The Cell

Cycle

Cell Reproduction

As stated in the cell theory, all cells come

from pre-existing cells

These new cells are created through cell

reproduction where a parent cell divides

to produce two identical daughter cells

Cell reproduction is important for growth

and repair

Cell Growth

Cells can receive important molecules

from the outside environment through

diffusion

Cells can eventually reach a point where

they are too large to perform efficiently

Simple Diffusion

Diffusion is the movement of particles from

an area of higher concentration to an area

of lower concentration until particle

concentration is equal throughout.

This occurs when there is a difference in

concentration between two areas which will

form a concentration gradient.

Concentrations will reach a dynamic

equilibrium where particles move at equal

rates in all directions.

Osmosis

Osmosis is the net movement of water across

a selectively permeable membrane

It is basically simple diffusion of water

molecules.

Osmosis occurs when there is a difference in

solute concentration across a selectively

permeable membrane.

Cell Growth

When the cell is too large, diffused materials

take longer to reach all parts of the cell

Therefore, if the ratio of cell surface area to

cell volume is too small, the cell can divide

The Cell Cycle The cell cycle is mostly spent in interphase which is

the growth phase of the cell. When it is ready, it can

enter the cell division phase which consists of mitosis

and cytokinesis.

Interphase

Most of a cell’s life is spent in interphase

This phase is for growth of the cell (G1 and G2) and replication of DNA (S) in preparation for mitosis

Replicated DNA (in the form of chromatin) is held together by centromeres and is not yet visible as individual chromosomes.

These can be called sister chromatids

Mitosis

Living cells must make new cells continually

in order to grow and reproduce.

Identical genetic material is passed on to

every new cell through mitosis.

Mitosis is the continuous process whereby

each cell can replicate its DNA and

produce a new nucleus for a new cell.

There are 4 steps to this process:

Prophase

The chromatin condenses to become

visible chromosomes

Nucleolus and nuclear membrane start to

disappear

Spindle fibres form in animal cells from the

centrioles at opposite ends of the cell

Prophase

Metaphase

The spindle fibres are attached to the

centromere of each double stranded

chromosome

Chromosomes are lined up along the

middle of the cell (equator)

Metaphase

Anaphase

The spindle fibres pull the centromeres

apart

One strand of each chromosome gets

pulled to opposite ends of the cell

(identical set on each side)

Anaphase

Telophase

Each end of the cell has a complete set of

chromosomes

Nuclear membrane forms around each set

Chromosomes unravel to chromatin

Spindle fibres disappear and nucleolus

starts to reappear

Telophase

Cytokinesis

Plant cells form a cell plate in the middle of

the ‘parent’ cell, which forms a new cell

wall between the two ‘daughter’ cells

In animal cells, the membrane pinches in to

divide the cytoplasm into two cells; the fold

is called a cleavage furrow.

Cytokinesis

Cell Cycle Recap

Interphase

G1

S

G2

Mitosis

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis