The areas of the lake or pond bottom that are not part of the littoral zone are referred to as the benthic zone. This zone contains fine sediment that is free of plant life because light levels are too low to support plant growth. The major trophic levels in the pelagic zone, or open water areas, are phytoplankton, zooplankton, planktivorous (plankton-eating) fish, and piscivorous (fish-eating) fish. The food web in the pelagic zone is connected to the inshore food web because many mobile organisms from the pelagic zone (especially fish) use the inshore areas for shelter and food.

 

TLS Online TPP Program

#Id: 3257

#Unit 3. Fundamental Processes

Intercalating agents, such as proflavin, acridine, and ethidium, cause the deletion or addition of a base pair or even a few base pairs.

TLS Online TPP Program

#Id: 3258

#Unit 3. Fundamental Processes

Intercalating agents are flat molecules containing several polycyclic rings that bind to the equally flat purine or pyrimidine bases of DNA, just as the bases bind or stack with each other in the double helix

TLS Online TPP Program

#Id: 3259

#Unit 3. Fundamental Processes

 Ultraviolet light induces the formation of a cyclobutane ring between adjacent thymines

TLS Online TPP Program

#Id: 3261

#Unit 3. Fundamental Processes

g-radiation and X-rays (ionizing radiation) are particularly hazardous because they cause double-strand breaks in the DNA, which are difficult to repair. If left unrepaired, double-strand breaks can be lethal to a cell.

TLS Online TPP Program

#Id: 3263

#Unit 3. Fundamental Processes

DNA is also subject to attack from reactive oxygen species (e.g., O2- , H2O2, and OH†). These potent oxidizing agents are generated by ionizing radiation and by chemical agents that generate free radicals. Oxidation of guanine, for example, generates 7,8-dihydro-8-oxoguanine, or oxoG. 

TLS Online TPP Program

#Id: 3264

#Unit 3. Fundamental Processes

The oxoG adduct is highly mutagenic because it can base-pair with adenine as well as with cytosine. If it base-pairs with adenine during replication, it gives rise to a G:C to T:A transversion, which is one of the most common mutations found inhuman cancers.