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(a)(i) In the presence of light, plants undergo photosynthesis to produce glucose which is either accumulated and  stored in the form of sucrose or translocation to other parts of the plant via the phloem.
(ii) High sugar concentrations result in high hydrolytic pressure due to the large difference in the concentration gradient. Since sugars are transported to other parts via the phloem through the process of translocation, pressure builds up there.
--> due to water potential

(b)(i) The sucrose concentration of phloem sap ingested by aphids and the percentage of oligosaccharides in honeydew have a positive relationship, where an increase in sucrose concentration from 0.3mol to 0.5mol resulted in an increase in percentage of oligosaccharides from 15% to 85%.
(ii) - To aid in digestion. Enzymes are biological catalysts which alter reaction pathways to speed up rate of reactions. By secreting enzymes, the process of breaking down sugars into oligosaccharides is sped up. Therefore, enabling the process of digestion to occur efficiently.
- Due to the high concentration of sucrose, it suggests a large difference in concentration between the aphids' gut and the phloem sap, which results in a quick of phloem sap into the gut. By secreting enzymes into the gut, aphids are able to reduce the concentration of sucrose in the gut. Therefore, promoting the flow of sucrose into its system.

(c)(i) Phloem saps are not a good source of essential amino acids for aphids. With reference to figure 11, only 1% of amino acids in phloem sap consist of essential amino acids unlike the high percentage of non-essential amino acids.
(ii) The difference in amino acid content between phloem and aphid protein for non-essential amino acids is accounted for by the aphid's ability to synthesise certain amino acids.

(d)(i) Antibiotics would reduce the number of bacteria present in aphids. Since such bacteria is used to synthesise sucrose and aspartic acid, a reduction in sucrose and aspartic acid would suggest Buchnera's role of synthesising essential amino acids.
(ii)  The percentage of essential amino acids in the phloem sap is too low for animals to obtain sugar from phloem saps for their diet. This is evident in figure 11 where the highest level of essential and non-essential amino acids in phloem sap are 8% and 100% respectively.

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1. a) (i) By producing sugar as a by-product of photosynthesis which is transported by translocation
(ii) High sugar concentration help to develop a higher concentration gradient to accumulate greater hydrostatic pressure for a more efficient process of translocation. (** use the term WATER POTENTIAL)
b)  (i) In lower sucrose concentration of phloem sap in aphids' diet, the percentage of oligosaccharide stays relatively constant showing no change. Then at intermediate sucrose concentration in between 0.25 mol to approximately 0.5 mol, the percentage of oligosaccharide rapidly increases with larger increments then starts to plateau at high concentrations of sucrose.  Generally, it shows a positive relationship showing a plateau-shaped graph.
(ii) By doing so, it can help increase the concentration gradient. Specifically, the water potential can increase from the reduced concentration of sucrose for faster digestion and absorption of the nutrients.
c) (i) The phloem sap contains less percentage of essential amino acids over non-essential amino acids, which makes the phloem sap an insufficient source of amino acids. In fact, there are two types of amino that are not contained in the phloem sap.
(ii) Aphids require more proteins for more various types of enzymes or immunoglobin to carry out the biological process as compared to plants.
d) (i) Different levels of antibiotics can be used to control the number of Buchmera to be produced in aphids.
(ii) In reference to Figure 11, the highest percentage of essential amino acids is less than 10% whereas the maximum for non-essential amino acids is at 100%. From this, there is a relatively lower content of essential amino acids than non-essential amino acids in the phloem sap at Figure 11, which makes phloem sap an insufficient source of amino acid nutrients for certain animals.

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1 ai) Active transport of sugar from the roots into phloem creates concentration gradient and high concentration of sucrose in phloem sap.

1 aii) High concentration of sucrose molecules causes osmosis to pull water into the sieve tubes, creating a high pressure to develop in the phloem.

1 bi) Until 0.25 mols of sucrose, there is 0% of oligosaccharides. Thereafter, there is a steep increase until 0.5 mols of sucrose when there is 80% of oligosaccharides. The percentage of oligosaccharides remained stagnant at 80 until 1.00 mols of sucrose.

1 bii) High solute concentrations might tamper with common functions such as osmosis.

1 ci) Phloem sap may not be a good source of protein for aphids as it is mostly composed of sucrose, and not protein that can be broken down by enzymes into amino acids.

1 cii) Phloem sap and aphid protein are produced for differing reasons, hence the amino acid content is optimised differently.

1 di) Antibiotics can added to phloem sap and fed to aphids. Aphid activity can be monitored before and after antibiotic treatment.

1 dii) Phloem sap has a high concentration of sugar which may not be an ideal diet for other organisms as it is diabetes inducing.

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Q1)(a)(i)The concentration of sugar in the phloem sap can be increased by having a higher rate of photosynthesis, allowing the plant to produce more sugar.

Q1)(a)(ii) This is due to the hydrostatic pressure in the sieve tubes. The higher the concentration of sugar, the larger pressure in the tube, the lower the concentration of sugar in the phloem sap.

Q1)(b)(i) As the sucrose concentration in the phloem increases, the % of oligosaccharide increases up till 0.5mol, where the % level of oligosaccharide would remain constant.

Q1)(b)(ii) excreting the enzyme would reduce the concentration of sugar as there would be a decrease in water loss through osmosis in the gut of the aphid. This would ensure a normal water content within the aphids.

Q1)(c)(i) The amino acid in the phloem sap contains 0-10% of essential amino acids, while containing 1-100% of non-essential amino acids. This shows that the phloem sap is not a very source of amino acids for the aphids as it does not contain a lot of the needed amino acids. It can be used as a side source of amino acid since it contains a small % of the needed amino acid, but not as a main source.

Q1)(c)(ii) The amino acid could have been used to synthesise others hence lowering the % of amino acids in their proteins.. In addition, the plant does not contain a high % the amino acids needed by the aphids, hence showing in the % of amino acids in their protein.

Q1)(d)(i) Antibiotics are compounds which inhibit the growth of microbes by targeting prokaryotic metabolism.

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1ai)

By actively pumping ions into the roots, the plant is able to create a concentration gradient where a high concentration is present in the phloem sap, and sugar is able to be actively transported.

1aii)

High concentration of sugar in the plant creates a chemiosmotic gradient that draws water in through osmosis/

1bi)

Up until 0.25 mol of sucrose concentration, the percentage of dligosaccharides was 0%. After that, the percentage of dligosaccharides increases until 85% at 0.50 mol, before it plateaus slightly. It reaches 80% at 1.0mol.

1bii)

The high concentration of solute makes it safe for the aphids to digest

1ci)

It is not a good source of amino acids for aphids, as there is a low percentage of essential amino acids in phloem sap, mostly at 1%. While the phloem sap has a percentage of non-essential amino acids, they are, non-essential as the aphid can produce these amino acids by themselves.

1cii)

Aphid protein amino acids are made specifically for the function of the aphid, while the phloem sap amino acids are made for the function of the plant, both are different organisms with different functions that require different amino acids

1di)

Antibiotics can be injected into the phloem sap of the plant, which will then be taken in by the aphid. The antibiotics will then be assessed to see if they are able to reduce the concentration of Buchnera within the aphids.

1dii)

Phloem has a high concentration of sugar present in a low concentration of essential amino acids. Not all animals have Buchnera either to convert the phloem sap to amino acids. Hence, few animals use it as a source of food.

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1. a) active transport of sugars into the phloem up the concentration gradient from the source

The high sugar concentration has a lower water potential, leading to the osmosis of water from the xylem into the phloem. As the phloem becomes turgid due to the water load, the pressure increases.

b) as dietary sucrose concentration increases from 0.15 to 0.25mol, the %oligosaccharides remains constant at about 0%. As dietary sucrose concentration increases from 0.25 to 0.5, the %oligosaccharides increases in a sigmoidal curve, with increasing gradient from 0.25 to 0.40 and decreasing gradient from 0.4 to 0.5. It then plateaus at 85% oligosaccharides, then decreases to about 82 from 0.75 to 1.00mol.

Reducing the solute concentration by converting to oligosaccharides would prevent the difference in water potential between aphid cells and the ingested sap from being too big. This would prevent the osmosis of water out of aphid cells, protecting it from shriveling.

c) There is one essential amino acid that aphids could obtain from phloem sap, with a percentage of 8% compared to only 1% in aphid proteins. This means that phloem sap is a good source of that one essential amino acid. Additionally, 6 essential amino acids are found in lower concentration in phloem sap, so an aphid could use phloem sap to obtain those. However, there are two essential amino acids that are not found in phloem sap, so phloem sap would be insufficient as a source of amino acids.

The plant seems to have a high proportion of one amino acid, with a much lower proportion of other amino acids. This could be because the plant requires less variety of amino acids, as proteins are not needed for movement from location to location for example.

d) By exposing some aphids to antibiotics. if a lack of aspartic acid is observed, then that suggests that Buchnera is present and produces aspartic acid.

Some animals who do not synthesise aspartic acid, possibly due to a lack of buchnera, may require it from external sources. As such, they would need to obtain it from phloem sap.

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1ai) The sugars such as sucrose move from source to the companion cell through active transport and the sugars move through plasmodesmata to the phloem sap, thus sugars move to regions of higher sugar concentration forming a very high sugar content in the phloem sap.

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1ai) The sugars such as sucrose move from source to the companion cell through active transport and the sugars move through plasmodesmata to the phloem sap, thus sugars move to regions of higher sugar concentration forming a very high sugar content in the phloem sap.

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aii) High sugar concentration in the phloem sap creates a water potential gradient, water flows from high water potential in the xylem to low water potential in the phloem sap. The entry of water into the phloem sap creates a high hydrostatic pressure to develop in the phloem.

b) i)- As dietary sucrose concentration increases from 0.25 to 0.50 mol the % of oligosaccharides increases exponentially
- When dietary sucrose concentration increases from 0.5 to 1.00mol, the % of oligosaccharides plateaus and no longer increases from 0.5 to 0.75mol, instead it stays constant and slightly decreases from 0.75 to 1.00mol of dietary sucrose concentration.

ii) - to prevent the formation of a greater water potential gradient, resulting in too much water entering the gut of the aphid through osmosis and disrupting the bodily function
- Too high of dietary sucrose concentration could be toxic to Aphids and so it has to be reduced through enzyme breakdown.

c) i)
-Phloem sap contains a low percentage of most essential amino acids that the aphid proteins contain more of as seen by the points in the graph representing the essential amino acids, only around 1% of the essential amino acids are present in the phloem sap meanwhile 10% of the amino acid is present in aphid proteins. -The phloem sap could be consumed so as to receive a low percentage of essential amino acids and a higher percentage of certain non-essential amino acids.
-The phloem sap is not very effective as a source of amino acids for aphids.

cii)- Amino acid content in phloem is lower for essential amino acids because these amino acids are not required for the plant and so it would not have to produce many of these types of essential amino acids, thus having a lower percentage content in the phloem sap whereas the aphid requires these essential amino acids and so its DNA codes for these specific essential amino acids thereby having a higher amino acid content in the aphid protein.

d)i)-antibiotics destroy pathogens such as bacteria. thus, in order to obtain evidence for the role of Buchnera in aphids, antibiotics should be given to the aphids and whether Buchnera is a bacteria will be known if the antibiotic destroys it using processes such as prevention of cell wall formation.

dii) The phloem sap has a high content of non-essential amino acids that animals can produce and low content of essential amino acids that animals such as aphids are unable to produce. It would not be very beneficial towards most animals to have phloem sap as the main part of their diet since they only provide high contnet of amino acids that they can already produce and could find better alternative sources of diet that have a higher content of non essential amino acids

Joshua

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1. a) (i) Plants increase sugar concentrations in phloem sap by performing active transport from a source to the companion cell, before diffusing through the plasmodesmata into the phloem sap.

(ii) Higher sugar concentrations lowers the water potential, allowing water from the xylem to move into the phloem through osmosis. The cell then increases in size and becomes turgid, increasing the hydrostatic pressure, hence causing a high pressure to develop.

b) (i) From 0 to 0.25 mols, the percentage of oligosaccharides in the honeydew remains constant at 0%. From 0.25 to 0.4 mols, the percentage of oligosaccharides increased at an increasing rate from 0% to 70%. From 0.4 to 0.5 mols it increases at a decreasing rate from 70% to 80%. From 0.5 to 0.75 mols, it stays constant at 0.8 mols. It then slightly decreases at 1.0 mols.

(ii) To maintain water potentials and homeostasis. To remove excess sugars that may not be needed for nutrition.

c) (i) Phloem sap is not an appropriate source of amino acids for aphids. This is because the percentage of essential amino acids found in aphids are lower in phloem sap. Only 3 of the non-essential proteins contained in phloem sap are higher than in aphid's amino acids.

(ii) Some amino acids may be used to synthesize others. The plant that the phloem sap comes from may need different concentrations of certain amino acids than aphids.

d) (i) Antibiotics would be able to reduce the number of or completely remove the Buchnera. This means that the concentration of essential amino acids and aspartic acid could be recorded from a solution containing antibiotics and one without. An increased concentration of essential amino acids and decreased concentrations of aspartic acid would indicate that the Buchnera does have a role.

(ii) The high sugar content of phloem sap would make it unsuitable for many animals, as they would require many adaptations to survive on it. This is also true for the concentration of amino acids, as it is low, which may be unsuitable for most animals. Figure 11 shows that it is missing many amino acids that organisms would require.

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1.
a)(i) they use active transport to pump nutrients into phloem sap from xylem.

a)(ii) High sugar concentrations causes the water from xylem to pass into the sieve tube cells of phloem by osmosis creating hydrostatic pressure.

b) (i) the sucrose concentration does not seem to be affecting the % oligosaccharides because it remains at 0% until 0.25 mol. After that with increase in sucrose concentrations the % oligosaccharides are also increasing significantly till 80% at 0.50 mol. There is a steep gradient. After which there seems to be no effect again because % is relatively constant until 0.1 mol.

b)(ii) to maintain water potential for homeostasis

c)(i) Phloem sap seems to arguably be a good source of amino acids for aphids. There is a positive correlation between the amino acid % in aphid proteins and amino acid % in phloem sap because the gradient is positive. But there seems to be relatively high variance between the data points

(ii)  some amino acids might be used up for cellular respiration. Not all of the sap is consumed.

d)(i) Antibiotics would act on the bacteria restricting its function. Any deficiencies could be recognised from that.

(ii) Figure 10 shows that the sucrose concentrations are very high for the sustenance of life and from Figure 11 we can see that the 5 of amino acid in phloem sap is also in low concentrations. It does not contain many amino acids necessary for survival.

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1 (a)[i]plants translocate the sugar to the target region of the plant (active transport from the sink to the source)

[ii]the increase in solute concentration causes water to move into the sieve tube by osmosis, creating a hydrostatic pressure
(b)[i]initially, when dietary sucrose concentration increases to 0.25mol, there is no impact on the percentage of oligosaccharides. when the dietary sucrose concentration increases further to 0.50mol, there is a steep increase in percentage oligosaccharides in the honeydew to 80%. as the dietary sucrose concentration continues to increase up to 1.00mol, the percentage oligosaccharides plateau
[ii]to prevent water loss
(c)[i]active transports of amino acids into the phloem by companion cells causes the phloem sap to be hypertonic. water moves via osmosis from the xylem into the phloem, creating a hydrostatic pressure. this hydrostatic pressure results in mass flow in which amino acids is transported away from the source
[ii] amino acids are synthesised in plants but in aphids, the amino acids are used to carry out functions of life
(d)[i]antibiotics can inhibit the growth of the Buchnera. so the use of antibiotics will result in little to no amino acids in aphids because it cannot be synthesised
[ii] amino acid percentage in phloem sap is approximately the same as amino acid percentage in aphid proteins, so there is no net movement of water

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a) i) Plants able to increase sugar concentration of phloem sap by increases production of glucose sugar molecules via photosynthesis.

ii) Large concentration of glucose sugar molecules produced create a pressure gradient, where sugars will constantly flow from high pressure to low pressure down pressure gradient

b) i) % of oligosaccharides first increases steeply as dietary sucrose concentration increases (Proportional relationship). At 0.50mol of dietary sucrose concentration, % of. oligosaccharides starts to plateau and flatten out around 80% as dietary sucrose concentration continues to increase to 1.00 mol.

ii) Enzymes are biological catalysts that speed up rate of reaction by providing an alternative pathway with lower Activation energy. Enzymes would have been used to speed up the conversion of sugars to oligosaccharides, enabling faster reduction of solute concentration of phloem sap ingested, thus allowing aphids to digest and excrete the digested waste more efficiently.

c) i) Phloem sap is not a dense source of amino acids as majority of amino acids present in high percentages in aphid proteins (around 10%), but present in low percentages in phloem sap (around 1%). Due to small % of amino acid in phloem sap compared to aphid proteins, phloem sap would not be considered as a heavy source of amino acids.

ii) Aphid proteins produce

d) i)

ii) Aspartic acid found in high concentrations in phloem sap is used to synthesise essential amino acids. A higher intake of phloem sap induces greater synthesis of essential amino acids from aspartic acid and sucrose, which is beneficial for nutrition of animals, as more amino acids are needed to form proteins in the body. Essential proteins used for maintenance and regulation of body tissues

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1a) i) Active transport
a) ii) high sugar, more volume, higher pressure
b) i) From 0 to 0.50 mol of sucrose concentration, the percentage of oligosaccharides will increase steeply. However, after 0.50 mol of sucrose, the percentage, the percentage of oligosaccharides starts decreasing steeply.
b ii) Homeostatic purposes, ensures that aphids have normal water content.
c) i) Phloem sap is a source of amino acids for aphids, but not the main source of aphids as shown in the upward sloping trend. However, the trend is not distinct as there are many outliers.
c) ii) Not all the phloem sap is fully digested resulting in the loss of amino acids. Some will become waste (undigested food).
Aphids only require a bit of the amino acids within the phloem sap.
d) i) Compare two aphids. Put antibiotics into one of their diets. Compare the aphids sucrose concentration in the body
d ii) - Easy source of amino acids in its habitat

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1ai) Photosynthesis allows sugar to be made. In order for the sugar concentration to be high, active transport takes place.

1aii) For higher pressure, there needs to be a concentration gradient of sugars. Hence, because of this concentration gradient, through osmosis, water can be drawn in. This allows a high pressure to develop in the phloem.

1bi) As the sucrose concentration increases, the percentage of oligosaccharides increases as well.

1bii) Reducing solute concentration means there is a higher water potential, therefore reducing water loss from the gut as osmosis will not take place?

1ci) It is not a very good source of protein because there are more non-essential amino acids at higher levels of amino acid percentage in phloem sap than essential amino acids.

1cii) Perhaps the phloem and aphids produce different types of amino acids.

1di) Perhaps they can be fed to aphids whose behaviours and chemical compositions can be monitored and tested on

1dii) Since there are more non-essential amino acids than essential amino acids, it is not useful to have phloem sap as part of the main diet. In figure 11, there is a larger number of essential amino acids in aphid proteins (most are concentrated around the 10% area of y-axis) than the amino acid in phloem saps. In phloem saps the essential amino acids are concentrated around the 1% area, whereas the non-essential amino acids are are spread out from the 10% to 100% region. Therefore, phloem saps are not useful as a main diet as there is a very small concentration of essential amino acids only, thus not providing enough nutrients for the animals.

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1ai) via active transport of sugars to the plant.
1aii) a higher sugar concentration explains that there would be a higher density of solutes in the solution. because of the higher sugar concentration, osmosis of water would occur, travelling at a high concentration to a low concentration (high concentration of sugar). Thus increasing the amount of water and pressure exerted onto the phloem.
1bi) there is an increase in oligosaccharide concentration between 0.25 to 0.5 mol of sucrose solution, with no further increase in oligosaccharide concentration from 0.5 onwards.
1bii) by secreting the enzyme and reducing the concentration of sugar, there would be a decrease in the water loss in the gut of the aphid via osmosis, since a high concentration of sugar would lead to a low water concentration in the gut cells of the aphid.
1ci) there is a poor concentration of amino acids that are essential to the aphids in the phloem of the plant, making the phloem sad a poor source.
1cii) since a plant source and the aphid source are different, the plant and the aphid would have different amino acids present. a plant and an aphid also require different amino acids thus the synthesis of the amino acids differ in plants and aphids.
1di) since aphids feed off the phloem sap of the plants, antibiotics can be injected into the phloem sap of the plants and administered to the aphids.
1dii) since phloem sap is high in concentration of sugar, animals would have to adapt to the high concentration of sugar dehydrating the cells of the animal, thus few animals use phloem sap as a source of food.

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A) Sucrose from the source is actively loaded into the phloem via active transport which requires ATP and moves against the concentration gradient
ii) the high sucrose concentration causes the movement of water from the xylem into the phloem via osmosis. Since water is non-compressible, a high hydrostatic pressure builds up in the phloem.
b)
i) from a sucrose concentration of 0.125 to 0.25, the % oligosaccharide present in the honeydew remains at 0,
as the concentration of sucrose increases from 0.25 to 0.55, the %oligosaccharide increases rapidly from 0 to 86%. from
from 0.55 to 1.00, the %oligosachide decreases gently from 86% to 82%
ii) a high solute concentration in the gut could cause dehydration as water moves out of the malphilgian tubules via osmosis, therefore by reducing solute concentration, less water is loss through the honeydew of the insect.
c) phloem is a good source of protein for the aphids as when protein concentration in the phloem sap is high, the amino acids in aphid protein increases suggesting that the aphid can absorb amino acids from this source.
Furthermore the presence of essential amino acids being absorbed by the aphids suggest that the phloem sap provides a source of these essential proteins that aphids can only obtain externally.
ii) one is a plant and one is aphid hence aphids may need a wider range of amino acids as compared to plants.
d) Antibiotics can be used to kill the Buchnera in a sample group of offspring while leaving a control group of aphids with no antibiotic treatment. The % concentration of essential amino acids in proteins can then be compared between the group of aphids with Buchnera and no Buchenera.
e) Very few organisms may have Buchenera present in their system to convert aspartic acid in phloem sap into essential amino acids, hence phloem sap may not be useful for obtaining essential amino acids.