Regents Living Environment – Mr. Skolnick Chapter 20 – Mitosis & Asexual Reproduction

What the Heck does 'Mitosis' Mean? §Every time a cell divides, it must ensure that its DNA (packaged into chromosomes) is faithfully partitioned between the two daughter cells. §Mitosis is the process of 'divvying up' the genome between dividing cells.

§To make this simple, let's imagine a cell with only one chromosome. Before a cell enters mitosis, we say the cell is in interphase:

§Every time a cell divides, it must first replicate all its DNA. Since chromosomes are simply DNA wrapped around protein, the cell replicates its chromosomes too:

§These two chromosomes, positioned side by side, are called sister chromatids. They are identical copies of one another. Before this cell can divide, it must separate these sister chromatids from one another. §First off, these chromosomes have to condense in a process called prophase:

§And then, the nuclear envelope breaks down:

§Then a large protein network called the spindle attaches to each sister chromatid and the chromosomes are aligned perpendicular to the spindle in a process called metaphase:

§Next, molecular motors pull the chromosomes away from the metaphase plate to the spindle poles of the cell. This is called anaphase:

§Once this process is completed, the cells divide, the nuclear envelope reforms, and the chromosomes relax and decondense during telophase. Then the cell can replicate its DNA again during interphase and go through mitosis once more.

§Mitosis is a process of cell division which results in the production of two daughter cells from a single parent cell. The daughter cells are identical to one another and to the original parent cell.

Summary of differences between animal cell mitosis and plant cell mitosis: §Plant cells don’t have centrioles, and asters. l The spindle does form, however. §The cell does not pinch in during telophase. l Instead, the cell plate forms, which becomes new cell walls between the two new cells. §In general, a cell spends most of its life in interphase.

Asexual Reproduction §Producing identical offspring: §What is a clone? §Binary Fission §Budding §Spore Formation §Regeneration §Vegetative Reproduction l Natural l Artificial

Rod-Shaped Bacterium, E. coli, dividing by Binary Fission (TEM x 92,750) §Unicellular organisms produce identical offspring by the process of binary fission, which is the simplest form of asexual reproduction. One parent cell becomes two identical daughter cells.

Budding in Hydra and Yeast §Budding occurs when a small piece of the parent cell breaks off and the small piece goes off to live and grow independently from the parent. Budding is unlike fission because the parent and buds are not the same size. The hydra, yeast, and sponge perform budding.

Spore Formation in Fungi §Spores are released from the parent, germinate, and produce new individuals. There are many types of spores; a protective wall usually surrounds a spore. Fungi, algae, and protozoa produce spores.

Regeneration in Starfish §The process of replacing lost body parts is regeneration. The hydra, planarian (flatworm), starfish, and earthworm can regenerate. Some organisms can regenerate an entire body, like the planarian and some can only regenerate a limb, like the crab.

Vegetative Reproduction: Natural §Asexual reproduction in plants: §Bulb: a short stem that is underground. New bulbs sprout from the old one and each new bulb gives rise to a new leafy plant. Tulips and onions. §Tuber: an enlarged part of the short stem that is underground. The “eyes” become tiny buds. Each bud becomes a shoot, which penetrates the soil and grows up. The bud also forms roots. Potatoes. §Runner: a stem that grows sideways and buds. Strawberries. §Rhizome: a stem that grows sideways and underground. Buds are produced. Ferns.

Vegetative Reproduction: Artificial §Cutting: cutting the stem, leaf, or root and placing it in water, soil: stimulates tissue growth. §Layering: a stem is placed under the soil, where it grows roots. §Grafting: joining together plants of closely related species. §Advantages of artificial vegetative reproduction: l new plants identical to the parent are produced. l faster than growing a plant from a seed.