1.1.1 Reflex actions are extra-rapid
responses to stimuli. This process
also involves the nervous system but
bypasses the brain.
126.96.36.199 Most ANIMAL cells have a
nucleus, cytoplasm and cell
membrane. Light receptors have
these cell components too.
188.8.131.52.1 The human central nervous system (CNS) consists
of the brain and spinal cord. When a receptor is
stimulated it sends a signal along the nerve cells,
also called NEURONES, to the brain. The brain then
coordinates the response.
184.108.40.206.1.1 Nerve Cells = Neurones
220.127.116.11.1.1.1 They carry information
as tiny electrical signals.
18.104.22.168.22.214.171.124 There are 3 different types of
neurones which each had a slightly
126.96.36.199.188.8.131.52.1 SENSORY neurones: Carry signals from
receptors to the spinal cord and brain.
184.108.40.206.220.127.116.11.2 RELAY neurones: Carry messages
from one part of the CNS to another.
18.104.22.168.22.214.171.124.3 MOTOR neurones: Carry signals
from the CNS to effectors.
126.96.36.199.188.8.131.52.3.1 This diagram shows a typical neurone (a
motor neurone), which has tiny branches
at each end and a long fibre that carries
184.108.40.206 Receptors are found in:
-Eyes -Ears -Tongue -Nose
220.127.116.11.1 Receptors are groups of specialised cells
that can detect changes in the
environment called STIMULI.
18.104.22.168.2 Each organ has
are sensitive to
of stimuli. For
22.214.171.124.2.1 Skin = Touch, Pressure,
Pain and Temperature
126.96.36.199.2.2 Nose = Chemicals in the air
188.8.131.52.2.3 Tongue = Chemicals in food
184.108.40.206.2.4 Eyes = Light
220.127.116.11.2.5 Ears = Sound and position
of the head
1.1.4 The nervous system allows the
body to respond to changes in the
environment in a process usually
coordinated by the brain.
18.104.22.168 When 2 neurones meet there is
a tiny gap called a SYNAPSE.
22.214.171.124.1 Signals cross this gap using chemicals.
One neurone releases the chemical into
the gap. The chemical diffuses across the
gap and makes the next neurone
transmit an electrical signal.
1.1.6 Reflex Actions
126.96.36.199 Sometimes a quick response is needed
when a receptor is stimulated. One that
does not involve the brain: this is a
188.8.131.52.1 Reflex actions happen without us
thinking. For example, you would pull
your hand away from a hot flame
without even thinking about it.
184.108.40.206.1.1 Reflex Arc is the nerve
pathway involved in a
220.127.116.11.1.1.1 Here's what happens:
18.104.22.168.22.214.171.124 1. Receptor detects a stimulus - a chance in the environment.
126.96.36.199.188.8.131.52.1 2. Sensory neurones sends impulses to relay neurone.
184.108.40.206.220.127.116.11.1.1 3. Motor neurone sends impulses to effector.
18.104.22.168.22.214.171.124.1.1.1 4. Effector produces a response.
126.96.36.199.188.8.131.52.184.108.40.206 An effector is any
part of the body that
produces the response.
220.127.116.11.18.104.22.168.22.214.171.124.1 Examples of effectors:
-A muscle contracting
-A gland releasing a
hormone or other
126.96.36.199 In a simple reflex action:
Stimulus -> Receptor -> Sensory
neurone -> Relay neurone ->
Motor neurone -> Effector
1.2 Control in the human body
1.2.1 Hormones are chemical substances that
regulate processes in the body. Hormones are
released by glands and travel to their target
organs in the bloodstream.
188.8.131.52 Several hormones are
involved in the female
184.108.40.206 Hormones can be used to control human fertility
and have advantages and disadvantages.
220.127.116.11.1 Hormones regulate the
functions of many cells and
18.104.22.168 The maintenance of a constant internal
environment is called HOMEOSTASIS
1.2.2 Water content in the body. Water in the body has to be controlled
to protect cells from either too much water entering or leaving them.
Water content is controlled by water loss from....
22.214.171.124 the lungs - when we exhale
126.96.36.199 the skin - through sweating
188.8.131.52 passing urine - produced by the kidneys
184.108.40.206 Ion (salts) content of the body. Ion levels are controlled to protect
cells from too much water entering or leaving them. Ion content is
controlled by loss of ions from...
220.127.116.11.1 the skin - through sweating
18.104.22.168.2 passing urine - produced by the kidneys
22.214.171.124.3 Temperature of the body. This is controlled to
maintain the temperature at which enzymes work
best. Body temperature is controlled by sweating,
shivering, and controlling blood flow to the skin.
126.96.36.199 Blood sugar levels This is controlled to provide cells with a constant
supply of energy. Blood sugar level is controlled by the release and
storage of glucose controlled by insulin.
1.2.3 Hormones in the menstrual cycle
188.8.131.52 Several hormones control this cycle, which
includes controlling the release of an egg each
month from an ovary. Theses hormones are
released by the ovaries and pituitary gland.
184.108.40.206 Follicle stimulating hormone, FSH is released by the pituitary gland.
FSH makes two things happen...
220.127.116.11.1 It causes an egg to mature in an ovary.
18.104.22.168.2 It stimulates the ovaries to releasee the hormone oestrogen.
22.214.171.124.2.1 Oestrogen makes two things happen...
126.96.36.199.2.1.1 It stops FSH being produced - so
that only one egg matures in a cycle.
188.8.131.52.2.1.2 It stimulates the pituitary gland
to release luteinizing hormone
(LH), which triggers ovulation (the
release of the mature egg from
1.3 Control in plants
1.3.1 Plants produce hormones and respond
to external stimuli, growing towards
sources of water and light, which they
need to survive.
184.108.40.206 A tropism is a
growth in response
to a stimulus.
220.127.116.11.1 Positive Tropism - the plant grows towards the stimulus.
Negative tropism - the plant grows away from the
18.104.22.168.1.1 Phototropism is a tropism where LIGHT is
the stimulus. A gravitropism (also called
Geotropism) is a tropism where gravity is
22.214.171.124 An auxin is a plant hormone
produced in the stem tips and roots,
which controls the direction of
126.96.36.199 Plant hormones are used in
weed killers, rooting powder
and to control fruit ripening.
188.8.131.52 Rooting powder: Contains
growth hormones which
make stem cutting quickly
184.108.40.206.1 The weed killer is
absorbed in larger
unties by the weeds
than the beneficial
plants, which stay
220.127.116.11.1.1 Selective weed killers contain
growth hormone that cause
the weeds to grow quickly
and then die.
18.104.22.168.1.1.1 Weed killers can be useful for
getting rid of dandelions in a
lawn without killing the grass,
or getting rid of thistles in a
field whiteout killing the wheat.
22.214.171.124.126.96.36.199 Using plant hormones
1.3.3 Sensitivity in Plants
188.8.131.52 The roots and shoots of a plant respond
differently to the same stimuli. Shoot =
positive phototropism and negative
gravitropism. Root = negative phototropism
and positive gravitropism
184.108.40.206 Auxins are a family of
hormones found in plants. They
are mostly made in the tips of
the shoots and roots, and can
diffuse to other parts of the
shoots or roots.
220.127.116.11 Shoots and roots respond
differently to high
concentrations of auxin:
Cells in shoots grow more.
Cells in roots grow less.
18.104.22.168 In a shoot, the shaded side contains
more auxin. This means that the shaded
side grows longer, causing the shoot to
bend towards the light.
22.214.171.124 In a root, the shaded side contains
more auxin, but this time the
shaded side grows less than the lit
side. This causes the root to bend
away from the light.
2.1.3 Photosynthesis is the chemical change
which happens in the leaves of green
plants. It is the first step towards
making food - not just for plants but
ultimately every animal on the plant.
2.1.4 Carbon dioxide and water are converted
into glucose and oxygen.
126.96.36.199 Some glucose is used
for respiration, while
some is converted
into insoluble STARCH
188.8.131.52.1 The stored starch can later
be turned back into glucose
and used in respiration.
Oxygen is released as a
by-product of photosynthesis.
2.1.5 Photosynthesis takes place in leaf cells. These contain chloroplasts,
which are tiny objects containing chlorophyll. The green substance,
chlorophyll, absorbs light energy, which the reaction needs.
2.2 Factors limiting photosynthesis
2.2.1 Without enough light, a
plant cannot photosynthesis
very quickly, even if there is
plenty of water and carbon
2.2.2 Increasing light intensity will boost
the speed of photosynthesis.
2.2.3 If it gets too cold, the rate of
photosynthesis will decrease. Plants cannot
photosynthesise if it gets too hot.
limited by the
carbon dioxide in
2.2.5 Even if there is plenty of light,
a plant cannot photosynthesise
if there is insufficient carbon
2.3 Plants and minerals,
2.3.1 Plants need to take in a
number of elements to stay
alive. The most important are:
Carbon, Hydrogen. Oxygen.
2.3.2 Plants get hydrogen and oxygen
from water in the soil, and
carbon and oxygen from carbon
dioxide and oxygen in the
atmosphere. Wa†er and carbon
dioxide are used to synthesise
food during photosynthesis.
Oxygen is used to release energy
from food during respiration.
2.3.3 Plants need a number of minerals for healthy
growth. These are absorbed through the roots as
mineral ions dissolved in the soil water.
184.108.40.206 Two important mineral ions
needed by plants are: Nitrate -
for making amino acids, which
are needed to make proteins.
Magnesium - for making
220.127.116.11.1 Deficient in nitrate = will
suffer from stunted growth
Deficient in magnesium =
leaves will turn yellow