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Summary Biology Edexcel A full notes (SNAB) topics 1-8
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Summary of 7 pages for the course Topic 5 at PEARSON (All notes)
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TOPIC 5ECOSYSTEM
Ecosystem – all organisms living in a particular area and all the abiotic factors
Habitat – place with a distinct set of conditions where an organism lives
Population – group of interbreeding individuals of one species in a habitat
Population size/abundance – the number of individuals of one species in a particular area
Community – all the organisms of different species that live in the same habitat and interact with each other
Distribution – where a species is within a particular area
Abiotic – non living/physical features of an ecosystem
- Solar energy input
- Climate i.e. rainfall, wind exposure and temperature
- Topography
- Oxygen concentration
- Edaphic factors – soil i.e. soil pH and mineral ion concentration
- Pollution
- Catastrophes e.g. earthquakes, floods
Population size varies because of abiotic factors
- When abiotic conditions are ideal, the organism can grow fast and reproduce successfully e.g. temperature of a
mammal’s surroundings - don’t have to use up as much energy maintaining body temperature so more energy can
be used for growth and reproduction so population size will increase
Biotic – living features of an ecosystem
- Competition
- Grazing, predation, disease – relationship between 2 organisms where one benefits at the other’s expense
- Mutualism
Biotic factors are density dependent – effects are related to the size of the population relative to the area available
Interspecific competition reduces population size
- Resources i.e. food available to both populations are reduced because they have to share
- So less energy for growth and reproduction
- So population sizes lower
Interspecific competition can affect the distribution of species
- One species out competes the other because it is better adapted to its surroundings
Intraspecific competition causes fluctuations to population size
- If resources are plentiful, the population of a species increases
- As the population size increases, more organisms compete for the same amount of space and food
- Eventually, resources become limiting because there isn’t enough for all the organisms so the population begins to
decline
- A smaller population means there is less competition for space and food which is better for growth and
reproduction so population starts to grow again
- Carrying capacity – maximum stable population size of a species that an ecosystem can support
Predator and prey population sizes are interlinked
- An increase in prey population means there more food available for predators so the predator population grows
- An increase in predator population means more prey are eaten so the prey population falls (although other factors
are involved e.g. availability of food for the prey)
- The decrease in prey population means there is less food for predators so the predator population decreases
Anthropogenic factors arise from human activity
The niche concept can explain the abundance of different species
- 2 species occupying the same niches will compete e.g. food source
- Fewer individuals of both species can survive in the area because the amount of food available to both species is
reduced
- There will be fewer individuals of both species in the same area
The niche concept can explain the distribution of different species as organisms can only exist in habitats where the
conditions that make up their role (niche) exist
SUCCESSION
Succession – change in a community over time
Primary succession – starts in newly formed habitats where there has never been a community before
Succession:
, 1. Pioneer species colonise bare rock
- Pioneer species can cope with extreme/hostile conditions because of xerophytic characteristics
- Pioneer species break up rock surface which allows organic material to accumulate with the broken rock as
the beginnings of soil
2. This causes a change in conditions which makes them less hostile
- The soil is able to retain water so small, shallow rooted plants e.g. mosses can germinate and survive
- These plants then die and decompose, adding more organic material which makes the soil
- Biodiversity is at its peak
- The conditions continue to improve and change so larger, taller plant species can colonise
- The new plants outcompete plants already existing and replace the existing community
3. A stable climax community is reached
- Normally dominated by trees
- Remains unchanged unless conditions in habitat change
- Lower biodiversity as dominant species has outcompeted others
- Types of species depended on climate of ecosystem
Climatic climax – climax community for a particular climate
As succession progresses, the number of niches and species increases
At each stage of succession, the species are better adapted to the conditions so the out compete already existing
species
Secondary succession – on bare soil, where an existing community has been cleared
Some pioneer species are adapted to take advantage of the new bare soil where there is little or not competition
- Seeds widely dispersed by the wind
- Rapid growth
- Short life cycle
- Abundant seed production
Deflected succession – community remains stable because human activity prevents succession (plagioclimax)
PHOTOSYNTHESIS
Phosphorylation – adding phosphate to a molecule e.g. ADP phosphorylated to ATP
Photophosphorylation – adding phosphate to a molecule using light
Photolysis – splitting of a molecule using light energy
Hydrolysis – splitting of a molecule using water e.g. ATP hydrolysed to ADP
Photosystem – cluster of photosynthetic pigments e.g. chlorophyll a, chlorophyll b and carotene surrounding a primary
chlorophyll molecule in the thylakoid membrane
- PSI absorbs best as wavelength of 700nm and PSII absorbs best at 680nm
6 CO 2+ 6 H 2 O+energy → C 6 H 12 O6 +6 O2
Chloroplasts
- Double membrane
- Thylakoids have large surface area so can absorb as much light energy as possible
Thylakoid membrane
- System of interconnected flattened fluid filled sacs
- Contains chlorophyll and electron carriers
- Contains ATP synthase molecule for make ATP
- Contains photosynthetic pigments (chlorophyll a, chlorophyll b and carotene)
Thylakoid space
- Fluid within thylakoid membrane sacs containing enzymes for photolysis
Stroma
- Fluid surrounding thylakoid membranes
- Contains all enzymes needed for light independent reaction
- Contains oil droplets which store non – carbohydrate organic material
Starch grain
- Stores product of photosynthesis
Granum
- A stack of thylakoids joined to one another with lamellae
DNA loops
- Contains genes for some proteins
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