Organisms respond to changes in their internal and external environments

Question 1

What are tropisms?

Answer 1

the response of a plant to a stimulus coming from a certain direction

Question 2

What are the two types of tropisms?

Answer 2

positive- plants growing towards stimulus
negative- plants growing away from stimulus

Question 3

What is phototropism?

Answer 3

shoots of plants growing towards light to photosynthesise - positive phototropism
shoots of roots growing away from light - negative phototropism

Question 4

What is gravitropism?

Answer 4

shoots of plants growing against gravity - negative phototropism
shoots of roots growing downwards with gravity - positive phototropism

Question 5

What is hydrotropism?

Answer 5

shoots of plants growing away from water - negative phototropism
shoots of roots growing towards water - positive phototropism

Question 6

What is thigmotropism?

Answer 6

shoots of plants growing towards objects they have touched - positive thigmotropism
explains why plants climb and attach to things

Question 7

What are plant growth factors?

Answer 7

hormone-like substances produced by cells throughout the plant that affect the growth of tissues in the plant (an example being auxins)

Question 8

What is IAA?

Answer 8

an example of an auxin which controls the elongation of plant cells
produced in the tips of shoots and tips of roots

Question 9

What happens to the shoots when light intensity changes?

Answer 9

the change in light intensity causes the movement of IAA from the light sides of the shoots to the shaded side
the shoot will then bend towards the light due to a greater concentration of IAA on the shaded side which elongates the one side
this is an example of positive phototropism

Question 10

What happens to the roots when light intensity changes?

Answer 10

IAA controls bending of the roots away fromt he light
IAA moves towards shaded side of the roots causing the elongation of cells on the shaded side and the bending of roots away from the light
this is negative phototropism

Question 11

How do shoots and roots move towards /against gravity?

Answer 11

IAA moves to the undersides of shoots/ roots causing elongation of ells, bending them and growing upwards/downwards
roots show positive gravitropism
shoots show negative gravitropism

Question 12

What would happen if the tip of a shoot was:
-removed
-covered with opaque material
-removed, put on agar and placed back
-agar put on half of shoot

Answer 12

• no bending due to no IAA
• no bending due to no IAA
• plant will bend and grow as normal - IAA will diffuse through agar
  -plant would bend only towards that side, as IAA will only be able to diffuse on that side

Question 13

What are the different type of receptors?

Answer 13

Photoreceptors (light)
Thermoreceptors (temp)
Chemoreceptors (chemicals)
Mechanoreceptors (pressure)
Proprioceptors (movement)

Question 14

What is the role of sensory receptors?

Answer 14

they detect a specific stimulus and convert the change in energy into the nerve impulse/generator potentials

Question 15

What is resting potential?

Answer 15

when there is no stimulus detected - ions move in and out of cell through ion channels and pumps

Question 16

What is generator potential?

Answer 16

When a stimulus is detected, causing membrane of receptors to become more excited and more permeable. There is a potential difference across the membrane as more ions can enter the cell

Question 17

What is the action potential?

Answer 17

When generator potential passes the ‘threshold level’ passing a detected stimulus onto the sensory neurone

Question 18

What are pacinian corupscules ?

Answer 18

mechanoreceptors that detect changes in pressure

Question 19

What is the structure of pacinian corupscules ?

Answer 19

sensory nerve ending surrounded by layers of connective tissue called lamellae

Question 20

How to pacinian corupscules respond to change in pressure?

Answer 20

-when stimulus is detetcted, lamelle become deformed and presson the sensory nerve ending which deforms the stretch-mediated sodium ion channels
-channels open and sodium ions diffuse in
-influx of ions changes potential difference across membrane creating a generator potential
-if potetnial reaches threshold level, it will trigger action potetnial which is passed onto CNS

Question 21

What are photoreceptors and where are they located?

Answer 21

receptors in the eye that detect changes in light
located in the fovea (in the retina)

Question 22

How do photoreceptors in the eye respond the change in light?

Answer 22

-light enters eye through pupil and is focused onto retina
-amount of light entering eye is controlled by muscles of iris
-Photoreceptors carry electrical impulses to the brain via the optic nerve (in the place called the blind spot)

Question 23

What are 2 types of photoreceptors?

Answer 23

rod and cone cells

Question 24

What are the features of cone and rod cells?

Answer 24

rods- monochromatic vision, multiple rod cells connect to a singular sensory neurone, low visual ascuity, high sensitivty to light
cones - trichromatic vision (blue/green/red), each cone cell has its own sensory neurone, high visual ascuity, low sensitivty to light

Question 25

What is spacial summation?

Answer 25

when a stimulus is detected from different areas

Question 26

What is visual ascuity?

Answer 26

The ability to distinguish between 2 points close together

Question 27

What are neurones?

Answer 27

Nerve cells that are responsibel for the conduction of electircal impulses (action potentials) in the body

Question 28

What is the role of sensory neurones?

Answer 28

transmit nerve impulses from receptor to relay neurone which travels directly to motor neurone

Question 29

What is a neurone cell body?

Answer 29

contains the cell organelles such as nucelus and large amounts of the Rough ER

Question 30

What are dendrons ?

Answer 30

extensions of the cell body that divide into smaller branches called dendrites.

Question 31

What is an axon?

Answer 31

a single long fibre that carries electrical impulses away from the cell body

Question 32

What are dendrites?

Answer 32

dendrites can conduct electrical impulses towards cell body

Question 33

What is a myelin sheath?

Answer 33

made up of Schwann cells that are rich in lipds called myelin - protects the axon and provides electrical insulation

Question 34

What are nodes of Ranvier?

Answer 34

exposed parts of the axon between Schwann cells and where there is no myelin sheath

Question 35

What takes place when a neurone is in resting potential?

Answer 35

Sodium potassium pump pumps 3 sodium ions in and 2 potassium ions out of cell.
The potential difference is at -70mV.
The outside of the cell membrane is more positive than the inside.

Question 36

What happens during depolarisation?

Answer 36

Stimulus is detected, so voltage gated sodium ion channels open allowing sodium ions to diffuse back in, depolarising the membrane.
The inside of the membrane is now more positive so an action potential is generated, reaching at around 40mV.

Question 37

What happens during repolarisation?

Answer 37

Voltage gated sodium ion channels close and potassium ion channels open.
Cell is less permeable to sodium ions but more to potassium ions.
This causes repolarisation as outside is more positive than inside.

Question 38

What happens during the refractory period /hyperpolarisation?

Answer 38

Voltage gated potassium ion channels are slow to close so there is an overshoot in number of potassium ions that diffuse out of cell.
Outside becomes more positive than inside
Sodium potassium pump re-establishes resting potential as it pumps 3 sodium ions out and 2 potassium ions into the cell

Question 39

What is a synapse?

Answer 39

junction between 2 or more neurones or between neurones and effector cells

Question 40

What is the gap between two neurones called?

Answer 40

Synaptic cleft

Question 41

What are the 2 types of neurones (before and after a synaptic cleft?)

Answer 41

presynaptic neurone
postsynaptic neurone

Question 42

What is the end of a synaptic neurone called?

Answer 42

synaptic knob- the swollen portion of a neurone

Question 43

How can you differentiate from presynaptic and postsynaptic neurones?

Answer 43

presynaptic have vesicles that contain neurotransmitters
postsynaptic have receptor sites complementary to specific neurotransmitters

Question 44

What is the junction between 2 neurones called?

Answer 44

cholinergic synapse

Question 45

What is the junction between a presynaptic neurone and a muscle called?

Answer 45

neuromuscular junction

Question 46

What happens when an action potential reaches the end of the presynaptic neurone?

Answer 46

-voltage gated calcium ion channels open
-calcium ions diffuse across the cell surface membrane into presynaptic knob by facilitated diffusion
-influx of Ca2+ causes vesicles which contain neurotransmitters to fuse with membrane of the presynaptic knob
-neurotransmitters fuse with membrane of presynaptic knob
-neurotransmitters are released into synaptic cleft by exocytosis and bind onto complementary receptors on postsynaptic neurone
-sodium ion channels open and sodium ions diffuse down concentration gradient into postsynaptic neurone
-depolarisation of membrane
-influx of sodium ions into postsynaptic neurone causes a new action potential
-enzyme acetylcholinesterase hydrolyses ACh into acetyl and choline to stop continuous action potentials
-they will then diffuse back into knob of presynaptic neurone
-ATP produced by mitochondria is used to combine acetyl and choline to reform ACh, stored in vesicles for future use

Question 47

What is ACh an example of and why?

Answer 47

An excitatory neurotransmitter - as it depolarises the postsynaptic membrane causing action potentials to be generated

Question 48

What is AChE?

Answer 48

Acetylcholinesterase - an enzyme that hydrolyses ACh into acetyl and choline

Question 49

What is an inhibitory neurotransmitter?

Answer 49

one that prevents an electrical impulse from being passed along further