Evolution of
Plants
p.334a
Why did it take so long for
plants to adapt for life on
land?


Ozone layer for?
Needed special adaptations for life on land
to

Retain water:
seasonal changes on land is more drastic than
in aquatic environment
 Special systems to absorb, retain, transport
water



Support system (water supports in aquatic
plants)
Reproductions without the aid of water
Adaptation for Life on Land
1.
2.
3.
Root system – absorb nutrients, water,
anchor plant
Shoot System – supports leaves (lignin),
conduct water and nutrients
Vascular system – special tissues for the
transport of water and nutrients


Xylem: water and nutrients
Phloem: food
Adaptation for Life on Land
cont.
4.
5.
6.
7.
Waxy cuticle – prevent water loss
Stomata – small pores in leaves that
allow for gas exchange
Reproductive System – delay gamete
formation and fertilization till conditions
are appropriate
Dominant sporophyte generation from
dominant gametophyte generation.
zygote only, no
sporophyte
green algae bryophytes
ferns
gymnosperms
angiosperms
Fig. 21-2, p.336
Adaptation for Life on Land
cont.
8.
9.
Pollen – male gamete independent of water
Seed – embryo plant can be dormant and
contain nutrients for the initial development
of the plant
Did all of these adaptations happen at once?
How do we know that these adaptations
happened and in what order?
Evolutionary Tree Of Land Plants
Unicellular
photosynthetic
Cyanobacteria
Common
Ancestor
Hetrerotroph
Protists
Algae
Moss
Pines
Fern
Flowering
plants
Covere
d seed
and
flowers
Importance of plants
 Food
Photosynthesis
 Oxygen
 Building
materials
 Fuels
 Clothes
 Other
types of constructions
 Aesthetics
Photosynthesis
What is photosynthesis?
shortest
wavelengths
(most
energetic)
gamm
a rays
range of most
radiation
reaching
Earth’s surface
x
rays
range of heat
escaping
from Earth’s
surface
ultraviolet
radiation
near-infrared infrared
radiation
radiatio
n
VISIBLE LIGHT
longest
wavelengths
(lowest
energy)
microwave
s
radio
waves
Wavelengths of light (nanometers)
Fig. 6-2, p.94
What is a wavelength
p.94
How do the pigments help
in photosynthesis?
• Pigment absorbs photons (energy
packets)
• ROYGBIV
• Plant pigments are
Mainly - Chlorophyll a - abundant, red
violet
- Chlorophyll b – blue range
Accessory - Caretenoid blue violet etc
Xanthophyll - yellow, brown, purple
Absorption Spectra of plant
pigments
chlorophyll
a
chlorophyll
b
beta-carotene
phycoerythrin
(a phycobilin)
Fig. 6-4, p.95
A crystal prism breaks up a beam of light into
a spectrum of colors, which are cast across a
droplet of water on a microscope slide.
part of an algal strand
stretched out across
a microscope slide
Heterotrophic bacteria
Autotrophic algae
Fig. 6-6, p.95
Fig. 6-7a1, p.96
Cross Section of Leaf
Upper
Epidermis
Lower
Epidermis
a section from the leaf, showing its internal organization
Fig. 6-7a2, p.96
central vacuole
chloroplast
b one photosynthetic cell inside the leaf
Fig. 6-7b, p.96
two outer membranes
Chloroplast
stroma
thylakoid
membrane
System - Grana
Thylakoid
Fig. 6-7c, p.97
Overview
1. Light dependent reactions
– Light energy absorbed
– Water split, oxygen released
– ATP and NADPH made
2. Light independent reactions (Calvin
Benson Cycle)
Carbon fixed (from CO2)
Products of Light R is used to make
sugars
LIGHTHARVESTING
COMPLEX
PHOTOSYSTEM II
PHOTOSYSTEM I
sunlight
NADPH
NADPH + H+
H+
H+
H+
H+
H+
H+ H+
H+
H+
H+
H+
thylakoid
compartment
thylakoid
membrane
ADP + Pi
ATP
stroma
Light Reaction
Fig. 6-9b, p.99
Light Reaction
• Clusters of chlorophyll a and b
molecules make up photosystems I
and II
• Chlorophyll absorbs light energy
• Electrons lost by one chlorophyll
replaced by another chlorophyll.
• Electrons lost are obtained from
water molecule
H 2O
2H+ + 2e- + 1/2O2
Light reaction ….
• Hydrogen ions (protons) accumulate
inside the thylakoids
• Creates a concentration gradient
• Hydrogen diffuses out through ATP
synthase to make ATP
• H+ + e- + NADP+
NADPH
6CO2
Calvin Cycle
ATP
6 RuBP
12 PGA
12
6 ADP
Calvin-Benson
cycle
ATP
12 ADP +
12 Pi
12 NADPH
4 Pi
12 NADP+
10 PGAL
12 PGAL
1 Pi
1
glucose-6-1-phosphate
Fig. 6-11, p.101
6CO2
It takes six turns
of the cycle to
make one
glucose
molecule
6 RuBP
ATP
10 PGAL get
phosphate
groups from
ATP. This primes
them for
reactions that
regenerate
RuBP.
12 PGA
Calvin-Benson
cycle
12 PGAL
1
glucose
ATP
NADPH
Rubisco attaches
C from CO2 to
RuBP. Resulting
intermediate splits
into PGA.
PGA gets
phosphate from
ATP, hydrogen
and electrons
from NADPH;
forms PGAL.
2 PGAL
combine to
form glucose.
Glucose enters reactions that
form carbohydrates.
Stepped Art
Fig. 6-11, p.101
Limiting Factors of
photosynthesis
•Light Intensity
•Temperature
•Carbon Dioxide
•Oxygen
C-3 Plants
 Stomata
close on hot dry
days
 CO2 levels fall and O2
levels rise
 Rubisco reacts with CO 2
and O2
 Photorespiration forms
only one PGA
 Half the number of Glu
molecules formed and
growth slows
stomata closed,
no CO2 uptake
RuBP
PGA
CalvinBenson
cycle
sugar
Fig. 6-12a3, p.103
stomata closed,
no CO2 uptake
C4 oxaloacetate mesophyll cell
cycle
CO2
RuBP
PGA
CalvinBenson
cycle
bundle-sheath cell
sugar
Fig. 6-12b3, p.103
C-4 Plants
 Special
adaptation for hot days when stomata
closed
 CO2 forms oxaloacetate (4C) with an enzyme that
does not compete with O2 in mesophyll cells
 Transferred to bundle sheath cells (surrounding the
veins)
 Reverse reaction generates CO2 and Calvin Cycle
is not effected
 Photosynthesis as usual
 Ex. Corn and grasses that grow well in the hot dry
summer months.
CO2 uptake at night only
C4
cycle
CalvinBenson
cycle
runs
at
night
runs
during
day
sugar
Fig. 6-12c3, p.103
CAM Plants
 Adapted
to desert conditions when stomates
are tightly closed in the daytime
 Same as C4 except
 Stomates open only at night and fix the CO2 as
the four C compound and store
 Reverse reaction during day when the Light
reaction and Calvin Cycle is active and provides
the CO2 for photosynthesis
 Why do these plants have a slow growth rate?
 Ex. Cactus
sunlight
LightDependent
Reactions
12H2O
6O2
ADP + Pi
ATP
6CO2
6 RuBP
LightIndependent
Reactions
NADPH
CalvinBenson
cycle
NADP+
12 PGAL
6H2O
phosphorylated glucose
end products (e.g., sucrose, starch, cellulose)
Fig. 6-13, p.104
Solar-powered Elysia chlorotica From:
Liz Summer
Collected from Martha’s Vineyard MA