Cell Growth and Reproduction. Cell Size Limitations Although it is the smallest unit of life, a cell still has all of the characteristics of life. A

Cell Growth and Reproduction

Cell Size Limitations

Cell Size Limitations Although it is the smallest unit of life, a

cell still has all of the characteristics of life. A cell is able to grow, but it is limited in how big it can grow because of the necessary functions it carries out…Remember organelles???


The plasma membrane lets nutrients into the cell and allows wastes to leave. Inside the cell, nutrients and wastes move by diffusion. Diffusion limits cell size because it is a fast and efficient process only over short distances.


Remember, a cell has a lot of cell parts or organelles to perform specialized functions. In order for them to work together quickly and efficiently, they need to be able to transport things VERY QUICKLY therefore they have to be VERY small.

Let’s take a look at our example…



Because a cell’s size can slow down the rate of diffusion, cells have to have a way of limiting their growth. Cells divide before they become too big and therefore unable to function well: The cell would either starve to death or

be poisoned from the buildup of waste products.

Why Divide???

Cells divide in organisms for:1. Cell repair2. Cell replacement3. Growth (lengthening of bones, etc)

Cell Reproduction

When cells divide, new cells are produced from one cell. Remember the cell theory? Part 3 of the cell theory stated that all cells come from pre-existing cells.

Cell Reproduction

- Cell division is the process by which new cells are produced from one cell.

- Cell division results in two cells that are identical to the original, called a parent cell. The two new cells are called the daughter cells. When exact copies are made of “body” cells, this is called MITOSIS.

Cell Reproduction-Important Structures

Organisms could not grow or function properly if the genetic material encoded in DNA was not passed from cell to cell. So when cells reproduce by dividing, they also pass along their DNA. But how???


Chromosome: the carrier of the genetic material that is copied and passed from generation to generation of cells Formed during cell division, it is only seen

right before and right after cell division It has to be accurate (mistakes =

mutations) It is a rod-shaped structure made of tightly

coiled DNA and protein


Chromatin: long strands of DNA coiled in a ball in the nucleus for most of a cell’s lifetime, chromosomes are

found in this form


Chromatid: half of the chromosome (individual sides). each part is called a sister chromatid


Centromere: a part of the chromosome that holds sister chromatids together; helps move the chromosome during cell division

Centromere

Chromosome

Sister chromatids

Supercoil within

chromosome

Continued coiling within

supercoilHistone

DNA


centromere

sister chromatids

Chromosome

The Cell Cycle (in Eukaryotes)

The cell cycle is the sequence of growth and division of a cell. Cell division is ONE stage. A cell will divide many times in its lifetime before it dies and is replaced by a new cell.

There are three stages of the cell cycle:1. The time BETWEEN cell divisions is called interphase.2. The time OF cell division is called mitosis. 3. When the cytoplasm divides and you officially have

2 new cells, it is called cytokinesis.

The Cell Cycle

GrowthGrowth

DivisionDivision

2 New Cells2 New Cells

The Cell Cycle (in Eukaryotes)

I- InterphasePeed- ProphaseMadly- MetaphaseAt- AnaphaseThe- Telophase Crapper- Cytokinesis

The cell cycle and Mitosis (in Eukaryotes)

Cell division occurs in a series of stages, or phases.


1st: InterphaseChromosomes are copied

Chromosomes are in theform of threadlike coils(chromatin) ***Interphase is the longest and busiest

phase of the cell cycle.


2nd: ProphaseMitosis begins (cells start to divide)

Chromatin condenses to formchromosomes

Centrioles (pole-like organelles) appear

Spindle fibers form between the poles

**Chromatin condenses to form chromosomes so this is where chromosomes become visible under a microscope**

spindle fibers


3rd: Metaphase

Chromatids (or pairs of chromosomes) attach to the spindle fibers

The chromosomes line up in the middle of the cell

spindles


4th: Anaphase

What happens: Centromeres at the center of the chromosome split

and sister chromatids are pulled apart to the opposite sides of the cell.


5th: Telophase

Chromosomes loosen up tobecome chromatin again

Mitosis ends

What happens:Two new nuclei are formed and a double membrane

begins to form around them.


6th: CytokinesisCell membrane moves inward and the cytoplasm divides

Two daughter cells arecreated – each with its own nucleus (with identical chromosomes)

What happens: The cell’s cytoplasm divides and separates into two new

identical cells.

Mitosis in a Plant Cell

The Results of Mitosis= Organization

Cells working together for the same function are called tissues

Similar tissues will form an organ

Several organs working together make up an organ system

The results of mitosis: Cancer• Cancer is cell reproduction gone wrong:

- It occurs when a cell loses control of its division and starts making cells even if they are not needed

• Cancer can be caused by 3 major things:1. UV radiation & radiation (too much sun, radiation exposure)

2. Environmental influences (ex. air pollution, smoking)

3. Viruses (a viral infection can damage genes)

Cancer Prevention

• Diets low in fat and high in fiber

• Daily exercise

• Not using tobacco

The stringy structures in the cell nucleus that contain DNA are __________.

Question 1

D. chlorophylls

C. genes

B. chromosomes

A. centromeres

Look at the diagram and identify the stage of mitosis that is depicted.

Question 2

D. telophase

C. anaphase

B. metaphase

A. prophase

Centromere

Sister chromatids

What is the process by which a cell's cytoplasm divides?

Question 3

D. mitosis

C. meiosis

B. telekinesis

A. cytokinesis

In multicellular organisms, groups of cells that work together to perform a specific function are called __________.

Question 4

D. cell cycles

C. tissues

B. organs

A. organ systems

Question 5Magnification of a plant cell reveals centromeres that have split and sister chromatids being pulled to opposite poles of the cell. This cell is in which phase of mitosis?

D. telophase

C. anaphase

B. metaphase

A. prophase

Question 6

Which phase of mitosis is depicted in this diagram?

D. telophase

C. anaphase

B. metaphase

A. prophase

Spindle Fibers

Disappearing nuclear envelope

Doubled chromosome

Question 7

What is the term used for the period of the cell cycle represented by the red arrow in this graph?

D. interphase

C. centrophase

B. metaphase

A. prophase DNA synthesis and replication

Rapid growth and metabolic

activity

Centrioles replicate; cell prepares for

division

Cytokinesis

Mitosis

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Cell Growth and Reproduction. Cell Size Limitations Although it is the smallest unit of life, a cell still has all of the characteristics of life. A