Exploring Cells and Organisation in GCSE Biology

Cell Structure and Function

Cells are the basic units of life and can be classified into two main types: prokaryotic and eukaryotic. Prokaryotic cells lack a true nucleus and membrane-bound organelles, while eukaryotic cells possess a well-defined nucleus and various organelles.

Eukaryotic Cell Organelles

• Nucleus: Contains the genetic material (DNA) and controls cellular activities.
• Cytoplasm: The gel-like substance surrounding the nucleus where many cellular processes occur.
• Cell Membrane: Selectively permeable barrier that regulates the movement of substances in and out of the cell.
• Mitochondria: Produce energy (ATP) through cellular respiration.
• Ribosomes: Sites of protein synthesis.
• Cell Wall (in plant cells): Provides structural support and protection.
• Chloroplasts (in plant cells): Carry out photosynthesis.
• Vacuole: Storage compartment for water, nutrients, and waste products.

Cell Specialisation and Microscopy

Cells can become specialised to perform specific functions within an organism. Microscopy techniques, such as light and electron microscopy, allow scientists to study cell structure and organisation in detail. Calculations involving magnification and scale are essential in microscopy.

Cell Division and Stem Cells

Cell division is a crucial process in growth, repair, and reproduction. Mitosis is the process by which a eukaryotic cell divides to produce two genetically identical daughter cells. The cell cycle and chromosomes play vital roles in mitosis. Stem cells have the remarkable ability to differentiate into various cell types and hold great potential in regenerative medicine.

Membrane Transport

Cells require the movement of substances across their membranes for survival. Processes like diffusion, osmosis, and active transport facilitate the movement of molecules and ions across cell membranes.

Organisation in Organisms

Hierarchical Organisation

Organisms exhibit a hierarchical organisation, from cells to tissues, organs, and organ systems, each with specific functions.

Human Organ Systems

• Digestive System: Breaks down food into smaller molecules for absorption and energy production.
• Respiratory System: Facilitates gas exchange (oxygen and carbon dioxide) between the body and the environment.
• Circulatory System: Transports substances (nutrients, gases, and waste) throughout the body via the heart and blood vessels. It includes components like red blood cells, white blood cells, and platelets.

These systems work together to maintain homeostasis and support life processes. Enzymes, gas exchange mechanisms, and the structure and function of the heart and blood vessels are crucial aspects of human physiology.

Non-Communicable Diseases

Certain diseases, such as coronary heart disease and cancer, are classified as non-communicable diseases and can have significant impacts on human health.

Plant Organisation

Plants exhibit specialised tissues like xylem (for water and mineral transport) and phloem (for transporting nutrients). Processes like transpiration and translocation are essential for plant survival and growth.

Worked Example: Microscopy Calculations

Problem: A cell measures 0.2 mm when observed under a light microscope with a magnification of 400x. Calculate the actual size of the cell.

Solution:

• Actual size = Observed size / Magnification
• Actual size = 0.2 mm / 400
• Actual size = 0.0005 mm or 0.5 micrometers (μm)