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Transcript of © Edco 2007 Exploring Science Biology Photosynthesis and plant responses Photosynthesis and Plant...
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Photosynthesis and Photosynthesis and Plant ResponsesPlant Responses
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Nutrition
• Animals get their food by eating other animals and plants.
• Plants make their own food by a process called photosynthesis.
Nutrition is the way in which living things get their food.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Photosynthesis
Photosynthesis:• is the way in which green plants make
food• converts solar (sun) energy into chemical
energy in food• takes place in the green parts of plants,
mostly in the leaves• is one of the main differences
between plants and animals.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Equation for photosynthesis
Photosynthesis can be summarised as:
Carbon dioxide
+Water
Sunlight Glucose
+OxygenChlorophyll
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Factors needed for photosynthesis
• Carbon dioxide (a gas)– passes into the leaves from
the air– enters the under-surface of
leaves through tiny openings called stomata.
• Water– enters the roots from the
soil– passes up through the
stem– enters the leaves in the
veins.
WaterCarbon dioxide
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
• Light– in the form of sunlight,
provides the energy for photosynthesis.
• Chlorophyll– is a green pigment or
dye made by plants– acts as a catalyst for
photosynthesis.
Factors needed for photosynthesis
WaterCarbon dioxide
Sun
Light
Chlorophyll
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Products of photosynthesis
• Glucose– is a sugar or carbohydrate– may be used in the plant for:
o respiration (i.e. it is broken down to release energy)
o storage in the form of starcho making cell walls (i.e. it is converted to cellulose).
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Products of photosynthesis
• Oxygen– is a gas– may be used in the
plant for respiration– mostly passes out
of the stomata into the air.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Experiment
To show that starch is made by a plant in photosynthesis
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
MethodTo 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.
2. 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.
3. Leave the plant in strong light for a few hours.
– To allow photosynthesis to take place.
4. Test some of the covered and uncovered leaves for starch.
– To show whether or not photosynthesis took place.
Aluminium foil
Light
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Experiment
To test leaves for starch
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
MethodTo test leaves for starch
1. Boil the leaves in water for a few minutes.
Leaves
Water
Tripod
Bunsen burner
This kills and softens the leaves.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
2. Soak the leaves in hot alcohol for ten minutes.
Method cont.To test leaves for starch
Boiling water Alcohol
Leaves
This removes the chlorophyll from the leaves. Removing the green colour allows any later colour changes to be seen.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
3. Rinse the leaves briefly in boiling water.
Method cont.To test leaves for starch
Leaves
Water
Alcohol makes the leaves stiff and brittle. Rinsing off the alcohol will soften the leaves.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
4. Add iodine solution to the leaves.
Method cont.To test leaves for starch
Iodine solution
Tile
Leaf
Iodine turns from a red-yellow colour to blue-black if starch is present.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ResultsTo 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.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ConclusionTo test leaves for starch
Starch is made by leavesin the presence of light.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Plant responses
• The ability to respond is one of the characteristics of life.
• Plants usually respond slowly (so that often we do not see their responses).
• Plants respond to light and gravity by growing towards or away from light or gravity.
• A tropism is the change in growth of a plant in response to an outside stimulus.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Phototropism
• The shoots (aerial parts) of a plant grow towards light due to phototropism.
• Phototropism allows shoots to get more light and make more food.
Phototropism is the change in growthof a plant in response to light.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Experiment
To investigate phototropism
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
MethodTo investigate phototropism
Set up the apparatus as shown in the diagram. Light
Light
Petri dish containing wet cotton wool sprinkled with seedlings
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ResultsTo 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.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ConclusionTo investigate phototropism
Seedlings grow towards the light.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Geotropism
• 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.
Geotropism is the change in growth of aplant in response to gravity.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
Experiment
To investigate geotropism
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
MethodTo investigate geotropism
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
Soaked seeds
Beaker
Damp compost
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ResultTo investigate geotropism
As the diagram shows:
The roots grow down towards
gravity
The shoots grow up away from gravity
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses
ConclusionTo investigate geotropism
Shoots grow away from gravity and roots grow towards gravity.
© Edco 2007 Exploring ScienceBiology
Photosynthesis and plant responses