cell communication 2

Regarding auxins: Indicate where they are produced in a plant.

Auxins are produced within the cells of apical shoot tips and young leaves.

resting potential

The potential difference between the two sides of the membrane of a nerve cell when the cell is not conducting an impulse.

Draw a graph that shows an action potential, then indicate what happens to sodium and potassium channels at key points in the graph.

http://projects.ncsu.edu/project/bio183de/Black/wrap/commun2_interactive/action_potential/action_potential.html

Compare signal transduction within a plant cell to that of animal cells.

plants do not have specialized cells for propagation of electrical signals; neurons and synapses are not present. Thus the speed of electrical conduction is much slower than in animals.Signaling molecules of plants utilize receptors, and signal transduction is similar to that of animal cells.Plants also have a transduction system whereby light acts as a signal. Specific wavelengths of light can penetrate the cell and interact with a light receptor molecule. (The light receptor is quite different from chlorophyll). • For animals, animals have a nervous system which can let the animal sense stimuli such as temperature and sharp objects.

Describe ways in which plants defend against herbivores and pathogens; what constitutes the "immune system" in plants?

-Plants utilize a variety of chemical defenses to deter herbivores and to respond to pathogens. When insect herbivores attack a plant, hormones are released to mobilize plant defenses.Hormones are produced at the site of wounding and volatile chemicals are released into the air. The hormones signal local defense responses within nearby cells and also diffuse throughout the plant to mobilize defenses in unharmed tissues. The volatile compounds released during a herbivore attack, also signal nearby plants to mobilize their defenses. Jasmonic acid is a hormone commonly produced in response to an attack. It inhibits the insect's ability to digest protein and travels through the plant inducing widespread production of defensive compounds.In some plants, the volatile compounds attract enemies of the herbivore.-Plants have resistance genes that protect against pathogens by strengthening defenses and generating a plant "immune system". This widespread resistance induced in a plant is called "systemic acquired resistance" and it constitutes a plant immune system of sorts.

Describe the myelin sheath and give its function.

-covers the axon and makes electrical conduction more rapid -Myelin Sheath: The fatty layer surrounding the axons of nerves that provides electrical insulation so that impulses can travel. It helps to increase the speed by which information travels along the nerve. -It is not continuous but is instead rather segmented. Action potentials are only generated in the spaces between myelin segments.

Regarding neurotransmitters: Indicate the role of neurotransmitters in conduction of electrical signals.

A chemical messenger produced by nerve cells, transported in the axon, and released at the synapse; causes chemical and electrical changes in adjacent cells.neurotransmitters are stored in vesicles that accumulate at the axon tips and when an electrical signal reaches the axon tip, the vesicles fuse to the plasma membrane at the synapse and release their contents by exocytosis. The molecules diffuse across the synapse and bind to receptors on the postsynaptic cell. This binding generates depolarization of the postsynaptic membrane

Explain, in general terms, how an electrical signal is conducted down an axon and why the signal only travels in one direction.

An action potential is a large depolarization of the neuronal membrane; it carries an electrical signal along the axon and moves only in one direction because sodium channels become inactivated. The high positive charge that spreads locally within the cytosol can cause sodium channels to the right (open channel) to open, but those to the left (inactivated) cannot respond to the sodium signal. Eventually, the inactivated channels will revert to their normal closed state, but by this time the signal has moved far to the right and sodium levels to the left have returned to the resting potential concentration.

hyperpolarization

An increase in the negativity of the inside of a cell membrane with respect to the resting membrane potential.

Regarding auxins: Describe how auxins cause plants to respond to light direction and to gravity (how is gravity sensed?)

As you learned earlier, plants respond to light by growing toward it, a process called phototropism. This is accomplished because the cells on the darker side of a stem elongate causing the stem to bend toward the light. The auxin stimulates the cells to elongate. Specialized cells in the root cap contain tiny granules called statoliths. These granules are pulled to the bottom of the cell by gravity. As a result, the auxin circling through the root tip is distributed equally on both sides of the root. This allows the cells on both sides to elongate and the root pushes downward. If a root is placed in a horizontal position, the statoliths settle on the sides of the root cap cells that face downward. This causes auxin to accumulate to higher levels on the lower side of the root. The effect of auxin on cell elongation in roots is the opposite of its effect on stem cells. Thus the root cells with low auxin elongate, causing the root to bend downward.

Distinguish between the following pairs: central nervous system vs. peripheral nervous system

Central Nervous System: The brain and nerves of the spinal cord. The system is central because all of the nerves of the body, except the cranial nerves which connect directly with the brain, enter or leave the spinal cord. Peripheral Nervous System: Consists of all of the nerves in the body, outside the CNS, that carry signals from the CNS to the muscles and organs as well as signals from the body into the CNS. The peripheral nervous system includes sense organs that keep the animal in touch with the external environment and cells which transmit this information to the central nervous system.

Distinguish between the following pairs: dendrite vs. axon

Dendrite: a neuronal fiber that conducts an electrical signal toward the cell body. The branching outgrowth of a neuron that carries information, in the form of a nerve impulse, into the cell body of the neuron. Each nerve usually has many dendrites. Axon: a neuronal fiber that conducts an electrical signal away from the cell body. The long, hairlike extension of a nerve cell that carries a message to the next nerve cell.

Regarding auxins: Describe how they are transported in the plant stem (what causes transport in the downward direction?)

From these sites auxins are transported down the stem and into the roots. While the direction of transport is downward, auxins can also move laterally within the stem. Within the root tips, they move in a circular direction.There are two types of carrier protein: one is designed to move auxin into the cell and is located in the upper part of the plasma membrane. The second carrier (called a PIN protein) can only transport auxin out of the cell and is located in the lateral and bottom regions of the plasma membrane. Thus, auxin can only move through the stem in a downward or lateral direction.

Indicate how light receptors in plant cells control various aspects of plant function

Light receptors are utilized to control seed germination, the timing of flowering, and chlorphyll production. Each type of receptor is designed to perceive light within a specific wavelength range.

Give two examples of interactions between the nervous system and endocrine system.

Pituitary is regulated by the hypothalamus which is part of the brain and the pituitary controls the secretion of hormones from the adrenal glands and the testes and ovaries • Environmental cues can be processed by the brain and used to regulate the secretion of hormones from endocrine organs throughout the body. For example, in seasonally breeding mammals the brain detects day length and only allows the pituitary to release LH and FSH at the appropriate time of the year. • Another way is that the nervous system and the endocrine system are interconnected by producing overlapping effects on physiology. For example, the rate of heart beat can be speeded up by direct stimulation from the central nervous system. So if the brain senses danger, heart rate increases. The hormone epinephrine produced by the adrenal glands, has the same function

Explain the role of voltage-gated calcium channels and ligand-gated sodium channels in communication between neurons.

The action potential opens up the channels and the ions (calcium or sodium) rush into the cytosol. The intercellular ion binds to vesicles and causes them to fuse with the presynaptic membrane, which releases neurotransmitters into the synaptic cleft. This causes neurotransmitters to be released which communicates with other neurons.

Distinguish between the following pairs: sensory neuron vs. motor neuron

The cells that receive and conduct signals through the nervous system are called neurons Sensory Neurons: Neurons that carry sensory information to the spinal cord and brain(CNS). Peripheral to CNS. Motor Neurons: Nerve cells of the brain and spinal cord that enable movement of muscles in various parts of the body. CNS to Peripheral

Describe the purpose of a reflex arc and indicate the role played by interneurons.

The purpose of a reflex arc is to enable the leg to jerk in response to an object (such as a hammer) before the sensation has reached the brain. It allows reflex actions to occur relatively quickly by activating spinal motor neuron without the delay of routing signals through the brain. An interneuron send receives the signal and transmits it to the dendrites of an appropriate motor neuron which sends a signal along its axon to a muscle in the body. Reflex Arc: The neural pathway that mediates a reflex action. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs.

repolarization

The re-establishment of the resting membrane potential after depolarization has occurred.

Indicate the role of multiple synapses in the function of neurons.

There are typically inhibitory as well as stimulatory synapses to a neuron.Electrical signals cannot cross a synapse without the help of a chemical such as acetylcholine.An electrical signal can only move in one direction across a synapse.Many synapses can be formed on the cell body and dendrites of a typical neuron.

Explain how voltage-gated ion channels and the sodium/potassium pump work together to maintain the resting potential of a neuron.

Voltage gated ion channels open and sodium channels open and sodium ions diffuse across the membrane which makes the membrane potential more positive. Depolarization occurs because more sodium ions are diffuse into the cell than potassium ions diffuse out of it. As the membrane potential reaches maximum depolarization, the voltage gates of the sodium ion channels begin to close and diffuse of sodium ions decreases. The potassium ion channels remain open and potassium ions continue to diffuse. The extra efflux of potassium ions causes the resting potential of the cell to be slightly more negative than usual. The sodium/potassium pump within the plasma membrane can reestablish the resting potential by pumping sodium out of and potassium into the cell. The membrane potential is controlled by the distribution of sodium and potassium ions across the plasma membrane. Voltage-Gated Channels: A class of transmembrane ion channels that are activated by changes in electrical potential difference near the channel; these types of ion channels are especially critical in neurons.

jasmonic acid

a hormone commonly produced in response to an attack. It inhibits the insect's ability to digest protein and travels through the plant inducing widespread production of defensive compounds.

action potential

a large depolarization that carries an electrical signal along the axon. A brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels. Action potentials sweep like a wave along axons to transfer information from one place to another in the nervous system.

synapse

a small space that separates an axon from another neuron. The space separating the axon terminals of a neuron from the dendrites of the next neuron in a neural pathway.

PIN protein

a type of carrier protein in plants that can only transport auxin out of the cell and is located in the lateral and bottom regions of the plasma membrane.

phytochrome

a type of plant receptor that perceives red light and has the important functions of eliciting seed germination and utilized by plants to measure relative lengths of days and nights

cryptochrome

a type of plant receptor that responds/perceives to blue light and its function is to elicit the production of chlorophyll in newly emerged seedlings

Regarding neurotransmitters: Name a common neurotransmitter.

acetylcholine

statoliths

granules found in cells at the root tips and in some tissues in plants that can help allow the plant to sense gravity

Regarding neurotransmitters: Explain where they are synthesized, how they are released from the axon, and how/when they are degraded.

synthesized and packaged into vesicles within the cell body, transported down the axon by microtubules, and after the neurotransmitter has been secreted and binds to a receptor, it is soon degraded by an enzyme to prevent continuous stimulation of the postsynaptic neuron.

membrane potential

the difference between electrical charges on each side of the neuron's membrane. The potential difference or voltage that exists between the inner and outer sides of a cell membrane. It exists in all cells but is capable of being changed by neurons and muscle cells.

Indicate the main function of cytokinins and explain how they interact with auxin in plant tissue cultures.

these hormones stimulate cell division (think cytokinesis). Cytokinins also influence cell differentiation and plant aging. Both auxins and cytokinins are used in plant tissue culture. Auxin promotes root formation, whereas cytokinin promotes both cell division and shoot formation.

phototropism

when plants respond to light by growing towards it. This is accomplished because the cells on the darker side of the stem elongate causing the stem to bend toward the light

depolarization

when the inside of the neuron becomes more positive than the resting potential. Depolarization: A process of changing the membrane potential from negative to more positive values.

Indicate whether or not plants can produce action potentials; if so give an example of a plant response to an electrical signal.

yes they can. Yhe action potential is propagated along the plasma membrane and can pass to adjacent cells, thus spreading throughout the plant. Example: The mimosa is a so-called "sensitive plant" that responds to touch by folding its leaves. This is generated by soybean cells when the plant is irradiated with 2 different wavelengths of light.