Chapter Two

Comprehension-based Questions & Answers:

Ques-1. What do you mean by eukaryotic cell? 

Ans: The cells in which the nucleus is well structured, meaning that the nuclear materials are well organized and surrounded by a nuclear membrane are called eukarvotic cells. There are two types of eukaryotic cells-somatic cell and gametic cell. In these cells, there are all types of organelles including ribosome. Most of the living cell is eukaryotic cell. 

Ques-2. Why are plastids called colour forming organs? 

Ans: The colored organelles present within the cytoplasm of plant cells are known as plastids. They are responsible for the formation of color of any plant part like leaves, flower and fruits. In absence of light plastids become colorless. The colorless plastids are known as leucoplasts generally present in the cell of roof and contex where light is not available. In presence of light, colorless plastids may develop color. So the plastids are known as the color forming organelles. 

Ques-3. How does skeletal tissue protect the brain? 

Ans: Skeletal tissue constitutes the structural framework of animal body, holds the muscles and protects the internal organs from injury. Brain is the most sensitive and important part of the body of vertebrate animals. So, its protection demands highest importance. There is a cover made up of hard bones around the brain known as skull. In the vieinity of the skull brain remain situated and its safety is maintained and protected from external injury. 

Ques-4. When chromatin fibres look like as chromosome?

Ans: Chromatin fibers become coiled during cell division and become more condensed, and then they are called chromosomes. Chromosomes carry the units of heredity and pass from generation to generation. 

Ques-5. Explain the reason why water-hyacinth floats in water. 

Ans: Water hyacinth has a special type of parenchyma tissue called aerenchyma that helps it to float in water. Aerenchyma is a special type of parenchyma tissue that has air filled spaces. They are usually big in size and the air filled spaces work as air bags. They are mostly found in aquatic plants such as, water hyacinths, which helps them to float in water. 

Ques-6. What is meant by endocrine gland? 

Ans: The glands which are ductless and the secretion from the glands are transported through blood or lymph and act at a distant organ are called endocrine glands. For example-Pituitary gland, thyroid gland, etc. 

Ques-7. Why nucleus is called the control center of cell? 

Ans: Nucleus is known as the control center of the cell as it performs the following functions: The nucleus contains the hereditary material of the cell, the DNA. It sends signals to the cells to grow, mature, divide and die. The nucleus is surrounded by the nuclear envelope that separates the DNA from the rest of the cell. The nucleus protects the DNA and controls the activities of the cell by regulating gene expression the nucleus is, therefore, the control room of the cell.