Exploring Cells and Biological Organization in GCSE Biology

Cell Structure and Types

Cells are the fundamental units of life and can be classified into two main categories: prokaryotic and eukaryotic. Prokaryotic cells (found in bacteria and archaea) lack a true nucleus and membrane-bound organelles, while eukaryotic cells (found in plants, animals, fungi, and protists) possess a well-defined nucleus and various organelles.

Key Organelles and Their Functions

• Nucleus: Contains the cell's genetic material (DNA) and controls cellular activities.
• Cytoplasm: The jelly-like substance where many cellular processes occur.
• Cell Membrane: Selectively permeable barrier that controls the movement of substances in and out of the cell.
• Mitochondria: Often called the "powerhouses" of the cell, they generate energy through cellular respiration.
• Ribosomes: Sites of protein synthesis.
• Cell Wall (in plant cells): Provides structural support and protection.
• Chloroplasts (in plant cells): Contain chlorophyll and are responsible for photosynthesis.
• Vacuole (larger in plant cells): Stores water, nutrients, and waste products.

Cell Specialisation and Microscopy

Cells can become specialized to perform specific functions within an organism. For example, nerve cells are specialized for transmitting electrical signals, while red blood cells are specialized for carrying oxygen. Microscopy techniques, such as light microscopy and electron microscopy (scanning electron microscopy and transmission electron microscopy), allow us to observe and study cellular structures in detail.

Worked Example: Calculating Magnification

Problem: If the size of a bacteria viewed under a light microscope is 0.2 mm on the image and its actual size is 2 μm, what is the magnification of the microscope?

Solution:

1. Convert the measurements to the same unit (mm): Actual size = 2 μm = 0.002 mm
2. Magnification = Size on the image / Actual size = 0.2 mm / 0.002 mm = 100x

Cell Division and Growth

Cell division is a crucial process that allows organisms to grow, repair damaged tissues, and reproduce. Mitosis is the process of nuclear division in eukaryotic cells, resulting in two genetically identical daughter cells. The cell cycle is a series of events that cells go through, including interphase (growth phase), mitosis (division phase), and cytokinesis (cytoplasmic division).

Stem cells are undifferentiated cells that have the ability to divide and differentiate into various specialized cell types. They play a crucial role in embryonic development, tissue repair, and regenerative medicine.

Membrane Transport

The movement of substances across cell membranes is essential for cellular functions. Diffusion is the passive movement of molecules from a region of higher concentration to a region of lower concentration. Osmosis is the diffusion of water molecules across a selectively permeable membrane. Active transport is the movement of substances against a concentration gradient, requiring energy from ATP.

Biological Organization

Organisms are organized at different levels, from cells to tissues, organs, and organ systems. In humans, major organ systems include the digestive system (responsible for breaking down food), respiratory system (facilitating gas exchange), circulatory system (transporting nutrients, oxygen, and waste), and many others. Plant organization includes specialized tissues like xylem (for water transport) and phloem (for transporting organic nutrients).

Non-communicable diseases, such as cardiovascular diseases (e.g., coronary heart disease) and cancer, are often related to lifestyle factors and can affect various organ systems.