Assumptions of the Biological Approach


  • All thoughts, feelings and behaviours have a physical basis.
  • To fully understand human behaviour, we must look at biological structures and processes.
  • All behaviours have a genetic basis.
  • Behaviour has evolved in the same way as physical characteristics.
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Biological Structures and Processes

Genes - The type of genes you have control your behavioural characteristics. People with mutated genes often behave differently. For example genes on chromosome 10, 11 and 20 have all been linked with alcoholism. The A2MP1 gene on chromosome 12 is associated with Alzheimers disease.

Brain - Areas of your brain control behavioural characteristics. People with damaged brain areas behave differently. For example reduced activity in the prefrontal cortex is linked to ADHD. Schizophrenia is linked to loss of brain tissue.

Neurochemistry - Neurotransmitters in your brain influence behavioural characteristics. Different levels of these chemicals make people behave differently. For example lower than normal levels of serotonin is linked to depression. Problems in producing dopamine causes Parkinson's disease.

Hormones - Chemicals in your blood influence behavioural characteristics. People with hormone inbalances behave differently. For example high levels of testosterone are seen in violent offenders. Oxytocin is produced in the mother after giving birth to help form a bond with the baby.

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Evaluation of the Biological Approach Assumptions


  • Scientific methods of investigation - the approach uses a range of objective and well-controlled methods, such as brain imaging, EEGs, family and twin studies. This makes the approach reliable.
  • Real life application - increased understanding of the brain has led to the development of drugs to treat illnesses. Thanks to these, sufferers can live a relatively normal life, rather than remain in hospital.


  • Cause and effect - it is assumed that mental illnesses are caused by neurochemical imbalances, but only because drugs that effect these chemicals reduce the symptoms of the illness. The association between to variables does not mean that one causes the other.
  • Deterministic - the approach believes behaviour is caused by biological processes over which we have no control. This has implications for the legal system because offenders may not be responsible for their actions.
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Genes - genes are short pieces of DNA. They tell the body which protein to make. Humans have around 25,000 gens. 50% of our genes come from our biological mother, and 50% come from our biological father.

Chromosomes - Chromosomes are made of coils of DNA. Humans have 23 pairs of chromosomes, so 46 altogether. One chromosome in each pair comes from a person's biological mother, and the other from their biological father. Cell nucleus - the nucleus of a cell contains the genetic information (chromosomes) that a person has. Genes do not influece behaviour directly. Genes tell the body which protein to make and how much. The human body is made of protein and all the chemicals used in the body are protein based. The proteins made affect both the structure of the nervous system and how the nervous system works. This is what affects behaviour



Nervous system

                                     Structure                                                                                    Function


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Genotype and Phenotype

An animals genotype is its actual genetic makeup, i.e. its genes or alleles.

An animals phenotype is the observable characteristics that the animal shows.These could be physical, behavioural or psychological. Phenotype is determined by the genotype and the environment.

E.G. cat's ears - purely genetic.

Phenotype - normal       OR phenotype - folded ears.

Genotype - fd-fd             OR genotype - Fd-Fd

Some genes are dominant. This means they will show in the phenotype even if there is only one pair in a chromosome.

Some genes are recessive. This means that they will only show in the phenotype if they are on both chromosomes.

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Methods for Investigating Genetic Influences

Family History Study - in a family history study, researchers recruit a sample of people who have a particular characteristic. These people are known as the probands in the study. They then look at the probands' relatives to see if they have the same characteristic. In their analysis, they take into account how closely related each relative is to the proband as the more closely related they are, the more genes they are likely to share. For example, you share more genes with your parents than your grandparents. The analysis looks for a relationship between how many genes are shared and how frequently the relative has the same characteristic as the proband. If a genetic influence is present, the closer a person's relationship with a proband, the more likely they should be to show the characteristic themselves.

Adoption study - In an adoption study, the probands are people who were adopted as children. They are compared with their adopted parents and their biological parents in the characteristic in question. If the proband and the parent have the same characteristic, they are said to be concordant. If a genetic influence is preset, concordances should be higher between the probands and their biological parents than between probands and adoptive parents.

Twin Study - A twin study is like a family history study, except that only two types of relationships are studied. Like the family history study, a sample of probands is recruited. In a twin study, the probands must all be one half of a twin pair. The researchers need to use both identical (MZ) and non identical (DZ) twins. MZ twins share 100% of their genes, whereas DZ twins share 50%. As in a family history study, the researchers are interested in the concordances between probands and their twins on a particular characteristic. If a genetic influence is present, concordance should be higher between MZ twins than DZ twins.

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Problems with Genetics Research

  • The more closely you are related to someone, the more likely you are to live in a similar environment.
  • Adopted children and not necessarily adopted at birth.
  • Adopted children may be place with similar families to their biological ones.
  • DZ twins are not treated as similarly as MZ twins, MZ twins look the same, are often dressed the same and may be treated by family members as a single unit. This is less likely with DZ twins as they may generally look different and may even be different sexes.
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Behaviour is thought to develop in the same way as physical characteristics. This is based around adaptiveness.

Characteristics are transmitted between generations via genes. Some characteristics are adaptive - they increase the chance of survival and reproduction.

Initially, there is a random change in DNA known as a mutation. This leads to a new characteristic. If the new characteristic means the individual is less likely to survive, the new gene will not be passed on, and so the mutation is maladaptive.

If the new characteristic increases the chance of survival, the individual passes the new gene on when the reproduce, and so the mutation is adaptive.

For example: The peppered moth - before the industrial revolution, white moths with black spots had a better chance of survival as they blended in with lichen on trees, however afterwards, the black ones survived becuase there was no lichen on trees, so they could blend in.

Giraffes with longer necks survived because they could reach more food on trees.

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Real Life Examples of Evolution

Intelligence - You can think about doing new things e.g. new ways to find food, real life problem solving such as how to cook food, communication etc.

Memory - If you have a good memory, you are more likelly to remember things such as where food is, where not to go to avoid danger etc.

Aggression - You can fight others to win things such as food, and you can also fight/kill people who are a threat to you. Also, you can hunt food.

Attractiveness - If you are more attractive, you are more likely to reproduce and your genes will carry on.

Phobias - Phobias force people to be scared of things that will put them in danger, for example a phobia of heights means that you will avoid high cliffs that you could fall off and die.

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Structure of a Neuron

The whole of the nervous system is made up of neurons. These are specially adapted cells that receive and send out electrochemical messages.

Dendrites - Receive nerve impulses from surrounding neurons.

Nucleus - Contains the genetic material and controls the activity of the cell.

Cell body - Connects the dendrites to the axon and contains the organelles.

Axon - Sends nerve impulses from the cell body to the nerve ending.

Myelin Sheath - Insulates the axon and makes the transmission of nerve impulses faster.

Nodes of Ranvier - Allows the nerve impulses to 'jump' accorss the gaps on the axon.

Terminal Button - Where the electrical signals stop and turn into chemical signals.

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Types of neuron.

Sensory neurons - Carry messages from receptors in the sense organs to the brain and spinal chord. They tell the brain about environmental stimuli. They have long dendrites and a short axon. They are unipolar, meaning they only transmit messages from receptors to the central nervous system.

Relay neuron - Carry messags from one part of the central nervous system to another. They connect sensory and motor neurons. They have short dendrites and short axons. They are multipolar, meaning they send and receive messages between the central nervous system, and effectors.

Motor neurons - Carry messages from the central nervous system to effectors, including muscles and glands. They have short dendrites and long axons. They are multipolar, meaning they send and receive messages between the central nervous system and effectors.

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Nerve Impulses - Action Potentials

All chemicals in the body have an electrail charge. They are called ions. The most important ions in the nervous system are sodium (+), potassium (+), calcium  (++), chloride (-) and a protein molecule (-). Neurons have semi-permeable membranes that allow some ions to pass through and block others.

When a neuron is at rest, the inside of the neuron is negatively charged (-70mV). This is because of how the ions arrange themselves, with more negative ions inside the axon.

When the cell body sends information, an action potential occurs. This is caused by depolarisation, where the charge reverses and becomes positive (+30mV). This si cause by ion channels opening.

Once an action potential has occured, the neuron returns to its resting state of being negatively charged. This is called repolarisation.

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Each neuron is seperated from the next by a gap called a synapse.

An action potential reaches the end of the neuron.

This triggers the release of neurotransmitters from tiny sacs called vesicles.

The neurotransmitter diffuses across the synapse.

The neurotransmitter molecules bind to the post synaptic receptor sites on the dendrites of the next neuron.

The chemical message is converted back into an action potential.

Enzymes release the neurotransmitter from the receptor sites.

Used neurotransmitter is taken up by the presynaptic neuron and new vesicles are formed.

The whole process starts again with a new action potential in the presynaptic neuron.

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Fight or Flight AND Rest and Digest

Symapthetic nervous system - A division of the ANS. It consists of a series of connections from the spinal cord to the major internal organs. It becomes more active when we are doing something that requires an expenditure of energy. For example, it prepares us to either fight/ protect our selves, or run away in stressful situations such as when someone threatens to hurt you.

Parasympathetic nervous system - A divsion of the ANS. It consists of a series of connections from the brain to the major internal organs. It is active most of the time, contrlling homeostatic functions and ensuring that we conserve energy. For example, it is at work on a normal, non stressful day, and is known as rest and digest.

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The Fight or Flight Response

1. Threat.

2. The hypothalemus recognises the threat.

3. Sympathetic nervous system is activated. - increased oxygen intake, slows down digestive system, glucose is sent to the muscles for respiration.

4. Adrenal glands release adrenalin. -  maintains high level of activity in the sympathetic nervous system.

5. Pituitary gland produces ACTH.

6. Adrenal medulla releases corticosteroids. -  increases blood sugar levels, increases blood pressure, increases the reaction to injuries.

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Reasons for the Changes caused by the Fight or Fli

Increased heart rate - speed up blood flow to vital organs because blood contains oxygen and glucose. It also improves the spread of adrenalin.

Faster breathing rate - increase oxygen intake for respiration.

Muscle tension - improve reaction time and speed.

Pupil dialation - improve vision.

Production of sweat - help temperature regulation.

Reduced digestion and immunity - save energy for priority functions such as running.

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