Aqa A-Level Biology Biol5

Front 1

What is a stimulus?

Back 1

A detectable change in the internal or external environment of an organism that produces a response in the organism

Front 2

What is taxis?

Back 2

A simple response by an organism, whose direction is determined by the direction of the stimulus. A directional response

Front 3

What is a positive taxis

Back 3

Movement towards the stimulus

Front 4

What is kineses

Back 4

An response where the organism does not move away from or towards the stimulus. Instead the more unpleasant the stimulus, the faster it moves and the more rapidly it changes direction

Front 5

What is a tropism?

Back 5

A response to directional stimuli that can maintain the roots and shoots of flowering plants

Front 6

What are the steps in a reflex arc?

Back 6

Stimulus, receptor, sensory neurone intermediate neurone, motor neurone, effector,response

Front 7

How is the nervous system divided?

Back 7

Front 8

What is a reflex?

Back 8

A rapid response to a stimulus which is automatic/not under conscious control

Front 9

What are the two divisions of the autonomic nervous system and what do they do?

Back 9

Sympathetic -stimulates effectors and so speeds up activity

Parasympathetic - inhibits effectors and so slows down activity

Front 10

Back 10

Front 11

Which part of the brain controls heart rate

Back 11

Medulla Oblongata

Front 12

How is heart rate controlled by chemoreceptors?

Back 12

Front 13

Back 13

Hint 13

Front 14

How does a Pacinian corpuscle respond to pressure?

Back 14

Front 15

What are the two different types of light detecting cells in the eye?

Back 15

Rod cells

Cone cells

Front 16

Why can rod cells only produce black and white images?

Back 16

Cannot distinguish between different wavelengths of light

Front 17

Why can rod cells respond respond to a low intensity of light?

Back 17

share a single sensory neurone so a certain threshold has to be exceeded before a generator potential is created in bipolar cells to which they are attached. Because more than one rod cell is attached to a single bipolar cell, there is a much greater chance that the threshold will be exceeded

Front 18

How is a generator potential created

Back 18

Rhodopsin must be broken down

Front 19

Why do rod cells have a low visual acuity

Back 19

Many rod cells linked to a single bipolar cell, they will only generate a single impulse regardless of how many neurones are stimulated. This means they cannot distinguish between separate sources of light that stimulated them

Front 20

Differences between rod and cone cells

Back 20

Front 21

Why can cone cells not respond to low light intensity

Back 21

Linked to separate bipolar cells so stimulation of a large number of cone cells cannot be combined to help exceed the threshold and create a generator potential

Front 22

What is the pigment in cone cells

Back 22

Idopsin

Front 23

Why do cone cells have a high visual acuity

Back 23

Own connection to bipolar cell which means that if two cone cells are stimulated the brain received two separate impulses

Front 24

Main features of hormonal and nervous system

Back 24

Front 25

Which cells do chemical mediators have an effect on

Back 25

Only cells in their immediate vicinity

Front 26

Two examples of chemical mediators and what they do

Back 26

Histamine - released in response to an allergen. Causes dilation of small arteries and arterioles

Prostaglandins - found incell membranes and also cause dilation of small arteries and arterioles

Front 27

Three types of plant tropism

Back 27

Photo

Geo

Hydro

Front 28

How does IAA work

Back 28

Front 29

Back 29

Front 30

What are the 6 things that make up a neurone and what are there functions

Back 30

Front 31

Bow is a resting potential established

Back 31

Na ions actively transported out of the axon

K ions actively transported into the axon. However the transport of Na is greater than K

Na ions diffuse back into the axon whilst K diffuse back out of the axon

However, most of the K ion gates are open, but the Na gates are shut. Therefore the outside of the axon is positive relative to the inside

Front 32

Describe be passage of an action potential

Back 32

Depolarisation

Stimulus causes Na voltage-gated channels to open, so Na ions diffuse into the axon

As more Na ions diffuse in, more Na channels open

Hyperpolarisation

. K ions diffuse out of the axon

Once the action potential has been established, Na voltage-gated channels close and K voltage-gated open. K ions diffuse out of the axonThis causes a temporary overshootRepolarizationK voltage-gated channels shut and resting potential is reestablished

This causes a temporary overshoot

Repolarization

K voltage-gated channels shut and resting potential is reestablished

Front 33

How does an action potential pass along a myelinated axon

Back 33

Myelinated sheath acts as an electrical insulator, preventing action potentials from forming. At nodes of Ranvier, action potentials can occur, so the action potential jumps from node to node(saltatory conduction), increasing the speed of the nerve impulse

Front 34

What factors affect the speed of the nerve impulse

Back 34

The myelin sheath

Diameter of axon- the greater the diameter, the faster the impulse

Temperature - this affects rate of diffusion of ions, therefore higher temperature means faster speed

Front 35

What are the purposes of the refractory period?

Back 35

Ensures the action potential travels in one direction only

Produces impulses that are separated from each other so can easily be distinguished

Limits the number of action potentials

Front 36

What is the all-or-nothing principle

Back 36

There is a certain level of stimulus, the threshold value, the needs to be exceeded for to trigger an action potential.

Front 37

How do organisms perceive the size of a stimulus

Back 37

The number of impulses in a given time

Different neurone with different threshold values.

Front 38

What is spatial summation

Back 38

A number of different presynaptic neurones together release enough neurotransmitter to exceed the threshold and genererate an action potential

Front 39

What is temporal summation

Back 39

A single presynaptic neurone releases neurotransmitter many times over a short period

Front 40

Describe transmittion across a synapse

Back 40

Front 41

What is the function of slow twitch muscle fibres and how are they adapted to it?

Back 41

Contract more slowly over a longer period. Useful for endurance work

Large supply of myoglobin (stores oxyen)

Supply of glycogen

Rich supply of blood vessels

Numerous mitochondria

Front 42

What is the function of fast twitch muscle fibres and how are they adapted to it?

Back 42

Contract more rapidly over a short period. Adapted to intense exercise.

Thicker and more numerous myosin

High concentration of enzymes involved in anaerobic respiration

Front 43

Describe transmission across a neuromuscular junction

Back 43

Synaptic vesicles fuse with the presynaptic membrane and release acetycholine. This diffuses across the to the postsynaptic membrane where it binds to receptors on Na ion channels which cause them to open so Na diffuses into, depolarising the membrane

Front 44

What happens to the I and A bands, the Z lines and the H zones when a muscle contracts

Back 44

I band become narrower

Z bands move closer together

H-zones become narrower

A band remains the same width