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In biology and ecology, an organism (in Greek organon = instrument) is a living being. The origin of life and the relationships between its major lineages are controversial. Two main grades may be distinguished, the prokaryotes and eukaryotes. The prokaryotes are generally considered to represent two separate domains, called the Bacteria and Archaea, which are not closer to one another than to the eukaryotes. The gap between prokaryotes and eukaryotes is widely considered a major missing link in evolutionary history. Two eukaryotic organelles, namely mitochondria and chloroplasts, are generally considered to be derived from endosymbiotic bacteria. The phrase complex organism describes any organism with more than one cell. Characteristics common to many organisms include:
These are not universal, however. Many organisms are incapable of independent movement, and do not respond directly to their environment. Microorganisms such as bacteria may not conduct respiration, using alternate chemical pathways instead. And many organisms are incapable of reproduction. Biological Organization
Environmental Organization
Classification The following articles are entry points for information about the classification of organisms:
Life span One of the basic parameters of organism is its life span. Some animals live as short as one day, while some plants can live thousands of years. Aging is important when determining life span of most organisms, bacterium, a virus or even a prion. Human anatomy Human anatomy or anthropotomy is a special field within anatomy. It studies organs and organ systems of the human body, leaving the study of tissues to histology and cells to cytology. The human body, like the bodies of all animals, is made up of systems, that are made up of organs, that are made up of tissues, that are made up of cells. Major systems of the human body: Cardiovascular system: blood circulations with heart and blood vessels The circulatory system or cardiovascular system is the organ system which circulates blood around the body of most animals. Functions Following are some basic functions of the human circulatory system: 1. Delivery of oxygen and nutrients to all parts of the body. 2. Collection of metabolic wastes and delivery to the excretory organs, e.g. kidneys. 3. Role in the immune system of defense against infection. 4. Transport of hormones. The human circulatory system is comprised of the blood, the vascular system, and the heart. The heart is the muscular organ which pumps the blood. The vascular system is made up of arteries, veins, and capillaries. Arteries are blood vessels that carry blood away from the heart. Veins are blood vessels that return blood to the heart. Capillaries are the smallest blood vessels, and are where the exchange of nutrients and gases takes place between the red blood cells and the body tissues. Humans have a double circulatory system which consists of separate but connecting circulations: the pulmonary circulation and the systemic circulation. Digestive system: processing food with mouth, stomach and intestines The gastrointestinal or digestive tract, also referred to as the GI tract or the alimentary canal or the gut, is the system of organs within multicellular animals which takes in food, digests it to extract energy and nutrients, and expels the remaining waste. The GI tract differs substantially from animal to animal. For instance, some animals have multi-chambered stomachs. Basic anatomy of the human alimentary canal In a normal human adult male, the GI tract is approximately 7 and a half metres long (25 feet) and consists of the following components: 1.Mouth 2.Pharynx 3.Esophagus and cardia 4.Stomach, which includes the antrum and pylorus 5.Bowel or Intestine: small intestine, which has three parts: *duodenum *jejunum *ileum, (not to be confused with the ilium, or hipbone). The ileum joins with the cecum at the ileocecal junction large intestine, which has three parts: *cecum.The vermiform appendix is a rudimentary, evolutionarily relict organ attached to the cecum.
*colon with :
ascending colon
transverse colon
descending colon and sigmoid flexure
*rectum, terminating in the anus
The liver secretes bile into the small intestine via the gallbladder and biliary system. The pancreas secretes an isosmotic fluid containing bicarbonate and several enzymes, including trypsin, chymotrypsin, lipase, and pancreatic amylase, as well as nucleolytic enzymes, into the small intestine.
Both these secretory organs aid in digestion. The dariotype is the center of the digestive system Endocrine system: communicating within the body using hormones The endocrine system is a control system of ductless endocrine glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. It does not include exocrine glands such as salivary glands, sweat glands and glands within the gastrointestinal tract.
Signal transduction of some hormones with steroid structure involves nuclear hormone receptor proteins that are a class of ligand activated proteins that, when bound to specific sequences of DNA serve as on-off switches for transcription within the cell nucleus. These switches control the development and differentiation of skin, bone and behavioral centers in the brain, as well as the continual regulation of reproductive tissues.
Diseases of the endocrine system are common, such as diabetes mellitus and thyroid disease. The field of medicine that deals with disorders of endocrine glands is endocrinology, a branch of the wider field of internal medicine. Immune system: defending against disease-causing agents The immune system is the collection of organs and tissues involved in the adaptive defense of a body against foreign biological material. It may be broken down into the adaptive immune system, composed of four lymphoid organs (thymus, lymph nodes, spleen and submucosal lymphoid nodules) and the group motile cells that are involved in the body's defense against foreign bodies. The term may also be used to refer to the totality of a body's defense systems, encompassing both the adaptive immune system and other passive defenses, such as the skin.
In multicellular organisms, the immune system is an organ system that acts as a defense against foreign pathogens (such as viruses, bacteria, parasites), some poisons, as well as cancer. Components of the immune system also function in the return of extracellular fluid to the blood.
Bacteria and monocellular organisms have an "immune system" designed to combat bacteriophages. They do this by simultaneously expressing restriction enzymes that cut DNA at certain sequences, and enzymes that protect their own DNA from this enzyme by methylating the same sequence. Therefore, the bacterium's DNA will not be damaged by the first enzyme because of the presence of the second enzyme. However, when a bacteriophage attempts to infect this bacterium, the viral DNA has not been protected, and gets degraded by the first enzyme. While study of the bacterial immune system provides useful insights into immunology, the remainder of this article will focus on higher organisms' immune systems, particularly the human immune system. Integumentary system:
skin, hair and nails
The integumentary system is often the largest organ system of an animal and human, comprising the skin, hair and nails.
The name comes from the Latin integumentum, which means "to cover".
The major components of the integumentary system are the cutaneous membrane, and its accessory structures (hair, nails, exocrine glands).
Muscular system:
moving the body
The muscular system is the biological system of animals that allows them to move internally and externally. The muscular system in vertebrates consists of three different types of muscles: cardiac, skeletal and smooth. Cardiac muscle is a striated muscle that makes up the heart. It is the only type of muscle consisting of branching fibers. Skeletal muscle consists of voluntary muscles attached to the frame of the skeletal system enabling bodily movement. Smooth muscle is the involuntary muscle that enables the movement of internal organs. Movement of all muscles is controlled through the nervous system.
There are about 700 muscles in the human body. Nervous system:
collecting, transferring and processing information with brain and nerves
The nervous system of an animal coordinates the activity of the muscles, monitors the organs, constructs and processes input from the senses, and initiates actions.
In animals with brains, the nervous system also generates and conducts thoughts and emotions. Thus it is the system that animates "animals". Chemicals that target the activity of nerves generally are the most rapidly acting toxins, typically causing paralysis and/or death.
Anatomy
The nervous system consists basically of two types of cells: Neurons are the primary cells of the nervous system Glia are secondary cells involved in nourishment and structural support.
Rapid signalling within the nervous system occurs by two primary mechanisms: Within neuronal nerve fibers by way of action potentials Between neurons by way of neurotransmitter diffusion across synapses.
Reproductive system:
the sex organs
A sex organ, or primary sexual characteristic, narrowly defined, is any of those parts of the body which are involved in sexual reproduction and constitute the reproductive system in an complex organism; namely:
Male: penis, testicles, scrotum, prostate, seminal vesicles, epididymis, Cowper's glands
Female: vulva, vagina, labia, uterus, Fallopian tubes, ovaries, Skene's glands, Bartholin's glands.
The Latin term genitalia is used to describe the sex organs, and in the English language this term and genital area are most often used to describe the externally visible sex organs or external genitalia: in males the penis and scrotum, in females the vulva. The other parts of the sex organs are called the internal genitalia.
A gonad is a sex organ that produces gametes, specifically the testes or ovaries in humans.
Organs of sexual anatomy originate from a common anlage and differentiate into male or female sex organs. Each sexual organ in one sex has a homologous counterpart in the other one. Respiratory system:
the organs used for breathing, the lungs
The respiratory system is the biological system of any organism that engages in gas exchange. Even trees have respiratory systems, taking in carbon dioxide and emitting oxygen during the day, consuming oxygen and producing carbon dioxide constantly.
Respiratory system in humans and animals
In humans and other mammals, the respiratory system consists of the lungs, the bronchi, which lead to the lungs, and the chest structures. They are all responsible for bringing air into and out of the lungs during respiration. Skeletal system:
structural support and protection through bones.
In biology, the skeleton or skeletal system is the biological system providing support in living organisms.
Skeletal systems are commonly divided into three types - external, internal, and fluid based, though hydrostatic skeletal systems may be classified separately from the other two since they lack hardened support structures.
Large external skeletal systems support proportionally less weight than endoskeletons of the same size, and thus many larger animals, such as the vertebrates, have internal skeletal systems. Examples of exoskeletons are found in arthropods, shellfish, and some insects: the skeleton forms a hard shell-like covering protecting the internal organs.
The phyla arthropoda and mollusca both have exoskeletons. Since exoskeletons necessarily limit growth, phyla with exoskeletons have come up with various solutions. Most molluscs have calcareous shells and as they grow, the diameter of the shell is enlarged without altering its shape. On the other hand, arthropods shed their exoskeletons to grow, a process known as molting. During molting the arthropod breaks down their old exoskeleton and then regenerates a new one which they then harden through various processes.
An internal skeletal system consists of rigid structures within the body, moved by the muscular system. If the structures are mineralized or ossified, as they are in humans and other mammals, they are referred to as bones. Cartilage is another common component of skeletal systems, supporting and supplementing the skeleton. The human ear and nose are shaped by cartilage. Some organisms have a skeleton consisting entirely of cartilage and without any calcified bones at all, for example sharks. The bones or other rigid structures are connected by ligaments and connected to the muscular system via tendons.
Hydrostatic skeletons are similar to a water-filled balloon. Located internally in cnidarians and annelids, among others, these animals can move by contracting the muscles surrounding the fluid-filled pouch, creating pressure within the pouch that causes movement. Animals such as earthworms use their hydrostatic skeletons to change their body shape as they move forward from long and skinny to short and stumpy. |