How do organisms grow?

How do organisms grow?

Paramecium 400xOnion 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.• 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.

The cell

BASIC GENETICS• Each cell in the human body contains two 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

Replication

Chromosomes, Chromatids and Centromeres

Centromere

Chromosome arm

Chromosome arm

Identicalchromatid

Chromatid

Anaphase

A packaged chromosome

Two identical chromosomes

Chromosomes

Sister Chromatids

Spindle fiberscentromerre

The Cell Cycle

• The series of events that cells go through as they grow and divide

Cell Cyclehttp://www.cellsalive.com/cell_cycle.htm

Cell Cycle

Interphase

The Cell CycleInterphase:

• 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.

Mitosis: PMAT

Mitosis• 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 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

MicrotubuleA cell at metaphase a spindle

mitosis

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)

Prophase• Chromatin

condenses into chromosomes.

•  The centrioles migrate to opposite ends of the cell.

• Spindle fibers and the aster forms.  

Late Prophase• The spindle

fibers have attached themselves to the chromosomes.  

Metaphase• The chromosomes migrate to the equator (middle) of the cell.

Anaphase• Begins with

the separation of the sister chromatids,

• by pulling chromosomes to opposite ends of the cell.  

Telophase• 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.  

Cytokinesis

• Division of cytoplasm

Summarize each phase in your own words

Asexual Reproduction• the cell just

divides into two identical cells.

Advantages:

• Widely dispersed populations can still reproduce.

• Cells are identical to parents and should survive well if conditions don't change.

Disadvantages:

• Cells are identical to parents and so are vulnerable to the same environmental stresses.

• The characteristics of the cells change very slowly

Regeneration

• Echinoderms exhibit this type of reproduction

Regeneration

• 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 • involves an

equal division of both the organism cytoplasm and nucleus to form two identical organisms. Paramecium

Budding • one parent

dividing its nucleus (genetic material) equally, but cytoplasm unequally

• Hydras, yeasts exhibit this type of reproduction.

Parthenogenesis• ("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)

• reproduction involving specialized single cells coming from one parent

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.

Natural vegetative propagation

Vegetative Propagation

Vegetative Propagationrunner

Artificial Vegetative Propagation Cutting

Artificial Vegetative propagationgrafting

Telomeres

• 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?

• 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 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

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 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

• 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.

Meiosis

• 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 :• 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)• The process of

crossing over occurs during this time allowing for genetic diversity in the genome.  

Metaphase I : • Tetrads line up

along the center (equator) of the cell.

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 : Two

cells form each containing a complete set of chromosomes in the form of chromatid pairs. (2 cells )

Prophase II• The process

continues moving the chromatid pairs toward the center of the cell.

• (2 cells )  

Metaphase II :• The chromatid

pairs line up along the center of the cell.

• (2 cells )

Anaphase II :• The chromatid

pairs split moving the individual chromosomes toward the opposite poles.

• (2 cells )

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 )

Gametogenesis

• Meiosis occurs in the gonads (sex organs).

• Testes of the male and is called spermatogenesis.

• The ovaries of the female and called oogenesis.

Oogenesis

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

Egg cell

Spermatogenesis• Four sperm cells are

produced from each primary spermatocyte (parent cell) in the tesitis

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

• Size• Motility• Number of

chromosomes• Food

Fertilization

• 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)

Fertilization

• After penetration of sperm head, fertilization envelope forms

• Prevents other sperms from entering