Cell Transport, Nervous System, and Excretory System

mostly made of a phospholipid bilayer, includes protein channels, protein pumps, carbohydrate chains, cholesterols and other substances
What makes up the cell membrane?
a fluid is a substance that does not have a fixed shape, and a mosaic is made by combining different smaller pieces
Why is the cell membrane referred to as a fluid mosaic?
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a double layered membrane, phosphate hydrophilic head, fatty acid hydrophobic tail
What is a (phospho)lipid bilayer?
Only certain items are allowed or let through the membrane. The cell membrane is an example of a semi-permeable membrane, because it allows only certain materials to pass through freely. It is also referred to as selectively permeable.
What is a semi-permeable membrane? How is this related to cell membranes?
Concentration is the amount of solute in a solution.
It can be determined by dividing the amount of solute by the volume of solution.
What is concentration? How is it determined?
difference in the amount of molecules across a space, or when molecules are present in different concentrations
What is a concentration gradient?
Equilibrium is when the number of molecules in an area are spread out equally. In terms of a membrane it means that the number of molecules on each side of the membrane is the same. Yes. Molecules are always moving; when a system reaches equilibrium the molecules continue to move, but there is no net movement (noticeable movement in one direction over another)
Explain equilibrium. Once equilibrium is reached do the particles stop moving?
Net movement is the overall, noticeable movement of particles. We use this when discussing osmosis and diffusion, because molecules are always moving. Even if we say that water is moving into a cell by osmosis there may be some moving out as well, but not having much effect on the overall concentrationmore will be moving out than in.
What is net movement, and why do we refer to it when discussing diffusion and osmosis?
transport where molecules move from an area of high concentration to low concentration, requires NO energy, examples are diffusion, osmosis and facilitated diffusion.
What does passive transport mean?
In general- the movement of particles from an area of high concentration to an area of low concentration. In terms of cell membranes it is the same except that the movement occurs across a semi-permeable membrane. Energy is NOT required, so it is a type of PASSIVE transport.
What is diffusion?
high to low
In terms of concentration, in which direction to particles move during diffusion?
No energy is needed. It is passive transport, and the movement of particles is from HIGH concentration to LOW concentration. The particles are moving DOWN the concentration gradient.
Is energy required for diffusion? Why or why not?
Diffusion of water through a semi-permeable membrane.
What is osmosis?
Similar: Diffusion and osmosis are both PASSIVE, they both involve the movement of molecules from HIGH concentration to LOW concentration (down the concentration gradient of what is moving)

Different: Diffusion involves any particles, and osmosis is diffusion of water specifically. (so osmosis is a type of diffusion)

How are diffusion and osmosis similar?different?
They are small protein channels that allow water (which is polar) to travel through the non-polar phospholipid bilayer. They are important because they are necessary to osmosis.
What are aquaporins? Why are they important?
The solution with the lower solute
concentration. (has less “stuff” in it)
Both solutions have the same solute concentration.
The solution with the higher solute concentration. (has more “stuff” in it)
Cytolysis occurs when water moves into a cell in a hypotonic solution. The water moves into the cell through osmosis (because there is more water- as a result of having less solute – outside of the cell), and the cell swells and can burst. The swelling/bursting is cytolysis.
What is cytolysis and when does it occur?
Plasmolysis occurs when water moves out of a cell in a hypertonic environment. The water moves out of the cell through osmosis (because there is less water- as a result of having more solute – outside of the cell), and the cell can shrink on itself. This shrinking is plasmolysis.
What is plasmolysis and when does it occur?
In both types of cells, osmosis will cause the net movement of water to be INTO the cells. In animal cells this causes a negative outcome. Animal cells will they do not have a cell wall, so the extra pressure in the cell will cause it to through cytolysis and breaking through the cell membrane. The result
is that the cell bursts/dies. I plant cells this is the “normal” state. The net movement of water into the cell causes extra pressure (turgor pressure) to be put on the cell walls. This provides extra overall.
Animal cells and plant cells react differently when in a hypotonic environment. Explain what happens to each, and why.
This occurs when particles need to move down a concentration gradient (HIGH to LOW), but cannot move directly through the membrane due to size, polarity or charge. Protein channels are used to allow passage of these particles. Energy is still NOT required because the particles are moving DOWN
their concentration gradient. Still a type of PASSIVE transport!
What does the term facilitated diffusion mean? When does it occur? What structures are involved?
Any type of transport across a membrane that requires energy. It occurs when particles are moving up a concentration gradient, or when particles are moving in bulk (large amounts) – through endo or exocytosis.
What is active transport, and when does it occur?
Is energy required for active transport?
Protein Pumps that are found in the cell membranes and use energy (ATP) to pump molecules up a concentration gradient (from LOW to HIGH concentration).
What are membrane-associated pumps?
A type of BULK transport (requires energy) where large amounts of material are brought into the cell by infolding the cell membrane to make a vesicle.
What is endocytosis?
Pinocytosis – “cell drinking” is endocytosis of Phagocytosis – “cell eating” is endocytosis of solids.
List and describe the two types of endocytosis.
A type of BULK transport (requires energy) where large amounts of material are released from the cell when a vesicle joins with the cell membrane and excretes (pushes out) what is inside.
What is exocytosis?
dendrites into cell body, through the axon, and out the axon terminals
Neuron direction of impulse
Information IN, Receive information (through stimuli) from the, environment or from other cells.
Sensory Neurons
Process information, thinking
Transmit information to the target. Information OUT.
Motor Neurons
Central Nervous System – made of the brain and spinal cord- surrounded by bone, membranes and fluid for protection; responsible for control and processing of information
What is the CNS? Describe the structure and function.
Peripheral Nervous System – made of paired spinal and cranial nerves; carries messages between the brain and spinal cord and the rest of the body.
What is the PNS? Describe the structure and function.
Sensory division – carries impulses from the skin, muscles, joints, and other organs to the brain and spinal cord.
Motor division – carries impulses from the brain and spinal cord to the muscles, glands, etc.
What are the divisions of the PNS?
Somatic -regulates activities under voluntary control; ex wiggling your fingers or toes
Autonomic – regulates activities that are involuntary or automatic; ex heart rate
What are the subdivisions of the Motor division? Describe each.
a signal to which an organism responds; any kind of detectable signal that carries information
What is a stimulus?
minimum level of a stimulus required to activate a neuron
What is the threshold?
Nerve impulses either go or they don’t. There is no in between or variation in strength. Either the threshold is met and the neuron is activated or it isn’t met and the neuron is not activated.
What does “all or nothing” mean in terms

of a nerve impulse?

An electrical disturbance or the movement of other ions.
What opens voltage gated channels?
Electrical charge across the membrane of a resting neuron. It basically means that the inside of a resting neuron has a negative charge, and the outside has a positive charge.
What is resting potential?
Another name for a nerve impulse. It is the reversal of the charges from their resting state. So when the sodium ions move into the neuron, the inside of the neuron becomes more positive.
What is action potential?
Stimulus threshold is met; sodium channels open; sodium ions rush into the neuron causing the next set of sodium channels to open; this repeats until the impulse gets to the axon terminal; neurotransmitters are released at the axon terminals through exocytosis; neurotransmitters are picked up by receptors, and if enough of the neurotransmitters are picked up to meet the threshold, the impulse will continue into the next neuron.
Describe, in detail, how a nerve impulse is triggered, and how it moves through the neuron.
A membrane that insulates the axon in some cells. It allows the neuron to move faster by “jumping” from one uncovered area of the axon to the next.
What is the myelin sheath? What is its purpose?
In what direction (in terms of the cell body) do Axons carry nerve impulses?
toward the cell body
In what direction (in terms of the cell body) do dendrites carry nerve impulses?
chemicals that transmit information from one neuron to another across a synapse
What are neurotransmitters?
the space between cells at a synapse
What is a synaptic cleft?
neurotransmitters are released at the axon terminals through exocytosis; neurotransmitters are picked up by receptors, and if enough of the neurotransmitters are picked up to meet the threshold, the impulse will continue into the next neuron.
How does a nerve impulse pass from a neuron to another cell? Describe the process.
The impulse will not continue.
What happens if a neurotransmitter is released by a neuron, but the nearest neuron does not have receptors for that particular neurotransmitter?
1. Enzymes break down neurotransmitters
2. Original neuron or helper cells absorb excess neurotransmitters.
3. diffusion of neurotransmitters
Once released, neurotransmitters should only affect nearby cells for a short time. What 3 mechanisms did we discuss in class for stopping neurotransmitters?
electro- the signals that pass through neurons are electrical in nature. They involve differences in electrical charges of ions and their movement. chemical- the ions in question are atoms, which are chemicals; also neurotransmitters are chemicals.
Why are neurons considered electrochemical signalers? Explain.
An organ system that involves the use of glands and hormones to communicate within an organism.
What is the endocrine system?
Hormones are chemicals that are released by glands into the blood stream. They attach to receptors on target cells and cause the target cells to perform a particular function.
What are hormones? How do they trigger target cells?
Nervous is quicker and endocrine is slower. Nervous is shorter in duration of impact – immediate; endocrine duration varies, but is longer than nervous. Nervous system uses electrical impulses and neurons; endocrine uses glands, hormones and blood to pass information
Compare and contrast the nervous system and the endocrine systems in terms of: quickness, duration, location, mechanism for “travel” (blood, neurons, etc.).
when the production/presence of a signal eventually increases the

production/presence of the same signal

Ex. Sodium ions enter the neuron. This triggers voltage gated

channels to open, which lets in more sodium ions. this process repeats

until the impulse reaches its conclusion at the axon terminals.

Remember: Positive feedback builds on itself.

What is a positive feedback loop?

Describe and give an example.

when the production/presence of a signal eventually decreases the

production/presence of that same signal

Ex glucose. Glucose is detected in the blood, insulin is released to

store excess glucose, glucose levels go down.

Remember: Negative feedback balances. Think of your thermostat.

What is a negative feedback loop?

Describe and give an example.

effector cells
What do motor neurons communicate with
if a cell swells when placed in a solution, then the solution is
Does a glycoprotein have a carbohydrate chain attached to it?

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