Microbes and Plant Diseases

The algae posses the chlorophyll pigments in the cells which allow these organisms to prepare the food by the process of photosynthesis. They are autotrophic because they can prepare the food on their own. The fungi are the heterotrophic or saprophytic organisms as they do not possess the chlorophyll pigments. They cannot prepare the food and depend on the other sources for food. 

An organism that is capable of synthesizing its own food from inorganic substances using light or chemical energy is called as autotrophic organism. It includes green plants, algae and certain bacteria. Algae are photoautotrophs meanings they use light as the source of energy to prepare their food.

Viruses are obligate filterable parasites capable of independent existence and when they enter inside the body of the host they start utilising the host machinery for its own reproduction. 

The apogeotropic or positively geotropic roots appear in Cycas sporophyte are called Corolloid roots or Corollorhiza. These roots looks like anthozoans or coelenterates. They contain Blue green algae or cyanobacteria like Nostoc and Anabaena, and perform symbiotic nitrogen fixation. They show mutual association with plant body.

So, the correct option is ‘Cyanobacteria’.

Agrobacterium is a genus of Gram-negative bacteria that causes tumors in plants. Agrobacterium tumefaciens is the most commonly studied species in this genus. It contains "Ti" plasmid or tumor inducing plasmid, that causes  crown-gall disease in plants. The disease is characterised by a tumour-like growth or gall on the infected plant, often at the junction between the root and the shoot. Tumors are incited by the conjugative transfer of a DNA segment (T-DNA) from the bacterial tumour-inducing (Ti) plasmid to the plant cell naturally when the bacterium infects the plant through  a wound.

Roots of the tobacco plants are infected by Meloidogyne incognita. RNA I method is used to develop resistance in these plants against infection.

Food poisoning is the condition in which there are certain substances in the food consumed that results in infection. The food contaminated with bacteria, parasites and viruses are the main sources for causing food poisoning. When the food poisoning is caused by Shigella, the symptoms includes diarrhea, fever, intestinal cramps, etc. The antibiotics are used for treatment. The common antibiotic is ampicillin, bactrim or ceftriaxone. 

Foliose lichen is the most complex lichen. It is a lichen with leafy body parts or thallus and which generally have a cortex on each side of the leafy lichen body part thallus. Crustose lichens are lichens that grow like a crust of paint on their substrate, and especially sqamulose crustose lichens, may not be attached to the substrate at the edges, giving a leafy appearance similar to foliose lichens, but there is no lower cortex on the leafy part. Fruticose lichens are lichens that have a form similar to a tiny leafless, branching shrub that may have the branches flattened, so as to appear leafy, but foliose lichens have a single cortex wrapping around the branches, whereas foliose lichens generally have an upper and a lower cortex. Gelatinous lichens may appear leafy, but lack a cortex or internal structure, having the photobiotic component diffuse throughout the no fruiting part of the lichen body, whereas in foliose lichens the algae are in a layer. In foliose lichens, the layer of tissue containing the photosynthetic component has the algae more diffuse in the fungus than in foliose lichens, where the algal layer is generally very distinct.

A lichen is a composite organism that arises from algae or cyanobacteria (or both) living among filaments of a fungus in a symbiotic relationship. The combined life form has properties that are very different from the properties of its component organisms. The fungus benefits from the symbiotic relation because algae or cyanobacteria produce food by photosynthesis. The algae or cyanobacteria benefit by being protected from the environment by the filaments of the fungus, which also gather moisture and nutrients from the environment, and (usually) provide an anchor to it. Thus, the correct answer is option C.

The photobiont supplies the association of organic carbon from photosynthesis, and the mycobiont ensures protection, and regulates the supply of minerals and water. The nutritional exchange between partners is probably much more complex than exchange of water and minerals for organic carbon.

Lichen is a stable symbiotic association between a fungus and algae. The combined life form has properties that are very different from the properties of its component organisms. Lichens come in many colors, sizes, and forms. The properties are sometimes plant-like, but lichens are not plants. 

In hot season, Usnea get dry and become highly inflammable. It easily catches fire and causes forest fire.

Letharia vulpina, commonly known as the wolf lichen, is considered toxic or harmful because it contains vulpinic acid, which was historically used to poison wolves and foxes.