Very simple cells, such as
Nanoarchaeum equitans, require a host to provide certain essential ingredients for life. Complex life-forms (like humans) require a whole ecosystem of other life-forms to survive (either externally, to provide food, or internally, in a symbiotic relationship).
What is the simplest cell that has been discovered so far that can live in an environment where there are no other life-forms, not even in a decomposed state? Does such an organism exist, or is all life inextricably dependent on other life?
If by "simplest" you mean smallest genome, then according to Brock's Biology of Microrganisms (13th ed, p 319) the smallest autotroph is Aquifex aeolicus, a chemolithotroph bacterium. It's genome is 1.5M bases, about 1/3 of that of E.Coli, and was sequenced in 1998 (https://www.ncbi.nlm.nih.gov/pubmed/9537320).
The genome is densely packed though and still carries some 1,500 open reading frames. The authors of the genome sequencing paper states that "metabolic flexibility seems to be reduced as a result of the limited genome size", which I guess is some evidence of "simplicity".
I'm not sure if this is exactly what you are looking for, but since I was looking for an answer to a similar question to you (what's the simplest living organism), I just found about this,
"The Simplest Living Organism Ever Has 437 Genes and Was Made in a Laboratory"
"a self-replicating bacterium invented by Venter and his team that contains just 437 genes, a "genome smaller than that of any autonomously replicating cell found in nature,"
Now I dont know if artificial organisms count in your question, and if it complies with the other requirements you were asking
Scientists Create Simple Synthetic Cell That Grows and Divides Normally
Five years ago, scientists created a single-celled synthetic organism that, with only 473 genes, was the simplest living cell ever known. However, this bacteria-like organism behaved strangely when growing and dividing, producing cells with wildly different shapes and sizes.
Now, scientists have identified seven genes that can be added to tame the cells’ unruly nature, causing them to neatly divide into uniform orbs. This achievement, a collaboration between the J. Craig Venter Institute (JCVI), the National Institute of Standards and Technology (NIST) and the Massachusetts Institute of Technology (MIT) Center for Bits and Atoms, is described in the journal Cell.
Identifying these genes is an important step toward engineering synthetic cells that do useful things. Such cells could act as small factories that produce drugs, foods and fuels detect disease and produce drugs to treat it while living inside the body and function as tiny computers.
But to design and build a cell that does exactly what you want it to do, it helps to have a list of essential parts and know how they fit together.
“We want to understand the fundamental design rules of life,” said Elizabeth Strychalski, a co-author on the study and leader of NIST’s Cellular Engineering Group. “If this cell can help us to discover and understand those rules, then we’re off to the races.”
Scientists at JCVI constructed the first cell with a synthetic genome in 2010. They didn’t build that cell completely from scratch. Instead, they started with cells from a very simple type of bacteria called a mycoplasma. They destroyed the DNA in those cells and replaced it with DNA that was designed on a computer and synthesized in a lab. This was the first organism in the history of life on Earth to have an entirely synthetic genome. They called it JCVI-syn1.0.
Since then, scientists have been working to strip that organism down to its minimum genetic components. The super-simple cell they created five years ago, dubbed JCVI-syn3.0, was perhaps too minimalist. The researchers have now added 19 genes back to this cell, including the seven needed for normal cell division, to create the new variant, JCVI-syn3A. This variant has fewer than 500 genes. To put that number in perspective, the E. coli bacteria that live in your gut have about 4,000 genes. A human cell has around 30,000.
“We want to understand the fundamental design rules of life. If this cell can help us to discover and understand those rules, then we’re off to the races.” —Elizabeth Strychalski, a co-author on the study and leader of NIST’s Cellular Engineering Group
Identifying those seven additional genes took years of painstaking effort by JCVI’s synthetic biology group, led by co-author John Glass. Co-lead author and JCVI scientist Lijie Sun constructed dozens of variant strains by systematically adding and removing genes. She and the other researchers would then observe how those genetic changes affected cell growth and division.
NIST’s role was to measure the resulting changes under a microscope. This was a challenge because the cells had to be alive for observation. Using powerful microscopes to observe dead cells is relatively easy. Imaging live cells is much harder.
Holding these cells in place under a microscope was particularly difficult because they are so small and delicate. A hundred or more would fit inside a single E. coli bacterium. Tiny forces can tear them apart.
To solve this problem, Strychalski and MIT co-authors James Pelletier, Andreas Mershin and Neil Gershenfeld designed a microfluidic chemostat — a sort of mini-aquarium — where the cells could be kept fed and happy under a light microscope. The result was stop-motion video that showed the synthetic cells growing and dividing.
This video shows JCVI-syn3.0 cells — the ones created five years ago — dividing into different shapes and sizes. Some of the cells form filaments. Others appear to not fully separate and line up like beads on a string. Despite the variety, all these cells are genetically identical.
This video shows the new JCVI-Syn3A cells dividing into cells of more uniform shape and size.
These videos and others like them allowed the researchers to observe how their genetic manipulations affected the cell growth and division. If removing a gene disrupted the normal process, they’d put it back and try another.
“Our goal is to know the function of every gene so we can develop a complete model of how a cell works,” Pelletier said.
But that goal has not been reached yet. Of the seven genes added to this organism for normal cell division, scientists know what only two of them do. The roles that the other five play in cell division are not yet known.
“Life is still a black box,” Strychalski said. But with this simplified synthetic cell, scientists are getting a good look at what’s going on inside.
Plants are all around us. From dandelions to oak trees, we cannot escape the presence of plants. This is a good thing, since not only do they turn carbon dioxide into oxygen, they are a good food source for most of the creatures on earth. The Resurrection Fern
[caption align=“aligncenter” width=“600”] Resurrection Fern[/caption]
Also called Selaginella lepidophylla, this autotroph is interesting in that it appears to resurrect from the dead. It lives in very dry climates and when there is a lack of water, it shrivels up into a grey ball and can stay like this for a number of years. When it finally rains, the resurrection fern grows and turns green. Even though it doesn’t necessarily die, this plant is interesting in that it can “come back” from the dead. The Corpse Lily Also called Amorphophallus titanum, you will have to wear a mask if you hope to approach this autotroph. The corpse lily is famous for its large size as well as one of its finer qualities–its smell. The corpse lily literally smells like rotting flesh which attracts animals that help pollinate the plant. For example, flies often visit many flowers due to their smell. If a fly touches another plant and enters the corpse lily, it has a chance to pollinate it and allow more corpse lilies to grow. Living Rocks Also called Lithops, these autotrophs are interesting in that they look like rocks! Living rocks are usually located in desert areas and and are fairly common. Why do they look like rocks? These autotrophs probably try to mimic rocks in order to protect themselves against heterotrophs that would eat them for nutrients and water. If you can’t see something, you can’t eat it, right?
[caption align=“aligncenter” width=“600”] Venus Fly Trap[/caption]
Venus Fly Traps Also called Dionaea muscipula, these plants often trap insects by eating them! If a fly lands on a Venus Fly Trap, it would activate the “trap” by touching the plant’s “hairs” and would be crushed by the plant. After doing so, a Venus Fly Trap receives nutrients from the insect. These plants are still autotrophic because they mainly receive food from sunlight. Ball Moss Also called Tillandsia recurvata, this plant likes to hang out in the air. It usually grows off of other things for support. Ball Moss usually receives its nutrients from rain and other materials that wash over it.
What are Heterotrophs
Heterotrophs are organisms which are unable to fix inorganic carbon and thereby utilize organic carbon as a carbon source. Heterotrophs use organic compounds produced by autotrophs like carbohydrates, proteins and fats, for their growth. Most living organisms are heterotrophs. Examples for heterotrophs are animals, fungi, protists and some bacteria. An overview of the cycle between autotrophs and heterotrophs is shown in figure 3.
Figure 3: Cycle between autotrophs and heterotrophs
Classification of Heterotrophs
Two types of heterotrophs can be identified based on their energy source. Photoheterotrophs uses sunlight for the energy and chemoheterotrophs uses chemical energy. Photoheterotrophs, like purple non-sulfur bacteria, green non-sulfur bacteria, and Rhodospirillaceae generate ATP from sunlight in two ways: bacteriochlorophyll-based reactions and chlorophyll-based reactions. Chemoheterotrophs can be either chemolithoheterotrophs, which use inorganic carbon as the energy source, or chemoorganoheterotrophs, which use organic carbon as the energy source. Example for chemolithoheterotrophs are bacteria like Oceanithermus profundus. Examples forchemoorganoheterotrophs are eukaryotes like animals, fungi and protists. A flow chart for the determination of a species as an autotrophs or heterotrophs is shown in figure 4.
Figure 4: A flow chart discriminating autotrophs and heterotrophs
Kingdom is the highest category in the hierarchical classification of organisms created by Carolus Linnaeus around 1750. Linnaeus recognized two kingdoms, plants and animals, a scheme that worked reasonably well for large multicellular organisms but failed as microscopes revealed diverse unicellular organisms. In 1959 Robert Whittaker devised a five-kingdom system that maintained kingdoms Plantae and Animalia but added kingdoms Monera, Protista, and Fungi (see Table).
|A COMPARISON OF THE FIVE KINGDOMS|
|Internal cell membranes||Absent Present (Prokaryotes)||Present (Eukaryotes)||Present (Eukaryotes)||Present (Eukaryotes)||Present (Eukaryotes)|
|Cell wall||Present||Present or Absent||Present||Present||Absent|
|Organization||Unicellular||Unicellular or Multicellular||Multicellular||Mainly Multicellular||multicellular|
|Mode of nutrition||Autotrophs or Heterotrophs||Autotrophs or Heterotrophs||Autotrophs||Heterotrophs||Heterotrophs|
|Representative groups||Archaea, eubacteria||Protozoa, algae, slime molds||Mosses, ferns, seed plants||Molds, yeasts, mushrooms||Animals with and without backbones|
|Note: An autotroph is an organism that uses solar energy or energy from inorganic chemicals to make organic molecules. A heterotroph obtains organic molecules by consuming other organisms or their products.|
Whittaker placed bacteria in their own kingdom, Monera, because of fundamental organizational differences between prokaryotic bacterial cells, which lack membrane-enclosed nuclei and organelles , and the eukaryotic cells of other organisms that possess internal membranes. Plantae, Fungi, and Animalia consist of complex, multicellular eukaryotic organisms that differ from each other in details of cell structure and in how they secure and process energy. Protista is a collection of single-celled eukaryotic organisms and simple multicellular forms, some animal-like, some plantlike.
Molecular evidence, particularly from ribosomal ribonucleic acid (RNA), suggests that the five-kingdom scheme is also too simple. Some biologists believe that Protista should be partitioned into three or more kingdoms. Similarly, kingdom Monera contains two very biochemically distinct groups of prokaryotes: archaebacteria, and eubacteria. A proposed system acknowledges this ancient evolutionary split by creating a higher level of classification, domain, above kingdom. This system distinguishes three domains: Archaea, Eubacteria, and Eukarya (containing protists, plants, fungi, and animals).
GK Questions & Answers on Science: Biology Terminology (Set 1)
Questions and Answers on Science: Biology Terminology (Set 1) consists of 10 MCQ to analyse various terms used in Biological processes which are important for various competitive examinations like IAS, PSC, SSC, Railway etc.
1. What is the process of intake of nutrients by an organism as well as the utilisation of these nutrients by the organisms called?
2. The mode of nutrition in which an organism makes its own food from the simple inorganic material like carbon dioxide and water present in the surrounding is called:
A. Heterotrophic nutrition
3. What is the mode of nutrition called in which organisms cannot make its own food from simple inorganic material and depends on other organisms for its food?
B. Heterotrophic nutrition
4. When an organism obtains its food from decaying organic matter of dead plants, dead animals and rotten bread, etc., it is called:
5. The nutrition in which an organism derives its food from the body of another living organism without killing it, it’s called:
6. The nutrition in which an organism takes the complex organic food materials into its body by the process of ingestion, the ingested food is digested and then absorbed into the body cells of the organism:
D. Heterotrophic nutrition
7. The process by which green plants make their own food from carbon dioxide and water by using sunlight energy in the presence of chlorophyll, is called:
8. Animals which eat only plants are called:
9. What is the process of taking food into the body called?
10. The process in which the food containing large, insoluble, molecules is broken down into small, water soluble molecules is called:
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6 Kingdoms Riddles
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Are All Plants Autotrophs?
Most plants are autotrophs because they make their own food. Some plant species are parasitic, meaning they get their nutrients from other sources. Parasitic plants are heterotrophic.
Any plant with green leaves is classified as an autotroph. The definition covers trees, mosses and flowering plants, to name a few. Most plants use photosynthesis to produce food in the form of sugar.
Plants are not the only organisms classified as autotrophs, although they are one of the most well-known examples. Phytoplankton, algae and some types of bacteria are also able to make their own food. Some of these organisms use chemosynthesis instead of photosynthesis.
Chemosynthesis uses the energy generated by chemical reactions to produce food. Some of the bacteria that live in the ocean use hydrogen sulfide to power chemosynthesis.
Parasitic plants are unable to make their own food. These plants feed off the roots or stems of their hosts.
Gymnosperms and angiosperms form spores and seeds respectively to propagate further plant generations via sexual reproduction. The gametes are transported through pollination. Asexual (vegetative) reproduction is also common in plants such as bulbs and tubers. Onions and potatoes form new offspring by budding, and strawberries develop adventitious roots, known as stolons, which give rise to new plants.[v] Protists can reproduce sexually by meiosis or asexually by simple cell division plants are unable to reproduce by one mitotic division. While some fungus-like protists produce spores, none produce seeds.
Pigments are chemical compounds which reflect only certain wavelengths of visible light. This makes them appear "colorful". Flowers, corals, and even animal skin contain pigments which give them their colors. More important than their reflection of light is the ability of pigments to absorb certain wavelengths.
Because they interact with light to absorb only certain wavelengths, pigments are useful to plants and other autotrophs --organisms which make their own food using photosynthesis. In plants, algae, and cyanobacteria, pigments are the means by which the energy of sunlight is captured for photosynthesis. However, since each pigment reacts with only a narrow range of the spectrum, there is usually a need to produce several kinds of pigments, each of a different color, to capture more of the sun's energy.
There are three basic classes of pigments.
There are several kinds of chlorophyll, the most important being chlorophyll "a". This is the molecule which makes photosynthesis possible, by passing its energized electrons on to molecules which will manufacture sugars. All plants, algae, and cyanobacteria which photosynthesize contain chlorophyll "a". A second kind of chlorophyll is chlorophyll "b", which occurs only in "green algae" and in the plants. A third form of chlorophyll which is common is (not surprisingly) called chlorophyll "c", and is found only in the photosynthetic members of the Chromista as well as the dinoflagellates. The differences between the chlorophylls of these major groups was one of the first clues that they were not as closely related as previously thought.
The picture at the right shows the two classes of phycobilins which may be extracted from these "algae". The vial on the left contains the bluish pigment phycocyanin, which gives the Cyanobacteria their name. The vial on the right contains the reddish pigment phycoerythrin, which gives the red algae their common name.
Phycobilins are not only useful to the organisms which use them for soaking up light energy they have also found use as research tools. Both pycocyanin and phycoerythrin fluoresce at a particular wavelength. That is, when they are exposed to strong light, they absorb the light energy, and release it by emitting light of a very narrow range of wavelengths. The light produced by this fluorescence is so distinctive and reliable, that phycobilins may be used as chemical "tags". The pigments are chemically bonded to antibodies, which are then put into a solution of cells. When the solution is sprayed as a stream of fine droplets past a laser and computer sensor, a machine can identify whether the cells in the droplets have been "tagged" by the antibodies. This has found extensive use in cancer research, for "tagging" tumor cells.