stomata



Openings in the
epidermis
Allow for gas exchange
Usually more on the
lower epidermis
Xylem
Upper epidermis
palisade
mesophyll
spongy
mesophyll
 Guard Cells


Kidney shaped cells
surrounding the stomata
Regulate the stomata
Regents Biology
cuticle
lower epidermis
Stomata
Phloem
Guard cells
Plant Homeostasis
 Function of stomates



CO2 in
O2 out
H2O out
 Function of guard cells


open & close stomates
close stomates when dehydrated
guard cell
stomate
Regents Biology
Transpiration
 Water evaporates from
the stomates in the
leaves

pulls water up from
roots
 Cohesion
 Adhesion
 Capillary Action
Regents Biology
Viewing the Leaf
Epidermis
Regents Biology
Vascular/Conducting Tissues
Xylem
• carry water & minerals up from roots
• supports the plant, holds it upright
Regents Biology
How does water move up
from the roots?
water molecules stick to
other water molecules
because opposite charges
attract
Regents Biology
water molecules stick
to molecules of
another substance
Phloem: food-conducting cells
 carry sugars (food) around the
plant wherever they are needed
 new leaves
 fruit & seeds
 roots
Regents Biology
Viewing Vascular Tissue
Xylem
Regents Biology
Phloem
Phloem
Xylem
Chloroplast Structure





Chlorophyll
 Pigment that absorbs light
Chloroplast
 Double membrane
containing chlorophyll
Thylakoids
 Flattened membrane sacs
Grana
 Stack of thylakoids
Stroma
 Regions between grana
Regents Biology
absorb
sunlight
sun
make
ENERGY & SUGAR
What is photosynthesis?
ATP
+
Details:
+
Details:
Details:
Why is photosynthesis important?
Regents Biology
Details:
PHOTOSYNTHESIS


CO2
ENERGY building reactions
 collect sun energy
 use it to make ATP
SUGAR building reactions
 take the ATP energy
 collect CO2 from air &
H2O from ground
 use all to build sugars
+
H2O
+ water
carbon
dioxide
Regents Biology
sun
ATP
C6H12O6
Sugars
+
O2
+
oxygen
Photosynthesis
 Is a REDOX process

Water is oxidized, carbon dioxide is
reduced
sun
 Consists of two processes ENERGY
The light reaction
 The Calvin Cycle

sugar
Regents Biology
building
reactions
SUGAR
building
reactions
ATPused
immediately
to synthesize
sugars
Photosynthesis
 Light reactions (grana)


light-dependent reactions
Convert solar energy to chemical energy
 Split H2O, release O2, produce ATP, and form
NADPH
 NADPH: electron carrier
 Calvin cycle (stroma)


light-independent reactions
sugar building reactions
 uses chemical energy (ATP & NADPH) to
reduce CO2 & synthesize C6H12O6
Regents Biology
H2O
CO2
Light
NADP 
ADP
+ P
CALVIN
CYCLE
LIGHT REACTIONS
ATP
NADPH
Chloroplast
O2
Regents Biology
[CH2O]
(sugar)
Excitation of Chlorophyll by Light
 When a pigment absorbs light

It goes from a ground state to an excited
state, which is unstable
e–
Excited
state
Heat
Photon
(fluorescence)
Photon
Regents Biology
Figure 10.11 A
Chlorophyll
molecule
Ground
state
 A photosystem


Is composed of a reaction center surrounded by a
number of light-harvesting complexes
When a chlorophyll molecule absorbs energy one if
its electrons gets bumped to a primary electron
acceptor
Thylakoid
Photosystem
Photon
Thylakoid membrane
Light-harvesting
complexes
Figure 10.12
STROMA
Primary election
acceptor
e–
Transfer
of energy
Regents Biology
Reaction
center
Special
chlorophyll a
molecules
Pigment
molecules
THYLAKOID SPACE
(INTERIOR OF THYLAKOID)
Thylakoid membrane has two photosystems
H2O
CO2
Light
NADP+
ADP
CALVIN
CYCLE
LIGHT
REACTIONS
ATP
NADPH
O2
[CH2O] (sugar)
Primary
acceptor
2
2 H+
+
O2
H2O
e
7
Fd
Pq
8
e
e–
Cytochrome
complex
3
NADP+
reductase
NADPH
5
+ H+
P700
e–
P680
Light
6
ATP
Regents Biology
NADP+
+ 2 H+
PC
e–
Light
1
Primary
acceptor
4
Photosystem II
(PS II)
Photosystem-I
(PS I)
 The organization of the thylakoid membrane
 Chemiosmosis: generates ATP by ATP synthase
in the thylakoid membrane
H2O
CO2
LIGHT
NADP+
ADP
LIGHT
REACTOR
CALVIN
CYCLE
ATP
NADPH
STROMA
(Low H+ concentration)
O2
[CH2O] (sugar)
Photosystem II
Cytochrome
complex
Photosystem I
NADP+
reductase
Light
2 H+
3
Fd
NADPH
Pq
H2O
THYLAKOID SPACE
1
(High H+ concentration)
NADP+ + 2H+
+ H+
Pc
2
1⁄
2
O2
+2 H+
2 H+
To
Calvin
cycle
STROMA
(Low H+ concentration)
Thylakoid
membrane
ATP
synthase
ADP
ATP
P
Regents Biology
H+
Noncyclic Photophosphorylation
 Light reactions elevate
electrons in
2 steps (PS II & PS I)

PS II generates
energy as ATP

PS I generates
reducing power as NADPH
ATP
Regents Biology
 The Calvin cycle in the stroma
H2O
Light
CO2
Input
3 (Entering one
CO2 at a time)
NADP+
ADP
LIGHT
REACTION
CALVIN
CYCLE
ATP
Phase 1: Carbon fixation
NADPH
O2
Rubisco
[CH2O] (sugar)
3 P
3 P
P
Short-lived
intermediate
P
Ribulose bisphosphate
(RuBP)
P
6
3-Phosphoglycerate
6 ATP
6 ADP
Calvin
cycle uses
more ATP
than
NADPH
CALVIN
CYCLE
3 ADP
3
ATP
Phase 3:
Regeneration of
the CO2 acceptor
(RuBP)
Regents Biology
P
6 NADPH
6 NADPH+
6 P
P
5
(G3P)
6
P
Glyceraldehyde-3-phosphate
(G3P)
1
Figure 10.18
6 P
1,3-Bisphoglycerate
P
G3P
(a sugar)
Output
Glucose and
other organic
compounds
Phase 2:
Reduction
Cyclic photophosphorylation
 If PS I can’t pass electron
to NADP…it cycles back
to PS II & makes more
ATP, but no NADPH

ATP
Regents Biology
 A review of photosynthesis
Light reaction
Calvin cycle
H2 O
CO2
Light
NADP+
ADP
+P1
RuBP
3-Phosphoglycerate
Photosystem II
Electron transport chain
Photosystem I
ATP
NADPH
Chloroplast
Figure 10.21
Regents Biology
G3P
Starch
(storage)
Amino acids
Fatty acids
O2
Light reactions:
• Are carried out by molecules in the
thylakoid membranes
• Convert light eneragy to the chemical
energy of ATP and NADPH
• Split H2O and release O2 to the
atmosphere
Sucrose (export)
Calvin cycle reactions:
• Take place in the stroma
• Use ATP and NADPH to convert
CO2 to the sugar G3P
• Return ADP, inorganic phosphate, and
NADP+ to the light reactions
Photosynthesis Overview
Regents Biology
A Look at Light
 Light is a form of electromagnetic
energy that travels in waves
 Wavelength
 Distance between
crests
 Determines the type
of electromagnetic
energy
Regents Biology
Light: absorption spectra
 Photosynthesis gets energy by absorbing
wavelengths of light (pigments)

chlorophyll a
 absorbs best in red & blue wavelengths & least in green

accessory pigments with different structures
absorb light of different wavelengths
 chlorophyll b, carotenoids, xanthophylls
Why are
plants green?
Regents Biology
Action Spectrum of a Pigment
 Profiles the relative effectiveness of
Rate of photosynthesis
(measured by O2 release)
different wavelengths of radiation
driving photosynthesis
(b)
Action spectrum. This graph plots the rate of photosynthesis versus wavelength.
The resulting action spectrum resembles the absorption spectrum for chlorophyll
a but does not match exactly (see part a). This is partly due to the absorption of light
by accessory pigments such as chlorophyll b and carotenoids.
Regents Biology
Alternative Mechanisms of Carbon
Fixation in Hot, Dry Climates
 Closed stomates conserve water, but…
CO2 is depleted
 O2 builds up
 Rubisco binds to O2 instead of CO2

 No ATP or glucose produced
RuBP

O
2
Regents Biology
CO2

H2O
O2
RuBisCo
photorespiration
corn
C4 plants
 A better way to capture CO2

1st step before Calvin cycle,
fix carbon with enzyme
PEP carboxylase
 store as 4C compound
 4C compound exported to bundle
sheath cells where they release
CO2 to be used in Calvin Cycle
Regents Biology
sugar cane
CAM (Crassulacean Acid Metabolism) plants

separate carbon fixation from Calvin cycle
by TIME
 close stomates during day & open stomates during
night
at night: open stomates & fix carbon
in 4C “storage” compounds
 in day: release CO2 from 4C acids
to Calvin cycle

 increases concentration of CO2 in cells

succulents, some cacti, pineapple
Regents Biology
It’s all in
the timing!
CAM plants
cacti
succulents
Regents Biology
pineapple
C4 vs CAM Summary
solves CO2 / O2 gas exchange vs. H2O loss challenge
C4 plants
separate 2 steps
of C fixation
anatomically in 2
different cells
Regents Biology
CAM
plants
separate 2 steps
of C fixation
temporally =
2 different times
night vs. day
How are they connected?
Respiration
glucose + oxygen  carbon + water + energy
dioxide
C6H12O6 +
6O2
 6CO2 + 6H2O + ATP
Photosynthesis
carbon
sun
+ water + energy  glucose + oxygen
dioxide
6CO2 + 6H2O + light  C6H12O6 + 6O2
energy
Regents Biology
Energy cycle
sun
Photosynthesis
plants
CO2
glucose
H2O
sugars
animals, plants
Cellular Respiration
ATP
Regents Biology
O2