B1A Edexcel

Biology edexcel summary 

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  • Created by: Dementia
  • Created on: 13-11-11 20:39

Energy and Biomass

Pyramid of Biomass: Biomass is how much each creature would weigh in each level of the pyramid. As you go up each trophic level the mass decreases.

Pyramid of numbers: This shows the number of organisms in a food chain but they’re not always in a pyramid shape. This is why the biomass is more effective as it always shows an accurate way the energy is lost in the food chain.

Energy disappears in a food chain. Plants convert a small percent of the light energy into glucose which the rabbit eats. It uses up some of the energy from the plant and stores the rest in its body. The fox then eats the rabbit to gain energy. Energy is lost through many ways like respiration and movement. The main cause of energy loss would be heat; this is especially true for mammals and birds whose body must be kept at a constant temperature. Material and energy are also lost in the waste from the droppings.

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Competition & Population

Plants compete for space, light, water and nutrients from the soilAnimals compete for space, food, water, mates, shelter, and nesting/breeding sites.

Intra-species: This competition can be within a species

Inter-species: competition between different species

Competition is one factor affecting the population; other factors include the amount of food or nutrient, the number of predators, and disease.

If the population of the prey increases so does the predators' population. However, as the population of predators increases, the population of prey will decrease.

This relationship is known as interdependencewhen living things rely on others for their existence.

Computer Modelling can be used to predict the future of the number of prey and predators. It's very quick but real ecosystems are very complicated and computer models are only an approximation of real life.

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Fossil show how today's species have evolved over million of years.

3 ways fossils can be formed:  

1) From gradual replacement by minerals: Things that don't decay can last long when burried, these are then replaced by minerals forming a rock-like substance allowing the fossil to stay distinct inside the rock.

2) From Casts + Impressions: Fossils form when an organism's burried in a soft material like clay which hardens around and it decays, leaving a cast of itself which leaves an impression.

3) From preservation in places no decays happen: glaciers (too cold), Peat bogs (too acidic), in amber or tar pits (no oxygen or moisture) 

Fossils found in rock layers tell us 2 things:

1) What the creatures and plants looked like

2) How long ago they existed- the deeper the rock the older the fossil

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Evolution 2

However, fossil records are incomplete because very few dead plants or animals turn into actual fossils (most decay away)

The fossil record of the horses provide strong evidence for the theory of evolution - shows the forefeet adapting to the modern environment.

If a species cannot evolve quickly enough, it will become extinct.

3 ways a species can become extinct:

1) The environment chamges quicker than the species can adapt

2) A new predator or species kills them all

3) They can't compete with another (new) species for food 

As the environment changes it will favour certain characteristics which will be present in more of the population

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Natural Selection

Charles Darwin's 2 theories:

1) Not all offspring surive, which shows that all struggle for survival. Being eaten, disease and competition causes many to die.

2) The organisms that have characteristics to survive and reproduce better (useful adaptions) will pass on these characteristics.

"Survival of the Fittest": the organisms with less survival value probably die away first, leaving the fittest to pass on their genes to the next generation.

Populations adapt to changes in the environment. These changes only occur from generation to generation. Natural selection says that over generation as they adapt to the different characteristics you will end up with totally different species.

Darwin's theory had many issues: It was the only explanation for our own existence but was bad news for the religious authority who tried to ridicule Darwin's ideas. This was also hard to accept by humans and easy to take the mick out of.  

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Keep: Kingdom - move and feed (organisms)

Ponds: Phylum - have a spinal cord

Clean: Class - have fur + produce milk

Or: Order - ape-like animals

Frogs: Family - human-like animals

Get: Genus - humans

Sick: Species - modern-day humans

The latin names can be identified by the order, as the two specific classifications are in italics and the first one will be capitalised. E.g Homo sapiens: This will be genus species

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Classification 2

Vertebrates are divided into 5 groups called classes:

Fish: live in water, have scales + gill for gas exchange

Amphibians: inhabit both land + water, need water for reproduction, able to breathe through their permeable skin and cold-blooded

Reptiles: more adapted to live on land, have dry-scaly skin, which stops them losing too much water, cold-blooded and lay eggs

Birds: most can fly due to the feathers, beaks to crack seeds or to catch preys

Mammals: Have fur to keep warm, give birth to their offspring and produce milk

Some organisms fit into more than one group.

For example Euglena - one celled organism photosynthesises like a plant but moves like an animal.

As more groups are added organisms like euglena can be suitably organised.

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Changing Species' Characteristics

Selective breeding: Individuals with specific characteristics are selected and bred to produce offspring with desirable features. This process reduces variation as the same animals or plants are bred from again and again.

Genetic Modification: Genes (DNA) from one organism are impanted into another organism to introduce certain characteristics, can be from the same or different species.

Ethical issues of GM crops: 

1) Some people say the GM crops affect the number of wildlife that live around the crops which reduces the number of species in an ecosystem.

2) Some people believe that GM crops are not safe as they may develop allergies in the food.

3) A big concern is that transplanted genes may get into the natural environment. 

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Human Activity and the Environment

Burning fossil fuels: like coal, oil and natural gas, cars and power station burn these in large quantities, releases CO2, causes acid rain

Releasing CFCs: Used in aerosols, old fridges, air-conditioning etc. They're thinning the ozone layer, which allows the harmful UV rays to reach Earth's surfaces, increasing the risk of cancer.

Deforestation: Trees are cut down for timber + to provide land for agriculture, increasing the loss of species, increases CO2 levels when burnt and decreasing photosynthesis to remove CO2 from the atmosphere.

General pollution + Waste disposal: human activity can pollute water, air and land. We also produce a lot of waste increasing the pollution in the atmosphere.

The population is increasing rapidly due to the medicines, which has stopped a widespread of deaths. Also due to the modern farming methods which provides food for all hungry mouths.

More humans = Greater Impact

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Farming methods

Intensive farming: produces large yield

Organic farming: produce a small quantity but provide lots of space for the animals and produce as little pollution as possible. The overall price is more due to the reasons below.

Intensive farms:

  • Cost a lot to set up
  • tend to specialise in one product
  • needs less land than organic farms
  • use fertilisers and pesticides (cost-effective)
  • Use machines to get the work done

Organic farm:

  • cost little (but a lot to run)
  • need more land than intensive farming to produce same volume
  • use organic fertilisers (costs more)
  • manual labour to get the work done
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