topic 5 (esher)

State the definition habitat

A place with a distinct set of conditions, where an organism lives. The conditions are determined by the mix of abiotic and biotic factors acting the on the habitat.

What is a trophic level?

Each of several hierarchical levels in an ecosystem, consisting of organisms sharing the same function in the food chain and the same nutritional relationship to the primary sources of energy.

State the definition abiotic factors

Non-living or physical (and chemical) factors

State the definition biotic factors

Living factors e.g. competition or disease

Describe the process of ecological succession

gradual stages of change where one community changes the conditions making it suitable for the next community of species (to outcompete the previous species). This continues until a stable climax community is reached.

State the definition of a pioneer species

The first organisms to colonise an area. primary succession = species that cope with extreme conditions e.g. lichens. secondary succession = fast growing species with short life cycle + abundant seed production e.g. poppies

State the definition of deflected succession

A community that remains stable only because human activity prevents succession from running its course. Examples include dredging a pond/lake

State the definition of secondary succession

A version of succession on bare soil where an existing community has been cleared e.g. after a forest fire. There will be a natural seed bank already present in the soil.

State the definition of primary Succession

Starts in a newly formed habitat, where there has never been a community before. Examples of primary succession include after volcanic activity.

What is a carbon sink?

A forest, ocean, or other natural environment viewed in terms of its ability to absorb carbon dioxide from the atmosphere either by dissolving or photosynthesis. Photosynthesis locks away the carbon in plant structures e.g. starch

State some examples of carbon sinks

Examples: peat bog, forests, coal, oceans

Describe how carbon moves through the carbon cycle

The two processes that remove carbon dioxide from the atmosphere are dissolving (i.e. into oceans) or photosynthesis (into plant material) The two processes that can release carbon dioxide back into the atmosphere are combustion (e.g. burning wood) or respiration (e.g. respiration by decomposers)

Define an autotroph

These are organisms that make their own organic compounds from inorganic compounds.

The Hill Reaction (practical)

Can measure the flow of electrons in light dependent reactions Grind up plant in isolation medium to release chloroplasts Spin in centrifuge to separate out chloroplasts Add DCPIP to isolated chloroplasts Measure time taken for DCPIP to go from blue to colourless DCPIP is reduced by electrons released from chloroplast Isolation medium is sugary and prevents osmosis of water out/into chloroplast

Describe the process of light-dependent reactions of photosynthesis

Light is absorbed by the chlorophyll and electrons become excited, moving up 2 energy levels Electrons leave the PSII and are accepted by the electron carrier system (embedded in the thylakoid membrane) Electrons are passed from carrier to carrier through a series of redox reactions Redox reactions release energy, which is used to form ATP from ADP +Pi by photophosphorylation Electron lost now return to PSI Electrons leave PSI (as per step 1 above) Photolysis of water produces OH- and H+ (enzymes for this found in the thylakoid space) 2H+ 2e- + NADP → Reduced NADP OH- replaces the electrons lost to the chlorophyll OH then combine to makes oxygen (and water)

Describe the process of light-independent reactions of photosynthesis

Also known as the Calvin cycle – occurs in the stroma Carbon dioxide is fixed to RuBP (a 5C) to make a 6C (catalysed by RuBISCO) This 6C compound instantly breaks down into 2x GP (a 3C) GP is then reduced to GALP. ATP provides energy for and reduced NADP provides hydrogen. 2/12 GALP are used to make a glucose molecule 10/12 GALP are used to regenerate RuBP

Write an equation for photolysis (in the light dependent reactions)

Splitting (lysis) of a molecule using the energy from light (photo) Replaces lost electrons (from the chlorophyll) in light dependent reaction H20 → 2H+ + 2e- + 1/2O2

ATP

Adenosine triphosphate is the most important energy transfer molecule within cells. It moves energy around the cell from energy-yielding reactions to energy-requiring reactions. Adding on a phosphate is a condensation reaction and removing a phosphate is a hydrolysis reaction. ATPase it the enzyme that catalyses the breakdown of ATP to ADP.

Describe the structure of a thylakoid membrane

A system on interconnected flattened fluid-filled sacs found in a chloroplast. Proteins, including the photosynthetic pigment chlorophyll, and electron carriers are embedded in the membrane (these are required for light dependent reactions of photosynthesis.)

Stroma

The fluid surrounding the thylakoid membranes in a chloroplast. It contains all the enzymes needed to carry out the light-independent reactions of photosynthesis.

Granum

A stack of thylakoid joined to one another. Grana (plural) resemble stacks of coins.

What is a photosystem?

In the thylakoid membranes photosynthetic pigments are arranged in clusters called a photosystem with several hundred pigment molecules surrounding a primary chlorophyll molecule. There are 2 types of chlorophyll molecule; they are structurally different and known as PSI and PSII.

Describe the structure of cellulose

A polymer of beta glucose. The beta glucose molecules are produced through photosynthesis. Individual beta glucose molecules are joined together by 1,4 glycosidic bonds to form long, straight chains of cellulose. Parallel chains are joined together by hydrogen bonds to form microfibrils. In the cell wall microfibrils are then laid down in a criss-cross manner, adding to the strength of cellulose.

Primary consumer

Group of organisms that feed on (primary) producers and are herbivores

Secondary / Tertiary consumer

Organisms which eat primary consumers. Secondary/tertiary consumers can be classified into one of two groups: carnivores, or meat eaters, and omnivores, which are plant and meat eaters.

What is gross primary productivity (GPP)?

The rate at which energy is incorporated into organic molecules by an ecosystem. It is usually expressed as units of energy per unit of area per year. GPP = NPP + R (You can think of it as the total amount of energy a plant converts from light to glucose)

What is net primary productivity (NPP)?

The rate at which energy is transferred into organic molecules that make up new plant biomass (essentially how much energy is left from GPP once the energy used for respiration has been used). This left-over energy is converted into biomass, so new cells. The amount of respiration remains fairly constant in plants, regardless of other conditions. NPP = GPP - R

Energy loss: producers to primary consumer

When an organism consumes another organism, some of this energy is used for respiration by the consuming organism, some of the eaten organism is inedible and some is lost in excretion of faeces and urine – this energy has now been ‘lost’ from the food chain. Whatever energy is left is made into new biomass and then is available for the next stage of the food chain. The efficiency of the energy transfer can be calculated.

State what is meant by limiting factors for photosynthesis

When a process is affected by more than 1 factor, its rate is limited by the factor furthest from the optimum value. Photosynthesis can be limited by light, temperature and carbon dioxide concentrations.

How do forests remove carbon dioxide from the atmosphere?

Trees remove carbon dioxide from the atmosphere by photosynthesis and lock in away in biomass (e.g. cellulose, proteins, other carbohydrates) Young forests are net removers of carbon dioxide

Random sampling (ecology)

Used if comparing a difference between two different areas Random samples avoid bias Use a quadrat (depending on investigation) to estimated abundance or percentage cover Abundance: count the number of a species in the quadrate and multiple over the total sample area Percentage cover: Work out what each square of the quadrat represents (e.g. 100 squares, each square represents 1%). Count the number of squares the species is present in.

Transect & systematic sampling (ecology)

Used when there is a gradual change in the independent variable over a distance. Can then sample systematically down the transect, taking measurements at equal intervals.

Why is some sunlight energy lost?

Some light will pass directly through the leaf without hitting a chlorophyll, some is reflected off the leaf, some waves of light will be the wrong frequency to be absorbed by the chlorophyll and the chlorophyll is not 100% efficient at converting the light into chemical energy.

Describe how temp records can be used as evidence for climate change

Exist for some parts of the world since 1780 Need to be taken away from large cities (to increase accuracy of data) Older data may be less accurate

Describe how peat bogs can be used as evidence for climate change

An example of a carbon sink Made of undecomposed plant material The anaerobic conditions prevent decay The carbon in the plants can be carbon-14 dated to determine the age The deeper the peat the older the peat Beetle exoskeletons/pollen in the peat can be identified and population size estimated to determine the climate at the time (depending on the beetle’s/plant’s preferred conditions)

Describe how dendrochronology can be used as evidence for climate change

Trees produce a new ring of xylem each year The outer ring is the newest ring The width of the ring can give an indication of the climate conditions during that year The wider the ring the warmer/wetter the conditions

Describe the greenhouse effect

This is natural process that keeps the Earth warm Most solar radiation is absorbed by the Earth. Some is emitted back as infrared radiation. Some of this escapes the Earth’s atmosphere and cools the Earth. Some is absorbed by greenhouse gases, warming the troposphere. Climate change is when we have MORE greenhouse gases, so trap MORE infrared radiation, warming the Earth and increasing global mean surface temp (GMST)

Why might some people say global warming is not happening?

Bias of scientists e.g. work for oil companies Natural cycle of cooling/warming The sun’s activity is causing changes in GMST Caused by natural disasters e.g. volcanic eruptions Carbon dioxide produced by other means e.g. volcanoes Other greenhouse gases e.g. methane from cows/rice paddy fields Models may not take all variables into consideration

Why are climate models not always reliable?

Models may not take all variables into consideration Trends may not continue into the future Older data may be inaccurate

Why would changing GMST change development rate of organisms?

Increase temperature increase kinetic energy of enzyme/substrate More kinetic energy = more collisions and more enzyme-substrate complexes formed Rate of reaction increases until the optimum temperature is reached If too hot bonds between R groups broken and therefore active site changes shape, reducing rate of reaction

State the definition for phenology

The study of seasons events in the lives of animals and plants e.g. flowering time, fruiting time, egg laying/hatching time, first appearance of migrant species Can be used as evidence of the effect of climate change on species.

State the definition for photoperiod

A species response to day length e.g. day length triggering flowering, egg hatching, seed germination This response (if a species has it) will be determined genetically This respond allows species to synchronize with periods of maximum food availability or pollination species etc.

How can DNA and protein sequencing be used to determine evolutionary relationships?

Used to compare the DNA sequences OR amino acid sequence in proteins of different species The more similarities in the proteins/DNA, the more similarly the species are genetically and the more closely related they are The more different the proteins, the more mutations have accumulated and the more genetically different they are, and the less closely related they are

How can DNA profiling be used to determine evolutionary relationships?

Process the DNA by either PCR or restriction enzymes Separate the DNA by length using gel electrophoresis Use Southern Blotting to visualise the DNA THEN compare the number of bands that are the same The more bands that are different, the more genetically different the two species are (and the more bands the same, the more genetically similar they are)

How can DNA hybridisation be used to determine evolutionary relationships?

Take 2 samples of DNA from 2 different species Heat the DNA samples until the DNA denatures Then mix the two samples – the DNA strands will try to combine by form by complementary base pairing Re-heat the sample and record the temperature it denatures The lower the temperature (to denature) the less bases matched, and the more genetically different they are

How can DNA molecule clocks be used to determine evolutionary relationships?

As species evolve the accumulate random mutations at a regular rate For a given gene the mutation rate is fairly constant This molecule change can be used as a molecular clock

Describe the process of speciation

Two populations become separated from each other and therefore become reproductively isolated from each other > gene flow is prevented between the two populations > different selection pressures act on the two populations > those with advantageous alleles survive and reproduce, and may pass on the advantageous allele to their offspring > over time the two populations become increasingly genetically different from each other > if reintroduced and they can no longer breed to produce fertile offspring then they are now different species.

Allopatric speciation

This occurs when two populations are geographically isolated from each other, resulting in the two populations becoming reproductively isolated and preventing gene flow. Over time this may results in two new species.

Sympatric speciation

This occurs when two populations become isolated from each other but in the same environment, and resulting in no gene flow between the two populations. Over time this may result in two new species. They could become isolated through behaviour (no longer recognising mating calls), temporal isolation (mating at different times), ecological isolation (species occupy different parts of a habitat)

Reproductive isolation

Two populations that cannot interbreed and therefore gene flow is restricted between the two populations. Reasons that could prevent reproduction are different locations, different mating calls, incompatible genitalia, different breeding times etc

Why might biofuels be described as carbon neutral?

Biofuels may be carbon neutral (i.e. the amount of carbon locked in the plant, matches the amount of carbon dioxide released when burnt)

How does deforestation (e.g. for growing biofuels) potentially contribute to global warming?

Forests are carbon sinks, so clearing the land can lead to a net production of carbon dioxide Less plants = less carbon dioxide removed from the atmosphere by photosynthesis Burning or decomposition of trees = more carbon dioxide in atmosphere Machinery needed for clearing land burns fossil fuels, which releases carbon dioxide

Describe the process of global warming

Climate change is when we have MORE greenhouse gases in the atmosphere (e.g. more methane, more carbon dioxide), so trap MORE infrared radiation that’s reflected from the earth’s surface, resulting in increasing global mean surface temp (GMST)