Cell Growth and Reproduction

Cell Growth and Reproduction Section 8.2 The cells that make up multicellular organisms come in a wide variety of sizes and shapes. Two Examples Red blood cell (8 micrometers in diameter) Nerve cells ( can be 1 meter in large animals) The cell with the largest diameter is an ostrich egg.

Surface Area-to-Volume Ratio p. 202 ***As the cell grows…the outer surface of a cell grows more slowly than the volume of material inside the cell. When the surface of a cell is no longer large enough to let in the proper amounts of food and let out wastes, the cell divides. This is the parent cell. If the cell grew too big, its surface area would be too small to permit enough food and oxygen to enter or waste products to leave. ***THE CELL WOULD DIE***

Cellular Characteristics Each cell has its own characteristics Size Rate of Growth Timing of Cell Division Sometimes the controls that regulate cell division do not operate properly-the cell divides in an uncontrolled manner (cancer) All body cells (somatic or autosomes) have the same set of genes, but use only the ones necessary for their functions. Example: Blood cells produce only what blood cells need. Specialized cells: Cells that perform a specific function in addition to all the ordinary activities that keep a cell alive. Example: Muscle cells – also contract

Cell Division Parent Cell: The cell that divides. Daughter Cell: The two cells that result. They have the same traits as the parent cell.. Traits: Characteristics that are passed on from parent to offspring. Example: hair color, eye color, tall, short Chromosomes: Hereditary information that determines the traits of an individual. They are thick rod-shaped bodies. Chromatin: Before cell division, a long molecule of DNA covered (wrapped) with proteins. Genes: A segment of DNA that controls a hereditary trait. Diploid (2n): The full complete set of chromosomes. Found in all Body Cells. (Autosomes/somatic) Haploid (n): Half the chromosome number. Found in sex cells. (Gametes) male sex cell (sperm) female sex cell (egg) (XY) male sex chromosomes (XX) female sex chromosomes 23 23

Cell Division Continued Fission: Simplest form of reproduction. A unicellular organism splits in two and forms two organisms. Budding: The growth of a small fragment on a larger parent cell. It contains complete genetic instructions but only a small amount of cytoplasm. NOTE: Fission and Budding are both forms of asexual reproduction. (single parent)

Sex Cells (Gametes) have only half of the (2n) diploid number haploid consist of one member of each chromosome Human Haploid #: 23 Cat Haploid #: 19

Structure of a Chromosome

The Cell Cycle Interphase: longest busiest phase (G-1 Phase – Growth) (S-Phase – Replication) (G-2 Phase – Synthesis) Mitosis: division (1st) Prophase (2nd) Metaphase (3rd) Anaphase (4th) Telophase Cytokinesis: cytoplasm divides

The Cell Cycle **Sequence of growth and division** MITOSIS: The division of chromosomes into two identical cells. Not dividing (period of growth) DNA Replicates Stage that cells spend most of their time.

4 Phases of Mitosis Metaphase

PROPHASE Chromosome become visible Nuclear membrane disappears Spindle Fibers appear The longest phase of mitosis

Metaphase Chromosomes line up along the equator (middle of the cell) Centromeres attach to spindles

Anaphase Centromeres split Sister Chromatids separate Chromatids move to opposite poles (ends of the cell) Anaphase

Telophase Last phase of mitosis Chromatids reach poles Chromosomes are not visible Spindle disintergrates (disappears) Nuclear membrane reappears New cell wall or cell membrane appears

Cytokinesis (cytoplasm divides) Following telophase, the cell’s cytoplasm divides. In cytokinesis: a cleavage furrow pinches the cell in half.

Cytokinesis In Plants The division begins in the middle with a cell plate laid across the equator

Cytokinesis in Animals The division begins from the outside (pinching inward)

Mitosis (stays the same) Each daughter cell has the same number of chromosomes as the parent cell that produced it. 46 46 46 46 46 46 46

Meiosis Process by which diploid cell divides to produce four haploid cells. These cells are called gametes (sex cells), they combine through sexual reproduction to form a diploid zygote. The zygote is the first cell of a new organism. Therefore, meiosis is essential for sexual reproduction. Spermatogenesis: production of sperm cells Oogenesis: production of eggs

Meiosis (produce gametes) (reduce the chromosome number) 46 cell 92 Cell replicated 46 46 End of Meiosis I 23 23 23 23 End of Meiosis II

Meiosis I and Meiosis II During Meiosis two nuclear divisions occur 1st Division: called Meiosis I 2nd Division: called Meiosis II Reduces the chromosome number to half The end result……4 haploid cells

Stages Of Meiosis - Meiosis I Prophase I - The beginning phase - DNA which was unraveled and spread all over the nucleus is condensed and packaged Homologous chromosomes (each made of two identical chromatids) come together and form tetrads (4 chromatids) Crossing over, in which chromatids within tetrads exchange genetic material, occurs Metaphase I - Middle stage - Tetrads line up along the equator of the cell

Stages Of Meiosis - Meiosis I Anaphase I - One copy of each chromosome still composed of two chromatids moves to each pole of the cell Telophase I - End stage - New nuclear membranes are formed around the chromosomes and cytokinesis (cytoplasm division) occurs resulting in two haploid daughter cells

Stages Of Meiosis - Meiosis II Prophase II - Cells do not typically go into interphase between meiosis I and II, thus chromosomes are already condensed Metaphase II - Chromosomes line up at the equator of the two haploid cells produced in meiosis I Anaphase II - Chromosomes made up of two chromatids split to make chromosomes with one chromatid which migrate to the poles of the cells Telophase II - Cytokinesis and reformation of the nuclear membrane in haploid cells each with one set of chromosomes made of one chromatid

Stages Of Meiosis: Meiosis I Interphase Mother cell Prophase I: Condensing Chromosomes Prophase I: Tetrad formation/ crossing over Metaphase I Anaphase I Telophase I Meiosis II

Stages Of Meiosis: Meiosis II The products of meiosis are 4 haploid cells each with a unique set of chromosomes. Telophase I Prophase II Metaphase II The products of mitosis are 2 diploid cells with identical chromosomes. Anaphase II Telophase II

Crossing Over Prophase I: Metaphase I Anaphase I Telophase I Tetrad formation/ crossing over Metaphase I Anaphase I Telophase I Because of crossing over, every gamete receives a unique set of genetic information. Telophase II

Meiosis I

Meiosis II

Mitosis (worksheet) Humans have how many chromosomes? Which mitotic stage does the cell spend most of its time? What is the most rapid dividing cells in the body? Fill – in – the blank The body cells of a cat is 38. That means its’ (4)____ number is 38. An egg cell would have (5) __ chromosomes. Sex cells are called (6)__. When an egg was fertilized it would have