Class 11 Biology - PUNJAB
Cell: The Unit of Life
The chapter 'Cell: The Unit of Life' forms the foundation of cell biology in the Class 11 Punjab (PSEB) curriculum. It explores the cell theory, the structural differences between prokaryotic and eukaryotic cells, and the detailed architecture of plant and animal cells. Students learn about the ultrastructure and functions of various cell organelles such as the plasma membrane, mitochondria, ribosomes, and nucleus. This chapter is extremely crucial for board exams as it carries substantial weightage in both objective and subjective sections, testing students on diagrams, structural details, and functional differences of cellular components.
Start Learning FreeKey Concepts
Cell Theory
Proposed by Schleiden, Schwann, and later expanded by Rudolf Virchow, it states that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells.
Prokaryotic vs. Eukaryotic Cells
Prokaryotic cells lack a true nucleus and membrane-bound organelles (e.g., bacteria), whereas eukaryotic cells possess a well-defined nucleus and various membrane-bound compartments (e.g., plant and animal cells).
Endomembrane System
A group of membranous organelles—including the endoplasmic reticulum, Golgi apparatus, lysosomes, and vacuoles—whose functions are coordinated for protein and lipid synthesis and transport.
Mitochondria and Plastids
Mitochondria are the powerhouse of the cell responsible for ATP production, while plastids (like chloroplasts) are found in plant cells and are responsible for photosynthesis.
Fluid Mosaic Model
Proposed by Singer and Nicolson, this model describes the plasma membrane as a fluid phospholipid bilayer with proteins embedded mosaic-like, allowing lateral movement of molecules.
Important Formulas
Board Exam Info
In Punjab (PSEB) Class 11 Biology exams, this chapter typically carries around 6 to 8 marks. Questions usually include structured diagrams (like ultrastructure of a plant/animal cell or mitochondrion), differentiation between prokaryotes and eukaryotes, and short-answer questions on organelle functions.
Frequently Asked Questions
What is the main difference between plant and animal cells?
Plant cells have a rigid cell wall, large central vacuoles, and plastids, which are generally absent in animal cells. Animal cells possess centrioles, which are typically absent in plant cells.
Why are mitochondria called the powerhouses of the cell?
Mitochondria produce cellular energy in the form of ATP (adenosine triphosphate) through aerobic cellular respiration, which is utilized for various metabolic activities.
Who proposed the Cell Theory and its modification?
The original Cell Theory was proposed by Matthias Schleiden and Theodor Schwann. Rudolf Virchow later modified it by adding the concept 'Omnis cellula e cellula' (all cells arise from pre-existing cells).
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