Biology 10th Class: Cell Structure and Function

Cells: The Basic Unit of Life

• Cells are the fundamental building blocks of all living things.
• Some organisms are single-celled, others are multicellular.
• Multicellular organisms are organized into levels: cells, tissues, organs, and organ systems.

Cell Theory

• All living things are made of cells.
• Cells are the basic unit of structure and function in an organism.
• Cells come from the reproduction of existing cells (cell division).

History of Cell Discovery: Hooke

• In 1665, Robert Hooke used a primitive microscope to examine cork.
• He observed small compartments and named them "cells" because they resembled small rooms monks lived in.

History of Cell Discovery: Leeuwenhoek

• In 1673, Anton van Leeuwenhoek was the first to view a live cell using a simple handheld microscope.
• He observed pond water samples and various other materials.

History of Cell Discovery: Schleiden & Schwann

• In 1838, Matthias Schleiden (botanist) concluded that all plants were made of cells.
• In 1839, Theodore Schwann (zoologist) concluded that all animals were made of cells.

History of Cell Discovery: Virchow

• In 1855, Rudolph Virchow observed dividing cells and stated that all cells come from pre-existing cells.

Cell Size Variation

• Bacterial cells are typically 0.1 – 5 μm.
• Animal cells are generally 10 – 30 μm.
• Plant cells range from 10 – 100 μm.
• Cell size is limited by the ratio of surface area to volume.

Why are Cells Small?

• Nutrients and waste are exchanged at the cell's membrane.
• As a cell grows, volume increases faster than surface area.

Number of Cells

• Organisms can be unicellular (one-celled) or multicellular (many cells).
• Multicellular organisms often have specialized cells.

Cell Specialization

• Cells in multicellular organisms specialize to perform specific functions.
• This process is called differentiation.

Specialized Animal Cells

• Examples include muscle cells, red blood cells, and cheek cells (epithelial cells).

Specialized Plant Cells

• Examples include guard cells (for gas exchange) and xylem cells (for transporting water and nutrients).

Cell Parts (Organelles)

• Organelles are specialized structures within a living cell.
• They perform specific functions.
• Some organelles have membranes; others do not.

Prokaryotes

• Prokaryotic cells lack a nucleus and other membrane-bound organelles.
• Prokaryotes are the simplest type of cell, believed to have evolved first.
• Prokaryotic cells have a single circular chromosome.
• Prokaryotic cells include bacteria.

Prokaryotic Cell Structure

• Nucleoid region: contains the cell's DNA.
• Cell membrane and cell wall surround the nucleoid region.
• Ribosomes are present in the cytoplasm for protein synthesis.

Eukaryotes

• Eukaryotic cells have a nucleus and other membrane-bound organelles.
• Eukaryotic cells are more complex than prokaryotic cells.
• They include protists, fungi, plants, and animals.

Eukaryotic Cell Structure

• Nucleus: contains the DNA and controls cellular activities.
• Nuclear envelope: the membrane surrounding the nucleus, has pores for material exchange.
• Cytoplasm: the jelly-like substance that fills the cell and surrounds organelles.
• Cell membrane: the outer boundary of the cell, controls the entry and exit of materials.
• Cytoskeleton: a network of proteins that give the cell shape, support, and movement, and help move organelles around.

Organelles

• Mitochondria: the power plants of cells, generate energy (ATP) by breaking down glucose.
• Chloroplasts: found only in plants and algae, use sunlight to make energy in a process called photosynthesis.
• Endoplasmic reticulum (ER): a network of membranes that synthesize and transport cell products (proteins and lipids)
  • Rough endoplasmic reticulum has ribosomes on its surface, involved in protein synthesis
    • Smooth endoplasmic reticulum synthesized lipids, regulates calcium, and breaks down toxins.
• Ribosomes: "protein factories" of the cell, make proteins.
• Golgi apparatus: modifies, sorts, and packages cell products from the ER for transport.
• Lysosomes: break down food, bacteria, and worn-out cell parts in cells.
• Vacuoles: fluid-filled sacs for storage (large in plant cells, small or absent in animal cells).
• Centrosomes: important for cell division; contain centrioles.
• Cilia and Flagella: structures for cell movement.

Endosymbiosis

• Endosymbiotic theory explains the origin of mitochondria and chloroplasts.
• It suggests that these organelles were once free-living prokaryotes that were engulfed by a larger cell