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Applications of microscopy in science education: gifted youth, public school, and the next-generation science standards (NGSS)


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Microscopy is not specifically mentioned in the Next Generation Science Standards (NGSS), and consequently secondary education limits its use to learning parts, procedures, and observing fixed specimen slides. However, when alternative approaches (See Section IV in this paper) are encouraged, microscopy provides opportunities for hands-on learning, engagement, use of models, and gaining a sense of size, scale, and hierarchical organisation. This article reviews living organism- and ecosystem-based microscopy originally designed for gifted and talented education, and how it could support the NGSS Life Science Framework. The paper begins with a review of curriculum, then discusses (1) five ongoing microscope applications relevant to the NGSS, including mini-ponds modelling ecosystem-organism functions; (2) data from pre- and post-testing as a measure of comprehensive learning; and, (3) a culminating communication project/exhibit on pond life, environmental conditions, and pollution effects.
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Journal of Biological Education
ISSN: 0021-9266 (Print) 2157-6009 (Online) Journal homepage:
Applications of microscopy in science education:
gifted youth, public school, and the next-
generation science standards (NGSS)
Joel I. Cohen
To cite this article: Joel I. Cohen (2020): Applications of microscopy in science education: gifted
youth, public school, and the next-generation science standards (NGSS), Journal of Biological
Education, DOI: 10.1080/00219266.2020.1720772
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Published online: 28 Jan 2020.
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Applications of microscopy in science education: gifted youth,
public school, and the next-generation science standards (NGSS)
Joel I. Cohen
T. W. Pyle Middle School, Montgomery County Public Schools Maryland (MCPSMD), Bethesda, MD, USA
Microscopy is not specically mentioned in the Next Generation Science
Standards (NGSS), and consequently secondary education limits its use to
learning parts, procedures, and observing xed specimen slides. However,
when alternative approaches (See Section IV in this paper) are encour-
aged, microscopy provides opportunities for hands-on learning, engage-
ment, use of models, and gaining a sense of size, scale, and hierarchical
organisation. This article reviews living organism- and ecosystem-based
microscopy originally designed for gifted and talented education, and
how it could support the NGSS Life Science Framework. The paper begins
with a review of curriculum, then discusses (1) ve ongoing microscope
applications relevant to the NGSS, including mini-ponds modelling eco-
system-organism functions; (2) data from pre- and post-testing as
a measure of comprehensive learning; and, (3) a culminating communica-
tion project/exhibit on pond life, environmental conditions, and pollution
Gifted and talented; biology
education; protists;
pollution; secondary
education; NGSS; Microscopy
Computer science is no more about computers than astronomy is about telescopes, biology is about micro-
scopes or chemistry is about beakers and test tubes. Science is not about tools. It is about how we use them, and
what we nd out when we do. Dijkstra (2000)
Biology teachers face numerous obstacles when introducing lessons dependent on the use of living
specimens in the classroom. By adopting such approaches, teachers comply with the mounting
pressures and constraints imposed on their curriculum (Wright and Boggs 2002), including the
time needed to meet state educational standards. For these reasons, many secondary and under-
graduate courses rely on dry mount specimen slides to teach introductory microscopy, with
students limited to basic observations and learning only basic operations.
This article follows one describing a cellular encounter (Cohen 2014) as one means to expand
principles of the NGSS while further challenging students in their education. Each paper provides
the means to work in extendersand accelerated activity while still covering the basics.
This paper contrasts experiences with teaching microscopy in two settings: (1) over 10 years of
teaching public-school seventh-grade biology classes, and (2) 7 years teaching a three-week summer
course for gifted and talented students. Over this time, the secondary course adopted standards,
homogenised lessons, common tasks and end-of-quarter assignments (MDE 2011;https://www. The microscopes use was limited to its opera-
tion, one procedural assessment, and viewing of xed specimen slides to distinguish between uni
CONTACT Joel I. Cohen
© 2020 Royal Society of Biology
and multicellular life. Elodea was the only live specimen used for viewing chloroplasts and a house
plant for viewing stomata, with no further opportunities for discovery or investigation.
While the NGSS are limiting in terms of advancing microscopy to any great degree (NGSS
LeadStates, 2013), other approaches recognise opportunities from expanding its use in biology. For
example, Storksdick (2015) sees using microscopy as a way to further the vision for science
education reform.He notes that the microscope allows exploration of the unseen, and aids in the
exploration of natural phenomena, facilitating labs that touch on the eight science and engineering
practices identied by NGSS (Table 1).
While states implementing the framework have noted that NGSS focuses much more on doing
science with real-world application as opposed to only memorizing content,(Fogarty 2016), states
and school systems seem unaware of professional positions for those trained in microscopy.
Scientists have developed new staining techniques and are using microscopes beyond the com-
pound light model. These new approaches can scientically illustrate and create images used to
diagnose illness by capturing organisms in what appears as an almost artistic format (Lutkoski
2019) so unique that images hang in art galleries.
Microscopes are also used to conrm the presence or absence of specic environmental patho-
gens detected by biolms. Colonies of bacteria begin to grow on the biolm strips which must later
be identied. This conrmation of a particular bacterium is made almost exclusively through the
microscope (Henk 2003).
Finally, microscopy jobs are growing and specialising. The box below shows one such position.
Compiling these ads would give students a real-world feel for opportunities that do not require
extensive post-graduate degrees. Thus, competency in microscopy, along with other biological
content, can lead to practical work outcomes.
The Analytical Instrumentation Facility (AIF) at NC State University is seeking an expert stascientist to lead
its eorts in biological electron microscopy and associated sample preparation techniques. The AIF is
a leading microscopy . . . .
The course developed for John Hopkins Centre for Talented Youth (CTY) has also changed from
previous approaches relying on prepared slides and a nal week focusing on DNA to one of
living specimens and objects of a size where compound light microscopes have a comparative
advantage. The course is titled Through the Microscope (SCOP), Session II, and employs the
microscope as a tool to explore, compare and contrast organisms representing the six kingdoms
of life.
The six kingdoms selected are consistent with the three-domain, six-kingdom classication
system that arose after the discoveries of Dr. Carl Woese, Kandler, and Wheelis (1990), regarding
distinctions between what have been termed the Archaea, Bacteria and Eukarya domains. Within
these domains, especially due to the separation of the Archaea from Bacteria, six kingdoms are
used instead of ve, as follows: Archaebacteria, Eubacteria, Protista, Fungi, Plantae, and Animalia.
This system is now the basis for classication in standard American textbooks (See for example,
Reece et al. 2014; Coolidge-Stoltz et al. 2009). Details of selected course activities are presented
subsequently, along with others available from the author in a companion workbook (Cohen
Table 1. Eight NGSS science and engineering practices for the classroom.
(1) Asking Questions and Dening Problems
(2) Developing and Using Models
(3) Planning and Carrying Out Investigations.
(4) Analysing and Interpreting Data
(5) Using Mathematics and Computational Thinking.
(6) Constructing Explanations and Designing Solutions
(7) Engaging in Argument from Evidence
(8) Obtaining, evaluating and communicating information.
Plausible opportunities to support NGSS core ideas through microscopy
Searching the NGSS web site ( for micro-
scopes or microscopy does not reveal any hits.As already noted by Storksdick (2015), theoretically
though, there seem to be several areas where students could extend their understanding of NGSS
disciplines in conjunction with microscopic laboratories. Table 2 identies ve component ideas of
seeming compatibility and mutual interest with the approaches described in this article. These ve
component ideas, out of a total of 14, that have the greatest potential to benet from the activities
described, when adjusted for age and grade level.
Opportunities for change
Introduction. In this section, ongoing approaches for using microscopy are considered in regard to
NGSS core ideas considered above. Examples benet from changes made over the time spent
teaching Through the Microscope (SCOP), oered by John HopkinsCentre for Talented Youth
(CTY). The curricular approaches and activities described were designed by the author, and used in
agreement with the courses administration provided by CTY sta(
The course is taught over a three-week period, beginning with the fundamentals of scale and
scope, followed by microscope theory, and operational procedures and safety. Special attention is
paid to Antonie van Leeuwenhoek, and his drawings made with the simple microscope,as they
were so striking, owing to the minuteness of the structures that he dealt with and the accuracy of his
observations,(Clay and Court 1975). Next, students begin studying living specimen growth and
development of organisms representing each of the kingdoms of life. Student preparation of
mounted slides and a culminating project on freshwater pond life and pollution follow.
This paper presents an analysis of some of these experiences, organisms selected, laboratory
objectives, and their culminating posters and presentations. The course now uses the microscope
to enter a world requiring the close observation of organisms their origins, their evolution,
Table 2. NGSS core ideas, components and ve possible areas of synergy with microscope applications.
NGSS Core Idea Core Idea: Details Component Ideas
Ideas Complementary to
LS1: Molecules to
Structures and processes LS1.A. Structure and function
LS1B. Growth and development of
LS1.C Matter and energy ow X
LS1.D Information processing X
LS2 Ecosystems Interactions, energy and
Interdependent relationships in ecosystems
Cycles of matter and energy transfer in
LS2.C: Ecosystem dynamics, functioning and
LS2.D: Social interactions and Group
LS3 Heredity Inheritance and Variation of
LS3.A: Inheritance of traits X
LS3.B: Variation of traits X
LS4 Biological
Unity and Diversity LS4.A: Evidence of common ancestry and
LS4.B: Natural selection X
LS4.C: Adaptation X
LS4.D: Biodiversity and humans
their behaviour, and their relationships with other species,(Wilcove and Eisner 2000; Green
It is intentionally designed to mirror the introduction to shore life provided by Rachel Carson in
her beginning to The Edge of the Sea,To understand the life of the shore, it is not enough to pick up
an empty shell and say This is a murex,or That is an angel wing.True understanding demands
intuitive comprehension of the whole life of the creature that once inhabited this empty shell: how it
survived amid surf and storms, what were its enemies, how it found food and reproduces its kind,
what were its relations to the particular sea world in which it lived,(Carson 1955).
The course is designed for a class of 12 advanced fth to fth graders, but it can be modied to t
32 as per public secondary school classes, with objectives set to high school standards. The relatively
short-term maintenance of a fresh water pond, stocked with protists and other organisms, can serve
as a model system for studying an organisms interaction with environmental concerns, including
diminished biodiversity.
Some of the key topics covered by the course curriculum include: understanding structure and
function of the cell and selected organelles; interactions between living organisms and their
environment; key vocabulary words; plant development beginning with seed germination; and
a culminating exhibitfeaturing a group-made pond poster. The course incorporates the micro-
scopes ability to illustrate various concepts necessary for learning and examining material germane
to these topics.
Many of these items would directly support long-term quarterly requests for proposals (RFA),
something now fashionable in conjunction with the NGSS. Success in students grasping complex
content in a short period is demonstrated in numerous ways throughout the course, but for this
paper, cumulative knowledge gained, as measured by the pre/post assessment is used, as seen in
Section V.
The following elements of the SCOP curriculum are a limited sample seemingly relevant to
NGSS component ideas, as shown in Table 2.
Use of protists
Aworld in a drop of water.So thought Anton van Leeuwenhoek, as he observed and drew his tiny
animalcules,(Silverstein and Silverstein 1969) for he was a person in the habit of examining
everything under the sun,(Grave 1984). Now, these are classied as protists, described as mostly
unicellular, widely divergent organisms with a nucleus. The complexity of their cellular structure,
some found in no other type of organism, is remarkable, being organisms that are neither plant,
animal or fungi. Because of their unique qualities, SCOP students examine a number of protists
each year. They serve as a microcosm of lifes diversity and are excellent when doing compare/
contrast analysis with specimens of the plant and animal kingdoms.
Thus, for this SCOP course, the microscope becomes that tool, when mastered, becomes an
extension of ones eye into the unknown, harbouring the potential for remarkable sightings, as if to
one having eyes poor of sight following a gift of a pair of glasses. The protists included in the course
are chosen to be representative of nutrition groups, including (a) heterotrophic or animal-like
protists (protozoa) and (b) autotrophic organisms, which are plant-like protists. The nal group,
decomposers/parasites, is not included to date.
Laboratory skills relevant to real-world microscopy
Many of the coursesspecimens are aquatic. Students learned to prepare samples from aqueous
media, sorting out the actual specimens from debris in the solution. Protist specimens include
Stentor, Spirogyra, Volvox, Euglena, Paramecium, Diatoms, Protozoa, seaweed, and Amoeba.
Forams (foraminifera) are also included, although only through xed slides at this time. With all
these Protists available, each day the students anticipated dipping their pipettes and gathering up
a few drops from the vials of pond water containing individual organisms. They learned that no
matter the label on the vial, other organisms could also dart across their eld of view. As their skills
matured, it mattered little whether they found the organism selected for that days study or
something entirely dierent that surprised them. Gradually that worry of nding the rightspeci-
men eased and they learned to pursue the names of whatever they found.
New techniques for mounting and slide preparation are available for school settings (see for
example, Dioni 2014). SCOP students became versed in making wet mounts, well mounts, and
permanent slides with xative. They were condent in their searches for live organisms, bringing
them into their plastic pipettes and then able to nd them again under the microscope. They
consulted with me as to whether the specimen would make a suitable permanent slide. Considering
the minute size of these organisms, these were signicant accomplishments for their age group.
Students also learn techniques for safely acquiring live organisms, and depositing on slides for
viewing, including the green hydra, another microscopic animal, a creature of Herculean adventure.
To the students, it was a colossal microorganism with tentacles to trap prey and draw it into its
mouth cavity, making it seem all too similar to the nine headed monster that Hercules defeated.
I would open the container holding the live specimens, packaged with algae for food, the hydra
moving around in about 20 ml of water.
The students rst viewed them through the stereoscopic dissecting microscope, reaching powers of
After a quick observation, the hunt began, with students watching for them to appear, and then carefully
pulling them up with their pipette, and depositing the drop or two of pond water on the slide.
Beginnings of life and cell formation
While the issue of common ancestry and evolution was only touched in SCOP, an explanation for
common ancestry is prominent in the NGSS. For SCOP, how cellular life began, in terms of
formation of a membrane, and from there, chemical reactions occurring inside the membrane,
could lead to a primordial cell. As such, the formation of a membrane, and the ability to see it from
purely chemical processes was of importance to SCOP, especially as students came to the course
with USB drives to record these primitive membranes (See Figure 1 as an example).
Figure 1. Simple membranes produced from chemical reactions by student with photo taken on digital microscope. Image is
Creating freshwater ponds
What eventually become mini-ponds begin by adding 2 containers of Carolina Brand Mystery Mix
to 1.5 gallons of spring water in a 10 gallon aquarium. After 1 week of maturation, a second batch of
organisms (Carolina Brand Review Set) was added to the aquarium. By mid-second week, a third
Carolina product was added (Pond Mixture Living) to the aquarium plus .5 gallon spring water. This
total was then divided to form 12 mini-ponds, using 250 ml glass specimen jars lled half way. The
left-over was kept in the aquarium, in case of spills or evaporation. As the ponds matured, new
organisms entered growth and development, all observed by the students as they learned to sample
their ponds.
Organisms sampled include Paramecium, Euglena, Volvox, Hydra, Planaria, Diatoms, various algae,
Daphnia and others as available. Separate samples were kept of tardigrades, Didinium, Cyclops,and
Stentor. Students studied these organisms to understand their means of movement, digestion, growth and
development, and reproduction. This was accomplished by preparation of fresh mount slides viewed
under simple digital microscope where still shots and video clips recorded on USB drives.
By end of 3 weeks, students could successfully move microorganisms from ponds to slides; take
pictures; estimate length or width; and name them correctly. Examples of pictures taken by students
are seen in Figures 2 (cyclops) and 3(tardigrade). Taken together, these outcomes could supple-
ment the limited work done on xed slide specimens required by Montgomery county curriculum.
Metric scale for microorganisms
The objects and their dimensions in metric scale, as seen in Table 3, are but a few of those used in
SCOP to congure a metric scale. This is constructed on special architect paper, and goes from 0 to
and a second range from 10° to 10
. Numerous images with their scale are made to place
upon the scale, so that when done there are two parallel lines, one for the range of positive
exponential scientic notation line above for the negative exponents or those objects of decreasing
size. Further details on this available from the author.
Figure 2. The Cyclops female with egg sacs, a member of the Crustacea, representative of the Animal kingdom. 100x. Slide mount
and photo by student.
Pre and post testing: measuring gain in cumulative knowledge
Over the past 7 years, the required pre- and post-course test has been modied to better elicit
student responses from lower to higher order thinking. In 2019, it had a total point value of 38, and
ranges from microscope procedures, scale of size, and optics, to questions requiring extrapolation as
to use of microscopes and pond organisms. CTY administration requires the collection of before
and after data to evaluate its course, students and instructor. The data from 2012 to 2019 are shown
in Table 4. Results indicate a sizeable increase in breadth and depth of knowledge from beginning to
end of the course.
Figure 3. A water bear, or Tardigrade, showing numerous body functions and carrying eggs in two internal sacks. X100. Student
prepared mount and photograph.
Table 3. Illustrative table showing approach taken for lessons on scope and scale, featuring scientic notation, metric
measurements, and objects to cut and paste.
Object Measured (Metric Units) and Placed on Scale Scientic Notation Size in Metric units
Height: students measure 10° 1.5 x 10° = 1.5 metres
Length: T. rex 10
1.2 x 10
= 1.5 decametre
Height: Empire State Building 10
4.3 x 10
metres = 4.3 hectometre
Height: Mt. Everest 10
8.8 x 10
metres = 8.8 kilometres
Hand: students measure width 10
1.3 x 10
metres = 1.3 decimetres
Finger: students measure length 10
1.2 x 10
metres = 1.2 centimetres
Organ: human heart 10
10 x 10
metres = 10 centimetres
Microorganism: water bear (tardigrade) 10
1.5 x 10
metres =1.5 nanometers
Table 4. Seven years of pre and post-testing data for the 3-week summer course, through the microscope.
Testing Year
# of stu-
# of Points
per test
Pre Test Score:
Class Average
Post test
Score: Class
Average Point
Value Increase
Percentage Post-
Percentage Pre-
2019 12 38 26 34 8 90 67
2018 11 37 17 30 13 81 57
2017 9 37 21 34 13 92 57
2015 13 36 18 26 8 72 50
2014 12 36 18 31 13 86 50
2013 12 34 17 27 10 79 50
2012 12 33 19 28 9 85 58
The test is taken by each of the 12 participating students, with an average age of 9 years old, an
average of seven boys and ve girls, each student having scored above grade level on tests
administered by John Hopkins before admittance.
Over the 7 years of available data, the average of all pre-test scores was 56%, followed 3 weeks later
with the post-test, having an average of 84%. This is a 28% increase by end of the course. In 3 weeks,
students have helped create a communityin the lab and focus on each topic, given the extra time
and resources available. The nal example of student work, as mentioned in the abstract, comes
from the presentation and construction of three freshwater pond posters.
While the trends in the pre/post data are evident, gains could be attributed to other factors
besides the interventions mentioned. To ensure a fair evaluation, the same test was used in both
instances. However, in an attempt to enhance validity, the pre-test was given in the second hour of
the rst day and students did not see the test again until the next to last day of the course. For the
sake of comparison, one might compare scores from Session I, having a totally dierent curriculum,
as compared to the curriculum and data described here. However, one teacher would not have
access to data evaluating another teacher.
Culminating pond poster: obtaining, evaluating and communicating information
As their technical skills matured, I focused on my second objective to teach comprehensively,
especially for the Protists, allowing them, as Rachel Carson had suggested, to understand their place
Figure 4. One section of Pond Poster emphasising tardigrade, planaria, and eects of human pollution.
in life, not just on a glass slide, but in their natural habitat what is it like to be a paramecium, how
did they move, and who chased after them as food. To do this, we made a pond in the classroom,
their natural habitat, and regularly sampled from it. In so doing, their original focus on microscopic
life reached back out to what the macroscopic.
It is easy to overlook these predatorprey relationships, as traditional microscope instruction is
about structure and function. We dont ask what it eats, or what it is eaten by. However, to
understand an organisms place in an ecosystem, such as a pond, this is exactly what was needed.
An example of one of the ponds is shown in Figures 4 and 5, each one emphasising the placement of
two organisms and the eect of pollution on their life cycle.
As their knowledge grew, we worked on group projects, where students adopted an organism,
sought out its niche and role in the pond ecosystem, and how its structure helped ensure its survival.
We spent time in the computer lab, with books, and to observe their slides and look again for live
specimens of their organism. Soon, it was time to talk to the class about what they had learned.
Figure 5. Second section of Pond Poster emphasising the paramecium and hydra, and eects of human pollution.
The author wishes to express his appreciation to many individuals at John Hopkins CTY, who have carefully
monitored and evaluated the annual changes made in the SCOP course, allowing it to reach its present
format. Second, numerous technical specialists at Carolina Biological Supplies have provided invaluable help and
insight on many of the products used, which have made the course and organisms what it is today.
Disclosure statement
No potential conict of interest was reported by the author.
Joel I. Cohen
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div class="title">Using Microscopy for Authentic Science Teaching: A Learning Sciences Perspective - Volume 21 Issue S3 - Martin Storksdieck
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A standard part of biology curricula is a project-based assessment of cell structure and function. However, these are often individual assignments that promote little problem-solving or group learning and avoid the subject of organelle chemical interactions. I evaluate a model-based cell project designed to foster group and individual guided inquiry, and review how the project stimulates problem-solving at a cellular system level. Students begin with four organism cell types, label organelles, describe their structures, and affix chemicals produced or needed for each organelle’s function. Students simulate cell signaling, cell recognition, and transport of molecules through membranes. After describing the project, I present measures of student participation and a rubric, compare individual versus group work, and highlight future modifications, including alignment with the Next Generation Science Standard of “Structure, Function, and Information Processing.”
Full-text available
To help students develop successful strategies for learning how to learn and communicate complex information in cell biology, we developed a quarter-long cell biology class based on team projects. Each team researches a particular human disease and presents information about the cellular structure or process affected by the disease, the cellular and molecular biology of the disease, and recent research focused on understanding the cellular mechanisms of the disease process. To support effective teamwork and to help students develop collaboration skills useful for their future careers, we provide training in working in small groups. A final poster presentation, held in a public forum, summarizes what students have learned throughout the quarter. Although student satisfaction with the course is similar to that of standard lecture-based classes, a project-based class offers unique benefits to both the student and the instructor.
Molecular structures and sequences are generally more revealing of evolutionary relationships than are classical phenotypes (particularly so among microorganisms). Consequently, the basis for the definition of taxa has progressively shifted from the organismal to the cellular to the molecular level. Molecular comparisons show that life on this planet divides into three primary groupings, commonly known as the eubacteria, the archaebacteria, and the eukaryotes. The three are very dissimilar, the differences that separate them being of a more profound nature than the differences that separate typical kingdoms, such as animals and plants. Unfortunately, neither of the conventionally accepted views of the natural relationships among living systems--i.e., the five-kingdom taxonomy or the eukaryote-prokaryote dichotomy--reflects this primary tripartite division of the living world. To remedy this situation we propose that a formal system of organisms be established in which above the level of kingdom there exists a new taxon called a "domain." Life on this planet would then be seen as comprising three domains, the Bacteria, the Archaea, and the Eucarya, each containing two or more kingdoms. (The Eucarya, for example, contain Animalia, Plantae, Fungi, and a number of others yet to be defined). Although taxonomic structure within the Bacteria and Eucarya is not treated herein, Archaea is formally subdivided into the two kingdoms Euryarchaeota (encompassing the methanogens and their phenotypically diverse relatives) and Crenarchaeota (comprising the relatively tight clustering of extremely thermophilic archaebacteria, whose general phenotype appears to resemble most the ancestral phenotype of the Archaea.
Theories summarize science, tell us what to measure when we test hypotheses, and help us study nature better. Nevertheless, organisms themselves embody genetics, development, morphology, physiology and behavior, and they are the units of populations, communities and ecosystems. Biologists seek to understand organisms, their diversification and environmental relationships--not theories and experiments per se--and discoveries of new organisms and new facts about organisms reset the research cycles of hypothesis testing that underlie conceptually progressive science. I argue here that recent disagreements about the fate of natural history are thus more apparent than real and should not distract us from addressing important issues. The conservation of biodiversity requires factual knowledge of particular organisms, yet we know little or nothing about most species, and organismal diversity is often poorly represented in biological education. Accordingly, I urge those who are especially concerned with teaching and conservation to seek increased financial and curricular support for descriptive natural history, which is so fundamental to many of the applied facets of biology.
With illustrations by Bob Hines. First Edition, 256 pages
  • R Carson
Carson, R. 1955. The Edge of the Sea. London: Staples Press. With illustrations by Bob Hines. First Edition, 256 pages. Clay, R. S., and T. H. Court. 1975. The History of the Microscope. London, UK: Holland Press.
Course Workbook for through the Microscope
  • J I Cohen
Cohen, J. I. 2019. Course Workbook for through the Microscope. Baltimore, Maryland. USA: John Hopkins Copy Service.
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