B2 biology revision


classification organises living organisms into groups 

based on characteristics

the largest groups are called kingdoms 

then split up into smaller smaller groups :







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Classification is important because it helps us understand how organisms are related and how they interact

They are grouped into five kingdoms 

Members of plant kingdom-multicellular/cell walls/energy from the sun to make own food by photosythesis 

Animal kingdom-multicellular/no cell walls/feed on other organisms

Fungi kingdom -single celled or multicellular/cell walls made of chitin/reproduce using spores

Protocitista kingdom-single celled/nucleus controlls cell

Prokaryote Kingdom -single celled/no neucleus 

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Arthropods and evolutionary relationships

Arthropods are split into four main groups 





Eveloutionary relationships can be shown on eveoloutionairy trees 

they show how closely related species are to eachother

some are common ancesters like dolphins and whales 

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organisms of the same species can breed together

a species in a group of organisms can interbreed to produce fertile offspring 

Bionomal system:

each species given a two part latin name reffering to genus the second refers to species 

bionomal system is used by scientists who speak different languages who can call them by the same name stops species being confused 

Variation in any species:

even if they look different they may have features in common eg whales and dolphins are closely related and look alike with similar habitats 

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Food chains and food webs

Food chains shows what eats what in an ecosystem 

food chains always start with a producer (make own food)

an animal that eats a producer is called a primary consumer 

secondary consumer eats primary consumers 

food webs are made up of lots of food chains joined together 

A change to the number of organisms can affect the food chains 

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pyramids of bio mass

pyramid of biomass=mass of living material at that stage of the food chain 

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Energy transfer and energy flow

all the energy from the sun is a source of energy for nearly all life on earth

plants absorb light for photosythesis to make their own food 

energy is passed through the food chain as animals eat the plants and eachother

trophic level energy is lost as heat from respiration

the amount of energy stored in each type of organism are presented and can be calculated energy lost at 1st trophic level =80 000kj-10000kj eg and so on differs on every diagram 

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Interactions between organisms

Population size is affected by competition for resources

Animals compete for food /water/shelter and mates 

plants compete for minerals in soil and water and light 

Some species rely on other species for survival

this is called interdependance two types:

parasitic relationship=parasites live on or in a host 

mutualistic relationship=both organisms benefit 

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Predators prey and adaptation

Size of population depends upon food 

population of prey increases predators will also increase

predators increase prey will decrease

Adaptations help organsisms to survive :

some adaptations keep anaimals safer than others

predators are adapted for hunting prey most predators have binocular vision eyes on front of head 

prey are adapted for avoiding predators 

prey have eyes on the side of their head they have a wide field of view to see predators 

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Adaptations to hot and cold environments

And some organisms are adapted to living in cold environments 

Anatomical adaptations to cold reduce heat loss like a layer of fat to insulate /larger in size and small ears give a smaller surface area

Some organisms are adapted to living in hot environments 

Annatomical to heat can increase heat loss 

being small large surface area heat can escape quicker

large ears large surface area

storing fat in one part of the body to prevent good insulation 

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Adaptations to dry environments

some desert plants have a small surface area to reduce water loss 

some have stems allowing more space for storing water

long shallow roots to absorb water

Some dessrt animals have no sweat glands 

some spend lots of time in underground burrows to prevent the moisture of the air getting to them 

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Theory of evolution

natural selection causes evolution

Charles darwin

As the environment changes some animals and plants species can survive and evolve to cope those that cant become extinct

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The carbon cycle

living organisms need carbon 

plants/animals take in chemicals as they grow

use elements to make new tissue

it works like so:::::

-plants remove co2 by photosythesis

carbon from co2 to make plant material

animals feed on plants both plant/animal respiration releases co2 back into the air

plants and animals eventually decay and when they die they are broken down by decomposers 

such as bacteria and fungi

release co2 back into the air/carbon recycled and used again combustion burning of fossil fuels 

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The nitrogen cycle and decomposition

Nitrogen is recycled in the nitrogen cycle


nitrogen is very unreactive 

neede to make proteins

plants gain nitrogen from soil and nitrates 

nitrogen in the air has to be turned into nitrates before plants can use it

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Human impact on the environment

Human population is increaseing

its rising exponentially (faster and faster)

birth rate higher/death rate lower

more population means less resources and more things like household waste

Increasing amounts of population are causing 

global warming

acid rain-fosil fuels produce sulfur dioxide and acid rains form damages soil and kills trees/fish

ozone depletion -CFCS used in aerosoles and fridges break down ozone and allows more harmful uv rays increasing risk of skin cancer

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Endangered species

endangered species are those at high risk of becoming extinct 

theres lots of causes:

climate change

habitat destruction




We can protect them by :education programmes/protected habitats/legal protectio(laws on hunting)

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conservation programmes

benefit wildlife and humans

protects human food supply over fishing fewer fish conservation ensures people of the future still have fish to eat

reducing damage to food chains conserving one species may help others survive

providing future medicines stop plants/animals becoming extinct 

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sustainable development

sustainable development - means providing for the needs of todays increasing population without harming the environment 

we can maintain sustainable resources such as wood and paper are being made from less cut down trees

-only burning wood products from sustainably managed forests 

-not buying certain fish 

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case study whales

some species are endangered

whales have commercial value and therefore increasingly becoming even more rare

using whales close to exitinction is happening

some are kept in captivity but some say this is unfair to the whales 

not much space 

but does allow breeding preventing extinction 

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