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Biology - cells and control (reflex arc (example in use (impulses travel…
Biology - cells and control
CT and PET scans and treating brain injury
CT scanning
uses x-rays to produce image
shows main structures, but doesnt show functions
but if scan shows diseased/damaged brain structure and patient has lost a function, function of this structure can be worked out
PET scanning
uses radioactive chemicals to show which parts of brain are active
very detailed and can show structure and function
can be useful for studying disorders that change brain's activity by seeing areas of the brain which are unusually (in)active
treating problems can be difficult
some areas in the brain are very hard to access. its not possible to remove tumours in brain by surgery
treatment may lead to permanent damage e.g. surgery on spinal cord could further damage it
difficult to repair damage as neurones in CNS dont repair themselves. scientists havent developed a way to repair nervous tissue in CNS
many things could go wrong e.g. injuries to brain/spinal cord, tumours and diseases like alzheimers or parkinsons
stem cells
cells differentiate to become specialised cells. the undifferentiated cells are called stem cells
stem cells can divide by mitosis to become new cells, which then differentiate
embryonic stem cells
found in early human embryos
can divide and produce any kind of cell at all
all different types of cell found in human come from few cells in early embryo
therefore stem cells are very important in the growth/development of organisms
adult stem cells
only found in certain places, such as in bone marrow
arent as versatile as embryonic - can only produce certain cells
used to replace damaged cells, e.g. skin or blood cells
plant stem cells in the meristem
this tissue found in the tips of roots and shoots (areas of the plant that are growing)
meristem produces unspecialised cells that can divide and form any cell type in the plant. this can occur for as long as the plant lives
unspecialised cells form specialised tissues such as xylem and phloem
brain strucures/functions
cerebellum
found at the bottom rear of brain, lump like strucure
controls fine movement of muscles and balance
medulla oblongata
found at the base of the brain, central link between brain and spinal cord
controls unconscious activities like breathing and heart rate
cerebral hemispheres
take up most of the space in skull and sit on left/right sides. together they are called cerebrum
perform huge variety of functions e.g. consciousness, memory, intelligence as well as visual/sensory processing
central nervous system
CNS is made up of neurones (nerve cells) which go to all parts of the body
sensory receptors detect change in the envvironment. e.g. receptors in eyes detect light, receptors in skin detect pressure
stimulus>receptor>sensory neurone>CNS>motor neurone>effector>response
when stimulus detected, info converted to electrical impulse and sent to CNS
CNS sends info to effector then effector responds (e.g. muscle contracts)
Mitosis and the Cell Cycle
most of cell cycle is interphase - cell grows, organelles grow and increase in number, protein synthesis occurs
mitosis produces 2 genetically identical diploid daughter cells. they are also genetically identical to the parent
multicellular organisms use mitosis to grow/replace cells that have been damaged
cell division and growth
cell differentiation - when a cell changes to become specialised
animals
all growth by cell division
animals grow when young, reach full growth then stop growing. cell differentiation is lost at a young stage
when cells are young they divide at a fast rate. once adult most cell division is for repair (replacing damaged/old cells)
plants
growth in height mainly due to cell elongation
cell division happens in tips of roots and shoots (meristems)
plants grow continuously - very old trees are still growing branches. plants continue to differentiate to develop new parts
cell elongation - plant cell expands making the cell bigger so making the plant grow
cancer
rate of cell division by mitosis is controlled by genes
when there is a change in genes that control this, the cell may start to divide uncontrollably
can result in mass of abnormal calls called tumour - if this tumour destroys surrounding tissues it is called cancer
growth percentile charts
assess a child's growth over time, so that an ooverall pattern in development can be seen and any problems highlighted (obesity, malnutrition, dwarfism)
a baby's growth can be regularly monitored to make sure it is growing normally - measurements can be taken length, mass, head circumference
e.g. 75th percentile means 75% of babies of this age are this weight
strucure/function of eye and eye defects and their treatment
the eye
cornea refracts light into eye
iris controls how much light enters pupil
lens refracts light, focsing it onto retina
retina - light sensitive. covered in receptor cells called cones and rods
rods more sensitive in dim light but cant sense colour
optic nerve carries impulses from receptors to brain
cones - sensitive to colours but not good in dim light
focusing on near/distant
near
lens is thicker and curved to refract light more
ciliary muscles contract, suspensory ligaments loosen
distant
lens is thinner - light is refracted less
ciliary muscles relax, suspensory ligaments tighten
stages of mitosis
anaphase - chromosome copies separated and moved to either end of cell on spindle fibres
telophase - membrane forms around each set of chromosomes to form nuclei
metaphase - chromosomes lined up on the spindle fibres across middle of cell
prophase - nucleus starts to break down, spindle fibres appear
stem cells in medicine
doctors use adult stem cells to cure some diseases e.g. sickle cell anaemia with stem cells in bone marrow
scientists have experimented with stem cells in very early human embryos
can use stem cells to make spec. cells to replace damaged cells e.g. new cardiac muscle cells can be transplanted into someone with heart disease
potential risks
rejection - body may trigger immune response if body thinks stem cells are foreign
tumour development - stem cells divide rapidly so tumours can develop if scientists are unable to control rate of division
disease transmission - if donor stem cells are infected with virus, this could be passed onto patient
ethical issues - human embryos shouldnt be used in experiments as it is a potential human life
neurone
motor neurone
many short dendrites carry impulses from CNS to cell body
long axon carries impulses from cell body to effector cells
myelin sheath insulates axon so that electrical impulses happen as quickly as possible
relay neurone
many short dendrites carry impulses from sensory neurone to cell body
long axon carries impulses from cell body to effector cells
sensory neurone
short axon carries impulses from the cell body to the CNS
long dendron carries impulses from recptor cells to cell body (in the middle of the neurone)
synapses
they are the connection between 2 neurones
neurotransmitters pass on the signal to the next neurone
nerve signal is transferred by chemical called neurotransmitters, which diffuse across the gap
transmission of nerve impulse is very fast, but slowed down by synapses as diffusion across the gap takes time
reflex arc
example in use
impulses travel along a sensory neurone
impulses passed along a relay neurone via a synapse
stimulation of pain receptors
impulses travel along motor neurone, via a synapse
bee stings finger
when impulses reach muscle, it contracts
reflexes are automatic rapid responses to stimuli - reduce risk of being injured
reflex arc means passage of info from receptor to effector during a reflex
neurones in reflex arc go through spinal cord or unconcious part of brain
quicker response as it you dont think about it
helps protect the eye
very bright light can damage the eye so there is a reflex that protects it
light receptors in eye send message to brain via sensory neurone
message travels to motor neurone via relay, which tells circular muscles in iris to contract and make pupil smaller
eye defects and how to correct
short-sightedness
lens is too curved, so distant objects appear blurry as light is refracted too much. or eyeball is too long
concave lenses can spread light more to treat this
long-sightedness
lens is too flat so it cannot refract light enough. or eyeball is too short
convex lenses bring light rays together
cataracts
clouding of the eye, restricts vision and can occur from birth
can be treated by replacing the lens with an artificial one
colour blindness
inability to see certain colours as they dont have enough cone cells in retina. it is usually genetic
no cure as cone cells cant be replaced