Science Unit 6 GCSE

Simple reflex actions are involuntary. They help an animal's survival. Simple animals rely on simple reflexes for most of their behaviour, they find it difficult to respond in to new situations.

The newborn reflexes are grasping, sucking, stepping and startling. Babies gradually replace these reflexes with behaviour learned through experience.

The pupil reflex stops bright light from damaging cells in the retina.

Complex animals can learn to link a new stimulus to a reflex action.

Pavlov's dog is an example of how animals condition their reflexes.

Conditioned reflexes increase an animal's chance of survival.

The reflex arc is the pathway that carries nerve impulses from one part of the nervous system to the next. 

A sensory neuron carries nerve impulses TO the cns, a motor neuron carries nerve impulses FROM the cns TO the effector.

A synapse is a tiny gap between neurons. Nerve impulses have to cross this gap. They do this by:

1) The sensory neuron releases a chemical into the synapse

2) The chemical diffuses across the synapse

3) The chemical arrives at the receptor molecules on the motor neuron's membrane

4) A nerve impulse is stimulated in the motor neuron

5) The chemical is absorbed back into where it came from to be used again.

Drugs affect the transmittion of nerve impulses across synapses. Ecstacy blocks where the chemical would go.

A neuron is a bundle of nerve cells. 

A fatty sheath (around the axon) insulates the neuron from neighbouring cells meaning that electrical nerve impulses are carried along the neuron very quickly.

Sometimes the brains conciously controls reflexes. Picking up a delicious hot plate of food is an example of this. 

Developing complex behaviour is called learning.

Neuroscientists map the cortex. They do this by :

> Studying patients with brain damage

> Electrically stimulating different parts of the brain

> Doing MRI scans of the brain

The cerebral coretex is the part of the brain concerned with intellegence, language, memory and conciousness.

Memory is the storage and retrival of information by the brain. 

There are two types of memory : Short term (30 seconds) and Long term (your entire life)

Looking for patterns makes humans memorise information more deeply. 

The best ways for humans to memorise is repetition and association.

Chemical synthesis provides important chemicals for:

> Food additives

> Fertilisers

> Dyes

> Plants

> Pharmaceuticals

Bulk chemicals are made on huge scale. These are things like sodium hydroxide, sulfuric acid and chlorine.

Fine chemicals are made in small quantities. These are things like drugs and pesticides.

An acid has a pH of less than 7. They produce aqueous hydrogen ions.

An alkali has a pH of more than 7. They produce aqueous hydroxide ions.

Indicators show whether a solution is acid, alkali or neutral. 

Acids make salt in most of their reactions. Salts are ionic compounds.

1) Do a risk assesment

2) Work out the amount of reactants to use

3) Do the reaction with suitable apparatus in the right conditions

4) Separate the product from the reaction mixture

5) Purify the product

6) Measure the yeild (percentage yeild = actual / theoretical x 100%)

Factors affecting the rate of reaction

> Concentration (Increasing concentration increases ROR)

> Temperature (Increasing temp increases ROR)

> Surface area (Increasing surface area increases ROR)

> Catalyst (Adding one increases ROR)

Frequency - the number of waves that a source makes every second. It's measured in hertz (Hz).

Wave speed = frequency x wavelength

Reflection - When waves are reflected, the angle of incidence equals the angle of reflection.

Refraction - When a wave travels through one medium to another, the speed changes. When a wave hits the new medium, it appears to bend.

Diffraction - When waves go through a narrow gap, they bend and spread out.

Radio waves          highest wavelength       

Microwaves

Infrared

Visible light

Ultraviolet

X-rays

Gamma rays           highest frequency

They can all travel through a vaccum and they all travel through space at the same speed.

Digital because they transmit information with higher quality. This is because 0 and 1 can still be recognised even if noise has been picked up, so the signal can be 'cleaned up'.