Human Body Organization: From Atoms to Ecosystems & Cell Basics

Human Body Organization

The human body is structured in a hierarchical manner, from the smallest components to the entire organism and its interactions within an ecosystem.

1. Subatomic Level

Consists of subatomic particles, i.e., protons, electrons, and neutrons (and sub-particles like quarks and leptons).

2. Atomic Level

Formed by atoms, the bioelements found in living beings. These include:

• Primary Bioelements: Essential for forming organic biomolecules (C, H, O, N, P, S), constituting 96% of dry living matter.
• Secondary Bioelements: Constitute 3% of dry living matter.
• Trace Elements: Present in small amounts but crucial for health (e.g., iron, iodine).

3. Molecular Level

Molecules are formed by grouping two or more atoms. Biomolecules in living beings include:

• Inorganic: Water and mineral salts.
• Organic: Carbohydrates, lipids, proteins, and nucleic acids.

4. Cellular Level

Molecules join to form cells, such as blood cells and nerve cells.

5. Tissue Level

A tissue is a group of similar cells working together to perform a function.

6. Organ Level

An organ is a group of tissues performing a specific function.

7. System Level

A collection of organs that perform a specific function.

8. Organism Level

All body systems form an organism.

9. Population Level

A group of human beings living in a given area.

10. Community Level

A group of humans and other living beings in an area.

11. Ecosystem Level

The interaction between living and non-living matter.

Cell Theory

Antonie van Leeuwenhoek used a simple microscope to observe unicellular organisms.

Robert Hooke discovered the cell in 1665 by examining cork slices under a compound microscope, observing tiny pores he called "cells."

Principles of Cell Theory:

1. Every organism is made of one or more cells.
2. The cell is the anatomical and physiological unit of living matter.
3. All cells come from preexisting cells by division.

Characteristics of Human Cells

Structure: Human cells are eukaryotic and heterotrophic.

Shape: Varied shapes include spheroid (leukocyte), stellate (neuron), discoid (blood cell), and fusiform (muscle cell).

Number: Billions of cells, approximately 250 types.

Size: Ranging from the smallest (spermatozoa) to the largest (egg cell and neuron).

Cell Structure

A light microscope reveals three main parts in a cell:

Cell Membrane

Function: Surrounds and protects the cell, controls material passage. Made of a lipid bilayer.

Nucleus

Function: Controls cell activity. Components include:

• Nuclear Envelope: Membrane with nuclear pores.
• Nucleoplasm: Liquid inside the nucleus.
• Chromatin: DNA in a non-dividing cell, condenses into chromosomes during cell division.
• Nucleoli: Site of ribosome production.

Cytoplasm

Fluid between the nucleus and cell membrane, containing water, cytoskeleton, and organelles (membranous and nonmembranous).