Transcript Photosynthesis Describe, using a word equation, how plants make their own food through photosynthesis “photosynthesis” “photo” means light… “synthesis” means to make… …so what do you think.

Photosynthesis
Describe, using a word equation, how
plants make their own food through
photosynthesis
“photosynthesis”
“photo” means light…
“synthesis” means to make…
…so what do you think the word photosynthesis could mean?
how plants make their food
oxygen
Energy from sunlight,
with chlorophyll as a
catalyst, is used to
combine CO2 and H2O to
form glucose and
release O2
Carbon dioxide
chlorophyll
glucose
Photosynthesis word equation
Watch the animation again…
Can you write what is
happening as a
word equation?
oxygen
chlorophyll
Carbon dioxide
glucose
Photosynthesis word equation
Carbon dioxide plus water,
with light and chlorophyll,
gives glucose and oxygen
Sugar is
transported to
all other parts of
the plant
Experiment
To show that starch is made by a
plant in photosynthesis
Method
To show that starch is made by a plant in photosynthesis
1. Leave a pot plant in
the dark for two days.
– To destarch the
leaves, i.e. the starch
moves out of the
leaves.
Place tinfoil over some
of the leaves of the
plant.
– To prevent light
reaching the leaves
and, therefore, to
prevent
photosynthesis. These
leaves act as a control
or comparison in the
experiment.
Aluminium
foil
Light
Leave the plant in
strong light for a few
hours.
– To allow
photosynthesis to take
place.
Aluminium
foil
Light
Test some of the
covered and
uncovered leaves for
starch.
– To show whether or
not photosynthesis
took place.
Aluminium
foil
Light
Experiment
To test leaves for starch
Method
To test leaves for starch
1. Boil the leaves in
water for a few
minutes.
This kills and
softens the leaves.
Leaves
Water
Tripod
Bunsen
burner
Method cont.
To test leaves for starch
2. Soak the leaves in
hot alcohol for ten
minutes.
This removes the
chlorophyll from the
leaves. Removing the
green colour allows any
later colour changes to be
seen.
Boiling
water
Alcohol
Leaves
Method cont.
To test leaves for starch
3. Rinse the leaves
briefly in boiling
water.
Alcohol makes the
leaves stiff and brittle.
Rinsing off the alcohol
will soften the leaves.
Leaves
Water
Method cont.
To test leaves for starch
4. Add iodine solution
to the leaves.
Iodine turns from a
red-yellow colour to
blue-black if starch is
present.
Iodine solution
Leaf
3
Tile
2
1
1
2
3
30 seconds
green
leaf
3 minutes
hot alcohol
in tube
4
white
leaf
boiling
water
in beaker
30 seconds
leaf turns black
warm water
yellow
iodine solution
Results
To test leaves for starch
• The leaves that were uncovered turn
blue-black.
– This shows that starch is present.
• The leaves that were covered remain
red-yellow.
– This shows that starch is not present.
Conclusion
To test leaves for starch
Starch is made by leaves
in the presence of light.
Plant responses
• The ability to respond is one of the
characteristics of life.
• A tropism is the change in growth of a
plant in response to an outside stimulus.
Phototropism
Phototropism is the change in
growth
of a plant in response to light.
• The shoots (aerial parts) of a plant grow
towards light due to phototropism.
• Phototropism allows shoots to get more light
and make more food.
Experiment
To investigate phototropism
Method
To investigate phototropism
Light
Set up the apparatus as shown in the diagram.
Light
Petri dish containing wet cotton wool
sprinkled with seedlings
Results
To investigate phototropism
Section A: the
seedlings grow
towards the light
and bend.
Section B: the
seedlings grow
straight up
towards the light.
Section C: the
seedlings turn
yellow and do not
grow.
Conclusion
To investigate phototropism
Seedlings grow towards the light.
Geotropism
Geotropism is the change in
growth of a
plant in response to gravity.
• The shoots of a plant grow away
from gravity.
– This means they grow upwards
towards the light.
• The roots grow towards gravity.
– This means they grow into the soil to
get a better grip and to absorb more
water.
Experiment
To investigate geotropism
Method
To investigate geotropism
Damp compost
1. Soak some large
seeds in water for a
day or two.
2. Set up the
apparatus as shown
in the diagram.
3. Leave the apparatus
in a warm dark
place for a few days.
Blotting paper
Beaker
Soaked seeds
Result
To investigate geotropism
As the diagram shows:
The roots grow
down towards
gravity
The shoots grow
up away from
gravity
Conclusion
To investigate geotropism
Shoots grow away from gravity and roots
grow towards gravity.
Summary
Describe, using a word equation, how
plants make their own food through
photosynthesis
Sunlight
Water + Carbon Dioxide  Glucose(energy) + Oxygen
Chlorophyll
Tropism – plants response to a stimulus e.g. Phototropism
H/W
• P105-107
• Q 1,3,5,6,7.