Download Seed dissection lab

IB Biology / IHS
NAME: _________________________________________________
go all the way through the seed coat.
Activity: a Seed
Adapted from “Seeds of Flowering Plants,” © Allyn & Bacon
Directions: The seed of a bean plant (= a bean!) has
two cotyledons. (See Fig. 2) That makes a bean
plant a dicotyledonous plant, or dicot for short.
Other flowering plants’ seeds have only one
cotyledon, so they are called monocotyledonous
plants, or monocots. Beans are produced in a pod,
the fruit of the bean plant. Like all fruits, the pod
was once the ovary of the flower.
√ Check off the tasks below as you complete them.
1. Percent gain in mass
Prior to the activity today you should have massed a
dry bean and put it in a cup of water. Take the bean
out of the water, pat it dry, and re-mass it. Then
calculate its % gain in mass. This is the formula:
% change = (new – old)
old
x 100
In some cases a seed coat needs to be tough enough to
withstand the digestive juices of animals that eat the
seeds, carry them a distance, and then disperse them
with their wastes into a new environment!
4. The inner seed
The inner seed of a bean is made entirely of embryo.
The embryo consists of two large cotyledons
(*what we just called "seed halves") and the tiny
future plant. The cotyledons contain stored food.
Slowly and gently pull the cotyledons apart until you
feel a point of attachment break. Then, lay the two
halves flat on a paper towel, like an open book, with
the tissues of the embryo at the top.
I have separated the two cotyledons of my seed.
5. The future plant
The tiny future plant may still be attached to one of
the cotyledons, or part of it may have broken off in
step 3 when the seed coat was removed. You should
be able to see the plumule, or embryonic shoot, and
the radicle, or embryonic root. Use Neil 9e figure
38.8(a) on p. 808, and the third ¶ on p. 808, to help
you! The radicle is the first structure to emerge when
a seed germinates.
Space for calculation & answer:
2. Exterior of a bean
A bean is covered by a protective seed coat (testa).
Find the place it was attached to its pod, a scar
called the hilum. Close to the hilum is the much
smaller micropyle, the pore where the pollen tube
entered the ovule! When you soaked the seed
overnight, it imbibed water through its micropyle.
I see my seed's plumule & radicle.
6. Future leaves
On the plumule are the first true leaves of the future
plant. Use a stereoscope or hand lens to examine
and count 'em.
I count (how many?) ________ tiny future leaves.
On my
soaked bean,
I see the hilum, seed
coat, & micropyle.
7. View of a seed, without its coat, from behind.
Fig. 1
3. Seed coat
Remove the seed coat. If the two halves* of the seed
start to come apart, hold them together. Use a hand
lens or stereoscope to examine the seed coat:
I can tell that the micropyle (circle one) does/does not
I understand this diagram
enough to label it by
drawing lines to these
labels:
cotyledons
plumule
point of attachment Fig. 2
radicle
well
IB Biology / IHS
8. No endosperm. Mature dicot seeds do not
contain endosperm. The endosperm was transferred
to the embryo’s cotyledons as the seed developed in
its pod. Scratch the surface of one of the cotyledons
with a dissecting needle. Then, put a drop of
Lugol’s iodine on it. What happens? Under the
stereoscope, observe the cotyledon cells – they are
very easy to see because of the stained amyloplasts
(starch-containing plastids) within them!!
I see cotyledon cells!
The end! "Seed" you later! Hope this has "bean" fun!
NAME: _________________________________________________