Nervous System, continued.

The nervous system is coordinated by the brain and allows the body to respond to changes in the environment. We take our responses in very quick "reflex" actions  in response to stimuli. (changes in the environment)

Receptors 

• are groups of specialised cells that detect stimuli, and turn them into "electrical" impluses. 
• they are located in the sense organs, (ear, skin, nose and eye)
• each are sensitive to particular kinds of stimulus. 

Skin: receptors sensitive to: touch, pain, pressure and temperature. 
Tongue: receptors sensitive to: chemicals in food.
Nose: receptors sensitive to: chemicals in the air. 
Eyes: receptors sensitive to: light 
Ear: receptors sensitive to: sound

Process:  A receptor is stimulated by a change --> a signal (electrical impulses)  is sent along the sensory nerves to the CNS (brain+spinal cord) --> the brain then co-ordinates (decision) --> impulses are then sent along the motor nerves to the effector where the response is produced.

Eg of Effectors 

• a muscle contracting to move the arm
• a gland releasing a hormone into the blood
• a muscle squeezing saliva from the salivary gland
• a muscle squeezing sweat from the sweat gland

2.77b Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

receptors, transform external energy into internal electrical impulses. 

1. Controlling body temperature:

Human enzymes usually work best at 37-38 degres.

2. Extremes of body temp are dangerous: 
 - high temp can cause dehydration, heat stroke and death if untreated 
- low temp can cause hypothermia and death if untreated


3. Body's temp is monitored by the brain, when your too cold or too hot the brain sends nerve impulses to the skin, which has 3 ways in increasing or decreasing the heat los from the body's surfaces.

a) Hair standing up on the skin traps more warm air (reduce heat loss) and less if they are lying flat (increase heat loss). Tiny muscles is what controls the hairs to do so. The capillary network which allows blood to move further away from the skin.

b) When the body is too hot, glands under the skin secret sweat onto the surface of the skin to increase heat loss by evaporation. When body is back to normal temperature, the skin stops secreting sweat. And the capillary network allows blood to move closer to the suface of the skin.

c) Blood vessels supplying blood to the skin can swell or dilate.

On a hot day: the blood vessels dilate (widen) it is called vasodilation and hairs are flat. This means more heat is carried by the blood to the skin, where it can be lost to the air. (sweat)

On a cold day: the blood vessels shrink down (swell), this is called vasoconstriction and hairs are raised. This reduces heat loss through the skin ounce the body temp is back to normal again.

2.77a Thermoregulation

Understand that homeostasis is the maintenance of a constant internal environment and that body water content and body temperature are both examples of homeostasis.

1. Homeostasis - Homeo = 'same' stasis = conditions

2. Homeothermic - Homeo = 'same' thermic = temp

3. Homeothermic eg: Mammels 
When environmental temp increases, their body temp stays constant.

4. Homeostasis

2.76 Sensitivity

Understand that organisms are able to respond to changes in their environment 

1. Characteristics of life = MRS GREN

S = Sensitivity (how you respond to changes in the environment).

2. Types of changes: Light levels, Temp levels and Chemical Levels.

3. To detect changes, organisms have receptors. 
4. To respond to changes, organisms have effectors.
5. Response = the organism is able to survive  the changes in the environment.

2.10 Effect of pH on the rate of reaction

 Understand how the functioning of enzymes can be affected by changes in pH

1. Lower PH (acidic) = the rate of reaction gradually decreases. 
Optimum PH = maximum rate = rate of reaction decreases. 
Higher Ph (alkaline conditions) = rate of reaction gradually decreses. 

Graph is more symmetrical. 

Acidic and Alkaline conditions change the shape of the ACTIVE SITE and this slows the reaction. 

2.9 Effect of Temperature on the rate of reaction

 Understand how the functioning of enzymes can be affected by changes in temperature

1. a) Increase in temp = increase in average KE of particles. 
b) increase in average KE of particles = more frequent collisions = more fruitful reactions. 
2. Particles = Substrate and the Enzyme 
 Reaction = E+S ---> ES(complex)--> E + Product formed. 

Low temp = low KE, few complexes formed and product will be formed slowly (slow rate of reaction)
Higher temp = KE of S and E increase --> more complexes formed = more product formed. 
Optimum temp (peak of curve) = rate of reaction declined very quickly because KE changes the shape of the ACTIVE SITE of the enzyme = denatured. (cannot produce any more product).

2.8b Enzyme Reactions

Understand the role of enzymes as biological catalysts in metabolic reactions. 

1. (Oxidation of oxygen) Respiration C6 H12 O6 + O2 ---> Energy + CO2 + H2O
    Substrate                                          Released          Product

2. Combustion (adding energy) = Without an enzyme - to break down glucose ---> carbon dioxide and water - we have to put energy into the glucose molecule bonds before they break and release a lot of energy.

3. Energy of Activation = initial energy added to glucose molecules.

The shape of the active site is affected by pH. This is why enzymes will only work at a specific pH, as well as a specific temperature. Change the pH (acidic) and the enzyme stops working.

Increasing the temperature to 60°C will cause a permanent change to the shape of the active site. This is why enzymes stop working when they are heated. We say they have become denatured.

Biological systems overcome the energy of activation by THE ENZYME.