Ratio of Surface Area to Volume

 As the cell grows, its volume increases much more rapidly than the surface area.  The cell might have difficulty supplying nutrients and expelling enough waste products.

Transport of Substances  Substances move by diffusion or by motor proteins.  Diffusion over large distances is slow and inefficient.  Small cells maintain more efficient transport systems.

The Cell Cycle  Cell division prevents the cell from becoming too large.  It also is the way the cell reproduces so that you grow and heal certain injuries.  Cells reproduce by a cycle of growing and dividing called the cell cycle.

 Interphase - the cell grows, carries out cellular functions, and replicates.  Mitosis - the cell’s nucleus and nuclear material divide.  Cytokinesis - a cell’s cytoplasm divides. The Cell Cycle

Interphase –G 1 (Gap 1 ) –S (DNA Synthesis) –G 2 (Gap 2 ) Mitotic (M) Phase Cytokinesis

The Cell Cycle

The Stages of Interphase  1 st stage - G 1  The cell is growing, carrying out normal cell functions, and preparing to replicate DNA.

 2 nd Stage – S  The cell copies its DNA in preparation for cell division. The Stages of Interphase

S phase Genetic material (chromosomes) duplicate)

 3 rd Stage - G 2  Cell prepares for division of nucleus (mitosis). The Stages of Interphase

Stages of Mitosis Prison (Prophase) Men (Metaphase) Are (Anaphase) Thin (Telophase)

Prophase  The cell’s chromatin tightens.  Sister chromatids are attached at the centromere.  Spindle fibers form in the cytoplasm.

 The nuclear envelope seems to disappear.  Spindle fibers attach to the sister chromatids.

Metaphase  Sister chromatids line up in the middle of the cell.

Anaphase  Microtubules of the spindle apparatus begin to shorten.  Sister chromatids separate.  Chromosomes move toward the poles of the cell.

Telophase  The chromosomes arrive at the poles and begin to relax.  Two new nuclear membranes begin to form and the nucleoli reappear.  The spindle apparatus disassembles.

Process by which the cytoplasm of a cell is divided in two; usually follows mitosis and meiosis. Cytokinesis

Microfilaments constrict, or pinch, the cytoplasm to create a cleavage furrow Cytokinesis in Animal Cells

Cell wall too rigid for microfilaments to constrict cell. Cell plate created. Cytokinesis in Plant Cells

How Cytokinesis Differs in Plants

Quality Control Checkpoints  The cell cycle has built-in checkpoints that monitor the cycle and can stop it if something goes wrong.  Spindle checkpoints also have been identified in mitosis.

A disease caused by severe disruption of the mechanisms that normally control the cell cycle. Cancer

Causes of Cancer  The changes that occur in the regulation of cell growth and division of cancer cells are due to mutations.  Various environmental factors can affect the occurrence of cancer cells.

Causes of cancer FoodFood Genetic mutationsGenetic mutations HormonesHormones RadiationRadiation TobaccoTobacco Weight & physical activityWeight & physical activity Workplace environmentWorkplace environment

Benign: An abnormal mass of essentially normal cells. Types of Tumors Malignant: A mass of abnormal cells resulting from uncontrolled cell division.

A mass of abnormal cells resulting from uncontrolled cell division Malignant Tumor

The spread of cancer cells beyond their original site Metastasis

Cancerous cells reproduce at an abnormally fast rate!

Cancer Treatment SurgerySurgery Radiation therapyRadiation therapy ChemotherapyChemotherapy A mix of the threeA mix of the three

Abnormal Cell Cycle: Cancer  Cancer is the uncontrolled growth and division of cells.  Cancer cells can kill an organism by crowding out normal cells, resulting in the loss of tissue function.

Stem Cells  Unspecialized cells that can develop into specialized cells when under the right conditions

Embryonic Stem Cells  After fertilization, the resulting mass of cells divides repeatedly until there are about 100–150 cells. These cells have not become specialized.

Adult Stem Cells  Found in various tissues in the body and might be used to maintain and repair the same kind of tissue  Less controversial because the adult stem cells can be obtained with the consent of their donor

 Producing offspring that are clones of the parent  No Diversity with asexual reproduction Next Slide

Process in which a single cell or set of cells produces offspring that inherit all their genetic material from one parent. Offspring are not diverse. Asexual reproduction

1.Binary Fission 2.Budding 3.Parthenogenesis 4.Regeneration Types of Asexual Reproduction

Binary Fission prokaryote A type of asexual reproduction in which a prokaryote replicates DNA, and divides in half, producing two identical daughter cells.

Offspring grows out of body of parent. Budding Yeast (Unicellular fungi) Hydra (Multicellular cnidarian)

In this form, if a piece of a parent is detached, it can grow and develop into a completely new individual. Echinoderms exhibit this type of reproduction. Regeneration

 Genetic material from two parents combines to produce offspring that are genetically different from the parents Next Slide

 The egg from a female & the sperm from the male combine through fertilization to form a zygote Next Slide  Egg and sperm are called Gametes (sex cells)

Two Methods of Reproduction Asexual –Offspring identical to the original cell or organism –Involves inheritance of all genes from one parent Sexual –Offspring similar to parents, but show variations in traits –Involves inheritance of unique sets of genes from two parents

Process in which genetic material from two parents combines and produces offspring that differ genetically from either parent. Leads to diversity in offspring. Sexual reproduction

Sperm, Eggs, & Fertilization Testes - male organ that produces sperm Ovaries - female organ that produces eggs.

Meiosis A type of cell division that produces four cells, each with half the # of chromosomes (haploid #) as the parent cell. Parent Cell 46chromosomes 23

In meoisis, the final cells have half the number of chromosomes as the parent cell.

1 chromosome of each pair is from your mother and 1 from your dad.1 chromosome of each pair is from your mother and 1 from your dad. 22 are alike, whether male or female (autosomes)22 are alike, whether male or female (autosomes) The 23rd chromosome is called the Sex Chromosome. It occurs as either X or Y.The 23rd chromosome is called the Sex Chromosome. It occurs as either X or Y. XY = male XX = female Humans have 46 Chromosomes (23 homologous pairs)

Karyotype A display of the chromosomes of an individual.

Male Karyotype

Female Karyotype

Homologous Chromosomes Two chromosomes in a matching pair.

Homologous Chromosomes 1.Each has the same sequence of genes. If one has gene for eye color, the other will too - at the same location. 1.Each has the same sequence of genes. If one has gene for eye color, the other will too - at the same location. 2.However, the genes might be slightly different versions.

Mitosis & Meiosis Difference Meiosis – 4 daughter cells with ½ the number (haploid number) of original chromosomes. Meiosis – 4 daughter cells with ½ the number (haploid number) of original chromosomes. Mitosis – 2 daughter cells with the same number of original chromosomes. Mitosis – 2 daughter cells with the same number of original chromosomes.

Comparison of Meiosis & Mitosis MeiosisMitosis DNA Replication1 time Nuclear divisions21 Number of daughter cells42 Daughter cell chromosome numberHaploid (n)Diploid (2n) Daughter cells identical to parentNoYes

Meiosis increases genetic variation

Crossing-over

Fertilization In humans, (2 23 ) 2 different possible zygotes – over 70.3 trillion! In humans, (2 23 ) 2 different possible zygotes – over 70.3 trillion! If crossover occurs only once, then (4 23 ) 2 4 octillion possible combinations. (27 0’s) If crossover occurs only once, then (4 23 ) 2 4 octillion possible combinations. (27 0’s)