Topic 5 - On the wild side: (Edexcel Unit 4)

Edexcel Biology Unit 4: Topic 5 Notes-

Detailed notes with diagrams and pictures, they are all condensed and as detailed as they can be. Topic 6,7,8 will be coming soon.


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  • Created on: 23-12-13 16:04
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Unit 4: Natural environment and Species Survival
Topic 5: On the wild side
5.1: The Biosphere
Biosphere: an area or a fraction of the Earth that is covered by living organisms.
-it is made up of many ecosystems.
An ecosystem is the community of organism interacting between themselves and the physical
and chemical environment.
Ecosystems consist of abiotic (abiotic environment) and the biotic factors (biota).
Abiotic factors:
These are the physical and chemical components of an ecosystem, which define the physical
conditions of it.
Such as:
-Solar energy output: affected by latitude, season, cloud cover and changes in Earth's orbit.
-Climate: rainfall, wind exposure and temperature.
-Topography: altitude, slope, aspect (direction that land faces) and drainage.
-Oxygen availability: important in aquatic systems, e.g.: streams are more oxygenated than pools.
-Edaphic factors: Soil factors: pH, minerals, salt, soil texture and consistency.
-Pollution: Air, water or land.
-Catastrophes: Events that drastically change an environment such as tsunami, flood or volcanic
Biotic factors:
These are the living organisms in an ecosystem which affect each other; an interaction between
Intraspecific competition:
-Interaction between the organisms of the same species.
Interspecific competition:
-Interaction between the organisms of different species.
(Note the italics are only to highlight the differences between the names, not how to write them)

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Biotic factors: are dependent on the number of organisms there are compared with the resources
Are density dependant
Plants compete for space, light and minerals.
Animals compete for food, shelter and a mate.
When the fastest competitor wins:
It eliminates
dominates the other species, is called competitive exclusion.
Predators: are species which eat other species, normally killing before they eat.
Herbivores: feed on plant matter, graze.
Symbiosis: relationship between two organisms living in intimate association.…read more

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Entirely new soil, surface, growth medium etc..
New land can form at river deltas, sand dunes and volcanic lava.
The first significant development is the formation of soil.
-Initial medium such as rock is eroded down over time to form most of the soil.
-external minerals can however be involved.
Climax soil has a layer called humus; which is the substance that comes from dead organic matter
(and faeces) that has decomposed over time.
-Humus helps retain water.…read more

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This occurs when an existing community is destroyed.
-Soil here is already present.
New species will come in due to dispersal etc...
-the species overtime will die and then carry on to develop into a new climax community.
Figure 2: Secondary Succession
Figure 2 ©Encyclopaedia Britannica D
Deflected succession is when a community is stabilised due to human interaction. Like a farm or a
lawn, or even a maintained woodland.
Energy transfer in an ecosystem:
Energy enters via photosynthesis.
Plants convert sunlight to organic molecules.…read more

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Also carnivores), eat other consumers. The carnivores at the top of the food chain are called the
top carnivores or the apex predators.
Animals that eat plants and plant matter.
Figure 3: Food chain:
Figure 3
The energy transfer in an ecosystem can be represented in a food chain. The position that a
consumer occupies is called its trophic level.
- Energy is transferred from one trophic level to next.
- This however can be more complex as a food web.…read more

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Fungi and bacteria
-feed on dead remains of organisms and excrement.
-they secrete enzymes to break down food before absorbing nutrients.
Efficiency of energy through ecosystem:
Dependant on how much energy is,
-captured by producers
-given to high trophic levels
Plants are not 100% efficient at absorbing light,
-only small fraction is used in photosynthesis.
In plants, light coming in:
-5% reflected,
-50% not used by chlorophyll, but to evaporate water.
-40% used by chlorophyll in chloroplasts.…read more

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Efficiency (E):
E = (NPP
GPP )×100
Disappearance of energy:
Energy is lost as it enters higher trophic levels, but where does it go?
-not all food available is eaten: limitations of feeding methods and some parts of plants will not
get eaten.
-some energy is lost in faeces and urine: Food matter is broken down and Cellulose is particularly
hard to break down; energy is used and wasted in this.…read more

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Figure 4 ©S-cool revision site
5.2: Climate Change
Evidence for Climate change:
Personal memory or `anecdotal' memory cannot be trusted to tell us if climate is changing.
We however have three different ways that we can tell climate change:
-Temperature records
-Pollen in beat bogs
Temperature records:
-Over time many people have collected and stored records of temperature in the air.
-These, even though old records may be inaccurate, provide a general insight into how the overall
temperature is changing.…read more

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One of the main things connected with Climate change is Global Warming.
-It's the gradual increase of temperature over time.
Greenhouse effect:
-The sun releases energy mostly as light.
-Most ultraviolet (UV) is absorbed by Stratosphere.
-The Earth absorbs some of this.
-The Earth warms up and radiates some of this energy back into space as infrared.
-Some of this is absorbed by gases in the atmosphere.
-The gases that are really good at doing this are called Greenhouse Gases.…read more

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Weather changes: At poles, cold, salty water sinks. Warm surface water replaces this. Melting ice
means less salinity. Slowing down of ocean currents are then a result of this. There are also
alterations in the patterns of heat and rainfall.
Coral Bleaching:
Microscopic algae live symbiotically with coral. When there is environmental stress, the coral starts to
die and mass bleaching of the coral occurs.
It's a controversial issue because a lot people don't believe it is happening.…read more


Khadijah AG

Thanks! These are great notes

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