OCR Biology B2a-h

B2a - Classification There are two ways to classify organisms: Artificial (based on observable characteristics) Natural (based on similarities in DNA) The seven levels of classification: Kingdoms - Animals, Plants, Fungi, Bacteria, Proctoctists Phyla/Phylum - Each Kingdom is sub-divided into Phyla. Animals = vertebrates (Arthropods, Cnidarians, Annelids, Molluscs) Class/Classes - Each Phylum is divided into classes (e.g. Arthropods) Orders - Each class is divided into orders (the class of mammals contains the orders 'Primates' and 'Carnivores' Families - Orders are divided into families (the order of carnivores contains 'Felidae' and primates contains ' Homindae') Genera - Families are divided into Genera (the family felidae contains the genus 'Panthera' and homindae contains 'Homo' Species - Genera are divided into species, just one type of organism is included (the genus pathera contains 'Leo' and 'Tigns' CNIDARIANS : SOFT-BODIED ORGANISMS MADE OF ONLY 2 LAYERS OF CELLSMOLLUSCS : SOFT, UNSEGMENTED BODIES (SHELL)ANNELIDS : RING-LIKE SEGMENTSARACHNIDS : 4 PAIRS OF JOINTED LEGSINSECTS : 3 PAIRS OF JOINTED LEGS, 2 WINGSMYRIAPODS : JOINTED LEGS ON EACH BODY SEGMENTCRUSTACEANS : MORE THAN 4 PAIRS OF JOINTED LEGSSPECIES = A group of similar organisms that are capable of inter-breeding to produce fertile offspringOrganisms are sometimes difficult to classify because: Many organisms do not fit into one group Hybrids Asexual organisms (e.g. bacteria) Evolution Organisms that are not closely related yet look similar probably look the same because of: Evolution Common ancestors Organisms that are closely related yet look very different probably look different because of: Evolution Different breeds

B2b - Energy FlowFood chains = show the transfer of energy from organism to organism Sun - Grass (producer) - Grasshopper (Primary consumer) - Shrew (Secondary Consumer - Owl (Tertiary Consumer)Plants = Photoautotroph - automatically creates own food in response to light (using sun's energy)Pyramid of numbers = show the number of organisms at each trophic levelPyramid of biomass = show biomass of total number of organisms at each trophic level. Always a true pyramid shape as energy is lost at each levelEfficiency of energy transfer = energy transferred to next level x100 energy in previous level

B2c - RecyclingCarbon enters living organisms by photosynthesisCarbon is released from living organisms by respiration and combustionThe key role of microbes in the carbon cycle is decomposing dead organisms and their wasteHumans are leading to an imbalance in the carbon cycle because of deforestation and combustionThe carbon cycle in a marine ecosystem: Carbon dioxide dissolved in water Photosynthesis leads to marine organisms producing carbon-compounds Feeding and digestions leads to marine animals using carbon to produce calcium carbonate shells Sedimentation leads to layers of shells at the bottom of the ocean forming sedimentary rocks (e.g. limestone) Volcanic eruptions and weathering starts the process again The nitrogen cycle:

B2c - RecyclingCarbon enters living organisms by photosynthesisCarbon is released from living organisms by respiration and combustionThe key role of microbes in the carbon cycle is decomposing dead organisms and their wasteHumans are leading to an imbalance in in the carbon cycle because of deforestation and combustionThe carbon cycle in a marine environment: Carbon dioxide dissolved in water Photosynthesis causes marine organisms to produce carbon compounds Feeding and digestion leads to marine animals using carbon to produce calcium carbonate shells Sedimentation leads to layers of shells at the bottom of the ocean forming sedimentary rock (e.g. limestone) Volcanic eruptions and weathering starting the process again The nitrogen cycle:

B2d - InterdependenceInterdependence = the relationships between organisms that live togetherCompetition: In habitats where organisms live together, there is often competition for resources such as: Food A mate Nesting materials Territory Water 2 types of competition: IntERspecific = competition between different species IntRAspecific = competition within a species Intraspecific is often more significant as members of the same species occupy the same ecological niche (way of life/role within ecosystem)Parasitic relationships : In a parasitic relationship, the parasite benefits whereas the host is harmed.Endoparasites = live inside the body e.g. tapewormEctoparasites = live outside the body e.g. tick, fleaMutualism = also called symbiosis; both species benefit. e.g. legume and nitrogen-fixing bacteriaBenefits to legume: Supplied with nitrate that can be combined with glucose to make amino acids, these join together to make proteins Enables the plant to grow in soil lacking nitrate to reduce competition with other plants Benefits to nitrogen-fixing bacteria: Supplied with food in the form of glucose from the plant's photosynthesis The nodules protects them from oxygen which would denature their enzymes

B2e - AdaptationsAdaptations are characteristics that make an organism better able to compete and survive within an environmentSurface area to volume ratio:SA : VOL (determined by size and shape)If you increase the size of the animal the SA : VOL decreasesOrganisms that have a large SA : VOL are either: Small Thin or Flat Organisms that have a small SA : VOL are either: Large Fat or Round COUNTER CURRENT HEAT EXCHANGE SYSTEM(OPPOSITE) (THE FLOW OF BLOOD) (TRANSFER OF HEAT FROM ONE PLACE TO ANOTHER) (PHYSIOLOGICAL ADAPTATION)Heat from the blood travelling through the artery is transferred into the colder blood flowing through the vein. This means that heat is retained close to the body's core, so enzymes are maintained at their optimum temperature.Biochemical adaptations (e.g. thermostable enzymes)Thermostable = thermo (heat) & stable (doesn't change)Enzyme = protein (doesn't change when exposed to heat)Denatured = active site has changed shape, reactions are not catalysed, reactions happen too slowly to maintain life e.g. respiration

B2f - Natural SelectionDarwin's theory of natural selection:Factors that may constitute 'struggle' for survival: Harsh environment Lack of food and water Natural competition Predators Mates & Breeding Lamarck's theory of natural selection: A characteristic that is used more and more by an organism becomes bigger and stronger, and one that is not used eventually disappears Any feature of an organism that is improved is passed onto its offspring Speciation = the development of a new species from an existing one, it is usually the result of: Geographical isolation Reproductive isolation

B2g - Population and pollutionPollutant Effect Negative consequence(s) Carbon dioxide and methane Global warming and greenhouse effect Ecosystem damagedSulphur dioxide Acid Rain Acidification of lakesCFC's Depletion of the O-Zone layer Skin cancer & eye damageFertilisers Eutrophication Stagnant water system

B2h - SustainabilityEndangered species = number of individuals of that species is very low and the species therefore is at risk of extinctionSustainable development = development which meets the needs of the present without compromising the ability of future generations to meet their own needs Fishing (increase mesh size, fishing quotas, limit of days at sea) Woodland (Leaving stumps of trees, replanting) Developed countries: Produce more waste Eat more food Use more energy