National 4 -Energy from the sun
Green plants are known as producers as they can make their own food using raw
materials from the environment and energy from sunlight. The process by
which green plants do this is known as photosynthesis and the food they make is
carbohydrate. Animals are known as consumers as they can’t make their own
food and eat green plants.
Energy from the sun
sun sun
Raw materials from
the environment
Green plants make
carbohydrate by
photosynthesis
Animals eat
green plants
CO2
National 4 and 5- Trapping light
To carry out photosynthesis
plants must be able to capture
light from the sun.
Plants do
this using a special pigment called
chlorophyll. Chlorophyll is found
within
structures
called
chloroplasts that are in the
cytoplasm of certain plant cells.
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chloroplasts containing
chlorophyll
cytoplasm
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National 4 and 5- Photosynthesis
When plants carry out photosynthesis they use water from the soil and carbon
dioxide from the air as raw materials and sunlight trapped by chlorophyll to
provide the necessary energy. Carbohydrate is produced in the form of glucose
and oxygen is produced as a by-product. This can be shown as a word equation:
carbon dioxide + water
raw materials
light energy
glucose + oxygen
chlorophyll
conditions
required
products
National 4 and 5- Affects of light on photosynthesis
When plants photosynthesise they make carbohydrate in the form of glucose
which is then stored as starch. Therefore it can be assumed that if a plant has
starch in its leaves then it has been photosynthesising, while if it does not have
starch in its leaves then it has not been photosynthesising.
The following experiment shows the effects of light on photosynthesis:
1. Place one plant in bright light and another
in a cupboard for a few days
water
2. Use a cork borer to remove a disc from
each leaf and place them in labelled tubes
of water as shown:
3. Place the tubes in a beaker of water and
heat the water until it boils.
4. Turn the Bunsen off
leaf disc from
plant in bright
light
leaf disc from
plant in cupboard
5. Pour the water out (use a wooden splint to hold the leaf discs in place), add
enough ethanol to cover the leaf discs and place the tubes back into the beaker
of water.
6. Once the green colour has been removed from the leaf discs, hold the disc in
place with a wooden splint and pour the ethanol into the waste ethanol bottle.
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7.Use iodine to test the leaf discs for starch.
Results
Conclusion
The leaf from the plant that had been in the light contained starch but the leaf
from the plant that had been in the dark did not. This shows that plants must
have light in order to carry out photosynthesis and produce glucose which is
stored as starch.
National 4 and 5- Affects of carbon dioxide on photosynthesis
In order to make glucose, and subsequently starch, by photosynthesis plants
must have carbon dioxide as a raw material. How much starch a plant can
produce by photosynthesis is directly affected by how much carbon dioxide the
plant has available to it.
The following experiment is set up to show the effects of carbon dioxide on
photosynthesis:
Sealed bell
jar
Plants are well watered
and kept in bright light
for 1 week
Potassium hydroxide
which removes CO2
from the air
Sodium bicarbonate
which adds CO2 to the
air
After one week a leaf from each plant was tested for starch using the same
method as in the affects on light on photosynthesis experiment.
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Results and conclusion
The plant that had a high quantity of carbon dioxide available to it had lots of
starch in its leaves while the plant that had a low quantity of carbon dioxide
available to it had no starch in its leaves. This shows that the process of
photosynthesis is dependant on carbon dioxide being available and if it is not
then photosynthesis cannot be carried out and starch is not produced.
Limiting factors and photosynthesis
Photosynthesis will be slowed down under the following circumstances
1. If light or carbon dioxide is in short supply
2. If the temperature is too low or high
Between points A and B the the rate of
photosynthesis is increasing and is not going
at its optimum rate. This means that light
intensity must be limiting the rate of
photosynthesis, so between points A and B
light intensity is a limiting factor.
After
point B the rate of photosynthesis does not
increase. This means that photosynthesis is
being carried out as fast as the plant can, so
after point B light intensity is not a
limiting factor.
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Rate of
photosynthesis
Whichever factor is responsible for slowing down photosynthesis (carbon
dioxide, light or temperature) is known as a limiting factor. The rate of
photosynthesis will increase until it reaches a maximum then it will level off.
Example of a limiting factor
B
A
Light
intensity
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Overcoming limiting factors
There are a number of ways to prevent carbon dioxide, light intensity or
temperature
becoming a limiting factor:
Potential
limiting
factor
Light
Carbon
dioxide
Temperature
Way of overcoming
Supplementary lighting (lighting
other than normal daylight)
Supplementary
lighting
Plant
s
When paraffin or propane are
burned they give off carbon
dioxide. By using heaters that
burn paraffin or propane carbon
dioxide can be supplied to the
plants
Parafin/
propane
heater
Heating
Advantages – the grower can produce crops earlier in the year than normal
- higher yields are possible
Disadvantages – these methods require electricity and fuel and are therefore
expensive
Level 4 E&O
Nat 4
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Photosynthesis- limiting factors
If any of the requirements (light, water carbon dioxide or suitable temperature are low
or missing the photosynthesis rate is limited.
By overcoming these limitations, faster growth rates can be achieved
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Energy
Living cells cannot survive without energy as it is required for numerous
functions carried out by the cell e.g.
Cell Division
Uptake of
chemicals
Cell Growth
Energy
Building up
large molecules
Muscular
contraction
Respiration
While energy can be released from many different foods, the main food
molecule used as a energy source in cells is glucose. However if cells released
energy from glucose in one large quantity as it is above, it would result in
damage to the cell. Cells avoid this by using a process known as RESPIRATION
to release energy from glucose in a large number of small steps. Each of these
steps is controlled by a different enzyme. As this is controlled by enzymes the
rate of respiration will be effect by temperature (refer back to enzymes).
Respiration takes the chemical energy from glucose and transfers it into other
molecules in the cell. Any energy which is not transferred into these cell
molecules is released as heat energy.
If oxygen is available to cells then they will use aerobic respiration to break
down glucose and release energy.
Aerobic respiration is the process where cells use oxygen to break down
food and release energy.
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In animal cells lactic acid is porduced during Aerobic respiration.
In plant and yeast cells ethanol and carbon dioxide are produce during Aerobic
respiration.
Investigation into anaerobic respiration in yeast
Background
In the absence of oxygen yeast will respire anaerobically and produce ethanol
and carbon dioxide.
Method
Thermometer
1. Boil a solution of glucose and
allow it to cool
To water
pump
Insulation
2. Set up the apparatus as
shown:
Layer of oil
Lime
water
3. The oil is added to prevent
oxygen being added.
4. The insulation is added to
prevent heat escaping.
5. Let experiment run for 24 hours
Boiled and cooled
glucose solution
and yeast
Thermometer
Results
Smell of flask
Appearance of lime
water
Temperature of
glucose solution (oC)
At start
Sugar
clear
21 oC
After 24 hours
alcohol
cloudy
26 oC
Conclusion
As there was no oxygen in the glucose solution we would expect the yeast to use
anearobic respiration and produce ethanol and carbon dioxide. The experiment
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proved this as after 24 hours the the flask smelt of alcohol and the lime water
had turned cloudy.
National 4 - Comparison of aerobic and anaerobic respiration
Aerobic
respiration (oxgen
available)
Respriatory
substrate
Glucose
Anaerobic respiration (no oxygen)
In animals
In plants and
yeast
glucose
glucose
Products
Carbon and water
dioxide
Lactic acid
Carbon and
ethanol
dioxide
Energy
Large number
Little
Little
Level 4 E&O
I can contribute to the design of an investigation to show the effects of different
factors on the rate of aerobic respiration and explain my findings.
Nat 4
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Factor affecting respiration
Respiration is used to release energy for use in cells. Oxygen may or may not be used in
both yeast and animal cells. When oxygen is available, yeast plant and animal cells use
oxygen to produce carbon dioxide and water. Without oxygen yeast and plant cells use
glucose to produce alcohol and carbon dioxide. Without oxygen animal cells use glucose
to produce lactic acid.
More energy is released per molecule of glucose when oxygen in present. The process in
enzyme controlled in all cases so is affected by temperature.
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