1
Q
Why do organisms respond to changes in their environment?
A
To increase survival.
Responses help organisms remain in favourable conditions and avoid harm.
2
Q
In flowering plants, where are the growth factors that control directional responses produced?
A
Growing regions
These growth factors are made in regions such as shoot and root tips, then move to other tissues.
3
Q
What substance controls cell elongation in tropic responses in flowering plants?
A
Indoleacetic acid
(IAA)
IAA is the main auxin named in the AQA specification.
4
Q
How does a shoot respond when exposed to light from one side?
A
It grows towards the light.
This directional growth response is phototropism.
5
Q
How does a root respond to gravity?
A
It grows towards gravity.
Roots are positively gravitropic, so they grow downwards.
6
Q
How does a shoot respond to gravity?
A
It grows away from gravity.
Shoots are negatively gravitropic, so they grow upwards.
7
Q
What happens to cells in plant shoots when IAA concentration increases?
A
They elongate more.
In shoots, IAA stimulates cell elongation, causing bending when distributed unevenly.
8
Q
What happens to cells in plant roots when IAA concentration increases above the optimum?
A
They elongate less.
In roots, higher IAA concentrations inhibit elongation, producing curvature during tropisms.
9
Q
Fill in the blank:
In phototropism, unequal distribution of IAA causes unequal cell ______ in the shoot.
A
elongation
Cells on one side grow faster than the other, so the shoot bends.
10
Q
Fill in the blank:
In gravitropism, the root bends because IAA causes less elongation on the ______ side.
A
lower
Gravity causes IAA to accumulate on the lower side of the root.
11
Q
What is a simple directional movement in which an organism moves towards or away from a stimulus?
A
Taxis
Taxis is directional, unlike kinesis, which depends on stimulus intensity rather than direction.
12
Q
What is a simple response in which an organism changes its rate of movement in response to stimulus intensity?
A
Kinesis
Kinesis helps organisms spend more time in favourable conditions without moving directly towards a stimulus.
13
Q
True or False:
Taxes and kineses can help keep a mobile organism in a favourable environment.
A
True
These responses improve the chance of remaining in suitable conditions.
14
Q
What type of response gives rapid protection from a harmful stimulus through an automatic pathway?
A
Reflex
Reflexes are quick, automatic and protective rather than conscious.
15
Q
How many neurones are involved in a simple reflex?
A
Three
The pathway includes a sensory neurone, a relay neurone and a motor neurone.
16
Q
Which type of neurone carries impulses from a receptor into a simple reflex pathway?
A
Sensory neurone
The sensory neurone transmits information from the receptor to the CNS.
17
Q
Which type of neurone passes impulses from the CNS to an effector in a simple reflex?
A
Motor neurone
The effector is usually a muscle or gland that carries out the response.
18
Q
Which type of neurone links the sensory neurone to the motor neurone in a simple reflex?
A
Relay neurone
The relay neurone is located within the CNS in a simple reflex arc.
19
Q
In required practical 10, what is investigated using a choice chamber or maze?
A
The effect of an environmental variable on animal movement.
The practical tests how a variable influences movement behaviour in a mobile organism.
20
Q
Name one apparatus AQA allows for required practical 10 on animal movement.
A
Choice chamber
A maze is the other permitted option named in the specification.
21
Q
What feature of sensory receptors ensures they respond only to one particular type of stimulus?
A
Specificity
Each receptor type is specialised to detect a particular stimulus such as pressure, light or chemicals.
22
Q
What electrical change is produced in a receptor when it is stimulated by the appropriate stimulus?
A
Generator potential
A generator potential is a local graded depolarisation produced in the receptor membrane.
23
Q
In sensory receptors, what name is given to the graded electrical potential produced directly by a stimulus?
A
Generator potential
If the generator potential reaches threshold, an action potential is triggered in the sensory neurone.
24
Q
What type of receptor structure in the skin detects pressure and vibration?
A
Pacinian corpuscle
Pacinian corpuscles are mechanoreceptors located deep in the skin and other tissues.
25
What type of **stimulus** does a **Pacinian corpuscle** detect?
Mechanical pressure
## Footnote
They respond to deformation caused by pressure or vibration.
26
What **ion channel type** is mechanically deformed when a **Pacinian corpuscle** is stimulated?
Stretch-mediated sodium ion channels
## Footnote
Mechanical pressure changes the membrane shape, opening sodium channels.
27
What **ion** enters the neurone when **stretch-mediated channels** open in a Pacinian corpuscle?
Sodium ions
## Footnote
Influx of Na+ depolarises the membrane and produces a generator potential.
28
# True or False:
**Generator potentials** in receptors are all-or-nothing events like **action potentials**.
False
## Footnote
Generator potentials are graded; their size depends on stimulus strength.
29
# Fill in the blank:
The **Pacinian corpuscle** responds to mechanical deformation by opening \_\_\_\_\_\_ channels.
Stretch-mediated sodium ion
## Footnote
These channels open when the lamellae are compressed.
30
What region of the **eye** contains the **photoreceptors** responsible for detecting light?
Retina
## Footnote
The retina lines the back of the eye and contains rods and cones.
31
Which **photoreceptor type** is specialised for vision in **low light intensity**?
Rods
## Footnote
Rods are highly sensitive to light but do not detect colour.
32
Which **photoreceptor type** allows **colour vision** in the human eye?
Cones
## Footnote
Cones contain different pigments sensitive to different wavelengths.
33
Which **photoreceptor type** provides the **highest visual acuity**?
Cones
## Footnote
Cones have a one-to-one connection with neurones, improving resolution.
34
Why do **rods** provide lower **visual acuity** than cones?
Many rods converge onto one neurone.
## Footnote
Convergence increases sensitivity to light but reduces detail.
35
# True or False:
**Rods** are responsible for **colour vision**.
False
## Footnote
Rods detect light intensity only; cones detect colour.
36
What feature of **cones** allows them to detect different **colours of light**?
Different optical pigments
## Footnote
Each cone type absorbs different wavelengths corresponding to colours.
37
# Fill in the blanks:
In the **retina**, rods are highly sensitive to \_\_\_\_\_\_ \_\_\_\_\_\_ but do not detect colour.
light intensity
## Footnote
This allows vision in dim conditions such as at night.
38
# True or False:
Each **cone cell** usually connects to a single **neurone** in the optic nerve pathway.
True
## Footnote
This one-to-one connection produces high visual acuity.
39
What structure carries **impulses** from the **retina** to the brain?
Optic nerve
## Footnote
Axons of sensory neurones from the retina form the optic nerve.
40
What property of **rods** makes them particularly useful for **night vision**?
High sensitivity to light
## Footnote
Rods can respond to very low levels of light but sacrifice resolution.
41
What does it mean that the **heart** is **myogenic**?
It generates its own electrical impulses.
## Footnote
Cardiac muscle initiates contraction without needing direct nervous stimulation.
42
Which structure in the wall of the **right atrium** acts as the heart’s natural **pacemaker**?
Sinoatrial node
| (SAN)
## Footnote
The SAN initiates the wave of excitation that sets the basic heart rhythm.
43
Where is the **atrioventricular node** found?
Between the atria and ventricles
## Footnote
The AVN lies in the septum between the atria, close to the atrioventricular valves.
44
Which specialised tissue carries the **wave of excitation** from the **AVN** down through the septum?
Bundle of His
## Footnote
This tissue conducts the impulse toward the apex of the heart.
45
What fibres spread the **excitation** through the **ventricular walls** from the apex upwards?
Purkinje tissue
## Footnote
Purkinje fibres ensure the ventricles contract from the bottom upwards for efficient ejection of blood.
46
Why is there a **delay** at the **atrioventricular node**?
To allow the atria to **finish contracting** before the ventricles contract.
## Footnote
This ensures the ventricles fill fully before ventricular systole begins.
47
Why do the **ventricles** contract from the **apex** upwards?
To **push blood out** into the arteries.
## Footnote
This helps force blood into the aorta and pulmonary artery efficiently.
48
# True or False:
The **sinoatrial node** is located in the **left ventricle**.
False
## Footnote
The SAN is in the wall of the right atrium.
49
# True or False:
The **atrioventricular node** prevents the ventricles from contracting too soon.
True
## Footnote
The AVN slows conduction briefly, creating a short delay.
50
# Fill in the blank:
Cardiac output can be calculated using the equation CO = \_\_\_\_\_\_ \_\_\_\_\_\_ × stroke volume.
heart rate
## Footnote
Cardiac output is the volume of blood pumped by the heart per minute.
51
What is **cardiac output**?
The **volume** of blood pumped by the heart per minute.
## Footnote
It depends on both heart rate and stroke volume.
52
Which **receptors** detect changes in **blood carbon dioxide concentration** and blood pH?
Chemoreceptors
## Footnote
These receptors help adjust heart rate when metabolic demand changes.
53
Where are **pressure receptors** found that monitor **blood pressure**?
In the aorta and carotid arteries
## Footnote
These baroreceptors detect changes in stretch in artery walls.
54
What is another name for **pressure receptors** involved in **heart rate control**?
Baroreceptors
## Footnote
They respond to changes in blood pressure by altering nerve impulses to the medulla.
55
Which part of the **nervous system** increases **heart rate**?
Sympathetic nervous system
## Footnote
Sympathetic stimulation sends impulses to the SAN to make it fire more frequently.
56
Which part of the **nervous system** decreases **heart rate**?
Parasympathetic nervous system
## Footnote
Parasympathetic stimulation, via the vagus nerve, slows the SAN.
57
What is the **effector** that changes the **heart rate** in response to autonomic input?
Cardiac muscle in the SAN
## Footnote
The SAN changes the frequency of excitation, altering overall heart rate.
58
How do **chemoreceptors** help increase **heart rate** during exercise?
They detect raised carbon dioxide and lower pH, then stimulate centres that increase heart rate.
## Footnote
This allows faster delivery of oxygen and faster removal of carbon dioxide.
59
# True or False:
**Pressure receptors** can trigger a reduction in **heart rate** when blood pressure rises.
True
## Footnote
Increased stretch increases impulses to the medulla, which can increase parasympathetic output.
60
# Fill in the blank:
The **wave of excitation** passes from the SAN to the AVN and then along the bundle of \_\_\_\_\_\_.
His
## Footnote
After this, Purkinje tissue carries the excitation through the ventricles.
61
Why would **heart rate** increase if **blood pressure** falls?
To help restore cardiac output and maintain blood flow.
## Footnote
Reduced stimulation of baroreceptors leads to more sympathetic influence on the heart.
62
A person has a **heart rate** of 75 beats per minute and a **stroke volume** of 80 cm3 per beat. What is their cardiac output?
6000 cm3 min-1
## Footnote
Cardiac output = 75 × 80 = 6000 cm3 min-1, or 6.0 dm3 min-1.
63
In a **motor neurone**, what is the long extension that **carries electrical impulses** away from the cell body towards an effector?
Axon
## Footnote
Motor neurones transmit impulses from the CNS to muscles or glands. The axon conducts the action potential along the neurone.
64
What insulating structure surrounds many **motor neurone axons** and increases the speed of **impulse transmission**?
Myelin sheath
## Footnote
The myelin sheath is formed by Schwann cells and allows impulses to travel faster via saltatory conduction.
65
# Fill in the blanks:
The electrical charge difference across the membrane of an **unstimulated neurone** is known as the \_\_\_\_\_\_ \_\_\_\_\_\_.
resting potential
## Footnote
Typically about −70 mV. It exists because of ion distribution and membrane permeability differences.
66
During the **resting state**, which ion has a higher concentration **outside the neurone** than inside?
Sodium ions
## Footnote
Na⁺ concentration is higher outside the axon, while K⁺ concentration is higher inside.
67
Which ion is at a higher concentration **inside the neurone** compared with outside during the **resting state**?
Potassium ions
## Footnote
Maintained by selective permeability and the sodium–potassium pump.
68
# True or False:
At **resting potential**, the neurone membrane is more permeable to **potassium ions** than to sodium ions.
True
## Footnote
K⁺ leak channels allow potassium ions to diffuse out more readily than Na⁺ diffuses in.
69
What is the rapid **reversal of membrane potential** caused by increased **sodium ion permeability** called?
Depolarisation
## Footnote
Voltage-gated Na⁺ channels open, allowing Na⁺ to diffuse into the neurone.
70
What name is given to the **electrical change** that travels along the **axon of a neurone**?
Action potential
## Footnote
The action potential propagates along the axon and forms the basis of nerve impulses.
71
# True or False:
The strength of an **action potential** varies depending on **stimulus intensity**.
False
## Footnote
Action potentials follow the all-or-nothing principle; they occur fully or not at all.
72
What principle states that once **threshold** is reached, an **action potential** occurs at full size?
All-or-nothing principle
## Footnote
A stimulus below threshold produces no action potential; above threshold produces a full response.
73
# Fill in the blank:
The jumping movement of impulses between **nodes of Ranvier** in **myelinated neurones** is called \_\_\_\_\_\_ conduction.
saltatory
## Footnote
Saltatory conduction greatly increases conduction speed because depolarisation only occurs at nodes.
74
What **term** describes the short period after an **action potential** when another cannot be generated?
Refractory period
## Footnote
Ensures impulses are discrete and limits the maximum frequency of nerve impulse transmission.
75
# True or False:
Increasing **axon diameter** generally increases the speed of **nerve impulse conduction**.
True
## Footnote
Larger diameters reduce internal resistance to ion flow.
76
What physical factor, related to **kinetic energy of ions**, can increase the speed of **nerve impulse transmission** when it rises?
Temperature
## Footnote
Higher temperatures increase ion movement, speeding up depolarisation and conduction.
77
What narrow gap separates the **presynaptic neurone** from the **postsynaptic cell** at a synapse?
Synaptic cleft
## Footnote
The synaptic cleft is the small space across which neurotransmitter diffuses.
78
Which part of the **presynaptic neurone** contains **synaptic vesicles** filled with neurotransmitter?
Synaptic knob
## Footnote
The synaptic knob is the swollen ending of the presynaptic neurone.
79
What structure in the **postsynaptic membrane** contains receptors that bind **acetylcholine**?
Ligand-gated sodium ion channels
## Footnote
Acetylcholine binds to receptors associated with sodium ion channels in a cholinergic synapse.
80
Which ion entering the **presynaptic knob** triggers **synaptic vesicles** to move to and fuse with the presynaptic membrane?
Calcium ions
## Footnote
Arrival of an action potential opens voltage-gated calcium ion channels.
81
What happens first when an **action potential** reaches the **presynaptic membrane**?
Depolarisation of the presynaptic membrane
## Footnote
This depolarisation opens voltage-gated calcium ion channels.
82
After **calcium ions** enter the synaptic knob, what process releases **acetylcholine** into the synaptic cleft?
Exocytosis
## Footnote
Synaptic vesicles fuse with the presynaptic membrane and release neurotransmitter.
83
Once released, how does **acetylcholine** cross the **synaptic cleft**?
Diffusion
## Footnote
Acetylcholine moves down its concentration gradient to the postsynaptic membrane.
84
What immediate effect does **acetylcholine binding** have on the **postsynaptic membrane**?
Sodium ion channels open
## Footnote
Sodium ions diffuse in, causing depolarisation of the postsynaptic membrane.
85
What name is given to the **depolarisation** produced in the postsynaptic membrane when **neurotransmitter binds**?
Excitatory postsynaptic potential
## Footnote
An excitatory postsynaptic potential makes the postsynaptic neurone more likely to fire.
86
What enzyme rapidly breaks down **acetylcholine** in the **synaptic cleft**?
Acetylcholinesterase
## Footnote
This prevents continuous stimulation of the postsynaptic membrane.
87
Why is transmission across a **cholinergic synapse** **unidirectional**?
Receptors are only on the postsynaptic membrane.
## Footnote
Vesicles release acetylcholine from the presynaptic side only, so impulses pass one way.
88
Why does **breakdown of acetylcholine** matter for **repeated signalling**?
It prevents continuous depolarisation.
## Footnote
The membrane can repolarise and be ready for a new signal.
89
# Fill in the blank:
In a **cholinergic synapse**, acetylcholine is hydrolysed into acetate and _\_\_\_\_.
choline
## Footnote
Choline is reabsorbed into the presynaptic neurone and reused to make acetylcholine.
90
What happens to **choline** after acetylcholine is broken down in the **synaptic cleft**?
It is reabsorbed into the presynaptic neurone.
## Footnote
It is recycled to synthesise more acetylcholine.
91
What is **temporal summation** at a synapse?
Addition of successive impulses from one neurone.
## Footnote
Rapid, repeated release of neurotransmitter can build depolarisation to threshold.
92
What is **spatial summation** at a synapse?
Addition of impulses from several neurones at once.
## Footnote
Neurotransmitter released from different presynaptic neurones combines at one postsynaptic neurone.
93
Why might one **excitatory impulse** fail to trigger an **action potential** in the postsynaptic neurone?
Depolarisation does not reach threshold.
## Footnote
A single excitatory postsynaptic potential may be too small on its own.
94
# True or False:
**Temporal summation** depends on impulses arriving from different **presynaptic neurones** at the same time.
False
## Footnote
That describes spatial summation; temporal summation is repeated impulses from one neurone.
95
# True or False:
**Spatial summation** can allow a postsynaptic neurone to reach **threshold** when several excitatory synapses are active together.
True
## Footnote
The combined depolarisations may be enough to trigger an action potential.
96
How do **inhibitory synapses** reduce the chance of an **action potential** being generated?
They hyperpolarise the postsynaptic membrane.
## Footnote
Inhibitory neurotransmitters often cause chloride ions to enter or potassium ions to leave.
97
What is the effect of **chloride ions** entering the **postsynaptic neurone** at an inhibitory synapse?
hyperpolarisation
## Footnote
The membrane potential becomes more negative and further from threshold.
98
How can an **inhibitory synapse** counteract an **excitatory synapse** on the same postsynaptic neurone?
By cancelling depolarisation
## Footnote
The combined effect may prevent threshold from being reached.
99
# True or False:
**Inhibitory synapses** make the inside of the postsynaptic neurone **less negative**.
False
## Footnote
They usually make it more negative, moving the membrane potential away from threshold.
100
What specialised region of a **muscle fibre** acts as the **postsynaptic membrane** at a neuromuscular junction?
Sarcolemma
## Footnote
The synapse is between a motor neurone and a muscle fibre rather than another neurone.
101
What is the usual effect when an **action potential** reaches a **neuromuscular junction**?
Contraction of the muscle fibre
## Footnote
Neuromuscular junctions are designed to ensure a reliable response in the muscle.
102
Give one structural feature that makes a **neuromuscular junction** well adapted for **rapid transmission** to a muscle fibre.
Many folds in the postsynaptic membrane.
## Footnote
These folds increase surface area for receptors and help transmission.
103
Compared with a typical **cholinergic synapse** between neurones, how does the amount of **acetylcholine released** at a neuromuscular junction differ?
More acetylcholine is released.
## Footnote
This helps ensure the muscle fibre reaches threshold.
104
Compared with many neurone-to-neurone synapses, how is the **postsynaptic membrane** at a **neuromuscular junction** adapted?
More receptors
## Footnote
The high receptor density increases the chance of depolarising the muscle fibre.
105
# True or False:
Both **cholinergic synapses** and **neuromuscular junctions** use acetylcholine as the neurotransmitter.
True
## Footnote
The difference is mainly in the type of postsynaptic cell and reliability of transmission.
106
# True or False:
A **neuromuscular junction** links one neurone directly to another neurone.
False
## Footnote
It links a motor neurone to a muscle fibre.
107
Why is transmission at a **neuromuscular junction** less likely to fail than at a **cholinergic synapse** between neurones?
It produces a larger end-plate potential.
## Footnote
More neurotransmitter, more receptors and membrane folds make transmission highly reliable.
108
# Fill in the blank:
The small depolarisation produced in the **muscle fibre membrane** at a neuromuscular junction is called an end-plate _\_\_\_\_.
potential
## Footnote
If this reaches threshold, an action potential spreads across the sarcolemma.
109
What would be the effect of a drug that blocks **voltage-gated calcium ion channels** in the **presynaptic membrane**?
Less acetylcholine released.
## Footnote
Without calcium ion influx, vesicles are less likely to fuse with the membrane.
110
What effect would a drug that **inhibits acetylcholinesterase** have on the **postsynaptic membrane**?
Prolonged depolarisation
## Footnote
Acetylcholine would remain in the cleft longer and continue to stimulate receptors.
111
What would happen if **receptor proteins** on the **postsynaptic membrane** were blocked by a drug?
Sodium ion channels would not open.
## Footnote
Acetylcholine could not trigger the usual depolarisation.
112
Predict the effect of a drug that prevents **synaptic vesicles** fusing with the **presynaptic membrane**.
Neurotransmitter would not be released.
## Footnote
No acetylcholine in the cleft means no postsynaptic depolarisation.
113
What would be the likely effect of a drug that increases **chloride ion movement** into the **postsynaptic neurone**?
Inhibition would increase.
## Footnote
Greater hyperpolarisation makes an action potential less likely.
114
Why can **low-frequency impulses** fail to produce a response, while **high-frequency impulses** can succeed?
Temporal summation
## Footnote
Repeated impulses arriving close together build the depolarisation to threshold.
115
Why can several **weak inputs** arriving together trigger an **action potential** when each alone cannot?
Spatial summation
## Footnote
Their combined excitatory effects can bring the postsynaptic membrane to threshold.
A-Level Biology (OCR)
flashcards
Decks in class (28)
# Cards
-
2: Biological Molecules119
-
2: Water & Inorganic Ions19
-
2: Cells52
-
2: Cell Division20
-
2: Membranes & Transport20
-
2: Exchange Surfaces37
-
2: Transport Systems39
-
2: Immune system36
-
2: Enzymes & Digestion16
-
3: Plant Transport20
-
4: Biodiversity & Classification32
-
4: Investigating Diversity12
-
4: Evolution42
-
4: Disease24
-
5: Photosynthesis23
-
5: Respiration17
-
5: Energy & Ecosystems35
-
5: Homeostasis57
-
5: Nervous & Hormonal Communication115
-
5: Muscles14
-
6: DNA & Protein Synthesis27
-
6: Meiosis & Genetic Diversity14
-
6: Inheritance12
-
6: Populations (Hardy–Weinberg)15
-
6: Ecosystems & Population Dynamics24
-
6: Gene Mutations & Expression58
-
6: Biotechnology & Genomics46
-
6: ATP & Energy Transfer (Integration)11
