Why are Cells Small? A eukaryote cell is very small with an average size of 10 microns across. 1 micron = 1/1,000,000 of a meter or 1 x 10-6m 1 micron = 1/1000 of a millimeter or 1 x 10-3mm

Why are Cells Small? A human is made of about 10 trillion cells. But the number of prokaryote cells both on and in one human is more than that!!! Prokaryote cells are much smaller than eukaryote cells.

Comparison of Prokaryote and Eukaryote Cells

Most Plants and Animals begin life as a fertilized cell

Egg Fertilization

But Rather than Growing Bigger Each fertilized cell (=zygote) DIVIDES and Divides and DIVIDES and DIVIDES .

Development of a Sea Urchin Embryo* Early development in a sea urchin (Lytechinus pictus) embryo illustrates how a single egg develops into a hollow blastula. Elapsed time about 18 hours. http://www.exploratorium.edu/imaging_station/gallery.php?Category=Mitosis&Section=Introduction

Modeling With your group: Fold your boxes Measure the volume Complete worksheet

Conclusions Cells are small to maximize their surface area A high surface area is critical to the rapid diffusion of material into and out of the cell.

Conclusions Rapid diffusion of glucose, oxygen, carbon dioxide and other molecules is necessary for the maintenance of cell function.

Conclusion A cell grows to its optimal size and then it divides in half. Each half will form a new cell that grows until it reaches its optimal size, and then it too will divide in half.

Exceptions! Large cells With your table design a cell that has a volume of 36 cm3 AND the largest possible surface area. Use whole number for each dimension! Consider: How do you maximize surface area?  

Exceptions Another type of large cell is an egg. A bird’s egg is one large cell. The yolk is a food source for the growing embryo. How is it possible for a bird’s egg to function when it is so large? Food is already present—diffusion isn’t needed to meet the nutritional needs of cell

Why are cells small? Small cells optimize the movement of material in and out of the cell DNA in the nucleus of the cell controls the activity of the cell. If a cell increased in size, its activity would increase. The quantity of DNA in the cell would not be able to control all the activities of the larger cell.

How do Cells Divide? 1 parent cell divides into 2 daughter cells. This decreases volume and increases surface area of each cell. When the cell divides in half, the material must be divided evenly except for the…

Prokaryote – cell division Cell division occurs through binary fission= reproduction (in prokaryotes) All genetic material (DNA) in the cell is found on one chromosome floating in the cytoplasm.

Prokaryote – cell division Cell division begins with replication (doubling) of the chromosome. The two chromosomes move to opposite ends of the cell. Cell splits apart into two daughter cells--each containing one chromosome and half of the cytoplasm Each daughter cell is genetically identical*

Cell Division in Prokaryotes AND Eukaryotes Histones DNA Cell Division in Prokaryotes AND Eukaryotes Chromosome = a structure in eukaryotes and prokaryotes made of a long strand of a DNA molecule bonded to histones. Histones are proteins that provide structure for the chromosome

Eukaryotic – Cell Division Each eukaryotic cell contains a nucleus with chromosomes. Each species has a characteristic number of chromosomes. Humans have 46 chromosomes in the nucleus of each of their cells (23 chromosomes from each parent)

Eukaryotic Cell Division Eukaryote cells are much more complex than prokaryote cells and the cell cycle is much more complex. Four phases of cell cycle. The cell cycle represents the entire lifetime of a single cell M phase (mitotic phase) G1 phase (gap 1) S phase (synthesis) G2 phase (gap 2) INTERPHASE

Interphase Longest part of cell cycle (90%). This is when the cell is “doing its job”. Divided into 3 phases G1 phase - (gap 1) - Period of cell growth, development and repair. Cell increases in size; proteins and organelles are produced.

This is what the nucleus of the cell looks like during interphase Interphase continued This is what the nucleus of the cell looks like during interphase This is what the nucleus of the cell looks like at the start of cell division S phase - (synthesis) – Preparation for cell division. Occurs in nucleus: All genetic material is doubled. The genetic material before mitosis begins is called chromatin. Chromatin is made of long strands of DNA wrapped around histones. Chromatin is not yet “condensed” into chromosomes and  fills up the entire nucleus.

Interphase Continued G2 phase - (gap 2) --Organelles (example: centrioles) and molecules specifically required for cell division are produced.

Cell Cycle Interphase

Mitotic Phase* Mitotic Phase – The division of the cell Includes Mitosis (4 phases) = division of the nucleus AND Cytokinesis = division of the cytoplasm  

Mitosis – Prophase What happens? Cell in Prophase What happens? Chromatin in the nucleus condenses and forms chromosomes Each chromosome is made up of two identical copies (sister chromatids), which are attached together in the middle (centromere).

During Prophase… Centrioles Spindles The nucleolus disappears. Sister Chromatids During Prophase… Centrioles Four found in the cytoplasm of each animal cell Move to opposite ends of the cell (2 on each side) Spindles Fan-like structures made of microtubules grow out from the centrioles towards the center of the cell The nucleolus disappears. The nuclear envelope breaks down*.  

Vocabulary Worksheet Quick vocabulary check! Centromere vs. sister chromatids Cytokinesis vs. Mitosis DNA vs. histone. Macromolecules Interphase Gap1 and Gap2 and Synthesis Mitotic Phase vs. Mitosis Chromosomes vs. chromatin

Metaphase Chromatids line up at the center of the cell. Each chromatid is attached to a spindle fiber at the centromere*  

Anaphase Anaphase Centromeres separate. Each sister chromatid becomes a separate chromosome. Spindles contract --causing chromosomes to move towards opposite ends of the cell near the poles of the spindles*.

Telophase Telophase Chromosome gathers at either end of the cell and begin to lose their shape. They turn back into ________________ A nuclear envelope forms around each group of chromosomes. Nucleolus forms in each nucleus. Spindle fibers break apart.   chromatin

Cytokinesis Division of cytoplasm Occurs at same time as telophase   Division of cytoplasm Occurs at same time as telophase Cell membrane pinched into two parts with one nucleus and an equal number of organelles in each part. New cell membrane forms around each cell*.

Cell Division*

Differences Between Plant and Animal Cell Division In plants--Spindle fibers form during prophase BUT there are no centrioles. In plants - Cytoplasm Does NOT pinch together Instead, a cell plate forms which divides the cell in half. Each half contains a nucleus and equal amounts of organelles and cytoplasm. New cell wall forms in cell plate

Cell Division in Eukaryotes Unicellular organisms = reproduction (one organism divides into two organisms) Multicellular organisms = growth, development and repair

Cell Division Complete packet!