electrogenic while a fish that has the ability to detect electric fields is called

electroreceptive . Most electrogenic fish are also electroreceptive.[1] The only group of electrogenic fish who are not electroreceptive come from the family Uranoscopidae. [2] Electric fish species can be found both in the ocean and in freshwater rivers of South America (Gymnotiformes ) and Africa (Mormyridae ). Many fish such as

sharks , rays and catfishes can detect electric fields and are thus electroreceptive, but they are not classified as electric fish because they cannot generate electricity. Most common bony fish (teleosts), including most fish kept in aquaria or caught for food, are neither electrogenic nor electroreceptive.

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Video of a complete electric organ discharge. The electric field potential is represented on a sagittal across the modelled fish. Hot tones represent positive potential values, while cold tones represent negative electric potentials. The black line indicates the points where the potentials are zero.

    Electric eels are fish capable of generating an electric field .

Audio recording of resting electric organ discharge of

Brachyhypopomus bennetti .

Electric fish produce their electrical fields from a specialized structure called an electric organ . This is made up of modified muscle or nerve cells, which became specialized for producing bioelectric fields stronger than those that normal nerves or muscles produce.[3] Typically this organ is located in the tail of the electric fish. The electrical output of the organ is called the electric organ discharge .

   Strongly electric fish

Strongly electric fish are fish with an electric organ discharge that is powerful enough to stun prey or be used for defense. Typical examples are the electric eel, the electric catfishes , and electric rays . The amplitude of the signal can range from 10 to 860 volts with a current of up to 1 ampere , according to the surroundings, for example different conductances of salt and fresh water. [5] To maximize the power delivered to the surroundings, the impedances of the electric organ and the water must be matched :

Strongly electric marine fish give low voltage, high current electric discharges. In salt water, a small voltage can drive a large current limited by the internal resistance of the electric organ. Hence, the electric organ consists of many electrocytes in parallel.

Freshwater fish have high voltage, low current discharges. In freshwater, the power is limited by the voltage needed to drive the current through the large resistance of the medium. Hence, these fish have numerous cells in series. [6]

Weakly electric fish

The elephantnose fish is a weakly electric fish which generates an electric field with its electric organ and then processes the returns from its electroreceptors to locate nearby objects. [7]

    Weakly electric fish generate a discharge that is typically less than one volt. These are too weak to stun prey and instead are used for navigation, object detection (electrolocation ) and communication with other electric fish (electrocommunication). Two of the best-known and most-studied examples are Peters's elephantnose fish (Gnathonemus petersii ) and the

black ghost knifefish (Apteronotus albifrons ). The males of the nocturnal

Brachyhypopomus pinnicaudatus , a toothless knifefish native to the Amazon basin, give off big, long electric hums to attract a mate. [8]

The electric organ discharge waveform takes two general forms depending on the species. In some species the waveform is continuous and almost

sinusoidal (for example the genera

Apteronotus, Eigenmannia and

Gymnarchus ) and these are said to have a wave-type electric organ discharge. In other species, the electric organ discharge waveform consists of brief pulses separated by longer gaps (for example Gnathonemus, Gymnotus,

Leucoraja ) and these are said to have a pulse-type electric organ discharge.

Jamming avoidance response

Main article: Jamming avoidance response

It had been theorized as early as the 1950s that electric fish near each other might experience some type of interference or inability to segregate their own signal from those of neighbors. This issue does not arise, however, because the electric fish adjust to avoid frequency interference. In 1963, two scientists, Akira Watanabe and Kimihisa Takeda, discovered the behavior of the jamming avoidance response in the knifefish Eigenmannia sp. In collaboration with T.H. Bullock and colleagues, the behavior was further developed.[9] Finally, the work of Walter Heiligenberg expanded it into a full neuroethology study by examining the series of neural connections that led to the behavior. [10] Eigenmannia is a weakly electric fish that can self-generate electric discharges through

electrocytes in its tail. Furthermore, it has the ability to electrolocate by analyzing the perturbations in its electric field. However, when the frequency of a neighboring fish's current is very close (less than 20 Hz difference) to that of its own, the fish will avoid having their signals interfere through a behavior known as jamming avoidance response. If the neighbor's frequency is higher than the fish's discharge frequency, the fish will lower its frequency, and vice versa. The sign of the frequency difference is determined by analyzing the "beat" pattern of the incoming interference which consists of the combination of the two fish's discharge patterns. [10]

Neuroethologists performed several experiments under Eigenmannia's natural conditions to study how it determined the sign of the frequency difference. They manipulated the fish's discharge by injecting it with curare which prevented its natural electric organ from discharging. Then, an electrode was placed in its mouth and another was placed at the tip of its tail. Likewise, the neighboring fish's electric field was mimicked using another set of electrodes. This experiment allowed neuroethologists to manipulate different discharge frequencies and observe the fish's behavior. From the results, they were able to conclude that the electric field frequency, rather than an internal frequency measure, was used as a reference. This experiment is significant in that not only does it reveal a crucial neural mechanism underlying the behavior but also demonstrates the value neuroethologists place on studying animals in their natural habitats.

     The human body is composed of a very large number of cells. For example, our skin cells protect the body and cover the organs and body cavities. All these cells have a certain lifespan .in which they live and are then replaced by new ones.

Generally, a life cycle of a cell include:

1. Cell growth

2. Cell division

3. Formation of cell daughters (new cells)

4. Separation from the parent cells

5. Finally, the death of cells

Theory of Cell

Furthermore, the theory of cell defines 3 main points about the cell which also shows the importance of cells and their life cycle. The 3 main points are:

1. All living things are based on one or more than one cell.

2. A cell is a basic block of life that can make single-celled organisms to multicellular organisms.

3. New Cells come from old cells by cellular division; also called asexual reproduction.

 Mitosis – How New Cells Are Born?

Mitosis is the basic platform where cells divide and introduce new cells – called daughter cells. In the formation of new cells, the parent cells have to complete several important tasks, such as growing, copying DNA, and becoming ready to divide. Generally, parent cells physically separate into two daughter cells.

Stages of Mitosis

Mitosis has 4 main stages which are:

1. Prophase – This is the first step in mitosis which brings many structural changes in the cells such as condensation of chromosomes. The condensation helps chromosomes to easier separate from each other in later stages.

2. Metaphase – In this phase, the chromosomes start to align in a plane called the metaphase plate. The cell also makes sure that, the process of alignment is correct before moving to the next stage. In case there is an issue with the alignment, the cell will not be able to move towards the next stage of the division until the issue is solved.

3. Anaphase – The chromosomes which were aligned in metaphase start to separate from each other as chromatids and move towards the opposite direction.

4. Telophase – In this phase, most parts of the cell are divided into two daughter cells. After this, the daughter cells start to normalize their structure to survive as separate cells.

How Do Cells Survive?

Like every living thing, cells have to get energy for living, growing, and reproducing. For example, plant cells get energy from the sunlight to make their food to survive. And in the human body, cells also get the energy to survive from the food we eat.

Cells must have to take important substances such as oxygen , food, and water from its environment and excrete waste products. If the cell is a single-celled organism, such as bacteria , then it has to get these things from the environment. But, if cells are part of a multicellular organism, such as humans, then they get necessary food and water when that multicellular organism will eat. Without these substances, cells will not survive and in a very short period, they will die.

How Do Cells Die?

Cells can die in many ways, such as heat, poison, lack of oxygen, dehydration, and infection from viruses or attacks from other cells. Overheating, poison, and infection can make the cells to swell-up and burst. Moreover, cells have genetic programing of self-destruction when they reach their maximum age. For example, the maximum lifespan of our red blood cells (RBCs) is 120 days (4 months). However, the RBCs can also die early due to lack of oxygen and infection caused by viruses, such as flu, and bacteria.

Interesting Facts

In around 4 months, all red blood cells in our body are replaced with new cells.

The average lifespan of a neuron in the human brain ranges from a few months to 3 years. However, neurons can also live longer than that 3 years in some cases.

Anaerobic microorganisms that don’t require oxygen for their survival.