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How do organisms grow?. How do organisms grow?. Paramecium 400x. Onion skin cells 400x. How do organisms grow?. How do organisms grow?. Living things grow by producing more cells. Cells will divide rather than growing larger.

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how do organisms grow1
How do organisms grow?

Paramecium 400x

Onion skin cells 400x

how do organisms grow3
How do organisms grow?
  • Living things grow by producing more cells.
  • Cells will divide rather than growing larger.
  • The larger a cell becomes, the more demands the cell places on its DNA and the more trouble the cell has moving enough nutrients and waste across cell membrane.
basic genetics
  • Each cell in the human body containstwo sets of 23 chromosomes
  • Mitosis identically replicates this information
  • Each cell therefore has the same

genetic material

  • Reproductive cells only have one set

of chromosomes. These combine to

make a new person with different

genetic material to both parents

chromosomes chromatids and centromeres

A packaged chromosome






Chromosomes, Chromatids and Centromeres

Chromosome arm

Two identical chromosomes


Chromosome arm

sister chromatids
Sister Chromatids


Spindle fibers

the cell cycle
The Cell Cycle
  • The series of events that cells go through as they grow and divide
the cell cycle1
The Cell Cycle


  • G1: The cell grows and does its job (produce proteins).
  • S: The cell will replicate (copy) the chromosomes.
  • G2 : The cell makes copies of all the other organelles.
  • All daughter cells contain the same genetic information from the original parent cell from which it was copied.
  • Every different type cell in your body contains the same genes, but only some act to make the cells specialise – e.g. into nerve or muscle tissue.
the spindle
The Spindle

A spindle is a web type structure made up of microtubule fibers. It is essential for mitosis because it arranges the chromosomes into their correct positions in preparation for cell division.

Mitotic center

A cell atmetaphase

a spindle


mitosis m phase how the cells divide
Mitosis (M Phase): How the Cells Divide:
  • Used for asexual reproduction as well as for growth and repair
  • There are four stages:
  • PMAT ( Prophase, Metaphase, Anaphase and Telophase)
  • Chromatin condenses into chromosomes.
  •  The centrioles migrate to opposite ends of the cell.
  • Spindle fibers and the aster forms.  
late prophase
Late Prophase
  • The spindle fibers have attached themselves to the chromosomes.  
  • The chromosomes migrate to the equator (middle) of the cell.
  • Begins with the separation of the sister chromatids,
  • by pulling chromosomes to opposite ends of the cell.  
  • the chromosomes reach the ends of their respective sides, the nuclear envelope reforms.
  • There are now two smaller cells each with exactly the same genetic information.  
  • Division of cytoplasm
asexual reproduction
Asexual Reproduction
  • the cell just divides into two identical cells.
  • Widely dispersed populations can still reproduce.
  • Cells are identical to parents and should survive well if conditions don't change.
  • Cells are identical to parents and so are vulnerable to the same environmental stresses.
  • The characteristics of the cells change very slowly
  • Echinoderms exhibit this type of reproduction
  • A piece of a parent is detached, it can grow and develop into a completely new individual

Planarians exhibit this type of reproduction.

binary fission
binary fission
  • involves an equal division of both the organism cytoplasm and nucleus to form two identical organisms.


  • one parent dividing its nucleus (genetic material) equally, but cytoplasm unequally
  • Hydras, yeasts exhibit this type of reproduction.
  • ("virgin birth"), the females produce eggs, but these develop into young without ever being fertilized.
  • occurs in some fishes, several kinds of insects, and a few species of lizards.
sporulation spore formation
sporulation (spore formation)
  • reproduction involving specialized single cells coming from one parent
vegetative propagation
Vegetative Propagation
  • the ability of plants to reproduce without sexual reproduction, by producing new plants from existing vegetative structures.
  • Vegetative propagation is an example of asexual reproduction.
  • Telomeres are specialized chromosome tips.
  • Telomeres are lost during cell division. This causes the chromosomes to SHORTEN each time they divide.
how is the cell cycle regulated
How is the cell cycle regulated?
  • Biochemical checkpoints--a clock provided by shortening chromosome tips, and chemical signals from outside and inside the cell--regulate the cell cycle.
  • Stem cells maintain the growth and specialization of a tissue.
stem cells
Stem cells
  • Stem cells are capable of producing specialized cells throughout the body. When a stem cell divides to form two new daughter cells, one specializes (to form a skin cell for example) while the other remains a stem cell--ready to divide again. As a result, skin cells can be replaced without having to divide themselves.
cell division
Cell division

All complex organisms originated from a single fertilized egg.

Every cell in your body started here, through cell division the numbers are increased

Cell then specialize and change into their various roles

cancer when the cell cycle goes awry
Cancer--When the Cell Cycle Goes Awry
  • cancer cells repeatedly go through the cell  cycle and, essentially, never die…they continue to grow uncontrollably.
  • Cancer is caused by a series of genetic mutations leading to the development of a tumor (an abnormal mass of cells).
big idea sexual reproduction
Big IDEA: Sexual Reproduction
  • This process involves two parents.  
  • Both parents contribute one gamete or sex cell to the process.  
  • The genetic information given to the offspring will be obtained equally from each parent.
  • The process that produces gametes or sex cells.
  • Occurs in the reproductive organs .
  • Before meiosis occurs the cell duplicates its chromosomes.

It halves the chromosome number from the original parent cell in the four cells it forms. 

prophase i
Prophase I :
  • Synapsis: The chromatid pairs pair up with their homologous pair, forming a tetrad.
  • This tetrad contains 2 original homologous chromosomes and their duplicates.
prophase i con t
Prophase I (con’t)
  • The process of crossing over occurs during this time allowing for genetic diversity in the genome.  
metaphase i
Metaphase I :
  • Tetrads line up along the center (equator) of the cell.
anaphase i
Anaphase I :
  • The tetrads split and move in opposite directions. During this phase the chromatid pairs move away from each other.
  • (1 cell )
telophase i
Telophase I :
  • Telophase I : Two cells form each containing a complete set of chromosomes in the form of chromatid pairs. (2 cells )
prophase ii
Prophase II
  • The process continues moving the chromatid pairs toward the center of the cell.
  • (2 cells )
metaphase ii
Metaphase II :
  • The chromatid pairs line up along the center of the cell.
  • (2 cells )
anaphase ii
Anaphase II :
  • The chromatid pairs split moving the individual chromosomes toward the opposite poles.
  • (2 cells )
telophase ii
Telophase II :
  • Each of the two cells will begin to split in half and produce 2 more cells bringing the total to 4 cells. Each of these cells contain 1/2 the normal number of chromosomes.
  • ( 4 cells )
  • Meiosis occurs in the gonads (sex organs).
  • Testes of the male and is called spermatogenesis.
  • The ovaries of the female and called oogenesis.
  • The production of eggs (ovum).
  • Eggs develop in the ovary from cells called primary oocytes (parent cells).
  • Meiosis in the primary oocyte results in the formation of one ovum and three cells called polar bodies.
  • The egg contains stored nutrients (yolk) and can not move.
  • Polar bodies have the same number of chromosomes as egg but less cytoplasm
  • Four sperm cells are produced from each primary spermatocyte (parent cell) in the tesitis
sperm cell
Sperm cell
  • Head made of nucleus that contains chromosomes and acrosome.
  • Mid piece made up of mitochondria.,
  • Flagellum is a whiplike tail.
compare the ovum sperm
Compare the ovum/sperm
  • Size
  • Motility
  • Number of chromosomes
  • Food
  • Union of egg and sperm produce a zygote.
  • n (sperm) + n (egg) ->2n(zygote)
  • (n=the number of chromosomes)
  • 23 chromosomes in one sperm + 23 chromosomes in one egg  46 chromosomes in zygote (fertilizated egg)
  • After penetration of sperm head, fertilization envelope forms
  • Prevents other sperms from entering