Biology Test 346

Plant cells are characterized by the presence of a cell wall, chloroplasts, and a large central vacuole. The cell wall provides structural support and protection; chloroplasts are involved in photosynthesis, converting light energy into chemical energy; and the large central vacuole helps maintain cell turgidity and stores nutrients and waste products

Ribosomes play a critical role in protein synthesis. They are the sites where genetic information encoded in messenger RNA (mRNA) is translated into proteins. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming the rough ER.

Using Gram stain, developed by Danish physician, Christian Gram in 1884, two kinds of bacteria were noted - those species of bacteria that are decolorized by alcohol are called Gram negative and those that retain the stain are called Gram positive. This property of bacteria is related with the structure and compositional differences between the walls of gram positive and gram negative forms. In the cell wall of Gram positive bacteria, both horizontal and vertical peptide linkages are present, due to which mesh is dense and hence the stain does not come out. Further outer layer of cell wall of Gram positive bacteria is made of teichoic acid. In the cell wall of Gram negative bacteria, either horizontal or vertical peptide linkage are present, due to which mesh is loose and hence stain comes out. Further outermost layer of cell wall of Gram negative bacteria is made of lipopolysaccharides.

DNA replication occurs during the S phase (Synthesis phase) of the cell cycle, ensuring that each daughter cell receives an exact copy of the DNA.

Helicase enzyme unwinds the DNA double helix by breaking the hydrogen bonds between the nucleotide bases, making the strands accessible for replication.

Transfer RNA (tRNA) is responsible for bringing amino acids to the ribosomes, where they are assembled into proteins according to the sequence specified by messenger RNA (mRNA).

Transcription is the process by which the genetic information encoded in DNA is copied into a strand of RNA, specifically mRNA, which then carries the code required for protein synthesis.

The species category is characterized by the highest level of morphological similarity among its members. Species consist of individuals that are capable of interbreeding to produce fertile offspring, sharing very close genetic and morphological characteristics. This is the most specific and fundamental unit of biological classification.

The presence of a notochord is a characteristic feature of the Phylum Chordata, which includes animals that at some stage in their development have a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. This phylum includes a wide range of animals, from simple sea squirts to complex mammals, including humans.

The cell theory, one of the fundamental principles of biology, states that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells. This theory emphasizes the role of the cell as the basic unit of life for all organisms. Viruses are considered exceptions to the cell theory as they do not have cellular organization and cannot replicate independently of a host cell.