Edexcel AS Biology Unit 2 - Topic 4

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Classification - Phylogeny

Phylogeny is the classification of a species according to shared characteristics, the resulting taxonomy will often reflect their evolutionary relationships

Sometimes, a resemblance arises in species from different branches of the evolutionary tree. This happens if species move into similar ecological niches or if one species is mimicking another. This works the other way round too; some species may seem dissimilar, when in fact they are closely related. 

The key to phylogeny is looking for characteristics that are due to common ancestors, rather than evolutionary pressure.  

Features that share a purpose, such as a streamline shape in sharks, are not useful when classifying by phylogeny. They tend to look for features that are "useless", as these were most likely one off accidents. 

Biologists look at the sections of non-coding DNA, and seeing which are similiar in different species. This is done by molecular systematics

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Classification - Taxonomy

Taxonomy is a form of classification that focuses on the physical similarites between species; for ease of naming and identification.

It is important to be able to chose key features, and ignore others. For example, many birds and insects are capable of winged flight, but they are very different groups.
The first scientist to make a formal system of taxonomy was Carl Linneaus. Linnean taxonomy is still the basis of the taxonomy we use today.

There are 8 levels of classification in taxonomy; 
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.  

There are 3 domains; Eubacteria, Archaebacteria and Eukaryotes
There are 5 Kingdoms; Animalia, Plantae, Fungi, Protista and Monera (or formerly known as Prokarya)

EXAM TIP: Know the main differences and similarities between the 3 domains 

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Conservation Part 1 - Threats To Biodiversity

Conservation is the study and protection of biodiversity and natural resources. It is about actively and carefully maintaining a balance between ecological needs and human requirements. (These two things are always in conflict)

Threats to biodiversity

  • Habitat destruction, such as deforestation.
  • Over-exploitation, such as whaling and over fishing. 
  • Competition from introduced species, such as grey squirrels Vs red squirrels in the UK

Mass extinction is a natural consequence of evolution, which causes entire species to die out. The mass extinction of over 50% of the Earth's population (death of the dinosaurs) led to the rise of mammals. 

There are 7 categories of species status; Extinct, Extinct in the wild, critically endangered, endangered, vulnerable, near threatened and least concern. 

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Conservation Part 2 - Reasons For Conservation

There are many different reasons and opinions for why we should conserve animals;

Ethical Reasons - Some people believe that all species have a right to live and exist. Humans should be responsible for the protection of animals on the planet.

Aesthetic Reasons - Biodiversity should be maintained for the enjoyment of future generations. Places with low biodiversity have a dull look about them. Many people take pleasure in walking and enjoying place with a rich, diverse eco-system. 

Economic Reasons - Money!

Practical Reasons - Many species provide humans with useful products such as food, medicines and industrial products

Ecological Reasons - The complexity of relationships within eco-systems means that no species exists in complete isolation (interdependance). Acts such as deforestation can have a detrimental effect, so conservation may be the only long term solution.

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Conservation Part 3 - Mechanisms Of Conservation

In situ conservation refers to the conservation of a species within it's habitat. So, this involves protecting the habitat and the species within in it, and allowing the species to grow and reproduce. 

Ex situ conservation is where organisms are removed from their natural habitat. It is more expensive than In situ conservation, but sometimes, it is all that can be done.

Coppicing is where trees are harvested by cutting them down to ground level and allowing them to regrow. Coppicing produces a range of microhabitats - Because the little guys are important too!

Zoos protect and conserve endangered species. 

Captive breeding programs increase the number of individuals of a species, ensure genetic diversity by exchanging animals with other zoos and reintroduce species back into the wild if feasible. 

Botanical gardens and Seed banks store seeds which are used to re-grow plants, and then re-collect the seeds from these plants. Seeds stored at -20, and are dried to stop metabolic rates. 

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Biodiversity Part 1

Biodiversity is a measure of how varied an ecosystem is. It is measured in three ways; 

  • Genetic Diversity is a measured of how many variations there are in the genetic code between individuals of a particular species, or different species. 
  • Species Diversity is the measure of how many different species are present in an area, and how many individuals there are of these species. 
  • Habitat Diversity is the measure of how many different habitats there are in an area.

A species is a group of organisms that share characteristics, can interbreed and they can produce fertile offspring. 

Different species can sometimes interbreed and produce hybrid offspring. However, the offspring are not fertile, meaning that the parents are still called separate species. An example of a hybrid is the Liger. 

A habitat is the area in which a species lives. Endemism refers to organisms which are unique to one habitat. For example, the New Zealand Kiwi bird. 

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Biodiversity Part 2 - The Importance Of Biodiversi

Many people think that the main concern is low biodiversity, when in fact it is the loss of biodiversity. An ecosystem relies on the interdependence of other species to maintain stability, and the loss of species can cause irreversible changes in an ecosystem.

Low biodiversity can still be problematic in certain situations, such as agriculture. Selective breeding creates crops with desirable characterists, that are very similar.
Lack of genetic diversity can make the crop as a whole highly susceptable to pests and diseases. In agriculture, growing one type of species/variety of crop is called monoculture.

Monoculture can lead to a particular type of species feeding off of and becoming dependent on that one main crop source. This leads to a massive loss of crops, further lowering the biodiversity.

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Biodiversity Part 3 - Measuring Biodiversity

Measuring biodiversity enables comparisons to be made between different areas or in the same area at different times.  

Species richness - The number of different species in a particular area. The greater the number, the richer the area. This factor does not take into account the number of individuals of a particular species, so a species of just one individual carries the same weight as a a hundred individuals in another species.

Species Evenness - This is a comparison of the size of the population of different species in an area.

Random sampling - throwing a quadrat down and couting the organisms in it. 
Random walking - selecting a number betweem 0 and 360, and walking.
Line transects - A line is drawn through the area to be examined.
Belt transects - similar to line, but a series of quadrats are placed in a line.


 

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Eukaryotic Cells and Their Structures

A eukaryote is any organism consisting of one or more cells that contain DNA in a membrane bound nucleus, seperate from the cytoplasm. 

Eukaryotes are; Plants, Animals, Fungi and Protists

Typical animal organelles

Mitochondria - an energy generating organelle with a double membrane.
Microtubules - hollow filaments of the protein Tubulin. Provide structural support.

Typical plant organelles

Chloroplasts - use CO2, water and light to build sugars. They are present in all green plants. Surrounded by a double membrane. Contain thylakoid membranes called grana which are the site of photosynthesis
Vacuoles - Consists of a membrane called the tonoplast (filled with cell sap). The vacuole keeps the cell firm. Filled vacuoles make the cell turgid.
Cell wall - Made of cellulose. Provides support and structure. Transport between the cells happens through the plasmodesmata.

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Prokaryotic Cells and Their Structures

A prokaryote is any organism whose DNA is suspended freely in the ctyoplasm. The DNA is looped.

Features of the bateria and archae; DNA, ribosomes, cytoplasm, cell membrane, cell wall and mesosomes.

Many pathogenic bacteria are surrounded by a protective layer called a capsule. The capsule protects bacteria from viruses. The capsule is usually composed of polysaccharides and water.

Some prokaryotic cells feature one or more flagella. These rotate to provide motility.
Many bateria also feature Pili. These are hollow protein structures used during the transfer of genetic material from one bacterium to another.

Plasmids are loops of DNA whch are present in both types of prokaryote.

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