Fundamental Unit of Life_2

Name the structure that maintains identical

chromatids bound.

How are the chromosomes classified in relation to

the position of the centromere? On the basis of the position of the centromere, the chromosomes are of 4 types:

• Telocentric

• Acrocentric

  
  

• Submetacentric

• Metacentric

Give the chemical nature of

• The nucleolus is composed of RNA and proteins which form around specific chromosomal regions.

• r-RNA, though also contains a small amount of DNA and proteins.

State two differences between outer and inner

nuclear membranes

• The outer nuclear membrane is studded with ribosomes

  and is continuous with Rough endoplasmic reticulum (RER) at some points.

• the inner nuclear membrane is smooth (not studded with ribosomes) and is not connected with Rough endoplasmic reticulum (RER)

  
  

• The outer layer is made of rough proteins

• Inner layer is made of smooth proteins

How many chromosomes does a human normally

diploid cell has?

State the function of secondary constriction.

• Secondary constriction is the site of r-RNA biosynthesis.

• Primary Constriction from a cytological point of view, is considered the centromere.

• Actually centromere ( as it plays most important role in chromatid separation during anaphase ) is present within the primary constriction.

• Secondary constriction is also known as nucleolar organiser region(NOR) involved in the formation of nucleolus.

Of which substance is chromatin made of?

Name the types of cells not having delimited nucleus.

• Prokaryotic cells (e.g. bacteria).

• Eukaryotic cells (e.g. monkeys)

Why the nucleus of plant cells is excentric in position?

• Due to the presence of a large central vacuole.

• Most mature plant cells have a central vacuole that occupies more than 30% of the cell's volume.

• The central vacuole can occupy as much as 90% of the volume of certain cells.

• The central vacuole contains large amounts of a liquid called cell sap, which differs in composition to the cell cytosol.

Enlist components of the nucleus.

• Nuclear membrane

• nucleoplasm

• nucleolus

  
  

• nuclear chromatin