Thirsty
Plants



 Grade
Level:

4
 
 Objectives:

Students
observe
transpiration
and
quantify
the
amount
of
water
retained
by
 lettuce
plants
as
compared
to
the
amount
cycled
back
into
the
air.


This
experiment
 demonstrates
the
important
role
of
plants
in
the
water
cycle.
 
 Time
Required:

About
4
to
5
hours
spread
out
over
5
to
6
weeks.
 
 45
minutes
for
initial
planting
and
exploration
of
AeroGarden
 15
minutes
everytime
water
is
added
(once
a
week
at
first,
and
then
every
2
to
3
days
 when
the
plants
are
mature.)
 
 45
minutes
for
transpiration
experiment
 
 1½
hours
when
plants
are
mature

 
 Content
Areas:

 Science
as
Inquiry‐
Develop
abilities
necessary
to
do
scientific
inquiry
 Life
Science:
Behavior
of
organisms
 Physical
Science:
Properties
and
changes
of
properties
in
matter

 Measurement:
Understand
measurable
attributes
of
objects
and
the
units,
systems
and

 processes
of
measurement;
use
appropriate
techniques
and
tools

 Data
Analysis:
Collect,
organize,
display
and
analyze
data
 
 Materials:

 AeroGarden
 Salad
Greens
Seed
Kit
 Balance
scale
or
food
scale

 Beaker
or
clear
1
liter
water
bottle,
graduated
with
lines
marking
at
least
100
ml
intervals
 Plastic
bags
(sandwich
size)
 Wide
mouth
glass
jar
2
½
to
3”
diameter
and
between
3
to
5”
tall.

 Water
Log
(provided)
–
make
one
copy
for
each
student.
 
 Introduction:

 Begin
the
activity
with
a
discussion
about
water
to
help
students
make
a
connection
between
 themselves
and
plants.

Share
that
our
bodies
are
about
60
percent
water
by
weight.

Where
 does
your
body
get
the
water
it
needs?
(Drinks
and
food)

What
happens
to
water
in
your
 body?
Does
it
stay
there
forever?

How
does
your
body
get
rid
of
water?
(sweating,
urine,
 excrement,
evaporation,
breathing‐
dry
air
enters
lungs
and
picks
up
moisture
from
your
lungs
 which
is
then
exhaled.)

What
factors
influence
the
amount
of
water
you
lose?
(heat,
wind,
 exertion,
internal
body
temperature,
humidity.)

Explain
that
just
like
you,
plants
use
and
lose
 water.


In
this
experiment
students
will
follow
water
as
it
move
through
lettuce
plants.

Ask
 students
what
they
think
happens
to
most
of
the
water
they
give
to
plants.


 


Take
some
time
to
familiarize
your
class
with
the
AeroGarden
so
that
students
understand
the
 function
of
each
component.


Discuss
similarities
and
differences
of
growing
a
plant
in
an
 AeroGarden
versus
in
soil.


Let
students
know
that
as
part
of
this
study,
they
will
have
a
chance
 to
harvest
and
eat
the
lettuce
AFTER
the
entire
unit
is
completed.


 
 Procedure:
 
 1) Plant
the
AeroGarden
and
give
each
student
a
copy
of
the
Water
Log.

 2) Divide
students
into
six
groups
and
assign
a
plant
to
each
group.


Let
students
name
 their
groups
and
record
the
location
and
planting
date
on
the
Water
Log.

Plant
the
 AeroGarden
and
record
the
date
on
the
Water
Log.

 3) As
the
lettuce
grows,
keep
an
accurate
record
of
the
amount
of
water
added
to
the
 AeroGarden
on
the
Water
Log.


Calculate
the
weight
of
water
added
(use
a
conversion
 of
1
ml
of
water
weighs
1
gram)
and
record
this
on
the
Water
Log.
 
 4) When
plants
are
about
1
or
2
inches
tall
(about
2
weeks
after
planting),
set
up
an
 experiment
to
demonstrate
transpiration,
which
is
the
loss
of
water
through
plant
 leaves.
 














TRANSPIRATION
EXPERIMENT
 a. Cut
a
plastic
baggy
into
a
circle
with
a
diameter
about
¼
inch
larger
than
 diameter
of
opening
on
glass
jar.
 
 b. Cut
a
slit
into
the
circle
from
outer
edge
to
the
center.


 c. Slip
the
plastic
circle
around
base
of
the
Seed
Pod
so
that
the
Seed
Pod
Label
is
 covered.

This
will
prevent
the
evaporation
of
water
from
the
AeroGarden
Bowl
 into
your
jar.
 d. Put
the
glass
jar
over
the
top
of
Seed
Pod
so
that
the
edges
of
the
plastic
circle
 extend
beyond
the
jar
opening.

(You
may
need
to
raise
the
Lamp
Hood
to
make
 room
for
your
glass
jar.

This
is
fine,
just
be
sure
to
lower
the
Lamp
Hood
once
 the
jar
is
removed.)
 e. Have
students
make
observations
the
next
day.

Questions:

Where
is
the
water
 on
the
jar
coming
from?

How
much
water
do
you
think
a
plant
loses
this
way?

 Have
students
estimate
what
percentage
of
water
added
to
the
AeroGarden
is
 lost
to
transpiration.

Let
them
know
that
you
will
actually
calculate
this
once
the
 lettuce
plants
are
mature.
 5) When
the
lettuce
plants
are
5
to
6
weeks
old,
weigh
each
plant
(remove
the
entire
Seed
 Pod
and
put
it
on
a
scale).
Record
weight
on
Water
Log
(Step
1).





 6) Calculate
the
total
volume
of
water
added
to
the
AeroGarden
and
record
it
on
the
 Water
Log
(Step
2).
 


7) Calculate
the
volume
of
water
each
individual
plant
used.
(Water
Log,
Step
3)
Assume
 that
each
Seed
Pod/Plant
is
using
the
same
amount
of
water,
so
each
lettuce
plant
uses
 1/7th
of
the
amount
of
water
added.


(If
you
planted
only
a
few
Seed
Pods
or
if
a
plant
 dies
along
the
way,
be
sure
to
adjust
the
ratio
accordingly.)

 


8) Calculate
the
weight
of
water
used
by
your
plant.
(Step
4
on
Water
Log.)
 
 9) Have
students
compare
the
weight
of
water
added
to
the
weight
of
the
plant
(lettuce,
 roots
and
Seed
Pod).


What
happened
to
the
water?


Does
it
all
go
into
the
lettuce
 leaves?

What
about
the
roots?

Students
will
realize
that
a
large
percentage
of
the
 water
added
to
the
AeroGarden
was
released
from
the
plant
into
the
air.


 


10) Don’t
forget
to
harvest
your
lettuce
and
enjoy
the
bounty!
 


Discussion/Summary:

Have
students
summarize
and
share
their
findings
about
how
much
 water
moves
through
a
plant.

Ask
students
what
factors
might
influence
the
amount
of
water
a
 plant
loses
to
transpiration.

Remind
them
of
their
initial
brainstorming
about
what
influences
 how
they
use/lose
water.

(Temperature,
wind,
humidity,
leaf
shape/surface
area/texture).



 
 Show
students
a
schematic
drawing
of
the
water
cycle
and
discuss
the
role
that
plants
play
in
 the
cycle.

What
happens
to
rain
water
in
the
soil?

Why
do
people
clear
plants
away
from
 irrigation
ditches?

What
impact
would
cutting
down
trees
have
on
the
water
cycle?

Help
 students
visualize
the
volume
of
water
that
plants
move
from
the
soil
to
the
air.

A
large
oak
 tree
can
transpire
40,000
gallons
of
water
(151,000
liters)
per
year.

How
many
gallons
a
day
is
 that?

How
much
space
in
your
classroom
would
that
take
up?

RESOURCES:

For
schematic
 drawing
of
the
water
cycle
see:
http://ga.water.usgs.gov/edu/watercycletranspiration.html
 
 Extensions:

 Continue
growing
lettuce
plants
and
record
amount
of
water
added
but
introduce
a
variable,
 such
as
wind
(from
a
fan)
and
see
how
much
more
water
is
lost
to
transpiration.
 
 Expand
transpiration
experiment
to
compare
the
amount
of
water
loss
during
the
day
 (AeroGarden
lights
are
on)
to
that
of
the
night
(AeroGarden
lights
are
off).

 


Graph
the
volume
of
water
added
over
time.

How
does
water
usage
change
as
the
plants
 grow?

Is
it
linear?
 
 Weigh
the
plants
every
week,
rather
than
only
at
the
end
of
experiment,
and
calculate
how
 much
water
is
lost
to
transpiration
each
week.

Does
the
rate
change
as
the
plant
grows?

A
 graph
showing
plant
weight
and
weight
of
water
lose
over
time
would
be
a
good
way
to
 examine
these
data.
 
 
 


WATER
LOG
(page
1
of
2)
 My
Name:
_________________________


 Other
members
of
my
group:
_________________________________________________
 _________________________________________________________________________
 



















 Group
Name:



















BACK
ROW
OF
AEROGARDEN


My
plant
location
in
the
 AeroGarden
is
position
number:
 _______________
 
 










 
 
 Date
Garden
Planted:







 










FRONT
ROW
OF
AEROGARDEN



 
 Picture
of
my
plant
_________
days
after
planting



 Date


Amount
Water
 Added
(ml)




























 




















































































CALCULATIONS











WATER
LOG
(page
2)



 Step
1:
 Weight
of
my
plant:
_______________grams
 
 Step
2:

 Total
Volume
of
Water
Added:
____________ml_
 
 Step
3:

 Volume
of
water
used
by
my
plant:
__________ml__
 

(Volume
from
Step
2)
÷
(7)
 
 
 
 Step
4:
 Weight
of
water
used
by
my
plant:
________
grams
 


(volume
from
Step
3)
x
(1
gram/1ml)
 
 
 
 Step
5:
 Describe
how
the
weight
of
your
plant
compares
to
 the
weight
of
water
used
by
your
plant.


Where
did
 the
water
go?