Diatoms in Forensic Science

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.