B1.2 Co-ordination and control

Carries impulses  (electrical signals)

Stimuli (changes in environment) are detected by receptor cells

Clustered together in sensory organs eg. eyes, nose, skin

Impulse carried along sensory neurons to the CNS

The CNS is made up of the brain and spinal cord.

Brain coordinates information and sends impulses along motor neurons to make effector organs respond

Effector organs are either glands or muscles, and they respond differently:

Muscles contract

Glands secrete hormones

Reflexes allow us to respond to danger quickly and coordinate basic subconscious bodily functions

Bypasses the brain to reduce time between stimulus and reflex action

Impulse is sent from receptor along sensory neuron to the CNS

Passes along relay neuron (generally in the spinal cord) to a motor neuron, which carries it to an effector organ

This is known as a reflex arc

There are junctions between nerves called synapses

To carry information through them an impulse has to secrete chemicals

These attach to the next nerve where a new electrical impulse (carrying the same information) is set up

Controlled by hormones made in the pituitary gland and ovaries

Average length of the cycle is 28 days (hahahHAHAHA I'M NOT BITTER AT ALL)

After around 14 days the egg is released (ovulation) 

Leaves body in menstrual blood if it is not fertilised by sperm

FSH is secreted from the pituitary gland and stimulates the ripening of an egg as well as the release of oestrogen from the ovaries

Oestrogen stimulates the thickening of the womb lining, inhibits FSH production and encourages LH secretion from the pituitary gland

When LH peaks, the mature egg is released

Oral contraceptives contain oestrogen to inhibit FSH production

This means no egg will mature and therefore will not be released, preventing pregnancy

Has to be taken regularly so the woman's natural hormones do not take over

First contraceptive pills contained only oestrogen but these had unwanted side effects such as high blood pressure and headaches

Now contain lower doses aong with progesterone, with reduced side effects

In some cases only progesterone, with even fewer side effects but these are less effective as they do not prevent the egg from maturing

Always overseen by a doctor as could cause health problems

Advantages: population control, smaller families meaning less poverty

Disadvantages: ethical objections (bleh)

Some women want children but do not naturally produce enough FSH to mature an egg

They can be given artificial FSH to stimulate the egg maturing and oestrogen production

Also used in IVF if fallopian tubes are damaged

Eggs collected from ovaries and fertilised outside the body

These develop into embryos, two of which are inserted into the womb, bypassing the damaged fallopian tubes

FSH is given to the woman to ripen as many eggs as possible, and then LH given at the end of the cycle to ensure they are all released - increasing chance of success

IVF expensive and not always successful

Some people have ethical objections to fertilising an egg and then denying some of the embryos life

Homeostasis keeps our internal environment constant so our organs can function

Water taken in by eating and drinking and lost in urine, sweat and by breathing

Salt lost through urine made in the kidneys and sweat

Nerves and hormones in the kidneys control concentration of urine and therefore the balance of mineral ions and water in the body

Body temperature kept at 37 degrees celcius - optimum temperature for enzymes

Sweat cools body up, shivering warms body up - contolled by nervous system

Blood glucose concentration controlled by hormones in pancreas to make sure cells are provided with a constant supply of energy

Plant roots sensitive to gravity and moisture

Plant shoots sensitive to gravity and light

Controlled by auxin -

Uneven distribution causes a shoot's phototropism  - auxin moves towards unlit side and makes it grow more so it bends until light is falling evenly on the plant

Auxin gathers at the bottom side of the roots and shoots after germination before they grow vertically

Auxin inhibits growth in roots, but encourages growth in shoots

Roots grow more in side with least auxin so they bend downwards, whereas shoots grow more in areas of high auxin concentration so they grow upwards - their gravitropisms are different

Plant hormones can be used in rooting powder for taking cuttings or as weed killer

Fertility treatment:

Allows older couples to have children once fertility has decreased

Raises issues such as 'what if the mother dies or falls ill while the child is still young' - unfair on the child

Some people have ethical objections - that IVF is aginst nature and God's will

Weed killer:

Increases cereal yield and allows food to be cheaper and more readily available

However the hormones used are produced synthetically and can damage the environment

E.g. Agent Orange used in the Vietnam War to find hidden guerrilla fighters by ********* the jungle, and damaged health of people sprayed