B2 Biology revision



Classification is organising living organisms into groups - Classification helps us understand how organisms are related and how they interact with eachother. Natural classification is based on the evolutionary relationships and genetic similarities between organisms whilst artificial classification is based on appearance rather than genes. It is used to identify organisms. Living things are divided into kingdoms which are  divided into smaller groups called phylum, class, order, family, genus and species. The genus is the group of closely related species - species are organisms which can interbreed and form fertile offspring.

Classification systems change over time - When scientists discover new species they have to adapt classification systems. Some species may fit into multiple groups or not fit into any. Therefore its hard to place them. DNA sequencing allows us to see genetic differenes between groups. This information can show us that some groups arent as closely related as we thought .

Evolutionary trees show relationships - Evolutionary trees show common ancestors between species. the more recent the common ancestor, the more closely related the two species.

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A species is a group of organisms which can interbreed to produce fertile offspring. There are problems with classifying species, however. Some organisms reproduce asexually. This means there is no interbreeding so these organisms dont fit in with the definition of a species. Also, if you interbreed a male from one species with a female from another you get a hybrid. Hybrids cannot reproduce therefore it is hard to classify them. Finally, evolution is a continuous process. Organisms change and evolve over time, sometimes so much that it will form a new species. It can be hard to classify them.

The binomial naming system - The binomial system gives animals a two part latin name and is used by scientists all over the world. It is understood worldwide so confusion is avoided. The name comes from the genus and the species.

Common ancestors - Similar species often share a common ancestor making them closely related in evolutionary terms. This gives them similar features. However this isnt always the case. Some closely related species may look very different if they have evolved to live in different habitats, eg Camels and Llamas. To explain the similarities and differences between species you have to consider how they're related in evolutionary terms and the type of environent theyve adapted to survive in.

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Pyramids of Biomass and Numbers

Biomass - Each bar in a pyramid of biomass shows the mass of living material at that stage in the food chain. Biomass pyramids are almost always pyramid shaped as biomass is lost at each stage in the food chain. To construct a pyramid of biomass you use the dry biomass of the organisms - measuring dry biomass can be hard though as you have to kill the organisms to work it out. It can sometimes be hard to construct a pyramid of biomass as some animals feed at more than one trophic level.

Numbers - Pyramids of numbers are similar to pyramids of biomass however they show the number of organisms at each stage of the food chain rather than their mass. Pyramids of numbers can be different shapes to pyramids of numbers. For example - one pear tree will feed many aphids, meaning the pear tree bar would be shorter than the aphid bar.

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Energy transfer and energy flow

Energy from the sun is the source of energy for almost everything on earth. Plants use a small percentage of the light energy from the sun to make food by photosynthesis. This energy then works its way through the food chain. Energy is lost at each stage as its used by animals for respiration and other processes which keep animals alive. Most energy is lost to the surroudings as heat and is also lost as waste products (ie Egestion and Excretion). Waste products and uneaten parts can be the start of a new food chain.

You hardly ever get food chains with more than 4 or 5 trophic levels as all the energy is usually lost by this point.

Numbers on food chains show how much energy is available at the next level. You can work out how much energy has been lost by taking the energy available at the next level from the energy that was available at the last level.

You can calculate efficiency by using this calculation:

efficiency = energy available at next level/energy available at previous level x100

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Interactions between organisms

Competition - Organisms compete to gain the things they need to survive, eg food and shelter. There are two types of competition - Interspecific competition is where organisms compete for resources against individuals of another species whilst Intraspecific competition is where organisms compete against individuals of the same species. Intraspecific competition has a bigger impact on organisms than interspecific as the same organisms have the same needs so they will compete for the same resources.                                                                               Prey and Predator - The population of any species is limited by the amount of food available. If the population of the prey increases so will the population of the predators. However if the population of the prey decreases, so will the population of the predator. Predator - Prey cycles are always out of phases with eachother. This is because it takes a while for one population to respond to changes in another. Eg - it takes time for populations to reproduce. 

Parastites live off a host. They take what they need to survive without giving anything back, harming the host. for example, tape worms absorb lots of nutrients from the host causing them to suffer from malnutrition. Fleas are parasites.

Mutualism is a relationship where both organisms benefit. Cleaner species such as oxpeckers live on the back of buffalo. They eat pests but also alert the animal to any predators.

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Adaptations are the features that organisms have to make them better suited to their environment. This means they can fight for resources more easily and will be more able to survive, reproduce and pass on their adaptations to offspring. Organsims can be specialists or generalists:

- Specialists are highly adapted to survive in a specific habitat.

- Generalists are adapted to survive in a range of habitats.

In a habitat where conditions are stable, specialists will out compete generalists as theyre more suited to the specific conditions. In a habitat where conditions are prone to change generalists will out compete specialists as they are adapted to a range of conditions.

Biochemical adaptations to extreme conditions - Some organisms can tolerate extreme conditions ie a very high or low pH or temperature. Organisms adapted to live in seriously extreme conditions are called extremophiles. Extremophile bacteria have enzymes which work best at high temperatures without being dentatured. Organisms that live in cold conditions have antifreeze proteins which interfere with the growth of ice crystals in the cells stopping them being damaged by ice.

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Adaptations to cold environments

Most adaptations to cold environments are based on reducing heat loss to the environment. Anatomical adaptations are adaptations to the body which help organisms survive. These may include having a thick coat or layer of blubber for insulation, Having a large size and compact body shape to give a small surface area to volume ratio to reduce heat loss (less heat can be lost through the surface of the skin), or having counter current heat exchange systems:

Animals like penguins have to stand on cold ice all day. Blood vessels going to and from the feet carry blood that flows in opposite directions. The vessels flow closely to one another allowing heat to transfer between them. Warm blood flowing through arteries warms the cold blood returning to the body meaning that although the feet stay cold, the body remains warm.

Many species have behavioural adaptations to the cold, for example some species migrate to warmer climates during the winter month. Other species hibernate to save energy. Other species such as penguins huddle together to keep warm.

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Adaptations to hot and dry environments

Living in hot environments is about increasing heat loss and reducing heat gain.

Animals that live in hot environments often spend the day in the shade to minimise the heat gain. They also reduce heat gain by being more active at night when its cooler. They can also increase heat loss by bathing in water. As the water evaporates it transfers heat from the skin to the surroundings.

Anatomical adaptations - animals that live in hot environments are often small. This gives them a large surface area to volume ratio which allows them to lose more body heat to surroundings. Other adaptations like having large ears can increase an animals surface area to volume ratio. Large, thin ears allow more blood to flow near the skins surface so heat can be radiated to the surroundings. Some animals eg camels store fat in one part of their body to stop the rest of the body being too well insulated.

Dry environments - desert plants have a rounded shape giving them a small surface area to volume ratio to minimise water loss. They also have a thick waxy layer for this and store water in their stems to allow them to survive in extreme drought. Desert animals have specialised kidneys that allow them to produce concentrated urine with low water content. They have no sweat glands and spend lots of time in underground burrows (more moisture).

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Evolution and Speciation

Natural Selection -Charles Darwin concluded that organisms that are the best adapted would be more successful competitors and would be more likely to survive. This idea is called 'survival of the fittest'. The successful organisms that survive pass on their strengths to their offspring and the organisms that are less well adapted would be less likely to survive and will not reproduce. Over time, successful adaptations become more common in the population and the species changes - it evolves.

Darwins theory wasnt perfect as he could give a good explaination as to why the characteristics appeared or how organisms passed them on. We now know that adaptations are caused by mutations in DNA.

Speciation is the development of a new species. A species may change so much due to natural selection that it becomes a completely new species. Speciation happens when populations of the same species change enough to become reproductively isolated - they can't interbreed to produce fertile offspring. This can be caused by geographic isolation: This is when a physical barrier divides a population of a species meaning the populations cant mix. Mutations create new features in the different populations. Natural selection spreads the mutations and eventually the species either side of the barrier will be so different they wont be able to reproduce.

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Theories of Evolution

Darwins theory went against common religious beliefs about creation meaning religious authorities ridiculed him. He also couldnt explain why the adaptations occured as DNA hadn't been discovered. There wasnt enough evidence to support him either.

Lamarck argued that if a characteristic was used a lot by an animal then it would become more developed. He argued that these characteristics could be passed on to the animals offspring. But people soon concluded that acquired characteristics dont have a genetic basis - therefore they can't be passed on to the next generation.

Lamarck's theory was rejected and now people accept darwins theory as it has been tested by different scientists.

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The carbon cycle and decomposition

The whole carbon cycle is powered by photosynthesis. In photosynthesis plants convert the carbon from CO2  in the air into sugars. Plants can then incorporate this carbon into other carbohydrates, fats and proteins. Eating passes the carbon compounds from the plant to animals in a food chain/web. Plant and animal respiration while the organisms are living releases CO2 back into the air. When plants and animals die and decay, theyre broken down by bacteria and fungi in the soil. These decomposers release CO2 back into the air by respiration as the material is broken down. Over millions of years material from dead plants/animals can form fossil fuels. When these are burned, CO2 is released back into the air.

Decomposition is slower in waterlogged/acidic soil. This is because the bacteria/fungi that are used to decompose material usually need oxygen to respire and produce energy. Waterlogged soils dont have much oxygen so the decomposers work slower. In acidic soil, the extremes of pH slow down the reproduction of decomposers or even kill them.

Carbon can be recycled in the sea. Many marine organisms make shells out of carbonates. When the organisms die the shells fall to the ocean floor forming limestone rocks. The carbon in these rocks returns to the atmosphere as CO2 during volcanic erruptions.

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The Nitrogen cycle

The atmosphere contains 78% nitrogen which is very unreactive and therefore cannot be used directly by plants or animals. Nitrogen is needed for making proteins for growth, however. Plants get their nitrogen from the soil so nitrogen in the air has to be turned into nitrates before plants can use it. Nitrogen compounds are then passed on in food chains/webs as animals eat plants (and eachother). Decomposers break down proteins in rotting plants/animals and urea in animal waste into ammonia. This returns nitrogen into the soil.

Nitrogen fixation is the process of turning nitrogen from the air into nitrogen compounds in the soil which plants can use. There are two main ways in which this happens:
Lightning: there is enough energy in lightning to make the nitrogen in the air react with oxygen to give nitrates.                                                                                                                                   Nitrogen fixing bacteria: In roots and soil.                                                                                    There are 4 main bacterias involved in the cycle:decomposers break down proteins and urea into ammonia
Nitrifying bacteria turn ammonia in decaying matter into nitrates                                        Nitrogen fixing bacteria turn atmospheric N2 into nitrogen compounds.                                          Denitrifying bacteria turn nitrates back into N2.                                         

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Human impact on the environment

Human population increase -is increasing exponentially (extremely quickly). Population increases when the birth rate is higher than the death rate. This growth in population is putting pressure on the environment - more resources are being used up and more pollution produced. The more developed countries in the world use lots of resources and create pollution.

increasing pollution is causing global warming. When more fossil fuels are burned, they release lots of CO2 which is a greenhouse gas. These gases trap heat in the atmosphere and cause global temperatures to rise. Scientists predict that global warming will cause sea levels to rise, weather systems to become less predictable and agricultural output to fail.

The burning of fossil fuels releases a gas called sulphur dioxide. This reacts with water in the atmosphere to form sulphuric acid which falls as acid rain. Acid rain damages soil and kills trees. Acid rain also raises the pH in lakes, damaging eco systems as many organisms are sensitive to changes in pH. It also damages limestone.

CFCs are used in aerosols and fridge coolants etc. They break down the ozone in the upper atmosphere allowing harmful UV rays to reach the earths surface. This increases the risk of acquiring skin cancer and kills plankton in the sea effecting the ecosystem as plankton are at the bottom of the food chain, eventually effecting us.

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Human impact on the environment

Indicator species  can be used to show pollution. Some species can only survive in unpolluted conditions: Lichens are used to monitor air quality - they are damaged by pollution. The cleaner the air, the greater the diversity of lichen. Mayfly larvae monitor water qualtity - The cleaner the water, the more mayfly larvae there are. Other species live in polluted conditions: Water lice, rat tailed maggots and sludgeworms all live in polluted water. Rat tailed maggots and sludgeworms show high levels of pollution.

Non living methods can also be used to show pollution . Sensitive instruments can measure the concentration of pollutants eg carbon dioxide in samples of air and water. Satellite data can also be used to indicate pollution levels. Eg, satellites can show where the ozone layer is thin or absent.

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Endangered species

Factors that can cause a species to become extinct include:If the number of habitats drops, its hard for organisms to find food and shelter. If the number of individuals drops, its hard to find mates, therefore hard to reproduce meaning less genetic variation. If the genetic variation drops (the number of alleles in a population), the species is less likely to to be able to adapt to changes in the environment or survive disease.

Conservation programmes are designed to help save endangered plants and animals. You can evaluate how successful one of these programmes is likely to be by looking at: genetic variation: the species being conserved should have enough genetic variation to survive the appearance of new disease. Viability of populations: populations should be able to reproduce so they should contain both males and females of reproductive age. They should also contain large enough populations so inbreeding doesn't take place. 
 available habitats: there should be plenty of suitable habitats to live in. This is especially important if the organism is a specialist
 Interaction between species: its important that species interact as they would in their natural environment.
The programmes benefit wildlife and humans aas they protect the human food supply, ensure minimum damage to food supples, provide future medicine and help with cultural aspects.

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Sustainable development

Sustainable development means providing for the needs of todays increasing population without harming the environment.

for example, fishing quotas have been introduced to stop certian species such as cod from becoming extinct and there are laws which state that logging companies must plant trees to replace the trees they cut down.

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