Transcript Document 322911

S3 BIOLOGY
UNIT 1: CELL BIOLOGY
SUB-UNIT 1.3
PRODUCING NEW CELLS
Cell division
• In a unicellular organism (Amoeba) cell division
is a form of reproduction which produces two
new individuals.
• In a multicellular organism (human being or
plant) cell division results in the growth of an
organism.
• Cell division is the means of increasing the
number of cells in an organism. It is the
nucleus that controls cell division.
Cell division: Animal cell
• Nucleus divides
• Two daughter nuclei separate
• Cytoplasm pinches off
• Two daughter cells are formed.
Cell division: Plant cell
• Nuclear division
• Laying down of cell wall.
• Two daughter cells formed
Chromosomes
Chromosomes are
threadlike structures found
in the nucleus.
Chromosomes carry
information necessary for
the development of the cell
and the survival of the
organism. All body cells
have a double set of
chromosomes and are said
to be diploid.
One set of chromosomes
come from the mother and
the other set comes from
the father.
Questions
a)State the main events that occur during cell
division.
b)How does cell division in a plant differ from
that in an animal?
c)Which cell structure controls all cell
activities including cell division?
d) Draw a diagram to show genes on a pair of
chromosomes:
Video time
• TWIG video clip : Cell division: Mitosis
• BBC - Learning Zone Class Clips - Mitosis
- Science Video
Mitosis
• Mitosis is the process of cell division
where the nucleus divides into two
daughter nuclei.
• Each nuclei has exactly the same
number of chromosomes as the original
nucleus.
Stages
of
Mitosis
1.
Chromosomes become shorter and thicker (like a double
thread).
2.
Each single thread is called a chromatid.
3.
The two chromatids are joined by a centromere.
4.
Chromosomes line up at the equator.
5.
Spindle fibres attach to the centromere of each
chromosome.
6.
The centromere splits and one chromatid moves to the
“north” pole and the other to the “south” pole.
7.
Finally a nuclear membrane forms around each group of
chromatids (now called chromosomes). Nuclear division
(mitosis) is complete forming 2 new daughter cells which
are identical.
Rap to watch
• http://www.bbc.co.uk/learningzone/clips/mi
tosis/13512.html
Chromosome complement
• Every species has a definite and characteristic
number of chromosomes present in each cell,
this is called the chromosome complement.
• Since chromosomes provide the genetic
information for each species, it is essential that
each new cell receives a full complement of
chromosomes.
• This ensures that animals and plants are
provided with all the characteristics of their
species.
Species
Diploid chromosome
complement
Onion
16
Rice
24
Fruit-fly
8
Cat
38
Human
46
Questions
a)Describe the process of mitosis in a cell
including the terms chromatid; centromere and
spindle fibre in your answer.
b)Why is it important that the chromosome
complement of daughter cells in a multicellular
organism is maintained?
Cancer
What?
Who?
Types?
Causes of cancer (case studies)
• Read the case studies and complete the
table.
• Think about
– How old the person was when they developed
cancer
– What you think the possible causes are
Causes of cancer (case studies)
POSSIBLE
CAUSES
Causes of cancer (case studies)
inherited
smoking
Old age
Lack of
exercise
Richard
70
Kate
35
Emily
35
Viral
infection
HPV
POSSIBLE
CAUSES
Old age
Daniel
sun
65
Peter
69
Myra
74
Old age
Unhealthy
diet
unknown
Old age
Causes of cancer (case studies)
• Most of the case studies developed cancer
over the age of 65.
• There are preventable and nonpreventable causes.
• Only a small proportion (5%) are
attributable to an inherited gene defect.
• Look at case study 5, you will see that
there isn’t always a clear cause.
• A healthy lifestyle can reduce your
chances… but there are no guarantees.
Preventable
Non-preventable
Smoking
Inherited
Unhealthy diet
Age
Lack of exercise
Unknown (biological
processes)
Overexposure to the sun
Infection with a virus
(e.g. HPV)
How does cancer develop?
The Road to Cancer
8
2
7
10
5
3
9
4
1
6
Key concepts
• Cancer is a disease of cells.
• Cancer develops when cell division
(mitosis) goes out of control.
• Cancer is a disease of old age.
Quiz answers
Working with Micro-organisms
• There are micro-organisms all
around us. It has been estimated
500 -1000 different species of
bacteria live on human skin.
• The experiment on the right
investigates micro-organisms in the
air. Each plate has a layer of
nutrient agar. Any microbe that
lands on this agar will grow and
multiply because they can feed on
the agar.
• Plate A was exposed to air for 30
minutes. Two days later bacteria
and fungi had grown.
• Plate B was not exposed to air and
no bacteria or fungi grew.
Why did microbes grow on plate A
and not plate B?
Aseptic technique
• Before learning about aseptic
technique you should be familiar with a
few terms.
• Watch the video and try to write down
the meanings of the following words:
Video: Working with cells | Wellcome Trust
WORD
MEDIUM
STERILE MEDIUM
CULTURE
PURE CULTURE
MIXED CULTURE
CONTAMINATION
DISINFECTANT
INNOCULUM
MEANING
Cell food
Cell food that is free from any bacteria or living
organisms
The growing micro-organisms in a nutrient rich
environment
A sample of only one type of micro-organisms growing in
a nutrient rich environment
A sample of more than one type of micro-organism
growing in a nutrient rich environment
The accidental introduction of foreign microorganisms to a culture sample.
A chemical used to eliminate foreign micro-organisms
from the working area.
A solution containing micro-organisms that is added to a
sterile, nutrient rich environment for observation.
Precautions and sterile technique
• In a microbiology laboratory it is important to take
precautions when working with micro-organisms. All
surface should be made of plastic and be sterile (have
no microbes living on them). These microbes can be
killed with disinfectant.
• Microbiologists working in the lab need to wear lab coats
to protect their clothing and be careful not to touch the
agar used to grow microbes.
• All glassware also must be sterilised. It is heated in an
autoclave at 121oC for 20 minutes to ensure all microbes
are dead – some can survive in boiling water!
Culturing a microorganism
In microbiology, Scientists grow microorganisms. They grow bacterial “cultures”
on agar plates.
The diagram shows the method used to inoculate (introduce) a
fungus to the petri dish.
Resistant spores
• All these precautions are taken so that the only microbe
growing in the agar plate is the one the microbiologist is
trying to grow. If these steps were not taken the wrong
microbe may be grown.
• The reason high temperatures of autoclaves and Bunsen
burners are used is to kill resistant spores. Some
bacterial cells can become endospores. This means
they produce a thick protective coat. Fungi can do
likewise.
• Only exposure to temperatures above 120oC applied
under pressure can kill these resistant spores.
Questions
a)
Why should a microbiologist wear a lab coat?
Protect clothing
b)
What is used to clean all surfaces before working
with microbes?
Disinfectant
c)
Why are these precautions taken?
Reduce risk of contamination
d)
How are resistant spores killed?
Expose to temperatures over 120oC
Cell culture: treatment of burns
• Watch the video and then write a short
report on the use of cell culture in the
treatment of burns.
• BBC - Learning Zone Class Clips Growing new skin cells - Science Video
Fermenters
• Biotechnological industries grow micro-organisms on a vast scale
to make vast quantities of useful products (e.g.
alcohol
_______________).
• Industrial fermenters are used to make these antibiotics,
enzymes and vaccines.
• The industrial fermenters are automated. This means they are
automatically controlled by computers. Sensors monitor the
conditions for growth and make sure they are right for the
product they are making.
The computers may monitor:
•
•
•
•
Temperature
Oxygen concentration
pH
Glucose concentration
The diagram below shows a
fermenter that is making a fungus.