SB2 - Cells & control Flashcards
What are organisms made up of many cells called?
Multicellular organisms
What do multicellular organisms need in order to grow?
New cells
When do cells divide?
- When an organism grows
- When an organism becomes damaged & needs new cells for repair
- When organisms reproduce asexually
What is the cell cycle?
The events that lead to cell division & DNA replication
What is Mitosis?
A type of cell division which produces daughter cells identical to the parent
What are the phases of the cell cycle?
- Interphase
- Mitosis
- Cytokinesis
What is interphase
- The cell grows, organelles (such as ribosome and
mitochondria) grow and increase in number - The synthesis of proteins occurs
- DNA is replicated (forming the characteristic ‘X’ shape) and energy stores are increased
What are the substages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
- Cytokinesis
What is Prophase?
The nucleus starts to break down and spindle fibres appear
What is Metaphase?
The chromosomes are lined up in the spindle fibres across the middle of the cell
What is Anaphase?
The chromosome copies are separated and moved to either end of the cell on the spindle fibres
What is Telophase?
A membrane forms around each set of chromosomes to form nuclei
What is Cytokinesis?
Two identical daughter cells form when the cytoplasm and cell membranes divide
How many daughter cells does mitosis produce?
2 genetically identical diploid cells
Where is a diploid number of chromosomes found in the body?
Body cells (46)
Where is a haploid number of chromosomes found in the body?
Gametes (23)
What is a gene?
A short section of DNA that codes for a protein and as a result controls a characteristic- therefore each chromosome carries many genes
How does cancer occur?
As a result of small changes in cells, that lead to uncontrolled cell division
What is a tumour?
The group of cells that results from this uncontrolled division
How does growth occur in animals?
Via cell division and differentiation
What is differentiation?
The process by which a less specialised cell becomes more specialised for a particular function
How does growth occur in plants?
Via cell division, differentiation and elongation
How can plant cells grow in a specific direction?
By absorbing water into their vacuoles
—> Controlled by auxins
At what time can plants differentiate?
Many types of cells retain the ability to differentiate throughout life
What are the types of stem cells?
- Embryonic
- Adult
- Meristem
What can embryonic stem cells differentiate into?
Any type of body cell
When do embryonic stem cells form?
When an egg and sperm cell fuse to form a zygote
How can scientists clone embryonic stem cells?
By culturing them
What can Adult stem cells differentiate into?
Many types of cells (including blood cells)
What can meristem cells differentiate into?
Any type of plant, and have this ability throughout the life of the plant
Where are meristem cells found?
Root shoot and tips
What is therapeutic cloning?
Involves an embryo being produced with the same genes as the patient.
Describe how therapeutic cloning works
The embryo produced could then be harvested to obtain the embryonic stem cells
—> Could be grown into any cells the patient needed
What is an advantage of therapeutic cloning?
They would not be rejected as they would have the exact same genetic make-up as the individual
What are the benefits with the use of stem cells in medicine?
- Can be used to replace damaged or diseased body parts
- Research into the process of differentiation
- Unwanted embryos from fertility clinics
could be used
What are the problems with the use of stem cells in medicine?
- People may have religious or ethical objections
- If growing cells are contaminated w/ virus - can pass onto individual
- Don’t completely understand the process of differentiation
- People may have religious or ethical objections
- Removal of stem cells = destruction of the embryo
Why may people have religious or ethical objections when using embryonic stem cells?
As it is seen as interference with
the natural process of reproduction
Why might not understanding the process of differentiation be a problem when using embryonic stem cells?
It is hard to control stem cells to form the cells we desire
What makes up our CNS?
- The brain
- Spinal cord
What is the CNS responsible for?
Controlling consciousness, movements thoughts and emotions, among other things
Where is the cerebral hemispheres located?
On the left & right hand sides
What are the functions of the cerebral hemispheres?
- Consciousness
- Memory
- Intelligence
- Visual & sensory processing
Where is the cerebellum located?
Bottom of the brain, on the rear side
What are the functions of the cerebellum?
Fine movements of muscles
—> Ensuring movements are smooth
Where is the medulla oblongata located?
In the brainstem, at the base of the brain
What are the functions of the medulla oblongata?
- Breathing
- Digestion
- Swallowing
- Sneezing
What scans can we use to look inside the brain?
- PET
- CT
What are CT scans?
Fire X-Ray radiation at the brain from several different angles to generate a 3D image of the brain
What are CT scans useful for?
- Examining bleeding
- Damage to brain structures
Why are CT scans not recommended for pregnant women and children?
As it exposes the patient to higher doses of radiation than a normal X-ray
How do PET scans work?
A radioactive ‘tracer’ is injected into the blood before the scan.
—> Scan itself is sensitive to the tracer - areas where the tracer builds up will be highlighted more brightly on the resulting scan.
Why will the tracer in a PET scan build up in certain areas?
As they will also be areas with greater blood flow
What are PET scans useful for?
Identifying cancerous tumours
Why is Investigating brain function and treating brain damage difficult?
- It is complex and delicate
- It is easily damaged
- Drugs given to treat diseases cannot always reach the brain
- It is not fully understood which part of the brain does what.
Why can’t certain drugs reach the brain when treating diseases?
Because of the membranes that surround it
Why might brain tumours be difficult to remove?
- Can push against other structures and blood vessels in the brain
- Can be buried deep in the brain or spinal cord - difficult to remove
What is the eye?
A sense organ containing receptors sensitive to light intensity and colour
Name some structures in the eye
- Retina
- Cornea
- Iris
- Ciliary muscles
- Lens
- Suspensory ligaments
What is the Retina?
Layer of light sensitive cells found at the back of the eye
What does the Retina contain?
- Rod cells
- Cone cells
What are cone cells sensitive to?
Colour
What are rod cells sensitive to?
Light
What is the Cornea?
The see-through layer at the front of the eye
What is the purpose of the cornea?
Allows light through Curved surface bends and focuses light onto the retina
What is the Iris?
Muscles that surrounds the pupil.
What is the purpose of the iris?
Contracts or relaxes to alter the size of the pupil
How does the Iris react to bright light?
The circular muscles contract and radial muscles relax
—> To make the pupil smaller- avoiding damage to the retina
How does the Iris react to dim light?
The circular muscles relax and the radial muscles contract
—> To make the pupil larger- so more light can enter to create a better image
What is the ciliary muscle and the suspensory ligaments?
Hold the lens in place
What is the ROLE of the ciliary muscle and the suspensory ligaments?
They control its shape and allow us to focus on objects nearer or further away
What is the Lens?
Transparent, curved surface on the front of the eye
What is the purpose of the Lens?
Reflects light onto the retina
What is accommodation?
The process of changing the shape of the lens to focus on near or distant objects
Describe how eyes focus on a near object?
● The ciliary muscles contract
● The suspensory ligaments loosen
● The lens is then thicker and more curved- this refracts the light more
Describe how eyes focus on a distant object?
● The ciliary muscles relax
● The suspensory ligaments tighten
● The lens then becomes thinner - light is refracted less
Name some eye defects
- Myopia
- Hyperopia
- Cataracts
- Colour blindness
What is Myopia?
And why might people have this?
Short-sightedness
—> lens is too curved, so distant objects appear blurry
What is Hyperopia?
And why might people have this?
Long sightedness
—> Lens is too flat, so it cannot refract light enough
How can myopia and hyperopia be treated?
- Spectacle lenses
- Contact lenses
- Laser eye surgery
- Replacement lens
How can spectacle lenses be used to treat myopia?
Concave lenses = spreads out the light to treat myopia
How can spectacle lenses be used to treat hyperopia?
Convex lenses = brings the rays together to treat hyperopia
How can laser eye surgery be used to treat myopia or hyperopia?
Lasers can be used to either reduce the thickness of the cornea or change its curvature
How can a replacement lens be used to treat hyperopia?
Either by:
* Replacing the lens with an artificial one made of clear plastic
- Adding the plastic on top of the natural lens
What are the risks of replacement lens?
- Damage to retina
- Cataracts developing
What are cataracts?
Clouding of the lens of the eye
How are cataracts fixed?
By replacing the lens of the eye in surgery w/ a plastic one
What is colour blindness?
The inability to see certain colours
Why does colour blindness occur?
As people with the condition do not have enough cone cells in their retina
—> Usually genetic
Can colour blindness be corrected?
No
What is are reflexes?
Automatic responses which take place before you have time to think
Why are reflexes important?
They prevent the individual from getting hurt
What are synapses?
Gaps between two neurons
What are motor neurones?
A type of neuron that carries impulses to effectors
What are relay neurones?
A short type of neurone found in the spinal chord and brain
—> Relay neurones link sensory, motor & other relay neurones together
What are sensory neurones?
A neurone that carries impulses from receptor cells towards the CNS
What is a reflex arc?
A neurone pathway consisting of a sensory neurone passing impulses to a motor neurone which allows reflexes to occur
Describe the reflex arc?
- A stimulus is detected by receptors
- Impulses are sent along a sensory neuron
- In the CNS the impulse passes to a relay neuron
- Impulses are sent along a motor neuron
- The impulse reaches an effector resulting in the appropriate response
What happens when an impulse reaches the end of the 1st neuron?
A neurotransmitter is released into the synapse
Describe how impulses are transmitted between synapses
● When the impulse reaches the end of the first neuron -
neurotransmitter is released into the synapse
● This neurotransmitter diffuses across the synapse
● When the neurotransmitter reaches the second neuron, it triggers the impulse to begin again in the next neuron
Why are there different speeds & frequencies of impulses?
Different neurotransmitters have different effects on the frequency and speed of the impulse in the second neuron
Why are synapses useful?
- As neurotransmitters are released from axon terminals so impulses only flow in one direction
- Allow fresh impulses to be generated - original impulse will not lose ‘strength’
What is myelin sheath?
A fatty substance which surrounds and insulates neuron axons
What is a benefit of myelin sheath?
Nerve transmission will travel faster
What is Myelin sheath produced by?
Schwann cells
How does the nervous system coordinate actions in response to stimuli?
- Receptor cells convert a stimulus into an electrical impulse
- This electrical impulse travels along sensory neurons to the CNS
- The information is processed & the appropriate response is coordinated, resulting in an electrical impulse being sent along motor neurones to effectors
- The effectors carry out the response
