Endocrine glands and hormones

Endocrine glands lack ducts and are hence, called ductless glands. Their
secretions are called hormones. The classical definition of hormone as a
chemical produced by endocrine glands and released into the blood and
transported to a distantly located target organ has current scientific
definition as follows: Hormones are non-nutrient chemicals which
act as intercellular messengers and are produced in trace amounts.
The new definition covers a number of new molecules in addition to the
hormones secreted by the organised endocrine glands. Invertebrates
possess very simple endocrine systems with few hormones whereas a large
number of chemicals act as hormones and provide coordination in the
vertebrates.

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Phyllotaxy

Phyllotaxy is the pattern of arrangement of leaves on the stem or branch. This is usually of three types – alternate, opposite and whorled . In alternate type of phyllotaxy, a single leaf arises at each node in alternate manner, as in china rose, mustard and sun flower plants. In opposite type, a pair of leaves arise at each node and lie opposite to each other as in Calotropis and guava plants. If more than two leaves arise at a node and form a whorl, it is called whorled, as in Alstonia.

Emasculation and Bagging

If the female flower is bisexual , removal of anthers from the flower bud before the anther dehisce using a pair of forceps this is called emasculation . Emasculated flowers have to be covered with a bag of suitable size made of butter paper to prevent contamination of its stigma with unwanted pollen . this process is called bagging

The salient features of genetic code

The salient features of genetic code (i)The codon is triplet. 61 codons code for amino acids and 3 codons donot code for any amino acids, hence they function as stop codons. (ii)One codon codes for only one amino acid, hence, it is unambiguous and specific (iii)Some amino acids are coded by more than one codon, hencethe code is. degenerate (iv)The codon is read in mRNA in a contiguous fashion. There areno punctuations. (v)The code is nearly universal:for example, from bacteria to human UUU would code for Phenylalanine (phe). Some exceptions to thisrule have been found in mitochondrial codons, and in someprotozoans. (vi)AUG has dual functions. It codes for Methionine (met) , and it also act as initiator codon

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