Course: Science 8 / Name: / Date:
Topic: Microscope images of cells (diatoms) / Unit: Cells and Systems / Grade: 8
  1. Purpose
use instruments effectively and accurately for collecting data (e.g., use a microscope to produce a clear image of cells)
estimate measurements (e.g., estimate the size of an object viewed under a microscope)
observe and record data, and produce simple line drawings (e.g., draw cells and organisms)
organize data, using a format that is appropriate to the task or experiment (e.g., compare the structure and function of two or more organisms, using charts and drawings)

SEMLessonDiatoms

B. Background / B. Displays/Resources
Phytoplankton are microscopic, single-celled plants that are found in almost every aquatic environment including fresh and marine waters and even moist soils. As producers (autotrophs), they form the basis of all aquatic food chains, giving off oxygen as a by-product of photosynthesis. The oceans produce 20 BILLION tons of phytoplankton per year which produce 65-75% of the world's oxygen.
Diatomsare one of the most common types of phytoplankton. A characteristic feature of these single-celled algae is that they are encased within a unique cell wall made of silicathat is almost like a glass house, thus allowing light to pass through to the chloroplast for photosynthesis. The construction of the cell wall (called the frustule) consists of two valves that fit into each other like a little pill box, with an amazing diversity in form that show complex shapes, sizes, and patterns. Some have elaborate ornamentation or small projections to bolster the plant's ability to floatin the water closer to the sunlight.
Due to the wide diversity in form, beautiful symmetry and exquisite design of diatom frustules, the cells are ideal subjects for study under the microscope. About a thousand times smaller than a pinhead, diatoms are commonly between 20-200 microns in length, and due to the intricate markings of certain species they are even used in testing the resolving power of microscope lens.
Many species of diatoms are restricted to certain regions with specific pH, salinity, and nutrient levels. When nutrient and light conditions are right, all diatoms are able to bloom - reproduce very quickly into huge numbers. Knowing what species grow where, scientists can use diatom communities as a tool for monitoring environmental conditions and are being used to monitor everything from water quality, effects of acid rain, and global climate change.Due to their sensitivity to pollutants, diatoms have frequently been used to evaluate the impact of domestic sewage or industrial waste on the aquatic environment. In a non-polluted environment there will usually be a very high diversity of kinds of different diatoms, while a polluted environment will show a very low diversity with only a few different kinds of diatoms. And because the cell walls of diatoms are composed of silicon, they are preserved in lake and ocean sediments. Thus, their fossils can be used to reconstruct past environmental conditions, such as climatic records, over time.
Under certain conditions great concentrations of diatom frustules can accumulate and be preservedenough to form sediments. Rock that is largely composed of diatoms is called diatomite. These deposits are of economic benefit with diatomite used commercially in high quality chemical filters, sugar refining, toothpaste,fireproof insulation, silver polish, paint, and as an abrasive agent in flea powder. / There are two basic body shapes of diatoms. Centric (round) and pennate (thin ellipse).


Scanning electron micrograph of centric diatom. Diameter of frustrule is ~10 μm.


Scanning electron micrograph of pennate diatom 5000X magnification.
  1. Introduction
  1. How could you distinguish between a plant cell and an animal cell?
  1. Can you use the naked eye to see cells?
  1. Can you use a light microscope to see cells?
  1. What do you think you could see using an scanning electron microscope?

  1. Clarifying
Living systems at all levels of organization (unicellular to multicellular) demonstrate the complementary nature of structure and function. Scientists refer to the overall shape of the organism as their “morphology”. There is a great deal of diversity in the morphology of cells from different organisms (plant, animal, bacterial. Cells are so small, it is difficult to observe cell structure without a microscope.
In this activity, you will view the general shape of single-celled plant cells called diatoms using a scanning electron microscope (SEM). Using the images produced, students will estimate the size of the cells and produce a detailed scientific drawing of the organism.
  1. Labwork
Sample of diatoms - scraping algal slime from the surfaces of rocks and pulling a fine mesh net through water are two methods for collecting these microscopic organisms. The best way to make the beautiful structures of the frustule visible is to remove the content from the cell. Hydrogen peroxide can be used for this. But it is also possible to find empty frustules of dead diatoms. In this lab activity we will be looking for the skeletal remains of diatoms on sand collected from a local freshwater lake.Please go to the listed website to find your samples.
Data Collection:
You will need to save a series of images (jpeg files) that can be used to create a composite of low to high magnification images similar to the example below:

Using the highest magnification image, make a detailed scientific drawing of a single diatom or a group of diatoms. Label the pores (using a key provided by your instructor, and be sure to indicate magnification).
Using the scale bar at the bottom left of the highest magnification image, estimate the size of the diatom in micrometers. Indicate the size of a single diatom on your drawing.
Analysis:
  1. Identify two life functions carried out by diatoms.
  1. How are diatoms adapted for making their own food?
  1. Although images are in black and white, what color(s) would you expect to see and why? Note: The colour of the diatom chloroplast is actually yellow-brown instead of the green we know of other creatures that use light as a source for energy.
  1. Identify any additional adaptations the diatom may have related to its shape and ornamentation.
/ You will need to go to this website to complete this activity: King’s University URL
  1. Summary
Could a magnifying glass or a laboratory microscope have been just as effective?
What other tests might have been more economic? more time-efficient? less technologically dependent? more environmentally friendly? less collaborative? less fun?
  1. Solitary Practice/Homework
Diatomaceous earth is a naturally occurring siliceous mineral compound made from the microscopic fossilized remains of diatoms. These plants have been part of the earth’s ecology since prehistoric times. It is believed that 30 million years ago the diatoms built up into deep, chalky deposits of diatomite.The fossilized skeleton of the microscopic diatoms are mined and ground up to a fine, white, crystalline powder. At the macro-scale, diatomaceous earth looks and feels like talcum powder, yet at the micro-scale each particle has sharp edges. Lightweight, gritty, and porous, diatomaceous earth finds a surprising array of uses.
a. Research uses of diatomaceous earth and how it is effective. / Diatomaceous earth


Scanning Electron Microscope Image of Diatoms (1500X Mag)


  1. Review
Diatoms are eukaryotic phytoplankton that play a large role in the global carbon cycle. Each spring, when nutrient levels, light levels, and temperatures are high, diatom populations soar across the world causing blooms. During these blooms, increased photosynthesis leads diatoms to sequester huge amounts of CO2.
CO2 levels have risen dramatically since the industrial revolution and blooms play an important role in sequestering atmospheric that CO2, but little is known about the specific mechanisms of these blooms, and how their ability to sequester CO2 will change as atmospheric levels continue to rise. Thus, it’s important for us to understand how diatoms bloom and what sort of conditions are required for their growth, in order for us to make accurate predictions about the future of the global carbon cycle and climate.
Diatoms also rely on Nitrogen and Phosphorus for their growth, and thus play a role in nitrogen and phosphorus cycles. Nitrogen is required to make amino acids – the building blocks of proteins. Phosphorus is required for DNA, while they use silica to make their glass shells. Samples of marine phytoplankton communities have shown that Nitrogen, Phosphorus and Silica exist in the ratio N:P:Si: 16:1:15.
a. Design an experiment that studies how diatoms grow in varying nutrient and light conditions.

SEMLessonTableSaltUse