10 – 1: cell growth and division
DESCRIPTION
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 LilyTRANSCRIPT
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.
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.
• 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
10.2 The Process of Cell Division
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.• Why is this?
DNA and protein molecules are spread throughout the nucleus in the form of Chromatin.
TEM
36
,000
Centromere
Sister chromatids
Exact copies of each other
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 CycleThe cell cycle represents the events in the
life of a cell.
InterphaseInterphase Growth Phase most time Growth Phase most time spent in this phasespent in this phase
G1 G1 Cell growthCell growthS S Replication of DNAReplication of DNAG2 G2 Final growth and prepare for Final growth and prepare for
divisiondivision
Mitosis Mitosis (M phase) (M phase) Division of the Division of the nucleus (can last hours to a few days)nucleus (can last hours to a few days)
4 Phases:4 Phases:1.1. ProphaseProphase2.2. MetaphaseMetaphase3.3. AnaphaseAnaphase4.4. TelophaseTelophase
• 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
Mitosis – 4 Stages of 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
Animal Cell Formation of a cleavage furrow
Cleavagefurrow
SE
M 1
40
Daughter cells
Cleavage furrow Contracting ring ofmicrofilaments
Cytokinesis - Plant
• Plant cells are surrounded by a Plant cells are surrounded by a cell wallcell wall
Plant CellPlant Cell Formation of cell Formation of cell plateplate
TEM
7,5
00
Cell plateforming
Wall ofparent cell
Daughternucleus
Cell wall New cell wall
Vesicles containingcell wall material
Cell plate Daughter cells
Mitosis Animation
5.4.3.
2.
1.
4.3.2.1.
Cleavagefurrow
Haploid daughter cellsforming
Sister chromatidsseparate
4.3.2. 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.