B4 B5 B6 Revision

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B4 B5 B6 Revision
B4 The Processes of life
B6 Growth and Development
B6 Brain and Mind
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B4 The Processes of life
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Features of all living things
Movement Respiration Sensitivity Growth Reproduct
ion Excretion Food
All living things are made up of cells.
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Enzymes
Enzymes are proteins that speed up chemical
reactions in cells. They need a specific
constant temperature to work at their optimum.
Enzymes become denatured (stop working) above
about 55oC.
Most enzymes work best at about 40oC.
The higher the temperature the faster molecules
move around and therefore (a) collide more
frequently and (b) collide with more energy. This
results in an increased rate of reaction.
lock and key
active site
The active site can be changed by heating above a
certain temperature and altering the pH, so that
the molecules can no longer fit and the reaction
cannot happen.
click to react
enzyme
molecule
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Enzymes at work in plants
Photosynthesis equation (takes place in
chloroplasts) light
energy 6CO2 6H2O ? C6H12O6
6O2
chlorophyll Carbon dioxide water
glucose oxygen
Chlorophyll absorbs light and uses the energy to
kick-start photosynthesis

• Glucose is used by plant cells in 3 ways
• Making other chemicals needed for cell growth
• Storing energy in starch molecules
• Releasing energy in respiration

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Diffusion (passive transport)
This is the movement of molecules from a region
of their high concentration to a region of their
lower concentration
Region of high concentration
Region of low concentration
Diffusion causes the molecules to become evenly
distributed due to their random movement. It is
like as if the molecules have moved from the
region of high concentration to the region of low
concentration.
Diffusion in the leaf happens through the
stomata- carbon dioxide in and oxygen out
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Osmosis is the same as diffusion but applies to
water molecules passing through a partially
permeable membrane.
partially permeable membrane
movement of water molecules
Starch molecules cannot pass through the
partially permeable membrane but water molecules
can.
High concentration of starch
Low concentration of starch
High concentration of water
Low concentration of water
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Osmosis in plant cells
cell
If too much water passes into a cell by osmosis
then it may rupture.
potato chip
low salt concentration
high salt concentration
the potato chip absorbs water and expands
the potato chip loses water and shrinks
Molecules like glucose are moved by active
transport.
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Minerals from the soil
Plants take in nitrogen from the soil as nitrate
ions, they are absorbed by root hair cells. The
cells use a process called active transport to
pump nitrates from the soil and into the roots
against their diffusion gradient.
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The rate of photosynthesis
Increasing the amount of light a plant receives
increases the rate of photosynthesis up to a
point.
Increasing the light intensity stops having an
effect on the rate of photosynthesis because one
of the other factors e.g. carbon dioxide, water,
chlorophyll or temperature is in short supply.
This factor is called the LIMITING FACTOR
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Environments and adaptations
A habitat is a place where an organism lives. A
quadrat is used to survey the plants in a square
metre. The positioning of a quadrat in the area
being investigated is random. Samples can be
taken at regular intervals along a straight line
called a transect.
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Energy for life

• Aerobic respiration
• Glucose oxygen ? carbon dioxide water (
  energy released)
• C6H12O6 6O2 ? 6CO2 6H2O
• What happens to the energy from respiration?
• used in active transport
• movement
• building molecules used for growth and repair

Anaerobic respiration Glucose ? lactic acid
(energy released) in animals Glucose ? ethanol
carbon dioxide ( energy released) in plants
and microorganisms
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Useful products from respiration
Bioethanol (used to fuel car engines) is made
from sugars in plant material. Yeast cells take
sugars and convert them into ethanol during the
process of anaerobic respiration, this is
called fermentation.
Biogas is a fuel obtained from animal manure or
human waste using bacteria, it produces methane
gas. The fuel can be used to heat buildings and
run electricity generators
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B4 Homeostasis
B5 Growth and Development
B6 Brain and Mind
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B5 Growth and Development
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Cytoplasm where proteins are made
Nucleus where the genes are located
DNA has a double helix structure
The base pairs always pair up the same way A to T
and G to C
adenine
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Each gene codes for a specific protein
cytoplasm
nucleus
C T A T G T
G- A- T- A- C- A-
C T A T G T
gene
The DNA unzips to expose the code
A copy of the code is made using RNA
The mRNA travels to the cytoplasm
The DNA zips up again
The mRNA is used to produce a protein
(using ribosomes)
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This is the simplest amino acid - valine
Protein is made up of amino acids joined together
in chains
The order of bases in a gene determines the order
of amino acids that make a particular protein.
The order of amino acids determines the 3D
structure of a particular protein.
The 3D structure of a protein determines its
function (job)
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Cell division
Mitosis involves copying the chromosomes exactly
Cell division by mitosis produces two new cells
identical to each other and to the parent cell
Meiosis is a type of cell division that produces
gametes, ie sperm and egg cells.
Cells produced by meiosis only contain half the
chromosome number of the parent cell
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A zygote divides by mitosis to form an embryo
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In a human embryo, up to the eight cell stage,
all the cells are identical and could produce any
sort of cell required by the organism (embryonic
stem cells)
After this point the cells become specialised and
form different types of tissue.
Adult and embryonic stem cells have the potential
to produce cells needed to replace damaged
tissues.
In carefully controlled conditions of mammalian
cloning, it is possible to reactivate inactive
genes in the nucleus of a body cell to form cells
of all tissue types.
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Making stem cells using the DNA from a patient
means the cells wont be rejected when they are
transplanted into the patient
This means that the patients immune system wont
attack the transplanted stem cells
X
The antibodies help to kill the foreign cell
foreign cell with antigen
White blood cells recognise it as a foreign cell
and make antibodies
With this technique the white blood cells do not
recognise the transplanted stem cells as foreign
and therefore dont attack them
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New cells in plants specialise into cells of
roots, leaves or flowers.
Some plant cells remain unspecialized and can
develop into any type of plant cell, unlike
animal cells.
Most plants continue to grow in height and width
throughout their lives, unlike animals.
Plant meristems divide to produce cells that
result in increased height, length of roots, and
girth of the plant.
If the hormonal conditions in their environment
are changed, unspecialised plant cells can
develop into a range of other tissues
Transport vessels xylem and phloem
Organs leaves, roots and flowers
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Cut stems from a plant can develop roots in the
presence of plant hormones (auxins) and grow into
a complete plant which is a clone of the parent.
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shoot tip
The action of light causes auxin to move across
the shoot tip from the side getting the light to
the shaded side.
This causes the cells on the shaded side to
elongate which causes the stem to bend towards
the light.
This helps the plant to grow towards the light
which helps its survival.
plant stem
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A
D
C
4
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DNA
cytoplasm
mRNA
amino acids
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B4 Homeostasis
B5 Growth and Development
B6 Brain and Mind
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Brain and Mind
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What are we sensitive to ?

• light

• sound

• pressure

• chemicals

• temperature

• orientation

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The 5 senses are

• sight

eye

• hearing

ear

• touch

skin

• taste

nose tongue

• smell

nose
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The retina contains light sensitive cells
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The lens refracts the light to focus on the retina
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The retina contains cells called cones which
enable colour vision
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The Ear
semi-circular canals which sense orientation
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The Tongue
The tongue has receptors which are sensitive to
chemicals and enable us to taste 4 types of
flavours.
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The Nose
The nose has receptors which are sensitive to
chemicals and enable us to smell and taste.
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The Skin
The skin has receptors that are sensitive to
touch, pressure and temperature changes.
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How the nervous system works
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nerve cell
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neurotransmitter
receptor site
axon
dendrite
synapse
acetylcholine
The neurotransmitter diffuses across the gap
Receptor molecules only bind to specific
chemicals, initiating a nerve impulse in the
motor neuron.
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At the end of a sensory neuron an impulse
triggers the release of chemicals into the
synapse, which diffuse across and bind to
receptor molecules on the membrane of a motor
neuron.
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Sequence
stimulus is detected by a receptor
nerve impulse travels along a sensory neurone
neurotransmitter diffuses across a synapse
nerve impulse travels along a relay neurone
at the same time
nerve impulse travels along a neurone to the brain
neurotransmitter diffuses across a synapse
nerve impulse travels along a motor neurone
muscle contracts / hormone is released from a
gland
Conscious awareness of the stimulus
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stimulus
receptor
sensory neurone (nerve)
central nervous system (brain and spinal cord)
motor neurone (nerve)
effector (muscle or gland)
nervous systems use electrical impulses
Fast and short lived responses
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Glands in the body
melanin
ADH
ACTH, FSH, LH, growth H
thyroxine
PTH
Involved in producing T cells
adrenaline
Insulin, glucagon
oestrogen, progesterone
testosterone
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Hormonal control
Control of blood sugar
High blood sugar level
Low blood sugar level
Hormones are chemicals which travel in the blood
insulin released from the pancreas
glucagon released from the pancreas
slow and long lasting
decrease in blood sugar level
increase in blood sugar level
homeostasis
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How can reflex actions be an advantage for
survival ?
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A new born baby has a set of reflex actions, eg
Grasping reflex Touching a babys palm will
cause the babys fingers to curl.
Sucking reflex Putting an object in a babys
mouth will cause the baby to suck the object .
Diving reflex Putting a baby in water will cause
the baby to hold its breath and move its arms
around
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Pupil reflex
When the surroundings get darker the iris relaxes
causing the pupil to dilate
When the surroundings get lighter the iris
contracts causing the pupil to get smaller
This reflex helps to protect the light sensitive
receptors in the eye when it is too light and to
get more visual information when dark.
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Some caterpillars have a poisonous toxin in their
skin.
Some birds develop a learned conditioned reflex
or have an evolved reflex to avoid eating
particular caterpillars on the basis of their
colours.
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Simple animals rely on reflex actions for the
majority of their behaviour
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This is a reflex response to move towards lighter
areas
This is a unicellular organism which needs light
to survive, eg plankton
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This is a reflex response to something moving
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Woodlouse
Light dry
Dark dry
Dark moist
Light moist
A reflex response to move to dark areas enables
it to hide from predators
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The disadvantage of these simple reflex
behaviours is not being able to respond
appropriately to new situations.
Eg what if a spider is waiting for the woodlouse
in the dark area !
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A reflex response to a new stimulus can be learned
Pavlovs dog
The final response has no direct connection to
the stimulus
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The brain can modify reflexes
For example, being given a hot plate and
instinctively wanting to drop it but yet holding
on to it.
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How the brain works
in a nut shell !
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Microscope slide of neurons in the brain
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Neurotransmitters
you dont have to know the structures
dopamine
seratonin
melatonin
Central nervous system
Peripheral nervous system
acetylcholine
adrenaline / epinephrine
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reasoning
spatial sense
visual
cerebral cortex
movement
auditory, speech
essential functions
The cerebral cortex is the part of our brain most
concerned with intelligence, memory, language and
consciousness.
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A variety of methods can be used to map the brain
CT scanner
MRI scanner
CT and MRI scanners can be used to get images of
structures.
PET scanners can be used to monitor activity in
the brain
PET scanner
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Electrical stimulation of the brain can be used
in studies
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MDMA - ecstasy
Ecstasy blocks the re-uptake of serotonin in the
synapses of the brain.
This causes an increase in the serotonin
concentration which leads to mood-enhancing
effects.
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During development, the interaction between
mammals and their environment results in neuron
pathways forming in the brain.
Here, neuron pathways in the visual cortex
interplay with neuron pathways in the motor
cortex in order to grab an object.
After many attempts the neuron pathways get fine
tuned to produce the responses that we intend.
Eventually we build up a vast array of efficient
pathways.
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Click 1 then 2 then 3 then 4
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The second set of nerve cells are not stimulated
enough to fire
2
One of the nerve cells in the second set receives
enough input to fire
One of the nerve cells in the second set receives
enough input to fire and this neuronal pathway is
strengthened by a nerve impulse from the brain
stem
3
4
The neuronal pathway doesnt need the extra input
to work
Brain stem
This gives you a very basic idea about how neuron
pathways are formed
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Learning is the result of experience where
certain pathways in the brain will become more
likely to transmit impulses than others.
This is why some skills may be learnt through
repetition.
The variety of potential pathways in the brain
makes it possible for animals to adapt to new
situations.
There is evidence to suggest that children may
only acquire some skills at a particular age, eg
language development in feral children.
A feral child is one who has been brought up by
wild animals from early childhood.
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Memory is basically the storage and retrieval of
information.
Verbal memory can be divided into short-term
memory and long-term memory.
Humans are more likely to remember information if

• they can see a pattern in it

• there is repetition of the information,
  especially over an extended period of time

• there is a strong stimulus associated with it,
  eg colour, light, smell, sound etc

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By the time you have become consciously aware of
the snake your brain has already set into play a
series of responses.
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9/20 x 100
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involuntary
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A
B
E
C
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B4 Homeostasis
B5 Growth and Development
B6 Brain and Mind