Cells and Control Flashcards
Describe what happens in each stage of the cell cycle.
- G1 - Growth
- S - DNA synthesis
- G2 - Growth and preparation for mitosis
- M - Mitosis (cell division)
Describe what happens in each stage of mitosis.
- Prophase - nuclear membrane disappears, chromosomes and their copies condense and so become more visible.
- Metaphase - chromosomes and their copies line up in the middle of the cell.
- Anaphase - chromosomes and their copies are pulled to opposite ends of the cell.
- Telophase - new membranes form around each set of chromosomes.
- Cytokinesis - the cell membrane pinches in and eventually divides into two daughter cells.
Explain how mitosis is important for an organism.
Growth - cell division creates more cells.
Tissue repair - replace damaged cells with new ones.
Asexual reproduction - to produce offspring that are genetically identical.
How do cancers grow?
Cancers are resultant of a change leading to uncontrolled cell division, by which they effectively grow indefinitely.
What constitutes growth in animals?
Increase in number of cells and cell size.
Describe the stages of growth in plants.
Mitosis occurs in the apical meristem.
Elongation occurs in the zone of elongation, and also elsewhere in the plant.
Differentiation occurs in the zone of maturation, roughly in line with the first root hair cells.
Describe the locations of different types of stem cells in plants and animals.
In plants, stem cells are present in the apical meristems in the tips of roots and shoots and can differentiate into any type of plant cell. In animals, embryonic stem cells (which can differentiate into any type of animal cell similarly to plant meristems) are present in the embryo. Adult stem cells are in bone marrow, yet can differentiate only into certain types of animal cells - not all.
Evaluate use of stem cells in medicine.
Stem cells could in theory be differentiated in a lab then transplanted into patients, especially interesting are nerve cells which could potentially be used to cure paralysis. Alongside ethical issues of embryonic stem cells, problems include disease transmission, inadvertently causing cancer, and rejection. The latter could be solved by taking immunosuppressant drugs indefinitely, which would then increase risk of infectious disease.
Describe the parts of the human nervous system, and hence the pathway taken by electrical impulses to and from the brain.
The Central Nervous System (CNS) consists of the brain and spinal cord, while the Peripheral Nervous System (PNS) is every other neurone in the body. Impulses travel through a sensory neurone to the CNS and a motor neurone from the CNS, as well as relay neurones inside the CNS to reach to and from the brain.
How does the nervous system detect stimuli?
Specialised receptor cells create electrical impulses in response to some event, in effect triggering a sensory neurone.
Explain the structure and adaptation of neurones.
A long fibre (dendron before, axon after cell body) runs end to end, insulated by a myelin sheath which increases the speed of the impulses. Tiny branches (dendrites) are at each end for communication of impulses between neurones.
Explain the function and action of synapses.
Synapses are small gaps between adjacent neurones. Impulses trigger nerve endings to release chemicals called neurotransmitters to diffuse across the gap, where they bind to receptors which stimulate the second neurone to transmit an impulse.
Describe the structure and function of the reflex arc.
The reflex arc enables reflex actions without consulting the brain and conscious thought, speeding up the response. Only a relay neurone is used in the CNS: the arc has structure receptor - sensory neurone - relay neurone - motor neurone - effector.
