Download Cell Division and Differentiation

Cell Differentiation and Division
Learning Objectives
You will have been successful if by the end of
this lesson you can:
• Describe and explain how cells are specialised to carry out
their function
• Explain the importance of differentiation in plant and animal
cells
• Describe the importance of cell division.
• Describe the main stages of the cell cycle and the events of
mitosis
Not all cells are equal!
These show basic animal and plant cells
Cells become specialised
All living organisms must be able to carry out the main features of
MRSGREN
Movement
Respiration
Sensitivity
Growth
Reproduction
Excretion
Nutrition
but individual cells may become specialised to be best at one of
those activities. This specialisation is called DIFFERENTIATION
Differentiation
Sperm Cells
These are essential for sexual
reproduction in animals. There
are specialised by having a tail
which moves them towards the
egg.
They have a nucleus with only
one set of chromosomes
(haploid) compared to other
cells which have 2 sets of
chromosomes
Nerve Cells
These cells are often very long and
can carry electrical impulses to and
from the brain.
Schwann cells surround the axon and
insulate the nerve impulse
Muscle Cells
• These are cells that are
specialised for movement.
• There are three main types
of muscle cell.
• They all contain protein
fibres that make the cell
shorten and contract or
relax and lengthen
Root Hair Cells
These are found on the
surface of the roots and
create a larger surface area
for absorption of water and
minerals
Xylem Cells in Plants
Carry water and minerals from
roots to leaves in plants
Phloem Cells
Sieve plates between cells
Tissues Organs and Systems
After cells specialise they must group
together to be effective. This creates a
tissue
The tissues will be specialised to perform one
role very effectively so different tissues will be
required to form organs
Organs have one or more main functions and often
many organs cooperate to do a more complex task
such as digestion
Levels of organisation in a multicellular organism
Cell
……………………
- the basic structural and functional unit of a living
organism.
Tissue
………………………
- a group of cells with similar structures, working
together to perform a shared function.
Organ
……………………
- a structure made up of a group of tissues,
working together to perform specific functions.
System
Organ
…………………
…………………………
- a group of organs with related
functions, working together to perform body functions.
Cell Division
Why do cells divide? What would happen if they didn’t?
 Organisms would only ever exist as
single cells – fine for bacteria but
not so good for plants and animals!
 Old and damaged cells
would never be replaced.
 Organisms wouldn’t reproduce.
Divide and grow
Most animals and plants start off life as just a single cell, but grow
to become adults containing billions and billions of cells.
How does one cell become billions and billions of cells?
The type of cell division that makes animals and plants grow is
called mitosis.
parent
In mitosis, a parent cell divides
cell
into two identical daughter cells.
These daughter cells divide in two,
mitosis
and so on.
Mitosis is also the way in old
and damaged cells are
replaced.
daughter cells
DNA, Chromosomes and Genes
gene
Chromosomes are
made of a material
called DNA.
Sections of DNA are
called genes and
each gene carries
the instructions to
make one protein.
Many genes are
located on a
chromosome.
Duplicating chromosomes
A cell’s chromosomes are usually long,
thin strands. Just before the cell divides,
however, the chromosomes become
shorter, thicker and more visible. They are
said to condense.
Each chromosome duplicates and becomes two strands, each one
called a chromatid. The two chromatids are joined at the
centromere.
chromatid
condensed
chromosome
centromere
In Your Books
1. Copy the diagram and add labels
 Chromosome
 Chromatid
 centromere
Chromosome
2. What material are chromosomes
made of?
3. What is the purpose of the
centromere?
4. What are small sections of the
chromosome that code for a
protein called?
5. Give 3 reasons why cells must
divide.
Chromosome
replicates
chromatid
centromere
What happens during mitosis?
What are the stages of mitosis?
Once the chromosomes have duplicated, mitosis takes place.
This is a continuous process but can be divided into several
parts:
 Each chromosome replicates so it contains two identical
chromatids.
 The chromosomes align in the middle of the parent cell.
 The two chromatids in each chromosome are pulled apart
into separate halves of the cell.
 The cell splits in two to produce two daughter cells, each
containing the same chromosomes.
Mitosis involves copying a cell and its chromosomes exactly, so it is
sometimes called copying division.
Chromosomes during mitosis
Your Task
•
•
•
•
•
Create an animation of mitosis.
Film it or produce a 3D model showing the main events.
Your parent cell must have 4 chromosomes at the start
Use colour to help you show this clearly.
You must label the cell and contents.
Chromosome
Cell membrane
Centromere