Biology B2

Understanding our environment - OCR gateway.

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  • Classification is organising living organisms into groups.
  • They show how organisims are related, (evolutionary relationships), and how they interact, (ecological relationships).
  • Natural classification systems are based on the evolutionary relationships and genetic similarities between organisms.
  • Artificial classification systems are based on appearence rather than genes.
  • Living things are divided into kingdoms which are then subdivided into... phylum, class, order, family, genus - a closely related species and species which can produce fertile offspring.
  • Classification systems change over time e.g. when new species are discovered and more knowledge is gained.
  • DNA sequencing allows us to see genetic differences.
  • Evolutionary realtionships can be shown on an evolutionary tree.
  • Studying lots of organisms means that lots of data is collected which is only possible due to advances in IT.
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  • A species is a group of organisms which can interbreed to produce fertile offspring.
  • It is hard to always classify organsims into species due to...
  • Asexual reproduction - organisms such as bacteria reproduce by making a copy of itself meaning there is no interbreeding.
  • Hybrids - a cross between two species but they are infertile so it's hard to class them.
  • Organisms change and evolve so they may have to be classified differently.
  • The binomal system is what gives species its name e.g. Homosapiens. The first part, Homo refers to the genus and the second part, Sapiens is the species.
  • Closely related species have recent common ancestors.
  • To explain the similarities and differences between species you have to consider how they are related in evolutionary terms and the type of environment they've adapted to survive in.
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Pyramids of biomass and numbers.

  • Each bar on a pyramid of biomass shows the mass of a living material at that stage of a food chain.
  • The organism at the bottom of the food chain goes at the bottom of the pyramid.
  • To construct a pyramid you need to use dry biomass.
  • This means the organisms must have no water in them before being weighed.
  • Pyramids of numbers show the number of organisms not their mass. 
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Energy transfer and energy flow.

  • Energy from the sun is the source of energy for nearly all life.
  • Plants use a small amount of this energy for photosynthesis. This energy then works its way through the food chain.
  • The energy is lost at each stage due to resperation and heat.
  • Material and energy is also lost from the food chain as waste.
  • Material and energy are both lost at each stage of the food chain.
  • This explains why you get biomass pyramids. Most of the biomass is lost and so doesn't become biomass on the next level.
  • Also it explains why you rarely get food chains with more than 5 trophic levels.
  • So much energy is lost at each stage that there's not enough to support organisms at above 5 trophic levels.
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Interactions between organisms.

  • Organisms compete to survive.
  • A species ecological niche is how it fits in to its ecosystem. It depends on where they live and what they feed on.
  • Interspecific competiton is where organisms compete for resources against another species.
  • Intraspecific competition is where organisms compete for resources against individuals of the same species.
  • Population of prey and predator are related.
  • Predator-prey relationships are out of phase with each other.
  • Parasites live off a host. They take what they need to survive but don't benifit the host.
  • Mutualism is a relationship where both organisms benefit.
  • Cleaner species e.g. oxpeckers live on the backs of buffalo. They eat pests on the buffalo providing them with a food source. Also they alert the buffalo to any predators by hissing.
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  • Adaptations help organisms survive.
  • Sepcialists are organisms which are highly adapted to survive in a SPECIFIC HABITAT. For example giant pandas only eat bamboo.
  • Generalists are organsims that are adapted to survive in a RANGE OF DIFFERENT HABITATS. For example black rats.
  • In a habitat were the conditions are stable a specialist will be better than a generalist but, if conditions are changing it will be the other way round.
  • Some organisms have biochemical adaptations to extreme conditions.
  • They are called extremophiles.
  • E.g. extremophile bacteria have enzymes which have a higher optimum temperature. These enzymes can work normally at temperatures that would denature enzymes from other organisms.
  • Organisms that live in cold environments have special antifreeze proteins.
  • These interfere with the formation and growth of ice in the cells. 
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Adaptations to cold environments.

  • Anatomical adaptations are features of an organism's body which help it survive.
  • Anatomical adaptations to the cold are:
  • Thick coat/layer of blubber which insulates the body and traps heat.
  • Small surface area to volume ratio which reduces heat loss.
  • Also 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 pass close together allowing heat to transfer between them. Warm blood flowing in arteries to the feet heats cold blood returning to the heart in the veins.
  • This means feet stay cold but it stops cold blood from cooling down the rest of the body.
  • Some organisms also have behavioural adaptations, e.g. migrating, hibernating or huddling.
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Adaptaions to hot and dry environments.

  • Behavioural adaptations include staying in the shade or underground, being active at night and bathing in water - water evaporates transfering heat from skin to the environment.
  • Anatomical adaptations include large surface area to volume ratio, large thin ears which allows more blood flow to the surface, storing fat in just one part of the body to stop insulation.
  • Some organisms are adapted to living in dry environments
  • Desert plants...
  • Have rounded shape giving them small SA:V ratio to minimise water loss.
  • Thick waxy layer (cuticle) and spines instead of leaves to reduce water loss.
  • Store water in their stems to allow them to survive in drought.
  • Shallow but extensive roots to absorb maximum water quickly.
  • Desert animals...
  • Specialised kidney that allows them to produce urine with low water content.
  • No sweat glands.
  • Spend lots of time underground.
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Evolution and specification.

  • Darwin came up with the thoery of evolution called natural selection.
  • He knew that organisms show wide variation and compete for limited resources in an ecosystem.
  • He concluded that the organisms best adapted are more likely to survive, 'survival of the fittest'.These successful organsims than reproduce and pass on there characteristics to their offspring.
  • New discoveries e.g. DNA helped develop the theory of natural selection.
  • New adaptations arrive because of mutations.
  • Over a long time an organism can evolve so much a new species is created, this is called specification.
  • This happens when populations of the same species change enough to become reproductively isolated - this means they can't interbreed.
  • Reproductive isolation can be caused by geographic isolation...
  • A physical barrier divides a population e.g. a river.
  • Different mutations then create new features in the two groups. Natural selection then occurs, if the features are successful they are passed on.
  • Since conditions on either side of the barrier will be different the organisms will adapt differently.
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Theories of evolution.

  • Darwins theory of evolution by natural selection was conterversial at the time because...
  • It went against religious beliefs.
  • Darwin couldn't explain why new characteristics appearered.
  • There wasn't enough evidence.
  • Lamark had a different theory...
  • He said that if a characteristic was used a lot by an animal then it would become more developed.
  • Lamark thought that these acquired characteristics could be passed on to the animals offspring.
  • However people concluded that acquired characteristics don't have genetic basis.
  • Now most people believe Darwins theory.
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Human impact on the environment

  • As human population rise so does the pressure on the environment.
  • Increasing amount of pollution is causing,
  • Acid rain, global warming and ozone depletion.
  • Indicator species show pollution e.g...
  • Lichens are used to monitor air quality. They are damaged by pollution so the cleaner the air the greater diversity of lichens.
  • Mayfly larvae are used to monitor water quality because they can't survive in polluted water.
  • Some species have adapted to living in polluted conditons. 
  • For example water lice, rat tailed maggots and sludgeworms all indicate polluted water.
  • Measuring pollution level with indicator species is quick. It's good at telling you if an area is polluted or not but not by how much.
  • Also factors such as temperture can determine if a species survives.
  • Another way to test for pollution is by non-living methods.
  • Sensitive instruments and satellite data can measure concentrations of pollution.
  • However this is more expensive than indicator species.  
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Endangered species

  • Many factors cause a species to become exitinct.
  • Habitats, number of individuals, genetic variation.
  • Conservation programes are designed to help save endangered species.
  • Genetic variation - the species being conserved must have enough variation to adapt.
  • Viabilty of populations - must be able to reproduce.
  • Available habitats - plenty of sutible habitats to live in.
  • Interaction between species - must interact like in the wild.
  • Conservations programmes benifit wildlife and humans.
  • Protecting human food supply - overfishing has led to reduced fish stocks, conservation programmes ensure a food source for future generations.
  • Ensuring minimal damage to food chains - if one species becomes extinct it has a knock on affect on the whole food chain.
  • Providing future medicines.
  • Cultural aspects - species can be important to a nations heritage.
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Sustainable development

  • Sustainable development means providing for the needs of today's increasing population without harming the environment.
  • What is being done to promote sustainable development?
  • Fishing quotas have been introduced to prevent some becoming extict.
  • There are laws that say if companies cut down trees they must plant more.
  • Whales are endangered...
  • They have commercial value when they're alive and dead - they're a tourist attraction, there meat and oil can be used and they can make cosmetics from a substance in their intestine.
  • The international whaling commission has got nations to stop whaling.
  • Norway is the only country that still catches whales.
  • However its hard to check countries are sticking to rules so lots of illegal whaling goes on.
  • Some whales are in captivity this causes different views...
  • They don't have much space.
  • Captive breeding programmes allow whales to be bred and released back into the wild.
  • Research helps understand them better.  
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This information is really helpful to me , I am now able to understand the natural selection clearly now. 

Thank you,



thank you so so so much!!! yours is one of the best that matches my specification sheet! thanks

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