Detecting+and+Responding


 * VCE Biology Unit 3: Signatures of life **


 * Area of Study 2: Detecting and responding **

__** Big Idea: Detection, transmission and response **__

This big idea is concerned with how organisms undergo detection and subsequent response to stimuli in their environments. Such processes are brought about through the endocrine and nervous systems, which are signalling systems. They are responsible for the coordination and regulation of organisms.



The endocrine system comrpises the hormones, a class of chemical messengers that are secreted into the bloodstream and transported around the body to regulate cell activity. The nervous system is responsible for receiving messages from the external and internal envirnonments of an organism, and for transmitting messages to body cells to regulate them in certain ways. The nervous systems sends messages along a nerve via electrical impulses and also through chemical messengers called neurotransmitters which are released where the nerve intersects another cell. The nervous system is responsible for detecting most external signals, via the //afferent// pathways; and then for determining an appropriate response in the //central nervous system// which is passed as a message through the //efferent// pathways.



In both processes, chemical messengers are able to regulate and coordinate cellular activity. They do this by binding to specfic receptors on membranes of target cells, causing various molecular changes in response. Generally, the endocrine system is slower to take effect, and it's changes are often longer lasting (metabolism, growth and development, mood) whereas the nervous system is much more rapid and used to respond quickly (heart rate, muscle contraction etc). The nervous system is able to respond quickly because of the speed of electrical signal transmission being very rapid. Plants provide good practical examples of hormones modulating growth as a detection and response couple through various **tropisms** (the growth of plants in response to stimulus such as light or water). Plants are able to respond to stimuli such as light, touch and gravity through the use of hormones, such as auxin.



Understanding signal transduction: how a chemical messenger can effect a response. In the above example, a chemical messenger (**ligand**), which might be a hormone, or a neurotransmitter, is shown **binding** a cell **receptor**. This process activates a chemical signal inside the cell, a process called **signal transduction**. Other chemicals, called **second messengers** are able to carry this signal, either to other parts of the cell, or into the **nucleus**. In other parts of the cell various cellular responses can occur, such as contraction of a muscle cell. If the messenger is carried to the nucleus, it can change **gene expression**, the product of **DNA** and allow for different protein products to be made.


 * __ Learning Activities __**

// (A useful segue into the discussion of detection of signals and responses - gets students to think about various demonstrations and explain them, prior to looking at theory) //

// How are your reflexes? // refer to pp 50-52 of Nature of Biology Book 2 Third Edition Activity Manual (Jacaranda, Australia 2006) (//Practical activity intended to demonstrate how a reflex arc functions, and the components of a negative feedback loop. Contains useful higher order thinking questions – Applications and issues – that help to teach the distinctions between the endocrine and nervous systems//)

// (A quick quiz to check the understanding of various stimulus response models for both endocrine and nervous systems - can be extended into an investigation of one of the systems, time permitting) //

// (An activity to test knowledge of the nervous system, in particular of receptors and signalling) //

[|Anatomy of a neuron] [|TSFX Notes - Nervous and endocrine systems] [|Signal transduction example]
 * __ Useful Links __**


 * __ Curriculum __**

[|VCAA - VCE Biology]

 (Practical activity intended to demonstrate how a reflex arc functions, and the components of a negative feedback loop. Contains useful higher order thinking questions – Applications and issues – that help to teach the distinctions between the endocrine and nervous systems) [|(useful link detailing neuronal structure)]