How Structure Determines Function in Living Organisms
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Homework type: Essay
Added: 6.02.2026 at 9:37
Summary:
Explore how the structure of living organisms determines their function, helping you understand key biological processes and life functions clearly and effectively.
Structures and Functions in Living Organisms
The exquisite orderliness of the living world reveals itself most clearly through the relationship between an organism's structure—how it is built—and its function—what it does. Living organisms, from the simplest bacterium to the intricate form of a human being, are composed of specialised structures that enable them not only to survive, but to thrive, adapt, and reproduce. In this essay, I will explore the pivotal ways in which living things are structured to fulfil their essential life processes. Drawing on examples from the British ecological landscape and scientific literature, I will examine the remarkable diversity of life, the sophisticated inner workings of cells, and the essential mechanisms like diffusion and osmosis which underpin existence. By teasing apart these relationships, we gain a deeper understanding of the fundamental unity and extraordinary variety of life on Earth.---
Fundamental Characteristics of Living Organisms
To begin, it is necessary to establish what is meant by a living organism. The most accepted definition, employed in UK schools and illuminated by authors such as Richard Dawkins in *The Selfish Gene*, refers to a living thing as an entity capable of carrying out certain life processes. These processes—often taught as Mrs Gren (Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition)—represent the shared characteristics distinguishing the animate from the inanimate.Nutrition, for example, is essential as it provides both energy and the raw materials for building new cellular structures. Growth, while evident in a sapling maturing into an oak within ancient British woodlands, also encompasses the less visible cellular enlargement and division taking place in all multicellular organisms. Reproduction ensures the continuation of species, whether through the flowering and pollination seen on the South Downs or the spawning of sticklebacks in British streams. Respiration—the release of energy from food—powers every activity, from a worm burrowing in the soil to marathon runners completing the London Marathon.
Excretion removes waste by-products that could be otherwise toxic, while sensitivity and movement enable an organism to respond to changes in the environment and seek favourable conditions. Not least, all living things demonstrate homeostasis: the delicate regulation of internal environments, seen in the way hedgehogs regulate their temperature or humans their blood sugar.
Each of these processes highlights the link between an organism’s structure and its function. Specialised structures at molecular, cellular, tissue and system levels carry out these vital tasks, a principle explored through the study of biology from Key Stage 3 up to A level across schools in the United Kingdom.
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Cellular Structures and Their Roles
All living things are composed of cells, a discovery dating back to Robert Hooke, the seventeenth-century English scientist, whose work with cork under a primitive microscope first revealed the compartmentalised nature of life. At a fundamental level, both plant and animal cells share core structures. The nucleus, containing the genetic material, is the command centre dictating cell activity and overseeing cell division—an idea explored through the inheritance experiments of Gregor Mendel and later work here in Cambridge and London. The cell membrane acts as a controlled gateway, meticulously selecting which substances may enter or exit, maintaining the internal balance vital for survival. The cytoplasm serves as the bustling locale where countless chemical reactions take place, facilitated by dissolved enzymes and nutrients.Plant cells, however, possess additional features reflecting their need to photosynthesise, stand upright, and withstand changing weather. Chloroplasts (containing chlorophyll) capture sunlight and convert it into chemical energy through photosynthesis—a process famously investigated by British botanist Joseph Priestley. The cell wall, made primarily of cellulose, bestows strength and allows plants such as stinging nettles to withstand strong winds across the fens. Vacuoles store water, sugars, and waste substances, helping maintain the rigidity (turgor) of non-woody stems like those of bluebells.
Animal cells, in contrast, lack cell walls and chloroplasts. Their flexible membranes and internal vesicles better suit fast movement and sensory response, a feature critical to creatures as diverse as red squirrels and blue tits. Animal cells also contain lysosomes which are responsible for the breakdown and recycling of cellular waste, and they store carbohydrates as glycogen—a highly branched form, particularly suited for quick energy release, for example during the explosive speed of a rabbit evading predators.
Other life forms possess unique cellular features. Protoctists are an eclectic group, mainly unicellular, sometimes sharing characteristics with plants (as in Chlorella) or animals (as in Amoeba). Fungal cells, with chitin-based walls, absorb nutrients from decaying matter—the familiar sight of bracket fungi on rotting logs attests to their ecological importance. Bacteria, lacking a distinct nucleus, deploy their genetic material directly in the cytoplasm. Their simple, robust nature enables survival in habitats as variable as a school canteen or the subways of London. Viruses, strictly speaking, are not cells at all, but packages of genetic material encased in protein, only able to reproduce by invading cells—a topic of urgent relevance in light of recent global health challenges such as COVID-19.
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Classification and Examples of Living Organisms with Structural Adaptations
The rich tapestry of British wildlife shows how varied adaptations underpin survival. Plants, such as wild peas or wheat in the fields, are multicellular and photosynthesise, harnessing light to manufacture sugars which may then be stored as starch. Their cellulose walls support delicate structures like leaves and strengthen mighty oaks. In contrast, animals such as foxes or woodlice are heterotrophic—they must consume organic material, lack the rigid cell walls of plants, and store carbohydrate as glycogen, enabling swift and flexible movement.Fungi, often overlooked, play vital roles in the breakdown of organic matter—mushrooms seen in damp woodlands producing spores, single-celled yeast enabling the rising of bread, or Penicillium mould observed by Alexander Fleming in his St Mary’s Hospital laboratory. Protoctists, such as Euglena found in British ponds, often straddle the divide between animals and plants, equipped both with chloroplasts and the ability to consume food. Bacteria, ubiquitous and hardy, thrive in places as mundane as the kitchen fridge or as hostile as local lakes polluted by acid rain. Viruses, while not alive in the traditional sense, wield immense influence—think of winter bouts of influenza or the continuous battle against tobacco mosaic virus in gardening.
Each of these groups demonstrates unique structural solutions to life’s problems, reflected in cell walls of different composition, the presence or absence of chloroplasts, and diverse strategies for nutrient acquisition and reproduction.
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Enzymes: Biological Catalysts Underpinning Metabolic Functions
Central to the function of every cell are enzymes. These astonishingly specific biological catalysts enable millions of life-sustaining reactions to take place at the mild temperatures and pressures typical of living organisms. Without them, essential tasks such as the conversion of starch to glucose during digestion (examined in depth in standard AQA GCSE Biology texts) simply would not occur at a rate compatible with life.Enzymes exhibit remarkable precision. In the lock and key model, the active site of an enzyme is shaped to fit a particular substrate, much as a key fits only one lock. This specificity explains why digestive enzymes such as amylase (in saliva) break down starch but not proteins, for which protease is needed instead. When conditions stray too far from those found in the body—if, for instance, the temperature rises above 40°C during a high summer heatwave—enzymes lose their carefully folded shapes (becoming denatured) and can no longer perform their function. Similarly, extremes of pH, such as that found in the stomach compared to the intestine, determine which enzymes are active where.
Metabolic processes such as respiration (in all cells), photosynthesis (in plants), or decomposition (in fungi) rely on suites of enzymes, and their importance extends to everyday life in the UK—for example, in the cheese and bread industries or the development of antibiotics.
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Mechanisms of Transport in Cells: Diffusion and Osmosis
No structure, regardless of design, is effective unless it enables the controlled movement of materials. Two vital transport processes in cells are diffusion and osmosis.Diffusion is the passive movement of particles from areas of higher to lower concentration, central to gas exchange in living things. In humans, this occurs in the alveoli of the lungs, where oxygen diffuses from the air into the blood, while carbon dioxide moves the other way. In plants, it enables the uptake of carbon dioxide required for photosynthesis—a process beautifully illustrated in any woodland walk in spring. A common classroom experiment employs agar blocks containing indicator dye; when acid is added, the colour change highlights the progress of diffusion, demonstrating its reliance on concentration gradients and permeability.
Osmosis, by contrast, is the net movement of water molecules through a partially permeable membrane, from a region of high water concentration to low. Its practical importance is seen in everyday experiments involving potato slices in salty or sugary solutions: if water enters the potato cells, they become turgid (firm), but if water leaves, the cells shrink and become flaccid—a process explaining why a cucumber left too long in salt will go limp. Osmosis maintains cell turgor and hydration, critical for upright stems and the crispness of lettuce in a sandwich.
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Integration of Structure and Function in Organism Survival
Time and again, the relationship between form and function is demonstrated. In plants, the thick cell wall and central vacuole help maintain structure and efficient water usage, enabling growth upwards towards light. Chloroplasts, arranged near the cell surface, maximise light capture for photosynthesis, a crucial adaptation in shady British woodlands.In animals, muscle cells are laden with mitochondria to release energy rapidly, suited for sprinting hares or migrating geese. Nerve cells are elongated with insulating sheaths facilitating swift transmission of signals, underpinning complex behaviours from hedgehog self-defence to human speech. Microorganisms boast structures that promote rapid replication or survival in harsh environments—bacterial spores remaining dormant for years in British soils, or viral coats designed to evade immune detection.
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