What animal is this?

I have seen this bug/worm twice on my dog's leg after taking him for a walk this week. I think that this is a leech, but my mom disagrees because she says leeches are not found where we live but are found around beaches. We live in Carmel Mountain San Diego: Google Maps. The closest beach is around 15 minutes away. The bug is approximately the size of a fingernail, and it did not do anything when I picked it up.

EDIT: We were just walking around my neighborhood, nowhere jungle-ish at all.

Animal Classification

The animal kingdom is separated into nine taxonomic ranks: Life > Domain > Kingdom > Phylum > Class > Order > Family > Genus > Species. Though this is the true classification for animals, the first two ranks are often omitted, and on occasion, an extra one - subfamily- is added.

Take the lion, for example. Below is the animal classification for the lion:

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Felidae
Subfamily: Pantherinae
Genus: Panthera
Species: Panthera leo

Another example is the blue whale, whose animal classification is as follows:

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Cetacea
Family: Balaenopteridae
Genus: Balaenoptera
Species: Balaenoptera musculus

Animal classification is the categorizing of animals and organisms hierarchically.

The ranking system is based on a fixed number of levels such as kingdom, family, or genus. The order goes:

Animal classification is based on an organisms decent from a common ancestor. Accordingly, the most important traits for classification are those inherited from a common ancestor. An example would be birds and bats, which both can fly, but this characteristic is not used to classify them into a class because they did not inherit this from a common ancestor. Despite their differences, both bats and whales feed their offspring milk, therefor this feature is used to classify them both as mammals.

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Subclass: Eutheria
Order: Cetacea

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Eutheria
Superorder: Laurasiatheria
Order: Chiroptera

*Note the similarities in bat and whale classification.


The history of zoology traces the study of the animal kingdom from ancient to modern times. Prehistoric man needed to study the animals and plants in his environment in order to exploit them and survive. There are cave paintings, engravings and sculptures in France dating back 15,000 years showing bison, horses and deer in carefully rendered detail. Similar images from other parts of the world illustrated mostly the animals hunted for food but also the savage animals. [2]

The Neolithic Revolution, which is characterized by the domestication of animals, continued over the period of Antiquity. Ancient knowledge of wildlife is illustrated by the realistic depictions of wild and domestic animals in the Near East, Mesopotamia and Egypt, including husbandry practices and techniques, hunting and fishing. The invention of writing is reflected in zoology by the presence of animals in Egyptian hieroglyphics. [3]

Although the concept of zoology as a single coherent field arose much later, the zoological sciences emerged from natural history reaching back to the biological works of Aristotle and Galen in the ancient Greco-Roman world. Aristotle, in the fourth century BC, looked at animals as living organisms, studying their structure, development and vital phenomena. He divided them into two groups, animals with blood, equivalent to our concept of vertebrates, and animals without blood (invertebrates). He spent two years on Lesbos, observing and describing the animals and plants, considering the adaptations of different organisms and the function of their parts. [4] Four hundred years later, Roman physician Galen dissected animals to study their anatomy and the function of the different parts, because the dissection of human cadavers was prohibited at the time. [5] This resulted in some of his conclusions being false, but for many centuries it was considered heretical to challenge any of his views, so the study of anatomy stultified. [6]

During the post-classical era, Middle Eastern science and medicine was the most advanced in the world, integrating concepts from Ancient Greece, Rome, Mesopotamia and Persia as well as the ancient Indian tradition of Ayurveda, while making numerous advances and innovations. [7] In the 13th century, Albertus Magnus produced commentaries and paraphrases of all Aristotle's works his books on topics like botany, zoology, and minerals included information from ancient sources, but also the results of his own investigations. His general approach was surprisingly modern, and he wrote, "For it is [the task] of natural science not simply to accept what we are told but to inquire into the causes of natural things." [8] An early pioneer was Conrad Gessner, whose monumental 4,500-page encyclopedia of animals, Historia animalium, was published in four volumes between 1551 and 1558. [9]

In Europe, Galen's work on anatomy remained largely unsurpassed and unchallenged up until the 16th century. [10] [11] During the Renaissance and early modern period, zoological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Andreas Vesalius and William Harvey, who used experimentation and careful observation in physiology, and naturalists such as Carl Linnaeus, Jean-Baptiste Lamarck, and Buffon who began to classify the diversity of life and the fossil record, as well as studying the development and behavior of organisms. Antonie van Leeuwenhoek did pioneering work in microscopy and revealed the previously unknown world of microorganisms, laying the groundwork for cell theory. [12] van Leeuwenhoek's observations were endorsed by Robert Hooke all living organisms were composed of one or more cells and could not generate spontaneously. Cell theory provided a new perspective on the fundamental basis of life. [13]

Having previously been the realm of gentlemen naturalists, over the 18th, 19th and 20th centuries, zoology became an increasingly professional scientific discipline. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography, laying the foundations for biogeography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. [14]

These developments, as well as the results from embryology and paleontology, were synthesized in the 1859 publication of Charles Darwin's theory of evolution by natural selection in this Darwin placed the theory of organic evolution on a new footing, by explaining the processes by which it can occur, and providing observational evidence that it had done so. [15] Darwin's theory was rapidly accepted by the scientific community and soon became a central axiom of the rapidly developing science of biology. The basis for modern genetics began with the work of Gregor Mendel on peas in 1865, although the significance of his work was not realized at the time. [16]

Darwin gave a new direction to morphology and physiology, by uniting them in a common biological theory: the theory of organic evolution. The result was a reconstruction of the classification of animals upon a genealogical basis, fresh investigation of the development of animals, and early attempts to determine their genetic relationships. The end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery. In the early 20th century, the rediscovery of Mendel's work led to the rapid development of genetics, and by the 1930s the combination of population genetics and natural selection in the modern synthesis created evolutionary biology. [17]

Research in cell biology is interconnected to other fields such as genetics, biochemistry, medical microbiology, immunology, and cytochemistry. With the sequencing of the DNA molecule by Francis Crick and James Watson in 1953, the realm of molecular biology opened up, leading to advances in cell biology, developmental biology and molecular genetics. The study of systematics was transformed as DNA sequencing elucidated the degrees of affinity between different organisms. [18]

Zoology is the branch of science dealing with animals. A species can be defined as the largest group of organisms in which any two individuals of the appropriate sex can produce fertile offspring about 1.5 million species of animal have been described and it has been estimated that as many as 8 million animal species may exist. [19] An early necessity was to identify the organisms and group them according to their characteristics, differences and relationships, and this is the field of the taxonomist. Originally it was thought that species were immutable, but with the arrival of Darwin's theory of evolution, the field of cladistics came into being, studying the relationships between the different groups or clades. Systematics is the study of the diversification of living forms, the evolutionary history of a group is known as its phylogeny, and the relationship between the clades can be shown diagrammatically in a cladogram. [20]

Although someone who made a scientific study of animals would historically have described themselves as a zoologist, the term has come to refer to those who deal with individual animals, with others describing themselves more specifically as physiologists, ethologists, evolutionary biologists, ecologists, pharmacologists, endocrinologists or parasitologists. [21]

Although the study of animal life is ancient, its scientific incarnation is relatively modern. This mirrors the transition from natural history to biology at the start of the 19th century. Since Hunter and Cuvier, comparative anatomical study has been associated with morphography, shaping the modern areas of zoological investigation: anatomy, physiology, histology, embryology, teratology and ethology. [22] Modern zoology first arose in German and British universities. In Britain, Thomas Henry Huxley was a prominent figure. His ideas were centered on the morphology of animals. Many consider him the greatest comparative anatomist of the latter half of the 19th century. Similar to Hunter, his courses were composed of lectures and laboratory practical classes in contrast to the previous format of lectures only.

Gradually zoology expanded beyond Huxley's comparative anatomy to include the following sub-disciplines:

Classification Edit

Scientific classification in zoology, is a method by which zoologists group and categorize organisms by biological type, such as genus or species. Biological classification is a form of scientific taxonomy. Modern biological classification has its root in the work of Carl Linnaeus, who grouped species according to shared physical characteristics. These groupings have since been revised to improve consistency with the Darwinian principle of common descent. Molecular phylogenetics, which uses nucleic acid sequence as data, has driven many recent revisions and is likely to continue to do so. Biological classification belongs to the science of zoological systematics. [23]

Many scientists now consider the five-kingdom system outdated. Modern alternative classification systems generally start with the three-domain system: Archaea (originally Archaebacteria) Bacteria (originally Eubacteria) Eukaryota (including protists, fungi, plants, and animals) [24] These domains reflect whether the cells have nuclei or not, as well as differences in the chemical composition of the cell exteriors. [24]

Further, each kingdom is broken down recursively until each species is separately classified. The order is: Domain kingdom phylum class order family genus species. The scientific name of an organism is generated from its genus and species. For example, humans are listed as Homo sapiens. Homo is the genus, and sapiens the specific epithet, both of them combined make up the species name. When writing the scientific name of an organism, it is proper to capitalize the first letter in the genus and put all of the specific epithet in lowercase. Additionally, the entire term may be italicized or underlined. [25]

The dominant classification system is called the Linnaean taxonomy. It includes ranks and binomial nomenclature. The classification, taxonomy, and nomenclature of zoological organisms is administered by the International Code of Zoological Nomenclature. A merging draft, BioCode, was published in 1997 in an attempt to standardize nomenclature, but has yet to be formally adopted. [26]

Vertebrate and invertebrate zoology Edit

Vertebrate zoology is the biological discipline that consists of the study of vertebrate animals, that is animals with a backbone, such as fish, amphibians, reptiles, birds and mammals. The various taxonomically oriented disciplines such as mammalogy, biological anthropology, herpetology, ornithology, ichthyology identify and classify species and study the structures and mechanisms specific to those groups. The rest of the animal kingdom is dealt with by invertebrate zoology, a vast and very diverse group of animals that includes sponges, echinoderms, tunicates, worms, molluscs, arthropods and many other phyla, but single-celled organisms or protists are not usually included. [27]

Structural zoology Edit

Cell biology studies the structural and physiological properties of cells, including their behavior, interactions, and environment. This is done on both the microscopic and molecular levels, for single-celled organisms such as bacteria as well as the specialized cells in multicellular organisms such as humans. Understanding the structure and function of cells is fundamental to all of the biological sciences. The similarities and differences between cell types are particularly relevant to molecular biology.

Anatomy considers the forms of macroscopic structures such as organs and organ systems. [28] It focuses on how organs and organ systems work together in the bodies of humans and animals, in addition to how they work independently. Anatomy and cell biology are two studies that are closely related, and can be categorized under "structural" studies. Comparative anatomy is the study of similarities and differences in the anatomy of different groups. It is closely related to evolutionary biology and phylogeny (the evolution of species). [29]

Physiology Edit

Physiology studies the mechanical, physical, and biochemical processes of living organisms by attempting to understand how all of the structures function as a whole. The theme of "structure to function" is central to biology. Physiological studies have traditionally been divided into plant physiology and animal physiology, but some principles of physiology are universal, no matter what particular organism is being studied. For example, what is learned about the physiology of yeast cells can also apply to human cells. The field of animal physiology extends the tools and methods of human physiology to non-human species. Physiology studies how for example nervous, immune, endocrine, respiratory, and circulatory systems, function and interact. [30]

Developmental biology Edit

Developmental biology is the study of the processes by which animals and plants reproduce and grow. The discipline includes the study of embryonic development, cellular differentiation, regeneration, asexual reproduction, metamorphosis, and the growth and differentiation of stem cells in the adult organism. [31] Development of both animals and plants is further considered in the articles on evolution, population genetics, heredity, genetic variability, Mendelian inheritance, and reproduction.

Evolutionary biology Edit

Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. Evolutionary research is concerned with the origin and descent of species, as well as their change over time, and includes scientists from many taxonomically oriented disciplines. For example, it generally involves scientists who have special training in particular organisms such as mammalogy, ornithology, herpetology, or entomology, but use those organisms as systems to answer general questions about evolution. [32]

Evolutionary biology is partly based on paleontology, which uses the fossil record to answer questions about the mode and tempo of evolution, [33] and partly on the developments in areas such as population genetics [34] and evolutionary theory. Following the development of DNA fingerprinting techniques in the late 20th century, the application of these techniques in zoology has increased the understanding of animal populations. [35] In the 1980s, developmental biology re-entered evolutionary biology from its initial exclusion from the modern synthesis through the study of evolutionary developmental biology. Related fields often considered part of evolutionary biology are phylogenetics, systematics, and taxonomy. [36]

Ethology Edit

Ethology is the scientific and objective study of animal behavior under natural conditions, [37] as opposed to behaviourism, which focuses on behavioral response studies in a laboratory setting. Ethologists have been particularly concerned with the evolution of behavior and the understanding of behavior in terms of the theory of natural selection. In one sense, the first modern ethologist was Charles Darwin, whose book, The Expression of the Emotions in Man and Animals, influenced many future ethologists. [38]

A subfield of ethology is behavioral ecology which attempts to answer Nikolaas Tinbergen's four questions with regard to animal behavior: what are the proximate causes of the behaviour, the developmental history of the organism, the survival value and phylogeny of the behavior? [39] Another area of study is animal cognition, which uses laboratory experiments and carefully controlled field studies to investigate an animal's intelligence and learning. [40]

Biogeography Edit

Biogeography studies the spatial distribution of organisms on the Earth, [41] focusing on topics like plate tectonics, climate change, dispersal and migration, and cladistics. It is an integrative field of study, uniting concepts and information from evolutionary biology, taxonomy, ecology, physical geography, geology, paleontology and climatology. [42] The origin of this field of study is widely accredited to Alfred Russel Wallace, a British biologist who had some of his work jointly published with Charles Darwin. [43]

Molecular biology Edit

Molecular biology studies the common genetic and developmental mechanisms of animals and plants, attempting to answer the questions regarding the mechanisms of genetic inheritance and the structure of the gene. In 1953, James Watson and Francis Crick described the structure of DNA and the interactions within the molecule, and this publication jump-started research into molecular biology and increased interest in the subject. [44] While researchers practice techniques specific to molecular biology, it is common to combine these with methods from genetics and biochemistry. Much of molecular biology is quantitative, and recently a significant amount of work has been done using computer science techniques such as bioinformatics and computational biology. Molecular genetics, the study of gene structure and function, has been among the most prominent sub-fields of molecular biology since the early 2000s. Other branches of biology are informed by molecular biology, by either directly studying the interactions of molecules in their own right such as in cell biology and developmental biology, or indirectly, where molecular techniques are used to infer historical attributes of populations or species, as in fields in evolutionary biology such as population genetics and phylogenetics. There is also a long tradition of studying biomolecules "from the ground up", or molecularly, in biophysics. [45]

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thank you for your information. i already have an answer in my assignment. this site is very helpful. keep on doing good things like this. Georgesplane November 20, 2010

@ Alchemy- If you were to name the classification of the seven major phyla of humans you would call us: Animalia [kingdom] Chordata [phylum] Mammalia [class] Primata [order] Hominidae [family] Homo [genus] Homo Sapiens [species].

A chimpanzee, for example, would have the same phylum, but different genus and species, from a human. An armadillo on the other hand would share the same kingdom, phylum and class, but would differ from the order down. GenevaMech November 20, 2010

@ Alchemy- The seven major divisions of taxa are based on a systems invented by a Swedish biologist in the 18th century. They are as follows (but note that these are the main classifications and there are many other sub classifications within each classification): Kingdom, Phylum, Class, Order, Family, Genus, and Species.

Biologists can use these classifications to show the relationship between different organisms. The more taxa two organisms have in common, the more closely they are related. Alchemy November 20, 2010

I always learn something new on this website. I would have thought that the class would have fallen just below kingdom, followed closely by phylums. Naming whether something is a plant, animal, or amphibian seems like it would have been the most logical way to classify something below the title of kingdom, but that just goes to show I am no biologist. What are the other different levels of classification in taxonomy? Now I'm curious to know how humans are specifically classified.


Invertebrates are animals that are missing a backbone. They are an incredibly diverse group and include over 90% of all animal species. Many invertebrates we know very little about or are even yet to be discovered.

The evolution of invertebrates was the Earth’s introduction to animals. The most ‘primitive’ invertebrates can easily be mistaken for plants or other types of organisms because they look so different to the animals we are familiar with.

These ‘primitive’ animals include organisms such as sponges, corals and anemones. Sponges are thought to be one of the first animals to have evolved. They retain some of the single-celled ancestry that animals evolved from. Sponges are able live and reproduce as a single-celled organism for a short period. Corals and anemones are slightly more advanced than sponges and belong to the same group of animals as jellyfish.

Insects, spiders and crustaceans all belong to a group of invertebrates called arthropods. Many of these invertebrates are very advanced and display complex behaviors and body types. Arthropods have complex bodies with hard external skeletons and jointed limbs.

Many species from these group show advanced behaviors. Bees for example communicate with each other by wagging their backside in various ways. Spiders produce complex webs to catch prey and stake out until an unsuspecting insect gets caught.

Arthropods are arguably the most successful group of animals on Earth. They are an incredibly diverse group and estimates of the total number of arthropod species is well over a million. Insects are particularly diverse and account for over half of all animal species.

Between jellyfish and insects there is a wide range of many other invertebrates. Some examples include worms, millipedes, centipedes, starfish, urchins, squid, octopi, oysters and snails.



With Animal Science, there are plenty of ways to get experience related to your major beyond the traditional classroom setting. Take a look at some of the student clubs and activities related to the Biology and Biotechnology option.

Nebraska Beef Industry Scholars Block and Bridle Club

What Is the Average Wildlife Biologist Salary?

According to the Bureau of Labor Statistics, the average Wildlife Biologist's salary is $57,710. Most Wildlife Biologists work full-time with the potential to work overtime or evening hours depending on their subject of study.

StateTotal EmploymentBottom 25%Median SalaryTop 75%
District of Columbia90$62,480$97,930$126,790
New Hampshire90$45,220$54,320$64,230
New Jersey140$50,420$77,870$91,710
New Mexico190$38,840$52,220$65,480
New York380$53,170$64,500$74,590
North Carolina430$44,160$52,520$65,320
North Dakota90$52,570$63,130$69,850
Rhode Island40$67,630$75,710$88,070
South Carolina310$35,310$45,870$61,220
South Dakota160$38,460$46,330$57,170
West Virginia120$36,200$46,700$63,150

Table data taken from BLS (

What's human? What's animal? And what of the biology in between?

F riday's report by the Academy of Medical Sciences on the increasingly fuzzy boundaries between the human and the animal is the latest in a long series of policy reflections on how to keep pace with developments in the biosciences.

It can justly be said that politics and regulation have not dealt well with our newfound capacities for muddying the boundaries between us and other species. And yet the last two decades have witnessed an unprecedented growth in bioscientific techniques that increasingly call into question what it means to be human. Take the human genome project: many of us may have intuitively suspected that we might have more genetically in common with the chimpanzee than even Darwin had envisaged, only then to be told of our cousinly closeness to the fruit fly, maize and the zebra fish.

Casting a glance back to the 1990s, trans-species transplantation seemed to promise a new era of limitless animal organs and tissues. Who knows, it may still. But that dream slowly sank from view amid concerns about potentially catastrophic trans-species disease, and increasing evidence of its poor performance in preclinical trials with primates. Move forward a decade and we have the trans-species embryo debate, resulting in legislative changes permitting a whole new class of research embryos incorporating animal DNA. So to the classical question of "what is an embryo", has been added the equally vexing puzzle "what is an animal".

Bioscientific hybrids are difficult to categorise, disorderly, existing on the fringes of the humanised animal and the animalised human. And yet policymaking has arguably had a poor track in getting to grips with and understanding trans-species innovation. Trans-species biologies present acute difficulties especially in terms of regulation because they confuse and traverse regulatory institutional boundaries.

In the UK, as elsewhere, regulatory agencies have tended to regulate humans on the one hand, and animals on the other, with little consideration for what might lie between. The tendency has been to deal with all things animal through the Home Office and its Animal Procedures Inspectorate, and to deal with all things human through the Department of Health. There are good and disturbing grounds for suspecting this division has become increasingly naive and meaningless, as the biosciences enter their trans-species future.

In the late 1990s the UK deemed it necessary to establish a regulatory body to manage the many murky trans-species hybrid implications of xenotransplantation, the UK Xenotransplantation Interim Regulatory Authority. But far from being a porous conduit between the DoH and the Home Office, UKXIRA found itself hamstrung. The Home Office would seek its advice on animal experiments involving primates but would not allow the authority to see confidential trial applications or the results of previous studies. This proved to be a poor basis on which to advise the DoH about the wisdom or otherwise of proceeding to clinical trials with humans. UKXIRA wasn't perfect, but it represented an important attempt to overcome the regulatory divide between the human and the animal. The government's decision to disband UKXIRA in 2006 could justifiably be viewed as myopic and short-sighted, given the trans-species direction of travel in the biosciences. In losing UKXIRA, the UK also lost important institutional experience and a model for dealing with interspecies biotechnological developments.

Even more recently, the UK trans-species embryo debate points to equally serious flaws in the regulation of the wild indeterminate zones between us and other animals. One strategy evident in the run-up to changes in legislation allowing the creation of trans-species embryos was to downplay that they might be trans-species at all. Just reflect for a moment on shifts in the language used to describe these embryos: the DoH, for instance, started out talking about "trans-species embryos" before finally settling on its preferred term, "human admixed embryos". In other words, these embryos might be a bit mixed up, but they're essentially human. No worries.

Such embryos would allow stem-cell scientists to use animal eggs rather than scarce human eggs to create stem-cell lines. The animal nuclei could be removed and replaced with human nuclei leaving only a residue of animal egg DNA behind. It was striking to see this process now described by some stem-cell scientists as "especiation" in place of the more scientifically conventional term "enucleation". In this way, the vexing animal is tidied away behind a thin veneer of language and rhetoric.

More worrying is the continuing confusion over whether trans-species embryos should be regulated by human or animal agencies – again, the Home Office or the DoH. That boundary comes down to potentially confused assessments of whether it is the animal or the human which "predominates" in the resulting embryo. I had the privilege of discussing this recently with an eminent UK reproductive scientist who had been involved in crafting the legislation. "Ultimately," he said, "it has to be either human or animal to be regulated . otherwise we would have to do away with our whole regulatory edifice." Well, that is exactly what we may have to do.

It could be argued that the report by the Academy of Medical Sciences searchingly arrives at a point of dissatisfaction with the bipedal and binary regulation of transbiology. Perhaps it's time for an overhaul of our institutions, their language and assumptions about what it is to be human, animal and the many murky zones in between.

3. Tarsier

Tarsiers are interesting creatures.These little guys grow to be a whopping five inches. They eat insects and have been known to jump from tree to tree and eat birds.

That&aposs right. They&aposre nocturnal, and move very, very fast using their bony fingers and long tail. Females usually have about one little baby tarsier per year. What else is unnatural about these creatures? They can twist their heads 180 degrees like an owl. If they were any bigger, I&aposd be terrified of them.

This once again proves that Mother Nature has more creativity than science fiction writers.

Animal Cell Structure

Animal cells have a variety of different organelles that work together to allow the cell to perform its functions. Each cell can be thought of as a large factory with many departments, like manufacturing, packaging, shipping, and accounting. Different organelles represent each of these departments.

There are lots of different animal cells that each carry out specialized functions. Therefore, not every animal cell has all types of organelles, but in general, animal cells do contain most (if not all) of the following organelles. Additionally, some organelles will be highly abundant in certain cells and not others.


The nucleus contains all the genetic material in a cell. This genetic information is called deoxyribonucleic acid (DNA). DNA contains all the instructions for making proteins, which control all of the body’s activities. Therefore, the nucleus is like the manager’s office of the cell.

DNA is an extremely precious and tightly regulated molecule. Therefore, it does not just exist naked in the nucleus! Instead, DNA is tightly wound around structural proteins called histones to form chromatin. When the cell is ready to divide to pass the genetic information on to new cells (the daughter cells), the chromatin forms highly condensed structures called chromosomes.

The nucleus regulates which genes are turned ‘on’ in the cell, and at what time. This controls the cell’s activity. The genes that are active at a given time will be different depending on the type of cell and the function it performs.

The nucleus is surrounded by a nuclear envelope (also called the nuclear membrane), which separates it from the rest of the cell. The nuclear envelope also contains pores that permit the entry and exit of some molecules.

As well as all the genetic material, there is also a sub-section of the nucleus called the nucleolus, which looks like a nucleus within the nucleus. The nucleolus is the site of ribosome synthesis. The nucleus is surrounded by a nuclear envelope (also called nuclear membrane), which separates it from the rest of the cell.

The nucleus also regulates the growth and division of the cell. When the cell is preparing to divide during mitosis, the chromosomes in the nucleus duplicate and separate, and two daughter cells form. Organelles called centrosomes help to organize the DNA during cell division.


Ribosomes are organelles found in both prokaryotic and eukaryotic cells. They are like mini machines that synthesize all the proteins in the cell. In any single animal cell, there can be as many as 10 million ribosomes! The ribosomes form the manufacturing department of the cell.

In the nucleus, a sequence of DNA that codes for a specific protein is copied onto an intermediate molecule called messenger RNA (mRNA). The mRNA molecule carries this information to the ribosome, and its sequence determines the order of amino acids in a polypeptide chain. The ribosome synthesizes this polypeptide chain, which eventually folds to become a protein. In animal cells, ribosomes can be found freely in a cell’s cytoplasm or attached to the endoplasmic reticulum.

Endoplasmic Reticulum

The endoplasmic reticulum (ER) is a network of flattened, membrane-bound sacs that are involved in the production, processing, and transport of proteins that have been synthesized by ribosomes. The endoplasmic reticulum is like the assembly line of the cell, where the products produced by the ribosomes are processed and assembled.

There are two kinds of endoplasmic reticulum: smooth and rough. The rough ER has ribosomes attached to the surface of the sacs. Smooth ER does not have ribosomes attached and has functions in storage, synthesizing lipids, removing toxic substances.

Golgi Apparatus

The Golgi apparatus, also called the Golgi complex or Golgi body, receives proteins from the ER and folds, sorts, and packages these proteins into vesicles. The Golgi apparatus is like the shipping department of the cell, as it packages proteins up for delivery to their destinations.

Like the ER, the Golgi apparatus also consists of a series of membrane-bound sacs. These sacs originate from vesicles that have budded off from the ER. Unlike the system of membranes in the ER, which are interconnected, the pouches of the Golgi apparatus are discontinuous.


Lysosomes are a type of vesicle. Vesicles are spheres surrounded by a membrane that excludes their contents from the rest of the cytoplasm. Vesicles are used extensively within the cell for metabolism and transport of large molecules that cannot cross membrane unaided.

Lysosomes are specialized vesicles that contain digestive enzymes. These enzymes can break down large molecules like organelles, carbohydrates, lipids, and proteins into smaller units so that the cell can reuse them. Therefore, they are like the waste disposal/recycling department of the cell.


Mitochondria are the energy-producing organelles, commonly known as “the powerhouse of the cell.” The process of cellular respiration occurs in the mitochondria. During this process, sugars and fats are broken down through a series of chemical reactions, releasing energy in the form of adenosine triphosphate (ATP).

ATP is like the energy currency of the cell. Think of each molecule like a rechargeable battery that can be used to power various cellular processes.


The cytosol is the gel-like liquid contained within cells. The cytosol and all the organelles within it – except for the nucleus – are collectively referred to as the cell’s cytoplasm. This cytosol consists primarily of water, but also contains ions, proteins, and small molecules. The pH is generally neutral, around 7.


The cytoskeleton is a network of filaments and tubules found throughout the cytoplasm of the cell. It has many functions: it gives the cell shape, provides strength, stabilizes tissues, anchors organelles within the cell, and has a role in cell signaling. It also provides mechanical support to allow cells to move and divide. There are three types of cytoskeletal filaments: microfilaments, microtubules, and intermediate filaments.

Cell Membrane

The cell membrane surrounds the entire cell and separates its components from the outer environment. The cell membrane is a double layer made up of phospholipids (called the phospholipid bilayer). Phospholipids are molecules with a phosphate group head attached to glycerol and two fatty acid tails. They spontaneously form double membranes in water due to the hydrophilic properties of the head and hydrophobic properties of the tails.

The cell membrane is selectively permeable, meaning it only allows certain molecules to enter and exit. Oxygen and carbon dioxide pass through easily, while larger or charged molecules must go through special channels, bind to receptors, or be engulfed.

Watch the video: Top10 Τα Πραγματικά Δυνατότερα Ζώα Στη Γη (November 2021).