1. 10 – 1: Cell Growth and Division

2. 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

3. 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.

4. 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).

5. 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

6. 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.

7. 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.

8. 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

9. 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)

10. 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

11. 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

12. 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

13. 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

14. 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.

15. 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

16. 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

17. Mitosis Animation

19. 2. 1. 5. 4. 3.

20. 2. 3. 4. 1.

21. 2. 3. 4. 5. 1. Cleavage furrow Sister chromatids separate
Haploid daughter cells forming
Sister chromatids separate 2. 3. 4. 5. 1.

23. 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

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

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

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