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

c

green alga

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

NucleicontainingDNA

Egg cell

Fertilized eggwith DNA fromboth 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

DNA double helix Single strand of DNA

Nucleotide

Cell

Nucleus 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 cells8. Cell: life’s fundamental unit of structure

and function9. Organelle: a structural component of a

cell10. Molecule: a chemical structure

consisting of atoms

Ecosystems

The biosphere

Organisms

Populations

Communities

Cells

Organelles

Molecules

Tissues

Organs and organ systems

Cell1 µm

Atoms

10 µm

50 µm