Cells and Their Functions

What are Cells?

• Cells are the smallest building blocks of living beings and the fundamental structure of organisms.
• Organisms can be unicellular (made of one cell) or multicellular (made of many cells).
• Humans have approximately 37.2 trillion cells.

Discovery of the Cell

• Robert Hooke coined the term "cell" in 1665 after observing cells under a microscope.
• He is credited with the invention of the compound microscope and identified the cell as the basic unit of life.

Types of Cells

• Eukaryotic Cells: Have a true nucleus and contain DNA, with cell division occurring by mitosis or meiosis.
• Prokaryotic Cells: Lack a true nucleus and have a nucleoid instead of DNA, with cell division occurring by binary fission.

Cell Growth and Metabolism

• Cell growth is achieved through metabolism, which is divided into:
  • Catabolism: Breaks down complex molecules to produce energy.
  • Anabolism: Utilizes energy to construct necessary molecules and perform biological functions.

Functions of Cells

• Key functions include cell division, transport, and metabolism.
• Cells transport substances through the cell membrane.

Cell Organelles

• Organelles are mini-organ systems within a cell, including:
  • Cell membrane
  • Nucleus
  • Ribosomes
  • Rough and smooth endoplasmic reticulum
  • Golgi apparatus
  • Centrioles
  • Mitochondria
  • Vacuoles
  • Cytoplasm

Cell Membrane

• Comprised of a phospholipid bilayer, it is semi-permeable and controls substance entry.
• The phospholipid head is hydrophilic, while the tail is hydrophobic.

Nucleus

• Encloses DNA within a double membrane called the nuclear envelope, featuring pores for substance exchange.
• Chromatin condenses to form chromosomes during cell division, and ribosomes are produced in the nucleolus.

Ribosomes

• Responsible for protein synthesis as directed by DNA.
• Can be found free in the cytoplasm or attached to the rough endoplasmic reticulum.

Endoplasmic Reticulum

• Rough Endoplasmic Reticulum: Studded with ribosomes that synthesize proteins for internal use or export.
• Smooth Endoplasmic Reticulum: Lacks ribosomes and synthesizes lipids, detoxifies drugs, and carries proteins.

Golgi Apparatus

• Modifies, sorts, and packages proteins and materials from the endoplasmic reticulum for storage or secretion.

Lysozymes

• Membrane-bound sacs containing enzymes that break down food substances and waste materials.

Centrioles and Vacuoles

• Centrioles: Aid in coordinating cell division in animal cells.
• Vacuoles: Store water, food, enzymes, and waste materials.

Cytoplasm

• A jelly-like substance that holds organelles in place.

Mitochondria

• Known as the powerhouse of the cell, they convert chemical energy from food into usable energy.
• Composed of an outer membrane and an inner membrane with folds known as cristae.
• Responsible for cellular respiration and contain their own DNA inherited from the mother.

Using a Microscope

• Steps include turning on the microscope, adjusting the light, placing the specimen, and focusing using coarse and fine adjustment wheels.
• Observers can switch to medium and high-power lenses for detailed examination.

Summary of Microscopes

• Microscopes magnify specimen structures, enabling detailed visualization which requires specimens to be focused using adjustment wheels.