Understanding Cells and Organisation in Living Systems

Cell Structure and Function

Cells are the fundamental units of life and can be classified as either prokaryotic (lacking a true nucleus) or eukaryotic (containing a membrane-bound nucleus). Eukaryotic cells are more complex and have several specialized organelles:

• Nucleus: Contains genetic material (DNA) and directs cellular activities
• Cytoplasm: Fluid matrix surrounding organelles where cellular processes occur
• Cell membrane: Selectively permeable barrier that regulates the movement of substances in and out
• Mitochondria: Produce energy in the form of ATP through cellular respiration
• Ribosomes: Sites of protein synthesis
• Cell wall (plants only): Provides structural support and protection
• Chloroplasts (plants only): Site of photosynthesis
• Vacuole: Storage compartment for nutrients, waste, and water

Cell Specialisation and Microscopy

Different cell types are specialized for specific functions within organisms. Microscopes allow us to study cells at higher magnifications. Light microscopes use visible light, while electron microscopes use beams of electrons to provide higher resolution and detail.

Microscope Calculations

Problem: An object appears 200 μm long under a light microscope with a total magnification of 400x. Calculate the actual size of the object.

Solution:

• Actual size = Size under microscope / Magnification
• Actual size = 200 μm / 400 = 0.5 μm

Cell Division and Stem Cells

Cell division is essential for growth, repair, and reproduction. Mitosis is the process by which a cell divides into two identical daughter cells. The cell cycle includes interphase (G1, S, G2 phases) and mitosis (prophase, metaphase, anaphase, telophase).

Stem cells are unspecialized cells capable of dividing and differentiating into various cell types. They play a crucial role in tissue regeneration and have potential therapeutic applications.

Membrane Transport

Cells require a constant exchange of materials across their membranes. Diffusion is the passive movement of particles from higher to lower concentration, while osmosis is the diffusion of water across a selectively permeable membrane. Active transport uses energy (ATP) to move substances against their concentration gradient.

Organisation in Living Systems

Hierarchical Organisation

Living organisms exhibit a hierarchical organization, ranging from cells to tissues, organs, and organ systems. This organization allows for efficient coordination and integration of various functions.

Human Body Systems

• Digestive System: Breaks down food into smaller molecules for absorption (enzymes, stomach, intestines)
• Respiratory System: Facilitates gas exchange (lungs, diaphragm)
• Circulatory System: Transports substances throughout the body (heart, blood vessels, blood components)

Disruptions in these systems can lead to non-communicable diseases like cardiovascular diseases (CHD) and cancer.

Plant Organisation

Plants have specialized tissues for transport and structural support:

• Xylem: Transports water and minerals from the roots to the leaves
• Phloem: Distributes organic nutrients (produced by photosynthesis) throughout the plant

Transpiration is the evaporation of water from leaves, while translocation refers to the movement of organic nutrients through the phloem.