Cell StructureChapter 3

ByMr. Kling

• Cell- The smallest unit capable of carrying out all the functions of life.

Examples of Cells

Amoeba Proteus

Plant Stem

Red Blood Cell

Nerve Cell

Bacteria

Discovery of the Cell

• The English scientist Robert Hooke used one of the first microscopes to observe a thin slice of cork in 1665. He saw a lot of little boxes, which reminded him of the small rooms where monks lived. He called then cells.

• In 1675, the Dutch scientist Anton van Leeuwenhoek used a microscope to look at a sample of clear pond water and saw single celled organisms.

Formation of The Cell Theory• In 1838, a German botanist, Matthias Schleiden

concluded that all plants were entirely composed of cells.

• In 1839, the German zoologist Theodor Schwann concluded that animals were entirely composed of cells.

• In 1855, the German physician Rudolph Virchow determined (while studying how disease affects living things) that cells only come from other cells.

• These 3 scientists are credited, together, as creating the cell theory.

The Cell Theory

• All living things are composed of 1 or more cells.

• In organisms, cells are the basic units of structure and function.

• Cells come only from existing cells.

History of Cells

• The first cells had no separate, internal parts (organelles). They are called prokaryotes.

• These were the only living things to exist for the first 2 billion years on Earth.

• Prokaryotes are the most common type of cells on Earth.

• Prokaryotes are very small (1-15 um).• Example: bacteria

History of Cells• About 1.5 billion years ago, cells developed a

nucleus and other membrane-bound cell parts (organelles). The cells are called eukaryotes.

• Eukaryotes can be larger (2-2,000 um).• Early eukaryotes were single-celled (unicellular).• Eventually, many eukaryotic cells joined together

and formed multicellular (many celled) organisms.• Each cell is able to specialize in certain activities.• Examples: nerve cells carry messages muscle cells

contract the outside of the cell membrane.

Two Types of Cells

• Prokaryotic• Eukaryotic

Prokaryotic

• Do not have structures surrounded by membranes

• Few internal structures

• One-celled organisms, Bacteria

http://library.thinkquest.org/C004535/prokaryotic_cells.html

Eukaryotic• Contain organelles surrounded by membranes• Most living organisms

Plant Animal

http://library.thinkquest.org/C004535/eukaryotic_cells.html

Cell Size

• Cells must be small.• There are approximately 100 trillion

(100,000,000,000,000) cells in the human body.

Why are cells so small?

• Surface-to-Volume ratio • Food, water, oxygen, and other materials must enter

through the surface. Waste products must leave through the surface.• As a cell grows, its volume increases more rapidly than

its surface area does.• As a cell size increases, it takes longer for information

and materials to reach their destination. Small cells are more efficient.

Eukaryotic Cell Parts (Organelles)• Animal Cell Parts• Cell Membrane- The outer bilipid boundary of a cell. Also called the plasma

membrane.• Cytoplasm- The jelly-like fluid in a cell.• Ribosomes- Site of protein synthesis.• Endoplasmic Reticulum- A folded membrane system used for a molecular

transport in the cell. There are 2 types of ER, smooth and rough. Rough ER has lots of ribosomes.

• Golgi Apparatus- Secretes waste products.• Mitochondria- Site of aerobic respiration in cells.• The energy distribution center of the cell.• Lysosomes- Site of the cellular digestion.• Microtubules- Long, slender, tube-shaped organelles that help give the cell

shape and support.

Animal Cell Parts (continued)• Microfilaments- Fine, threadlike organelles that help give the cell

shape and support.• Cilia- Hair-like structures on the outside of the cell that help the cell

move. Example: The cilia that surround a paramecium.• Flagella- Hair-like structure that helps the cell move. Example: The tail

of a sperm cell. • Nucleus- Contains most of the cell’s DNA.• Nuclear Envelope- The membrane that surrounds the nucleus.• Chromatin- The DNA and proteins in the nucleus of a nondividing cell.• Chromosome- DNA in a coiled, rod-shaped form that occurs during cell

division.• Nucleolus- Site in the nucleus where ribosomes are created.

Plant Cell Parts• Plant cells have all the parts of animal cell, plus a few

more.– The additions:

• Cell Wall- A strong, rigid layer on the outside of the cell membrane.• Vacuoles- A fluid-filled cavity that stores waste products. In a

mature plant cell, the vacuole typically takes up 90% of the volume.• Plastids- An organelle in which food or pigments are stored. There

are 3 types:» Chloroplasts- Contain chlorophyll.» Chromoplasts- Contain orange carotenes, yellow xanthophylls, and

various red pigments.» Leucoplasts- Store food such as starches, proteins and lipids. Especially

common in potato tubers.