Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The nucleus is a large, centrally located spherical organelle bounded by a double-layered membrane called the nuclear envelope.
The nuclear membrane has pores that allow the transfer of material from inside the nucleus to its outside, i.e., to the cytoplasm.
The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide. Chromosomes contain information for the inheritance of features from parents to the next generation in the form of () molecules.
Functional segments of are called genes. In a cell which is not dividing, this is present as part of chromatin material, which appears as an entangled mass of thread-like structures.
The nucleus plays a central role in cellular reproduction, the process by which a single cell divides and forms two new cells.
In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane. Such an undefined nuclear region containing only nucleic acids is called a nucleoid.
The cytoplasm is the fluid content inside the plasma membrane. It contains many specialized cell organelles, each performing a specific function for the cell.
Organisms with cells lacking a nuclear membrane are called prokaryotes ( = primitive; = nucleus), while organisms with cells having a nuclear membrane are called eukaryotes.
📐Formulae
💡Examples
Problem 1:
Explain why the nucleus is referred to as the 'control center' of the cell.
Solution:
The nucleus directs the chemical activities of the cell and carries genetic information.
Explanation:
The nucleus contains (genes), which holds the instructions for protein synthesis and metabolic activities. It also determines how the cell will develop and what form it will exhibit at maturity by directing chemical activities.
Problem 2:
Differentiate between the nuclear region of an Amoeba and a Bacteria.
Solution:
Amoeba has a well-defined nucleus with a nuclear membrane, while Bacteria has a nucleoid.
Explanation:
Amoeba is a , so its genetic material is enclosed within a double-layered nuclear membrane. Bacteria is a , meaning its nuclear region lacks a membrane and consists of naked nucleic acids called a .
Problem 3:
What is the physical state of the genetic material in a non-dividing cell?
Solution:
In a non-dividing cell, genetic material exists as chromatin.
Explanation:
When the cell is not undergoing division, the is present as an entangled, thread-like mass known as chromatin. It only condenses into rod-shaped when the cell is ready to divide.