Diatoms in Forensic Science Quiz Crafted
by-
Dr. Munish Kr. Mishra
Assistant
Professor, Department of Forensic Science,
Sam
Higginbottom University of Agriculture,
Technology and Sciences (SHUATS),
Prayagraj
Introduction to Diatoms
Diatoms (Bacillariophyceae) are
unicellular, photosynthetic, autotrophic organisms that have a characteristic
structurefrustules, comprising two thecas i.e. silica cell walls. Each frustule
is made up of two halves which are known as valves, one of which is slightly
smaller than the other and fit together one inside the other. Depending on the
shape of the frustule, the diatoms are subdivided into two major
orders-Centrales and Pennales. The Centrales are radially symmetric and the
Pennales have bilateral symmetry. The diatoms are a highly diverse taxon,
comprising more than 200000 species. Diatoms generally range in size from
2-200μm and are composed of a cell wall comprising silica. This siliceous wall
can be highly patterned with a variety of pores, ribs, minute spines, marginal
ridges and elevations which can be utilized to delineate genera and species.
In drowning deaths there is a
suspicion of ante-mortem or postmortem drowning. In these medico legal aspects
diatom test plays a very important role to ascertain the cause of death.
Therefore, in drowning related death a correlation has to be established
between the diatoms extracted from the organ samples and the water samples
collected from the putative sites of drowning for the successful determination
of drowning deaths in Forensic laboratories .
Diagnosis of drowning deaths in
forensic pathology is one of the most difficult tasks and number of tests were
developed to confirm the cause of drowning deaths. Diatom test has emerged as
one of the most important tests in forensic science by detection of diatoms in
tissues samples. Diatom analysis can further used in forensic science by
identifying the individuals, clothing or belongings from the sites of
investigation. The two factors for the diatoms test are the concentration of
diatoms in the lungs and the development of a river monitoring program in the
district of the study. Continuous monitoring of fresh water sites and
comprehensive species level inventories of diatom flora at these sites may be
useful in the medico legal investigation of drowning deaths.
Here is the List of Questions with Answers along with explanation
Ques 1. Diatoms are algae, but
what other classification can apply to them?
a)
Zooplankton
b)
Phytoplankton
c)
Meroplankton
d)
Nekton
Answer – (b) Phytoplankton
Explanation:
Phytoplankton, also known as microalgae, are similar to terrestrial plants in
that they contain chlorophyll and require sunlight in order to live and grow.
Most phytoplankton are buoyant and float in the upper part of the ocean, where
sunlight penetrates the water. Phytoplankton also require inorganic nutrients
such as nitrates, phosphates, and sulfur which they convert into proteins,
fats, and carbohydrates.
The
two main classes of phytoplankton are dinoflagellates and diatoms.
Dinoflagellates use a whip-like tail, or flagella, to move through the water
and their bodies are covered with complex shells. Diatoms also have shells, but
they are made of a different substance and their structure is rigid and made of
interlocking parts. Diatoms do not rely on flagella to move through the water
and instead rely on ocean currents to travel through the water
Ques 2. What is the main form
of nutrition for diatoms?
a)
Microorganism
b)
Photosynthesis
c)
Water solutes
d)
Plant material
Answer – (b)
Photosynthesis
Explanation: Diatom
cells within frustules contain chloroplasts, the organelles in which
photosynthesis occurs. Chloroplasts contain chlorophyll , the
pigment molecule that allows plants and other photosynthetic
organisms to capture solar energy and convert it into usable
chemical energy in the form of simple sugar. Hence the main source of nutrition
in diatoms is photosynthesis.
Ques 3. Which one of the
following is not a diatom?
a) Nostoc
b) Navicula
c) Cyclotelle
d) Pinnularia
Answer – (a) Nostoc
Explanation:
Cell
of diatoms are surrounded by cell wall having two parts or frustules. Frustules
make two overlapping halves (the epitheca and the hypotheca).
Nostoc is
blue green algae which has characteristic peptidoglycan cell wall and
heterocyst, a transparent thick walled empty cell which is present in
intermittent position in filaments of BGA and serves as site of nitrogen
fixation. Option A is correct.
Navicula is
a small boat shaped eukaryotic autotrophic diatom (class Bacillariophyceae)
which contributes 1/4th of oxygen in earth’s biosphere. Option B is
incorrect.
Cyclotelle is
member of class bacillariophyceae which is well known for its polymorphism in
structure of central valve of frustules which is otherwise identification
criteria in other diatomaceous species. Option C is incorrect.
Pinnularia is
a freshwater alga with characteristic silicon cell wall and hence is a diatom.
Option D is incorrect.
Therefore, the correct
answer is option A.
Ques 4.What is a diatom's
skeleton called?
a)
Exoscutum
b)
Shell
c)
Frustule
d)
Cover
Answer – (c)
Frustule
Explanation:
The
skeleton of diatom is known as “frustule”, which is made up of two valves of
different size. The larger valve is called epitheca, which connects the smaller
valve or “hypotheca” with the help of a “cingulum”, also called set of girdle
bands
Ques 5. Diatoms
reproduce by binary fission?
a)
True
b)
false
Answer –
(a) True
Explanation:
Reproduction among these organisms is asexual by binary fission, during
which the diatom divides into two parts, producing two "new" diatoms
with identical genes. Each new organism receives one of the
two frustules – one larger, the other smaller – possessed by the
parent, which is now called the epitheca ; and is used to construct a
second, smaller frustule, the hypotheca. The diatom that received the
larger frustule becomes the same size as its parent, but the diatom that
received the smaller frustule remains smaller than its parent. This causes the
average cell size of this diatom population to decrease.
Ques 6.What is the main
feature of a diatom's shape?
a)
Tubular
b)
Branching
c)
Symmetry
d)
Diamond
Answer – (c)
Symmetry
Explanation:
The main feature of diatoms shape is the symmetry in
their cell wall. Diatoms are divided into two groups that are distinguished by
the shape of the frustule: the centric
diatoms and the pennate
diatoms.
Pennate diatoms are bilaterally symmetric. Each one of their valves have
openings that are slits along the raphes and their shells are
typically elongated parallel to these raphes. They generate cell movement
through cytoplasm that streams along the raphes, always moving along solid
surfaces.
Centric diatoms are radically symmetric.
Ques 7. Diatom
belongs to which of the following group.
a)
Myxophyceae
b)
Bacillariophyceae
c)
Rodophyceae
d)
Zoophyceae
Answer – (b)
Bacillariophyceae
Explanation:
As
algae, diatoms are protists. Diatoms have been placed in the division
Bacillariophyta, which is distinguished by the presence of an inorganic cell
wall composed of hydrated silica.
Ques 8.What is the main role
of diatom in forensic science?
a)
In determination of suspected drowning
and dumping cases
b)
Confirmation of suspected drowning
/dumping site
c)
Confirmation of anti mortem and
postmortem drowning
d)
All the above
Answer – (d)
All the above
Explanation:
The
main goal of diatom analysis in forensics is to differentiate a death
by submersion from a post-mortem or ante-mortem or postmortem immersion of a
body in water. Laboratory tests may reveal the presence of diatoms in the body.
Since the silica-based skeletons of diatoms do not readily decay, they can
sometimes be detected even in heavily decomposed bodies. As they do not occur
naturally in the body, if laboratory tests show diatoms in the corpse that are
of the same species found in the water where the body was recovered, then it
may be good evidence of drowning as the cause of death. The
blend of diatom species found in a corpse may be the same or different from the
surrounding water, indicating whether the victim drowned in the same site in
which the body was found. Hence options A, B, and C all are correct.
Ques 9. Which
of the following statements is not correct regarding diatoms?
a)
Diatoms are aquatic unicellular Algae.
b)
Diatoms have an extracellular coat
composed of magnesium
c)
Acid digestion technique is used to
extract diatoms
d)
Presence of diatoms in the femoral bone
marrow is an indication of ante mortem inhalation of water
Answer – (b)
Diatoms have an extracellular coat
composed of magnesium
Explanation:
All
the 3 options are Correct about diatoms except B as the extracellular coating
of diatoms is composed of silica not
magnesium.
Ques 10. The cell wall of diatom
is made up of
a)
Silica oxide
b)
Magnesium oxide
c)
Polypeptide
d)
Mucopeptide
Answer –
(a)
Silica oxide
Explanation:
Diatoms
are algae with distinctive, transparent cell walls made of silicon dioxide
hydrated with a small amount of water. Silica is the main component of glass
and hydrated silica is very like the mineral opal, making these algae, often
called as "algae in glass houses" more like "algae in opal
houses". The cell wall of diatom is called as frustule. Thus, the
correct answer is option A.
Ques 11. Diatom is a –
a)
Plant (Algae)
b)
Animal
c)
Bacteria
d)
Virus
Answer – (a)
Plant (Algae)
Explanation: Diatoms are a major group
of algae specifically microalgae, found in the oceans, waterways
and soils of the world. Living diatoms make up a significant portion of the
Earth's biomass: they generate about 20 to 50 percent of
the oxygen produced on the planet each year, The study of diatoms is a branch of phycology. Diatoms are
classified as eukaryotes, organisms with a membrane-bound cell
nucleus, that separates them from
the prokaryotes archaea and bacteria. Diatoms are a type
of plankton called phytoplankton, the most common of the
plankton types. Diatoms also grow attached to benthic substrates, floating
debris, and on macrophytes. They comprise an integral component of
the periphyton community. Another classification divides plankton
into eight types based on size: in this scheme, diatoms are classed as
microalgae.
Ques 12. Diatom are classified
into -------orders
a) 2
b) 4
c) 6
d) 8
Answer –
(a) 2.
Explanation:
Diatoms
are divided into two Orders. The Centrales
and the Pennales
Ques 13. Centrale diatoms are
a)
Elliptical in shape
b)
Circular in shape
c)
Star shaped
d)
Spinous shaped
Answer –
(b) Circular in shape
Explanation:
The
Centrales (now called the Biddulphiales) is the one of two order of taxonomic
classification of diatoms which have valve striae arranged basically in
relation to a point, an annulus or a central areola and tend to appear radially
symmetrical, and circular in shape.
Ques 14. Which of the following
organ is more appropriate for diatom analysis in confirmation of drowning and
dumping?
a)
Lungs
b)
Intestine
c)
Kidney
d)
Bone marrow
Answer – (d)
Bone marrow
Explanation:
Bone
marrow is considered to be the best as it proves the hypothesis of antemortem
drowning as well as it is the organ which is least affected by contamination
during post-mortem submersion.
Ques 15. Larger half of diatom’s
frustules is also known as-
a)
Epetheca
b)
Cell coat
c)
Hypotheca
d)
Siliceous coat
Answer – (a)
Epetheca
Explanation: An
epitheca is the larger half of a frustule. The epitheca overlaps the hypotheca.
In Greek epitheca means outer sheath.
Ques 16. In which of the
following sample diatom finding is none.
a)
Sea water
b)
River water
c)
Saline water
d)
none
Answer – (b)
Well water
Explanation: Because
the well structure is a deep, narrow and closed space where the reach of
sunlight is comparatively very low and the main form of nutrition in diatom is
the photosynthesis which requires a good amount of sunlight this is why the
diatom finding in well water is comparatively low or none.
Ques 17. You
can clean your teeth with diatoms.
a)
True
b)
False
Answer – (a) True
Explanation: when
a diatom dies it leaves behind shells made from organic compounds and silica.
This silica from diatoms, has mild abrasive properties due to which they are used
in tooth powder and tooth pastes to clean the teeth.
Ques 18. If diatom is found in
bone marrow, it suggest that
a)
Death due to dumping
b)
Death due to drowning
c)
Death due to suffocation
d)
None of these
Answer –
(b)
Death due to drowning
Explanation: Bone
marrow is a closed circulatory organ of the human body. Diatoms are not
naturally present inside the body. They inters inside the body by inhalation of
surrounding water through mouth or nose and can reach to the closed circulatory
organ only and only when the circulation is on which means antimortem or
drowning before death. As the circulation is stopped when the person is dead
and so the diatoms cannot reach to these closed circulatory organ such as
femur, bone marrow etc.
Ques 19. Which of the following
method/s are used for extraction of diatom from viscera
a)
Acid digestion method
b)
Enzymatic method
c)
Soluene 350 method
d)
All of these
Answer – (d)
All of these
Explanation: Various
methods have been suggested for extracting diatom frustules from the water
samples as well as organ samples. These include the use of enzymes, chemical
solubilizers, mechanical action related centrifugation processes and strong
acids for digesting the other organic material so that the insoluble diatom
frustules can be extracted. Enzymatic digestion method: Enzymatic digestion method was also being used
as one of the method for diatom extraction. It is actually adapted from DNA
extraction techniques in which Proteinase K and sodium dodecyl sulphate (SDS),
traditionally used to digest proteins and cell plasma membranes in DNA
extraction, have proven to be effective in isolating diatoms.
Soluene-350
method: Soluene-350 is a solubilizer
which has gained some popularity to be used in diatoms extraction. This method
has been employed for the destruction of tissue. this method was again used for
the extraction of diatoms from fresh water and seawater samples.
Acid
digestion method: One of the most commonly known methods is the acid digestion
method. This method has been employed by researchers all over the world. The
most common acids used in acid digestion methods are nitric acid, sulfuric acid
and hydrochloric acid. However, this method was criticized to be hazardous,
pollutive, disorganized and dangerous
Hence
all the above options are correct.
Ques 20. Diatom is major
producers and form aquatic-
a)
Food
b)
Oxygen
c)
Food chain
d)
Silicates
Answer – (C)
Food chain
Explanation:
Diatoms
produce long-chain fatty acids. Diatoms are an important source of these energy
rich molecules that are food for the entire food web, from zooplankton to
aquatic insects to fish to whales. In the ocean, diatoms are eaten by tiny
animals called zooplankton. Zooplankton in turn sustain larger organisms, like
fish, so many animals in the ocean depend on diatoms either directly or
indirectly for their survival. Diatoms are responsible for over 40 percent of
photosynthesis in the world's oceans, and without them, the ocean would be
unable to support the amount of life that it does. Diatoms are a key source of
food and energy for other organisms in many freshwater ecosystems as well.
Snails, caddis fly larvae, small crustaceans and filter feeders like clams are
among the many animals in freshwater systems that graze on diatoms.