B4 B5 B6 Revision
B4 The Processes of life
B6 Growth and Development
B6
Brain and Mind
B4
The Processes of life
Features of all living things
Movement
All living things are made
Respiration
up of cells.
Sensitivity
Growth
Reproduction
Excretion
Food
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
click to react
enzyme
molecule
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.
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
1. Making other chemicals needed for cell growth
2. Storing energy in starch molecules
3. Releasing energy in respiration
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
= eg oxygen
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
Osmosis is the same as diffusion but applies to water
molecules passing through a partially permeable membrane.
partially permeable membrane
= starch
= water
movement of water molecules
Low concentration
of starch
High concentration
of starch
High concentration
of water
Low concentration
of water
Starch molecules
cannot pass through
the partially permeable
membrane but water
molecules can.
cell
Osmosis in plant cells
If too much water passes into a cell
by osmosis then it may rupture.
potato chip
low salt concentration
the potato chip absorbs
water and expands
high salt concentration
the potato chip loses
water and shrinks
Molecules like glucose are moved by active transport.
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.
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
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.
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
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
B5
Growth and Development
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
Each gene codes for a specific protein
nucleus
cytoplasm
G- C
g
e
n
e
A- T
T- A
A- T
C- G
A- T
AThe
The
copy
mRNA
DNA
mRNA
of zips
unzips
the
travels
is code
used
upto
again
to
is
expose
to made
the
produce
cytoplasm
the
using
acode
protein
RNA
(using ribosomes)
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)
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
A zygote divides by mitosis to form an embryo
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.
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 patient’s 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 don’t attack them
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
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.
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
A
4
D
C
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16
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DNA
cytoplasm
mRNA
amino acids
B4 Homeostasis
B5 Growth and Development
B6 Brain and Mind
Brain and Mind
What are we sensitive to ?
• light
• sound
• pressure
• chemicals
• temperature
• orientation
The 5 senses are:
• sight
eye
• hearing
ear
• touch
skin
• taste
nose & tongue
• smell
nose
The retina contains light sensitive cells
The lens refracts the light to focus on the retina
The retina contains cells called cones which enable colour vision
The Ear
semi-circular canals
which sense orientation
The Tongue
The tongue has receptors which are sensitive to
chemicals and enable us to taste 4 types of flavours.
The Nose
The nose has receptors which are sensitive to
chemicals and enable us to smell and taste.
The Skin
The skin has receptors that are sensitive to touch,
pressure and temperature changes.
How the nervous system works
nerve cell
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.
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.
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
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
at the
same
time
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
Glands in the body
melanin
ADH
ACTH, FSH, LH, growth H
thyroxine
PTH
Involved in producing T cells
adrenaline
Insulin, glucagon
oestrogen, progesterone
testosterone
Hormonal control
Control of blood sugar
High blood
sugar level
Low blood
sugar level
insulin
released
from the
pancreas
glucagon
released
from the
pancreas
decrease in
blood sugar
level
increase in
blood
sugar level
homeostasis
Hormones are chemicals
which travel in the blood
slow and long lasting
How can reflex actions be an advantage for survival ?
A new born baby has a set of reflex actions, eg:
Grasping reflex: Touching a baby’s palm will
cause the baby’s fingers to curl.
Sucking reflex: Putting an object in a baby’s
mouth will cause the baby to suck the object .
Diving reflex: Putting a baby in water will cause the
baby to hold it’s breath and move it’s arms around
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.
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.
Simple animals rely on reflex actions
for the majority of their behaviour
This is a reflex response to move towards lighter areas
This is a unicellular organism which
needs light to survive, eg plankton
This is a reflex response to something moving
Woodlouse
Light & dry
Dark & dry
Dark & moist
Light & moist
A reflex response to move to dark areas
enables it to hide from predators
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 !
Pavlov’s dog
The final
response
has no
direct
connection
to the
stimulus
A reflex response to a new stimulus can be learned
The brain can modify reflexes
For example, being given a hot plate and instinctively
wanting to drop it but yet holding on to it.
How the brain works
in a nut shell !
Microscope slide of neurons in the brain
Neurotransmitters
[you don’t have to know the structures]
dopamine
Central nervous system
seratonin
melatonin
Peripheral nervous system
acetylcholine
adrenaline / epinephrine
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.
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
Electrical stimulation of the
brain can be used in studies
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.
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.
Click 1 then 2 then 3 then 4
1
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
3
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
4
The neuronal pathway doesn’t need the extra input to work
Brain stem
This gives you a very basic idea about how neuron pathways are formed
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.
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
By the time you have become consciously aware of the snake
your brain has already set into play a series of responses.
9/20 x 100
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involuntary
A B
E C
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B4 Homeostasis
B5 Growth and Development
B6 Brain and Mind