Science- B1

'Healthy' and 'Fit'

Being healthy doe snot mean being fit. being healthy is being free of infections and diseases where as being fit means you can perform physical tasks.

Blood is pumped around the body under pressure.

Systolic pressure is when the heart contracts (this is when the blood is at  its highestt pressure). whilst diastolic is when the heart relaxes and it is at its lowest pressure. Blood pressure is measured in mm of mercury (mmHg). In a normal healthy person it should be no more than 135 (systolic pressure) over about 85 (diastolic pressure). Apart from the heart contracting there are other factors that cause increase in heart pressure: Smoking, being overweight, drinking too much alcohol, and being under a lot of stress.

These factors can cause heart disease.

Smoking causes high blood pressure as it has carbon monoxide which combine with haemoglobin in red blood cells which reduces the amount of oxygen they can carry, to make up for this causes the heart to beat faster in order to carry blood around the body. the heart contract more frequently, which increases blood pressure. Also nicotine is addictive, it increases heart  rate, the heart contracts more often, increasing blood pressuure.

A poor diet can also cause an increase in blood pressure. Saturated Fats can cause a build up of cholestrol { this can cause a build up of plaque in the vein  stopping oxygen from reaching the heart. This can cause stroke and heart attack which are a diisease of a heart.

1. The cornea refracts (bends) light into the eye

2. The iris controls how much light enters the pupil

3. The lens also refracts light, focusing it onto the retina

4.  The retina is the light sensetitive part and it is covered in receptors called rods and cones, which detect light.

5. Rods are more sensetitive in dim light but can not sense colour

6. Cones are sensetitive to different light but are not so good in dim light (red-green colour blindness is due to the lack of certainspecialised cone cells).

7. the optic nerve carries impulse from the receptors to the brain.

The Central Nervous System (CNS) coordinates information:

The nervous system uses electrical impulses to allow very quick responses.  Reflex actions  are automatic (done without thinking) so they are even quicker. this means the conscious brain is not involve in a reflex arc. the sensory neuroneconnects to a relay neurone in the spinal cord  (CNS) - whioch links directly to the right motor neurone.

Neurones transmit information around the body  as electrical impulse:

1. The electrical impulse (Stumili) is passed along the auxon of the cell.

2. Neurones have branched endings (dendrites) so they can conect with lots of other neurones.

3. they have a sheath along along the axon that acts as an electrical insulatoor, which the electrical impulse.

4. They are long , which also speeds up the impulse (connecting with another neurone slows the impulse down, so one long neurone is better then lots of short ones joined together).

5. the connection between two neurones is called a synapse. It  is basically a tiny gap:

• the electrical impulse triggers the release of tranmitter chemicals, which diffuse arcross the gap.
• these chemicals bind to receptor molecules in the membrane of the next neurone. This sets off a new electrical impulse
• stimulant druges increase the amount of transmitter chemical at some synapses, which increase the frequency of impulses along neurone 2
• Depressants bind with receptor molecules on the membrane of neurone two blocking the electrical impulse. This decreases brain activity

Homoestasis is maintaining a constant internal environment:

conditions in your body need to be kept steady so that cells can function properly. This involves balancing inputs ( stuff going into your body) with ooutputs (stuff leaving). For example:

• Levels of Co2 - respiration constantly produces CO2, which you need to get rid of.
• Water content  - you need to keep a balance between the water that you gain (in drinks, foods, and from respiration) and the water you pee, sweat and breathe out.
• Body temperature - you need to get rid of excess body heat when you are hot, but retain heat when the environment is cold.

A mechanism called negative feedback  works aurimaticallly to help you keep all thse things steady.

Negative Feedback:

Changes  in the environment triiggers a response that conteracts the changes - e.g.  a rise iin body temperature causes a response that lowers body temperatuure This means that the internal environment tends to stay about a norm, the level at which the cells work best. this only works within certain limits - if the environment changes too much thn it might not be possibly yo conteract it.

Body Temperatuure is Controlled by the Brain!

All enzymes  have a optimum temperature they work best at. For enzymes in the human boy it is about 37 C

• there is a thermoregulary cantre in the brain which  acts as your own ppersonal thermostat
• it contains receptors that are sensetive to the blood temperatuer in the brain. It also recievs immpulses from thskin that provide information about skin temperature. The brain can respond to this information and bring about changes in the body's temperature using nervous and hormonal systems to initiate temperature control mechanisms