Cell Cell Growth and ReproductionGrowth and Reproduction

Cell Size LimitationsCell Size LimitationsCell ReproductionCell Reproduction

Cell Cycle Cell Cycle MitosisMitosis

Cell Size LimitationsCell Size LimitationsJust like us, cells come in a variety of Just like us, cells come in a variety of sizes!sizes!

What determines a cell’s size?What determines a cell’s size? DNADNA DiffusionDiffusion Surface Area – to – Volume RatioSurface Area – to – Volume Ratio

Cell Size LimitationsCell Size Limitations

DNADNA

DNA provides the blueprints or instructions DNA provides the blueprints or instructions for protein synthesis.for protein synthesis.

Cells cannot survive unless there is Cells cannot survive unless there is enough DNA to support the protein needs enough DNA to support the protein needs of the cell.of the cell.

Cell Size LimitationsCell Size Limitations

DiffusionDiffusionNutrients and wastes are moved around a cell Nutrients and wastes are moved around a cell using diffusion.using diffusion.

Usually diffusion is fast and efficient over short Usually diffusion is fast and efficient over short distances, but when a cell gets too big it becomes distances, but when a cell gets too big it becomes slow and inefficient!slow and inefficient!

Cells can’t be too big because they would die Cells can’t be too big because they would die before nutrients reached the organelles that need before nutrients reached the organelles that need them!them!

Cell Size LimitationsCell Size Limitations

Surface Area –to-Volume RatioSurface Area –to-Volume RatioAs a cell’s size increases, its volume increases faster As a cell’s size increases, its volume increases faster than its surface area.than its surface area.If a cell size is doubled, the cell would require 8 times If a cell size is doubled, the cell would require 8 times more nutrients and would have 8 times more waste!more nutrients and would have 8 times more waste!The surface area would only have increased by 4 and The surface area would only have increased by 4 and therefore the plasma membrane would not have enough therefore the plasma membrane would not have enough surface area to let in the nutrients and let out the wastes.surface area to let in the nutrients and let out the wastes.The cell would either starve to death or become The cell would either starve to death or become poisoned by its own waste!poisoned by its own waste!Usually, cells divide before they get too big to control this Usually, cells divide before they get too big to control this factor.factor.

Cell ReproductionCell Reproduction

The cell theory states that “all cells come The cell theory states that “all cells come from pre-existing cells.”from pre-existing cells.”Cell division is the process by which this Cell division is the process by which this happens!happens!Cell division results in two cells that are Cell division results in two cells that are identical to the original parent cell.identical to the original parent cell.All organisms grow and change; worn out All organisms grow and change; worn out tissues are repaired or replaced by newly tissues are repaired or replaced by newly produced cells!produced cells!

The Cell CycleThe Cell Cycle

The cell cycle is the sequence of growth and The cell cycle is the sequence of growth and division of a cell.division of a cell.It starts with 2 general periods:It starts with 2 general periods: Period of GrowthPeriod of Growth

The majority of a cell’s life is spent in growth!The majority of a cell’s life is spent in growth!This phase is known as INTERPHASE!This phase is known as INTERPHASE!

During INTERPHASE, a cell grows in size and carries on During INTERPHASE, a cell grows in size and carries on metabolism.metabolism.

Chromosomes are duplicated in preparation for divisionChromosomes are duplicated in preparation for divisionInterphase is like the training before a big race!Interphase is like the training before a big race!

Period of DivisionPeriod of DivisionThis phase is known as MITOSIS!This phase is known as MITOSIS!In MITOSIS, two daughter cells are formed each containing a In MITOSIS, two daughter cells are formed each containing a complete set of chromosomes.complete set of chromosomes.

INTERPHASEINTERPHASE

3 stages3 stages G1 – Cell grows rapidly and protein G1 – Cell grows rapidly and protein

production is highproduction is high S – Cell copies its chromosomes and DNA S – Cell copies its chromosomes and DNA

synthesis occurssynthesis occurs G2 – Short growth period in which G2 – Short growth period in which

mitochondria and other organelles are made mitochondria and other organelles are made and parts needed for cell division (centrioles) and parts needed for cell division (centrioles) are manufacturedare manufactured

INTERPHASEINTERPHASE

MITOSIS: Many phases of DivisionMITOSIS: Many phases of Division

1)1) PROPHASE – longest phase of mitosisPROPHASE – longest phase of mitosis Chromatin (DNA strands) coil up into visible Chromatin (DNA strands) coil up into visible

chromosomeschromosomes They look kind of hairy!They look kind of hairy! Each chromosome is made of two identical Each chromosome is made of two identical

halves called SISTER CHROMATIDShalves called SISTER CHROMATIDS These halves are held together by a These halves are held together by a

CENTROMERECENTROMERE

PROPHASEPROPHASE

PROPHASE CONTINUED…PROPHASE CONTINUED…

As prophase continues, the nucleus As prophase continues, the nucleus begins to disappear as the nuclear begins to disappear as the nuclear envelope and the nucleolus disintegrate.envelope and the nucleolus disintegrate.

At this time, the CENTRIOLES begin to At this time, the CENTRIOLES begin to migrate to opposite poles of the cellmigrate to opposite poles of the cell

The SPINDLE begins to form between the The SPINDLE begins to form between the centrioles.centrioles.

PROPHASE CONTINUED…PROPHASE CONTINUED…

CENTRIOLES

SPINDLE FIBERS

METAPHASEMETAPHASE

2)2) METAPHASE-short second phase of METAPHASE-short second phase of mitosismitosis

The doubled chromosomes become The doubled chromosomes become attracted to the spindle fibers by their attracted to the spindle fibers by their centromerescentromeres

The chromosomes begin to line up on the The chromosomes begin to line up on the midline or equator of the spindlemidline or equator of the spindle

METAPHASEMETAPHASE

ANAPHASEANAPHASE

3) ANAPHASE – Third 3) ANAPHASE – Third phase of mitosisphase of mitosis Sister chromatids Sister chromatids

begin to separatebegin to separate Centromeres split Centromeres split

apart and the apart and the chromatids are pulled chromatids are pulled apartapart

TELOPHASETELOPHASE

4) TELOPHASE – Fourth phase of mitosis4) TELOPHASE – Fourth phase of mitosis Chromatids are pulled to opposite poles of the Chromatids are pulled to opposite poles of the

cellcell Nucleolus reappears and new nuclear Nucleolus reappears and new nuclear

envelope forms around each new set of envelope forms around each new set of chromosomeschromosomes

New double membrane begins to form New double membrane begins to form between two new nucleibetween two new nuclei

TELOPHASETELOPHASE

CYTOKINESISCYTOKINESIS

The cell’s cytoplasm The cell’s cytoplasm finally divides and the finally divides and the cell starts to pinch cell starts to pinch along the equator of along the equator of the cell forming two the cell forming two new cells!new cells!

MITOSISMITOSIS

MITOSISMITOSIS