CELL GROWTH AND

REPRODUCTION

SECTION 5.1-5.2

L. Cumpton

Energizer

Getting Through Materials move through cells by diffusion.

Oxygen and food move into cells while waste products move out of cells. How does the size of a cell affect how efficiently materials get to all parts of a cell? Work with your partner. One of you draw a

square 2 inches by 2inches. Your partner will draw one half of this size. How much longer do you think it would take to get from the cell membrane to the center of your square compared to that of your partner? What is the advantage of cells being small?

Recall: The Cell Theory

All living organisms are composed of one or more cells. Cells are the smallest unit of living organisms. Cells arise only from previously existing cells.

How does this apply to cell growth and reproduction? Cells have to have an organized way to

reproduce and grow if they are going to make up ALL living organisms!

What Limits the Size of a Cell?

Ratio of surface area to volume Surface area is the

area covered by the cell (plasma) membrane

Volume refers to the space taken by the inner contents of the cell (organelles in the cytoplasm and the nucleus)

Where does the cell cycle?

• The cell cycle occurs in eukaryotic cells.

• Prokaryotic cells undergo binary fission.

Interphase

G1: cell grows, carries out normal cell functioning

S: cell copies (duplicates) its DNA Chromosomes: structures

that contain the genetic information that is passed from generation to generation of cells

Chromatin: the relaxed form of DNA in the cell’s nucleus

G2: cell prepares for division of the nucleus and “takes inventory”

Mitosis

Mitosis includes division of the cell nucleus (mitosis) and division of the cell cytoplasm (cytokinesis)

Mitosis occurs only if the cell is large enough and the DNA is undamaged.

Cells divide at different rates

The rate of cell division varies with the need for those types of cells.

Some cells are unlikely to divide (G0).

Surface Area to Volume Ratio

Volume increases faster than surface area.

Surface Area to Volume Ratio

Since the volume increases much more rapidly than the surface area, the cell might have difficulty supplying nutrients and expelling enough waste products.

The cell’s small size allows it to SUSTAIN itself more readily. Diffusion over large distances is slow and

inefficient because it relies on random movement of molecules and ions.

Cell Cycle

What happens when a cell reaches its size limit?

IT STOPS GROWING OR DIVIDES!

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Mitosis

During mitosis, the cell’s replicated genetic material separates and the cell prepares to divide into two cells.

Accurate separation of the cell’s replicated DNA allows the genetic information to pass into the new cells intact.

Chromosomes

Dividing cells spend most of their time in this phase

Chromosomes condense at the start of mitosis. DNA wraps around proteins (called

histones) that condense it.

DNA doublehelix

DNA andhistones

Chromatin

SupercoiledDNA

DNA plus proteins is called chromatin.

Condensed, duplicated chromosome

chromatid

telomere

centromere

telomere

Chromosomes

Chromosomes are shaped like an X

Each half of this X is called a sister chromatid Contains identical copies of

DNA Sister chromatids are held

together at the centromere Telomeres protect DNA and

do not include genes

During prophase, chromatin condenses into tightly coiled chromosomes.

Mitosis: Prophase

Mitosis: Prophase

As prophase continues, the nucleolus seems to disappear.

Microtubules, called spindle fibers, form in the cytoplasm.

In animal cells, centrioles (microtubles) migrate to the poles of the cells.

Mitosis: Metaphase

During metaphase, the chromosomes line up in the middle, or equator, of the cell.

Mitosis: Anaphase

During anaphase, sister chromatids separate to opposite sides of the cell.

Mitosis: Telophase

During telophase, the new nuclei form and chromosomes begin to uncoil, relax, or decondense.

Mitosis: Cytokinesis

After mitosis is complete, during cytokinesis, the cell divides the cytoplasm and forms two identical daughter cells.

Cytokinesis differs in plant and animal cells. In animal cells, the

membrane pinches closed.

In plant cells, a cell plate forms.

Binary fission is similar in function to mitosis.

Asexual reproduction is the creation of offspring from a single parent. Binary fission produces two daughter cells

genetically identical to the parent cell. Binary fission occurs in

prokaryotes.

parent cell

DNA duplicates

cell begins to divide

daughter cells

Asexual Reproduction

Environment determines what form of reproduction is most advantageous.

– Asexual reproduction is an advantage in consistently favorable conditions.

– Sexual reproduction is an advantage in changing conditions.

Asexual Reproduction

Some eukaryotes reproduce through mitosis.

Budding forms a new organism from a small projection growing on the surface of the parent.

bud

Hydra

Yeast

Asexual Reproduction

Fragmentation is the splitting of the parent into pieces that each grow into a new organism.

• Vegetative reproduction forms a new plant from the modification of a stem or underground structure on the parent plant.

Asexual Reproduction

Multicellular organisms depend on interactions among different cell types.

Tissues are groups of cells that perform a similar function.

Organs are groups of tissues that perform a specific or related function.

Organ systems are groups of organs that carry out similar functions.

CELL TISSUE ORGAN

vascular tissue

leaf

stem

lateralroots primary

root

SYSTEMS

root

syste

msh

oot

syste

m

Specialized cells perform specific functions.

Cells develop into their mature forms through the process of cell differentiation.

Cells differ because different combinations of genes are expressed.

A cell’s location in an embryo helps determine how it will differentiate.

Outer: skin cells Middle: bone cells Inner: intestines

Stem cells are unique body cells.

Stem cells have the ability to divide and renew themselves remain undifferentiated in form develop into a variety of specialized cell types

Stem cells are classified into three types.– totipotent, or growing into any other cell type– pluripotent, or growing into any cell type but a totipotent

cell– multipotent, or growing into cells of a closely related cell

family

Multicellular Life

First, an egg is fertilized by a sperm cell in a petri dish. The egg divides, forming an inner cell mass. These cells are then removed and grown with nutrients. Scientists try to control how the cells specialize by adding or removing certain molecules.

Stem cells come from adults and embryos.– Adult stem cells can be hard to isolate and grow.– The use of adult stem cells may prevent transplant

rejection.– The use of embryonic

stem cells raisesethical issues

– Embryonic stem cellsare pluripotent andcan be grown indefinitelyin culture.

Multicellular Life

The use of stem cells offers many currently realized and potential benefits.

– Stem cells are used to treat leukemia and lymphoma.– Stem cells may cure disease or replace damaged

organs.– Stem cells may revolutionize the drug development

process.

Multicellular Life