There is compelling evidence that mitochondria and chloroplasts were once primitive bacterial cells. This evidence is described in the endosymbiotic theory. How did this theory get its name? Symbiosis occurs when two different species benefit from living and working together. When one organism actually lives inside the other it's called endosymbiosis. The endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a permanent relationship. Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.
It's Just a Theory
In everyday speech, people use the word theory to mean an opinion or speculation not necessarily based on facts. But in the field of science, a theory is a well established explanation based on extensive experimentation and observation. Scientific theories are developed and verified by the scientific community and are generally accepted as fact.
Mitochondria Have DNA
Mitochondria and chloroplasts have striking similarities to bacteria cells. They have their own DNA, which is separate from the DNA found in the nucleus of the cell. And both organelles use their DNA to produce many proteins and enzymes required for their function. A double membrane surrounds both mitochondria and chloroplasts, further evidence that each was ingested by a primitive host. The two organelles also reproduce like bacteria, replicating their own DNA and directing their own division.
Cell compartmentalization and its origins
Structure and function of mitochondria and chloroplasts. Endosymbiosis.
Cell compartmentalization and its origins
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Answer
Verified
Hint: Genetic material is mostly concentrated in the nucleus only. However certain other organelles also possess DNA and thus carry out production of various proteins for their cellular functioning.
Complete answer:
The DNA present in organelles is mostly circular resembling the DNA found in prokaryotes. This organelle DNA is circular in shape as compared to the nuclear DNA which is present in the linear form. Mitochondria is a eukaryotic cell organelle which is bounded
by a double membrane. It contains its own DNA, often abbreviated as “mtDNA” encoding 37 genes and ribosomes. These genes are responsible for producing various enzymes for carrying out oxidative phosphorylation in mitochondria.
Plastids are the plant cell organelles which are bounded by a double membrane. They are also involved in the metabolism of energy in the cells. Plastids also contain their own DNA and proteins. The plastid DNA encodes genes for formation of various proteins for
carrying out metabolic reactions.
The mitochondria and plastid are therefore known as the semi-autonomous organelles.
On the other hand, other organelles do not contain their own genetic material which can be inherited in further generations.
Hence, the correct answer is option (A).
Note: Mitochondria are also known as the powerhouse of a cell as it is responsible for generating most of the chemical energy in a cell to carry out various biochemical reactions. Adenosine triphosphate is the small molecule that stores the chemical energy produced by mitochondria. Plastid is also a cell organelle bounded by cell membrane. These organelles are involved in the process of photosynthesis and storage of various products like starch.
Answer
Verified
Hint: These organelles are found in the cytoplasm of eukaryotic cells. One out of these two is absent in the animal cells and is only found in plant cells. The other one serves as an energy-producing organelle for the cells.
Complete answer:
The two organelles containing their own genetic material are mitochondria and plastids.
Mitochondria are sites of respiration in the cell. They are called the cell's engine since they synthesize ATP compounds rich in energy. The
Cell uses the energy contained in ATP.
Plastids present in the plant cells have their own genome (DNA). They reproduce themselves (they possess the ability to divide).
Except for RBCs & Bacteria species, mitochondria occurs in plant and animal cells. They seem to be colorless. Plastid is a double membrane-bound organelle involved in food synthesis and storage, typically found in photosynthetic plant cells.
A plastid containing chlorophyll which is a green
pigment is called chloroplast whereas a plastid containing pigments is called a chromoplast apart from green color. A plastid deficient in pigments is called a leucoplast and is primarily used in food storage.
ATP is the cell's "currency" of chemical energy that drives the metabolic activities of the cell. This mechanism is called aerobic respiration, which is the reason for oxygen-breathing by animals. Without mitochondria, there would probably be no higher animals because their
cells could only receive energy from anaerobic respiration, a method far less effective than aerobic respiration. In reality, mitochondria enable cells to generate 15 times more ATP than they could otherwise, and to survive complex organisms, including humans, need large quantities of energy.
Note: Significant evidence indicates endosymbiosis to be the solution to the puzzle. Symbiosis is a relationship in which two distinct species of organisms exist in a similar, mutual relationship. Endosymbiosis (endo means within) is a special type of symbiosis in which one organism resides within the other.