Feb caps

Question 1

write the symbol equation for photolysis

Answer 1

H2O –> ½ O2 + 2e- + 2H+

Question 2

Describe photoionisation of chlorophyll

Answer 2

light energy is absorbed by the chlorophyll and
the energy results in the electrons becoming
excited and raising up an energy level to leave
the chlorophyll. Therefore the chlorophyll has
been ionised by light. Some of the energy from
the released electrons is used to make ATP and
reduced NADP in chemiosmosis.

Question 3

Where does the light-dependent reaction (LDR) occur?

Answer 3

Thylakoid membrane

Question 4

What are the three key reactions in the LDR?

Answer 4

Photoionisation of chlorophyll
Photolysis
Chemiosmosis

Question 5

describe chemiosmosis in 4 key
stages

Answer 5

Step 1: The electrons that gained energy and left the
chlorophyll move along a series of proteins embedded
within the thylakoid membrane.
Step 2: As they move along, they release energy and some of
the energy from electrons is used to pump the protons
across chloroplast membranes.
Step 3: An electrochemical gradient is created. The protons
pass through the enzyme ATP synthase, which results in
the production of ATP.
Step 4: The protons combine with the co-enzyme NADP to
become reduced NADP. As the protons move from a high to
low concentration gradient this is known as chemiosmosis.

Question 6

why is the LIR temperature sensitive?

Answer 6

It involves the enzyme Rubisco

Question 7

What is the role of ATP in the Calvin cycle?

Answer 7

To provide the energy to reduce GP to TP
To provide the energy to regenerate RuBP from
TP

Question 8

What is the role of NADPH in the Calvin cycle?

Answer 8

To provide an H to reduce GP to TP

Question 9

What is the triose phosphate used for?

Answer 9

1 To donate one carbon each turn of the cycle to
go towards making a hexose sugar
2 To regenerate RuBP so the cycle can continue

Question 10

Which molecules from the LDR are used in the
LIR?

Answer 10

1 ATP
2 Reduced NADP

Question 11

Where does the LIR occur?

Answer 11

The stroma of the chloroplast

Question 12

What can the hexose sugars made be used
for?

Answer 12

Whilst glucose is the product, this
monosaccharide can join to form disaccharides
such as sucrose, and
polysaccharides such as cellulose and starch. It
can also be converted into glycerol and
therefore combine with fatty acids to make
lipids for the plant.

Question 13

draw the calvin cycle

Question 14

draw glycolysis

Question 15

describe glycolysis

Answer 15

Substrate level phosphorylation
- The glucose has 2 phosphate
groups added to it from 2 ATP
molecules.
Phosphorylation makes the
glucose-2-phosphate unstable
and it splits into two x 3-carbon
compounds, triose phosphate
(TP).
The 2 TP molecules are oxidised
to form 2 pyruvate molecules by
removing an H from each. The H
is picked up by 2 NAD molecules
to become reduced NAD. This
process also releases 4 ATP.

Question 16

Where do the four stages of aerobic
respiration occur?

Answer 16

1. Glycolysis - cytoplasm
2. Link reaction - Mitochondrial matrix
3. Krebs cycle - Mitochondrial matrix
4. Oxidative Phosphorylation - Cristae /inner
   mitochondrial membrane

Question 17

What are the products of glycolysis?

Answer 17

2 x pyruvate
Net gain of 2 ATP
2 X reduced NAD

Question 18

describe the key stages in
the link reaction.

Answer 18

The pyruvate made in
glycolysis is oxidised to
acetate.
NAD picks up the hydrogen
and becomes reduced NAD.
A carbon atom is lost as
carbon dioxide.
Acetate combines with
coenzyme A to produce acetyl
coenzyme A.

Question 19

draw the link reaction

Question 20

describe the key stages in the
Krebs cycle.

Answer 20

The acetyl CoA reacts with a four-carbon molecule, releasing
coenzyme A and producing a six-carbon molecule that enters the
Krebs cycle.
In a series of oxidation-reduction reactions, the Krebs cycle
generates 8 reduced coenzymes, 2 ATP by substrate-level
phosphorylation, and 4 carbon dioxides are lost.

Question 21

draw the krebs cycle

Question 22

What are the products of the Krebs cycle (from 1
glucose molecule originally) ?

Answer 22

6 x reduced NAD
2 x reduced FAD
4 x carbon dioxide
2 x ATP

Question 23

What is the role of oxygen in oxidative
phosphorylation?

Answer 23

Oxygen is the final electron acceptor in the electron
transport chain. The oxygen combines with the
electrons and the protons to form water.

Question 24

what happens to the reduced co-enzymes in this
stage?

Answer 24

All of the accumulated reduced coenzymes release
the hydrogens which are split into protons (H+) and
electrons (e-).

Question 25

describe how ATP is produced in oxidative phosphorylation.

Answer 25

electrons are passed down a series of electron carrier proteins embedded in the inner mitochondrial membrane, losing energy as they move along (electron transport chain). The small amount of energy the electrons release pumps protons from the mitochondrial matrix into the intermembrane space by active transport. This creates an electrochemical gradient across the membrane. Therefore, the protons move down the electrochemical gradient back into the matrix via ATP synthase making ATP.

Question 26

Where does anaerobic respiration occur?

Answer 26

the cytoplasm

Question 27

Why is it important that NAD is re-oxidised in anaerobic respiration?

Answer 27

So that it can be reused in glycolysis and ensure ATP continues to be produced.

Question 28

describe the nitrogen cycle (include ammonification, nitrification, nitrogen fixation and denitrification)

Answer 28

Nitrogen-fixing bacteria can break the triple bond between the two nitrogen atoms in nitrogen gas in the atmosphere and fix this nitrogen into ammonium ions. The bacteria are either free-living in the soil or symbiotic (mutualistic relationship), living in the root nodules of plants. This is common in leguminous plants such as clover and beans. Nitrification The ammonium ions in the soil are converted to nitrite and then nitrate ions in the soil by nitrifying bacteria. This is a two-stage oxidation reaction. Denitrification This stage is not useful as it returns the nitrogen in compounds back to nitrogen gas in the atmosphere, so it cannot be absorbed by plants. Anaerobic denitrifying bacteria do this. Ammonification Proteins, urea and DNA can be decomposed in dead matter and waste by saprobionts. These are bacteria and fungi that can digest waste extracellularly and return ammonium ions to the soil; this is saprobiotic nutrition.

Question 29

describe The role of saprobionts in decomposition.

Answer 29

These microbes will respire on dead or waste organic matter. This will cause decay and recycle nutrients into the soil so plants can absorb the nitrates/phosphates via active transport in their root hair cells

Question 30

describe the role of mycorrhizae

Answer 30

Mycorrhizae are fungal associations between plant roots and beneficial fungi. The fungi entwined around the plant roots provide a larger surface area for water and mineral absorption. The fungi part of the mycorrhizae acts like a sponge and can absorb and hold onto water and minerals surrounding the root

Question 31

describe The role of bacteria in the nitrogen cycle

Answer 31

Bacteria are used in saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification to convert nitrogen-containing compounds into other N-containing compounds

Question 32

Why do organisms need nitrogen?

Answer 32

To create amino acids/proteins, DNA, RNA and ATP.

Question 33

What is phosphorous needed for?

Answer 33

To create DNA, RNA, ATP and phospholipid bilayers

Question 34

Describe how the phosphorous cycle differs from the nitrogen cycle

Answer 34

Phosphorous is not found as a gas in the atmosphere. Instead, it is mainly found as a phosphate ion, in mineral form in sedimentary rocks.

Question 35

Why are fertilisers needed when growing crops?

Answer 35

To replace the nitrate and phosphate ions lost when plants are harvested and removed from nutrient cycles as crops.

Question 36

What are the two types of fertilisers?

Answer 36

natural (manure) artificial (inorganic chemicals).

Question 37

What are the pros and cons of each type of fertiliser?

Answer 37

Natural fertilisers are cheaper, and often free if the farmer owns animals. However, the exact minerals and proportions cannot be controlled. Artificial fertilisers are chemicals created to contain exact proportions of minerals. Their high solubility means that larger quantities are washed away with rainfall and therefore have a greater impact on the environment.

Question 38

What is leaching?

Answer 38

This is when water-soluble compounds are washed away, often into rivers or ponds.

Question 39

Describe eutrophication (4 marks)

Answer 39

This is when nitrates leached from fertilised fields stimulate the growth of algae in the pond. The excessive growth of algae creates a blanket on the surface of the water which blocks out light. As a result, the plants below cannot photosynthesise and die. Bacteria within the water feed and respire on the dead plant matter. This results in an increase in bacteria, which are all respiring and using up the oxygen within the water. Eventually, fish and other aquatic organisms die due to the lack of dissolved oxygen in the water.

Question 40

What is a taxes response?

Answer 40

A simple response in which an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus.

Question 41

What is a kinesis response?

Answer 41

When an organism changes the speed of movement and the rate it changes direction.

Question 42

Name 3 stimuli that simple organisms respond to by taxes and kinesis

Answer 42

1 light 2 moisture 3 chemicals

Question 43

More complex organisms have a nervous system. Draw a flow diagram to show a simple reflex response.

Answer 43

Stimulus --> Receptor -->Coordinator-->Effector-- >Response

Question 44

Which two structures comprise the central nervous system (CNS)?

Answer 44

the brain and spinal cord

Question 45

which structures comprise the peripheral nervous system (PNS)?

Answer 45

Receptors, sensory and motor neurones

Question 46

Which stimuli does the Pacinian corpuscle detect?

Answer 46

Pressure

Question 47

Where do you find many Pacinian corpuscle receptors?

Answer 47

Deep in the skin of the fingers and feet

Question 48

draw and label a pacinian corpuscle

Question 49

Describe how the pressure detected in the Pacinian corpuscle can generate an action potential.

Answer 49

In the resting state, Na+ channels are too narrow for Na+ to diffuse into the sensory neurone therefore resting potential is maintained. When pressure is applied it deforms the neurone plasma membrane, stretches and widens the Na+ channels so Na+ diffuses which leads to the establishment of a generator potential.

Question 50

Describe how the resting potential is maintained

Answer 50

The resting potential is maintained by a sodium-potassium pump, involving active transport and therefore ATP. The pump moves 2 K+ions in and 3 Na+ ions out. This creates an electrochemical gradient and results in K+ diffusing out and Na+ diffusing in. Due to the membrane being more permeable to K+, more are moved out resulting in the -70mV.

Question 51

draw and label the graph to show where the following are occuring: Resting state Repolarisation Depolarisation Refractory period

Question 52

describe depolarisation

Answer 52

1. A stimulus provides the energy that can cause the sodium voltagegated channels in the axon membrane to open. This causes Na+ to diffuse in, which increase the positivity inside of the axon. 2. This causes more voltage-gated channels to open, so even more Na+ diffuse in. 3. When a threshold of +40mV is reached inside the axon, the voltagegated sodium channels close and instead voltage-gated potassium ion channels open

Question 53

describe repolarisation

Answer 53

this results in potassium ions diffusing out, and the axon becomes negative again and is repolarised.

Question 54

describe hyperpolarisation

Answer 54

Temporarily the axon becomes more negative than the -70mV and is hyperpolarised.

Question 55

What is meant by the all-or-nothing principle?

Answer 55

If the depolarisation does not exceed the -55 mV threshold, then an action potential and the impulse are not produced (Nothing). Any stimulus that does trigger depolarisation to -55mV will always peak at the same maximum voltage (All). Bigger stimuli instead increase the frequency of action potentials.

Question 56

State the three factors that affect the speed of conductance and explain how

Answer 56

1 myelination and saltatory conduction here are gaps between the myelin sheath, called nodes of Ranvier. The action potential jumps from node to node (saltatory conduction), which means the action potential travels along the axon faster as it doesn’t have to generate an action potential along the entire length (just at the nodes of Ranvier). 2 Axon diameter With a wider diameter, the speed of conductance increases. A wider diameter means that there is less leakage of ions and therefore action potentials travel faster. 3 Temperature A higher temperature increases the speed of conductance for two reasons: 1. The ions diffuse faster 2. The enzymes involved in respiration work faster. Therefore there is more ATP for active transport in the Na+/K+ pump.

Question 57

What is the refractory period and give three reasons why it is important

Answer 57

After an action potential has been generated, the membrane enters a refractory period when it can’t be stimulated, because sodium channels are recovering and can’t be opened. This is important because: 1. It ensures that discrete impulses are produced, meaning that an action potential cannot be generated immediately after another one to make sure that each is separate from another. It ensures that action potentials travel in one direction. This stops the action potential from spreading out in two directions which would prevent a response. It limits the number of impulse transmissions. This is important to prevent overreaction to a stimulus and therefore overwhelming the senses.

Question 58

describe the actions at a cholinergic synapse

Answer 58

An action potential arrives at the synaptic knob. Depolarisation of synaptic knob leads to the opening of Ca2+ channels and Ca2+ diffuses into the synaptic knob. Vesicles containing acetylcholine neurotransmitters move towards and fuse with the presynaptic membrane. Acetylcholine is released into the synaptic cleft. Acetylcholine diffuses down a concentration gradient across the synaptic cleft, to the post-synaptic membrane; acetylcholine binds by the complementarity of shape to receptors on the surface of the post-synaptic membrane. Na+ ion channels on the post-synaptic membrane open and Na+ diffuse in; if enough acetylcholine binds, and enough Na+ diffuse in to raise the membrane potential above the -55mV threshold, then the post-synaptic neurone becomes depolarised. The acetylcholine is degraded by acetylcholinesterase into choline and acetate and released from the receptor; the Na+ channel close and the post-synaptic neuron can re-establish resting potential; the neurotransmitter is transported back into the presynaptic neuron where it is recycled.

Question 59

What is meant by summation?

Answer 59

The rapid build-up of neurotransmitters in the synapse helps generate an action potential

Question 60

What is the difference between spatial and temporal summation?

Answer 60

Spatial summation: many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to exceed the threshold value. Temporal summation: One neurone releases neurotransmitter repeatedly over a short period of time to add up to enough to exceed the threshold value