Cells
The Building Blocks
of Life:
Cell Division and
Reproduction
All living things are made of cells
Plant Cells
Animal Cells
Cell Theory
• The current cell theory
states that:
– All living things are
made of cells.
– Cells are the basic unit
of structure and
function in living things.
– Living cells only come
from other living cells.
What Are Cells Made Of?
• Organelles, or “tiny organs”, are the
structures that make up a cell.
• Organelles were discovered by Robert
Hooke in 1665 while looking at cork
cells.
– Nucleus, mitochondria, chloroplasts, cell
wall, cell membrane, lysosomes, vacuoles,
ribosomes, cytoplasm, etc.
How Do Organisms Grow?
• Organisms do not grow by increasing cell
size.
• Why Not?
• Instead organisms grow by creating more
cells.
– This process is called cell division.
Cell Division
• Cell division occurs in a series of
stages or phases.
• The most important concept is that:
– A parent cell divides into two daughter
cells.
Two Types of Cell Division
Mitosis forms
identical
daughter cells
Meiosis forms daughter
cells with half the
chromosomes of parent
cell
Cellular Reproduction
Why is Reproduction Needed?
• Cell reproduction is necessary to:
– keep the species going
– replace the death of cells
– increase the size of organisms (due to size
limit of cells)
– produce new individuals.
2 Forms of Reproduction
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Asexual Reproduction
Mitosis
A single parent
No special sex cells
No special sex organs
Genetically identical to
parents
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Sexual Reproduction
Meiosis
2 parents
Special sex cells =
gametes (sperm/egg)
• Special sex organs =
gonads (ovaries/testes)
• Not genetically identical to
parent (1/2 chromosomes
from mom, ½ from dad)
Mitosis – Asexual Reproduction
Result is two identical cells
Meiosis - Sexual Reproduction
Result is daughter cells with half the chromosomes
Egg and Sperm Cells –
Fertilization
Fertilization is the fusion of two cells, a sperm cell and an egg cell.
Each of these cells contains ½ of the chromosomes needed.
What are Chromosomes?
• Chromosomes are found in the nucleus of
the cell.
– Chromosomes are made of DNA = genetic
material that directs the cell’s activities.
• DNA codes for traits and is passed on from parent to
offspring (in both sexual and asexual reproduction)
– All organisms have a characteristic number of
chromosomes.
• Humans have 46 chromosomes (2N)
• Chromosomes are arranged in pairs: 23 pairs (N = ½
the number of chromosomes; 1 from each pair)
What are the Phases of
Cell Division
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Phase 1:
Phase 2:
Phase 3:
Phase 4:
Phase 5:
Phase 6:
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Cell Division – Interphase:
Chromosomes are Copied
• Chromosomes look threadlike – called
chromatin.
• Centrioles appear outside the nucleus.
• Near the end of phase 1 cell division
begins:
– Chromosomes are copied
Interphase
Cell Division – Prophase:
Mitosis Begins
• Mitosis is the process of cell division
where the nucleus divides into two nuclei
and two identical daughter cells are
formed.
Prophase
Cell Division – Metaphase:
Chromosomes attach to spindle
• In metaphase the chromosomes attach
themselves to the spindle fibers.
• The centromere is what attaches the
chromosomes to the spindle fiber.
Metaphase
Cell Division – Anaphase:
Chromosomes begin to separate
• In anaphase the chromosomes begin to
separate.
• The centromere splits and each pair of
chromatids begin to move toward the
ends of the cell.
Anaphase
Cell Division – Telophase
Two new nuclei form
• In telophase two new nuclei form
• Chromosomes uncoil and are
surrounded by a nuclear membrane.
• A nucleolus reappears.
• Cell division is complete.
Animal and Plant Telophase
Cell Division – Cytokinesis
Two daughter cells form
• In Cytokinesis two new daughter cells
form.
• Cell membrane “pinches” cell in the
middle forming two identical daughter
cells.
– In plant cells a cell wall forms around each
daughter cell.
• Process of cell division is now over.
Plant Cell Cytokinesis
Cell Reproduction: Key Terms
• Cell = the basic building block of all living
things
• Organelles = tiny organs, structures, that
make up a cell and are responsible for cell
function.
• Chromosomes = genetic material found in
the nucleus that directs the cell’s
activities, made of DNA.
• Cell division = the process of cell
reproduction where a parent cell creates
new daughter cells.
Cell Reproduction: Key Terms
• Mitosis = cell division that results in two
daughter cells that are genetically identical
to parent.
• Meiosis = cell division that results in 4
daughter cells, each having ½ the
chromosomes of the parent.
• Asexual reproduction = process where a new
individual organism is created from only one
parent; offspring is genetically identical to
parent.
Cell Reproduction: Key Terms
• Sexual reproduction = process where a new
individual organism is created from two parents;
offspring is not genetically identical to parent.
• Gametes = specialized sex cells involved in
sexual reproduction (male = sperm, female =
egg)
• Gonads = specialized sex organs where gametes
are created by meiosis (male = testes, female =
ovaries)
• Fertilization = the fusion of gametes that results
in the formation of a new organism, or offspring.
Cell Reproduction: Key Terms
• Internal fertilization = fertilization that
takes place inside an organism.
• External fertilization = fertilization that
takes place outside an organism.
What Is Cell Specialization?
• In multicellular organisms, cells not
only complete their own life activities,
but also perform a function that
contributes to the life of the organism.
• Within multicellular organisms there is
division of labor or specialization.
– The work of keeping the organism alive is
divided up among different parts of the
organism.
Levels of Specialization
Cells combine to form
Tissues combine to form
Organs combine to form
Organ systems combine to form
Organism
More Specialization
Students combine to form
Classes combine to form
Grades combine to form
Schools combine to form
District