Unit A Reproduction

3B
Investigation
Examining Seeds
Recall, from Grade 8 science, that the chloroplasts in
the leaves of a plant produce starch. This starch is
used by the plant as a food supply. Where does a seed
get the energy to grow the first shoots and leaves?
Seeds are part of the diet of a variety of animals,
including humans. Starch is one molecule that is
produced by plants that animals eat. Iodine is a
chemical that turns a blue-black colour when starch
is present.
Question
Does a plant seed contain other components, in
addition to the embryo?
Prediction
Write a prediction about what you will find inside
plant seeds.
Experimental Design
In this investigation, you will examine bean and corn
seeds and identify the structures of the embryo. You
will also identify structures that may contain starch, a
common plant food molecule. You will test the seeds
with iodine to determine the presence of starch.
Materials
• safety goggles
• disposable gloves
• apron
• dry lima-bean seeds
• dissecting needle
• magnifier (lens or loupe) or dissecting microscope
• pipette
• iodine solution
• corn seeds soaked in water for 24 h
• forceps
• scalpel
INQUIRY SKILLS
Questioning
Hypothesizing
Predicting
Planning
Procedure
Conducting
Recording
Analyzing
Evaluating
Synthesizing
Communicating
Exercise care and caution when using sharp dissecting
needles and scalpels.
Wear your safety goggles, gloves, and apron throughout
this investigation. Iodine irritates eyes and skin, and
may stain clothing.
1. Obtain a dry bean seed, and a bean seed that has
been soaked in water for 24 h. Use Figure 1 to
help you identify the various parts of the seed.
Compare the appearance of the two seeds.
Record your observations.
bean seed
(front view)
bean seed
(side view)
Figure 1 Bean seed anatomy
bean seed
(split open)
cotyledon scar
epicotyl
hypocotyl
radicle
cotyledon
embryo
2. Use your fingers to gently remove the seed coat
from the soaked bean seed.
3. Carefully insert the dissecting needle into the
joint between the two seed halves.
4. Locate the parts of the embryo, and examine
them with a magnifier or the dissecting microscope.
Draw and label a diagram of the embryo.
5. Using a pipette, carefully add individual drops
of iodine to various parts of the embryo. On
your diagram, use a coloured pencil to indicate
where the iodine changed colour.
6. With a magnifier, examine a kernel of corn that
has been soaked in water. Look for the embryo
(Figure 2). On one of the flat sides, you should
see a pale oval area with a narrow ridge along
100 Unit A Reproduction
NEL