Topic 6:A Level Biology Edexcel Salters
Nuffield Questions and Solutions
4 trophic levels - ANS--Producers (photosynthesising organisms e.g. plants)
-Primary Consumers (herbivores)
-Secondary Consumers (carnivores)
-Decomposers - (bacteria, fungi)
Why is the transfer of energy between trophic levels only about 10% efficient? -
ANS-Producers do not obtain all available solar energy - reflection, transmission
through leaf, incorrect wavelength
Photosynthesis converts light to chemical energy, but the reaction process uses some
energy e.g. respiration and photosynthesis reactions
Consumers - feeding is inefficient e.g. urine and faeces of undigestible materials,
respiration and heat loss
Describe the 4 key contributors of the carbon cycle - ANS-1. Combustion - CO2
released when fossil fuels are burnt
2. Decomposition - saprotrophic microorganisms secrete hydrolytic enzymes to break
down complex carbon-containing organic molecules - absorbed and used for respiration
-> CO2 released
3. Oceans - CO2 diffuses in and out, forming carbonic acid - too much CO2 in the sea
can cause acidification and be dangerous for organisms
4. Plankton - phytoplankton photosynthesise and use carbon to produce cacium
carbonate shells - sink to ocean floor and form limestone and chalk, locking away
carbon
Describe the carbon cycle - ANS-Carbon is fixed from atmosphere CO2 by
photosynthesising plants and plankton to form organic compounds Returned
to atmosphere by respiration (of plants, animals and decomposers),
combustion
Describe the 4 stages of the nitrogen cycle - ANS-1. Nitrogen Fixation - from
atmospheric N2, nitrogen fixing bacteria (on root nodules of legumes) and lightning
cause N2 to be converted into ammonia and then into nitrogen compounds in plants 2.
Ammonification - decomposers convert nitrogen compound from dead organisms into
, ammonium compounds
3. Nitrification - ammonium is converted by nitrifying bacteria into nitrites and then into
nitrates
4. Denitrification - denitrifying bacteria convert nitrates from soil into nitrogen gas, which
is released into atmosphere
Describe how decomposers break down plant and animal compounds - ANS--
hydrolysis
- enzymes
- produced by saprotrophic microorganisms and excreted
- cellulose broken into B glucose monomers
- starch broken into A glucose monomers
Describe the structure/components of a bacterial cell - ANS-Peptidoglycan cell wall -
prevents swelling/bursting, maintains shape and provides support and protection
Cell Membrane - smaller than eukaryotic, site of respiration enzymes as no
mitochondria, infoldings called mesosomes increase SA
Flagellum - helical rotations for movement
Chromosomal DNA - single circular DNA, in cytoplasm
Plasmids - smaller circles of extra DNA, coding for advantageous genes that can be
passed between bacteria during conjugation
Pili - attach to host cells/ used in sexual reproduction, vulnerable to viral infection
Capsule - protects pathogenic cells from being recognised as foreign as their markers
are hidden from antibodies
Explain the classification of bacteria - ANS-- shape - cocci (spherical), bacilli (rod),
spirilla (squiggly)
- gram stain - positive (thick peptidoglycan cell wall so remains purple), negative (thin
cell wall so red dye can be taken up as alcohol disrupts the purple dye) - respiration -
obligate aerobe, obligate anaerobe, facultative aerobe (can respire both aerobically and
anaerobically but aerobic more efficient so where possible, it will respire aerobically)
Describe the process of binary fission - ANS-- DNA and plasmids replicate - the
Nuffield Questions and Solutions
4 trophic levels - ANS--Producers (photosynthesising organisms e.g. plants)
-Primary Consumers (herbivores)
-Secondary Consumers (carnivores)
-Decomposers - (bacteria, fungi)
Why is the transfer of energy between trophic levels only about 10% efficient? -
ANS-Producers do not obtain all available solar energy - reflection, transmission
through leaf, incorrect wavelength
Photosynthesis converts light to chemical energy, but the reaction process uses some
energy e.g. respiration and photosynthesis reactions
Consumers - feeding is inefficient e.g. urine and faeces of undigestible materials,
respiration and heat loss
Describe the 4 key contributors of the carbon cycle - ANS-1. Combustion - CO2
released when fossil fuels are burnt
2. Decomposition - saprotrophic microorganisms secrete hydrolytic enzymes to break
down complex carbon-containing organic molecules - absorbed and used for respiration
-> CO2 released
3. Oceans - CO2 diffuses in and out, forming carbonic acid - too much CO2 in the sea
can cause acidification and be dangerous for organisms
4. Plankton - phytoplankton photosynthesise and use carbon to produce cacium
carbonate shells - sink to ocean floor and form limestone and chalk, locking away
carbon
Describe the carbon cycle - ANS-Carbon is fixed from atmosphere CO2 by
photosynthesising plants and plankton to form organic compounds Returned
to atmosphere by respiration (of plants, animals and decomposers),
combustion
Describe the 4 stages of the nitrogen cycle - ANS-1. Nitrogen Fixation - from
atmospheric N2, nitrogen fixing bacteria (on root nodules of legumes) and lightning
cause N2 to be converted into ammonia and then into nitrogen compounds in plants 2.
Ammonification - decomposers convert nitrogen compound from dead organisms into
, ammonium compounds
3. Nitrification - ammonium is converted by nitrifying bacteria into nitrites and then into
nitrates
4. Denitrification - denitrifying bacteria convert nitrates from soil into nitrogen gas, which
is released into atmosphere
Describe how decomposers break down plant and animal compounds - ANS--
hydrolysis
- enzymes
- produced by saprotrophic microorganisms and excreted
- cellulose broken into B glucose monomers
- starch broken into A glucose monomers
Describe the structure/components of a bacterial cell - ANS-Peptidoglycan cell wall -
prevents swelling/bursting, maintains shape and provides support and protection
Cell Membrane - smaller than eukaryotic, site of respiration enzymes as no
mitochondria, infoldings called mesosomes increase SA
Flagellum - helical rotations for movement
Chromosomal DNA - single circular DNA, in cytoplasm
Plasmids - smaller circles of extra DNA, coding for advantageous genes that can be
passed between bacteria during conjugation
Pili - attach to host cells/ used in sexual reproduction, vulnerable to viral infection
Capsule - protects pathogenic cells from being recognised as foreign as their markers
are hidden from antibodies
Explain the classification of bacteria - ANS-- shape - cocci (spherical), bacilli (rod),
spirilla (squiggly)
- gram stain - positive (thick peptidoglycan cell wall so remains purple), negative (thin
cell wall so red dye can be taken up as alcohol disrupts the purple dye) - respiration -
obligate aerobe, obligate anaerobe, facultative aerobe (can respire both aerobically and
anaerobically but aerobic more efficient so where possible, it will respire aerobically)
Describe the process of binary fission - ANS-- DNA and plasmids replicate - the
