Organization in the Living World :Long Answer Type Questions
Question 1. Draw a well labelled diagram of a plant cell.
Question 2. Draw a well labeled diagram of an animal cell.
Question 3. How do bacteria survive during changed surrounding temperature and water conditions?
Like other plant cells, bacteria also have a cell wall which lies outside the plasma membrane.
Bacterial cell wall is composed of a substance called N-acetyl glucosamine which serves as impermeable and protective layer.
Muramic acid is also present in the cell, wall. This rigid cell wall enables bacteria to survive in extremely hot or extremely cold surroundings.
Similarly, bacterial cell can also resist change in surrounding medium. In hypotonic medium where there is abundant water, the water enter the cells through osmosis.
The cell swells and exerts pressure on cell wall to burst. But the wall also exerts an equal pressure against the cell which prevents the cell from bursting and destroying.
This makes bacteria the most resistant organisms on land. The cell wall is like a boon for bacteria.
Question 4. Give a brief account of organization and function of nucleus.
In both plant and animal cell there is a nucleus. Nucleus was first discovered by Robert Brown (1831). Nucleus is generally round in shape but it shows variation in shape.
It is surrounded by a double layered nuclear membrane. The nuclear membrane has several pores on it which allow the transfer of materials from inside to outside.
The fluid content of the nucleus is called nucleoplasm which contain chromosomes. Chromosomes are composed of DNA and protein, DNA or Deoxyribonucleic acid is the genetic material.
The functional segments of DNA are called genes which are hereditary units. During cell division the units are transferred from parents to the off springs along with chromosomes.
In a non-dividing cell, entangled mass of thread like structures called chromatin is seen while chromatin material gets organized into rod-shaped chromosomes in a dividing cell. A nucleolus, ribosomes also lie in the nucleoplasm.
The organisms which have a well organized nucleus with nuclear membrane are called Eukaryotes while those which lack a well organized nucleus surrounded by nuclear membrane are called prokaryotes. Such a nucleus is called nucleoid.
Nucleus controls all the metabolic activities of the cell. It plays an important role in reproduction by participating in cell division. Nucleus contains hereditary unit which plays an important role in inheritance of characters from parents to the off springs.