GRADE 8 TERM 1
NATURAL SCIENCES
Curriculum
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Photosynthesis
Variables and fair tests
Carrying out practical
investigations
Respiration
PHOTOSYNTHESIS
Skills
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Understanding the process of
photosynthesis
Identifying and
understanding variables
and using them to carry out
investigations
Understanding the process
of respiration and testing the
theory using an experiment
Resources
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Textbook
Worksheets
A variety of leaves
Heat source/spirit or Bunsen
burners
Glass containers/test tubes
Ethanol/methylated spirits
Iodine solution
White surfaces
Slaked lime (to make lime
water) and
Drinking straws
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Photosynthesis
The need for energy drives interactions
between living organisms
The conservation of energy
Interdependence
Living organisms rely and interact with one another.
The most important interaction is the search for energy or food
as this is essential to sustain life.
The sun is the ultimate source of energy
The sun is the source of energy for all living things.
The sun gives energy in the form of light and
heat
Radiant energy
Living organisms can’t use this radiant energy directly; it needs
to be transformed into a different form.
Energy can never be created
or destroyed, it can only be
transformed from one form to
another.
https://en.wikipedia.org/
wiki/Conservation_of_
energy
This transformation process is called photosynthesis.
The process of photosynthesis
Photosynthesis is therefore taking radiant energy from the sun
(light) as well as carbon dioxide, converting it into potential
energy (energy that is stored in an object) which is stored in
food and released as oxygen. When animals eat plants, they
consume energy made by the plants.
Photo = means light
Synthesis = means to make
Carbon dioxide + water + sunlight
Plants use carbon dioxide (from the air), water (from the soil)
and energy from the Sun in a series of chemical reactions to
produce glucose (food). This process is called photosynthesis
Carbon dioxide + water + sunlight
glucose +oxygen
© e-classroom 2015 1
glucose +oxygen
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GRADE 8 TERM 1
NATURAL SCIENCES
PHOTOSYNTHESIS
Photosynthesis
Given off into the air
Starch
Stored food in the
other parts of the plant
Turns iodine dark blue
Carbo Dioxide
Enters through the
stomata of the leaves
Water
Absorbed
from the roots
https://goo.gl/JgGdn2
Sugar
Chlorophyll
Traps light
energy to
make
food
http://sactree.com/pages/302
Ox
yg
en
Light
Plants convert glucose into
other compounds
Plants change glucose into starch, cellulose and
other chemical compounds to enable processes
such as growth and reproduction.
Checklist for photosynthesis;
Plants change glucose molecules into starch, as
plants need this to store energy.
Sunlight – in the form of radiant
energy.
Chlorophyll – the green pigment in
the cells of a plant which allows for
absorption of radiant energy from
the sun.
Water – plant roots absorb water
from the soil.
Carbon dioxide – plants absorb
carbon dioxide, specifically through
the plants leaves.
Plants use radiant energy to
produce glucose from sunlight and
water.
Glucose is a simple sugar used by
the plant for food.
Oxygen is released.
Carbon
Dioxide
+
Water
+
Light
Energy
Sugar Oxygen
Glucose is also converted intoà cellulose. This
cellulose gives plants support and allows them
to grow tall.
G
G
G
G
G
G
G
G
Starch
Green leaves for
photosynthesis
https://goo.gl/eJq2DR
+
Many glucose molecules join together to make
starch.
© e-classroom 2015 Energy is stored
in the form of
starch
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GRADE 8 TERM 1
NATURAL SCIENCES
PHOTOSYNTHESIS
Activity 1
1. What is radiant energy?
2. Explain in detail the process of photosynthesis, use a diagram to illustrate your answer.
3. Write down the word equation for photosynthesis.
4. Plants convert glucose into other compounds, explain.
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GRADE 8 TERM 1
NATURAL SCIENCES
Variables and fair tests
What are variables?
Variables are any factors that have an effect on
an investigation.
PHOTOSYNTHESIS
Conducting an investigation to
show that leaves produce starch
Hypothesis: Green leaves produce starch.
There are three types
1. Independent (x) – what will be changed on
purpose
2. Dependent (y) – what is being measured
3. Controlled – keeping something consistent
to draw conclusions,
Apparatus needed:
• green leaf
• beaker of water
• Bunsen burner
• matches
• tweezers
What are fair tests?
Method:
• Light the Bunsen burner.
• Boil water in a beaker using the Bunsen burner.
• Put a green leaf into the boiling water.
• Using the tweezers take the leaf out the boiling
water and place it on the white tile, allow to cool.
• Pour ethanol into a small beaker and put the
leaf inside.
• Using the tongs hold this beaker in a larger
beaker filled with boiling water for 10 minutes.
• Rinse the leaf in warm water and spread it on
the tile.
• Using the dropper, place the iodine solution
on the leaf.
An investigation where all the variables are kept
the same.
What is a practical investigation?
These are experiments and tests in order to
gather more information.
This is done by following six steps also known
as the scientific method, in order to get
information that is valid, reliable and useful.
How to carry out practical
investigation?
There are six steps;
1. Observe and ask questions such as why or
how?
2. Set up a hypothesis (a possible explanation)
to the question being investigated
3. Plan your investigation (variables, method,
and equipment).
4. Conduct the investigation and record your
results.
5. Analyse the results and conclude by
processing and interpreting results.
6. Evaluate the investigation to decide if there
may be a better way to get results.
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white tile
ethanol
tongs
dropper
iodine solution
Results: From this experiment, you will discover
that leaves contain starch. The ethanol extracts
chlorophyll from plant cells and the boiling
water breaks the cell walls and stops chemical
reactions from taking place. When the Iodine
turned black/ blue it indicated that starch was
present in the leaves.
Watch this YouTube clip using
iodine to test a leaf for starch
https://goo.gl/phJO2A
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GRADE 8 TERM 1
NATURAL SCIENCES
PHOTOSYNTHESIS
Activity 2
1. Explain the difference between an independent and dependent variable. Give an example of
each.
2. Name and explain the six steps in carrying out a practical investigation.
3. Write a report on the investigation of whether green leaves produce starch by using the following
headings, hypothesis, apparatus, method, results, and conclusion.
Hypothesis Apparatus Method Results Conclusion © e-classroom 2015 5
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GRADE 8 TERM 1
NATURAL SCIENCES
PHOTOSYNTHESIS
Respiration
Respiration is when glucose is broken down and energy is
released within a cell.
We need energy to survive!
Green plants produce glucose during photosynthesis and
energy is released from the food that is eaten.
Food contains energy (potential energy). This energy can be
released from food by a series of chemical reactions. Again this
process is called respiration.
Respiration (in all living organisms) is the process by which
energy is released from food in a series of chemical reactions
Glucose + oxygen
energy + carbon dioxide + water
• Oxygen is needed for respiration.
• Plants absorb oxygen from the atmosphere.
• During respiration, glucose and oxygen is broken down to
produce energy, carbon dioxide and water.
For example: A cow eats the grass. Grass contains starch made
during photosynthesis. The grass is digested and glucose is
released into the blood stream. The cow breathes in oxygen
(produced by the plant) and uses the energy that is released
by respiration for growth and essential life processes. The cow
breathes out carbon dioxide which the plant takes in, and uses
the carbon to make sugar molecules.
Watch this YouTube clip about
the process of respiration in
plants.
Photosynthesis:
plants use the energy from the sun to make food.
https://goo.gl/qZXYDQ
Respiration:
food is broken down and energy is released.
Activity 3
1. What is respiration?
2. Write the formula for respiration in words.
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GRADE 8 TERM 1
NATURAL SCIENCES
PHOTOSYNTHESIS
3. What is the difference between respiration and photosynthesis and explain how they are related?
4.
What are A and B?
What are C and D?
Experiment
Testing for the presence of carbon dioxide
in exhaled air using clear lime water.
Hypothesis: Clear lime water turns milky in the presence of
carbon dioxide.
Apparatus: clear lime water (a solution made
from calcium hydroxide and water), a beaker,
straw
Straw
Lime water
Method: Place the lime water in a beaker.
Exhale through a straw until bubbles float to the surface.
Results: Clear lime water turns milky when carbon dioxide is dissolved in
it. The carbon dioxide reacts with calcium hydroxide to form calcium,
carbonate. Calcium carbonate is what makes the solution cloudy or
milky.
Activity 4
1. Name the gas that turns clear lime water cloudy?
2. Explain why the lime water turns cloudy.
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