Marine Science 9693: AS (2025-27)

Water

Earth processes

Interactions in marine ecosystems

Classification and biodiversity

Examples of marine ecosystems

Particle theory and bonding: An understanding of particle theory, including the structure of atoms and ions, and how they bond together to form compounds, helps to explain the properties of water and other substances important to marine life.

Solubility in water: Sea water is a solution made up of many different solutes dissolved in water. Various environmental factors affect the solubility of salts and gases in sea water. Hydrogen ion concentration is particularly important, as this affects pH.

Density and pressure: Density is a measure of the mass of a defined volume of water, and is affected by temperature, pressure and salinity. Density differences help to maintain temperature and salinity gradients in the oceans, which affect the distribution of organisms.

Tectonic processes: The movement of tectonic plates is responsible for the formation of many different features of the ocean floor, including hydrothermal vents and ocean trenches, and phenomena such as earthquakes and tsunamis.

Weathering, erosion and sedimentation: Weathering of rocks results in the production of small fragments, which may be eroded (carried away) and deposited elsewhere as sediment. The balance between the rate at which sediments are eroded and deposited in the littoral zone determines the type of shore that forms.

Tides and ocean currents: Twice each day, the level of the seas and oceans rises and falls, in a pattern determined by the alignment of Earth, Moon and Sun. The magnitude of these changes in level, known as tides, is also affected by environmental factors such as winds. Winds and temperature, along with other factors, also give rise to ocean currents. These currents ensure that the water in all the world�s oceans is able to mix, via the global ocean conveyor belt.

Interactions: Different species of organism may live in a close relationship with one another, which is known as symbiosis. Parasitism, commensalism and mutualism are types of symbiosis, differing from one another in the degree of benefit gained by the host and by the symbiont.

Feeding relationships: Producers harness an energy source � through either photosynthesis or chemosynthesis � to convert inorganic substances to organic substances, which contain energy that becomes available to consumers. The rate at which producers transfer energy into organic substances and produce biomass is measured as productivity, and this is affected by factors such as the availability of light. Energy is lost as it passes along a food chain, and this results in a decrease in the energy content of the organisms at each trophic level.

Nutrient cycles: Nutrients are materials that are required by organisms for an energy supply, and for growth and maintenance of body tissues. The availability of nutrients has a large effect on productivity, and therefore on the types and numbers of organisms that live in different parts of the oceans at different times.

The classification of marine organisms: Organisms are classified in a hierarchical system, in which the largest group is the domain. Each type of organism belongs to a particular species, which is given a universally recognised two-word name called a binomial. Dichotomous keys are made up of pairs of contrasting descriptions, constructed so that the sequential choice of one of each pair leads to the name of the organism.

Key groups of marine organisms: The number of phyla living in the oceans is considerably greater than on land. The adults and larvae of many different types of organism are planktonic, drifting in ocean currents. Crustaceans, echinoderms, bony fish and cartilaginous fish are some of the more obvious animals in the oceans, while macroalgae (seaweeds) and seagrasses form the basis of many food chains.

Biodiversity

Populations and sampling techniques: Biotic and abiotic factors affect the distribution and abundance of different types of organism in the marine environment. It is important to select appropriate techniques to study distribution and abundance in particular circumstances � for example, whether sampling should be random or systematic. The data collected can be analysed to look for correlations between abundance and a particular environmental factor.

The open ocean: Depth zones in the oceans range from the surface layers to the very deepest parts in the benthic zones. The oceans have considerable influence on global climate and on the composition of the atmosphere, with which they continually interact.

The tropical coral reef Tropical coral reefs are built by tiny coral polyps, which live in close association with photosynthetic zooxanthellae and are therefore limited in their distribution to areas where abundant light is available and temperatures are warm. The polyps themselves are consumers and require a source of small organisms that they can capture and digest. Changes to biotic or abiotic factors in the oceans can lead to the erosion of coral reefs. Artificial structures can be provided as a substrate on which reef communities can develop.

The rocky shore: Organisms living on rocky shores experience variations in temperature and salinity, availability of water and exposure to sunlight at different stages of the tidal cycle. High on the shore, these abiotic factors are the main influence on the distribution and abundance of species, but lower down the shore biotic factors such as competition and predation have the greatest influence.

The sandy shore: Organisms cannot attach securely to the unstable substrate on sandy shores. The variations in abiotic factors through the tidal cycle can be even greater than on a rocky shore, and relatively few types of organism have adaptations � such as the ability to burrow � that enable them to live there.

The mangrove forest: Mangroves have adaptations for surviving in environments where they are partly submerged in salt water. They grow on muddy shores in tropical and subtropical regions, and have a major influence on biodiversity. They are of great value to human coastal communities, although many human activities pose serious threats to mangrove forests.

explain the changes of state in water, between solid, liquid and gas, in terms of the kinetic particle theory

describe the structure of the atom, including the nucleus containing protons and neutrons, surrounded by electrons arranged in shells

understand that sea water is a mixture of different elements and compounds

describe (including through the use of diagrams) the covalent bonding in a water molecule, limited to the sharing of electron pairs between atoms

identify (including from diagrams) covalent molecules, including water, carbon dioxide, oxygen, sulfur dioxide and glucose

describe (including through the use of diagrams) the ionic bonding in sodium chloride, limited to the loss and gain of electrons to form ions and the subsequent attraction between positive and negative ions

identify (including from diagrams) ionic substances, including sodium chloride and calcium carbonate

state the chemical name and formula of salts found in sea water, including sodium chloride (NaCl ), magnesium sulfate (MgSO4) and calcium carbonate (CaCO3)

explain the formation of hydrogen bonds in water

explain how hydrogen bonding in water affects the properties of water, limited to solvent action, density, and specific heat capacity

explain the terms solute, solvent, solution and solubility

describe how soluble salts, such as sodium chloride, dissolve in water by the dissolution of ions

explain the effect of water temperature on the solubility of salts

define the term salinity as the concentration of dissolved salts in sea water (note that the unit for salinity used in this syllabus is parts per thousand (ppt))

(PA) investigate the effect of salinity on the freezing point of water

explain the effect of surface run-off, precipitation and evaporation on the salinity of sea water

describe the pH scale as a measure of the hydrogen ion concentration in water, including the terms acidic, neutral and alkaline (calculations relating to hydrogen ion concentration are not required)

(PA) use litmus indicator to determine if a substance is acidic or alkaline or Universal Indicator and pH probes to measure the pH of water samples

state that oxygen has a low solubility in water

describe the effect of water temperature, water pressure (depth), atmospheric pressure and salinity on the solubility of gases in water and the implications this has for marine organisms (knowledge of the gas laws is not expected)

explain how water temperature, water pressure and salinity affect the density of sea water

recall and apply the formula: density = mass � volume, with units of kg m�3, kg and m3 respectively

state that the density of ice is lower than sea water, causing ice to float

explain the importance of ice floating, limited to its action as a thermal insulator and as a habitat for marine organisms

describe how temperature and salinity gradients form in water columns to produce ocean layers, including the surface layer, thermocline, halocline and deep ocean, and how subsequent mixing of these layers may occur

describe the structure of the Earth, limited to crust (oceanic and continental), mantle and core

describe and apply the theory of plate tectonics and the evidence supporting the theory limited to

the geological matching of rock formations on different continents

distribution of similar fossils and living organisms on different continents

paleomagnetic stripes on the ocean floor

the jigsaw fit of the continental coastlines

identify and describe the three types of plate boundary as convergent, divergent and transform

explain how tectonic processes produce ocean trenches, mid- ocean ridges, hydrothermal vents, abyssal plains, volcanoes, earthquakes and tsunamis

state that the water coming from hydrothermal vents is under pressure, hot and rich in dissolved nutrients and that this forms the hydrothermal vent plume

understand that the effects of the hydrothermal vent plume can be detected some distance from the hydrothermal vent site

explain how the chimneys form at hydrothermal vents, including reference to temperature and solubility of salts

distinguish between weathering and erosion

describe the three main types of weathering: chemical, physical and organic, and be able to describe an example of each type

describe the four main types of erosion: by ice, water, wind and gravity

describe sedimentation as the deposition of suspended particles

understand how the speed of water flow and particle size affect the removal, transport and deposition of particles

define the littoral zone as the intertidal region on a shoreline, between the highest and lowest spring tide marks

state examples of the littoral zone, including rocky shores, sandy shores, muddy shores, estuaries and deltas

describe how weathering, erosion and sedimentation give rise to the morphology of rocky shores, sandy shores, muddy shores, estuaries and deltas

explain how tides are produced, and how the alignment of the Earth, Moon and Sun, coastal geomorphology, wind, air pressure and size of water body affect the tidal range

explain the formation of spring and neap tides

interpret tide tables and graphs in terms of tidal height, tidal range, spring and neap tides

describe how wind, temperature, density, the Coriolis effect (limited to the deflection of currents clockwise in the northern hemisphere and anticlockwise in the southern hemisphere) and the shape of the seabed produce ocean currents and upwelling

explain the formation of the global ocean conveyor belt and its importance in moving sea water around the Earth

discuss the causes and effects of El Ni�o and La Ni�a events during the El Ni�o Southern Oscillation (ENSO) cycle in the Pacific Ocean

describe the meaning of parasitism, commensalism and mutualism, and understand that they are all examples of symbiotic relationships

describe parasitic relationships, including the relationship between copepods and marine fish

describe commensal relationships, including the relationship between whales and barnacles

describe mutualistic relationships, including the relationship between boxer crabs and anemones

explain the following terms in relation to feeding relationships: consumer (including primary, secondary, tertiary and quaternary), producer, herbivore, carnivore, omnivore, decomposer, predator, prey, food chain, food web, trophic level

represent and interpret feeding relationships in an ecosystem as food chains and food webs

understand that producers can be photosynthetic or chemosynthetic

explain that photosynthesis captures the energy of sunlight and makes some of the energy available to the food chain, and, it can be summarised by the word equation carbon dioxide + water ?li?ght? glucose + oxygen chlorophyll (further details of photosynthesis and balanced chemical equations are not required at AS Level)

(PA) investigate the effect of light intensity on the rate of photosynthesis (use of fresh water plants is acceptable)

understand that some of the glucose produced by photosynthesis is used to produce biomass

understand that some of the glucose produced by photosynthesis is used in respiration to provide usable energy and can be summarised by the word equation glucose + oxygen ??? carbon dioxide + water (further details of respiration and balanced chemical equations are not required at AS Level)

define productivity as the rate of production of biomass per unit area or volume per unit of time and explain how high primary productivity may influence food chains

calculate and explain the energy losses along food chains

draw, describe and interpret pyramids of energy, numbers and biomass, including those that incorporate parasites and periods of plankton / algal bloom

understand that nutrient is a generic term for substances that are required by an organism for growth, repair, energy or normal metabolism

understand that nutrients can include gases such CO2, ions such as Mg2+, CO32�, PO43� and NO3� and organic compounds such as carbohydrates, lipids and proteins

state the chemical elements that make up carbohydrates, lipids and proteins

state that large molecules are made from smaller molecules, limited to starch and cellulose from glucose, proteins from amino acids, and lipids from fatty acids and glycerol

understand that some nutrients supply organisms with a source of essential elements and these elements have important biological roles:

nitrogen, which is used to make proteins, chlorophyll and DNA

carbon, which is used to make all organic compounds

magnesium, which is used to make chlorophyll

calcium, which is used to make bones, shells and coral skeletons

phosphorus, which is used to make DNA and bones

understand that some nutrients are soluble and that there is a reservoir of these nutrients dissolved in the ocean which is available to producers and consumers

explain the processes by which the reservoir of dissolved nutrients is replenished, including upwelling, run-off, tectonic activity, dissolving of atmospheric gases, excretion and decomposition

understand that the reservoir of dissolved nutrients is depleted by uptake into organisms

outline how marine snow transfers energy-containing organic material from surface waters to the deep ocean

understand that the nutrients taken up by organisms in food chains can be removed by harvesting

explain why productivity may be limited by the availability of dissolved nutrients

describe the carbon cycle, limited to combustion, photosynthesis, respiration, decomposition, formation of fossil fuels, formation and weathering of rocks containing carbonate ions

describe the classification of species into the taxonomic hierarchy of domain, kingdom, phylum, class, order, family, genus and species

understand and use the binomial system of species nomenclature

construct and use simple dichotomous keys based on easily identifiable features

(PA) make observations and drawings from unfamiliar structures or specimens from the key groups in topic 4.2 and additionally Cnidaria in topic 5.2

define plankton as a diverse collection of generally microscopic organisms that have limited motility and drift in water currents

understand that phytoplankton are producers which absorb nutrients from their environment (like all producers) and obtain their nutrition by photosynthesis; examples include microscopic algae such as diatoms and dinoflagellates

understand that zooplankton are consumers; examples include larvae, copepods and larger animals such as jellyfish

state the main features of a typical adult echinoderm, limited to pentaradial symmetry and tube feet

understand the ecological and economic importance of echinoderms, including the crown of thorns starfish

state the main features of a typical adult crustacean, including carapace, segmented abdomen, jointed legs and two pairs of antennae

understand the ecological and economic importance of crustaceans, including Antarctic krill

state the main internal and external features of a typical adult bony fish, including bony skeleton, operculum, gills, swim bladder, scales, externally visible lateral line, fins (pectoral, caudal, pelvic, anal and dorsal)

understand the ecological and economic importance of bony fish, including the Peruvian anchoveta

state the main internal and external features of a typical adult cartilaginous fish, including cartilaginous skeleton, gill slits, gills, denticles, lateral line, fins (pectoral, caudal, pelvic, anal and dorsal)

understand the ecological and economic importance of cartilaginous fish, including the blue shark

understand that bony fish and cartilaginous fish are both chordates (i.e. in the phylum Chordata) and that all organisms in this phylum share common features (at some point in their development), including notochord, dorsal neural tube, pharyngeal slits and post-anal tail

state the main features of a typical macroalga, such as kelp, including holdfast, stipe, gas bladders and blades

understand the ecological and economic importance of macroalgae, including kelp

state the main features of a typical marine plant, such as seagrass, including rhizome, roots, flowers and leaves

understand the ecological and economic importance of marine plants, including seagrass

explain that biodiversity can be considered at three different levels:

genetic diversity (variation in the genes of a species)

species diversity (number of species and their relative abundance)

ecological diversity (variation in ecosystems on a regional and global level)

understand the importance of marine biodiversity in terms of the services / benefits it provides, including:

maintaining stable ecosystems (for example, diversity in communities maintains complex interactions between all organisms and the physical environment)

protection of the physical environment (for example, coral reefs protect coastlines)

climate control (for example, phytoplankton absorb CO2 and release O2)

providing food sources (for example, algae, crustaceans and fish)

providing a source of medicines (for example, anticancer drugs such as keyhole limpet hemocyanin (KLH))

explain, using marine examples, the terms ecosystem, habitat, niche, species, population and community

explain the terms biotic factor (including intra- and inter-specific competition, symbioses, predation and disease) and abiotic factor (including salinity, temperature, pH, oxygen concentration, carbon dioxide concentration, light availability, turbidity, wave / tide action, nutrient availability and exposure to air) and identify those factors that affect an organism in a named marine ecosystem

understand the mark�release�recapture method for estimating population size of a named species

apply the Lincoln index and identify the limitations of this method (the equation and symbols for the Lincoln index will be provided in the question papers)

describe random and systematic sampling and understand their advantages and disadvantages

(PA) use suitable methods, including frame quadrats, line transects, belt transects and mark-release-recapture, to investigate the distribution and abundance of organisms in the littoral zone (note that candidates should be taught the importance of designing an ethical and safe method)

use Simpson�s index of diversity (D) to calculate the species diversity of a habitat and interpret different values of D (the equation and symbols for the calculation of D will be provided in the question papers)

use Spearman�s rank correlation (rs ) to analyse the relationships between the distribution and abundance of species and abiotic or biotic factors (the equation and symbols for the calculation of rs will be provided in the question papers)

identify the world�s five oceans as the Arctic, Atlantic, Pacific, Indian and Southern, and understand that these oceans are inter-connected and encircle the Earth as a World Ocean

identify zones found in the open ocean, limited to epipelagic, mesopelagic, bathypelagic, abyssopelagic and benthic zones, and describe these zones in terms of light penetration

explain the importance of oceans and their interaction with the atmosphere:

as carbon sinks

as sources of oxygen

in temperature buffering

in global climate control

identify regions of the oceans as polar, temperate, or tropical

describe the conditions required for tropical coral reef formation

describe and compare the four types of tropical coral reef: fringing, barrier, patch and atoll, in terms of their proximity to the coast and lagoon structure (if present)

describe corals as animals in the phylum Cnidaria that form sessile colonies of polyps, often having a symbiotic relationship with zooxanthellae

understand that the two general types of coral, hard (for example, staghorn) and soft (for example, sea fan) vary in the extent of calcification and population size of zooxanthellae

describe the structure of a typical hard coral polyp, limited to tentacle, nematocyst, mouth, stomach, calyx, theca and basal plate, and describe the functions of these structures

explain how corals obtain their nutrition, including the mutualistic relationship between the polyps of some corals and zooxanthellae

discuss the importance of coral reefs, including tourism, food source, coastal protection, medicines and biodiversity

discuss the causes and effects of reef erosion, including pH change, temperature change, predation, physical damage and the presence of sediment

discuss the use of artificial reefs

identify the different zones on a typical exposed rocky shore, limited to splash zone, upper shore, middle shore, lower shore and subtidal zone and describe the changing abiotic factors across these zones during one tidal cycle

explain how biotic and abiotic factors interact to affect the distribution and abundance of organisms in the different zones on the rocky shore (candidates should study a range of named organisms from the different zones)

explain, using named examples, the adaptations that organisms have to living in the different zones (for example the adaptations to prevent desiccation)

describe the sandy shore as an ecosystem with an unstable, shifting substrate that is porous

explain how the biotic and abiotic factors that affect a sandy shore lead to a relatively low biodiversity

(PA) investigate the effect of particle size on the permeability of substrates

explain, using named examples, the adaptations that organisms have to living on a sandy shore

describe the mangrove forest as a tidal ecosystem featuring salt tolerant trees and other plants, together with populations of other species, all interacting in the littoral zone of some tropical and subtropical coasts

outline the conditions required for the formation of mangrove forest

explain how the red mangrove tree, Rhizophora mangle, shows adaptations to its environment, including:

prop roots for stability in unstable substrates and supplementary oxygen uptake due to low oxygen concentrations in the substrate

salt exclusion by the roots

viviparous reproduction using propagules

explain the ecological importance of mangrove forests in terms of:

nursery area for juveniles of many animal species

sediment trapping which stabilises and protects the coastline and prevents sediment build up on coral reefs and seagrass beds

discuss the importance of mangrove forests, including tourism, food source, coastal protection, timber, fuel source and biodiversity

discuss the threats to mangrove forests, including temperature change, over-harvesting, storm damage and change in coastal land use