Marine Science 9693: A (2025-27)

Physiology of marine organisms

Energy

Fisheries for the future

Human impacts on marine ecosystems

General cell structure: All living organisms are formed of units called cells, which have many features in common. Each cell is separated from its immediate environment by the cell surface membrane, and contains genetic material and organelles within the cytoplasm. An understanding of the structure of the cell surface membrane enables us to understand its functions. We use microscopes to visualise cells. The images produced can be studied and interpreted to increase understanding of cell structure.

Movement of substances: Diffusion and facilitated diffusion across cell membranes are passive processes. Osmosis is a particular type of diffusion involving water. Active transport however uses energy provided by the cell to move substances against their concentration gradient. Water potential is a measure of the relative number of water molecules, and their freedom to move, in a solution. Water diffuses down a water potential gradient and can move freely through cell membranes.

Gas exchange: Aerobic respiration requires oxygen and produces carbon dioxide. These two gases diffuse into and out of the organism, from and to its environment. This process is called gas exchange. Smaller marine organisms often allow the gases to diffuse across their whole body surface, but most larger organisms have specialised surfaces across which gas exchange takes place. They may also have methods of ventilating these surfaces.

6.4 Osmoregulation: Sea water has a similar water potential to the body fluids of most marine organisms, and therefore many species do not need to regulate their water content. Other species are osmoregulators and control the water content of their bodies. Most marine organisms can survive within only a small range of salinity, and are termed stenohaline. Euryhaline species can live in a range of salinities. Salmon are an example of a euryhaline osmoregulator, spending part of their life cycle in the sea and part in fresh water.

Photosynthesis: Photosynthesis is a two-stage process in which energy is harvested from light by pigments, and then transferred to organic compounds. These compounds can be used to synthesise biomass or to provide useful energy for life processes. Photosynthesis takes place in chloroplasts, whose structure enables these stages to take place efficiently. If a requirement for photosynthesis is in short supply, it may act as a limiting factor, preventing the rate of photosynthesis from increasing.

Chemosynthesis: Hydrothermal vents provide a habitat for a very unusual community of living organisms adapted to the unique conditions found there. As there is no light, bacteria use energy from inorganic chemicals to produce organic substances. This forms the basis of the food web. The bacteria live in symbiosis with tubeworms.

Respiration: Organisms require constant supplies of energy to maintain life processes. Respiration releases energy from organic nutrients in a usable form, as ATP.

Life cycles: Many species of marine organisms have complex life cycles with several different stages, in which one or more stages are adapted for dispersal. Marine mammals have simpler life cycles. The female gametes of most invertebrates, and some vertebrates such as bony fish, are fertilised outside the body of the female, but fertilisation is internal in mammals and sharks.

Sustainable fisheries: Modern fishing methods can harvest so many fish that there is a danger that fish populations may be reduced beyond the point at which they can recover. Sustainable exploitation can be achieved by collecting information about fish stocks, regulating fishing and rehabilitating depleted stocks.

Marine aquaculture: Increasingly, marine organisms are grown in controlled systems, as an alternative to harvesting from the wild. Aquaculture systems may be intensive or extensive, and both types can have a range of positive and negative social, economic and environmental impacts that should be considered when developing an aquaculture project.

Ecological impacts of human activities: Human activities, whether taking place on land or at sea, frequently affect marine ecosystems. Oil spills, run- off from terrestrial industries and agriculture, and the use and disposal of plastics, have become serious issues, with potentially very significant and widespread effects. Bioaccumulation of heavy metals and other toxins can also have considerable negative impacts.

Global warming and its impact: The Earth�s atmosphere naturally contains carbon dioxide, which produces the greenhouse effect, helping to maintain a temperature on Earth that is suitable for life. However, increasing quantities of carbon dioxide, resulting at least partially from human activities, are enhancing the greenhouse effect and causing global warming. Global warming is already producing a range of negative impacts on the marine environment.

Ocean acidification: Carbon dioxide dissolves in sea water to form a weak acid, and increasing concentrations of atmospheric carbon dioxide therefore lead to a decrease in the pH of sea water. This has damaging effects on many marine organisms, particularly those such as corals and molluscs whose skeletons and shells contain calcium carbonate.

Conservation of marine ecosystems: Local, regional and global conservation efforts can go some way to reducing and even reversing harmful effects on marine ecosystems, but their implementation can sometimes be difficult and expensive.

recognise the following organelles and other cell structures and outline their functions:

cell surface membrane

nucleus

rough and smooth endoplasmic reticulum

ribosomes

Golgi body

mitochondria

chloroplasts

cell wall

large permanent vacuole

describe the fluid mosaic model of membrane structure, including an outline of the structure and functions of phospholipids and proteins, limited to carrier and channel proteins

understand the selectively permeable nature of membranes and relate this to the transport (active and passive) of substances across a membrane

describe and interpret photomicrographs, electron micrographs and drawings of typical animal and plant cells

recall and apply the formula: magnification = image size � actual size

(PA) make observations, drawings and magnification calculations from unfamiliar structures or specimens

describe and explain the processes of diffusion, facilitated diffusion, osmosis and active transport

understand the concept of water potential and explain how dissolved solutes affect the water potential of a solution or cell (knowledge of solute potential is not required)

(PA) investigate diffusion and osmosis using plant tissue and non-living materials, such as Visking tubing and agar

calculate surface areas and volumes of simple shapes (all formulae and relevant symbols will be provided) to illustrate the principle that surface area to volume ratio decreases with increasing size

(PA) investigate the effect of changing surface area to volume ratio on diffusion using agar blocks of different sizes

(PA) investigate the effects of immersing plant tissues in solutions of different water potentials, using the results to estimate the water potential of the tissues

explain the movement of water between cells and solutions with different water potentials and explain the different effects on plant and animal cells

understand that the raw materials and waste products of respiration must be moved to and from the surface of organisms

discuss how surface area to volume ratio is dependent on the size and shape of an organism, and relate this to the need for specialised gaseous exchange surfaces and transport systems in larger animals

describe gaseous exchange by simple diffusion, pumped ventilation and ram ventilation, in examples including coral polyps, grouper and tuna

relate an organism�s method of gas exchange to its habitat and motility

explain why marine organisms may need to regulate their water content and ion content, with reference to the composition of sea water and of body fluids

explain the terms osmoconformer and osmoregulator with reference to marine mussels and tuna

explain the terms euryhaline and stenohaline with reference to salmon, marine mussels and tuna

outline the processes of osmoregulation in e.g., salmon

understand that white light is composed of a range of colours, each with a different wavelength

differentiate between the terms wavelength, intensity and penetration in the context of light

describe the effect of wavelength on the penetration of light to different depths

understand that photosynthesis is the process that nearly all marine producers use to fix carbon, and it can be summarised as: 6CO + 6H O ?li?ght? C H O + 6O

understand that photosynthesis is a two-stage process, light-dependent and light-independent

explain that energy is transferred as ATP and reduced NADP from the light-dependent stage to the light-independent stage (Calvin cycle) and is used to produce organic molecules

describe the structures in a typical chloroplast, to include outer membrane, inner membrane, stroma, thylakoids, thylakoid membrane, thylakoid space and grana

state the sites of the light-dependent and the light-independent stages in the chloroplast

describe the role of chloroplast pigments (chlorophyll a and accessory pigments) in light absorption in the grana

relate the presence of accessory pigments, including xanthophylls and phycobilins, in marine producers to the penetration of different wavelengths of light

(PA) describe and use chromatography to separate and identify chloroplast pigments (reference should be made to Rf values)

interpret absorption spectra of chloroplast pigments and action spectra for photosynthesis

describe the light-dependent stage as the photoactivation of chlorophyll resulting in the photolysis of water and the transfer of energy to ATP and reduced NADP (details of cyclic and non-cyclic photophosphorylation are not required)

describe the light-independent stage (Calvin cycle) as the fixation of carbon dioxide using the enzyme rubisco and the ATP and reduced NADP formed during the light-dependent stage (details of intermediate compounds are not required)

describe and explain the effect of limiting factors of photosynthesis, including light intensity, wavelength of light, carbon dioxide concentration and temperature on the rate of photosynthesis

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

describe chemosynthesis as the fixation of carbon using the chemical energy of dissolved substances; these substances include hydrogen sulfide, methane, hydrogen and iron

understand that chemosynthetic bacteria at hydrothermal vents fix the energy into a form that other organisms can use, which allows the formation of a food chain

describe the symbiotic relationship between the giant tubeworm, Riftia, found at hydrothermal vents, and the chemosynthetic bacteria Endoriftia

explain that Endoriftia uses the energy from hydrogen sulfide to fix carbon thereby producing organic compounds such as glucose (word and chemical equations are not required)

understand that aerobic respiration is the process that organisms use to release the energy they require in the form of ATP when oxygen is available

represent aerobic respiration using word and chemical equations glucose + oxygen ? carbon dioxide + water C6H12O6 + 6O2 ? 6CO2 + 6H2O

understand that in conditions where oxygen is limited or unavailable, most organisms also use anaerobic respiration which yields far less ATP per molecule of glucose (word and chemical equations are not required)

describe the structure of a mitochondrion, including matrix, outer membrane and inner membrane forming cristae

state the sites of aerobic respiration and anaerobic respiration in a cell

describe metamorphosis, larval stage, sessile and non-sessile with reference to life cycles of marine animals

describe the differences between simple and complex life cycles, to include marine mammals (simple) and crustaceans (complex), relating to the presence or absence of a larval stage and metamorphosis

outline the importance of different stages in the life cycle of sessile and non-sessile organisms

discuss the advantages and disadvantages of internal and external fertilisation, and subsequent investment in the care of offspring, with reference to tuna, sharks and whales

explain the need for the sustainable exploitation of fisheries, with reference to a named marine organism

discuss the impact of modern fishing technology, including sonar, purse seine fishing, benthic trawling and factory ships, on populations and habitats

describe the principal information needed to decide how best to exploit fisheries on a sustainable basis, limited to recruitment, growth, natural mortality, fishing mortality, age of reproductive maturity, fecundity and dependency on particular habitats

outline the principal tools used to ensure that fisheries are exploited on a sustainable basis, including:

restriction by season

restriction by quotas

restriction by licensing

restriction of location, including refuge zones, no-take zones and marine protected areas (MPAs)

restriction of method, including minimum mesh sizes and the compulsory use of rod-and-line

restrictions on the size of organism that can be retained

restriction of fishing intensity, including restrictions on the number of boats, boat and engine size, and the amount of fishing gear (for example, maximum net size, maximum number of traps)

monitoring, including air and sea patrols, satellite tracking, inspection of catch and fishing gear

imposition of fines, confiscation of boats and gear, imprisonment

consumer-orientated tools, including labelling, publicity campaigns and price tariffs

discuss the advantages and disadvantages of the tools in 8.2.4, to include their effectiveness and impact on non-target species

discuss the long-term and short-term sociological and economic impacts of, restrictions on fishing and of unrestricted fishing

discuss the advantages and disadvantages of strategies for the rehabilitation of depleted stocks, including replanting mangroves, building artificial reefs and introducing cultivated stock to the wild

describe intensive and extensive aquaculture techniques, with reference to named marine organisms

outline the process of aquaculture including in salmon, marine mussels and shrimp

explain the requirements for the long-term success of aquaculture projects, limited to availability of stock, availability of clean water, availability of feed, efficiency of use of feed, availability of labour, disease management, availability of location, market demand, access to market and return on investment

discuss the principal impacts of aquaculture, limited to habitat destruction, overexploitation of feedstocks, pollution, escape of cultured stock, introduction of (potentially) invasive species, spread of disease, competition for resources, reduction in the exploitation of native stocks, social impacts and economic impacts

explain the impacts on marine water quality, habitats, organisms and food webs of:

the oil industry

agriculture

renewable energy installations

sewage disposal

refuse disposal

desalination plants

fishing practices (including dredging and blast fishing)

explain the bioaccumulation of toxins and their biomagnification along food chains, including heavy metals in antifouling paint and mercury from the combustion of fossil fuels

understand that microplastics are plastic particles with a diameter of less than 5 mm and that there are two broad categories; primary microplastics and secondary microplastics

describe how most plastics do not biodegrade (non- biodegradable) but can be broken down to form secondary microplastic fragments, through the action of UV radiation, wind action and wave action, and how temperature affects this process

discuss the impacts of plastics and microplastics on the marine ecosystem, including:

uptake of microplastics by plankton

transfer of microplastics along the food chain

absorption of toxic compounds and their release after being taken up

ingestion of plastics by marine organisms

risk to humans if plastics or toxins enter the human food chain

entanglement (for example, ghost fishing nets)

discuss strategies to limit the release of plastics and microplastics into the marine ecosystem

describe how the natural greenhouse effect creates the Earth�s ambient temperature

explain how the enhanced greenhouse effect leads to global warming

describe the evidence for global warming

discuss and evaluate the evidence for and against the hypothesis that human activity significantly contributes to global warming

describe the possible impacts of global warming on the marine environment, including sea level rise, coral bleaching, changes in the distribution of species and potential changes to the global circulation of sea water

explain the relationships between atmospheric carbon dioxide, dissolved carbon dioxide and acidity in the ocean, and understand how the oceans help to limit the increase in atmospheric carbon dioxide concentrations

describe how carbon dioxide reacts with water to form hydrogen ions and hydrogen carbonate ions, and, the impact this has on pH and carbonate ion availability

describe the impact of 9.3.2 on hard corals and shelled organisms

(PA) investigate the effect of pH on the loss of mass of empty mollusc shells

understand the need for conservation in terms of maintaining or enhancing biodiversity

understand how the International Union for Conservation of Nature (IUCN) Red List can assist in prioritising decisions on local, regional and global marine conservation projects

explain the meaning of the terms invasive species and endangered species, as defined by the IUCN

understand why invasive species pose a threat to native marine species and ecosystems

evaluate the viability of potential conservation projects from given information

discuss strategies for conserving marine species, including:

MPAs and no-take zones

captive breeding and release programmes

legislation both locally and globally, including CITES and IWC moratorium

UNESCO biosphere reserves

the role of marine zoos and aquaria

ecotourism

control of invasive species

understand that due to the scale of many marine ecosystems, international cooperation and legislation is necessary, but not always possible (for example, non-universal sign-up to IWC moratorium or CITES), and the implications of this for conservation