Test: Plant Diversity - 3 - Class 11 MCQ

Mycoplasma is a genus of bacteria that lack a cell wall around their cell membrane. Without a cell wall, they are unaffected by many common antibiotics such as penicillin or other beta-lactam antibiotics that target cell wall synthesis. They can be parasitic or saprotrophic.

Mycoplasmas are the smallest prokaryotic organisms that can grow in cell-free culture medium.

Nocard and Roux, 1896, were first to isolate Mycoplasma mycoides, the causative agent of contagious bovine pleuropneumonia. Ivanowsky, 1891, established existence of viral diseases when he observed pathogenicity of juice from tobacco plant with mosaic symptom even after filtration through filter candles that strain out the bacteria. Alfred D. Hershey and Martha Chase used radioactive phosphorus and radioactive sulfur and showed that when bacteriophage T2 infects its host cell, Escherichia coli, the phosphorus-containing DNA of the viral particle, not the sulfur-containing protein of the viral coat, enters the host cell and serves the genetic information for viral replication. Plant MLOs are also called as phytoplasmas and were discovered by Doi and Ishii, 1967, from phloem elements of plants infected with mulberry dwarf. Thus, the correct answer is option B.

Mycoplasmas are the smallest and simplest self-replicating bacteria. Unlike all other prokaryotes, the mycoplasmas have no cell walls, and they are consequently placed in a separate class Mollicutes (mollis - soft; cutis - skin).

Cholesterol is a waxy, fat-like substance that's found in all the cells in your body. Your body needs some cholesterol to make hormones, vitamin D, and substances that help you digest foods. Your body makes all the cholesterol it needs.

Uneven division of Mycoplasma cells forms minute structures which are called as elementary bodies. Germination of elementary bodies forms a chain of spherical corpuscles that undergo fragmentation to produce more elementary bodies. These elementary bodies multiply by binary fission/fragmentation/budding to produce new Mycoplasma cells. Thus, they serve a major role in reproduction. So, the correct answer is option C.

Pathogenesis and disease sites of infection by M pneumoniae and U urealyticum. Most mycoplasmas that infect humans and other animals are surface parasites, adhering to the epithelial linings of the respiratory and urogenital tracts.

Acholeplasmataceae can grow in a medium without cholesterol because for growth they do not need any sterols as in their outer membrane it is already present.

Virus and viroids are the obligate parasites which cannot exhibit functions of the living organisms as growth and reproduction. Mycoplasma is the smallest bacteria which does not possess a cell wall. The organism is living and can perform functions like growth and reproduction through binary fission. 
Thus, the correct answer is option A.

In 1898, Nocard and Roux were the first to isolate a mycoplasma species in culture from bovine; however, it was not until 1944 when Mycoplasma pneumoniae, known then as Eaton agent or Eaton's agent, was isolated and described from a patient with primary atypical pneumonia.

Mycoplasma in liquid media observed with phase- contrast microscope. Mycoplasma strains in liquid media was followed by phase- contrast microscopy. Similar pattern of development is common to all strains. The filaments found to break up into chains of coccoid elements. These chains further fragmented to yield shorter chains and single coccoid element, which characterized the stationary and decline phases of growth and it becomes circular or ring shaped.

Mycoplasmas are the smallest prokaryotic organism that lacks cell wall but has rigid plasma membrane rich in sterols and lipoglycan. The absence of rigid cell wall allow them to change their shape according to the environment, i.e., pleomorphic.

Cell wall is absent and plasma membrane forms the outer boundary of the cell. Due to the absence of cell wall these organisms can change their shape and are pleomorphic. Lack of nucleus and other membrane-bound organelles.

Most M. pneumoniae infections are self-limiting; however, clinicians routinely treat pneumonia caused by Mycoplasma pneumoniae with antibiotics. All mycoplasmas lack a cell wall and, therefore, all are inherently resistant to beta-lactam antibiotics (e.g., penicillin). Mycoplasmas are very small compared to other bacterias. That's important because many antibiotics kill bacteria by weakening those walls. Since mycoplasma bacteria don't have them, some antibiotics, like penicillin, won't work against them.

New plants can grow from older plants, through the method of vegetative propagation such as grafting and budding. It is a form of asexual reproduction seen in plants. The same tissue helps in the vegetative propagation. This tissue has undifferentiated cells which divide paving way for the growth of the plant.

Tetracycline is an antibiotic which is used in the treatment of infections in the lungs, reproductive organs, and cholera. This medicine may cause teeth discoloration in the children.

The disease is caused by a plant pathogenic mollicute, Phytoplasma (earlier known as mycoplasmalike organism or MLO) and is transmitted by the insect vector, Hishimonus phycitis which belongs to the group of leafhoppers.

Phytoplasmas are plant mycoplasma like organisms (plant MLO) that lacks cell wall but have rigid plasma membrane and exhibit pleomorphy. Little leaf of brinjal is caused by phytoplasma and is characterized by extreme reduction in leaf size and excess growth of axillary shoot with short internodes. Bunchy top of papaya is caused by MLO and is characterized by faint mottling of upper leaves, reduced growth of leaves, petiole and internode followed by cessation of apical growth to give “bunchy top”. Witches-broom of potato condition caused by phytoplasma and is characterized by loss of apical dominance of the branches and phyllody. Citrus canker is not caused by mycoplasmas but by the bacterium Xanthomonas axonopodis. 
Thus, the correct answer is option C.

The roles of Mycoplasma pneumoniae, M. hominis and Ureaplasma urealyticum in diseases of humans are currently under investigation. M. pneumoniae, which causes primary atypical pneumonia, is a well established pathogen of the respiratory tract.

Two groups of bacteria devoid of cell wall peptidoglycans are the Mycoplasma species, which possess a surface membrane structure, and the L-forms that arise from either Gram-positive or Gram-negative bacterial cells that have lost their ability to produce the peptidoglycan structures.
Mycoplasma have high nutritional demands and can grow on PPLO agar with beef heart infusion and 10–20% horse serum. The serum provides Mycoplasma with the cholesterol and long-chain fatty acids required for growth. The optimum pH for Mycoplasma culture is pH 7.8–8.0. Cells may die when the pH drops below pH 7.0.
L-form bacteria replicate in various ways, including budding, filamentous growth and binary fission. Some species of L-forms such as Proteus can form large bodies that replicate by division. In other instances, granules bud from the body of the bacterium and give rise to small L-form colonies. L-forms can be generated in the laboratory from many bacterial species that usually have cell walls, such as Bacillus subtilis or Escherichia coli. ... The L-forms are generated in a culture medium that is the same osmolarity as the bacterial cytosol (an isotonic solution), which prevents cell lysis by osmotic shock.
Thus, Option D is the correct answer.

Aster yellow is a plant disease that is caused by a phytoplasma bacterium. They feed on the phloem tissue of the infected plant.The structural elements of phloem consist of  sieve tubes, companion cells, phloem parenchyma and secretory cells. The sieve tube is the conducting element of the phloem.

Mycoplasmas are fastidious and can be cultured only on complex medium containing cholesterol. Viruses are acellular structures that cannot perform the vital activities outside the host. Hence, both depend on their cholesterol requirement on the host . Mycoplasmas are surface parasites and can be grown on cell-free culture medium containing sterols, fatty acids, and preformed purines and pyrimidines. Viruses are obligate intracellular parasites, with acellular structure, cannot independently fulfil the characteristics of life and hence can be cultured in living cells only. Mycoplasmas are not always parasite but also exist as parasite and saprophytes. Viruses are present as inactive acellular structures outside their host. Thus, the Correct answer is option B.

The liquid phase of the cell which is surrounded by unit cell membrane is called as cytoplasm; both mycoplasmas and animals have cytoplasm. Mycoplasmas have 70S ribosomes which are arranged in a helical superstructure which is a eukaryotic character. Animals are holozoic which refers to engulfment of whole/part of plant/animal in liquid/solid state. Mycoplasmas exhibit an osmotrophic mode of nutrition wherein the pre-digested food is diffused through the body surface while food is first ingested by animals followed by its internal digestion. The plasmids with the ability to integrate themselves into cellular chromosomes are termed as episomes. Mycoplasmas contain only minimum and essential genes and plasmids, the extra chromosomal DNA, are not present in them. Thus, the correct answer is option C.

Mycoplasma is the smallest bacteria which does not possess a cell wall. It is a prokaryote organism. They are composed of a single cell and are non-motile. The cell contains the cell membrane, proteins, DNA and ribosomes. The absence of a cell wall renders the organism as insensitive to most of the antibiotics.

Mycoplasma pneumoniae is a very small bacterium in the class Mollicutes. It is a human pathogen that causes the disease mycoplasma pneumonia, a form of atypical bacterial pneumonia related to cold agglutinin disease. M. pneumoniae is characterized by the absence of a peptidoglycan cell wall and resulting resistance to many antibacterial agents. Most M. pneumoniae infections are self-limiting; however, clinicians routinely treat pneumonia caused by Mycoplasma pneumoniae with antibiotics. All mycoplasmas lack a cell wall and, therefore, all are inherently resistant to beta-lactam antibiotics (e.g., penicillin). Mycoplasmas are very small compared to other bacterias. That's important because many antibiotics kill bacteria by weakening those walls. Since mycoplasma bacteria don't have them, some antibiotics, like penicillin, won't work against them.

Mycoplasma (plural mycoplasmas or mycoplasmata) is a genus of bacteria that lack a cell wall around their cell membranes.
They lack membrane-bound organelles like mitochondria, chloroplasts, etc.
Thus, Option D is the correct option.