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Living organisms can respond to change by
- Nervous system
- Hormones
Name of system
Nervous
speed
fast
nature of response
electrical impulses
example

brain and spinal cord –
sending messages e
...

hand moving away from
hot object

Hormonal
slow
chemicals secreted into
the blood
- insulin to control
blood sugar
- Sex hormones to
mature the body

Nervous system
Sensitivity – detect food/avoid danger
- Stimulus : change in environment
- Receptors : cell which detect this change e
...
eye/ear
- Effectors : take action after receiving message from CNS e
...
muscle or
gland
- Response : reaction produced

stimulus

receptor

coordinator

effector

response

CNS – CENTRAL NERVOUS SYSTEM
Consists of brain & spinal cord
Controls and coordinates responses between receptors and effectors
1
...
Detected by receptors - skin
3
...
g
...
pick up the stimuli
- The effectors produce a response e
...
glands secrete hormones and
muscles contract
- Messages are sent up electrical impulses and the response is rapid
Hormones
- Chemical messengers – produced by glands and coordinate many
processes in the body
- released by organs in response to stimuli and are transported to a target
organ in the bloodstream : the target organ will differ for each hormone
- the act more slowly over a longer period of time than the nervous
system e
...
oestrogen the sex hormone
Insulin
- produced by the pancreas
- helps control amount of sugar in the blood
- release is stimulated by high blood sugar levels
- targets all cells
- causes sugar to be taken up by the cells, thus lowering blood sugar
levels
- liver : glucose converted to glycogen
- pancreas : insulin produced here
The release of insulin causes:
- The conversion of glucose to glycogen in the liver, glycogen stored in
liver
...

- An increase in the rate of respiration by the body’s cells
- An increase in the rate of uptake of glucose from the blood into the
cells of the body
Diabetes
Diabetes is a condition where the body does not produce enough insulin to
keep the blood glucose level at a normal level
Symptoms
- Glucose in the urine
- Thirsty
Nervous system and hormones

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- Frequently urinating
- Lethargy
- Irritable, confused and go into a coma
Long term effects
- Eye damage and possible blindness
- Heart disease
- Strokes
- Kidney failure
These complications are usually due to high blood sugar levels damaging the
capillaries that supply the part of the body involved
Can be controlled by
- Diet low in carbohydrates
- Injecting with insulin (insulin is a protein and must be injected or it
would be broken down by the protein enzyme in the stomach)

Hormonal system summary
- Consists of glands which secrete hormones
- Hormones are chemical messengers in the blood
- The response is slower and may last a few minutes of many years

Nervous system and hormones

Page 3

Insulin summary
- This hormone controls blood glucose levels
- It is produced in the pancreas (gland) and has its effect in the liver
(target organ)
- Insulin lowers blood sugar levels by converting glucose to glycogen to
be stored in the liver or more glucose is used in respiration in the liver
Diabetes summary
- It is a condition in which the blood glucose control mechanism fails
- Symptoms :
- Glucose in the urine
- Lethargy
- Thirst
- Long term effects:
- Eye damage
- Kidney failure
- Heart disease
- Strokes

Sensitivity in plants
Plant responses
- All living things have the ability to sense changes in the environment and
respond to them – sensitivity
- Plants can respond by moving in response to certain stimuli, this gives
them a better chance of survival
- Movements are called tropism and are controlled by a hormone
Plants respond to:
- Light: phototropism
- Gravity: geotropism
- Water: hydrotropism
Plant hormones
- Organic compounds which promote, inhibit or change plant growth
- Chemical messengers
- E
...
auxin
Auxin
- Responsible for plants growth towards the light

Nervous system and hormones

Page 4

- Plants will bend towards the light this ensures that the plant stem and
leaves receive more light than they otherwise would if there was no
such response
...
This stimulates the shoot ti
grow

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