January 5, 2016

Inter First Year Botany Important 4 Marks Questions from 9-11 Chapters

Q: Describe the structure of nucleus.
A: Nucleus: Nucleus was first described by Robert Brown.
It shows:
Chromatin
Nuclear matrix
Nucleoli and
Nuclear envelop.

The nuclear envelop contains two membranes which enclose perinuclear
space. The nuclear envelop shows minute pores called nuclear pores
through which the nucleoplasm is in contact with the cytoplasm.

The nuclear matrix or nucleoplasm contains nucleolus and chromatin.
The nucleolus is a darkly stained region in the nucleus and it is the
site of RNA synthesis. The chromatin appears as a loose indistinct
network of nucleo -protein fibers during interphase.

During metaphase and anaphase it appears as distinct number of
chromosomes. The chromatin is made up of DNA, histone proteins,
nonhistone proteins and RNA. The chromosome shows a primary
constriction called centromere.

Q: Give a brief account of the types of chromosomes based on the
position of centromere.
A: Based on the position of centromere the chromosomes can be
classified into 4 types:

Metacentric chromosome: Centromere is in the middle and the chromosome
shows two equal arms.

Sub-metacentric chromosome: Centromere is present near to the middle
with one short and one long arm of chromosome.

Acrocentric chromosome: The centromere is situated close to one end
with one extremely short arm and one very long arm.

Telocentric: The centromere is present at one end.

Q: Briefly describe the cell theory.
A: M. Schleiden, a botanist and T.Schwann, a zoologist together
proposed the cell theory. According to this theory all plants and
animals are composed of different kinds of cells which form tissues.

Schwann also proposed that the bodies of all plants and animals are
composed of cells and products of cells.

The animal cells are bounded by a plasma membrane, whereas the plant
cells have a cell wall surrounding the plasma membrane. These
observations gave way to formulate the cell theory as:

All living organisms are composed of cells and products of cells.
Thus cell is the structural and functional unit of life.
Later the cell theory was modified by Virchow as: All living organisms
are composed of cells and products of cells. Thus cell is the
structural and functional unit of life. 'All cells arise from
pre-existing cells'.

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