B2 Revision

B2 Revision for GCSE

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  • Created by: Lizzie
  • Created on: 20-05-12 14:30


Living organisms are classified into five kingdoms which are;

Plants - Use light energy to produce food during photosynthesis; plant cells have a cell wall made from the cellulose. Examples = roses, oak trees, wheat.

Animals - Feed on other organsims; multicellular meaning their bodies are made up of lots of different cells but have no cell walls. Examples = slugs, ladybirds, lions.

Fungi - Makes spors instead of seeds when they reproduce: cells have a cell wall made from chitin. Examples = yeast, mushrooms, mould.

Protocist - Made up of just one cell. Examples = algae, Euglena, Amoeba.

Prokaryotes - Have no nucleas; have a cell wall but it is not made from cellubse. Example = Bacteria.

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Artificial Classification

  • Based on one or two characteristics to make identification of an orgasnism easier. For example, birds that always live by or on the sea can be called seabirds.

Natural Classification

  • Based on evolutionary relationships and is much more detailed. Animals that are more closesly related are more likely to be in the same group.

Sequencing the bases in DNA has enabled scientists to know much more about how closely related organisms are, and has often meant that organisms can be reclassified.

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Grouping Organisms

A species is a group of organisms which are capable of interbreeding to produce fertile young meaning the young can grow and have babies of their own.

All organisms are named by the binomial system which works like this;

  • Two parts to each name, the first is the genus and the second is thre species.
  • The genus parts start with a capital letter and the species part with a lower case.

All organisms are classified into a number of different groups, starting with their kingdom and ending with their species.

Kingdom, Phylum, Class, Order, Family, Genus, Species.

Hybrids - If two individuals of different species breed they can produce offspring that are sterile. The hybrids that are formed are unable to produce offspring of their own.

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Pyramids Of Biomass

Pyramids of biomass (and numbers) can both be used to represent feeding relationships between organisms in a food chain or web. Pyramids of biomass show the dry mass of living material at each stage of the food chain.

Pyramids of biomass may look different to pyramids of numbers if;

  • Producers are very large
  • A small parasite lives on a large animal

Although pyramids of biomass are a better way of representing trophic levels they are difficult to construct because;

  • Some organisms feed on organisms from different trophic levels
  • Measuring dry mass is difficult as it involves removing all the water from an orgasnism.
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The atmoshpere contains approximately of 0.04% carbon dioxide. However, this is enough to supply all plants in the world. Plants use carbon dioxide to make food in photosynthesis. Carbon passes along food chains and webs, even when plants and animals die and decompose. Carbon Dioxide is put back in the atmosphere by plants and animals respiring and the burning of fossil fuels.

Carbon dioxide is also absorbed from the air by oceans. Marine organisms make shells made of carbonate, which become limestone rocks. The carbon in limestone can return to the air as carbon dioxide during volcanic erruptions.

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The Nitrogen Cycle

  • Plants take in nitrogen as nitrates from the soil to make proteins for growth.
  • Feeding passes nitrogen compounds along a food chain or web.
  • The nitrogen compounds in dead plants and animals are broken down by decomposers and returned to the soil.

A number of micro-organisms recycle the nitrogen;

  • Decomposers are soil bacteria and fungi which convert protenins into ammonia.
  • Nitrifying bacteris converts the ammonia to nitrates.
  • Denitrifying bacteria convert nitrates into nitrogen gas.
  • Nitrogen-fixing bacteria living in the soil fix nitrogen gas.
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There are many types of pollution but the three that have caused much concern are;

  • Carbon dioxide, from increased burning of fossil fuels, which may incres the greenhouse effect and global warming.
  • CFCs, from aerosols, which destroy the Ozone layer.
  • Sulfur dioxide, from burning fossil fuels, causing acid rain.

You can measure pollution by using direct methods such as attatching oxygen probes to computers and special chemicals that can beused to indicate levels of nitrate pollution from fertilisers.

There are advantages to the different methods of measuring pollution;

  • Using indicator orgasnismsn is cheaper, does not need equipment that cn go wrong and monitors pollution levels over long periods of time.
  • Using direct methods can give more accurate results at any specific time.
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Compete or Die

Plants and animals comptete to survive because if they do not their species will die out.

What plants compete for;

  • Water and minerals for health and growth
  • Light for photosythesis
  • Space for growth

What animals compete for;

  • Food and water
  • Shelter from bad weather
  • A mate to breed with.

An ecological niche is the role of a certain animals. For example, the "role" of a red squirrel is to live in the woods and eat acorns which is it's ecological niche. The grey squirrel is similar to the red squirrel as they have a similar ecological niche but the grey squirrel is more succesful as it is bigger and stronger than the red squirrel.

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Organisms in cold conditions are adapted to;

  • keeping warm
  • be able to move on the snow

So, they have excellent insulation to cut down heat loss and animals that live in cold habitats are usually very large with small ears which helps decrease heat loss as it decreases the surface area to volume ratio.

Animals try to avoid the cold by changing their behaviour. Some migrate long distances to warmer areas and others slow down their body processes and hibernate.

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Heat loss of organisms depends on their volue to surface area ration.

Organisms in hot, dry areas have adaptations such as;

  • increase of heat loss
  • be able to move on the sand
  • be able to cope with a lack of water

To cope with dry conditions, organisms have behavourial, anatomical and physiological adaptations like;

  • Camels can sruvive with little water because they can produce very concentrated urine.
  • Cacti reduce water loss because their leaves have been reduce to spines.
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Natural Selection

Charles Darwin wrote a theory of natural selection to explain how evolution might happen. It says that if animals and plants are better adaptred to their environment, they and their following generations are more likely to survive. Natural selection is difficult to study because it usually takes thousands of years to see the effect.

At first, many people did not agree with Darwin's theory as some people thought he did not have enough evidence to back up his theory and people thought that God had created all species but now, Darwin's theory is now more accepted as it explains lots of observations.

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