CHAPTER 4 A Tour of the Cell Modules 4.1 – 4.5

The Art of Looking at Cells Artists are often inspired by biology and biology depends on art The paintings of Wassily Kandinsky (1866-1944) show the influence of cellular forms

Illustration is an important way to represent what scientists see through microscopes The anatomist Santiago Ramón y Cajal (1852-1934) was trained as an artist He drew these retina nerve cells

INTRODUCTION TO THE WORLD OF THE CELL The microscope was invented in the 17th century Using a microscope, Robert Hooke discovered cells in 1665 All living things are made of cells (cell theory)

4.1 Microscopes provide windows to the world of the cell The light microscope enables us to see the overall shape and structure of a cell Image seen by viewer Eyepiece Ocular lens Objective lens Specimen Condenser lens Light source Figure 4.1A

Electron microscopes were invented in the 1950s They use a beam of electrons instead of light The greater resolving power of electron microscopes allows greater magnification reveals cellular details

Scanning electron microscope (SEM) Scanning electron micrograph of cilia Figure 4.1B

Transmission electron microscope (TEM) Transmission electron micrograph of cilia Figure 4.1C

4.2 Cell sizes vary with their function Below is a list of the most common units of length biologists use (metric) Table 4.2

Cell size and shape relate to function Figure 4.2

4.3 Natural laws limit cell size At minimum, a cell must be large enough to house the parts it needs to survive and reproduce The maximum size of a cell is limited by the amount of surface needed to obtain nutrients from the environment and dispose of wastes

A small cell has a greater ratio of surface area to volume than a large cell of the same shape Surface area of one large cube = 5,400 µm2 Total surface area of 27 small cubes = 16,200 µm2 Figure 4.3

4.4 Prokaryotic cells are small and structurally simple There are two kinds of cells: prokaryotic and eukaryotic Prokaryotic cells are small, relatively simple cells They do not have a nucleus

A prokaryotic cell is enclosed by a plasma membrane and is usually encased in a rigid cell wall The cell wall may be covered by a sticky capsule Prokaryotic flagella Ribosomes Capsule Cell wall Inside the cell are its DNA and other parts Plasma membrane Nucleoid region (DNA) Pili Figure 4.4

4.5 Eukaryotic cells are partitioned into functional compartments All other life forms are made up of one or more eukaryotic cells These are larger and more complex than prokaryotic cells Eukaryotes are distinguished by the presence of a true nucleus

An animal cell Smooth endoplasmic reticulum Nucleus Rough endoplasmic reticulum Flagellum Not in most plant cells Lysosome Centriole Ribosomes Peroxisome Golgi apparatus Microtubule Plasma membrane Cytoskeleton Intermediate filament Microfilament Mitochondrion Figure 4.5A

The plasma membrane controls the cell’s contact with the environment The cytoplasm contains organelles Many organelles have membranes as boundaries These compartmentalize the interior of the cell This allows the cell to carry out a variety of activities simultaneously

A plant cell has some structures that an animal cell lacks: Chloroplasts A rigid cell wall

Rough endoplasmic reticulum Nucleus Ribosomes Smooth endoplasmic reticulum Golgi apparatus Microtubule Central vacuole Not in animal cells Intermediate filament Cytoskeleton Chloroplast Microfilament Cell wall Mitochondrion Peroxisome Plasma membrane Figure 4.5B