Reproduction
The Cell Theory
• The 4 main points of the cell theory are:
All living organisms are made of one or more cells
Cells are the basic unit of structure and function
in all organisms
All cells come from previously existing cells
Organisms are controlled by single cells working
together
Animal Cells
Plant Cells
So what’s the difference?
• Plant cells – rigid cell wall which
provides structure and support for the
cell
• Plant cells – have chloroplasts that
enable them to make their own food
through photosynthesis
Organelles
• A typical cell has many organelles,
specialized structures that perform specific
functions in the cell
Nucleus – the control center of the cell
Nuclear Membrane – encloses the cells
genetic material or DNA (Deoxyribonucleic
Acid)
Nucleolus – darker area within the nucleus
that makes ribosome parts
Cell Organelles Continued…
Ribosomes – small, cell structures involved in
the making of proteins
Cell Membrane – the membrane that holds all
the cell contents together
Cytoplasm – the gel-like substance within the
cell that supports the structures of the cell
Cell Organelles Continued…
Endoplasmic Reticulum – transports materials to
different parts of the cell
Mitochondrion – an oval-shaped organelle that
makes energy for a cell to use. The power-house
of the cell
Golgi Body – packages and moves (secretes)
waste out of a cell
Vacuole – stores water, food, wastes and other
materials in the cell
Lysosome – breaks down food, wastes and worn-
out cell parts
Cell Division
Part One: Mitosis
In the nucleus
• In non-dividing cells, the genetic material is
stored as thin DNA super coils called
CHROMATIN
• When a cell divides, the chromatin will shorten
and thicken into CHROMOSOMES
• One strand of a double stranded chromosome is
called a CHROMATID
Draw a double stranded chromosome. Label
chromosome, chromatid and centromere
Chromatid
Chromosome
Chromatid
Centromere
Mitosis
• MITOSIS: a process by which the nucleus of a
cell divides while maintaining the chromosome
number
One cell two cells
New cells have identical genetic material
(DNA) of the parent cell
• Four stages of division (Prophase, Metaphase,
Anaphase and Telophase - PMAT) plus a period
of growth and metabolism called Interphase
The Cell Cycle
Phase One: Prophase
• Chromatin contracts and becomes visible (spaghetti). It
is now called CHROMOSOMES
• Each is a double chromosome with a pair of SISTER
chromatids which are joined to each other by a
centromere
• Chromosomes begin to move towards the equator
(center) of the cell
• Nuclear membrane disintegrates (breaks down)
• CENTRIOLES will form SPINDLE FIBERS that will
attach to each centromere and move around the
chromosomes
Prophase
Phase Two: Metaphase
• The centromeres of each chromosome line up along
equator ( looks like praying hands)
• Centromeres divide so the doubled chromosomes
become two identical single stranded sister
chromatids
• Centrioles are now at the poles of the cell and are
attached to each centromere by spindle fibers
Metaphase
Phase Three: Anaphase
• The spindle fibers begin to shorten and the
chromosomes begin moving to opposite
ends or poles of the cell (fingers)
• Each side gets one chromatid from each
double stranded chromosome
Anaphase chromosomes
Phase Four: Telophase
• Begins when single stranded chromosomes reach
the poles
• Chromosomes uncoil and turn into chromatin
• Nuclear membrane reappears
• Reverse of prophase
• Division of the cytoplasm or CYTOKINESIS is
completed by pinching off in animals or by building
a cell wall in plants
Telophase
Interphase
• Period between divisions
• Longest part of the cell cycle
• Cell is growing and metabolizing
• Nuclear membrane present
• Genetic information in the form of chromatin and
cannot be seen with a microscope
• Before division each strand of DNA will replicate
(copy) itself to become double stranded
• Near the end of interphase the DNA begins to
condense (shorten)
Interphase
What’s the point of Mitosis?
• Mitosis creates identical copies of cells for:
1. growth
2. Repair/regeneration of damaged tissue
3. Asexual reproduction (animals) or
vegetative reproduction (plants)
Asexual Reproduction
• Reproduction that involves only one parent; parent and
offspring have identical genetics
• No special reproductive cells or organs used to create
offspring
• Occurs through mitosis and cytokinesis
• Both single and multi-celled organisms, plants and simple
animals can reproduce asexually
• In multi-cellular organisms, the offspring develop from
undifferentiated, unspecialized cells from the parent
• Usually a rapid form of reproduction
Binary Fission
• Simplest form of asexual reproduction
• Parent divides into two approximately equal
sized daughter cells
• Bacteria: circular chromosome attaches to
plasma membrane then replicates, cell wall
separates each copy
• Protozoa: eg. Amoeba become circular and use
mitosis
Budding
• New individuals develop from small
outgrowths of the parent (buds)
• May develop colonies (sponges) or break
off to be individuals (hydra, yeast)
• Some organisms can both bud and
reproduce sexually
Spores
• Specialized single cells that are released
from the parent organism, germinate and
grow by mitosis
• New cells differentiate to form a new
organism
• Can reproduce quickly and in large quantities
• Often have thick protective coats
• Eg. Fungi, algae, protozoa
Regeneration
• The ability to regrow lost body parts
• Some animals can regrow entire new
organisms from parts
• Ability to regenerate decreases as organisms
increase complexity
• Even simple organisms that can regenerate
entire organisms generally prefer to utilize a
different method to reproduce
Vegetative reproduction
• MERISTEM: area on plant with unspecialized cells (cells
that can become any kind of cell) that frequently divide
using mitosis
• Meristematic cells can be found in the vegetative
structures of a plant (roots, stems, leaves)
• Given proper treatment, meristem cells can reproduce
mitoticlly then differentiate into new independent plants
• Structures include bulbs, corms, tubers, runners,
rhizomes
• Can also be artificially propagated using cuttings,
layerings or grafting
Bulb
• short underground
stem with
thickened storage
leaves
• small new bulbs
sprout from the
old ones
• Eg. onions, tulips
Corm
• short underground stems with no fleshy leaves
• Eg. gladiolas, crocuses
Tuber
• enlarged part of an
underground stem
that contains stored
food
• potatoes (eyes are
tiny buds)
Runner
• AKA stolon
• is a stem that runs sideways and contains
buds
• Eg. strawberry
Rhizome
• a stem that
grows sideways
under the
ground
• ferns, irises
Cutting
• a stem, root or
leaf cutting
used to make a
new plant
Layering
• part of a stem is bent and covered in soil
• once it roots the original can be cut off
• Eg. raspberries, roses
Grafting
• stem or bud removed
from one plant and
permanently joined
to another plant
• Eg. grapes and many
seedless fruits