CellsCellsThe Building The Building

Blocks of Life:Blocks of Life:Cell Division and Cell Division and

ReproductionReproduction

All living things are made of cellsAll living things are made of cells

Plant Cells Animal Cells

Cell TheoryCell Theory• The current cell theory

states that:

– All living things are made of cells.

– Cells are the basic unit of structure and function in living things.

– Living cells only come from other living cells.

What Are Cells Made Of?What Are Cells Made Of?

• OrganellesOrganelles, or “tiny organs”, are the , or “tiny organs”, are the structures that make up a cell.structures that make up a cell.

• OrganellesOrganelles were discovered by Robert were discovered by Robert Hooke in 1665 while looking at cork Hooke in 1665 while looking at cork cells.cells.– Nucleus, mitochondria, chloroplasts, cell Nucleus, mitochondria, chloroplasts, cell

wall, cell membrane, lysosomes, vacuoles, wall, cell membrane, lysosomes, vacuoles, ribosomes, cytoplasm, etc.ribosomes, cytoplasm, etc.

How Do Organisms Grow?How Do Organisms Grow?

• Organisms do not grow by increasing cell size.

• Why Not?• Instead organisms grow by creating more

cells.– This process is called cell divisioncell division.

Cell DivisionCell Division

• Cell division occurs in a series of stages or phasesphases.

• The most important concept is that:– A parent cell divides into two daughter A parent cell divides into two daughter

cells.cells.

Two Types of Cell DivisionTwo Types of Cell Division

Mitosis forms identical daughter cells

Meiosis forms daughter Meiosis forms daughter cells with half the cells with half the chromosomes of parent chromosomes of parent cellcell

Cellular ReproductionCellular Reproduction

Why is Reproduction Needed?Why is Reproduction Needed?

• Cell reproduction is necessary to:– keep the species going– replace the death of cells– increase the size of organisms (due to size

limit of cells)– produce new individuals.

2 Forms of Reproduction2 Forms of Reproduction

• Asexual Reproduction• Mitosis• A single parent• No special sex cells• No special sex organs• Genetically identical to

parents

• Sexual Reproduction• Meiosis• 2 parents• Special sex cells =

gametes (sperm/egg)• Special sex organs =

gonads (ovaries/testes)• Not genetically identical to

parent (1/2 chromosomes from mom, ½ from dad)

Mitosis – Asexual ReproductionMitosis – Asexual ReproductionResult is two identical cellsResult is two identical cells

Meiosis - Sexual ReproductionMeiosis - Sexual ReproductionResult is daughter cells with half the chromosomesResult is daughter cells with half the chromosomes

Egg and Sperm Cells – Egg and Sperm Cells – Fertilization Fertilization

Fertilization is the fusion of two cells, a sperm cell and an egg cell.

Each of these cells contains ½ of the chromosomes needed.

What are Chromosomes?What are Chromosomes?

• Chromosomes are found in the nucleus of the cell.– Chromosomes are made of DNA = genetic

material that directs the cell’s activities.• DNA codes for traits and is passed on from parent to

offspring (in both sexual and asexual reproduction)

– All organisms have a characteristic number of chromosomes.

• Humans have 46 chromosomes (2N)• Chromosomes are arranged in pairs: 23 pairs (N = ½

the number of chromosomes; 1 from each pair)

What are the Phases ofWhat are the Phases of Cell Division Cell Division

• Phase 1: Phase 1: InterphaseInterphase

• Phase 2: Phase 2: ProphaseProphase

• Phase 3: Phase 3: MetaphaseMetaphase

• Phase 4: Phase 4: AnaphaseAnaphase

• Phase 5: Phase 5: TelophaseTelophase

• Phase 6: Phase 6: CytokinesisCytokinesis

Cell Division – Cell Division – Interphase:Interphase:Chromosomes are CopiedChromosomes are Copied

• Chromosomes look threadlike – called Chromosomes look threadlike – called chromatin.chromatin.

• Centrioles appear outside the nucleus.Centrioles appear outside the nucleus.

• Near the end of phase 1 cell division Near the end of phase 1 cell division begins:begins:– Chromosomes are copied Chromosomes are copied

InterphaseInterphase

Cell Division – Cell Division – Prophase:Prophase:Mitosis BeginsMitosis Begins

• MitosisMitosis is the process of cell division is the process of cell division where the nucleus divides into two nuclei where the nucleus divides into two nuclei and and two identical daughter cells are two identical daughter cells are formed.formed.

ProphaseProphase

Cell Division – Cell Division – Metaphase:Metaphase:Chromosomes attach to spindleChromosomes attach to spindle

• In In metaphasemetaphase the chromosomes attach the chromosomes attach themselves to the spindle fibers.themselves to the spindle fibers.

• The The centromerecentromere is what is what attachesattaches the the chromosomes to the spindle fiber.chromosomes to the spindle fiber.

MetaphaseMetaphase

Cell Division – Cell Division – Anaphase:Anaphase:Chromosomes begin to separateChromosomes begin to separate

• In In anaphaseanaphase the chromosomes begin to the chromosomes begin to separate.separate.

• The The centromere splitscentromere splits and each pair of and each pair of chromatidschromatids begin to move toward the begin to move toward the ends of the cell.ends of the cell.

AnaphaseAnaphase

Cell Division – Cell Division – TelophaseTelophaseTwo new nuclei formTwo new nuclei form

• In In telophasetelophase two new nuclei form two new nuclei form

• Chromosomes uncoilChromosomes uncoil and are and are surrounded by a nuclear membrane.surrounded by a nuclear membrane.

• A A nucleolus reappearsnucleolus reappears..

• Cell division is complete.Cell division is complete.

Animal and Plant TelophaseAnimal and Plant Telophase

Cell Division – Cell Division – CytokinesisCytokinesisTwo daughter cells formTwo daughter cells form

• In In CytokinesisCytokinesis two new daughter cells two new daughter cells form.form.

• Cell membrane “Cell membrane “pinchespinches” cell in the ” cell in the middle middle forming two identical daughter forming two identical daughter cells.cells.– In plant cells a cell wall forms around each In plant cells a cell wall forms around each

daughter cell.daughter cell.

• Process of cell division is now over.Process of cell division is now over.

Plant Cell Cytokinesis

Cell Reproduction: Key TermsCell Reproduction: Key Terms

• CellCell = the basic building block of all living things

• OrganellesOrganelles = tiny organs, structures, that make up a cell and are responsible for cell function.

• ChromosomesChromosomes = genetic material found in the nucleus that directs the cell’s activities, made of DNA.

• Cell divisionCell division = the process of cell reproduction where a parent cell creates new daughter cells.

Cell Reproduction: Key TermsCell Reproduction: Key Terms

• MitosisMitosis = cell division that results in two daughter cells that are genetically identical to parent.

• MeiosisMeiosis = cell division that results in 4 daughter cells, each having ½ the chromosomes of the parent.

• Asexual reproductionAsexual reproduction = process where a new individual organism is created from only one parent; offspring is genetically identical to parent.

Cell Reproduction: Key TermsCell Reproduction: Key Terms

• Sexual reproductionSexual reproduction = process where a new individual organism is created from two parents; offspring is not genetically identical to parent.

• GametesGametes = specialized sex cells involved in sexual reproduction (male = sperm, female = egg)

• GonadsGonads = specialized sex organs where gametes are created by meiosis (male = testes, female = ovaries)

• FertilizationFertilization = the fusion of gametes that results in the formation of a new organism, or offspring.

Cell Reproduction: Key TermsCell Reproduction: Key Terms

• Internal fertilizationInternal fertilization = fertilization that takes place inside an organism.

• External fertilizationExternal fertilization = fertilization that takes place outside an organism.

What Is Cell Specialization?What Is Cell Specialization?

• In multicellular organisms, cells not In multicellular organisms, cells not only complete their own life activities, only complete their own life activities, but also perform a function that but also perform a function that contributes to the life of the organism.contributes to the life of the organism.

• Within multicellular organisms there is Within multicellular organisms there is division of labor or specialization.division of labor or specialization.– The work of keeping the organism alive is The work of keeping the organism alive is

divided up among different parts of the divided up among different parts of the organism.organism.

Levels of SpecializationLevels of Specialization

Cells combine to form

Tissues combine to form

Organs combine to form

Organ systems combine to form

Organism

More SpecializationMore Specialization

StudentsStudents combine to form combine to form

ClassesClasses combine to form combine to form

GradesGrades combine to form combine to form

SchoolsSchools combine to form combine to form

DistrictDistrict