⭐️SB2 - Cells And Control Flashcards
What is the cell cycle for?
Growth and repair of cells by producing more
What are diploid cells?
Cells with two copies of each chromosome - 46 in total
What are haploid cells?
Cells with 1 copy of each chromosome
23 in total
What is the first step before mitosis?
Interphase -where the cell makes extra sub cellular parts and dna replication occurs
What are the sections of the cell cycle?
Interphase Prophase Metaphase Anaphase Telophase Cytokenisis
What happens at prophase?
The nucleus starts to break down and spindle fibres appear
What is mitosis?
Cell division where the cell splits to form two daughter cells which are identical to the parent cell
What happens in metaphase?
The chromosomes line up on the spindle fibres across the middle of the cell
What is anaphase?
Where the chromosome copies are separated and move to either side if the cell on the spindle fibres
What is telophase?
Where a membrane forms around each set of chromosomes to form nuclei
What is cytokinesis?
The step just after mitosis where a cell surface membrane forms, separating the two nuclei. In plants, a cell wall also forms
Why does asexual reproduction rely on mitosis?
As the organism has to reproduce by itself and the offspring are clones as they have the same chromosomes as the parent
Give examples of organisms that produce asexullly
Strawberries, potatoes, aphids
Give an advantage of asexual reproduction
It’s much faster than sexual reproduction as a partner doesn’t need to be found
Give a disadvantage of asexual reproduction
Asexual reproduction doesn’t produce variation so e.g. one disease could wipe the whole population
Why are some cells cancerous?
As they undergo uncontrollable cell division
What is growth?
An increase in size as a result of an increase in number or size of cells
What are percentile charts?
Charts that map a baby’s growthin relation to others of the same age by measuring things like mass and length
How were percentile charts created?
By measuring a large number of babies and dividing them into 100 groups allowing us to find the percentile
What is a percentile?
% of readings below a certain value
What does it mean if the 25th percentile for an 8 month baby’s mass is 8kg?
Then the 25 percent of 8 month old babies have a mass below 8kg
Why is it useful to plot a babies mass?
To identify whether or not they are growing normally as they should remain near the same percentile curve throughout their growth
What is cell differentiation?
The process that changes less specialised cells into more specialised ones specific to their function
How is a red blood cell specialised?
- has no nucleus so there’s more space for red haemoglobin molecules
- has a large surface area for oxygen to diffuse in and out quicker
How are fat cells specialised?
-cytoplasm of fat cells is filled with fat droplets which is stored until the body needs it as energy.
How are neurones specialised?
Have a long fibre that carries electrical impulses around the body and many connections to other neurones
How are muscle cells specialised?
They have contractile proteins that allow the cell to shorten
What are meristem “
The cells of a plant that rapidly divide by mitosis and specialise into other cells and are found at the end of each shoot and root
What do meristems undergo?
Mitosis, elongation and differentiation
Name two specialised cells in a plant?
Xylem cells and root hair cells
What are the adaptations of a xylem cell?
- thick wall to withstand water pressure
- has small pores in the wall for water and mineral salts to enter and leave the vessel
- has no cytoplasm so there’s room for water
- the cells don’t have cell walls between each other and so form a tube
How do you calculate % change?
(Final value-starting value)/starting value times that answer by 100
Why do meristem cells have many ribosomes?
Because ribosomes provide the cell with protein and that is needed for cell division and elongation
What are stem cells?
Cells that can divide repeatedly over a long period of time to produce cells that differentiate
Where are stem cells found in plants?
In the meristems in the end of each shoot and root
What’s significant about plant stem cells?
They can usually differentiate into any specialised cell throughout the plants life
What’s significant about embryonic stem cells?
They can differentiate into any specialised cell
What happens when embryonic cells continue to divide?
The embryo starts to develop different areas that become different organs. Stem cells here become more limited to the stem cells they can produce
What are adult stem cells?
The stem cells that can only produce the type of specialised cell in the tissue around them
What do adult stem cells allow?
The tissue to grow and replace old or damaged cells
Where are blood stem cells found?
In the bone marrow of long bones
How have scientists used adult and embryonic stem cells in medicine?
In bone marrow transplants, and treat diseases like diabetes
How are stem cells used tor treat diseases?
By stimulating stem cells to produce the specialised cells that are needed and then injecting them where necessary
What are the problems with using stem cells?
- if they continue dividing in the body, they could cause cancer
- if the immune system the stem cells from another person as they are foreign objects to the body - called rejection
What happens to stem cells in the brain once an embryo is 3 weeks old?
They start to differentiate into neurones which make up most of the brain
Where is the cerebral cortex?
At the front top of the brain split into two central hemispheres
What did gage’s accident teach scientists when he for up normally and was able to walk and talk but became ill tempered and lazy after?
That the front of the cerebral cortex is involved in controlling personality
What is the cerebral cortex used for?
Most of our senses, language memory’s behaviour and consciousness
How do the two cerebral hemispheres work in relation to the rest of the body?
The right hemisphere communicates with the left side of the body and vice versa
What is the cerebellum for?
Controls balance, posture and coordinates timing and fine control of muscle activity
Where is the cerebellum located?
At the base of the brain
Where is the Medula oblongata?
At the bottom of the brain right by the spinal chord
What does the medula oblongata control?
Heart rate, breathing rate and reflexes like vomiting, swallowing and sneazing
What are the mass of neurones that make up the medula oblongata connected to?
The spinal chord which is about the width of a finger and consists of many nerves that carry info between the brain and the rest of the body
How can functions of the brain be investigated through surgery?
By placing electrodes the apply electrical currents to the brain and asking the patient what they feel
How can the brain be investigated without surgery?
Scanning
How is a CT scan carried out?
Where an x ray beam moves in a circle around the head and detectors measure the absorption of X rays.
How is a CT scan useful?
Shows the shape and structures of the brain in a series of ‘slices’ and differences in the shapes in the brain can be linked to differences in the way people think and act suggesting functions of those parts
What does a PET scan show?
Brain activity
How does a PET scan work?
The patient is injected with radioactive glucose and the more active the cells, the more glucose taken in.
How are results of a PET scan detected?
The radioactive atoms cause gamma rays which the scanner detects and more gamma rays come from parts containing more cells
How can scientists match activities with certain areas of the brain using a PET scan
As carrying out activities during a PET scan causes specific areas of the brain to become more active
What does damage of the spinal chord cause?
The reduced flow of info between the brain and parts of the body
What happens if you damage your nerves?
Loss of feeling in the legs if you damage your lower spinal chord and damage in the upper spinal chord by your neck can cause quadriplegia
What is quadriplegia?
Loss of feeling in both arms and legs
Why doesn’t the body repair the spinal chord when damage occurs?
As there are no adult stem cells that differentiate into neurones in the spinal chord
How can spinal chord damage be treated?
- new stem cell injections that are being developed
- wires can be used to electrically stimulate nerves but the patient will never regain full control or feeling
Why can a brain tumour affect the patient?
As it may squash parts of the brain and stop them working
What are the methods of treating a brain tumour?
- Cutting the tumour out
- killing the cells with high energy x ray beams in radio therapy
- injecting drugs to actively kill dividing cells in chemotherapy
Why may chemotherapy nit work?
Due to the blood-brain-barrier which is a natural filter that only allows certain substances to get from the blood into the brain
How can scientists examine the brain on living tissue?
By growing brain tissue in their lab using stem cell techniques
What is the central nervous system CNS made up of?
The brain and spinal chord and they control your body
What is the nervous system made up of?
Brain, spinal chord and nerves, allowing your body to communicate using electrical signals called impulses
Where is the sciatic nerve?
Connects the heel to the spinal chord and is the thickest nerve
What does the vertebrae do?
Protects the spinal chord
What is a stimulus?
Anything your body is sensitive to
What makes an organ a sense organ?
Contains receptor cells that detect stimuli e.g. skin has receptor cells that detect stimulus of temp. Change
What do receptor cells create?
Impulses that travel to the brain
What is a response?
The impulses sent to parts of the body from the brain in order for something to happen as a result of a stimulus
What is the function of a sensory neurone?
To carry impulses from receptor cells towards the CNS
What is neurotransmission and where does it happen?
It is the transmission of impulses and happens in the neurones
How are neurones adapted to carry impulses?
They have a long cell body and long extensions
How is an impulse from a receptor cell transmitted through a sensory neurone?
The impulse passes through a tiny branch called a dendrite, and is then transmitted along the dendron and the axon.
What are axon terminals?
Allow impulses to be transmitted to other neurones
From where to where does an impulse on a sensory neurone move?
From dendron to axon
How are sensory neurones adapted to their function?
- Dendrons and axons are long to allow fast neurotransmission over long distances
- the myelin sheath around dendron and axon electrically insulates the neurone from neighbouring neurones to stop the signal loosing energy
Where are the eyes receptor cells?
The retina
What receptor cells are in the retina?
Cones and rods
What are cones?
Receptor cells sensitive to light some defat red and others detect green or blue .
How do cones work?
Generate impulses in sensory neurones which lead into the brain through the optic nerve and this info is processed into full colour vision in the back of the cerebral hemispheres
What do rods do?
They detect differences in light intensity
When do rods work best?
In very dim light
Why is your colour vision poor in dim light”
Because cones only work in bright light
What do the ciliary muscles do?
Alter the shape of the lens
What is the cornea?
Clear cloudless covering that focuses light
What is the retina?
A layer of cones and rods at the back of the eye
How is the amount of light entering the eye controlled?
By muscles in the iris which fan constrict or dilate the pupil
Why is the size of pupils controlled?
As bright light can damage receptor cells in the retina
How does the cornea mostly focus the light onto one point on the retina?
By refracting the light rays to bring them together
What does the lens do?
Fine tunes the focussing done by the cornea
When do the ciliary muscles make the lens fatter?
To focus light from near objects as fatter lens causes more refraction
When do the ciliary muscles make the lens thinner?
To focus light from distant objects
What does it mean if you’re short sighted?
Distant objects appear blurred
What does it mean if you’re long sighted?
Close up objects appear blurred
Why are some people short sighted?
Because the rays of light from distant objects are focussed in front of the retina. This could be because the eyeball is too long or the cornea is too curved and so refraction happens more than it should
Why are some people long sighted?
Because the rays of light from close objects are focused behind the retina. This could be as the eyeball is too short or the cornea isn’t curved enough
How can short sightedness be corrected?
With a diverging lens to spread out rays before they reach the eye
How can long sightedness be corrected?
With a converging lens to bend rays before they reach the eye
How can a laser correct long or short sightedness?
By cutting away some of the cornea and then reshaping it
What is a cataract?
When a protein builds up inside a lens and makes it cloudy.
How can cataract be treated?
By reloading the clouded lens with a plastic one and restoring full vision
Why are some people colour blind?
As some of their cones don’t work properly
What is the most common form colour blindness?
red green colour blindness where cones that detect green light are faulty making it hard to tell the difference between reds, greens and browns
How is colour blindness corrected?
It cant be corrected
What are effectors?
Things like glands and muscles where impulses from a brain are sent to
What neurone carries an impulse to an effector?
A motor neurone
What are relay neurones?
Short neurones that are found in the spinal cord and link motor neurones and sensory neurone.
What don’t motor and relay neurones have?
A dendron
Where do axon terminals on a motor neurone pass the impulse to?
The effector cell
What is a synapse?
Where one neurone meets another and has a tiny gap.
What happens when an impulse reaches an axon terminal?
A neurotransmitter substance is released into the gap which is detected by the next neurone and releases an impulse
Give to reasons synapses are used in the nervous system
- As neurotransmitters are only released in one direction from axon terminals
- they allow many fresh impulses to be generated in many neurones connected to one neurone so the original impulse doesn’t need to be split and loose strength
Give an example when a reflex is used?
If you touch a very hot object and you need to pull your finger away quickly so you don’t want to waste time thinking about it
What are the characteristics of reflex actions in the body?
They are responses that are automatic and very quick to protect the body
What neurone pathway do reflex actions use?
A reflex arc.
How are reflex arcs helpful?
The arc bypass the parts of the brain involved in processing information so responses are quicker than ones that need processing
What are the steps in a reflex arc?
- Stimulus is detected by the receptor
- Impulse is transmitted along sensory neurone
- Impulse goes to relay neurone via synapses in the spinal chord
- Impulse travels along motor neurone
- Impulse reaches the muscle to contract
Give examples of when reflex arcs are used in the body
- protecting the eye from bright light and causing the pupil to contract
- when you burn yourself
