20 Top Wildlife Sanctuaries in India | Biology Blog

                        Top 20 Wildlife Sanctuaries In India

Protecting wild plant and animal species and their habitats is known as wildlife conservation. In addition to preserving nature for future generations to enjoy, wildlife conservation aims to raise awareness of the value of wildlife and wilderness areas for both people and other species.

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What are Mollusc : Biology Blog

                          Phylum Mollusca (clade) – mollusks

•  very successful phylum: over 93,000 named, living species
• The largest number of living species for animals after Arthropoda
•  mostly aquatic, but over 35,000 terrestrial species (more than all terrestrial vertebrates)
•  includes snails, slugs, clams, oysters, chitons, cuttlefish, octopi, etc.
•  from microscopic to 21 m (giant squid – largest invertebrate)
•  economically important (food, ornamentation, currency, pests) 
  

Defining Characteristics Of Mollusks:

 Bilateral symmetry with true coelom; usually have a differentiated head unsegmented (some argument as to whether lost during evolution or never present in phylum)

 Three main body parts: muscular foot, visceral mass, and mantle muscular foot – used for locomotion, food capture, attachment · may be solid or have tentacles or maybe a “wing” or fin in pelagic forms· covered with soft epithelium and · may secrete mucus to glide on 



 Visceral Mass – contains most of the internal organs, including these systems:

a. Digestive system – more complicated than in phyla to this point (true coelom)

· complete (separate mouth and anus)

· mouth, stomach, intestine

· radula – rasping “tongue” with rows of microscopic, chitinous “teeth” used to scrape or drill for food



b. Excretory system – simplest animals with the efficient excretory system

· nephridia – tubular structures that gather wastes from the coelom

· walls of nephridia reabsorb useful compounds (sugars, salts, water, etc.)

· ability to reabsorb is why the system is considered efficient

· wastes discharged into mantle cavity; gills pump wastes out of animal

c. Circulatory system

· some have a closed system, most have an open system

· if open, coelom is generally confined to a small area around the heart

· heart may have three chambers

· some fast cephalopods have auxiliary hearts to speed blood movement


d. Reproductive System And Life Cycle

· Most have separate sexes; however, many snails are hermaphrodites

· Trochophore – ciliated free-swimming larva of many marine mollusks

· Veliger – the second stage in the development of most marine snails and bivalves; has beginnings of foot and mantle

 mantle -

1. Folds (often 2) from the dorsal body wall

2. Enclose a cavity between the mantle and visceral mass (the mantle cavity)

3. Mantle cavity - may act as lung or enclose gills

· Gills are filamentous projections of mantle

· Gills are rich in blood vessels

· Gills have a large surface area for gas exchange

· Continuous pumping keeps the flow of water into and out of the mantle cavity

· May have siphons to move water in (incurrent) and out (excurrent) of the mantle cavity

· Bring in oxygenated water and send out deoxygenated water

· May be used to bringing in food (in bivalves)

· May be used for jet propulsion (in cephalopods)



Shell (if present) – Secreted by mantle, usually on the outside, but on inside in some snails, squid, and cuttlefish,  and lost in slugs, nudibranchs, and octopus

· provides protection
· one or two valves (shells)

· outer layer - horny protein layer; protects inner layers from eroding

· middle layer - densely packed crystals of calcium carbonate (calcite or aragonite)

· inner layer - pearly - increases in thickness throughout the life of mollusk

· pearls form between the inner layer and mantle in bivalves


Mollusk classification


a. Class Polyplacophora (clade) – chitons

•  ~1000 living species
•  marine; shell is segmented with 8 overlappings, calcareous plates
•  body beneath the shell is not segmented
•  the head is greatly reduced
•  foot used for locomotion and for holding onto substrates 

b. Class Gastropods (clade) – snails and slugs

•  The name means “stomach foot”
•  ~70,000 living species
•  mostly marine, but abundant in freshwater, and many are terrestrial
•  most have a shell
• · single shell, if present
• · operculum found in most marine gastropods – a horny plate that forms a covering “door” when the snail withdraws into its shell
• · coiling (spiral twisting) of the shell due to one side of larva growing faster than the other side
• · shell has been lost in the course of evolution for slugs and nudibranchs (sea slugs) 

 c. Class Bivalvia (clade) – the bivalves

•  Includes clams, oysters, scallops, and mussels
•  ~20,000 living species
•  2 shells (valves) hinged together
•  strong adductor muscles used to pull shells together typically with siphons - most are filter feeders (food trapped on mucus on gills) 

•  complex folded, ciliated gills
•  no distinct head or radula
•  most have a strong muscular foot (many different adaptations) 

•  some can move by clapping their shells together (scallops); however, most bivalves are sessile for most of their adult lives, tethered to some substrate by strong threads they secrete or using their foot as an anchor
•  scallops have many eyes on soft body parts next to the edges of their shells 

•  freshwater mussels the most endangered group in North America, and Alabama has the highest diversity of freshwater mussels in the world 

d. Class Cephalopoda (clade) – the cephalopods (“head foot”)

•  includes octopus, squids, cuttlefish, and nautilus
•  ~800 living species
•  0-1 shells, internal or external octopi – no shell
• squid and cuttlefish – internal shell remnant used for support nautilus – chambered shell, superficially resembling snails
•  highly developed nervous system giant axons –great for research
• elaborate eyes (some up to 40 cm across – largest known eyes) most intelligent invertebrates; complex behavior
• many are skillful hunters
•  foot modified into grasping tentacles with suckers
•  built for speed – jet propulsion using siphons (they are fast-moving predators)
•  most have a closed circulatory system (only mollusks with this)
•  strong beak for biting; radula used to pull prey in squid and octopi can release a dark “ink” to cloud water for escaping predators or even for trapping prey
•  cuttlefish are famous for changing color to match the background or for messaging, using chromatophore pigment pouches; most octopi and squid can do this as well.  For example Oyster, snail, squid, devilfish 

EX: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devilfish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton)

Cell Cycle - Phases , Diagram , Types and Comparison

                                          

                                              Cell Cycle

In every organisms Cell continuously undergoes a series of events like growth , development & reproduction and completes its life cycle called the Cell Cycle . After the formation  of the Cell , it  first goes  under   resting period where they grows in size, its nuclear material increases, and prepare itself  for the next division.

• Duration of cell cycle - The duration of the  every cell cycle varies to  25 – 30 hr in different cells except  in case of  organisms like in Ecoli, the cell cycle is completed in 20 minutes,

• Stages of the cell cycle –

1. Interphase - Interphase is the interval period between two successive divisions when the cell does not show any division. But it prepares itself for it by synthesizing new proteins and nucleic acid. This phase is also known as the preparatory phase.
   
   
2. G1 Phase - It is the first gap phase where the cell grows physically larger, make copies cellular organelles, and makes the molecular building blocks that will need in later steps.
   
   
3. S phase -The S phase, or synthesizing phase is the phase where , the cell synthesis a complete copy of the DNA in its nucleus along with it also duplicates a microtubule-organizing structure called the centrosome. The centrosomes helps to  separate DNA during the M phase.
   
   
4. G2 Phase - In this phase the cell grows more, makes proteins and organelles, and begins to reorganise  its contents in preparation for mitosis. 
   
   
5. M Phase - M phase is the phase where a cell tends to divide and generating daughter cells. The stage is divided into two  stages -

Karyokinesis - The division of the nucleus is called karyokinesis. The term karyokinesis was proposed by Schneider in 1887. Karyokinesis has  following phase - prophase, metaphase, anaphase, and telophase.

Cytokinesis - Division of Cytoplasm in the cell is known as Cytokinesis proposed by Whiteman in 1887. 

• Types of Cell division -  Basically cell division is responsible for reproduction and growth in organisms . In both the processes chromosomes are properly distributed into the daughter cells. The process of cell division was firstly observed in 1882 by Fleming in a reptile Triturus masculosa but Beler studied it is in detail in 1920. 

There are three types of division - mitosis, meiosis, and amitosis.

                                                    Mitosis

The exact replication of the parent cell followed by its division into two daughter cells which are identical and contain the same number of chromosomes as found in the parent cell. This nuclear division was first observed by Strasburger in plant cells and by Fleming in animal cells. Fleming used the term mitosis fir this division. Mitosis takes place in somatic cells.

Process -   It is completed in four steps.

• Prophase
• Metaphase
• Anaphase
• Telophase. 

Prophase –

• · In the nucleus, the genetic material is loosely bundled in a coil called chromatin.
• · At the onset of prophase, the chromatin fibers become tightly coiled and condense into discrete chromosomes.
• · Inside the nucleus, the nucleolus also disappears from view.
• · The centrioles begin to move to opposite ends of the cell and the spindle fibers extend from the centromere.
• · Some fibers cross the cell to form the mitotic spindle fibers.

Metaphase

• · The term metaphase is derived from the Greek word 'meta' which means 'after'.
• · In the prometaphase after the microtubules are attached to the prometaphase, the chromosomes start pulling the chromosomes towards the ends of the cell.
• · The centromeres of the chromosomes assemble along with the metaphase plate also known as the equatorial plane.
• · It is an imaginary line that is in between the centrosome poles and is called the spindle equator.
• · This helps to ensure that when the chromosomes are separated the new nucleus will receive one copy of each chromosome. 

Anaphase

• · After the metaphase stage the chromosomes proceed to the anaphase stage.
• · The term anaphase is derived from the Greek word "ava" which means "up", or "against", or "back", or "re".
• · First the proteins that bind the sister chromatids are cleaved making the sister chromatids as separate daughter chromosomes and are pulled apart towards the respective centrosomes to which they are attached.
• · The microtubules at the poles pull the set of a chromosome that is attached to it the opposite ends of the cell. At the end of anaphase, the microtubules all degrade. 

Telophase

• · Telophase is derived from the Greek word "telos" meaning "end".
• · It is a reversal of prophase and prometaphase events. In the telophase stage, the polar microtubules continue to lengthen elongating the cell.
• · The daughter chromosomes attach at opposite site ends of the cell.
• · New membranes are formed around the daughter nuclei.
• · The chromosomes spread and are no longer visible under the light microscope.
• · The spindle fibers also disperse, cytokinesis may also begin during this stage. 

Cytokinesis

• · Cytokinesis is a separate process that begins at the same time as the telophase.
• · Cytokinesis is not a phase of mitosis, it is a separate process necessary for completing cell division.
• · In animal cells, a pinch like a cleavage furrow containing a contractile ring develops at the position of the metaphase plate separating the nuclei.
• · In the animal and plant cells the division of cells is driven by vesicles derived from the Golgi apparatus.
• · In plant cells, the rigid wall requires a cell plate to be synthesized between the two daughter cells.

Significance of Mitosis

• · Mitosis division is responsible for the growth and development of a single-celled zygote into a multicellular organism.
• · The chromosome number remains the same in the cells produced by this division.
• · The daughter cells have the same characters as those of the parent cell.
• · Mitosis division helps in maintaining the proper size.
• · Mitosis also helps in restoring wear and tear in body tissues, replacing damaged or lost parts, healing wounds, and regeneration of detached parts.
• · This method of multiplication is seen in unicellular organisms.
• · Mitotic division of cells is unchecked and it may result in uncontrolled growth of cells leading to cancer or tumor. 

                                                            Meiosis 

Meiosis is a special complicated type of cell division. Meiosis is also known as a reduction division. In this type of division four daughter cells are formed from a parent cell. J.B. Farmer in 1905 coined the term meiosis.

Meiosis is divided into meiosis I and meiosis II stages. It is further divided into Karyokinesis I and Cytokinesis I and Karyokinesis II and Cytokinesis II respectively.

Meiosis I

• · The pairs of homologous chromosomes, made up of two sister chromatids are split into two cells.
• · The resulting daughter cells contain one entire haploid set of chromosomes.
• · The first meiotic division reduces the ploidy of the original cell by a factor of two.
• · It produces two haploid cells (N chromosomes, 23 in humans).
• · Hence meiosis first is referred to as a reductional division.
• · A diploid human cell contains 46 chromosomes and is said to be 2N because it contains 23 pairs of homologous chromosomes. 

Prophase 1 – It is the longest phase of meiosis 1. It consists of the following steps –

Leptotene - At this stage condensation of chromatin starts and the fine chromatin fibers appear with granule like chromomere on them. The chromomere is the region where chromatin fibers are highly coiled.

Zygotene

• · Zygotene is also known as zygonema, it is derived from the Greek word that means 'paired threads.
• · The chromosomes in this line up with each other into homologous chromosome pairs.
• · This stage is known as the bouquet stage, due to the way the telomeres cluster at on end of the nucleus.
• · Synapsis of homologous chromosomes takes place in this stage.

Pachytene

• · The pachytene stage is also known as pachynema and is derived from Greek which means "thick threads".This is the stage where chromosomal crossing over occurs.
• · Nonsister chromatids of homologous chromosomes exchange segments over homologous regions.
• · Sex chromosomes are not identical and they exchange information over a small region of homology.
• · Chiasmata is formed where the exchange happens.

Diplotene

• · The diplotene stage is also known as diplonema, which is derived from the Greek word meaning "two threads".
• · During this stage there is the degradation of the synaptonemal complex and the homologous chromosomes separate a little from one another.
• · The chromosomes in this stage uncoil a little, this allows transcription of DNA.

Diakinesis

• · During the stage of diakinesis the chromosomes condense further.
• · The word diakinesis is derived from the Greek word which means "moving through".
• · This stage is the first part of meiosis where the four arms of the tetrads are visible.

Metaphase I
The homologous chromosomes align along the equatorial plane, this alignment happens due to the continuous counterbalancing forces exerted on the bivalents by the microtubules emanating from the kinetochores of the homologous chromosomes.

Anaphase I

As each chromosome has only one functional unit of a pair of kinetochores, the whole chromosomes are pulled towards the opposite poles which result in the formation of two haploid sets.

Telophase I

• The first phase of the meiotic division ends when the chromosomes arrive at the poles.
• The daughter cells now have half the number of chromosomes, the chromosomes consist of a pair of chromatids.
• The microtubules of the spindle network disappear and the nuclear membrane surrounds each haploid set.
  

Significance - 

• It plays an important role in sexual reproduction.
  
• The process of meiosis helps in the maintenance of chromosomes number in the species.
  
• It may lead to origin of new species.

                                                          Amitosis

In this type of cell division, the nucleus becomes elongated and constriction appears in the center or at the end due to which daughter nuclei produced are not in equal size. Nuclear division is not always followed by wall formation. This type of division takes place in some fungi and algae. 

Comparison between mitosis and meiosis - 

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Function Of Essential Amino Acid

                                    Amino Acid

Amino acids are organic compounds containing amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid.

Amino Acids Structure

Amino acids have the general form H2NCHRCOOH.
(or)

 

General properties of Amino Acids

• ·         Amino acids are soluble in water and insoluble in hydrocarbon solutions.
• ·         They are crystalline solid substances.
• ·         They have very high melting point compared to their boiling point.

List of Amino Acids

There are around twenty amino acids, which are involved in the construction of proteins. The lists of twenty amino acids are:

Alanine, aspartic acid, asparagines, arginine, cytosine, cysteine, glycine, glutamine, glutamic acid, histidine, isoleucine, leucine, lysine, methionine, Proline, phenylalanine, serine, tyrosine, threonine, tryptophan and Valine,

Essential Amino Acids 

There are few amino acids which are essential for human beings such as: phenylalanine, Valine, threonine, tryptophan, isoleucine, methionine, leucine, lysine, and histidine. They are very much essential, as they cannot be bio synthesized by our body.

Nonessential Amino Acids 

 There are few amino acids, which are non essential for human beings as they can be easily bio synthesized by our body. The non essential amino acids are: Alanine, cysteine, cystine, glutamine, glycine, glutamate, arginine, tyrosine, serine, asparagines, aspartic acid, selenocysteine and Proline.

Functions of Essential Amino Acids:

• ·         Phenylalanine: Helps in boosting memory power and also helps to maintain a healthy nervous system .
• ·         Valine: Helps in growth of muscles.
• ·         Threonine: It promotes the functioning of immune system. 
• ·         Tryptophan: Plays a vital role in maintaining our appetite.
• ·         Isoleucine: Plays a vital role in synthesis of hemoglobin and it is a major component of RBC (red blood cells)
• ·         Methionine: Helps in maintaining a good and healthy skin.
• ·         Leucine: It promotes the synthesis of growth hormones.
• ·         Lysine: They are involved in the synthesis of enzymes and other hormones.
• ·         Histidine: Helps in the production and synthesis of both RBC (red blood cells) and WBC (white blood cells)

Functions Non Essential Amino Acids:

• ·         Alanine: Helps in removal of toxic from our body.
• ·         Cysteine: It provides resistance to our body and inhibits the growth of hairs, nails and etc.
• ·         Cystine: It functions as an antioxidant and protects our body against radiation and pollution.
• ·         Glutamine: It is necessary for the synthesis of RNA and DNA.
• ·         Glycine: It acts as a neurotransmitter and plays a vital role in healing wounds.
• ·         Glutamate: Helps in removal of toxic from our body.
• ·         Arginine: It promotes the biosynthesis of proteins.
• ·         Tyrosine: It plays a vital role in the production of T3 and T4 thyroid hormones.
• ·         Serine: Helps in growth of muscles.
• ·         Asparagines: Helps in the formations of purines and pyrimidines for the DNA synthesis.
• ·         Aspartic acid: It is similar to asparagines amino acids. It promotes the synthesis of other amino acids.
• ·         Proline: Helps in regeneration of new skin.

Classification of Amino Acids

Amino acids are placed into seven groups based on their substituent.

• ·         Aliphatic amino acids: Alanine, glycine, isoleucine, leucine, Proline and Valine.
• ·         Aromatic amino acids: phenylalanine, tryptophan and tyrosine
• ·         Acidic amino acids: aspartic acid and glutamic acid.
• ·         Basic amino acids: arginine, histidine and lysine.
• ·         Hydroxylic amino acids: serine and threonine.
• ·         Sulphur containing amino acids: cytosine and methionine.
• ·         Amidic amino acids: asparagines and glutamine.