CHAPTER 1 - The Cell Cycle (part 1)
 How do organisms grow?
 How do broken bones mend?
 How do people age?
 What is cancer?
 How do organisms make more of themselves?
The basic unit of life
 All living things – made up of one or more cells
 Cell theory – cell is the basic unit of life and its fundamental role in biology
 All things began as a simple cell – even humans
Cell Theory
 Technological advancements such as improved microscopes have helped to study
living things in detail
 Cell theory are:
– All living organisms are composed of one or more cells
– Cells are the basic units of structure and function in all organisms
– All cells come from previously existing cells
– The activity of an entire organism depends on total activity of its
independent cells
Inside the basic unit of life – the cell
 Numerous membrane bound organelles, that perform specific functions
 Nucleus – bounded by double-layered porous membrane = nuclear membrane
keeps the cell’s genetic material (DNA – deoxyribonucleic Acid)
 DNA – forms long strands of chromatin throughout nucleus
 Nucleolus – darker area in nucleus that makes ribosomes which make substances
used for cell functioning
 cell membrane – separates contents of cell from surrounding
 Jelly-like material = cytoplasm enclosded by cell membrane – supports nucleus
and other organelles
 Endoplasmic reticulum – series of canals where materials are transported to
other parts of the cell
 Mitochondria transform energy for cell
 Golgi bodies – package useful materials and secrete outside of cell to other places
in organism
 Vacuoles – fluid-filled storehouses that contain water, food, wastes
 Lysosomes – break down food, digest wastes
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
Understanding the Cell Cycle
 Humans begin as a single cell
 Adults – made of several hundred trillion cells
 One cell – divided into two – two becomes four and so on
 Each new cell must have a complete nucleus (complete set of DNA) = mitosis
 Before it can begin, nucleus must make a copy of itself (chromatin) = 2 sets of
DNA = replication
 The replicated chromatin coils up to form double stranded chromosomes joined at
middle by centromere
 After replication – 2 complete sets of DNA are bundled up together as double
stranded chromosomes
The Cell Cycle (part 2)
Phases of Mitosis in an Animal Cell
 Prophase – double stranded chromosomes are large and dense, spindle fibers
begin to form and stretch across the cell from centrioles at opposite ends
 Metaphase – tugging action of spindle fibers pull double-stranded chromosomes
into line in middle of cell
 Anaphase – spindle fibers begin to contract and shorten = pulls centromere apart
so that each of replicated strand moves to opposite ends (poles) of cell
 Telophase – complete set of chromosomes at each pole of cell, spindle fibers
disappear, nuclear membrane forms around each set of chromosoms
 Nucleolus appears within each nucleus, single stranded chromosomes uncoil into
thin strands of chromatin = 2 nuclei in one cell (itself ready to divide)
Cell division
 At the end of mitosis = 1 cell with 2 identical nuclei
 Animal cells – the cell membrane pinches in near the middle of the cell, dividing
the cytoplasm into 2 new cells
 Plant cells – a cell plate develops across the center of the cell wall forming a new
cell wall between the two new cells
 In both – each new division is an exact copy of the original
 Number of chromosomes in nucleus of each cell is the same number in the
original cell
Interphase
 Greater portion of time spent for a cell is called interphase (between)
 Used to be thought as an inactive period however now we know differently
 Cell grows, replicates its DNA, becomes prepared for first phase of mitosis
 Cell cycle is responsible for growth and development of all of your body cells
 Cells that continually divide = tissues that form organs and organ systems
The Cell Cycle (part 3)
 Cell cycle ensures that number of chromosomes in nuclei of your body remains
constant
 Chromosomes vary from species to species
 Dogs = 78 chromosomes, tomato plants have 24, humans have 46
 While growing, mitosis and cell division add to total number of cells in body
 Cells don’t live forever
 Die when receive instructions to do so
 Mitosis and cell division are necessary for cells to be replaced
 3 billion cells die each minute, die as a result to damage, not enough food or
oxygen,
Regeneration and Aging
 Cut skin – usually heal in short amount of time
 Bone breaks – take longer
 This is because of mitosis – capable of repairing injured tissue
 Repair of injured cells or making of lost body parts = regeneration
 Aging – we age because as cell die, either they are not replaced or replaced slowly
 Results in change of structure and function of major body systems
 Skin wrinkles, bones lose density, immune system is weakened
Aging
 Collect several product advertisements from magazines that use the word “aging”
 What do the advertisements claim the products will do?
 Base on what you know about aging, assess the credibility of each ad
 Do some have any scientific merit?
 Make a poster to display your results
Cancer – the cell way out of control
 Normal conditions – instructions in DNA control rate of cell division
 Cell can destroy itself if genetic material in nucleus is damaged of something
inside goes wrong
 Cells begins to divide uncontrollably = cancer
 Interferes with surrounding cells and disrupts their ability to function, stock piles
on top of others which results in a tumour or lump in one area
 Some cases, the cancerous cells move to other parts of body and grow and divide
uncontrollably, consume all of the oxygen and nutrients
 Tobacco, asbestos, chemicals, some viruses, radioactivity and ultraviolet radiation
have all been linked to cancer in humans
Asexual Reproduction in Bacteria, Protists, Fungi and Animals
 Mitosis and cell division are the basis for asexual reproduction
 Asexual reproduction – formation of a new individual that has identical genetic
information to its parent
 Bacteria – kindgom Monera, unicellular organisms without a true nucleus
– Reproduce asexually through binary fission – parent cell divides so that
each new cell contains a single chromosome carrying complete DNA
identical to that of the parent
 Unicellular organisms in kingdom Protista, for example the amoeba
 DNA or protists is contained in a true nucleus where mitotic cell division results
in formation of 2 identical offspring
 Molds, yeasts, mushrooms are a part of the Fungi kingdom
 Bodies consist of many thin hyphae which grow over the surface and other
organisms to receive food
 Fragmentation – small piece breaks away and grows into individual hyphae
(must contain DNA to be identical to parent)
 Budding – yeasts do this by making a copy of nucleus, then a tiny bud forms on
cell wall which continues to grow larger with the new nucleus and eventually
breaks apart to be its own cell
 Spore – moulds do this in which a spore (reproductive cell) grows into a new
individual through mitotic division
– Spores are stored in sporangium case and when they are mature, take on
certain colors
Asexual Reproduction in Animals
 Kingdom Animalia – animals divided into vertebrates (with backbones) or
invertebrates (without backbones)
 Invertebrates – sponges, jellyfish, insects – make up 97% of all animal species
 Most invertebrates – reproduce asexually
 Flatworm – divides into 2 and regenerate the parts they are missing, one regrows
a tail while the other regrows a head
 Some animals – sponges or hydras reproduce by budding where a cell near the
base undergoes mitosis to produce a new group of cells (bud) which completes
development, breaks a part and becomes a new individual
The Cell Cycle (part 4)
Asexual Reproduction in Plants
 Ability of plants to reproduce asexually and to repair themselves = mitotic cell
division
 Asexual reproduction ensures that each new branch has same DNA as parent
 Meristem – growing areas in roots and stems made up of unspecialized cells that
undergo mitosis repeatedly to make new cells
 Certain times – meristematic cells specialize into cells that make up roots, stems,
leaves in plant
 Once plant structures mature – cells do not divide under normal conditions, but if
damaged, meristematic cells activate and repair
 Cuttings are lengths of parent stem – used to establish offspring that are exact
copies of parent = cloning (process by which identical offspring are produced
from single cell or tissue)
 Not all plants reproduce asexually in the same way
 New plants from roots – meristem cells in roots divide mitotically to produce
stems, leaves and other roots – dandelions, weeds
 New plants from stems – meristematic cells in stem divide to produce cells that
will become a new plant – strawberries have runners in which new plants grow
from the tips
 Layering – ability of some plants to reproduce more easily from stems than from
other plant parts (blackberry, raspberry, rose bushes)
 Branch of parent plant is bent down to ground and part of it covered with soil =
roots will grow from the buried stem and exposed tip will grow a new shoot
 Grafting – use the ability of stems to reproduce
 Stems from plants with desirable qualities can be attached or grafted to rooted
stock of similar plant
 Used with apples, grapes, roses