Insect Abdomen: Appendages found on the abdomen

Insect abdomen is the third functional region of insect body. It is located behind the thorax and contains 6-10 segments. There are various types of appendages arise from the abdomen.

Cerci

Located close to anus.

-Blattodea: simple and jointed cerci

Via ediacaran.mech.northwestern.edu

-Orthoptera: simple and not jointed cerci

-Dermaptera: Sclerotized, forceps like cerci

Dermaptera forcep like cerci via gallurapestcontrol.com

-Thysanura: Long filamentous cerci

Long filamentous cerci of Thysanura

-Ephemeroptera larvae: Wing like cerci that helps to move forward in water.

Wing like cerci -Ephemeroptera larva

Styles

Can be seen in Cockroach and Lepisma. It is regarded as the vestige of the walking limb.

via microscopy-uk.org.uk

Median caudal filament

This is a thread like projection arising from he center of the last abdominal segment between the cerci.

Abdominal Prolegs

Can be seen in Lepidopera.

via entomology.umn.edu

Abdominal Gills

These are respiratory organs and found in nymphs of some aquatic insects.

Cornicles

These are located dorsally on the abdomen as paired secretory structures.

      

Female External Genitalia

Ovipositors are used for oviposition and it is formed by the modification of 8-9 abdominal segments. Thysanura, Orthoptera, Thysanoptera and some Hymenoptera insects contain true ovipositors.

Ovipositor places egg inside caterpillar 

Egg is released (naturecloseups.com)

-The ovipositor is modified as a poison injecting sting ( Wasps, bees..etc)

via amazingnature.us

-Hind end of the abdomen is extended to work as an ovipositor

Male genitalia

Modification of 9^th abdominal segment makes the copulatory organ of males which is consist of aedeagus and pair of lateral claspers to grasp and hold the abdomen of the female during mating. 

Special reactions/tests for Urea, Formamide, Oxamide, Salicylamide, Succinimide, Phthalimide

Urea

Urea nitrate and oxalate: Take a concentrated solution of urea, to one portion, add a few drops of con. HNO₃: the white crystalline urea nitrate (m.p. is 163°) is precipitated; to another portion, add con. Oxalic acid solution and scratch with a glass rod. White crystals of urea oxalate (m.p. is 171°) are separated. In an excess of water both salts dissolve.

Biurate reaction: Take 0-2 g of urea into a dry test-tube and heat gently above the melting point. NH₃ is evolved. After 2 minutes the liquid rapidly solidifies with the formation of biuret.

2NH₂CONH₂à NH₂CONHCONH₂ + NH₃

Dissolve the solid residue in a few ml. of warm 10% NaOH solution. Stand it to cool and add 1 drop of dil. CuSO₄ solution. A purple coloration is obtained. A pink/purple coloration is due to containing two -CONH- groups attached to one another, or to the same carbon atom or nitrogen atom. Therefore the same colouration is also given by malonamide, oxamide and by proteins/peptides.

Urease test: Urease enzymes can hydrolys Urea to Ammonium carbonate. The reaction is specific. It is used for solutions of urea to which the biuret test cannot be applied.

Action of hypobromite: Add sodium hypobromite solution to a solution of urea. The brisk effervescence is given.

NH₂CONH₂ + 3NaOBr à N₂ + CO2 + 3NaBr + 2H₂O

Formamide

Boil 1 ml of formamide in a test-tube. NH₃is evolved from it.  CO is produced, but cannot be ignited in the presence of the NH₃.

Oxamide

Biuret test: Oxamide does not need any preliminary treatment to proceed with the test. Shake 1 g of oxamide with 1ml of 10% NaOH solution. Add 1 drop of very dilute CuSO₄ solution to it and mix well. A pink coloration is produced.

Sulphuric acid test: Heat 0-3 g of Oxamide with con. H₂SO₄. CO and CO₂ are evolved.

Salicylamide

FeCl₃ coloration: Take the solid into a test tube. Add FeCl₃ solution and shake. An intense violet coloration is produced as the Phenolic groups are present.

Succinimide

Reduction: Take about 1 g of succinimide and an equal amount of Zn dust into a dry hard-glass test tube and mix well. Heat strongly. Soak a pinewood splinter in con.HCl and place it in the mouth of the tube. The splinter is turned red by the vapour of pyrrole which is formed by reduction.

Fluorescein reaction: Take about 1 g of Succinimide, 1 g of resorcinol and 2 drops of con. H₂SO₄ into a dry test tube and fuse all of it together. Cool and add water. Then add NaOH solution in excess. A green fluorescent solution is produced.

Phthalimide

Phthalein reaction: Take about 1 g of Phthalimide, 1 g of phenol and 2 drops of con. H₂SO₄ into a dry test-tube and fuse all together very gently. Let it cool and add water. Then add NaOH solution in excess. A red coloration is produced which is decolorized by acids.

Fluorescein reaction: Repeat the above test, using resorcinol instead of phenol. A green fluorescent solution is produced on the addition of NaOH solution.

Polymerase Chain Reaction ( PCR )

This is a method to produce very large numbers of copies of specific DNA sequences without cloning. Therefore PCR can amplify specific sequences or add sequences such as  endonuclease  recognition  sequences as primers to cloned DNA.

PCR consists of 5 main components.

-Target DNA

-Single stranded Oligonucleotides (primers)

-d NTPs (dATP, dCTP, dTTP, dGTP)

-Taq DNA polymerase

-Termocycler

There are three main steps in PCR.

Step1:  Denaturation. The mixture of excess primer and DNA fragment is heated to about 95° C causing the double strands of target DNA to be denatured into single strands.

Step 2: Annealing of Primers. The temperature is dropped down between about 35⁰- 65°C

As the temperature decreases the single strands of DNA reassociate into double strands. Large excess of primer allows two primers anneal or bind to their complementary sequences on the target DNA leaving the rest of the fragment single-stranded.

Step 3: Primer Extension. The temperature is raised to 70⁰- 75°C Taq  polymerase is added. Taq polymerase extends the primer into a complementary copy of the entire single-stranded fragment, in the 5’-3’ direction.  As both the DNA strands are replicated, two copies of the original fragment are gained.

This process is repeated many times. At each time, the number of DNA copies doubles. This is continued until enough copies are gained for the analysis. 

Differences between physisorption and chemisorption

Different kinds of bacteriophages (phages)

M13

Filamentous.

About 870nm in length and 6nm in width.

Consists of single stranded DND (ssDNA).

Three kinds of capsomeres build the capside.

Infects E. coli by adsorbing to the cell and entering through F pilli. Therefore only infect F⁺ and HFr cells. Also male specific.

Does not kill the host. Particles are released by budding, therefore when the particles are released, the host cell is alive.

An efficient vector in gene cloning as it can hold longer pieces of foreign DNA.

T phage

Structure is composed of icosahedral head, double stranded DNA and a tail.

Infects E.coli

 Main types of T phages are T2, T4 and T12.

In the infection linear DNA of the phage is released to the host cell and becomes circular by replicating that later produces a long DNA chain known as ‘Concatamen’. This coils into the phage’s head by headfull mechanism while packaging.

Infection kills the host cell as the new particles are released outside by bursting the host cell.

Lambda (λ)

Composed of head and tail.

Head is consisting of double stranded linear DNA.

At both 5’ ends of the DNA strand, 12 complementary base pair, single stranded segments are present. These two ends are known as “cos ends”.

Because of the cos ends, phage chromosome circularizes before replication. Concatamen is produced during the replication and during the packaging, Terminase enzyme cuts off the cos ends.

Host cell is E.coli.

MS2

Contains the smallest known genome.

Super coiled single stranded DNA.

Infect only through sex pilli. Therefore male specific.

Infect E.coli.

Phi×174(ΦX174)

Contains a single stranded circular DNA.

After adsorption, synthesizes the complementary strand and becomes double stranded.

Use as a positive control in DNA sequencing.

G4

Structurally similar to ΦX174 phage.

Can infect susceptible E.coli cells. 

Serotonin the neurotransmitter

Serotonin i.e. 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter that is said to be helping to relay signals from one area of the brain to another. However its primary functions are found in gastrointestinal tract as 90% of total serotonin is located in the enterochromaffin cells in the gut. 

Serotonin is made via a unique biochemical conversion process that begins with Tryptophan. Tryptophan is a building block to proteins. In the synthesis of serotonin, Tryptophan hydroxylase the enzyme combines with tryptophan to form 5-hydroxytryptophan metabolite that later converts to Serotonin.

Via wikipedia.org

As mentioned earlier serotonin helps to distribute messages across the brain. Brain cells related to mood, appetite, sleep, memory, learning, temperature regulation, sexual desire and some social behaviour are influenced either directly or indirectly by serotonin due to the widespread distribution in the brain. 

It can also affect the functioning of the cardiovascular system, muscles, and various elements in the endocrine system.

When it comes to mental health, it is widely believed that a serotonin deficiency plays a role in depression but there is no way to measure its levels in the living brain. Therefore, there have not been any studies proving that brain levels of this or any neurotransmitter are in short supply when depression or any mental illness develops. People who suffer from depression shows lower serotonin levels in blood levels but still it is not revealed that whether the blood levels reflect the brain's level of serotonin.

Antidepressant medications such as SSRIs (selective serotonin reuptake inhibitors) and SNRIs (serotonin and norepinephrine reuptake inhibitors) that work on serotonin levels are believed to lower the symptoms of depression, but their exact function is not fully understood.

Recent studies show that when the Mycobacterium vaccae, which occurs naturally in soil and is often breathed in when spending much time nature, is injected into mice, it stimulates neuron growth and causes serotonin levels in blood to increase. So that the bacteria could have antidepressant benefits but it is not yet revealed whether it has an effect on human.

Use of colorimeter for the determination of the concentration of a solution

Absorbance is important in determining concentration of a substance in a sample through colorimeter analysis. Colorimeter measures the intensity of colour and light transmittance by the sample to achieve the concentration. When a beam of light passes through a coloured solution, the amount of light absorbed depends on the nature of the molecules absorbing the light, their concentration and thickness (path length) of the solution. The ratio of transmitted intensity to original intensity s known as the “transmittance”, T.

Transmittance (T) = I/I₀

I = intensity of the transmitted light

I₀ = intensity of incident light

The Beer- Lambert law states that there is a logarithmic dependence between the transmittance and the absorbance. Therefore the transmittance is expressed in terms of absorbance;

Absorbance (A) = -log₁₀ T

                             = -log₁₀ (I/I₀)

According to this, the absorbance becomes linear with concentration considering;

A = ℰ ℓ C

ℰ = Molar absorbance coefficient

ℓ = path length

C = concentration of the solution

Therefore in dilute solution,

A = -log₁₀ (I/I₀) = ℰ ℓ C

Molar absorbance coefficient indicates the absorbance under a standard set of conditions, i.e. the light travelling 1cm through a solution of 1moldm^-3. In a material with a low absorption coefficient, light is poorly absorbed and vise versa. This depends on the material and on the wave length of the light.

When using the colorimeter the path length i.e. the width of the glass cell is constant. Also the concentration of one solution used at one specific wave length. Therefore ℰ is also constant through the measurements. This shows out clear relationship between the absorbance and the concentration.

A ∝ C as ℓ and ℰ are constant

The glass cell/ container with plane parallel faces are transverse by monochromatic radiation in the colorimeter. If the glass cell is filled with non absorbing solution, there is 100% transmittance; therefore the absorption would be zero.

Colorimeter applies only in relation to the visible region. Also Beer- Lambert law is applicable for 0.800-0.200 absorbances.

In the experiment, firstly the absorbance reading of the colorimeter should be zeroed using distilled water as distilled water is used to prepare the solutions. 

Also before taking the measurements of the absorbance value in each solution, the glass cell should be washed with distilled water in order to prevent interferences to the reading. It is important not to touch the two smooth surfaces of the glass cell and wipe out the additional drops remain on the surfaces of the glass cell, using a tissue. Otherwise the beam of the radiation would be scattered incorrectly and interfere the accuracy of the reading.

When filling the cell, air bubbles should not be remained inside the cell as it would decrease the absorbance value.

When refilling a glass cell with a different solution, small amount of the new solution should be used to rinse the cell before filing as it would give more accurate results.

Spectrophotometer also uses a monochromatic light to pass though a solution and measure its absorbance. The principle of spectrophotometer and colorimeter is same but a colorimeter can only use one wavelength at a time and have a fixed number of wavelengths that can be used. Also they have to be in visible range only.

A spectrophotometer on the other hand can not function like a colorimeter but take a spectrum of a solution across the entire wave spectrum especially in UV – IR. Therefore use of spectrophotometer is beneficial than a colorimeter and useful to determine concentration of unknown solutions.

Diversity of bacteria according to nutritional requirments, temperature, Oxygen conditions and water activity

Nutritional type	Energy source	Carbon source	Examples
Photoautotroph	Light	Inorganic carbon, i.e. CO2	Some purple and green bacteria (Chromatium)
Photoheterotroph	Light	Organic compounds	Some purple and green bacteria (Rhodospirillum)
Chemoautotroph (Lithotroph, Lithoautotroph)	Inorganic compounds; H2, H2S, NH3	CO2	Many Archaea and few bacteria (Nitrosomanas)
Chemoheterotroph (Heterotroph)	Organic compounds	Organic compounds	Few Arcaea and many bacteria (Pseudomonas)

Type	Minimum (0C)	Optimum (0C)	Maximum (0C)
Psychrophile	Below 0	10-15	Below 20	Contain unsaturated fatty acids in plasma membrane to tolerate.
psychrotroph	0	15-30	Above 25	Able to grow at low T but prefer moderate T
Mesophile	10-15	30-40	Below 45	Most bacteria especially the ones associated with warm-blooded animals.
Thermophile	45	45-70	Above 100	Contain Saturated fatty acids in plasma membrane. High glucose and carbon content as well as high melting point for DNA.
Hyperthermophile	80	80-115	Above 115	Contain phytane and modified proteins in plasma membrane. High glucose and carbon content as well as high melting point for DNA.

Type	Aerobic condition	Anaerobic condition
Obligate aerobe	Growth	No growth
Microaerophiles	Growth; when the O2 is at very low level	No growth
Obligate anaerobe	No growth; O2 is toxic	Growth
Facultative anaerobe/ facultative aerobe	Growth; Not essential to grow but utilized when available	Growth
Aerotolerant anaerobe	Growth; neither essential nor utilized	Growth

Type	Speciality
Halophile	Require NaCl for growth
Halo tolerant	Able to grow at moderate salt concentrations but grow best in the absence of NaCl
Osmophile	Able to grow in high levels of suger
Xerophile	Able to grow in dry conditions

Bonding in transition metal complexes:- Valence bond theory, Crystal field theory, Molecular orbital theory

There are three theories of metal to ligand bonding in complexes.

Valence bond theory

 Coordination compounds contain complex ions, in which ligands form coordinate bonds to the metal. Thus the ligand must have a lone pair of electrons, and the metal must have an empty orbital of suitable energy available for bonding. The theory considers which atomic orbitals on the metal are used for bonding. From this the shape and the stability of the complexes are predicted. The theory has two main limitations. Most transition metal complexes are coloured, but the theory provides no explanation for their electronic spectra. Further, the theory does not explain why the magnetic properties vary with temperature. For these reasons it has largely been superseded by the crystal field theory. However it is of interest for study as it shows the continuity of the development of modern ideas from Werner’s theory.

Crystal field theory

The attraction between the central metal and ligands in the complex is considered to be purely electrostatic. Thus bonding in the complex may be ion-ion attraction (between positive and negative ions such as Co³⁺ and Cl^-).  Alternatively, ion-dipole attractions may give rise to bonding (if the ligand is a neutral molecule such as NH₃ or CO).  This theory has been remarkably successful in explaining the electronic spectra and magnetism of transition metal complexes. Particularly when allowance is made for the possibility of some covalent interaction between the orbitals on the metal and ligand. When some allowance is made for covelencey, the theory is often renamed as the ligand field theory. Three types of interaction are possible. The σ overlap of orbitals, π overlap of orbitals, or dπ – pπ bonding (back bonding) due to π overlap of full d orbitals on the metal with empty p orbitals on the ligands.

Molecular orbital theory

Both covalent and ionic contributions are fully allowed for in this theory. Though this theory is the probably the most important approach to chemical bonding, it has not displaced on the other theories. This is because the quantitative calculations involved are difficult and lengthy, involving the use of extensive computer time. Much of the qualitative description can be obtained by other approaches using symmetry and group theory.

Reference: Inorganic chemistry, J.D Lee 

Preparation of solid derivatives of Carbonyl compounds (aldehydes & ketones) :- 2, 4- Dintrophenylhydrazones, Semicarbazones

The systematic procedure that involves several steps and preparations is carried out to identify unknown compounds to some extent. The preparation of derivatives usually establishes the identification of the unknown with certainty. Here the term derivative is simply referred to a compound prepared from an unknown, in order to identify the unknown compound. An ideal derivative should be a crystalline, easily purified solid with a sharp melting point, which can be prepared readily from the unknown in one direct and unambiguous step.

Many carbonyl compounds can be synthesized from the esterification reaction. There are excellent and conveniently prepared derivatives which use to identify carbonyl compounds. Oximes, Phenyl hydrazones, 2, 4-dinitrophenylhydrazones and semicarbazones are some of the best derivatives of aldehydes and ketones. In the preparation of each of these types of derivatives, the elimination of a water molecule between a molecule of the carbonyl compound and a molecule of the reagent is involved.

Dinitrophenylhydrazine is relatively sensitive to shock and friction. It is a red to orange solid usually supplied wet to reduce its explosive hazard. This is often used as a qualitative test for carbonyl groups, associated with aldehydes and ketones. The hydrazone derivatives can be used as evidence toward the identity of the original compound. These are usually yellow-red colour crystals. Crystals of different hydrazones have characteristic melting and boiling points allowing the identification of the unknown substance.

Semicarbazone is one of the most commonly used derivatives to identify aldehydes and ketones. It is a derivative of an aldehyde or ketone formed by a condensation reaction between a ketone or aldehyde and the reagent; semicarbazide. As semicarbazides are not very stable in the free form, they are usually stored in the laboratory in the form of their hydrochloride salts. Many semicarbazones are off white, crystalline solids, useful for the identification of the parent carbonyl group by melting point analysis.

conductometric titrations

In conductometric titrations, the electrical conductivity of an electrical solution is continuously monitored as one reactant is added. The accurate endpoint of can be determined by detecting a sudden change in the conductivity of the solution. It is particularly useful in titrating weak acids against weak bases. According to Ohm’s law;

I = E/R                                        

Also,

R ∝ l

R ∝ 1/A                                                   

Therefore;

R = ρ l/A

ρ = RA/l

I = Current, E= electromotive force, R= Resistance, l = Length, A= cross section area, ρ= Resistivity

The reciprocal of resistivity is conductivity. It can be expressed as K.

K = 1/ ρ

    = 1l / RA

    = G l/A

G is the conductance.

In the titration, the conducting material is the solution. So the conductance depends on the type of ions in the solution and their concentration. If the solution is located between two electrodes at constant distance and cross section area, conductance will increase when the concentration of the solution decreases.

Also when l and A are constant it is clear that,

K ∝ G

These conditions can be obtained by using a conductivity cell that consisting a pair of platinum electrodes connected to the conductivity bridge which provides current to the cell. The meter will give out the calculated conductivity of the solution.