Cell biology is a fundamental topic in the International Baccalaureate (IB) Biology syllabus. This study note document will cover the essential aspects of cell biology, including cell theory, cell structure, membrane dynamics, and cell division. Each section will break down complex ideas into digestible parts, using examples and illustrations to enhance understanding.
The cell theory is a cornerstone of biology, providing a unifying concept that is universally accepted. It consists of three main ideas:
Note:
Robert Hooke coined the term "cells" in the 1660s after observing the structure of cork under a microscope. The cell theory was later developed by Matthias Schleiden and Theodor Schwann in 1837.
All living cells perform several essential functions:
Example:
Example: Paramecium, a unicellular organism, exhibits all these functions. It moves using cilia, ingests food particles, and expels waste.
The surface area to volume ratio is crucial for cell efficiency. A higher ratio allows for more efficient transport of materials in and out of the cell.
$$ \text{Surface Area} = 6a^2 \ \text{Volume} = a^3 \ \text{Surface Area to Volume Ratio} = \frac{6a^2}{a^3} = \frac{6}{a} $$
Common Mistake:
A common misconception is that larger cells are more efficient. In reality, smaller cells have a higher surface area to volume ratio, making them more efficient in nutrient uptake and waste removal.
Cell specialization allows multicellular organisms to have cells with specific functions. This is achieved through the expression of different genes in different cell types.
Example:
Example: In humans, red blood cells are specialized for oxygen transport, while neurons are specialized for transmitting nerve impulses.
Stem cells are undifferentiated cells with the potential to differentiate into various cell types. They are classified into:
Tip:
Stem cells have significant potential in regenerative medicine, offering possibilities for treating conditions like Parkinson's disease and spinal cord injuries.
Understanding cell theory requires the ability to:
The origin of cells is a fundamental question in biology. The most widely accepted hypothesis is that life began from simple organic molecules that eventually formed more complex structures.
The endosymbiotic theory explains the origin of eukaryotic cells from prokaryotic organisms. It suggests that mitochondria and chloroplasts were once free-living bacteria that were engulfed by a host cell.
Note:
Mitochondria and chloroplasts have their own DNA and double membranes, supporting the endosymbiotic theory.
Prokaryotic cells, such as bacteria, have a simple structure:
Eukaryotic cells have a more complex structure with membrane-bound organelles:
Exocrine pancreatic cells produce digestive enzymes, while palisade mesophyll cells in plants are specialized for photosynthesis.
Feature Prokaryotic Cells Eukaryotic Cells Size Small (1-10 µm) Larger (10-100 µm) Nucleus Absent Present Organelles Few, non-membrane-bound Many, membrane-bound DNA Circular, in nucleoid Linear, in nucleus
Microscopes are essential tools for studying cells:
Drawing cells accurately requires understanding their structure and proportions. Practice by sketching different cell types and labeling their parts.
Skills in this area include:
The phospholipid bilayer forms the basic structure of cell membranes. Phospholipids have hydrophilic heads and hydrophobic tails, creating a semi-permeable membrane.
Membrane proteins serve various functions:
The fluid mosaic model describes the cell membrane as a dynamic structure with proteins floating in a sea of lipids. This model was proposed by Singer and Nicolson in 1972.
Transport across cell membranes can be passive or active:
Active transport involves carrier proteins and ATP. Bulk transport includes:
Skills in this area include:
Estimating osmolarity involves understanding the movement of water across membranes and its effect on cells.
The cell cycle consists of interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).
Mitosis is the process of nuclear division, consisting of:
Cancer results from uncontrolled cell division due to mutations in genes that regulate the cell cycle.
Skills in this area include:
Cell biology is a vast and intricate field that forms the foundation of many biological concepts. Understanding cell theory, cell structure, membrane dynamics, and cell division is crucial for mastering this topic in the IB Biology syllabus. By breaking down complex ideas and using real-world examples, this study note aims to provide a comprehensive and accessible overview of cell biology.