Exploring cells under the microscope

An introduction to microscopes

The history of the invention and use of microscopes for examining living cells is a little grey. There were a number of inventors who were working with lens and successfully managed to magnify their specimens until the individual cells were visible when see through their microscopes.

Two of the more recognised inventors of the microscope are Robert Hook and Antoni van Leeuwenhock.

Robert Hooke

1635 - 1703

He was also responsible for the "Hooke's law" in physics.

Hooke microscope

Using the Hooke microscope he invented, he was able to observe many details that were previously hidden to the naked eye. He published his observations in a booked titled "Micrographia".

discoverer of "cells"

1665: first to discover "cells". In reality, he observed the dead cell walls of plant cells as seen in his biological drawing.

Antoni van Leeuwenhock

1632 - 1723

He was a self-taught man in science, sometimes known as the "father of microbiology".

Leeuwenhoek’s microscope

He was a lens maker, and the reason his microscope was so powerful was because of the high quality spherical lens he used.

He did not share with anyone the secret to how he made his lens.

first to witness living cells

Using the microscope he invented, he was first to witness and describe living cells observed under the microscope.

1673: observed human cells including blood cells and sperm cells; unicellular organisms like protozoa and bacteria.

light microscope

This usually costs a few hundred dollars upwards to a thousand dollars.

The light microscope allows users to prepare wet mount slides to view cells under relatively high magnification.

Cell structures that are not visible under the light microscope include the endomembrane system, mitochondria and vesicles.

electron microscope

Google states that electron microscopes cost approximately 1 million dollars, thus they are not readily available for use.

There are two main categories of electron microscopes - the transmission EM (TEM) and the scanning EM (SEM).

TEM images are 2D, and usually provide details on the internal composition of a sample.

SEM images usually feature the surfaces of samples, and tend to have a more 3D look.

The rest of the images on this page feature photos of cells observed either by me or my students using the light microscope in the Biology laboratory.

Plasmolysis in hydrilla cells

These images was taken using a handphone camera by one of my ex students when they placed hydrilla leaves in a concentrated salt solution.

No staining was required as cells were filled with chloroplasts. Cell wall remained intact, while the cell membrane pulled away from the cell wall during plasmolysis.

Occasionally it may be a little challenging to focus on individual hydrilla cells as the leaf itself consists of a few layers of cells. The goal is to allow the microscope to focus on one layer of cells so that the cell contents are visible.

Plasmolysis in Rhoeo discolor cells

Rhoeo discolor, more commonly known as "Moses in the cradle" plant was used in this experiment. The lower epidermis of the Rhoeo discolor leaves are normally purple in colour.

The lower epidermis was peeled off and placed in a concentrated salt solution to observe plasmolysis. No staining was required as the cell was filled with purple pigment.

Similar to the hydrilla cells, the cell wall maintained its shape while the cell membrane pulled away from the cell wall during plasmolysis.

a pair of guard cells create a stoma

A pair of guard cells will create an opening called stoma (plural: stomata). The pair of guard cells control the size of the stoma, thus controlling the amount of gases entering and leaving the leaf.

The relative amounts of respiration and photosynthesis determine the direction in which oxygen and carbon dioxide enter or leave the leaf.

guard cells on lower epidermis

Guard cells tend to be located on the lower epidermis of leaves (as compared to the upper epidermis).

Transpiration is the loss of water vapour mainly via the stomata; it occurs all the time as long as the stomata are open.

This reduces the amount of transpiration occurring to reduce the risk of the plant wilting due to excessive water loss.

guard cells contain chloroplasts

Epidermal cells do not contain chloroplasts. However, chloroplasts are found in guard cells.

This allows photosynthesis to occur in guard cells, which indirectly encourages water molecules to enter the cell via osmosis.

Turgid guard cells will allow the stoma to open wider.

Observing mitosis

Mitosis is a type of nuclear division that produces genetically identical daughter nuclei. It is typically subdivided into 4 (or 5) phases - PMAT.

Observable features of each of these stages under the light microscope include:

Prophase (early and late): chromatin condenses into chromosomes (arranged randomly)
Metaphase: chromosomes align at metaphase plate (equator of cell)
Anaphase: separation of sister chromatids, sister chromatids (now known as sister chromosomes) move to opposite poles of the cell (the moving is not observable)
Telophase: chromosomes decondense into chromatin, nuclear envelop reforms. Usually you will observe a single cell with two nuclear envelopes - this means that telophase is taking place, while cytokinesis has yet to occur (or is only beginning to occur).

Normally garlic or onion bulbs are sprouted, roots will grow. When the roots are growing, this implies active cell division (thus mitosis) is occurring as there will be an increase in cell number as the roots increase in size. The region of the root where most of the cell division occurs is the root tip, meaning the ends or the tips of the root.

In order to observe a large number of cells undergoing mitosis, it is best to observe the root tip of the roots and not other parts of the roots.

The following images were taken and shared with me by my students.

mitosis in root tip cells

The root tip is the region of the root that actively undergoes cell division when the root is growing.

This region is where you will find the largest proportion of cells at various stages of mitosis.

Even so, note that majority of the cells are still at interphase even at the root tip.

telophase

Two nuclear envelopes are beginning to reform within a single cell.

This means cytokinesis, where the cell plate formation is either in the early stages or has yet to take place.

metaphase

Chromosomes align at the equator during metaphase.

To be very precise, it is the centromere region of the chromosomes that align at the equator.

The ends of the sister chromatids are floating about, resulting in this classic metaphase look.

anaphase

Sister chromatids separate and move to opposite poles of the cell.

They can be called sister chromosomes now.

Observing pollen grains (from the liliy flower)

When the anthers are mature, they will split open, thus releasing the pollen grains. Students caught a few of these pollen grains and prepared a wet mount to examine the external features of the lily pollen grain.

single pollen grain, with surface relatively rough too.

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