Chapter 7, Problem 26A

Summary Introduction

Introduction:

Each cell has different organelle to perform specific tasks. Membrane bound organelle make it possible for different processes to occur simultaneously in a cell. A cell is involved in energy transformations, food digestion, excretion of wastes and cell division. One of the main functions of the cell is also to produce proteins. Ribosomes are the sites where proteins are synthesized. They are made of RNA and proteins and are not membrane bound.

Answer to Problem 26A

B. nucleolus

Explanation of Solution

Explanation/justification for the correct answer :

B. Nucleolus- Within the nucleus of a cell is a structure that is the site for ribosome production. It is called nucleolus. Nucleolus produces ribosomes. The ribosomes may move freely in the cytoplasm or are attached to endoplasmic reticulum. A cell has many ribosomes to produce a variety of proteins.

Explanation for incorrect answer :

A. nuclear pore- The nuclear membrane has large number of pores called nuclear pores which allow movement of substances in and out of the nucleus. They are not the sites for synthesis of ribosomes. So, this is an incorrect option.

C. chromatin- Within the nucleus is a complex DNA attached to a protein. It is called chromatin. it carries the genetic material of the cell. It does not produce ribosomes. So, this is an incorrect option.

D. endoplasmic reticulum- It is a membrane system of folded sacs and interconnected channels that act as the site for protein synthesis. Ribosomes are attached to ER at some places and such ER is called rough ER. So, this is an incorrect option.