Unlike Physical sciences, Biological sciences have very few universally applicable principles rather there are numerous exceptions which has made it a science of expectations. These expectations are based on adaptations to different environments, modes of leaving and feeding. The living beings show various degrees and directions of evolution in their different parts.
Dicotyledonous plants have two cotyledons in their seeds. The seeds of parasitic plant, Cuscuta, are devoid of any cotyledons.
Dicot leaves have reticulate venation while monocot leaves have parallel venation. However, a number of monocots like Smilex have reticulate venation while some dicots like Calophyllum have parallel venation.
Roots are normally positively geotropic. In mangrove plants like Sonneratia Pneumatophores are present.
Roots are non green and non photosynthetic. But, they are green and photosynthetic in Tinospora.
DNA is the hereditary material in all organisms except in some viruses, Riboviruses,
where RNA functions as the hereditary material.
DNA is usually double stranded but in Bacteriophages, it is single stranded. On the other hand RNA is commonly single stranded but in Rheovirus it is double stranded.
The heart of reptiles is three chambered but in Crocodiles it is four chambered.
All land animals drink water but Desert or Kangaroo Rat never does so.
Lungs are absent in fishes but in Lung fishes lungs as well as gills are present.
Birds fly but Ostrich and Kiwi do not do so.
Mammals are viviparous but Ornithorynchus and Echidna are oviparous mammals.
Erythrocytes of mammals are circular and biconcave but that of Camel and Llama are oval and flat.
Larval stage is juvenile stage and does not take part in reproduction but Axolotal larva of American Salamander can reproduce sexually.
Young ones are produced by fertilization of eggs with the help of sperms. However, the drones of Honey Bee develop from unfertilized eggs.
Biology – A Science of Expectations
