Biology Chapter 3: Cell as the Unit of Life

Key Components of Animal Cells

• Irregularly shaped and eukaryotic, featuring a membrane-bound nucleus and organelles.
• Size typically ranges from 10 to 30 micrometers, smaller than human hair.
• Lacks a cell wall, permitting various shapes and aiding the evolutionary diversity of the animal kingdom.

Discovery of Cells

• The term "cells" was introduced in 1665 by Robert Hooke, who studied cork tissue under a microscope and described honeycomb-like structures.
• Antonie Van Leuwenhoek improved microscopy, first observing human cells and bacteria, expanding knowledge of the microscopic world.

Animal Cell Size and Shape

• Varies widely from microscopic cells to the largest known animal cell, the ostrich egg (over 5.1 inches).
• Common shapes include flat, oval, rod-shaped, curved, spherical, concave, and rectangular.
• Most cells require a microscope for observation.

Animal Cell Organelles

• Cellular components classified as membrane-bound or non-membrane-bound, each fulfilling specific functions.
• Organelles categorized based on presence of membrane:
  • Membrane-bound: Nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria.
  • Non-membrane-bound: Ribosomes, cytoskeleton.

Nucleus

• Double-membraned organelle storing genetic material and controlling cellular processes.
• Houses nucleoli and chromosomes; crucial for inheritance.
• Functions: DNA replication, transcription (RNA synthesis), and regulating cell growth and reproduction.

Endoplasmic Reticulum (ER)

• Network of tubular membranes found in eukaryotic cytoplasm, existing as rough ER (with ribosomes) and smooth ER (without).
• Rough ER synthesizes and processes proteins; smooth ER is involved in lipid metabolism.
• Continuous folds extend to the nuclear membrane, present in most eukaryotic cells excluding sperm and red blood cells.

Cell Organelles Functions

• Genetic Control: Organelles like the nucleus manage genetic material.
• Cellular Protection: Membranes protect cell contents.
• Protein Synthesis: Rough ER synthesizes proteins; ribosomes play a key role.
• Energy Production: Mitochondria generate ATP through cellular respiration.
• Storage & Structural Support: Organelles like vacuoles provide storage and structural integrity.