Biology Test - 46

Calcitonin hormone works antagonistically to parathormone.

Calcitonin is involved in helping to regulate levels of calcium and phosphate in the blood, opposing the action of parathyroid hormone.

Similarly, calcitonin and parathyroid hormone (PTH) are antagonistic hormones because calcitonin functions to decrease blood calcium levels whereas PTH functions to increase blood calcium levels.

Phloem always flows from a sugar source to a sugar sink.

• The accepted mechanism used for the translocation of sugars from source to sink is called the pressure flow hypothesis.
• As glucose is prepared at the source (by photosynthesis) it is converted to sucrose (a disaccharide).
• The sugar is then moved in the form of sucrose into the companion cells and then into the living phloem sieve tube cells by active transport.
• This process of loading at the source produces a hypertonic condition in the phloem.

Azospirillumare free-living nitrogen-fixing bacteria present in the soil.

Azospirillum is a Gram-negative, microaerophilic, non-fermentative and nitrogen-fixing bacterial genus from the family of Rhodospirillaceae. Azospirillum bacteria can promote plant growth.The genus Azospirillum belongs in the alpha-Proteobacteria class of bacteria. Azospirillum are gram-negative, do not form spores, and have a slightly-twisted oblong-rod shape.

Plasmids are used as cloning vectors because they can be multiplied in culture.Plasmids come in many different sizes and are used for many different purposes in biotechnology. They first made their mark in the field of recombinant DNA in the 1970s, being used as a tool to insert genes into bacteria to encourage their production of therapeutic proteins such as human insulin.

Bt-cotton, bt-brinjal and golden rice are genetically modified crops.Bacillus thurin-giensis (Bt) crops are plants genetically engineered (modified) to contain the endospore (or crystal) toxins of the bacterium, Bt to be resistant to certain insect pests.Golden rice is a genetically modified, biofortified crop. Biofortification increases the nutritional value of crops. Golden rice is genetically modified to produce beta-carotene, which is not normally present in rice.

In predation, one species is benefitted where as the other is harmed. It is (+ –) type of populationinteraction

• Helicases -DNA helicases are a class of molecular motors that catalyze processive unwinding of double stranded DNA. In spite of much study, we know relatively little about the mechanisms by which these enzymes carry out the function for which they are named. Most current views are based on inferences from crystal structures.
• Primers - These are required for DNA synthesis because no known DNA polymerase is able to initiate polynucleotide synthesis. DNA polymerases are specialized for elongating polynucleotide chains from their available 3′- hydroxyl termini. In contrast, RNA polymerases can elongate and initiate polynucleotides.
• DNA ligases - Mammalian DNA ligase I effectively seal single-strand breaks in DNA and joins restric- tion enzyme DNA fragments with staggered ends. The enzyme is also able to catalyze blunt-end joining of DNA.
• Topoisomerases - DNA topoisomerases are able to solve topological problems resulting from replication, transcription, recombination, and reorganization of the chromatin. Further on, topoisomerases change the state of supercoiling of the DNA and therefore, have great impact on gene activity.

Metamorphosis is a process by which one form of an organism gets transformed into another form and finally develops into the adult form.

Pheretima Posthuma is the taxonomic name for earthworm which belongs to the Phylum Annelida. These are elongated worms. They develop from the egg and form the larvae which develop directly to form the adult. There are no changes occurring in the body of earthworms or they do not form any structures while passing through the larval stage of the life cycle.

PCR technique was invented byKarry Mullis.Clearly, PCR is enormously important for both the scientist and the non-scientist alike. The technique was developed by Kary Mullis in the 1980s, and he received the 1993 Nobel Prize in chemistry as a result.PCR (polymerase chain reaction) is a method used in molecular biology to make millions of physical copies of a specific DNA sequence, for example, a gene. It has several key ingredients: a DNA template to copy, short DNA sequences called “primers”, and a master mix containing the rest of the necessary molecules.

Sickle cell anaemia is an autosomal recessive trait whereas haemophilia is an X-linked recessive trait. Both the diseases are related to blood.