B2: Cells And Control Flashcards
What is the cell cycle?
• A series of events that take place in a cell involving cell growth, DNA replication and cell division
• It is described as the lifecycle of a cell
What is interphase?
The longest stage of the cell cycle that involves cell growth, the synthesis of new organelles and DNA replication
What does DNA replication involve?
• Double helix ‘unzips’ exposing two strands
• DNA bases align next to complementary bases on the DNA strands
• Complementary base pairs join
• Two identical DNA molecules formed
What is a chromosome?
A linear SNA molecule tightly coiled around proteins
What is mitosis?
A form of cell division that produces two diploid ‘daughter’ cells, both genetically identical to the parent cell.
Why is mitosis important in organisms?
• Asexual reproduction
• Growth
• Repair of damaged cells
• Cell replacement
State the stages of mitosis ?
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Outline Prophase?
DNA condenses,chromosomes become visible
Nuclear membrane disappears
Outline metaphase?
Chromosome line up along the cells equator
Outline anaphase?
• Spindle fibres attach to each chromosome
• ‘Arms’ of each chromosome pulled to opposite poles
• Chromatids separated
Outline telophase ?
Nucleus of the cell divides
New membrane forms around each set of chromosomes
What does cytokinesis involve?
• Division of the cell membrane and cytoplasm
• Two genetically identical ‘daughter’ cells produced
What is cancer?
• Non-communicable disease
• Uncontrolled cell division (due to damaged DNA) results in the formation of a primary tumour
• Tumour cells break off and spread to other tissues forming secondary tumours
What are percentile charts?
• A chart used to monitor growth
• Measurements (e.g. fetal length or head circumference) can be compared to the expected values at a certain age
What can doctors determine from percentile charts?
• Slower growth than normal (below the bottom line)
• Faster growth than normal (above the top line)
• Abnormal growth (irregular growth patterns)
What are stem cells ?
Cells that are unspecialised and capable of differentiating into a range of cell types
What is meant by ‘differentiation’?
• The process by which stem cells become specialised (have a specific function)
• Some genes switch on or off, determining cell type
Why is cell differentiation important?
It enables the formation of specialised tissues with specific functions e.g. muscle tissue.
What are embryonic stem cells?
Stem cells found in very early embryos that are unspecialised and capable of differentiating into any cell type
What is the function of embryonic stem cells?
Enable the growth and development of tissues in human embryos
What are adult stem cells?
Stem cells that can differentiate into a limited range of cell types e.g. bone marrow stem cells
What is the primary function of adult stem cells?
Replacement of dead cells e.g. replacement of red blood cells which only live for 120 days
Where are stem cells found in plants?
Meristems
Where is meristem tissue found?
In regions of the plant where cells are continuously dividing e.g. root tips, shoot tips
What are meristematic stem cells?
Stem cells found in meristems that are unspecialised and capable of
differentiating into any cell type during the life of a plant
How can stem cells be used in medicine?
• Stem cells collected
• Stem cells stimulated to differentiate into specific cell types e.g. heart muscle cells
• Specialised cells transplanted into the patient
• Used to treat damage or disease e.g. heart disease
Where can embryonic stem cells be collected from?
• Donor stem cells removed from embryos grown in vitro
• Patient’s own stem cells removed from the umbilical blood before birth
What are the benefits of using stem cells in medicine?
• Treat damage or disease e.g. heart disease, type 1 diabetes
• Treat diseases that would otherwise be untreatable
• Used in scientific research
• Growing organs for transplants
What are the risks of stem cell use in medicine?
• Transplanted stem cells could cause tumours
• Finding suitable stem cell donors is a difficult task
• Stem cells may be rejected by the body
• Potential side effects
• Long term risks of using stem cells unknown
What is the central nervous system?
Brain and spinal cord
What is the spinal cord?
A long, thin structure composed of neurones that extends from the medulla oblongata down the spine.
What is the function of the spinal cord?
Connects the peripheral nervous system (nerves outside of the CNS) to the brain.
Describe the structure of the brain ?
Consists of three main regions:
• Cerebrum
• Cerebellum
• Medulla oblongata
Describe the structure of the cerebrum ?
• Largest region of the brain
• Divided into two hemispheres
What is the function of the cerebrum?
Involved in:
• Intelligence
• Language
Memory
• Emotion.
• Visual and sensory processes
What is the function of the left cerebral hemisphere?
Left hemisphere receives sensory information from the right side of the body and controls muscle coordination on the right
What is the function of the right cerebral hemisphere?
Right hemisphere receives sensory information from the left side of the body and controls muscle coordination on the left
Where is the cerebellum located?
Lower region of the brain
What is the function of the cerebellum?
Involved in:
• Coordination of muscles
• Voluntary movement e.g. walking
• Non-voluntary movement e.g. balance
What is the function of the medulla oblongata?
Controls automatic processes in the body e.g. breathing rate, heart rate, peristalsis
What methods, other than surgery, are used by doctors to observe the brain?
• CT scan
• PET scan
What is a CT scan?
A procedure that uses X-rays to produce
3D cross-sectional images of the brain
Describe how CT scans are useful to investigate brain function?
• CT scans show damaged regions of the brain e.g. areas of swelling, bleeding
• Observations of the patient’s symptoms can enable scientists to determine the function of the damaged region
What does a PET scan involve?
• Radioactive substance injected into a patient’s bloodstream and taken up by tissues in the brain
• Radiation emitted by tissues detected, enabling the identification of active and inactive regions of the brain
Describe how PET scans are useful to investigate brain function ?
• Show which areas of the brain are active and which areas are not
• Comparisons of brain activity in healthy patients and patients with brain damage allow scientists to determine the functions of inactive regions
Why is it difficult to treat damage to the CNS?
• Damage to neurones is permanent and cannot be repaired (as nerve cells don’t divide by mitosis)
• Hard to reach some areas of the brain
• Risk of further permanent damage to other areas of the CNS during surgery
What is the function of the nervous system?
Allows an organism to rapidly react to environmental and internal changes
What are neurones?
Nerve cells adapted to quickly transmit nerve impulses. They are the functional units of the nervous system.
What is the function of the axon?
• Carries impulses away from the cell body
• Enables the transmission of nerve impulses over long distances
What is the function of the dendrites and dendrons?
• Carry impulses towards the cell body
• Dendrites provide a large surface area to receive impulses
What is the role of the myelin sheath?
• Electrically insulating layer
• Surrounds the axon and increases the speed of impulses
Outline the function of a sensory neurone?
Carries impulses from receptors to the central nervous system
Describe the structure of a sensory neurone?
• Long dendron carries impulses from receptors to the cell body
• Cell body found part way along the neurone
• Short axon carries impulses from the cell body to the CNS
Outline the function of a motor neurone?
Carries impulses from the central nervous system to effectors
Describe the structure of a motor neurone?
• Short dendrites carry impulses from the CNS to the cell body
• Cell body found at one end of the neurone
• Long axon carries impulses from the cell body to the effectors
Outline the function of a relay neurone?
Carries impulses from sensory neurones to motor neurones within the central nervous system
Describe the structure of a relay neurone?
• Short dendrites carry impulses from sensory neurones to the cell body
• Short axon carries impulses from the cell body to motor neurones
Describe how the central nervous system coordinates a response to a stimulus (6 steps)?
1.Stimulus
2.Sensory receptor detects stimulus
3.Sensory receptor sends impulses along sensory neurone to CNS
4.CNS coordinates response
5.CNS sends information to effector along motor neurone
6.Effector produces a response to the stimulus
What is a synapse?
A small gap between neurones across which a nerve impulse is transmitted via
neurotransmitters
How are nerve impulses transmitted across a synapse?
1.Nerve impulse reaches presynaptic neurone
2.This triggers the release of neurotransmitters
3.Neurotransmitters diffuse across the synapse
4.They bind to receptors on the postsynaptic neurone
This stimulates an impulse in the postsynaptic neurone
Why do synapses slow down the transmission of nerve impulses?
It takes time for the neurotransmitters to diffuse across the synapse and bind to receptors on the postsynaptic neurone.
What is a reflex?
• Automatic response to a stimulus by the body
• Involuntary - does not involve conscious part of the brain
• Protective mechanism e.g. a withdrawal reflex is initiated when a hot object is touched to prevent burns
Describe the reflex arc?
stimulus → sensory receptor → sensory
neurone → relay neurone → motor neurone → effector → response
Outline the structure and function of the cornea?
• Transparent outer covering of the eye
• Refracts light entering the eye
Outline the structure and function of the iris?
• Pigmented ring of circular muscles and radial muscles
• Controls the size of the pupil to alter how much light enters the eye
What is the pupil?
A hole in the iris centre that allows light rays to enter the eye
Outline the structure and function of the lens?
• Transparent, bi-convex structure
• Suspensory ligaments attach the lens to a ring of ciliary muscle
• Refracts light, focusing it onto the retina
What is the function of the ciliary muscles and suspensory ligaments?
Change the shape of the lens (accomodation) to focus light onto the retina
Outline the structure and function of the retina?
• Light sensitive layer composed of rod and cone cells
• Converts light energy into neural signals which are sent to the brain via the optic nerve
What are rod cells?
Cells in the retina that are sensitive to low light intensity (dim light)
What are cone cells?
Cells found in the retina that are sensitive to high light intensity (bright light) and can detect different colours.
What is the function of the optic nerve?
It transmits nerve impulses to the brain from the retina.
Describe how dim light affects the size of the pupil?
• Light receptors detect dim light
• Circular muscles relax
• Radial muscles contract
• Pupil dilates
• More light enters the pupil
Describe how bright light affects the size of the pupil?
• Light receptors detect bright light
• Circular muscles contract
• Radial muscles relax
• Pupil contracts
• Less light enters the pupil
Why is the iris reflex important?
It prevents bright light from damaging the retina.
What is accommodation?
• Process by which the elastic lens changes its shape (with the aid of ciliary muscles and suspensory ligaments) to focus on near or distant objects
• Light is focused onto the retina
Describe how the eye focuses on near objects?
• Near object
• Ciliary muscles contract
• Suspensory ligaments slacken
• Lens becomes more convex (more rounded)
• Light is refracted more
• Light rays focused onto the retina
Describe how the eye focuses on distant objects?
• Distant object
• Ciliary muscles relax
• Suspensory ligaments tighten
• Lens becomes less convex (less rounded)
• Light is refracted less
• Light rays focused onto the retina
What is long-sightedness?
• Can focus on distant objects clearly
• Cannot focus on near objects
What are the causes of long-sightedness?
• Eyeball is too short
• Lens is less elastic (usually age-related)
• light rays are not focussed onto the retina, instead converging behind the retina
How is long-sightedness treated?
• Using a convex lens (causes light rays to converge) in glasses or contact lenses
• Replacement lenses
• Laser eye surgery
What is short-sightedness?
• Can focus on near objects clearly
• Cannot focus on distant objects
What are the causes of short-sightedness?
• Eyeball is too long
• Lens is too thick and too rounded
• light rays are not focussed onto the retina, instead converging in front of the retina
How is short-sightedness treated?
• Using a concave lens (causes light rays to diverge) in glasses or contact lenses
• Replacement lenses
• Laser eye surgery
What are cataracts?
• A cloudy patch forms on the lens of the eye which negatively affects vision
• Vision becomes blurry, difficult to see the intensity of colours, problems with glare etc.
How are cataracts treated?
The clouded lens is exchanged for a synthetic lens during surgery.
What is colour-blindness?
• A deficiency of the eye that makes it difficult to distinguish between colours
• e.g. individuals with red-green colour blindness have difficulty differentiating between red and green
What is the cause of colour-blindness?
Damage to cone cells in the retina
