CELL GROWTH and DIVISION
                                            (Chapter 10 and 11.4)

        There are limits to cell growth that force cells to divide instead of simply growing much
larger. In order for cells to divide, they must reproduce the genetic material inside of them
along with their organelles. Each growing and dividing cell undergoes a series of steps called
the cell cycle, culminating in mitosis. This is the process by which cells divide and result in two
new genetically identical cells.
        Sex cells (sperm and eggs) are also formed by a process of cell division. Because sex
cells have only one set of chromosomes instead of one set of chromosome pairs, they undergo a
unique type of cell division called meiosis.
        Because cell growth and division that happens too rapidly can result in large, resource-
and space-using masses of cells called tumors, the cell cycle must be precisely regulated. When
these regulating mechanisms go awry, a disease called cancer can result.

1. Explain how each cell creates a genetically identical copy of itself (telling the story)
2. Relate knowledge of the cell cycle and known cancer-causing agents to explain why certain
factors cause cancer (constructing)
3. Use knowledge of meiosis to explain why you might have physical features from each of
your parents

What we observe                         Patterns in what we observe         Explanation(s)
New tissue grows back where             Cells reproduce to form new cells
there was a cut or scrape.

We were once just one cell (a
fertilized egg called a zygote)
                                        Cells must grow in size
Some egg cells are really large,                                            Cells increase cytoplasm volume
even bigger than the baby                                                   and number of organelles during
version of that animal (e.g.,                                               interphase, using ATP energy
birds)                                                                      released during respiration.
                                        Cells stay small instead of
Organisms are made up of                growing large                       Limits to cell size: DNA
trillions of tiny cells instead of a                                        accessibility, surface area to
few dozen large cells.                                                      volume ratio

New cells are identical to parent       Genetic material must be            DNA replication during S phase
cells and can carry out the same        duplicated and passed on during     and equal distribution of DNA
functions (skin cells produce skin      cell division                       during mitosis
All human cells have 46
chromosomes (except sex cells),     New cells have the same number
even after several rounds of        of chromosomes as the parent
division.                           cells
Flies have 8 chromosomes, even
after several rounds of division

Chimney sweeps had high rates
of cancer; soot was caught in the
folds of their skin                 Both genetics and outside          Cancer is caused when
Retinoblastoma and breast cancer    sources have an effect upon        something causes an error
appear in several family            causing cancer                     (mutation) in a gene that
members.                                                               regulates the cell cycle
People exposed to lots of X-rays
and UV light have higher rates of

After a sperm and egg combine,
the new baby's cells don't have
92 chromosomes, but only 46.        Genetic material (chromosomes)     In meiosis, each sex cell (sperm
Someone may have features of        must come from both the mom        or egg) only has 1 chromosome
both their mom and their dad.       and the dad, but not all of each   from each of the 23 pairs

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