Topic 2 - Cells and Life Flashcards
mitosis defnition
when a cell reproduces itself to form two genetically identical diploid daughter cells
6 stages of cell cycle and mitosis
I PMAT C
What happens in interphase?
- cell needs to grow and increase amount of sub - cellular structures such as mitochondria and ribosomes
- it duplicates its DNA and forms X - shaped chromosomes
What happens in prophase?
- chromosomes condense getting shorter and fatter
- nuclear membrane breaks down
- centrioles are copied and move to opposite ends of cell
What happens in metaphase?
- chromosomes line up at middle of the cell ( equator )
What happens in anaphase?
- spindle fibres extending from the centriole contract separates 2 sister chromatids at the centromere
- sister chromatids go towards opposite ends of cell
What happens in telophase?
- new nuclear membranes form around each of the sets of chromosomes
- 2 daughter nuclei in parent cytoplasm
What happens in cytokinesis?
cytoplasm separates to form two genetically identical daughter cells each with 2 sets of chromosomes
What are the three uses of mitosis
- growth
- repair tissue by replacing damaged cells
- reproduce by asexual reproduction to produce genetically identical clones
problem with asexual reproduction
- there is no genetic variation in the species so are all susceptible to same diseases
- no evolutionary potential
how do cells know when to stop dividing?
- once we have reached adult size or repaired damaged cells a gene in our nucleus tells the cell to stop dividing
how do cancers form?
- a mutation may occur in that gene resulting in a cell that divides by mitosis uncontrollably
- makes masses of undifferentiated cells known as tumours
- these tumours can spread and invading normal tissue, causing cancer
cell differentiation
when stem cells express the correct genes to make the proteins they need, allowing them to differentiate
why are specialised cells important for the human body?
it helps multicellular organisms to work more efficiently because different cell types can carry out different functions
cell elongation
where a plant cell expands making the plant grow
growth in animals
- all growth in animals is due to cell division
- when they’re young cell division happens at a fast rate
- once animals reach adult size, cell division is mostly only for repair
- cell differentiation lost at an early stage
growth in plants
- growth in height mainly due to cell elongation
- cell division just happens in the meristems ( tips of r&s)
- plants grow continuously so continue to differentiate to develop new parts
percentile charts
used to assess a child’s growth over time and compare it to children the same age and gender
what are stem cells?
stem cells are undifferentiated cells that are not yet specialised for a specific function
totipotent embryonic stem cells
can differentiate into every type of specialised cell, so very important for growth + development of human body
multi-potent adult stem cells
they are only found in certain places (e.g : bone marrow ) and can only differentiate into certain specialised cells
what are adult stem cells used for in the body?
they are used to replace damaged cells
adult cells used in medicine
- people with blood diseases can have bone marrow transplants which contain adult stem cells
- these adult stem cells can differentiate to turn into new blood cells replacing faulty ones
how could embryonic stem cells be used in medicine
- under certain conditions, could be stimulated to differentiate into any kind of specialised cell
- can be used to replace faulty cells in tissues with no stem cells like spinal cord
issues involving using stem cells
- tumour development : stem cells divide very quickly
- disease transmission : donor stem cell could be infected with virus
- rejection : immune system may recognise cells as foreign and trigger a response to get rid of them.
ethical issue involving embryonic stem cell
- human embryos shouldn’t be used as each one is a potential human life
what are sensory receptors?
- groups of cells that detect stimuli
(changes in the environment) and initiate responses to them
CNS ( Central Nervous System )
Consists of the brain and spinal cord and co-ordinates and controls the human body
what are effectors?
- muscles or glands that respond to nervous impulses and bring about a response to a stimulus
transmission of information to and from CNS
stimulus -> receptor -> sensory neurone -> relay neurone(CNS) -> motor neurone -> effector -> response
sensory neurones
they carry information as electrical impulses from the sensory receptor to the CNS
relay neurones
they carry information as electrical impulses from the sensory neurones to the motor neurones and found in CNS
motor neurones
they carry information as electrical impulses from the CNS to the effector
dendrons
carry electrical impulses towards cell body
axons
carry electrical impulses away from cell body
myelin sheath
acts as an electrical insulator around axon, speeding up rate of electrical impulse
what are synapses?
a minute gap or junction between neurones through which they communicate with each other
how do electrical impulses get transmitted between neurones?
- when an electrical impulse reaches the end of the first neurone
- it triggers the release of neurotransmitters ( chemical messengers )
- they diffuse down the concentration gradient and bind to receptor on next neurone
- new electrical impulse generated and moves down next neruone
why are synapses useful?
- only one end of neurone can make neurotransmitters so it makes sure impulses only travel in 1 direction
- slow down the passage of information so it isn’t harmful
what are reflexes?
- they are exceedingly rapid, automatic responses to certain stimuli.
- they protect our bodies from harm by minimising exposure to harmful stimuli
how do reflexes do this?
- it minimises the distance impulses have to travel around the body, so minimises number of neurones and synapses that must be crossed
- it goes through the unconscious part of brain
example of how reflex arc works?
check 23/3/23 in Bio exercise book
