Science GCSE (1) Biology OCR Gateway

The CNS co-ordinates information.

It consists of the brain and spinal cord.

The nervous system is made of three neurones; Relay, Sensory and Motor.

If a change is detected (stimulus), the sensory neurone will carry the info from receptors to the CNS.

The CNS then sends the info along a motor neurone which gets carrieds to the effector.

The effector then responds accordingly

Stimulus->Receptor->Sensory->CNS->Motor->Effector->Response

Reflex actions stop us injuring ourselves.

Its efficient and doesnt need the concious brain to think about the correct response.

The nervous system uses electrical impulses which are very quick.

The sensory neurone connects to a relay neurone in the spinal cord.

This is directly linked to a motor neurone.

�Reflex actions have a� protective role.

The electrical impulse is passed along the axon of the cell.

The neurones have branched endings (dendrites) which connect to the other neurones.

The insulating sheath along the axon speeds up the electrical impulse.

Their length also allows speeds up the electrical impulse.

The gap between two neurones is called a synapse.

The electrical impulse triggers the realease of transmitter chemicals which diffues across the gap.

They then bind with receptor molecules on the membrane of the next neurone.

This sets off a new impulse.

Stimulants increase the amount of transmitter chemicals, this increases the frequency of impulses along hte next neurone.�

Depressants decrease brain activity by binding with rceptor molecules and blocking the electrical impulse.

It maintains a constant internal environment.

These include; carbon dioxide levels, water content and body temperature.

Negative feedback is a mechanism that works automatically to keep all the above balanced.

Negative feedback counteracts the changes in environment.

This only works within a certain limit and if conditions become to extreme, negative feedback will not be able to counteract it.

The human bodies' enzymes have an optiumum temperature (a temperature they work best at)

This is 37 degrees.

The thermoregulatory centre in your brain controls the internal temperature of the body.

Too hot; Hairs lie flat, sweating (transfers heat into the surroundings), vasodilation (blood vessels dialte to allow the blood to flow close to the skins surface, heat radiated to surroundings.) Dehydration is a consequence of being to hot.

Too cold; hairs stand on end trapping air, little sweat, shivering (generates heat), vasoconstriction (The blood vessels near the surface constrict reducing heat loss.) Hypothermia is a consequence of becoming too cold.

Our glucose levels must be kept steady. Changes in blood sugar are monitored and controlled by the pancreas.

Eating carbohydrates puts glucose into the blood.

Respiration in cells removes glucose.

Exercise also removes glucose.

Insulin is a hormone released by the pancreas when blood sugar is too high. The insulin then makes the liver turn the glucose into glycogen which can be stored.

If glucose levels are too low, then the liver turns glycogen back into glucose and is released into the blood stream - insulin is not released.

Diabetes is a condition that affects a persons ability to control blood sugar.

Type 1 - the pancreas produces little or no insulin

Controlled by - monitoring blood sugar and injecting insulin when necessary. The dosage is dependant on the persons diet and how active they are.

Type 2 - the body becomes resistant to insulin so the cells don't respond properly to the hormone.

Controlled by - a careful diet low in carbohydrates.

<span style="background-color: #cc99ff;">Auxins are plants hormones that control growth in the tips of roots and shoots.</span>

-<span style="background-color: #cc99ff;">produced in tips</span>

-<span style="background-color: #cc99ff;">diffuses backwards</span>

-<span style="background-color: #cc99ff;">stimulates cell elongation.</span>

-<span style="background-color: #cc99ff;">promotes growth in shoots</span>

-<span style="background-color: #cc99ff;">inhibits growth in tips</span>

-<span style="background-color: #cc99ff;">involved in response to light and gravity</span>

<span style="background-color: #cc99ff;">Shoots are positively phototropic. If a shoot tip is exposed to light, more auxins accumulate on the shaded side. This makes the cells elongate faster forcing it to grow upwards this is also partly due to negative geotropism making an unequal distribution of auxins on the lower side.</span>

<span style="background-color: #cc99ff;">Roots are positively geotropic. Extra auxins inhibit growth, this means the cells on top elongate faster which means they bend downwards. Roots are negatively phototropic. If roots become exposed to light then auxins accumulate on the shaded side. The inhibitor causes cell elongation on the shaded side so the roots bends downwards.</span>

Selective weed killers

-produced to selectively target broader-leaved plants which tend to be weeds.

-they disrupt their growth patterns, eventually killing them.

Growing from cuttings with rooting powder

-rooting powder contains plant growth hormones and adding them to a plant cutting will allow a clone to grow successfully

Controlling ripening

-used to delay ripening to allow for transportation

-a ripening hormone is then added when they arrive to induce ripening.

Controlling dormancy

-some seeds won't germinate until they have undergone certain conditions (dormancy)

-a hormone called gibberellin is then added to break dormancy and allows th seeds to germinate.

-this allows seeds to germinate at times of the years that they wouldn't naturally.

The nucleus of most of our body contains genetic material in the form of chromosomes.

Humans have 23 pairs of chromosomes.

Chromosomes carry genes.

Genes control the development of different characterisitics.

A gene is a short length of a chromosome.

A gene is a piece of a DNA molecule.

The DNA is coiled up to form the arms of the chromosome.

There can be different versions of the same gene. E.g. Brown eye gene and blue eye gene.

These different versions are called alleles.

Gamete formation.

Gametes are sperm and egg cells. In each gamete there are 23 chromsomes so when fertilisation occurs, the child will be born with 46 chromosomes.

23 from the Father and 23 from the Mother.

The shuffling up of chromosomes leads to genetic variation

Fertilisation

The randomness of fertilisation make sit unknown as to which two gametes will join together.

Mutations

Gene mutations can create new characteristics which leads to more variation.

Features can be deterined by a number of things.

Health can be determined by diet etc but can also be partly to do with genetics.

Intelligence can be dependant on your upbringing, school etc. But max possible iq is often thought to be determined by genetics.

Sporting ability, genes can determine your potential but training can influence this.