To Start

1. To Start What's the difference? Which one is ‘better’?

2. The Need for Communication

3. Learning Objectives • State why multicellular organisms require communication systems • Give reasons for the need to respond to changes in the internal and external environment and to co-ordinate the activities of different organs • Describe the importance of cell signalling to a multicellular organism • Describe the differences between neuronal and hormal systems of cell signalling

4. Single Celled Organisms • Can survive by just a few processes, mostly simple diffusion • Can produce simple life forms only • Relatively inefficient • Limited in development opportunities and evolutionary potential

5. Multicellular Organisms • Being multicellular allows for: • Cell specialisation that leads to: • Division of labour that leads to: • Greater overall efficiency that leads to: • Increased complexity, higher life forms, improved chances of survival and a greater possibility of evolution

6. For Example: Single Celled Agar Species Multicellular Agar Species Spherical multicellular organism Crucial features that differentiated uni- from multicellular species.  Two types of cells - about 2000 “somatic” cells with flagella that lie on the surface of a ball of jelly (or “glycoprotein-rich extracellular matric”).  These somatic cells allow coordinated swimming so that the whole ball can swim in one direction Also 16 large reproductive cells (“gonidia”) that can form sperm and eggs, which can cross-fertilize another Volvox and produce a zygote.  These zygotes undergo meiosis (becoming haploid again, like their parents), and grow inside the “female”, eventually bursting free as the mother. Can also reproduce asexually • Unicellular algarChlamydomonasreinhardtii, has flagella, threadlike organelles that can be whipped about to move the cell though the water.  • This species has been used extensively in studies of movement and organelle differentiation.  • Its genome was sequenced in 2007.  • Here’s what it looks like (note the flagella): What do these differences mean for survival? 2 minute discussion

7. Cell Life • All cells undergo metabolic processes in order to survive • These metabolic processes are controlled and facilitated by enzyme activity • Enzymes require specific conditions in order to perform optimally • These conditions must therefore be controlled • What sorts of conditions and environmental factors impact on enzyme activity – 2 minutes to write down as many as you can think of

8. Homeostasis • Because of these specific requirements for optimal enzyme activity, it is necessary to maintain a constant internal environment • This is far easier said than done and requires both systems of stimulus perception and response or • Communication and coordination

9. External Environments • Changes in the availability of food, water and shelter in the outside world have a direct and often immediate influence on the functioning of the body • Temperature – changes in temperature externally rapidly influence the internal temperature. A change of just half a degree to core temperature can have massive and sometimes catastrophic effects on cellular function. • Sweating • Vasoconstriction / dilation • Shivering • Changes to body posture • Some changes are immediate, some slow, some lasting just a few minutes or even seconds, some many months or years • Physical changes seen in animals frequently in response to changing weather or seasonal pressures or temperature include: • Moulting • Pigmentation in coats or skin

10. Maintaining a Constant Internal Environment • Enzyme activity governs cellular processes • Cellular processes and metabolism result in the production of waste products • Waste products diffuse out of the cell and into the surrounding intra-cellular fluid or tissue fluid that baths all cells • This fluid sees a rapid increase in toxic build-up as metabolism progresses or speed up • These toxins must be responded to in one of two ways: • What are they?

11. Maintaining a Constant Internal Environment • When the body is experiencing toxic build up it can do one of two things: • Reduce the speed of cellular metabolism, therefore reducing the speed of build up of these products – what’s the problem with this? • Act to remove those waste products all together, this therefore requires a system of communication (toxic build up must be detected) and transport (these products must be physically removed from the area and the body)

12. Maintaining a Constant Internal Environment • The blood and circulatory system is used to move waste products from their area of production to their area of excretion • Tissue fluid high in toxin concentration results in the diffusion of these substances into the blood • Concentrations of substances in the blood are closely monitored by a range of receptors and feedback mechanisms that then result in alterations to the functioning of various organs and organ systems around the body • Cellular respiration produces Carbon Dioxide that, when in high levels, results in an increasingly acidic pH within the tissues and, therefore, within the blood that cannot be tolerated. This pH change is highly damaging to the enzymes in the area and can prevent metabolic processes by inhibiting their action. • This control requires: • A transport system that is responsive to the demands of specific areas of the body depending on their level of activity, • Receptors that can detect minute changes in concentration, • And then systemic and body-wide control and response that may require a range of different and seemingly un-associated cells, tissues or organs to behave differently for a duration of time.

13. Communication Systems • Communication begins on a cellular level • What are the characteristics of an effective communication system? • Effective communication systems are ones that: • Extend to all regions of the body so that all areas can be communicated with • Allow cell-to-cell communication • Can act quickly should they need to • Can produce responses that last varying lengths of time

14. Cell Signalling • Cell-to-Cell signalling or communication happens through the use of chemicals • Cells release chemical signals into the surrounding area that result in changes within the cells around them • These changes often also include the further release of chemicals by those responding cells resulting in a domino effect or ‘cascade’

15. Cell Signalling Neuronal Hormonal Chemicals released from glandular tissues that must then be transported in the blood Although these chemical signals are transported throughout the entire body via the circulatory system they only affect specific target cells Target cells can only be signalled to using hormones if they have the required receptor on their surface with which to bind to the chemical and ‘read’ the message. • Uses a network of neuronal cells that link to form entire nerves – the body’s ‘wiring’ • Gaps between neurons called synapses must be crossed to allow for the continuation of the signal • These cells therefore use chemical signals or neurotransmitters to cross this gap and continue the ‘message’ • Although the nervous system uses electrical impulse to communicate with itself and the body, these electrical impulses are generated using chemicals and