Transcript Plant Cell
Questions 1. Are the cells of the small plant larger or smaller than those of the larger plant? Are the cells of the small animal larger or smaller than those of the large animal. 2. Can you make a general statement that compares the number and size of cells in small organisms to those in large organisms. 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? 1. The larger cell has more trouble moving nutrients and waste across the cell membrane. 2. The larger the cell, the more demand the cell places on its DNA. DNA “Overload” • DNA is found in the nucleus of the cell • Why can’t a cell grow without limit? When a cell grows, it does not make more copies of its DNA. If the cell grew continuously, there would be information crisis. 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 • Town analogy: A small town has only a 2 lane street. As the town grows there is more traffic on the 2 lane street. 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. – Both prokaryotic and eukaryotic singlecelled organisms and many multicellular organisms can reproduce asexually. Ex. hydra, bacteria, yeast 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. – Most animals and plants, and many single-celled organisms, reproduce sexually. 10.2 The Process of Cell Division • Cells divide to form two new cells called daughter cells • This process is called 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 Section 10-2: Cell Division • Prokaryotes – less complicated division – • Replicate DNA – divide everything up between 2 cells. Eukaryotes – more complicated division 2 Main Stages 1. Mitosis – division of the nucleus 2. Cytokinesis – division of cytoplasm 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 DNA and protein molecules are spread throughout the nucleus in the form of Chromatin. Chromatin condenses during cell division. • Before division, the chromosome (DNA) is replicated • The replicated chromosome consists of 2 identical “sister” chromatids. – One chromatid goes to each new cell – Held together near the center by centromere Sister chromatids Exact copies of each other Centromere TEM 36,000 • Chromosomes are only visible when the cell divides. • Why is this? Chromosomes (a closer look) • Chromatin is a complex of DNA coiled around proteins called histones • The DNA and histone molecules then form beadlike structures called nucleosomes. • 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 Mitosis (M phase) Division of the nucleus (can last hours to a few days) 4 Phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase Mitosis – Prophase first and, longest phase • DNA condenses into chromosomes • 2 centrioles (microtubules) take positions on opposite sides of the nucleus • Spindle begins to form • What is a spindle? A fanlike microtubule structure that helps separate chromosomes. Prophase cont’d • Chromosomes coil more tightly • Nucleolus disappears • Nuclear envelope breaks down Metaphase – second phase, takes a few minutes • Chromosomes line up across middle of the cell • Microtubules connect the centromere of each chromosome to the two poles of the spindle Anaphase – third phase • Centromeres that join the “sister” chromatids together split. • Chromatids separate (now individual chromosomes) • The copies move away from each other to opposite sides of the cell (2 groups) Telophase – fourth, final phase • Chromosomes uncoil and relax • Nuclear envelope reforms around each cluster of chromosome • Spindle breaks down • A nucleolus becomes visible in each daughter nucleus. Kinetochore • Kinetochore – a disk of protein bound to the centromere that is an attachment site for microtubules that assist in cell division 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 Cleavage furrow Cleavage furrow SEM 140 Animal Cell Formation of a cleavage furrow Contracting ring of microfilaments Daughter cells Cytokinesis - Plant Cell plate forming • Wall of parent cell Daughter nucleus Plant cells are surrounded by a cell wall TEM 7,500 Plant Cell Formation of cell plate Cell wall Vesicles containing cell wall material New cell wall Cell plate Daughter cells Mitosis Animation Cell Division - Prokaryotes Prokaryote unicellular bacteria with no nucleus Binary Fission DNA is replicated, cell doubles in size and splits 2. 1. 3. 4. 5. 1. 2. 3. 4. Cleavage furrow Sister chromatids separate 1. 2. 3. 4. Haploid daughter cells forming 5.