Answers to 81

1
Answers to 8-1

• 1. Homologous chromosomes are chromosomes that
  are similar in shape, size and genes they carry.
• 2. A DNA molecule is a molecule of nucleic acid.
  A chromosome consists of DNA and proteins.
• 3. A prokaryotic chromosome consists fo a
  circular DNA molecule and associated proteins and
  is attached to the inner side of the cell
  membrane. Eukaryotic chromosomes are rod-shaped,
  associated with histone and nonhistone proteins,
  and found within the cells nucleus.

2
Answers to 8-1

• 4. Sex chromosomes are chromosomes that
  ditermine the sex of an organism. All of the
  other chromosomes in an organism are called
  autosomes.
• 5. Divide the diploid number by 2
• 6. No. By using table 8-1, students should give
  examples of simple organisms that have more
  chromosomes than more-complex organisms.

3
Biology

• 8-2 Cell Division

4
Objectives

• Describe the events of binary fission
• Describe the events of the cell cycle
• Summarize the phases of mitosis
• Compare cytokinesis in animal cells with
  cytokinesis in plant cells

5
Cell Division

• All cells come from the division of existing
  cells.
• Cell division differs in prokaryotes and
  eukaryotes

6
Cell Division in Prokaryotes

• Binary fission- the division of a prokaryotic
  cell into two off-spring cells
• Cell divides the chromosome, grows to nearly
  double the size, forms a cell wall between the
  chromosomes and splits into two new cells

7
Cell Division in Eukaryotes

• Both the cytoplasm and the nucleus divide
• Two types of division
• Mitosis-results in new cells with genetic
  material that is identical to that of the
  original
• Meiosis- reduces the chromosome number by half in
  new cells, the cells join together later forming
  the full genetic complement

8
(No Transcript)
9
Cell Division
10
The Cell Cycle

• The repeating set of events that make up the life
  of a cell
• The time between cell divisions is interphase
• Cell division consists of mitosis and cytokinesis
• Cytokinesis is the division of the cytoplasm

11
The Cell Cycle- Interphase

• Consists of 3 parts G1, S, and G2
• Is what occurs most in cells
• G1 is the first stage when offspring cells grow
  to full size
• S phase is when the cells DNA is copied.
• G2 is when cell prepares for cell division

12
Mitosis

• The division of the nucleus
• Consists of 4 phases
• Prophase
• Metaphase
• Anaphase
• Telophase

13
Phases of mitosis- Prophase

• First stage of mitosis
• Shortening and coiling of DNA into tight
  chromosomes
• During S phase chromosomes are copied and
  connected by centromere
• Nucleolus and nuclear membrane break down and
  disappear

14
Phases of mitosis- Prophase (cont.)

• Centrosome- an organelle near the nucleus of a
  cell that contains the centrioles (in animal
  cells) and from which the spindle fibers develop
  in cell division.
• Centriole- a minute cylindrical organelle near
  the nucleus in animal cells, occurring in pairs
  and involved in the development of spindle fibers
  in cell division.

15
Phases of mitosis- Prophase (cont.)

• Spindle fiber- made of microtubules and radiates
  from the centrosomes in preparation for mitosis
• mitotic spindle- the entire array which separates
  the chromatids
• Kinetochore fibers- attach to the kinetochore ( a
  disk shaped fiber) in the centromere region of
  each chromosome

16
Stages of Mitosis - Metaphase

• Second phase of mitosis
• During this phase the kinetochore fibers move the
  chromosomes to the center of the cell
• Once in the center of the cell the chromosomes
  are held in place by the kinetochore fibers

17
Stages of Mitosis - Anaphase

• Chromatids separate at the centromere and move
  toward opposite ends of the cell

18
Phases of Mitosis - Telophase

• 4th phase of mitosis
• When chromosomes reach opposite ends of the cell
  the spindle fibers disassemble and the
  chromosomes move to a slightly less coiled state
• A nuclear envelope forms around the chromosomes
  and a nucleolus forms in each of the new cells

19
Cytokinesis

• During telophase the cell divides by cleaving
  midway between the poles
• This area is called the cleavage furrow
• Cell plate- vesicles formed by the golgi
  apparatus. This separates the plant cell into
  two cells.