▶️ Answer/Explanation
(a)
(i) The sea lion is a secondary consumer because it eats fish, which are primary or secondary consumers. It belongs to trophic level 3.
(ii) The relationship between orca whales and sea otters is a predator-prey relationship, as orcas hunt and feed on sea otters.
(b)
Ex situ conservation involves protecting a species outside its natural environment, such as in aquariums, zoos, or marine reserves. This method allows scientists to:
- Monitor health and provide optimal conditions for survival.
- Run captive breeding programs to increase population numbers.
- Act as a backup if the species disappears in the wild.
- Be useful when natural habitats are severely damaged or dangerous.
(c)
A limitation of pyramids of energy is that they don’t account for decomposers, which play a key role in recycling energy and nutrients. Also, species that feed at multiple levels can make it hard to assign accurate trophic positions.
Markscheme:
(a)
- (i) Secondary consumer / third trophic level / trophic level 3 / 3
- (ii) Predation / predator-prey relationship
(b)
- Protecting species outside their natural habitats in zoos/aquariums/botanical gardens
- Essential requirements can be managed/monitored
- Allows breeding programs
- Useful when there is a serious decline/destruction of natural habitats OR when there is a threat to individuals in the wild
(c)
- Do not show seasonal variations in energy transfers OR
- Difficult to assign species to a specific trophic level OR
- Do not show energy transfer to decomposers
▶️ Answer/Explanation
(a)
Carbon dioxide is lost during aerobic respiration, where organic compounds are broken down to release energy.
(b)
Marine organisms can also obtain carbon through photosynthesis, particularly those containing symbiotic algae, or by absorbing dissolved carbon compounds like CO₂ or bicarbonate ions from seawater.
(c)
- Energy enters marine ecosystems via sunlight, which is captured by photosynthetic organisms like phytoplankton.
- This energy is then transferred through the food web as organisms consume other organisms.
- However, only a small proportion (around 10%) of the energy is passed on to each next level.
- A large part of the energy is lost as heat during metabolic processes like respiration, or as undigested matter.
- Unlike nutrients, energy is not recycled in ecosystems and must be continuously supplied.
(d)(i)
Crustaceans contain more carbon relative to their body mass compared to jellyfish, so they are a richer source of carbon in food chains.
(d)(ii)
It can be a disadvantage, as large jellyfish have low carbon density and a lower surface area to volume ratio, which can limit gas and nutrient exchange. Additionally, their high water content offers little nutritional value to predators.
Alternatively, you could say it’s an advantage because a larger body size might help avoid predation or allow for greater reproduction, depending on context.
Markscheme:
a.
• Aerobic/cellular respiration
• Gas exchange/diffusion
Note: Photosynthesis and breathing are not acceptable answers.
b.
• Photosynthesis
• Absorption of dissolved CO2/carbonate/hydrogencarbonate directly from seawater
c.
• Light energy is converted to chemical energy (in carbon compounds) via photosynthesis
• Chemical energy flows through food chains via feeding relationships
• Only ~10% of energy transfers between trophic levels
• Energy is lost as heat through respiration
• Energy is not recycled in ecosystems
• Some energy remains trapped in undigested detritus/fossil fuels
d.i.
Crustaceans are richer in carbon (more carbon per unit volume) compared to jellyfish which have little carbon relative to total body size.
d.ii.
Advantages:
• Can capture larger prey
• Lower predation rates
• Greater reproductive capacity
Disadvantages:
• Slower movement for predator avoidance/prey capture
• Higher metabolic demands
• Lower surface area:volume ratio affecting gas/nutrient exchange
• More vulnerable to mechanical damage
Note: Must clearly state whether advantage or disadvantage.
▶️ Answer/Explanation
a.
From the table:
Females (pond 9):
Upstream = 2.05 mg, Downstream = 2.09 mg
Difference = 2.09 − 2.05 = +0.04 mgMales (pond 9):
Upstream = 1.57 mg, Downstream = 1.45 mg
Difference = 1.45 − 1.57 = −0.12 mg
b.
- The height of the dam appears to influence temperature differences.
- High dams tend to cool the downstream water (negative temperature difference).
- Low dams tend to warm the downstream water (positive temperature difference).
- One example (pond 5) shows no temperature change (0.0 °C difference).
c.
- There is a general negative trend in the graph: as temperature increases, dry mass decreases, which supports the hypothesis.
- However, the trend line is shallow and data points are widely scattered, particularly at higher temperatures.
- An exception is that female mayflies in water >10°C have the highest dry mass, which contradicts the hypothesis in that range.
- So, the graph partially supports the hypothesis but has notable exceptions.
d. Analyse the data to find the effect of flooding and tree felling by beavers on the activity of bats.
From the bar graph:
- Bat activity (feeding passes) is lowest in forest (F) and meadow (M) habitats.
- Tree felling alone (FG) slightly increases activity compared to forest.
- Flooding alone (MF) also increases activity compared to meadow.
- The highest activity is in flooded forest with canopy gaps (FFG) — where both flooding and tree felling occur.
- Thus, both tree felling and flooding increase bat activity, but flooding has a greater effect overall, especially when combined with tree felling.
e.
f.
Trout and bats compete for mayflies, as both consume them as a food source.
g.
Criterion: Biodiversity
Harmful: If beaver activity reduces native species or causes habitat degradation, leading to a loss of biodiversity, they would be considered damaging.
Helpful: If beavers increase habitat complexity (e.g., creating ponds and wetlands), this might increase biodiversity by supporting more species — thus, they could be beneficial.
Other valid criteria might include impact on water quality, erosion, or alteration of food webs.
Markscheme:
a.
I. female: «+» 0.04 «mg»
AND
II. male: «–» 0.12 «mg»
Both needed.
b.
a. height of dam affects the temperature
b. high dams tend to cool the water
c. low dams tend to warm the water
d. pond 5/one pond shows no change/stays the same
c.
a. trend lines support «the hypothesis»
OR
trend shows a negative correlation shown «between increased temperature and size»
Do not credit answers with just numbers.
Accept “line of best fit” wtte.
b. the trend line is shallow / small slope
OR
there is a large amount of scatter at higher temperatures (reducing the certainty)
OR
wide/overlapping ranges so no significant difference «(at» 9°C)
c. (hypothesis not supported because) females in water over 10°C have the highest «mean dry» mass
Words other than “hypothesis not supported” may be used: “as opposed to”, “whereas”, to express deviation from support.
d.
a. both flooding and tree felling increases bat passes/activity / WTTE
b. flooding has greater/increase on bat passes/activity / WTTE
OR
flooding has the greater impact than tree felling on bat passes
c. supporting argument from the data
e.
a. arrow pointing from trout to human
b. arrows pointing from mayflies to trout and bats
Award [1 max] if answer does NOT show all 4 organisms.
f.
bats and trout compete for mayflies
g.
a. criterion
b. reason that beavers damage
c. reason that beavers help
eg,
a. biodiversity
b. if indigenous species are eliminated biodiversity is reduced, then the beavers would be seen as damaging
c. if biodiversity increases (due to the engineering of waterways), then beavers could be a benefit
Consider criteria something that may be dealt with from a range of perspectives.
Other possible criteria: abiotic disturbance changes to food webs diversity
▶️ Answer/Explanation
a. Energy flow in an ecosystem
- Energy enters the ecosystem from sunlight.
- Producers (mainly green plants) capture light energy through photosynthesis.
- The light energy is converted into chemical energy in the form of organic compounds.
- Consumers obtain energy by eating plants or other animals.
- At each trophic level, most energy is lost as heat during respiration.
- Only about 10% of the energy is transferred to the next trophic level.
- Decomposers use energy from dead organisms and waste products.
Energy flows in one direction and cannot be recycled in the ecosystem.
b. Role of plants in atmospheric carbon dioxide levels
- Plants absorb carbon dioxide from the atmosphere during photosynthesis.
- They convert carbon dioxide into glucose and other organic compounds.
- Plants release carbon dioxide back into the atmosphere through respiration.
- When plants die and decompose, some carbon is returned as carbon dioxide.
- If decomposition is incomplete, carbon can be stored in peat or fossil fuels.
Burning plant material or fossil fuels releases stored carbon as carbon dioxide.
c. Classification and naming of a newly discovered plant species
Naming:
- The plant is given a binomial name (genus + species), e.g., Rosa canina.
- The genus name starts with a capital letter; the species name is lowercase.
- This naming system is standardized and used globally.
Classification:
- Scientists study the plant’s features: structure, reproductive organs, and genetic material.
- The plant is grouped with similar species based on shared characteristics.
- Modern classification often uses DNA or protein sequence comparisons.
- Plants are organized into clades—groups that share a common ancestor.
- Cladograms are diagrams that show evolutionary relationships between species.
- Classification is now based more on evolutionary history than on just physical traits.
Markscheme:
Answer to part (a): Energy flow in ecosystems
a. Energy from the sun is captured by plants/autotrophs
b. Light energy is converted to chemical energy by photosynthesis
c. Energy is passed to animals/consumers/along the food chain
d. At each stage in the food chain energy is lost by respiration/as heat
e. Much less energy/only about \(10\%\) is available at each stage/trophic level of the food chain
f. Some energy is made available to decomposers when organisms die/parts fall to the ground
g. Energy cannot be recycled
Answer to part (b): Plants and carbon dioxide
a. Plants reduce the amount of carbon dioxide in the atmosphere by photosynthesis
b. Carbon dioxide is fixed/converted into organic substances/sugars (OWTTE)
c. Plants respire which releases carbon dioxide into the atmosphere
d. Plant decomposition may release \(\mathrm{CO}_2\)
e. Carbon in dead plants is trapped/stored in fossil fuels/peat
f. Combustion of plants/wood/fossil fuels adds to the amount of carbon dioxide in the atmosphere
Answer to part (c): Plant classification and naming
Naming:
a. Binomial nomenclature / (plant is) given a binomial/double name
b. First name is the genus and second name is the species / genus initial upper case and species lower case
c. Names (of plant species) are international/are universally understood/are published in journals
Classification:
d. Study the characteristics/structure/reproduction/chemical properties/DNA (of the plant)
e. Put/classify (the plant) in a group/genus with other similar species
f. Natural classification corresponds with evolution / natural classification is based on many features
g. Analogous features/features due to convergent evolution should not be used
h. Hierarchy of groups/taxa (in traditional classification) / 3 or more taxa in correct sequence (kingdom-phylum-class)
i. Two or more of bryophyta, filicinophyta, coniferophyta and angiospermophyta named
j. A clade is a group of organisms evolved from a common ancestor
k. Base sequences/amino acid sequences used to group organisms into clades/deduce evolutionary relationships
l. Cladograms show the relationships between clades/likely evolutionary divergence of clades
m. Each branch point/node represents where species are formed via divergent evolution
n. Species are now classified into a sequence of clades (rather than a rigid hierarchy of taxa)