cells and control

biology - topic 2

how many chromosomes in a human body cell

46

how many chromosomes in a human gamete

23

mitosis

asexual reproduction, growth and replacement of damaged cells

stages of mitosis

prophase, metaphase, anaphase, telophase

cell cycle stages

interphase, prophase, metaphase, anaphase, telophase, cytokinesis

interphase

subcellular structures and DNA duplicate

prophase

nuclear membrane dissapears and chromosomes condense

metaphase

chromosomes line up in pairs

anaphase

spindle fibres pull chromatids to each side

telophase

new nuclear membrane forms around chomosomes

cytokinesis

cell membrane and cytoplasm split

growth in animals

all growth happens by cell division at an early age then stop, cell differnetiation happens early

growth in plants

cell division in roots and shoots, cell elongation causes change in height, cell differentiation occurs throughout a plants life

cancer

uncontrollable growth in cells, forms a lump of cells called a tumour

stem cells

undifferentiated / unspecialised cells - important for growth and development of organisms

embryonic stem cells

divide into / produce any kind of cell

adult stem cells

only produce certain cells / found in certain cells / replace damages cells

plant stem cells

found in meristems (roots and shoots), divide by mitosis

benefits of stem cells

cure diseases, replace faulty cells / damaged tissues, stimulated to differentiate into specialised cells

drawbacks of stem cells

lack of research / knowledge, tumour / cancer development, disease transmission, rejection

ethical reasons for use of stem cells

curing suffering patients is more important than embryos, embryos used in research are often unwanted ones from fertility clinics which means theyd end up destroyed

ethical reasons against use of stem cells

embryos are potential human lives

cerebral cortex

largest part of brain, memory, behaviour, most senses, consciousness, language

cerebellum

movement, balance

medulla oblongata

controls breathing rate, controls heart rate

spinal cord

carries signal between brain and rest of body

PET scan

identifies structure and function, uses radioactive glucose which decays causes gamma ray emission to be detected by scanner, scans slices of body at a time

CT scan

uses x-ray to only identify structure and scans slices of body at a time, images are built up into detailed pictures, risk of exposure to low levels of ionising radiation

nervous system pathway

stimuli, receptor, sensory neurone, relay neurone, motor neurone, effector, response

sensory neurone

carries information as ellectrical impulse from receptor to CNS

relay neurone

carry impulse through CNS to motor neurone

motor neurone

carries impulse from CNS to effector

effector

muscle / gland

sensory neurone adaptations

cell body, dendrites, dendron, axon, myelin sheath, axon terminals

motor neurone adaptations

cell body, dendrites, myelin sheath, axon, axon terminals

dendrites

recieve impulses from other neurons / receptor cells 

dendron

where impulses travel through

cell body

contains nucleus

axon

where impulses travel through

myelin sheath

insulates and speeds up neurotransmission

axon terminals

pass impulses to other neurones / effector cells

synapse

gap between neurones

how does electrical impulse diffuse across a synapse

electrical impulse comes to the end of a neurone and reaches a synapse, electrical impulse then stimulates a chemical called a neurotransmitter to diffuse across the gap, chemical binds with receptor molecules on next neurones membrane which stimulates next neurone to transmit a new electrical impulse

purpose of a reflex arc

automatic, rapid responses to stimuli to prevent injuries

reflex arc pathway

stimulus is detected by receptors, impulses are sent along a sensory neurone to a relay neurone in the CNS via a synapse and then along a motor neurone, impulse reaches uscle and muscle contracts

iris 

controls diameter of pupil

cornea

refracts light

lens

refracts light to focus it on retina

pupil

hole in middle of eye that lets light in

optic nerve

carries impulse to brain

retina

contains cones and rods ( receptor cells sensitive to colour and light intensity )

sclera

tough outer layer

suspensory ligaments

controls shape of lens

ciliary muscles 

controls shape of lens

iris muscles

radial, circular

radial muscles

span from centre to outside like a radius

circular muscles

in circles around centre

what happens to the iris in dim light

pupil will dilate as radial muscles will contract and circular muscles will relax

what happens to the iris in strong light

pupil will constrict as radial muscles will relax and circular muscles will contract

short-sightedness

ras of llight are focused in front of retina because eyeball is too long or cornea is too curved

how to fix short-sightedness

diverging lens spreads rays of light before it reaches eye

long-sightedness

light from close objects comes into focus behind eyeball, eyeball too short or not curved enough

how to fix long-sightedness

converging lens bends rays before it reaches the eye

cataract

protein builds up inside ends causing it to become cloudy, lens can be replaced

colour blind

cones dont work properly causing you to struggle seeing colours