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Cell Theory
The invention of the compound microscope in the 17th century stimulated the interest in living things not visible to the naked eyes. Thus, Robert Hooke discovered 'cells' in 1665 by examining cork slices (,under a crude microscope. He was actually describing the spaces occupied by the cells limited by the cellulose walls. Hooke and his contemporaries also described cells from other plants and animals.
Figure: A generalized plant (a) and animal (b) cell. No one cell of either plant (a) or animal (b) has all the characteristics shorn in these composite figures. Both these are
However, cell theory, one of the greatest and most basic generalizations of biology, was formulated only about 200 years later. Two German investigators, Schleiden a botanist (1838), and Schwann, a zoologist (1839) are credited with presenting independently the first concise, yet comprehensive, statements about the cell. They pointed out that, "All plants and. animals are made up of small fundamental units called cells and that some organisms are unicellular and others, multicellular." Subsequent researched to the expansion of this concept by including further information on cells. We know that cells are surrounded by cell membrane and contain cytoplasm and nucleus and, most importantly, cells divide into roughly equal daughter cells by a process called cell division. Thus it became known that new cells come into existence only by the division of previously existing cells. In other words, cells do not arise by spontaneous generation from nonliving matter. It follows that all cells living today can trace their ancestry back to those which existed in ancient times.
Alfred Sturtevant and Seymour Benzer's studies of recombination in both Drosophila and bacteriophage demonstrated which of the following? A. The gene is an indivisible unit and
Pattern of Limb Development The first visible sign of limb development is the appearance of ridge or thickening on each lateral side of the embryo of amniotes. The ridge call
Q. Which is the form of protozoan reproduction that generates more variability? Sexual reproduction always generates extra genetic variability than asexual reproduction. That i
Rothera's Test It is highly sensitive for both acetoacetic and acetone. Although it is one of the oldest methods still it is widely used. Procedure: - Take about 5ml of
If a person has a stomach ulcer (that is aggravated by excessive hydrochloric acid {HCl} secretion ), why on earth would he or she be drinking milk to feel better, when milk is als
Q. How respiratory pigments act? Respiratory pigments are oxygen-carrying molecules present in the blood. When the oxygen concentration is high for instance, in the pulmonary a
TYPES E.R. consists of two types - 1. Rough E.R. 2. Smooth E.R. R o ugh E.R. S m o o th E.R.
Deciduous Senescence - Senescence Only the leaves senesce as in many trees. The senescence of leaves, or abscission occurs when at the base of a leaf a layer of cells is laid
porifera canal system skeleton
Determine about the National Adult Reading Test The National Adult Reading Test (NART; Nelson, 1982) allows the researcher to obtain an estimate of an individual's IQ prior to
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