10 – 1: Cell Growth and Division

How do living things grow? Grow by producing more cells. (Cells do not increase in size) A human adult has about 10 trillion – 100 trillion cells in their entire body. About how many cells does a newborn baby have? Answer: Much less Cells Dividing Blood Lily

Limits to Cell Growth 2 reasons why cells divide rather than grow? The larger cell has more trouble moving nutrients and waste across the cell membrane. The larger the cell, the more demand the cell places on its DNA.

Exchanging Material What substances may move through the cell membrane? Answer: Food, oxygen and water enters. Waste leaves the cell. The rate materials exchange depends on the surface area of the cell The rate materials are used depends on the cell’s volume (size).

Ratio of Surface Area to Volume Surface to volume ratio Volume increases faster than surface The cell uses materials faster than it can get them in

Asexual Reproduction Asexual reproduction - a single parent producing an offspring. The offspring produced are, in most cases, genetically identical to the parent. Asexual reproduction is a simple, efficient, and rapid way for an organism to produce a large number of offspring.

Sexual Reproduction In sexual reproduction, offspring are produced by the fusion of two sex cells – one from each of two parents. The offspring produced inherit some genetic information from both parents, therefore they are genetically different.

10.2 The Process of Cell Division Cells divide to form two new cells called daughter cells This process is called mitosis (cell division) Before it can occur, what has to happen? The cell replicates, or copies, all its DNA DNA is condensed into a manageable form (chromosome) so it can be divided precisely

Chromosomes Chromosomes – bundled packages of DNA that contain genetic information Every organism has a specific number of chromosomes Fruit flies – 4 Dog - 78 Carrots – 18 How many chromosomes do humans have? 46 (23 pairs)

Chromosomes Chromosomes are only visible when the cell divides. Sister chromatids Chromosomes are only visible when the cell divides. Why is this? DNA and protein molecules are spread throughout the nucleus in the form of Chromatin. Exact copies of each other Centromere TEM 36,000

Chromosomes (a closer look) Before division, the chromosome (DNA) is replicated The replicated chromosome consists of 2 identical “sister” chromatids. Held together near the center by centromere The chromosome “X” shape we usually see drawn is a duplicated chromosome made of supercoiled chromatin

Eukaryotic Cell Cycle The cell cycle represents the events in the life of a cell. Interphase  Growth Phase most time spent in this phase G1  Cell growth S  Replication of DNA G2  Final growth and prepare for division Mitosis (M phase)  Division of the nucleus (can last hours to a few days) 4 Phases: Prophase Metaphase Anaphase Telophase

Mitosis – 4 Stages of Cell Division Chromatin condenses into chromosomes. The nucleus begins to disappear Spindle fibers begin to form at centrioles Chromosomes move to the center of the cell Centrioles migrate to opposite ends of the cell Spindle fibers attach to the chromosomes at the centromere Sister Chromatids are pulled apart by spindle fibers (microtubules) connected to the centromere Nucleus begins to re-form Cleavage furrow forms Nucleus continues to form Cytokinesis Occurs (cells actually divide) Two diploid cells have been formed

Cytokinesis Division of the cytoplasm Occurs at the same time as telophase Actin (blue) and microtubules (orange) at the end of cytokinesis in a green urchin zygote.

Cytokinesis - Animal Animal cells are surrounded by a cell membrane Animal Cell  Formation of a cleavage furrow Cleavage furrow SEM 140 Cleavage furrow Contracting ring of microfilaments Daughter cells

Cytokinesis - Plant Plant Cell  Formation of cell plate TEM 7,500 Cell plate forming Wall of parent cell Daughter nucleus Cell wall New cell wall Vesicles containing cell wall material Cell plate Daughter cells Plant cells are surrounded by a cell wall Plant Cell  Formation of cell plate

Mitosis Animation

2. 1. 5. 4. 3.

2. 3. 4. 1.

2. 3. 4. 5. 1. Cleavage furrow Sister chromatids separate Haploid daughter cells forming Sister chromatids separate 2. 3. 4. 5. 1.

Questions for whiteboards: Show how a cell looks normally while it’s doing it’s job as a tissue, muscle, bone or nerve cell. Focus on what genetic material looks like in nucleus

Questions for whiteboards: Show how a cell would look as it’s getting ready to divide. Again, focus on nucleus and genetic material

Questions for whiteboards: Using two circles, “X”s and a mitochondria show why efficiency is different between large and small cells.

Questions for whiteboards: List some problems that cells might encounter if they were to grow to large.