A2 BIOLOGY EDEXCEL UNIT 4 TOPIC 5.1 and 5.2

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KEY TERMS

ecology- the study of living organisms in their environment and how the interact with the biotic and abiotic factors in that environment

biosphere- the part of the atmosphere inhabited by living organisms

ecosystem- the community (all the populations of different species interacting with each other) and abiotic environment interacting together

species- group of organisms that can breed to produce fertile offspring (eg. zonkey and liger wouldnt normally breed but occasionally produce fertile offspring)

population- how many of the same species are in the same area

biodiversity- the range of different things living in an ecosystem

habitat- the characterists of the type of environment where an animal lives

niche- a set of specific ways of living that can only be occupied by one species in certain habitat

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ECOLOGY KEY TERMS

succession- where an ecosystem develops from nothing

litteral zone- area around water edge (algea often grows first)

anthropogenic factors- biotic or abiotic factors that arise from human activity

primary succcession- pioneer phase (botanical mavericks/ organisms that can cope with extreme conditions)- they start to break up thte surface of the soil so they change the conditions in a habitat just enough to make it suitable for other species

climax community- a community dominated by trees (sometimes they are not trees eg. Scotland) this remains unchangable and often has the lowest biodiversity

dominant species-  largest or most abundant

secondary succession- existing community has been cleared, secondary succession starts eg. forest fire, ploughed field (this would otherwise lead to forest climax community)

deflected succession- community remaims stable because human activity prevents succession eg. sheep grazing, mowing, burning

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BIOTIC AND ABIOTIC FACTORS

BIOTIC FACTORS:

biotic factors are generally density dependent- he effects are related to the size of the population relative to the area available.

mutualism / grazing / predation / parasitism/ intraspecific competition (competition withing species) / interspecific competition (competition against other species)

epiphite- plants that grow on other plants eg. orchids

ABIOTIC FACTORS:

oxygen availability / solar energy input / climate / edaphic (soil factors) / pollution / topography (slopes, cliff face etc.)

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PRODUCERS AND PRODUCTIVITY

Foodchains begin with photosynthesis becuase it starts with the producers, the photosynthesisng plants.

autotrophs- self feeding (because they cannot move, run or hide) they are able to make their own organic compounds from inorganic compounds

primary productivity- the rate at which energy is incorporated into organic molecules in an ecosystem

other autotrophs are chemosynthetic atotrophs- make organic molecules using energy released from chemical reactions

productivity and biodiversity are linked- primary productivity of terrestrial vegetation is usually positively correlated with plant diversity; high productive=high plant diversity. There is higher animal diversity when higher primary productivity. Not always a positive correlation between plant productivity and animal diversity, eg. eutrophic lake- increased algal productivity creates layer on water so lower diversity of animals underneath especially when algae die and decompose so oxygen is used up by decomposition.

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OVERVIEW OF PHOTOSYNTHESIS

CO2 is reduced

reaction uses more energy to break bonds than make the products so energy is released. products are at lower energy level so act as a store of energy.

releasing hydrogen from water- water is split into hydrogen and oxygen but requires energy, process= photolysis

storing hydrogen in carbohydrates- H2 reacts with CO2 to store hydrogen. CO2 reuced to form carbohydrate fuel glucose (stored and converted to other molecules)

Photosynthesis is controlled by enzymes and the reactions occur in two main stages:

  • Light-dependent reactions= energy from light and hydrogen from photolysis of water- produces reduced NADP, ATP and waste product oxygen
  • Light-independent reactions= uses reduced NADP and ATP to reduce CO2 to carbohydrates
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STRUCTURE OF A CHLOROPLAST

          

Palisade mesophyll cells in leaves are packed with loads of chloroplast

*thylakoid membrane (contains proteins inc. photosynthetic pigments and electron carriers), *stroma (contains enzymes needed to carry out L-ID R) *starch grains (store the product of photosynthesis), *DNA loops (the chloroplasts contain genes for some of their protiens), *smooth outer membrane (freely permeable to CO2 and H2O), *smooth inner membrane (contains many transporter molecules- regulates what passes in and out inc. sugars and proteins synthesised in the choloplast but used within the chloroplast).

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LIGHT-DEPENDENT REACTION

(1) light absorbed by the thylakoid membranes in chlorophyll and energy from light raises 2 electrons to higher energy level= 'exceited state'

(2) electrons leave 'excited' chlorophyll and pass along electron carriers in thylakoid membrane- these molecules make up the electron transport chain

(3) electrons pass along the carriers alternating between being oxidised or reduced losing energy

(4) the energy lost is used in the synthesis of ATP- process called photophosphorylation

(5) electrons lost must be replaced- replaced by photolysis (splitting of water) catalysed by and ezyme in the thylakoid space as it produces hydrogen ions, oxygen gas and electrons

(6) electrons that have passed along chain combine with co-enzyme NADP and hydrogen ions to produce water and reduced NADP

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THE ROLE OF ATP

ADENINE---RIBOSE---PHOSPHATE---PHOSPHATE---PHOSPHATE

The highest energy released occurs when the bond between the second and third phosphate groups breaks because it requires the least energy to break and then releases a lot a energy when it bonds with surrounding water molecules. This energy can then be used to drive energy-requiring reactions in the cell.

ATPase catalyses the breakdown of ATP to ADP:

ATP in water ----> ADP + hydrated P + energy

HOW TO MAKE ATP

photophosphorylation- the addition of P to ADP and light to make ATP.

ATP in water is a better way of storing the chemical potential energy, it therefore transports energy around the cell

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LIGHT-INDEPENDENT REACTION

This takes place in the stroma and uses reduced NADP and ATP from the light-dependent reaction.

CO2 reduced to carbohydrate

NADP acts as a hydrogen carrier keeping hydrogen loosly bonded so it doesnt react with the oxygen 

Oxygen goes from H2O to CO2

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CALVIN CYCLE

(http://images.tutorvista.com/content/nutrition/calvin-cycle-diagramatic-presentation.jpeg)

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