What makes something an
organism?
 Organization
 Growth and Development
 Reproduction
 Response
Cell division occurs in all
organisms, but performs
different functions
In unicellular organisms
- for reproduction
In multicellular organisms
- for growth, development,
and repair
Growth
 Multicellular organisms grow
because the number of cells
increases
 Larger organisms have more cells than
smaller organisms
 Cells do grow, but their
growth is limited
Development
 Cells become specialized to perform
certain functions as the organism
develops
 specialized
cells continue
to divide
Repair
 Cells need to be replaced as they age
and die
 This happens at different rates based on
the type of cell
 Cell division heals
and repairs things
like cuts and
broken bones
Cell division in eukaryotic cells
Genetic material for a cell
found in the
nucleus
 contains information needed
for growth, maintenance, and
reproduction
When cells divide into two
new cells, each has a full set of
genetic material
 genetic material is
contained in a
molecule called DNA
 What type of large molecule is DNA?
 DNA  deoxyribonucleic acid
 chemical that contains the information
for an organism’s growth, reproduction,
and maintenance
 Made of two twisted strands called a
double helix
 Looks like a twisted ladder
• DNA usually exists as a mass of loose
strands
 Before a cell divides:
 DNA gets wrapped around proteins and
compacted to form chromosomes
 Chromosomes are made of two identical
structures called chromatids
 Chromatids are held together at the
center by a centromere
chromatid
Cell Cycle
 The normal sequence of
development and division of a cell
 All living things live, grow,
reproduce, and die in this process
 Consists of 2 parts
 Interphase
 Cell division phase
Phases of the Cell Cycle
Interphase
Cytokinesis
Prophase
Telophase
Metaphase
Anaphase
Phases of the Cell Cycle
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Mitosis
Interphase
 Part of the cell cycle where a cell carries
out its functions
 Cell is:
 growing and preparing for cell
division
 Transporting materials
 Cellular respiration
DNA replicates
Mitosis
 Stages of the cell cycle where the
nucleus divides
 Only occurs in eukaryotes
 Prepares DNA for cell division
Mitosis is
divided into 4
phases
 Prophase
 Metaphase
 Anaphase
 Telophase
Prophase
 DNA condenses to form
chromosomes
 The nuclear membrane disappears
X
X
X
Metaphase
 Chromosomes line up in the
middle of the cell
X
X
X
Anaphase
 Chromatids separate and are
pulled to opposite sides of the cell
>
>
>
>
>
>
Telophase
 New nuclear membrane forms
around each group of chromosomes
 Chromosomes return to threadlike
form
Cytokinesis
 Cell pinches, dividing the cytoplasm
 Two daughter cells are formed
Cytokinesis
 cytoplasm is divided
 Occurs immediately after mitosis
 Results in the parent cell splitting into
two genetically identical daughter cells
 They each have a complete set of DNA
Cytokinesis
 Different in plant and
animal cells
 Animal cells Fiber ring forms
and contracts,
pulling the
membrane
inward
 Plant Cells
 Cell wall prevents the cell
membrane from pinching
 Cell plate grows between the 2
nuclei and develops into a
membrane
 Eventually, it becomes part of
the cell wall of each new cell
 At the end of the cell cycle:
 Two daughter cells are
genetically identical
to the parent cell but
smaller
 They have about half of the
parent cell’s cytoplasm
 The daughter cells grow to
about the size of the parent
cell before they divide again
 How much of the cell cycle is spent in
each phase?
cell grows and carries out
normal activities;
organelles duplicate
DNA replicates
and
chromosomesdu
plicate
cell grows and
prepares for
mitosis
 Use the
diagram on
page 81 of your
textbook to
draw a diagram
of the cell cycle
Asexual
Reproduction
Sexual
Reproduction
One parent
Two parents
What may be different about the offspring
produced by asexual reproduction and the
offspring produced by sexual reproduction?
 Asexual Reproduction
 one organism
produces one or
more new organisms
that are genetically
identical to it and
live independently
of the parent
 Types of asexual reproduction
 binary fission
 budding
 regeneration
 Binary Fission
 Cell division as reproduction
 in prokaryotes
 Budding
 Groups of cells (buds) form on the
parent’s body
 When there are enough
cells and the bud is large
enough, the bud breaks
off and lives separately
from the parent
 Regeneration
 New tissues grow at an injury site to
replace body parts.
 Sometimes, the
injury site breaks the
organism in half, so
when the two pieces
regenerate, two new
organisms are
formed
 Sexual Reproduction
 The offspring gets half of its mother’s
genetic material and half of its
father’s genetic material to create a
full set of DNA
 The offspring starts as
a single cell that goes
through cell division
many times to create
the multicellular
organism
Comparing Asexual and Sexual Reproduction
Asexual Reproduction
Sexual Reproduction
- Cell division
- Cell division and other
processes
- One parent organism
- Two parent organisms
- Rate of reproduction is
rapid
- Rate of reproduction is
slower that rate for asexual
reproduction
- Offspring have genetic
information from two
parents
- Offspring are genetically
identical to parent