CELLS What is a cell simplest unit of

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 1000 X – 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 fig 6. 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 Cells Atoms 10 µm Communities Molecules Tissues Populations Organisms 50 µm Organs and organ systems