CELLS
What is a cell?
• simplest unit of life
• structural and functional component of
living things
• all organisms are made of cells
• single celled: unicellular
• many cells: multicellular>>specialization
• all cells are related by their descent from
other cells
Studying Cells
• cells are tiny
• light microscope—passes visible light through specimen
– LM up to 1000X
– resolving limit 200 nm (bacterium)
– live cell observation
• electron microscope—focuses beam of e- through or on
– SEM
– TEM
– prep kills cell
green alga
c
Cell Fractionation
• study of cell structure and function
• isolate components of cells based on size
and density
• biochemistry & cytology
– presence of cellular respiration enzymes
– large numbers of mitochondria
cell fractionation campbell fig6.5 pg 97
Major Cell Types
• prokaryotic
– bacteria
– plasma membrane, cytosol, chromosomes,
ribosomes
– DNA in cytoplasm, region called nucleoid (no nuclear
membrane)
• eukaryotic
– protists, fungi, plants, animals
– plasma membrane, cytosol, chromosomes,
ribosomes
– DNA in nucleus (surrounded by nuclear membrane)
– membrane bound organelles
Size of Cells
• prokaryotic: typically 1-5 μm
• eukaryotic: typically 10-100 μm
• surface to volume ratio: generally keeps
cells small
– as cell grows, volume grows more than s.a.
– larger organisms--more not larger cells
• selective barrier of plasma membrane
– limited amount of substance crosses/sec.
campbell fig 6.8 pg 99 surface to vol ratio
A Closer Look at Cells
• The cell is the lowest level of organization that
can perform all activities of life
• The ability of cells to divide is the basis of all
reproduction, growth, and repair of multicellular
organisms
LE 1-5
25 µm
The Cell’s Heritable Information
• Cells contain DNA, the heritable information
that directs the cell’s activities
• DNA is the substance of genes
• Genes are the units of inheritance that transmit
information from parents to offspring
LE 1-6
Sperm cell
Nuclei
containing
DNA
Egg cell
Fertilized egg
with DNA from
both parents
Embryo’s cells
With copies of
inherited DNA
Offspring with traits
inherited from both parents
• Each DNA molecule is made up
of two long chains arranged in a
double helix
• Each link of a chain is one of
four kinds of chemical building
blocks called nucleotides
LE 1-7
Nucleus
DNA
Nucleotide
Cell
DNA double helix
Single strand of DNA
A Hierarchy of Biological
Organization
1. Biosphere: all environments on Earth
2. Ecosystem: all living and nonliving things
in a particular area
3. Community: all organisms in an ecosystem
4. Population: all individuals of a species
in a particular area
5. Organism: an individual living thing
A Hierarchy of Biological
Organization (continued)
6. Organ and organ systems: specialized
body parts made up of tissues
7. Tissue: a group of similar cells
8. Cell: life’s fundamental unit of structure
and function
9. Organelle: a structural component of a
cell
10. Molecule: a chemical structure
consisting of atoms
The biosphere
Ecosystems
Organelles
1 µm
Cell
Cells
Atoms
10 µm
Communities
Molecules
Tissues
50 µm
Populations
Organs and organ systems
Organisms