The cells that make up multicellular organisms come in a wide variety of sizes and shapes. Two Examples 1.Red blood cell (8 micrometers in diameter) 2.Nerve cells ( can be 1 meter in large animals) The cell with the largest diameter is an ostrich egg.

Cell Size Limitations 1.Diffusion limits cell size 1.Remember this is the job of the plasma membrane Diffusion is an efficient process over short distances but as distances become larger, diffusion is inefficient Example: Mitochondria at the center of the cell 2.DNA limits cell size 1.Remember the nucleus contains the DNA blue prints for protein production… proteins are used by almost all organelles to perform critical functions It takes time to copy and make proteins 3.Surface area-to-volume ratio 1.As the cell size grows… its volume increase much faster than its surface area

If the cell grows too big, it reaches a point where the surface area is not large enough to transport resources (food, oxygen…) or waste products to allow the cell to survive…. The Cell Would Die!!! In fact, cells divide before they become too large to function properly.

Cell Reproduction Cell Theory – (all cells come from pre- existing cells) Cell division: the process by which new cells are produced from one cell. Cell division results in two cells that are identical to the original, parent cell.

1. Size 2. Rate of Growth 3. Timing of Cell Division Sometime the controls (enzymes) that regulate cell division do not operate properly—the cell divides in an uncontrolled manner—Cancer A malignant growth resulting from uncontrolled cell division.

Cell Characteristics Body Cells are autosomes or somatic cells Sex Cells are gametes Gene..a segment of DNA that controls a heredity trait All body cells have the same set of genes, but use only the ones necessary for their functions Ex. 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. Ex. Muscle cells-also contract

Cell Division Parent Cell: Original cell Daughter Cell: The two cells that result. (They have the same traits) Chromosomes: Heredity information that determines the traits of an individual. (They are thick rod-shaped bodies.) Chromatin: Long strands of DNA wrapped with protein.

Traits: Characteristics that are passed on from parent to offspring. Ex. Hair color, eye color, tall, short

Diploid (2n): The full set of chromosomes. Found in all body cells (autosomes/somatic cells) In Humans (46) Haploid (n): Half the chromosome number. Found in sex cells (gametes) In Humans (23)

Gametes (Sex Cells) Male sex cell (sperm) (23) Male sex chromosome (XY) Male symbol Female sex cell (egg) (23) Female sex chromosome(XX) Female symbol

Gametes Sex Cells (Gametes): Have only half(1/2) the diploid (2n) number. Haploid consist of one member of each chromosome. (see chart p. 265) Humans Haploid # Cats Haploid # ---19

Sperm FormationEgg Formation Pg. 1001

Reproductions Sexual Reproduction: Involving two parents Asexual Reproduction: (single parent) (A) Fission (B) Budding

Fission: Simplest form of reproduction. A unicellular organisms splits and forms two organisms. Budding: the growth of a small fragment on a larger parent. It contains complete genetic instructions but only a small amount of cytoplasm.

Structure of a Chromosome (p.205)

Chromosomes duplicate

The Cell Cycle (p. 206) The sequence of growth and division of a cell. As a cell proceeds thru its cycle….it has a period of growth and a period of division. Majority of a cell’s life is spent in the growth period known as interphase. Mitosis: division of chromosomes into two identical daughter cells. Cytokinesis: Cytoplasm divides

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

Now get the old stand bys……. Transparencies with totally cool diagrams……

The Cell Cycle **Sequence of growth and division** MITOSIS: The division of chromosomes into two identical cells. 1.Not dividing (period of growth) 2.DNA Replicates 3.Stage that cells spend most of their time. Interphase

4 Phases of Mitosis

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 Chromitids move to opposite poles (ends of the cell)

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) IN PLANT CELLS Division begins in the middle with a cell plate...laid across the equator IN ANIMAL CELLS Division begins from the outside Cleavage furrow forms at the equator of the cell and the plasma membrane pinches in along the equator.

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

Mitosis in an onion root

Mitosis (stays the same) Each daughter cell has the same number of chromosomes as the parent cell that produced it. 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 (reduce the chromosome number) cell Cell replicated End of Meiosis I End of Meiosis II

Meiosis I and Meiosis II During Meiosis two nuclear divisions occur 1 st Division: called Meiosis I 2 nd Division: called Meiosis II Reduces the chromosome number to half

Meiosis I

Meiosis II

A comparison of mitosis and meiosis

HOMOLOGOUS CHROMOSOME THESE ARE PAIRED CHROMOSOMES THAT ARE INHERITED FROM EACH PARENT. THEY CARRY THE SAME TRAIT BUT MAYBE A DIFFERENT FORM. EXAMPLE MOTHER MAY HAVE BROWN HAIR AND FATHER HAS BLACK HAIR. SAME CHROMOSOME.

CROSSING OVER AN EXCHANGE OF GENETIC MATERIAL.. THIS RESULTS IN GENETIC DIVERSITY, VARIATION. A SEXUAL REPRODUCTING ORGANISM WILL SURVIVE BETTER IN A CHANGING ENVIRONMENT.

Example ABCDEF abcdef chromosome After crossing over the result maybe ABCdef abcDEF new chromosome

1.Humans have how many chromosomes? 2.Which mitotic stage does the cell spend most of its time? 3.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

A comparison of mitosis and meiosis: summary