Lesson 1
Homework for next Tuesday (28/11): find out what can be done to
1/ slow down the growth of microbes
2/ kill microbes
Population and population growth:
A population is a group of animals or plants living in the same habitat. Populations are able to
grow very quickly in good conditions. However, some factors limit population growth:
- climate
- disease
- lack of food
- overcrowding
Experiment: Growth conditions needed by woodlice
Aim: to test which environmental conditions are preferred by woodlice
Input variable to be changed: light intensity
Outcome variable to be measured: Number of woodlice measured every minute during 10
minutes
Variables to be kept the same: temperature, humidity, etc…
Time (min)
0
1
2
3
4
5
6
7
8
9
10
Number of woodlice
Conclusion: Woodlice “prefer” dark conditions.
This is because in the dark, they are:
- less likely to dry out
- less visible to predators
Lesson 2
Human population:
Human population is now growing very quickly as many factors that used to limit the growth
of our population are controlled in our modern life.
Limiting factor
Disease
Overcrowding
Lack of food
Lack of water
Means of control
Bacteria and bacterial growth
Microbes (also called micro-organisms) are organisms which are so tiny that they can only be
observed using a microscope  microscopic organisms
Microbes include bacteria, fungi and viruses.
Microbes can be found in air, soil and untreated water, on and in plants, on and in animals.
Experiment: Which conditions are best for microbes to grow?
Condition
Freezing
and dry
Freezing
and wet
Cold
(Fridge)
and dry
Cold
(Fridge)
and wet
Class result
Conclusion:
Microbes grow the best in wet and damp conditions
Lesson 3
Control of microbial population:
Researched based lesson
Encouraging population growth
Some microbes are really useful for humans:
Warm
and dry
Warm
and wet
Hot and
dry
Hot and
wet
Lesson 4
Recap of what was learnt last lesson in the form of a spider diagram
Some microbes are decomposers: they can make dead things rot.
Things that rot are called biodegradable, things that never rot are called non-biodegradable.
Examples of biodegradable things:
- apples
- humans
- wood
- plants
Examples of non-biodegradable things:
- glass
- metal
- some plastics
- cans
In the lab, they are grown in nutrient broth.
Limiting the growth of microbes
Microbes cannot grow, or will grow very slowly in food which is:
- kept in the fridge or the freezer
- dry (packet of crisps, dried pasta)
- vacuum packed (no air)
- very salty (salted cod, crisps)
Killing microbes
In some places, all microbes have been killed in a process called sterilisation. A place or an
object without microbes is called sterile (e.g. clean syringes).
Microbes can be killed by:
- heat (flame tools, boil water for more than 10 min)
- pressure (pressure cooker = autoclave) Demo autoclave
- chemicals (bleach, alcohol)
- filtration (filters with microscopic holes)
- radiations (UV light)
Microbes are not killed by cold temperatures.
Lesson 5
Record and discuss results from Mouldy bread experiment
Competition : Give homework on dandelions
When organisms have a need for the same limited resource, e.g. shelter and food for animals,
competition takes place.
For example, Robins compete for their territory, animals which compete for food with
humans are called pests.
Competition also happens between plants for light, water and nutrients.
Exercise on keys
Lesson 6: Experiment: Which weed is the best competitor?
Weed
Sample
1
Sample
2
Sample
3
Sample
4
Sample
5
Total
Dandelion
Plantain
Daisies
Conclusion:
Lesson 7
Who eats whom in an environment?
Food is energy
A food chain shows the movement of energy between plants and animals. The arrow
shows the direction of the flow of energy.
For example:
Meadow:
grass
Sea Rock pool:
Tree: oak tree
seaweed
snail
limpet
caterpillar
hedgehog
seagull
black bird
Food web:
A food web is made up of many interconnected food chains.
cat
Fox
Owl
Weasel
Hedgehog
Vole
Rabbit
Worm
Snail
Oak
Grass
leaves
1/ Please write down all the food chains that you can find in this food web (6)
e.g. grass
grass
rabbit
rabbit
fox
weasel
fox
Oak leaves
vole
weasel
fox
Oak leaves
vole
owl
Oak leaves
worm
hedgehog
fox
Oak leaves
snail
hedgehog
fox
2/ What would happen if all the voles disappeared?
The weasel will not have as much food, they might start to die off. However, some will
survive as they can also eat rabbits.
3/ What would happen if the voles were present but the owl disappeared?
The owls would die as their only source of food as disappeared.
In a food chain, energy is lost at each level because plants and animals have to use
some of it to live.
Grass
Snail
Hedgehog
Energy
Lesson 8
Food pyramids show the number of organisms at each level of the food chain
Pyramids of numbers
Pyramids of numbers show they number of organisms at each level of the food chain.
Remember
- you need lots of salads to feed one rabbit, lots of rabbits to feed one fox, lots of
foxes to feed one eagle
- therefore, the number of organisms decreases (goes down) as you go up the food
chain
- there are always less predators than prey, otherwise predators would starve to
death!
For example:
grass
rabbit
fox
Fox