Cell Growth and Reproduction

Cell Size Limitations  Although it is the smallest unit of life, a cell still has all of the characteristics of life. A cell is able to grow, but it is limited in how big it can grow because of the necessary functions it carries out…Remember organelles???

Cell Size Limitations  The plasma membrane lets nutrients into the cell and allows wastes to leave. Inside the cell, nutrients and wastes move by diffusion. Diffusion limits cell size because it is a fast and efficient process only over short distances.

Cell Size Limitations  Remember, a cell has a lot of cell parts or organelles to perform specialized functions. In order for them to work together quickly and efficiently, they need to be able to transport things VERY QUICKLY therefore they have to be VERY small. Let’s take a look at our example…

Cell Size Limitations

 Because a cell’s size can slow down the rate of diffusion, cells have to have a way of limiting their growth. Cells divide before they become too big and therefore unable to function well: The cell would either starve to death or be poisoned from the buildup of waste products.

Why Divide???  Cells divide in organisms for: 1. Cell repair 2. Cell replacement 3. Growth (lengthening of bones, etc)

Cell Reproduction  When cells divide, new cells are produced from one cell. Remember the cell theory? Part 3 of the cell theory stated that all cells come from pre-existing cells.

Cell Reproduction - Cell division is the process by which new cells are produced from one cell. - Cell division results in two cells that are identical to the original, called a parent cell. The two new cells are called the daughter cells. When exact copies are made of “body” cells, this is called MITOSIS.

Cell Reproduction-Important Structures  Organisms could not grow or function properly if the genetic material encoded in DNA was not passed from cell to cell. So when cells reproduce by dividing, they also pass along their DNA. But how???

Cell Reproduction-Important Structures  Chromosome: the carrier of the genetic material that is copied and passed from generation to generation of cells Formed during cell division, it is only seen right before and right after cell division It has to be accurate (mistakes = mutations) It is a rod-shaped structure made of tightly coiled DNA and protein

Cell Reproduction-Important Structures  Chromatin: long strands of DNA coiled in a ball in the nucleus for most of a cell’s lifetime, chromosomes are found in this form

Cell Reproduction-Important Structures  Chromatid: half of the chromosome (individual sides). each part is called a sister chromatid

Cell Reproduction-Important Structures  Centromere: a part of the chromosome that holds sister chromatids together; helps move the chromosome during cell division

Section 8.2 Summary – pages Centromere Chromosome Sister chromatids Supercoil within chromosome Continued coiling within supercoil Histone DNA

Cell Reproduction-Important Structures centromere sister chromatids Chromosome

The Cell Cycle (in Eukaryotes)  The cell cycle is the sequence of growth and division of a cell. Cell division is ONE stage. A cell will divide many times in its lifetime before it dies and is replaced by a new cell.  There are three stages of the cell cycle: 1. The time BETWEEN cell divisions is called interphase. 2. The time OF cell division is called mitosis. 3. When the cytoplasm divides and you officially have 2 new cells, it is called cytokinesis.

The Cell Cycle Growth Division 2 New Cells

The Cell Cycle (in Eukaryotes) I-Interphase Peed-Prophase Madly-Metaphase At-Anaphase The-Telophase Crapper-Cytokinesis

The cell cycle and Mitosis (in Eukaryotes) Cell division occurs in a series of stages, or phases.

The cell cycle and Mitosis (in Eukaryotes) 1 st : Interphase Chromosomes are copied Chromosomes are in the form of threadlike coils (chromatin) ***Interphase is the longest and busiest phase of the cell cycle.

The cell cycle and Mitosis (in Eukaryotes) 2 nd : Prophase Mitosis begins (cells start to divide) Chromatin condenses to form chromosomes Centrioles (pole-like organelles) appear Spindle fibers form between the poles **Chromatin condenses to form chromosomes so this is where chromosomes become visible under a microscope** spindle fibers

The cell cycle and Mitosis (in Eukaryotes) 3 rd : Metaphase Chromatids (or pairs of chromosomes) attach to the spindle fibers The chromosomes line up in the middle of the cell spindles

The cell cycle and Mitosis (in Eukaryotes) 4 th : Anaphase What happens: Centromeres at the center of the chromosome split and sister chromatids are pulled apart to the opposite sides of the cell.

The cell cycle and Mitosis (in Eukaryotes) 5 th : Telophase Chromosomes loosen up to become chromatin again Mitosis ends What happens: Two new nuclei are formed and a double membrane begins to form around them.

The cell cycle and Mitosis (in Eukaryotes) 6 th : Cytokinesis Cell membrane moves inward and the cytoplasm divides Two daughter cells are created – each with its own nucleus (with identical chromosomes) What happens: The cell’s cytoplasm divides and separates into two new identical cells.

Mitosis in a Plant Cell

The Results of Mitosis = Organization Cells working together for the same function are called tissues Similar tissues will form an organ Several organs working together make up an organ system

The results of mitosis: Cancer Cancer is cell reproduction gone wrong: - It occurs when a cell loses control of its division and starts making cells even if they are not needed Cancer can be caused by 3 major things: 1. UV radiation & radiation (too much sun, radiation exposure) 2. Environmental influences (ex. air pollution, smoking) 3. Viruses (a viral infection can damage genes)

Cancer Prevention Diets low in fat and high in fiber Daily exercise Not using tobacco

The stringy structures in the cell nucleus that contain DNA are __________. Question 1 D. chlorophylls C. genes B. chromosomes A. centromeres

Look at the diagram and identify the stage of mitosis that is depicted. Question 2 D. telophase C. anaphase B. metaphase A. prophase Centromere Sister chromatids

What is the process by which a cell's cytoplasm divides? Question 3 D. mitosis C. meiosis B. telekinesis A. cytokinesis

In multicellular organisms, groups of cells that work together to perform a specific function are called __________. Question 4 D. cell cycles C. tissues B. organs A. organ systems

Question 5 Magnification of a plant cell reveals centromeres that have split and sister chromatids being pulled to opposite poles of the cell. This cell is in which phase of mitosis? D. telophase C. anaphase B. metaphase A. prophase

Question 6 Which phase of mitosis is depicted in this diagram? D. telophase C. anaphase B. metaphase A. prophase Spindle Fibers Disappearing nuclear envelope Doubled chromosome

Question 7 What is the term used for the period of the cell cycle represented by the red arrow in this graph? D. interphase C. centrophase B. metaphase A. prophase DNA synthesis and replication Rapid growth and metabolic activity Centrioles replicate; cell prepares for division Cytokinesis Mitosis