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 of 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.
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.
Kinetochore
• Kinetochore – a disk of
protein bound to the
centromere that is an
attachment site for
microtubules that assist
in cell division
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
Cell Division - Prokaryotes
Prokaryote  unicellular bacteria with no nucleus
Binary Fission  DNA is replicated, cell doubles in size
and splits
10.3 Control of the Cell Cycle
• Cells of certain tissues divide constantly
(bone marrow, blood, skin), while others
once developed seldom divide (muscle
and nerve)
• What mechanism controls cell division?
– Cyclins – proteins that regulate the timing of
the cell cycle
– Growth factors – external regulatory proteins
that speed up or slow down division
(important in wound healing and
development of embryos)
Mitosis Animation
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• Phases of Cell Division in onion root tip