Exploring Cells and Organisation in Biology

Cells: The Building Blocks of Life

Cells are the fundamental units of life, with two main types: prokaryotic and eukaryotic. Prokaryotic cells lack a true nucleus, while eukaryotic cells have a membrane-bound nucleus and various organelles.

Eukaryotic Cell Structure

• Nucleus: Stores genetic material (DNA) and controls cell activities.
• Cytoplasm: Gel-like substance where organelles are suspended.
• Cell Membrane: Selectively permeable barrier controlling movement in/out of the cell.
• Mitochondria: Site of cellular respiration, producing ATP energy.
• Ribosomes: Site of protein synthesis.
• Cell Wall (plants): Rigid structure providing structure and protection.
• Chloroplasts (plants): Site of photosynthesis, capturing light energy.
• Vacuole: Storage compartment for nutrients, waste, and water.

Cell Specialisation and Microscopy

Cells can become specialised to perform specific functions in organisms. Microscopes like light and electron microscopes allow us to study cell structures and organelles in detail. Calculations involving magnification and scale are essential.

Worked Example: Calculating Actual Size

Problem: A cell measures 12 mm on a micrograph with 1000x magnification. What is the cell's actual size?

Solution:

1. Magnification = Image Size / Actual Size
2. 1000 = 12 mm / Actual Size
3. Actual Size = 12 mm / 1000 = 0.012 mm = 12 micrometers (μm)

Cell Division and Stem Cells

Mitosis is the process of cell division producing two genetically identical daughter cells. It involves the cell cycle stages: interphase, prophase, metaphase, anaphase, and telophase. Chromosomes duplicate and separate during mitosis.

Stem cells are unspecialised cells with the ability to divide and differentiate into various specialised cell types, beneficial in regenerative medicine.

Membrane Transport

Movement of substances across cell membranes occurs via:

• Diffusion: Net movement of particles from high to low concentration, down the concentration gradient.
• Osmosis: Diffusion of water molecules across a selectively permeable membrane.
• Active Transport: Movement of substances against the concentration gradient, requiring energy from ATP.

Organisation in Living Organisms

Hierarchical Organisation

Living organisms are hierarchically organised from cells to tissues, organs, and organ systems.

Human Body Systems

• Digestive System: Breaks down food, absorbs nutrients with help from enzymes.
• Respiratory System: Facilitates gas exchange (oxygen/carbon dioxide).
• Circulatory System: Heart pumps blood through vessels, transporting oxygen/nutrients.

Diseases like cardiovascular disease (CVD), heart disease, and cancer are non-communicable diseases affecting specific body systems.

Plant Organisation

Plants have specialised tissues like xylem (transports water/minerals) and phloem (transports food). Transpiration and translocation facilitate water/nutrient movement.