Aqa a2 biology writing the synoptic essay

You will have a total of 2hr 15mins to complete a mark paper worth UMS. Of these, 25 are available for the essay question, you only need to do one of the two titles. It follows that the essay should take you about 40mins. Do not spend too long on the essay at the expense of the other questions.

Aqa a2 biology writing the synoptic essay

Toward the stimulus positive taxis 2. The central nervous system CNS — brain and spinal cord 2. The peripheral nervous system PNS — Made up of pairs of nerves that originate either from the brain or the spinal cord The peripheral nervous system This is divided into: Reflex arcs contain just 3 neurons: A sensory neuron 2.

An intermediate neuron 3. A motor neuron There are several stages of a reflex arc: Coordinator intermediate neuron 6. The sympathetic nervous system — Speeds up activities and thus allows us to cope with stressful situations fight or flight response The parasympathetic nervous system — Inhibits effects and slows down activities.

This allows energy to be conserved. Controls under normal resting conditions The two divisions are antagonistic meaning that their effects oppose one another Control of heart rate Changes of the heart rate are controlled by a region of the brain called the medulla oblongata which has two main divisions One division is connected to the sinoatrial node through the sympathetic nervous system The other is connected to the sinoatrial node via the parasympathetic nervous system Control by chemoreceptors Chemoreceptors are found in the wall of the carotid arteries and detect hanges in pH as a result of CO2 concentration When CO2 concentration in the blood is too low, chemoreceptors detect the drop in pH and send impulses to the section of the medulla oblongata responsible for increasing heart rate This section then increases the number of impulses sent to the S.

A node via the sympathetic nervous system This results in an increase in heart rate which then causes blood pH to return to normal.

Control by pressure receptors Pressure receptors occur in the wall of the carotid arteries and the aorta When blood pressure is too high — impulses are sent to the medulla oblongata which then sends impulses to the S.

A node via the parasympathetic nervous system decreasing the heart rate When blood pressure is too low — impulses are sent to the medulla oblongata which then sends impulses to the S. A node via the sympathetic nervous system, increasing the heart rate Section 9.

This means that it can convert the information to a form that the human body can interpret.

Aqa a2 biology writing the synoptic essay

This is achieved by using the energy of a stimulus into a nerve impulse called a generator potential. Both receptors convert light energy into a nervous impulse and are therefore acting as transducers Rod cells Cannot distinguish between different wavelengths Many rod cells are connected to the same neuron and so can function at low light intensities.

A threshold must be reached in the bipolar cells to which they are attached to and so since they can all contribute to reaching this threshold, they will function at lower light intensities Rod cells breakdown the pigment rhodopsin to generate an action potential. Rhodopsin is easily broken down in low light intensity Since more that one rod cell is connected to the same neuron, only one impulse will be generated.

It is impossible for the brain to determine which rod cells were stimulate to begin with and so it is not possible to determine exactly the source of light This results in rod cells having a relatively poor visual acuity and so are not very effective in distinguishing between two points close together Cone cells There are three types of cone cells, each of which respond to a different avelength The colour interpreted depends of the proportion of each type of cone cell stimulated Cone cells are connected only to one bipolar cells, this means that they cannot combine to reach a threshold.

As a result of this a high light intensity is required to create a generator potential Cone cells breakdown the pigment iodopsin to create a generator potential Iodopsin can only be broken down by a high light intensity Since cone cells are connected to a single bipolar cell, when two adjacent cells are stimulated, two separate nervous impulses will be sent to the brain.

This means that it is easier to determine the source of the light. As a result, cone cells are responsible for higher visual acuity since they allow you to better distinguish between two points Light is concentrated by a lens to the centre of the eye called the fovea.

This region receives a high light intensity and therefore has more cone cells. The peripheries of the eye receive a low light intensity and therefore consist mainly of rod cells. Principles of coordination In mammals, there are two main forms of coordination: The nervous system — Uses nerve cells that can pass electrical impulses along their length.

The result is the secretion of chemicals by the target cells called neurotransmitters. The response is quick, yet short lived and only acts on a localised region of the body.

Aqa a2 biology writing the synoptic essay

The hormonal system — Chemicals are transported in the blood plasma which then reach target certain cells, thus stimulating them to carry out a function. The responses due to secretion of hormones often act over a longer period of time, yet are slower to act. Chemical mediators Nervous and hormonal forms of communication are only useful at coordinating the activities of the whole organism.

At the cellular level they are complimented by chemical mediators. Chemical mediators are secreted by individual cells and affect other cells in the immediate vicinity.

A common example of this type of coordination is the inflammation of certain tissues when they are damaged or exposed to foreign agents. Two examples of chemical mediators are:Synoptic biology unit 5 synoptic essay questions titles This document contains biology essay titles and mark schemes used in Creative writing camp massachusetts writer help A-level Biology Past papers, summary notes aqa past exam questions by topic for AQA Biology psychology case studies borderline personality disorder A-level Unit 5.

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