Biological explanations of obesity | AQA A-Level Psychology Revision
- Revision Notes
- Aug 6
- 23 min read
Updated: Aug 14
For 7182 specification, first teach in September 2025
AQA A-Level Psychology | Free Revision Notes
Estimated study time: 60 minutes
These biological explanations of obesity A-Level Psychology revision notes examine how inherited genetic vulnerability and neural mechanisms may contribute to obesity. You will explore how genes may influence a person’s susceptibility and how the hypothalamus regulates hunger, satiation and body fat. These explanations build directly on the regulation of hunger and satiation [Neural control of eating] and chemical signals involved in appetite [Hormonal control of eating], before being compared with restraint and disinhibition [Psychological explanations of obesity].
Learning Objectives 🎯
By the end of this revision page, you should be able to:
Define a biological explanation of obesity.
Explain how genetic inheritance may create a vulnerability to obesity.
Explain how neural mechanisms involved in eating may contribute to obesity.
Apply genetic and neural explanations to unfamiliar scenarios.
Analyse the relationship between genes, the hypothalamus and eating behaviour.
Evaluate biological explanations of obesity using evidence, methodological issues and psychological debates.
Revision Notes 📚
What does the AQA specification require?
Within the Eating behaviour option, AQA requires students to study:
Neural and hormonal mechanisms involved in controlling eating behaviour, including the hypothalamus, ghrelin and leptin.
Biological explanations of anorexia nervosa, including genetic and neural explanations.
Biological explanations of obesity, including genetic and neural explanations.
Psychological explanations of obesity, including restraint theory, disinhibition and the boundary model.
For this lesson, you must be able to describe and evaluate two broad biological explanations:
Genetic explanations
Neural explanations
You should also understand how the two explanations could be connected rather than treating them as completely separate accounts.
What is a biological explanation?
A biological explanation accounts for behaviour or psychological outcomes using physical processes within the body.
For obesity, biological explanations may focus on:
Genetic inheritance.
Biological vulnerability.
Brain structures involved in hunger and satiation.
The hypothalamus.
Neural responses to signals about energy and stored fat.
The interaction between neural and hormonal mechanisms.
This reflects the broader assumptions studied in genes, biological structures and neurochemistry [The biological approach].
Biological explanations do not necessarily claim that a person has no control over their eating behaviour. Instead, they propose that inherited and physiological differences may make weight regulation more difficult for some people than for others.
Genetic explanations of obesity
A genetic explanation proposes that inherited genetic factors contribute to a person’s vulnerability to obesity.
Genes contain biological information passed from parents to their children. Differences in genes may contribute to differences in:
Appetite.
Sensitivity to hunger.
Sensitivity to satiation signals.
Regulation of energy intake.
Biological regulation of body fat.
The functioning of neural or hormonal systems involved in eating.
A person may therefore inherit a genetic predisposition which makes obesity more likely.
A predisposition is an increased vulnerability, not a guarantee that an outcome will occur.
Genetic vulnerability, not genetic inevitability
A crucial distinction is:
Genetic vulnerability does not mean genetic inevitability.
A person may inherit characteristics that increase the likelihood of obesity, but environmental and psychological factors may affect whether that vulnerability is expressed.
Relevant environmental influences could include:
Food availability.
Learned food preferences.
Social and cultural influences.
Patterns of restraint and disinhibition.
Opportunities for physical activity.
This means that a genetic explanation can be compatible with an interaction between nature and nurture.
A strong answer should avoid saying:
“The person has an obesity gene, so they will become obese.”
A more accurate explanation is:
“The person may have inherited a genetic vulnerability which increases the probability of obesity, particularly in an environment that encourages greater energy intake.”
Genotype and phenotype
The genotype is a person’s inherited genetic constitution.
The phenotype refers to the observable characteristics that develop through an interaction between genetic inheritance and environmental influences.
Applied to obesity:
The genotype may include inherited biological characteristics affecting appetite or weight regulation.
The phenotype may include observable eating patterns or body weight.
The phenotype is not necessarily produced by genes alone because environmental experiences may influence how the vulnerability is expressed.
This distinction helps avoid an overly deterministic genetic explanation.
A single gene or several genetic influences?
A genetic explanation does not have to propose that one gene independently causes obesity.
Complex human outcomes may involve the combined influence of several genes. These inherited influences may affect different parts of the biological systems involved in eating and weight regulation.
The important examination point is that:
Genes may increase vulnerability.
Genes may influence biological mechanisms.
Genes do not operate in isolation from the environment.
Genetic inheritance does not mean the outcome is unavoidable.
Unless a question supplies the name of a particular gene, a clear explanation of genetic vulnerability is usually more valuable than an unsupported list of gene names.
Family studies and genetic explanations
Family studies examine whether obesity appears more frequently among biological relatives.
If obesity is more common among close biological relatives than among less closely related individuals, this is consistent with a genetic contribution.
However, biological relatives often share environments as well as genes. They may share:
Food availability.
Eating habits.
Attitudes towards food.
Cultural influences.
Patterns of activity.
Family similarity cannot therefore prove that genes caused the similarity.
Twin studies and concordance
Twin studies can compare monozygotic twins, who share all of their genes, with dizygotic twins, who share approximately half of their variable genes.
Concordance refers to the extent to which both twins share the same characteristic.
A genetic explanation predicts that:
Concordance for obesity should be higher among monozygotic twins than among dizygotic twins.
This pattern would support genetic influence because the pair with greater genetic similarity also shows greater similarity in the characteristic.
However, an important limitation remains:
Monozygotic twins may also experience more similar environments.
Higher concordance cannot isolate genes completely from environmental similarity.
If concordance is below 100%, genes cannot be the only influence.
Adoption evidence
Adoption research can help separate genetic and environmental explanations.
Researchers may compare an adopted person’s characteristics with:
Their biological relatives, with whom they share genes.
Their adoptive relatives, with whom they share an environment.
Greater similarity with biological relatives would support genetic influence. Greater similarity with adoptive relatives would support environmental influence.
Even this method cannot produce a perfectly controlled comparison because:
Prenatal biological influences are shared with the biological parent.
Adoptive placement may not be random.
The individual’s experiences cannot be controlled experimentally.
How genes could influence obesity
A complete genetic explanation should describe a possible pathway from inheritance to behaviour.
A useful structure is:
A person inherits a genetic vulnerability.
The genetic difference affects a biological mechanism involved in eating or weight regulation.
Hunger, satiation or the regulation of stored energy may operate differently.
The person may consume more food than their body requires or may find weight regulation more difficult.
Over time, this vulnerability may contribute to obesity.
The explanation becomes more convincing when genes are connected to their possible biological effect.
Avoid writing:
“Obesity runs in families, so it is genetic.”
This identifies a possible pattern but does not explain the mechanism.
Neural explanations of obesity
A neural explanation focuses on the role of the brain and nervous system.
The hypothalamus is a brain structure involved in the homeostatic regulation of eating. It receives information about the body’s internal state and helps regulate:
Hunger.
Food intake.
Satiation.
Energy balance.
Stored body fat.
A neural explanation proposes that differences or disruption in these regulatory mechanisms could contribute to overeating and obesity.
This section builds directly on hypothalamic control of eating [Neural control of eating].
Homeostatic control
Homeostasis is the regulation of internal conditions around an appropriate level.
Applied to eating, a homeostatic system should:
Detect when energy is required.
Produce hunger.
Encourage food consumption.
Detect when sufficient energy has been consumed.
Produce satiation.
Reduce or stop eating.
If the mechanisms that initiate or stop eating do not function effectively, food intake may not match the body’s energy requirements.
Hunger and satiation
Hunger is the biological drive that motivates eating.
Satiation is the process that causes eating to stop during or following a meal.
Do not confuse satiation with simply deciding that a meal should end. In a biological explanation, satiation involves internal signals that reduce the motivation to continue eating.
Obesity may be explained biologically if:
Hunger signals are unusually strong.
Satiation signals are unusually weak.
Hunger continues for longer than required.
Eating does not stop when sufficient energy has been consumed.
The brain does not respond normally to information about stored energy.
The hypothalamus
The hypothalamus receives and processes information relevant to eating.
The dual-control account distinguishes two areas:
The lateral hypothalamus, associated with hunger and the initiation of eating.
The ventromedial hypothalamus, associated with satiation and stopping eating.
According to this account:
A reduction in available energy activates mechanisms associated with hunger.
The person becomes motivated to eat.
Eating increases available energy.
Satiation mechanisms become active.
Eating stops.
A disruption at any stage could contribute to excessive intake.
The AQA mark scheme accepts detailed discussion of the lateral hypothalamus and ventromedial hypothalamus, including evidence from lesion research.
The lateral hypothalamus
The lateral hypothalamus, often abbreviated to LH, has been described as a hunger centre.
Its activation is associated with the initiation of eating.
A neural explanation might propose that excessive activity in mechanisms associated with hunger could:
Increase motivation to eat.
Cause hunger to occur too frequently.
Make hunger difficult to satisfy.
Contribute to excessive food intake.
However, the idea of a single, isolated hunger centre may be too simple. Eating is likely to involve interacting brain areas and bodily signals.
The ventromedial hypothalamus
The ventromedial hypothalamus, often abbreviated to VMH, has been described as a satiation centre.
It is associated with signals that reduce eating.
If VMH functioning is disrupted:
Satiation may be delayed.
The individual may continue eating for longer.
Meal size may increase.
Excessive energy intake may contribute to weight gain.
Lesion research has found that damage to the VMH can be followed by hyperphagia, meaning excessive eating.
AQA’s 2025 mark scheme identifies lesion evidence involving the VMH and overeating as relevant discussion of hypothalamic control.
Hyperphagia
Hyperphagia means excessive eating.
In a neural explanation:
Damage or disruption to neural mechanisms associated with satiation may cause hyperphagia because the signal to stop eating is weakened or delayed.
Hyperphagia describes the eating behaviour. It is not another word for obesity.
Hyperphagia may contribute to obesity.
Obesity is the longer-term outcome being explained.
Neural and hormonal mechanisms interact
Neural regulation does not operate independently of the rest of the body.
The hypothalamus responds to information carried by hormones and other biological signals. Two hormones named in the specification are:
Ghrelin, associated with hunger.
Leptin, associated with signalling stored fat and satiation.
Understanding these signals requires knowledge from ghrelin and leptin [Hormonal control of eating].
The process may be summarised as:
Hormonal signals carry information about the body’s internal state.
The hypothalamus receives and processes the information.
Neural mechanisms influence hunger or satiation.
Eating behaviour changes.
Energy intake affects stored body fat.
This interaction means that a problem described as neural may also involve hormonal signalling.
Ghrelin and hunger
Ghrelin is released when the stomach is empty and is associated with increased hunger.
In normal regulation:
An empty stomach is associated with increased ghrelin.
The signal contributes to hunger.
Eating occurs.
Ghrelin levels reduce following food intake.
When explaining obesity, be cautious. Ghrelin should not simply be described as “the obesity hormone”.
The relevant point is that disruption or individual differences in hunger signalling could contribute to increased food intake.
Leptin and stored fat
Leptin is produced in connection with stored body fat and contributes to signalling satiation.
It provides the brain with information about the body’s energy stores.
In normal regulation:
Fat stores produce leptin.
Leptin communicates information about stored energy.
The hypothalamus responds to this information.
Appetite and food intake should be reduced when sufficient energy is stored.
If the signalling system does not operate effectively, the brain may fail to respond appropriately to information about energy stores. Food intake may therefore remain higher than required.
The important distinction is:
Ghrelin is associated with increasing hunger.
Leptin is associated with signalling stored energy and reducing food intake.
Lipostatic regulation
The lipostatic account proposes that the body regulates stored fat around a biologically influenced level.
Information about fat stores is communicated to the hypothalamus, which adjusts eating behaviour.
If stored fat falls:
Hunger may increase.
Food intake may rise.
The body resists further weight loss.
If stored fat rises:
Signals associated with satiation should reduce intake.
This account may help explain why long-term weight regulation can be difficult. Biological systems may resist movement away from the level around which body fat is regulated.
Genetic and neural explanations may be connected
Genetic and neural explanations do not need to compete.
Genes may influence the development or functioning of:
The hypothalamus.
Hunger mechanisms.
Satiation mechanisms.
Hormonal signalling.
The body’s regulation of stored energy.
A combined biological pathway might be:
Inherited vulnerability → altered functioning of appetite-regulation mechanisms → weaker satiation or stronger hunger → increased food intake → increased risk of obesity
This is still a biological explanation because both the original vulnerability and the mechanism are biological.
Applying biological explanations to a scenario
Consider this example:
Several of Niall’s biological relatives have experienced similar difficulties with weight regulation. Niall reports feeling hungry soon after eating and often continues eating after other people say they feel full. A brain scan identifies unusual activity in an area of the hypothalamus involved in satiation.
A developed application might explain:
Similarity among biological relatives is consistent with a genetic vulnerability, although it does not prove genetic causation.
Feeling hungry soon after eating may indicate atypical biological regulation of hunger.
Continuing to eat after others feel full may suggest reduced sensitivity to satiation signals.
Unusual hypothalamic activity supports a neural explanation.
If mechanisms associated with satiation are less effective, Niall may continue eating beyond the body’s energy requirements.
Application structure
For an application question, use:
Scenario detail → biological concept → mechanism → link to obesity
For example:
Niall continues eating after others feel full. This could indicate disruption to neural mechanisms involved in satiation. If his hypothalamus does not respond effectively to satiation signals, he may consume more energy than required, increasing his vulnerability to obesity.
Avoid writing:
“Niall eats a lot because of his hypothalamus.”
This is too vague and does not explain the mechanism.
Distinguishing genetic and neural application
Scenario detail | Most relevant explanation | Reason |
Several biological relatives have similar weight difficulties | Genetic | Suggests inherited vulnerability |
Monozygotic twins are more similar than dizygotic twins | Genetic | Greater genetic similarity is associated with greater concordance |
Damage to an area of the hypothalamus | Neural | Directly concerns a brain structure |
Continuing to eat despite sufficient intake | Neural | May indicate disruption to satiation |
Unusual responses to hunger or satiation signals | Neural | Concerns biological control of eating |
A biological relative and an adopted individual are similar | Potentially genetic | Similarity exists despite different rearing environments |
Evaluating Genetic Explanations
Evidence from genetically related individuals
A strength of genetic explanations is that they can be investigated using:
Family studies.
Twin studies.
Adoption studies.
Measures of concordance.
If greater genetic similarity is associated with greater similarity in obesity, this supports a genetic contribution.
This is more persuasive than simply observing that obesity appears in families because twin and adoption designs attempt to separate genes from environment.
However, these methods cannot isolate genetic influence perfectly.
Shared environmental influences
Family and twin evidence may be affected by shared environments.
Relatives may share:
Food preferences.
Eating routines.
Socio-cultural influences.
Attitudes towards dieting.
Opportunities for activity.
Monozygotic twins may also be treated more similarly than dizygotic twins.
Therefore:
Higher concordance among genetically similar individuals may partly reflect greater environmental similarity.
This weakens the conclusion that genes alone account for the pattern.
Concordance is not usually complete
If genetic similarity were sufficient to determine obesity, monozygotic twins should always show complete concordance.
When one genetically identical twin differs from the other, this indicates that:
Genes are not the only influence.
Environmental experiences matter.
Psychological processes may matter.
The genetic explanation is probabilistic rather than deterministic.
This supports an interaction between nature and nurture.
Genetic evidence identifies vulnerability, not a complete mechanism
Finding that obesity is heritable does not by itself explain exactly how the genes affect behaviour.
A complete explanation should connect inheritance to:
Appetite regulation.
Hunger.
Satiation.
Neural functioning.
Hormonal signalling.
Without a biological pathway, the account may identify vulnerability without explaining the process through which it produces eating behaviour.
Ethical and social implications
Genetic explanations may reduce personal blame by showing that weight regulation can be affected by inherited vulnerability.
This may challenge the assumption that obesity results entirely from poor self-control.
However, genetic explanations also carry risks:
They may encourage biological fatalism.
A person may believe that change is impossible.
Genetic risk may be mistaken for certainty.
Individual differences may be labelled without considering environmental influences.
The distinction between predisposition and inevitability is therefore ethically as well as scientifically important.
Evaluating Neural Explanations
Evidence from lesion research
Research involving damage to the hypothalamus provides evidence that neural structures are involved in eating.
If damage to mechanisms associated with satiation is followed by hyperphagia, this supports the claim that the hypothalamus contributes to stopping food intake.
This evidence is useful because it links:
A physical change in the brain.
A change in eating behaviour.
A possible pathway to obesity.
Limitations of animal research
Much of the evidence concerning hypothalamic lesions has come from animal research.
Animal studies allow researchers to:
Manipulate specific brain areas.
Control conditions.
Measure food intake carefully.
Investigate possible cause-and-effect relationships.
However, findings may not generalise fully to human obesity because:
Human eating is influenced by cognition.
Cultural and social factors affect eating.
Humans may restrain or disinhibit their eating.
Human obesity develops within a complex environment.
The AQA mark scheme identifies the reliance on animal studies as a relevant limitation of evidence about neural control.
Lesions may have wider effects
Damage to a brain area may affect more than one process.
For example, a lesion may influence:
Movement.
Motivation.
Arousal.
Hormonal regulation.
General health.
A change in eating after brain damage cannot automatically be attributed to a single hunger or satiation centre.
This challenges an overly simple dual-control account.
Short-term and long-term effects may differ
The effects of hypothalamic damage may change over time.
An animal may initially show substantial changes in eating, but the behaviour may later become less extreme. This suggests that:
Other neural systems may compensate.
Hunger and satiation involve several interacting mechanisms.
The hypothalamus should not be treated as two isolated on-and-off centres.
Therefore, lesion evidence supports neural involvement but may not support a simple version of the explanation.
Cause and effect in human evidence
If a person with obesity shows unusual neural activity, it may be difficult to establish the direction of causality.
Two possibilities are:
Neural differences contributed to overeating and obesity.
Long-term eating patterns or changes in body fat altered neural functioning.
This is the cause-and-effect problem.
A developed evaluation should state:
Neural differences associated with obesity do not necessarily prove that those differences caused it. The neural pattern could have developed as a consequence of long-term changes in eating or body weight.
Neural explanations can be scientifically investigated
A strength of neural explanations is that biological mechanisms can be studied using objective methods.
Researchers may investigate:
Brain structures.
Neural activity.
Responses to biological signals.
Changes following brain damage.
Patterns of food intake.
Objective measurement can improve scientific credibility because findings are less dependent on a participant’s personal account.
However, a biological measurement is only useful if it is interpreted accurately. Finding a neural correlate does not automatically establish a cause.
Evaluating Biological Explanations Overall
Biological reductionism
Biological explanations may be criticised as reductionist because they reduce obesity to genes, brain structures and physiological signals.
This can be useful because it produces:
Clear hypotheses.
Measurable variables.
Testable biological mechanisms.
Potential treatment targets.
However, it may overlook:
Restraint and disinhibition.
Learned food preferences.
Social and cultural influences.
Individual decision-making.
The wider food environment.
This criticism can be developed using levels of psychological explanation [Holism and reductionism].
Biological determinism
Genetic and neural accounts may appear biologically deterministic because they explain weight through internal physical causes.
A strongly deterministic interpretation could imply that the person has little control over their eating or body weight.
This may:
Reduce personal blame.
Recognise genuine biological vulnerability.
Encourage sympathy and support.
It could also:
Promote fatalism.
Underestimate personal agency.
Ignore changes in environment or behaviour.
This evaluation links to biological forces and personal control [Free will and determinism].
Nature and nurture
Biological explanations emphasise nature, whereas psychological and social explanations emphasise nurture.
A purely biological account may struggle to explain why individuals with similar genetic vulnerability can have different outcomes.
A more complete account may involve:
Genetic predisposition.
Neural and hormonal appetite regulation.
Learned food preferences.
Cultural influences.
Psychological restraint and disinhibition.
This comparison develops the interaction between heredity and environment [The nature-nurture debate].
Comparison with psychological explanations
Biological and psychological explanations focus on different mechanisms.
Biological explanations | Psychological explanations |
Focus on genes and neural processes | Focus on thinking and patterns of eating |
Explain biological vulnerability | Explain how restraint may lead to disinhibition |
Emphasise hunger and satiation | Emphasise self-imposed dietary boundaries |
Often use objective biological evidence | Often investigate eating behaviour and cognition |
May be biologically deterministic | May place greater emphasis on learned or cognitive influences |
The next lesson examines dietary restraint and the boundary model [Psychological explanations of obesity].
A comparison should do more than describe both sides. Explain what the alternative reveals:
Psychological explanations demonstrate that overeating can be influenced by restraint and disinhibition. This suggests that neural appetite regulation alone may not provide a complete explanation of obesity.
Practical applications
Biological explanations may have practical value because they suggest that interventions should consider biological differences in:
Hunger.
Satiation.
Hypothalamic regulation.
Hormonal signalling.
Genetic vulnerability.
This may support a more individualised approach rather than assuming that the same strategy will work for everyone.
However, identifying a biological mechanism does not automatically produce an effective intervention. Obesity may involve several interacting factors, so changing one mechanism may not address all influences.
Stigma and responsibility
Biological explanations may reduce stigma by challenging the view that obesity is simply caused by laziness or a lack of willpower.
They show that eating and weight regulation may be influenced by:
Inherited vulnerability.
Brain mechanisms.
Hunger signals.
Satiation signals.
However, biological explanations must not replace one stereotype with another. It would be equally inaccurate to claim that people have no agency or that biology makes change impossible.
A balanced conclusion is:
Biological explanations can reduce unfair blame while recognising that biological vulnerability interacts with psychological, social and environmental influences.
Overall conclusion
Biological explanations provide a scientifically grounded account of how inherited vulnerability and neural regulation may contribute to obesity. Genetic research can demonstrate patterns of heritability, while neural evidence shows that hypothalamic mechanisms are involved in hunger and satiation.
However, genes do not produce inevitable outcomes, family and twin studies cannot fully separate nature from nurture, and neural evidence may rely on animal research or correlational findings. Biological explanations are therefore most convincing as part of an interactionist account that also includes psychological and environmental influences.
Planning an extended response
For an extended question, divide your answer between knowledge and evaluation.
Knowledge and understanding
Explain:
Genetic inheritance and vulnerability.
The distinction between predisposition and inevitability.
Family, twin or adoption evidence.
The hypothalamus.
Hunger and satiation.
The lateral and ventromedial hypothalamus.
How disruption could contribute to overeating and obesity.
The interaction between neural and hormonal signals.
Application
For each scenario detail:
Identify the relevant biological clue.
Name the genetic or neural concept.
Explain the mechanism.
Connect it explicitly to obesity.
Evaluation
Develop points such as:
Support from family, twin or adoption evidence.
Shared environmental influences.
Concordance below 100%.
Animal research and generalisation.
Problems with simple lesion explanations.
Cause and effect.
Biological reductionism.
Biological determinism.
Practical applications.
Comparison with psychological explanations.
Nature-nurture interaction.
Key Words 🔑
Key word | Student-friendly definition | How it may be used in an exam |
Biological explanation | An explanation based on physical processes such as genes, brain structures or bodily signals | Use it as the overall category for genetic and neural explanations |
Genetic explanation | An explanation proposing that inherited genetic factors contribute to obesity | Explain family resemblance or genetic vulnerability |
Genetic predisposition | An inherited vulnerability which increases probability without making the outcome inevitable | Avoid claiming that genes guarantee obesity |
Genotype | A person’s inherited genetic constitution | Explain the biological vulnerability a person inherits |
Phenotype | Observable characteristics produced through the interaction of genotype and environment | Explain why similar genotypes may not produce identical outcomes |
Heritability | The extent to which differences in a characteristic within a population are associated with genetic differences | Use when interpreting family or twin evidence |
Concordance | The degree to which two related individuals share the same characteristic | Compare monozygotic and dizygotic twins |
Monozygotic twins | Twins who develop from the same fertilised egg and share all their genes | Higher concordance may support genetic influence |
Dizygotic twins | Twins who develop from separate fertilised eggs and share approximately half their variable genes | Use as a comparison group in twin research |
Neural explanation | An explanation focusing on the brain and nervous system | Explain obesity using hypothalamic mechanisms |
Homeostasis | Regulation of an internal condition around an appropriate level | Explain how eating and stored energy are normally regulated |
Hypothalamus | A brain structure involved in regulating hunger, satiation and other internal conditions | Identify the central structure in a neural explanation |
Lateral hypothalamus | An area associated with hunger and initiating eating | Apply it when a scenario suggests unusually strong hunger |
Ventromedial hypothalamus | An area associated with satiation and stopping eating | Apply it when a person continues eating despite sufficient intake |
Hunger | A biological drive which motivates eating | Explain the initiation of food consumption |
Satiation | The process that causes eating to stop during or after a meal | Explain how weak stopping signals could contribute to overeating |
Hyperphagia | Excessive eating | Link damage to satiation mechanisms with increased intake |
Ghrelin | A hormone associated with increased hunger when the stomach is empty | Distinguish it from leptin in an exam |
Leptin | A hormone associated with stored body fat and signalling satiation | Explain communication between fat stores and the hypothalamus |
Biological determinism | The view that behaviour is governed by internal biological factors | Evaluate whether the explanation underestimates personal agency |
Biological reductionism | Explaining a complex outcome using lower-level biological processes | Evaluate whether social and psychological influences are neglected |
Hints from the Examiner Reports 💡
Examiner hint: Keep every paragraph focused on obesity. In the 2025 Eating Behaviour section, some otherwise descriptive answers remained in the middle mark bands because they did not clearly explain how the material related to obesity.
Examiner hint: Do not confuse hunger and satiation. The lateral hypothalamus is associated with initiating eating, while the ventromedial hypothalamus is associated with stopping eating.
Examiner hint: Distinguish ghrelin from leptin precisely. The 2025 report noted that some students muddled the two hormones and their mechanisms. Ghrelin is associated with hunger, while leptin communicates information about stored fat and satiation.
Examiner hint: Answer every part of the question. When an extended question refers to two mechanisms, both must be explained accurately rather than discussing one in detail and briefly naming the other.
Examiner hint: Evidence must be used to construct an argument. The 2025 report found that stronger students fully elaborated discussion points and used evidence effectively rather than merely naming studies.
Examiner hint: Animal lesion research can support a neural explanation, but high-level evaluation should consider whether findings generalise to human obesity.
Examiner hint: Make application psychologically precise. A family history may support genetic vulnerability, while continued eating despite sufficient intake may support disruption to satiation. Do not simply repeat the scenario.
Examiner hint: For a discussion question, avoid writing a long description followed by a brief list of generic limitations. Integrate evidence, counterarguments and their implications throughout the response.
Common Mistakes ⚠️
Mistake: Saying that a gene directly and inevitably causes obesity.
Why this is incorrect:A genetic explanation usually concerns vulnerability rather than certainty. Environmental and psychological influences may affect whether the vulnerability is expressed.
How to improve:Use phrases such as “increases susceptibility”, “creates a predisposition” or “raises the probability”.
Mistake: Assuming that obesity running in a family proves genetic transmission.
Why this is incorrect:Family members usually share food, culture, routines and other environmental influences as well as genes.
How to improve:Explain why twin or adoption evidence may provide a stronger test, while still recognising its limitations.
Mistake: Treating heritability as the percentage of one person’s obesity caused by genes.
Why this is incorrect:Heritability concerns variation within a population. It does not divide one individual’s outcome into a genetic and environmental percentage.
How to improve:Use heritability when discussing differences across a group, not the cause of one person’s characteristics.
Mistake: Saying that monozygotic twins have identical experiences.
Why this is incorrect:They share their genes, but they may experience different environments. They may also be treated more similarly than dizygotic twins.
How to improve:State that twin studies compare genetic similarity, but environmental similarity remains a possible confounding influence.
Mistake: Describing the lateral hypothalamus as the satiation centre.
Why this is incorrect:The lateral hypothalamus is associated with hunger and initiating eating.
How to improve:Remember: lateral starts eating, ventromedial helps stop eating.
Mistake: Describing the ventromedial hypothalamus as producing hunger.
Why this is incorrect:The ventromedial hypothalamus is associated with satiation.
How to improve:Link VMH disruption with delayed stopping or hyperphagia.
Mistake: Confusing ghrelin and leptin.
Why this is incorrect:Ghrelin is associated with hunger, while leptin communicates information about stored fat and contributes to satiation.
How to improve:Write the two mechanisms separately before explaining how the hypothalamus responds to them.
Mistake: Calling hyperphagia another word for obesity.
Why this is incorrect:Hyperphagia means excessive eating. It may contribute to obesity but is not the same outcome.
How to improve:Write the causal link explicitly: weakened satiation may cause hyperphagia, which may increase the risk of obesity.
Mistake: Assuming that a neural correlate is automatically a neural cause.
Why this is incorrect:Unusual neural activity may cause eating changes, but it may also result from long-term eating patterns or changes in body weight.
How to improve:Evaluate the direction of cause and effect.
Mistake: Evaluating animal research by saying only that humans are different.
Why this is incorrect:This is too vague to demonstrate why generalisation is difficult.
How to improve:Explain that human eating is also influenced by cognition, culture, restraint and social context.
Mistake: Writing generally about the hypothalamus without linking it to obesity.
Why this is incorrect:A question about biological explanations of obesity requires an explanation of how disruption could increase food intake or weight.
How to improve:End each neural paragraph with the behavioural consequence and its connection to obesity.
Mistake: Describing restraint theory in detail instead of evaluating biology.
Why this is incorrect:Restraint and disinhibition belong to psychological explanations.
How to improve:Use psychological theory only as a direct comparison showing that biology may be incomplete.
Exam-Style Questions ✍️
Question 1
Which of the following best describes a genetic predisposition to obesity?
A. A gene makes obesity unavoidable.B. Inherited factors increase vulnerability to obesity.C. Obesity is caused only by a shared family environment.D. Eating behaviour cannot be affected by experience.
[1 mark]
Question 2
Explain what is meant by concordance in twin research.
[2 marks]
Question 3
Explain how twin research could be used to investigate a genetic explanation of obesity.
[4 marks]
Question 4
Explain how disruption to the ventromedial hypothalamus might contribute to obesity.
[4 marks]
Question 5
A researcher compares three groups of relatives. The researcher finds the following pattern:
Group | Relative concordance for obesity |
Monozygotic twins | Highest |
Dizygotic twins | Intermediate |
Unrelated individuals | Lowest |
Explain what the pattern suggests about genetic explanations of obesity. Identify one conclusion that cannot be drawn from these results.
[4 marks]
Question 6
Jasmin says that she feels hungry soon after eating and rarely experiences a strong feeling of satiation. Several of her biological relatives have experienced similar difficulties with weight regulation. Tests suggest that Jasmin responds atypically to signals received by the hypothalamus.
Use biological explanations to explain Jasmin’s weight-regulation difficulties.
[6 marks]
Question 7
Explain one limitation of neural explanations of obesity.
[4 marks]
Question 8
Evaluate biological explanations of obesity.
[8 marks]
Question 9
Samir has experienced difficulties regulating his weight since childhood. His biological father and two biological siblings have experienced similar difficulties. Samir says he becomes hungry quickly and often continues eating after other people have stopped. A researcher suggests that Samir’s hypothalamus may not respond effectively to information about stored energy.
Discuss biological explanations of obesity. Refer to Samir in your answer.
[16 marks]
Answers and mark scheme
Question 1
Answer: B
A genetic predisposition increases vulnerability but does not make obesity inevitable.
[1 mark]
Question 2
Award up to two marks:
Concordance is the extent to which both members of a pair share the same characteristic.
In obesity research, it concerns whether both twins show obesity or similar weight-related outcomes.
[2 marks]
Question 3
Award one mark for each relevant point, up to four marks:
Researchers could compare monozygotic and dizygotic twins.
Monozygotic twins share all their genes, while dizygotic twins share approximately half their variable genes.
Concordance for obesity could be calculated for each type of twin.
Higher concordance among monozygotic twins would support genetic influence.
Credit other clear explanations of the design.
[4 marks]
Question 4
Award up to four marks:
The ventromedial hypothalamus is associated with satiation.
Disruption may weaken or delay signals to stop eating.
The person may continue consuming food after sufficient energy has been obtained.
Continued excessive intake or hyperphagia may contribute to obesity.
[4 marks]
Question 5
Award up to four marks:
The highest concordance among monozygotic twins is consistent with genetic influence.
Monozygotic twins are more genetically similar than dizygotic twins.
The intermediate and lower concordance rates suggest that increasing genetic similarity is associated with increasing similarity in obesity.
The pattern cannot prove that genes caused obesity because groups may also differ in environmental similarity, or because correlation does not establish causation.
[4 marks]
Question 6
Award one mark for each clear application, up to six marks:
Similar difficulties among biological relatives are consistent with genetic vulnerability.
Jasmin may have inherited characteristics affecting appetite or weight regulation.
Feeling hungry soon after eating may indicate atypical hunger regulation.
Weak satiation may involve neural mechanisms associated with the hypothalamus.
Atypical responses to signals received by the hypothalamus support a neural explanation.
Continued hunger or weak satiation may increase food intake and contribute to weight-regulation difficulties.
Credit other accurate applications of genetic or neural explanations.
[6 marks]
Question 7
Award marks as follows:
One mark for identifying a relevant limitation.
Up to three further marks for developing its effect.
Possible answer:
Much evidence about the hypothalamus comes from animal lesion studies. These studies allow researchers to investigate cause and effect, but human eating is also influenced by cognition, culture and learned behaviour. Findings from animals may therefore not provide a complete explanation of human obesity.
Other relevant limitations include:
Lesions may affect several functions.
The dual-control account may be oversimplified.
Human neural findings may be correlational.
Neural differences may be a consequence rather than a cause.
Neural explanations may be biologically reductionist.
[4 marks]
Question 8
Indicative content may include:
Knowledge
Genetic inheritance and predisposition.
Family, twin and adoption evidence.
Genotype and phenotype.
Hypothalamic regulation of eating.
The lateral and ventromedial hypothalamus.
Hunger, satiation and hyperphagia.
Interaction between neural and hormonal signals.
Evaluation
Support from greater concordance among genetically similar individuals.
Shared environmental influences in family and twin studies.
Concordance below 100%.
Difficulty identifying the precise pathway from genes to behaviour.
Support from hypothalamic lesion research.
Problems generalising animal findings.
Lesions may affect several functions.
Cause-and-effect problems in human neural research.
Scientific objectivity.
Biological reductionism and determinism.
Comparison with psychological explanations.
Nature-nurture interaction.
Practical and ethical implications.
For the highest marks, evaluation should be developed and linked directly to the explanatory value of the biological account.
[8 marks]
Question 9
Indicative content may include:
Knowledge and understanding
Genes may create an inherited vulnerability to obesity.
Genetic predisposition increases probability rather than producing certainty.
Family and twin similarity may support heritability.
The hypothalamus regulates hunger and satiation.
The lateral hypothalamus is associated with initiating eating.
The ventromedial hypothalamus is associated with satiation.
Atypical responses to information about stored energy may disrupt appetite regulation.
Neural and hormonal mechanisms interact.
Application to Samir
Similar difficulties in Samir’s biological father and siblings are consistent with genetic vulnerability.
A familial pattern does not prove causation because relatives may share environments.
Becoming hungry quickly may indicate atypical hunger regulation.
Continuing to eat after others stop may indicate weakened satiation.
The proposed hypothalamic response provides a neural explanation.
Failure to respond effectively to stored-energy information may increase food intake.
Evaluation
Genetic similarity may support inherited vulnerability.
Shared family environments provide an alternative explanation.
Genetic vulnerability is not inevitable.
Animal lesion evidence supports hypothalamic involvement.
Animal findings may not generalise completely to human eating.
The hypothalamus is unlikely to consist of two isolated control centres.
Neural differences may be a cause or consequence.
Biological explanations are objective and scientifically testable.
They may be reductionist or deterministic.
Psychological explanations such as restraint and disinhibition provide alternatives.
An interaction between biological and environmental influences may offer a fuller explanation.
A high-level answer will use specialist terminology accurately, apply several details from Samir’s situation and develop evaluation rather than listing brief strengths and limitations.
[16 marks]
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