Responding to Changes in the Environment

Question 1

Why do organisms respond to changes?

Answer 1

To increase their chance of survival and ensure internal conditions are always optimum for metabolism

Question 2

What is a Taxis and give an example?

Answer 2

Directional movement in response to a stimulus. The direction of the stimulus effects the result

For example, woodlice show a tactic response to light. They move away from a light source. This helps them survive as it keeps them concealed under stones during the day and keeps them in damp conditions

Question 3

What is a Kinesis and give an example?

Answer 3

Nondirectional movement in response to a stimulus. The intensity of a stimulus effects a result.

Woodlice show a kinetic response to humidity in high humidity. They move slowly and turn less often, so they stay where they are. And as air gets drier, they move faster and turn more often, so they move into a new area.

Question 4

How do you investigate Taxis and Kinesis?

Answer 4

1. To investigate the effect of light intensity on woodlouse movement, cover 1/2 of the lid with black paper and put damp filter paper in both sides of the base to maintain humidity
2. Place ten wood lies in the centre of the chamber and position the lid on the mesh so it’s lined up with the base
3. After 10 minutes, take off the lid and record the number of wood lice on each side of the chamber
4. Repeats by gently moving wood lice back to the centre. Using a soft paint brush. you should find that most wood lice end up on the dark side of the choice chamber, a tactic response to light

Question 5

What’s the difference between receptors and effectors?

Answer 5

Receptors- Cells or proteins on cell surface membranes that detect a stimuli
Effector- Cells that bring about a response to a stimuli to produce an effect.

Question 6

What are the three types of neurons?

Answer 6

Sensory- Transmit electrical impulses from receptors to the central nervous system

Motor- Transmit electrical impulses from the central nervous system to effectors.

Relay- Transmit impulses between sensory and motor neurons

Question 7

What is a reflex arc?

Answer 7

This is a rapid, involuntary response to a stimulus by going through the spinal cord instead of the brain- so it happens automatically.

They help organisms avoid damage to the body because the response happens quickly.

Question 8

What is a trophism?

Answer 8

A trophism is the response of a plant to a directional stimulus by regulating their growth.

Question 9

What are the two types of trophism?

Answer 9

• phototropism’s
• Gravitropism’s

Question 10

What is a phototropism?

Answer 10

This is the growth of a plant in response to light shoots. up positively phototrophic and grow towards lights, roots are negatively phototrophic and grow away from lights

Question 11

What is a Gravitropism?

Answer 11

This is the growth of a plant in response to gravity shoots. a negatively gravitropic and grow upwards while roots are positively gravitropic and grow downwards

Question 12

What is an Auxin?

Answer 12

Auxins are hormone like chemicals that speed up or slow down plant growth. They are produced in the growing regions of the plants and moves to where they’re needed in other parts of the plant

Question 13

Give an example of an auxin and explain how it works?

Answer 13

Indoleacetic Acid (IAA)- IAA is an important auction that’s produced in the tips of shoots and roots in flowering plants. It’s moved around the plant to control trophism’s.

It moves to the more shaded parts of the shoots and roots, so there’s uneven growth allowing elongation and the shoot to bend towards the light.

Question 14

What is a receptor?

Answer 14

Can be cells, or proteins specific to a type of molecule to respond to a specific stimuli

Question 15

What are the three types of receptors?

Answer 15

MECHANORECEPTORS- pressure

PHOTORECEPTORS- light

CHEMORECEPTORS- detect certain chemicals

Question 16

Talk about the Resting Potential.

Answer 16

When a nervous system receptor is in resting state, there is a difference in charge between the inside and the outside of the cell. The inside is negatively charged relative to the outside. This means there is a voltage across the membrane, or a potential difference.
The potential difference when a cell is at rest is called its resting potential. This is generated by ion pumps and ion channels

Question 17

What is a Generator Potential

Answer 17

When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell, altering the potential difference. The change in potential difference due to a stimulus is called the generator potential. A bigger stimulus excites the membrane more, causing bigger movement of ions and a bigger change in potential difference

Question 18

What is an Action potential?

Answer 18

If the generator potential is big enough, it will trigger an action potential. an action potential is an electrical impulse along a neuron. This is only triggered if the generator potential Reaches a certain level called the threshold level.

Question 19

Give the process of an action potential being made.

Answer 19

• there is a potential difference between inside and outside the cell
• the potential difference when cell is at rest is called the resting potential
• When a stimulus is detected, the membrane becomes more permeable causing the ions to diffuse accross and the potential difference to increase.
• This change in potential difference is known as the generator potential
• If the generator potential is large enough it triggers an action potential- an electrical impulse along a neuron

Question 20

What is a Pacinian Corpuscle?

Answer 20

• A type of mechanoreceptor found in the skin
• contains a sensory neuron ending wrapped in lamellae

Question 21

Talk about the stimulation of a Pacinian Corpuscle

Answer 21

1. When a Pacinian Corpuscle is stimulated, the lamellae are deformed and pressed on the sensory nerve ending.
2. This causes the sensory neurons cell membrane to stretch, deforming the stretch mediated sodium ion channels.
3. The channels open, and sodium ions diffuse into the cell, creating a generator potential
4. if the generator potential reaches the threshold, it triggers an action potential

Question 22

Talk about the Retina

Answer 22

Light is detected by photoreceptors which are absorbed by light sensitive optical pigments. Light bleachs these pigments altering membrane permeability to sodium ions.

• a generator potential is created meaning an action potential can be created which would lead to an electrical impulse being sent over the bipolar neurone then to the optic nerve then to the brain.

Question 23

Talk about Rods

Answer 23

Sensitivity to Light- High as many rods connect to 1 neurone so many action potentials can be made

Sensitivity to colour- LOW as only sensitive to light levels

Visual Acuity- LOW as many rods connect to one neuron and light from 2 points can be duistinguished and one impulse is sent

Question 24

Talk about Cones

Answer 24

Sensitivity to Light- LOW as only 1 cone is connected to a bipolar neurone so take more light to reach a threshold

Light- HIGH as different types of cones contain a different pigment. When stiumulated together, we ssee different colours

Acuity- seperate impulses can be sent so many action potentials can be reached.

Question 25

Talk about the control of heart rate- structure.

Answer 25

Cardiac Muscle is myogenic- contraction is initiated by the muscle itself not via nerves

The *Sinoatrial Node (SAN) sets the frequency at which the cardiac muscle cells contract sending out regular impulses to the atrial walls causing atria to contract.

Question 26

Talk about contraction of the heart

Answer 26

1. SAN generates an electrical impulse which spreads from SAN accross both Atria causing them to contract simultaneously
2. The Septum prevents the impulse from crossing the venticles
3. The impulse reaches the AVN which passes the impusle onto the bundle of His fibres which conduct the impulses down the porcine fibres
4. The impulse gets carried to the walls of ventricles getting them to contract.
   - short delay at AVN to allow atria to be emptied

Question 27

How is heart rate controlled?

Answer 27

• done by autonomic nervous system
• The rate of which the SAN generates impulses is controled by the brain
• It changes in response to internal stimuli alike changes in blood

Question 28

Talk about the Medulla

Answer 28

Electrical impulses from these receptors are sent to the medulla via sensory neurons which processes info and sends to SAN via:

• Sympathetic Neurons- more for activity
• Parasympathetic Neurons- for relaxation

Question 29

Talk about the resting potential of a myelinated neuron

Answer 29

• 3 sodium ions are actively transported out of the axon in exchange for two potassium ions via a NA/K pump
• The concentration of sodium ions builds up as channels are closed
• Outside is less negative than inside creating a potentual difference
• resting potential- -70mv

Question 30

What is the first stage of action potential creation of a myelinated neuron

Answer 30

DEPOLARISATION- a stimulus excited a membrane on cell-surface so membrane becomes more permeable to sodium ions. Sodium ion channels open and sodium diffuses in while potassium doesnt so inside is less negative

Question 31

What is the second stage of action potential creation of a myelinated neuron

Answer 31

REPOLARISATION- Sodium ion channels close while potassium open so potassium diffuses out of neurone and the inside becomes more negative and voltage returns to normal level

Question 32

What is the third stage of action potential creation of a myelinated neuron

Answer 32

HYPERPOLARISATION- Voltage gated potassium ion channels are still open for a short time meaning too many ions diffuse out of neurone and voltage becomes more negative than resting potential. Potassium ion channels close restoring resting potential

Question 33

How does the action potential move in an unmyelinated axon?

Answer 33

• In unmyelinated axons, the action potential travels continuously along the entire length of the axon membrane
• Each section of membrane undergoes depolarization and repolarization in sequence
• This results in a slower conduction of the nerve impulse compared to myelinated axons
• The action potential is regenerated at each point along the axon to maintain the signal strength

Question 34

How does the action potential move in an myelinated axon?

Answer 34

• Action potentials can only occur at the nodes of Ranvier (gaps between myelin sheaths)
• The action potential “jumps” from node to node in a process called saltatory conduction
• This makes the transmission of nerve impulses much faster than in unmyelinated axons
• The myelin sheath acts as an electrical insulator, preventing ion movement through the membrane except at the nodes

Question 35

What is the all or nothing principle?

Answer 35

The strength of a stimulus is not reflected in the size of the action potential, but rather in the frequency of action potentials generated

Question 36

What is the process of synaptic transmission?

Answer 36

1. When an action potential reaches the presynaptic membrane, it triggers voltage-gated calcium channels to open
2. Neurotransmitters (like serotonin) diffuse across the synaptic cleft
3. The neurotransmitter binds to specific receptor proteins on the postsynaptic membrane
4. This can trigger various responses in the postsynaptic neuron, depending on the neurotransmitter

Question 37

What is summation?

Answer 37

Summation is the process where multiple stimuli that individually are below threshold can add together to trigger an action potential

Question 38

What are the two types of summation?

Answer 38

Temporal summation: When multiple stimuli arrive at the same point on a neuron in quick succession, their effects can add together to reach threshold

Spatial summation: When multiple stimuli arrive at different points on a neuron simultaneously, their effects can combine to reach threshold

Question 39

What is synaptic inhibition

Answer 39

Synaptic inhibition is when neurotransmitters cause a decrease in the likelihood of the postsynaptic neuron generating an action potential

Question 40

What is synaptic excitation?

Answer 40

While synaptic excitation (like what happens with serotonin) makes an action potential more likely

Question 41

How do inhibitory neurotransmitters work?

Answer 41

• Making the postsynaptic membrane more negative (hyperpolarization)
• Preventing depolarization from reaching threshold