Exploring Cells and Organisation in GCSE Biology

Cell Structure and Function

Cells are the fundamental units of life, and their structure determines their function. There are two main types of cells: prokaryotic and eukaryotic.

Prokaryotic Cells

Prokaryotic cells are simpler and lack a true nucleus and membrane-bound organelles. They are typically smaller than eukaryotic cells and include bacteria and archaea.

Eukaryotic Cells

Eukaryotic cells are more complex and contain a nucleus and various organelles, each with specific functions. Key organelles include:

• Nucleus: Contains the genetic material (DNA) and controls cellular activities.
• Cytoplasm: The jelly-like substance where chemical reactions occur.
• Cell membrane: Selectively permeable barrier that regulates the movement of substances in and out of the cell.
• Mitochondria: Powerhouses of the cell, responsible for energy production through cellular respiration.
• Ribosomes: Site of protein synthesis.
• Cell wall (in plant cells): Provides structural support and protection.
• Chloroplasts (in plant cells): Contain chlorophyll and are the site of photosynthesis.
• Vacuole: Storage compartment for water, nutrients, and waste products.

Cell Specialisation and Microscopy

Cells can become specialized to perform specific functions within an organism. Microscopy techniques, such as light and electron microscopy, are used to study cells and their structures.

Microscopy Calculations

Problem: A specimen is observed under a light microscope with a magnification of 400x. If the observed length of a cell is 20 mm, calculate the actual length of the cell.

Solution:

• Given: Magnification = 400x, Observed length = 20 mm
• Actual length = Observed length / Magnification
• Actual length = 20 mm / 400 = 0.05 mm or 50 μm

Cell Division and Growth

Cell division is crucial for growth, repair, and reproduction in organisms. Mitosis is the process of cell division in somatic (body) cells, involving the replication and equal distribution of genetic material to daughter cells. The cell cycle is a series of phases that regulate mitosis.

Stem cells are undifferentiated cells with the ability to divide and develop into different cell types. They play a vital role in growth, repair, and potential medical treatments.

Membrane Transport

The movement of substances across cell membranes is essential for cellular function. Processes like diffusion, osmosis, and active transport facilitate the exchange of materials between cells and their environment.

Organisation in Organisms

Organisms exhibit a hierarchical organization, starting from cells and progressing to tissues, organs, and organ systems. In humans, major systems include the digestive, respiratory, circulatory, and others involved in processes like enzyme action, gas exchange, blood circulation, and more.

Non-communicable diseases like cardiovascular diseases and cancer can affect these systems. In plants, specialized tissues like xylem and phloem facilitate the transport of water, minerals, and nutrients, contributing to processes like transpiration and translocation.

Further Resources:

• BBC Bitesize: Cells and Organisation
• Exam Board Specifications: OCR GCSE Biology, AQA GCSE Biology