Topic 2 - Cell Cycle & Eye 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
State the three stages of the cell cycle
Stage 1 - interphase
Stage 2 - mitosis
Stage 3 - cytokinesis
What is interphase?
The longest stage of the cell cycle that involves cell growth, the synthesis of new organelles (sub cellular structures) and DNA replication
What does DNA replication involve?
Double helix “unzips” exposing two strands
DNA bases align next to complementary based on the DNA strands
Complementary base pairs join
Two identical DNA molecules formed
What is a chromosome?
A linear DNA molecule tightly coiled around proteins
What happens to chromosome during DNA replication?
The DNA in each chromatid is replicated.
What is mitosis?
A form of cell divisions 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 four stages of mitosis
Prophase
Metaphase
Anaphase
Telophase
Outline prophase
DNA condense, chromosomes become visible
Nuclear membrane disappears
Outline metaphase
Chromosome line up along the cell equator
Outline anaphase
Spindle fibres attach to each chromosome
Chromatids pulled to opposite poles
Chromatids separated
Outline telophase
Cell begins to separate
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
A cell divides by mitosis once every 2 minutes. Calculate the number of identical cells present after 10 minutes
What is cancer?
Non-communicable disease
Uncontrolled cell division (due to damaged DNA) results in the formation of a primary tumour
Tumour cells breaks off and spread to other tissues forming secondary tumours
What are percentile charts?
A chart used to monitor growth
Measurements (e,g fetal length) can be compared to expected values at a certain age
What can doctors determine from percentile charts?
Slower growth than normal
Faster growth than normal
Abnormal growth
Describe growth in animals
Cell division occurs in all body cells. It occurs at a slower rate in adults that in younger animals as growth stops and cell division is only required for replacement and repair
Most cells differentiate at an early stage and become specialises. Some adult stem cells retain their ability to differentiate.
Describe growth in plants
Cell division can only occur in meristematic tissue. The rate of cell division remains the same throughout a plants life.
Meristematic stem cells can differentiate into any cell type for as long as plant lives.
Cell elongation occurs in all cells. Cells expand and enlarge, enabling growth of the plant.
What are stem cells?
Cells are that are unspecialised and capable of differentiating into a range of different cell types.
What is meant by differentiation
The process by which stems cells become specialised (have a specific functions)
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 tissues
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?r
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 region of the plant where cells are continuously dividing e,g root tips, shoot tips
Where 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 use 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?
Treats damage or diseases e,g heart disease, Type 1 diabetes
Used in scientific research
Growing organs for transplants
What are the risks of stem cells use in medicine?
Transplanted stem cells could cause tumours
Finding suitable stem cell donors is a difficult task
Stems cells may be rejected by the body (immunosuppressive drugs may have be taken)
Potential side effects
Long terms risks of using stem cells unknown
Stem cells may become contaminated during preparation and when transplanted transmit infections to the patient, making them sicker.
What are the ethical issues related to the use of stem cells in medicine?
The embryos that were used to provide stem cells are destroyed which is seen as unethical and a waste of potential human life
May lead to the reproductive cloning of humans.
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 systems (nervous outside of the CNS) to the brain
Describe the structure of the brain
Cerebrum
Cerebellum
Medulla oblongata
A = cerebellum B = medulla oblongata C = cerebrum
Describe the structure of the cerebrum
Largest region of the Brain
Divided into two hemispheres
What is the function of the cerebrum?
Intelligence Language Memory Emotions Visual and sensory process
Where is the cerebellum located?
Lower regions of the brain
What is the function of he cerebellum
Coordination of muscles
Voluntary movement
Non-voluntary movement
What is the function of the medulla oblongata?
Controls automatic processes in the body e,g breathing rate, heart rate, peristalsis
What methods are used to observe the brain other than surgery?
CT scan
PET scan
Wha is a CT scan?
Uses X rays to produced 3D cross sectional image of the Brain
Describe how CT scans are useful investigate brain function
CT scans show damaged regions of the brain e,g area of swelling, bleeding
Observations of the patients symptoms can enable scientists to determine the function of damaged region
What does a PET scan involve?
Radioactive substances 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 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?
Damaged 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 damaged 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 functional units of the nervous system.
What is the function of the axon
Carries imputes 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 functions of a sensory neurone
Carries impulses from receptors to 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 CNS to cell body
Cell body found at one end of neurone
Long axon carries impulses from cell body to the effectors.
Outline the function of a relay neurone
Carries impulses from sensory neurones to motor neurones within the CNS
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 central nervous system coordinates a response to a stimulus
Stimulus
Sensory receptor detects stimulus
Sensory receptor sends impulses along sensory neurone to CNS
CNS coordinates response
CNS sends information to effector along motor neurone
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?
Nerve impulses reacts presynaptic neurone
This triggers the releases of neurotransmitters
Neurotransmitters diffuse across the synapse
They bind to receptors on the postsynaptic neurone
This stimulates an impulse in the postsynaptic neurone
Why do synapse 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 mechanisms e,g withdrawal reflex is initiated when a hot object is touched to prevent burns.
Describe the reflex arc?
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 allow 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 muscle and suspensory ligaments?
Change the shape of the lens (accommodation) 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 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) 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
Rods detect dim light Circular muscles relax Radial muscles contract Pupil dilated More light enters the pupil
Describe how bright light affects the size of the pupil
Cones 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 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 focuses onto the retina
Describe how the eye focuses on distance 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 distance 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 focused onto the retina instead converging behind the retina
How is long-sightedness treated?
Using a convex lens or laser eye surgery
What are cataracts?
A cloudy patch forms on the lens of the eye which negatively affects Vision
Vision becomes blurry, difficulty to see the intensity of colour, problems with glare
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
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
