ONION CELLS LAB
Lab Report
Student’s full name: Homoud Alrasheed
Teacher: Aladdin BODON
GRADE: 9 A
GLOBAL CONTEXT: Scientific and technical innovation
ATL SKILL(S): Thinking, Communication
OCTOBER 22, 2019
Aim
All living things are made up of tiny little components called cells. A cell is a basic unit of all
forms of life, but it is also the smallest living thing in the world. Cells consist of an outside
boundary called the cell membrane. Inside the cell there is a structure that consists of material
which is called the cytoplasm. A plant cell contains a cell wall in addition to the components
mentioned previously. Plant cells have distinct features and arrangement under the microscope.
The aim of this lab is to examine the structures of a typical plant cell, an onion cell. We can use
the microscope to examine the onion cells features. We aim also to investigate if the microscope’s
different magnifications have a significant role in identifying these features.
Hypothesis
If the microscope is used at 400X total magnification, then most of the major organelles will be
visible in the onion cell and they will be arranged beside each other in large groups, because the
magnification is high enough to give clear details of these cells
Variables
Variables
Independent Different microscope Changing the objective lenses give
variables magnifications different magnification of the cells
and therefore different view of the
organelles
Dependent variables Visibility of organelles Clearness and details of the
organelles varies with changing
magnification
Controlled variables Cells’ source Stays the same
Iodine solution
1
Materials
Glass microscope slides
Microscope
Plastic cover slips
Onion thin layer
Iodine solution
Methods
1. take a thin skin layer of onion
2. put the thin skin layer of onion on the slide and add a drop of iodine solution
3. put on the cover slide on top of the slide
4. examine it on the microscope
Data
The microscope revealed several cells in the onion skin layer.
Data Analysis
In this lab we used a compound microscope to look at cells. When observing the onion cell, we
noticed that the cells looked like brick structure and within the cells, small dots (the nuclei) can be
seen. When we first looked into the microscope, the microscope’s total magnification was 400X
so there were about a hundred rows of rectangular cells but as we changed magnifications, the
number of cells in the field of view decreased.
When we viewed the onion cells at 1000X total magnification, we noticed the nuclei of the cells
looked clearer and larger and we were able to study the cell with more understanding than when
we used the first magnification. The organelles that we were able to see in this type of cell were
the nucleus, the cytoplasm and the cell wall. The cell membrane is a boundary structure that
surrounds the cell. It appeared in our slides as a thin rectangle surrounding the cell. The cytoplasm
which the jellylike fluid inside the cell was also clear. Aside from the actual cells, we were able to
see air bubbles within the onion cell slide.
We stained the onion cell with iodine solution. The layers of an onion contain simple sugars
(carbohydrates) some of which are stored as starch (starch granules). Iodine tends to bind to starch,
it stains the starch granules when the two come in to contact making them visible. Iodine as a stain
allows for the little starch molecules to be visible under the microscope. Although onions are
plants, we could not see any chloroplasts in their slides. This is because of the fact that the
chloroplast necessary for photosynthesis is largely present in the leafy part of the onion, which is
2
exposed to the sun and absent in the bulb which is below ground and away from sunlight. We also
notice that the plant cells have a regular shape. This is because they have a cell wall made up of
cellulose which maintains its shape. Through more readings, I found out that compound
microscope has lesser magnification as compared to Electron microscope.
Conclusion
The stated hypothesis is somewhat correct and incorrect. It stated that all cells will be together in
a large group, which was correct. An incorrect statement in the hypothesis is that most of the
important organelles are visible through the microscope. The organelles that can be seen are the
cell wall, the cell membrane, the nucleus, and the cytoplasm. We can see those organelles due to
the fact that they are the largest organelles in the cell and also due to the dye (iodine) which brought
them out. Overall, we have learned that onion cells (plant cells) are rectangular and are always
with other plant cells and that the smaller organelles cannot be seen with just our school
microscope.
Evaluation
The method we used could have some drawbacks. One of these could happen in obtaining the
cells. As thicker cells will not allow us to have a good visibility of the cell contents. Artifacts could
also happen such as the formation of bubbles inside the mounted slides which could make a harder
viewing of the cells. Organelles that can be seen under the light microscope are mainly the nucleus,
cytoplasm, cell membrane, chloroplasts and cell wall. Technically everything else are not visible
under the light microscope, even if we use the highest magnification available on light microscope
(usually with the magnification of 1,000x) in this lab. Electron microscopes will be a better choice
for us to see these organelles since the electron microscopes has a magnification with highest
magnification to more than 200,000x.
