Cell Size, Phases and Division

Surface area to volume ratio

6:14:1

2:1

-Which SA/V ratio would be more efficient to a cell?

A large SA/V ratio…..6:1

Surface area to volume ratio

Each time a cell doubles in size, its surface area increases by a factor of four but its volume increases by a factor of eight. It would mean that the cell would need 8 times the normal amount of nutrients and make 8 times the normal amount of wastes.

All cells are relatively the same size. Why?

1. Surface area-to-volume ratio

• As a cell grows the volume increases much more rapidly than the surface area–Diffusion is slow

–The larger the cell the more food and the more wastes; not efficient.

Cell Size, cont.

Increase size of cell Decrease rate of Diffusion

Wastes

NutrientsOxygen

Water

Cell Size, cont.

2. DNA limits the size of a cell

DNA codes for proteins, the larger the cell, the more proteins it needs.

The cell can’t make instructions fast enough

DNA makes up the chromosomes inside the nucleus

DNA and Cell Division

For the most of a cell’s lifetime, chromosomes exist as chromatin – long strands of DNA wrapped around proteins.

Under an electron microscope, chromatin looks somewhat chaotic resembling a plate of spaghetti.

-This is necessary for the information to be copied.

Cell Cycle

The cell cycle is a sequence of growth and division in a cell.

Foldable Instructions• Fold one piece of

white paper hot dog style.

• Cut down the middle seam (hot dog) & tape the short ends together.

• Accordion fold the paper to make 8 equal tabs.

The Cell Cycle

Draw the diagram of the cell cycle on square 1 of foldable

Foldable: Tab 1

Interphase• The majority a cell’s life cycle is spent in

a period of growth known as Interphase.

• Three stages

–G1- Growth

–S- DNA synthesis/replication

–G2- preparation for mitosis

• No Chromosomes are visible.

• DNA exists as chromatin

Interphase

Draw the diagram of interphase on square 2 of foldable

White fish blastula Onion root tip

Foldable: Tab 2

Chromosome

centromere

Sister chromatid

Draw the diagram of the chromosomeon square 3 of foldable

Foldable: Tab 3

Cell Division

• The cell then enters mitosis or the period of nuclear cell division in which two daughter cells are formed, each containing a complete set of identical chromosomes.

Prophase

• Nuclear membrane breaks down

• Chromosomes condense (appear)

• Centrioles develop

• Spindle fiber appears

Draw the diagram of prophase on square 4 of foldable

Foldable: Tab 4

Metaphase

• Spindle fibers attach to chromosomes

• Chromosomes

“met” @ the middle.

Draw the diagram of the metaphase on square 5 of foldable

Foldable: Tab 5

Anaphase

• Sister Chromatids are pulled apart towards the poles.

Draw the diagram of anaphase on square 6 of foldable

Foldable: Tab 6

Draw and identify the phase of Mitosis?What phase of the cell cycle will the 2 daughter ell

be in?

• Sister Chromatids are now at opposite poles and uncoil.

• Nucleus starts to reform

Telophase

Draw the diagram of the telophase on square 7 of foldable

Foldable: Tab 7

Cytokinesis occurs -Two new cells

Foldable: Tab 8

Cytokinesis

Cleavage furrow

Cell plate

Anaphase

Prophase

Metaphase

Interphase

Cytokinesis

Telophase

Mitosis

• In Mitosis, everything is identical.

• Takes place in somatic cells (body cells, ex: lung, skin, heart, stomach, etc.)

Results of Mitosis

• Replace old or damaged cells.

• Occurs fastest in skin cells.

• Some cells like brain cells do not divide.

• During early development, mitosis produces the cells needed to make tissues and organs.