prophase - when chromosomes coil up and condense, nuclear membrane breaks down (chromosomes lie free in cytoplasm)
metaphase - when chromosomes line up at centre of cell
anaphase - when spindle fibres pull chromosomes apart, each copy pulled to opposite ends of cell
telophase - 2 nuclear membranes form around chromosomes
cytokinesis
happens before telophase ends, end of mitosis
cell membrane divides to form 2 separate cells
cell growth
increase in size or mass
due to cell differentiation, cell division
plants grow by cell elongation
cell growth in animals
all happens by cell division
grow when young, stop growing once reached full growth
when young, cells divide at fast rate
when adult, cell division for repair (replace old/damaged cells)
cell differentiation lost at an early stage as cells are replaced
cell growth in plants
mostly by cell elongation
cell division in tips of roots and shoots (meristem)
grow continuously, differentiate continuously to develop new parts
cancer
uncontrolled cell division
could be due to change in gene which controls cell division (the rate at which cells divide is controlled by genes)
leads to mass of abnormal cells (tumour)
if a tumour invades and destroys surrounding tissue, it is cancer
growth percentile charts
shows overall pattern in development, easy to highlight problems (obesity, malnutrition, dwarfism)
measures length, mass and head circumference
can help see inconsistent patterns (small baby with big head)
stem cells
undifferentiated cells
can divide by mitosis to become specialised
found in early human embryos (potential to produce any cell needed)
adult stem cells found in bone marrow but they arent as versatile as embryonic stem cells (can only produce certain cells, not any cell)
in adults, stem cells used to replace damaged cells (skin, blood)
meristem
plant tissue where cells which divide by mitosis are only found
found in areas of plant when growing (root, shoot)
produce unspecialised cells which divide to form any cell needed
can divide and differentiate any cell for as long as plant lives (embryonic stem cells only as embryo)
forms specialised cells like xylem and phloem
stem cells and medicine
sickle cell anaemia can be cured with bone marrow transplant sometimes (adult stem cells produce new red blood cells). allograft (donor stem cells) or autograft (own stem cells transported)
extracting embryonic stem cells can be stimulated to differentiate into specialised cells
replace damaged cells due to disease or injury (cardiac stem cells transported into someone with heart disease)
risks of using stem cells in medicine
tumour development as stem cells divide very easily
disease transmission as donor stem cells may be infected with a virus (live inside cells) so recipient gets sicker
rejection as the stem cells may be recognised as foreign and so body attacks new cells. immunosuppressant drugs can be taken but this makes them susceptible to more disease
ethical issues of using stem cells in medicine
argument of using human embryonic cells as each is a potential human life
argument as curing suffering patients is more important than potential life
central nervous system
made up by brain and spinal cord
spinal cord
long column of neurones from base of brain down to spine
neurones may branch off and connect with other parts of body
relays information between brain and rest of body
brain
made up of billions of interconnected neurones
cerebrum - largest part of brain, divided into 2 cerebral hemispheres (2 halves). right hemisphere controls muscles on left side of body, left hemisphere controls muscles on right side of body. responsible for movement, intelligence, memory, language, vision
cerebellum - responsible for muscle coordination, balance
e.g if area of brain is damaged and patient cant see, it controls vision
PET scanner
uses radioactive chemicals
shows which part of brain is active when inside scanner
very detailed - shows structure and function
2D images
shows if areas in brain are active/inactive (help study disorders)
e.g alzheimers has reduced activity in some parts of brain, PET scans show reduction compared to normal brain
difficulties when treating problems in cns
hard to repair damage and repair nervous tissue
not easy to access - hard to get into some parts of brain, may be at risk of damaging other areas of brain
treatment can lead to permanent damage (injuring spinal cord needs surgery, but may damage more during surgery)
the nervous system
made up of neurones
stimulus (change in environment) detected by receptors (cells that detect stimuli) which send nerve impulses to the coordinator (brain/spinal cord, chooses response) which ultimately sends an effector (muscle/gland which causes response) to cause a response
cell body has extensions to connect to other neurones (dendrite, dendron carry nerve impulses towards cell body, axon carries nerve impulses away from cell body)
some axons surrounded by myelin sheath (electrical insulator) whcich speeds up impulse
sensory neurone
one long dendron carries nerve impulses from receptor cells to cell body (middle of neurone)
short axon carries nerve impulses from cell body to cns
motor neurone
lots of short dendrites carry nerve impulses from cns to cell body
long axon carries nerve impulses from cell body to cns
relay neurone
lots of short dendrites carry nerve impulses from sensory neurone to cell body
axon carries nerve impulse from cell body to motor neurone
synapse
connection between 2 neurones
electrical impulses cant travel through synapses (chemical -neurotransmitter- released which diffuse across gap)
nerve impulse arrives at synapse
chemical messenger released into synapse
neurotransmitter diffuses across synapse
neurotransmitter binds with receptor on next neurone
neurotransmitter binds with receptor to stimulate impuse in next neurone
transmitting nerve impulse is very fast but slowed down accross synapse as diffusing neurotransmitters takes time
reflexes and reflex arcs
automatic, rapid responses to stimuli
passing information in a reflex (receptor to effector) = reflex arc
neurones in reflex arc go through spinal cord or unconscious part of brain
how reflexes prevent injury
stimulus detected by sensory receptors, impulses sent along sensory neurone to relay neurone in cns
impulse reaches a synapse between sensory and relay neurone so neurotransmitters are released, which causes impulses to be sent along relay neurone
synapse between relay and motor neurone, neurotransmitters released, causes impulse to be sent along motor neurone
impulse travels across motor neurone to effector
muscle/gland contracts and causes a response (move)
dont spend time thinking about response, quicker than normal
reflexes in the eye
very bright light damages the eye so reflexes help protect it
light receptors detect very bright light and send message along sensory neurone to brain
message travels along relay and motor neurone, which tells circular muscles in iris to contract, making the pupil smaller so less light enters the eye
Cornea refracts (bends) light into the eye
Iris controls how much light enters the pupil
Lens refracts light and focuses it onto the retina
Pupil lets light into the eye when open, contracts when there is a lot of light
Ciliary muscles change the shape of the lens to adjust focus
Retina is the light-sensitive part of the eye, covered in light-sensitive cells (rods and cones) which detect color
Rod cells are sensitive in dim light and cannot sense color
Cone cells are sensitive to color (red, blue, green) and are found in the fovea
Fovea is the most sensitive part of the retina, containing cones for color vision
Blind spot is the point on the retina where the optic nerve enters, and there are no rods/cones