A2 Human Biology Unit 5

Text questions

P94/Q1

A large proportion of potential chemical energy (consumed as food), at each trophic level is transfered to the surroundings in the form of thermal energy. Hence, chemical potential energy locked in the tissues of the young would cover only a small proportion of the total energy demand of the parent animal.

P95/Q2

False

P97/Q3

The electrons are transferred to the molecule of chlorophyll in Photosystem II.

The electrons after being transferred via Photosystem I "own" Electron Carrier System are associated ("reunited") with hydrogen ions from the photolysis of water and reduce NADP to NADPH2:

NADP + 2H⁺ + 2e → NADPH₂ (reduced NADP)

The electrons are transferred to the electron acceptor. The electron acceptor passes the electrons down a series of electron carriers (the Electron Carrier System). The electrons will lose their energy as they go, hence:

ADP + P + energy → ATP

P97/Q4

The light-independent reactions can take place both at daytime and in the darkness. The term "dark reactions" suggests that they take place only when it is dark, which is not true.

P98/Q5

ATP is used to convert ribulose phosphate (1 phosphate group) to ribulose bi-phosphate (2 phosphate groups).

P98/Q6

0.02 x 18.800 kJ m-2 day-1 = 376 kJ m-2 day-1

P100/Q7

Pyruvate + CoA + NAD → AcCoA + CO₂ + NADH (reduced NAD)

P101/Q8

Stage of respiration	Number of NADH molecules produced	Number of NADH molecules produced from one glucose molecule
Glycolysis	2	2
Link reaction	1	2
Krebs cycle	3	6
TOTAL	-	10

P103/Q9

RQ = CO2 / O2
0.9 = ?CO2 / 5.4

Hence: ?CO2 = 0.9 x 5.4 = 4.86cm�

P103/Q10

The RQ will drop from 1.0 to a lower value (possibly 0.7). The reason for this drop will be the use of the fat reserves in the process of respiration during the extended flight of the locust. The RQ for triglycerides is 0.7

P104/Q11

Producers and Primary Consumers.

P106/Q12

0.1 x 0.1 = 0.01 (1%).

P107/Q13

Since a young animal is growing new cells/tissues, it will convert a higher proportion of chemical potential energy in food into chemical potential energy in its tissues. It is synthesising its own lipids, proteins, etc., which are the main component of the new cells/tissues.

Assignment

P108/Q1	a)	CO₂ absorbed from the atmosphere as a substrate in photosynthesis 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
	b)	product of photosynthesis (e.g. glucose)
P108/Q2	a)	The cells of the fungus are difficult to separate from the cells of the algae, therefore it is difficult to establish the percentage of the photosynthetate transferred from the algal partners to the fungal partners.
	b)	Lichens use photosynthetate for respiration, therefore some percentage of radioactive (14)C will be released as (14)CO₂ to the atmosphere. This will distort/reduce the percentage of CO₂ actually transferred from algae to the fungal partner cells.
P109/Q3		Polyols are water soluble. They lower WP of the cells. WP of clean rainwater is 0, therefore osmosis will take place → lichen will absorb water rapidly.
P109/Q4	a)	Light dependant reactions of photosynthesis take place on thykaloids (chloroplast membranes). During these reactions ATP is produced. If thykaloids are damaged, light dependant reactions will be affected and the production of ATP will be inhibited.
	b)	ATP is used in light independent reactions (the Calvin cycle) of photosynthesis.
P109/Q5		Chlorophyll which has been broken down as a result of its exposure to high doses of SO₂ will be chemically different from normal chlorophyll. Hence, it will produce a different chromatogram to the one produced by normal chlorophyll. Rf values for the broken down chlorophyll and normal chlorophyll will be different.
P110/Q6		Graph
P110/Q7		Increased concentrations of SO₂ reduce the rate of CO₂ uptake in U. subfloridana more, than in any other species. Hence, SO₂ will limit the distribution of U. subfloridana more, than the distribution of the other species. The uptake of CO₂ in L. conizaeiodes is least affected by increased SO₂ levels. Hence, the distribution of this species is least affected by increased concentrations of SO₂.

Examinations

P110/Q1	a)	(i) 6250 - 1250 = 5000 5000/1250000 x 100% = 0.4% (ii) Big loses of light energy caused by: Reflection of light at the surface of water Cconversion of visible light into heat, which then is absorbed by water Transmission of light (through leaves, chlorophyll not hit).
	b)	% conversion rate of chemical potential energy (ChPE) from one trophic level to the ChPE in the next one is small. A lot of energy is lost due to respiration, as well as energy being locked in faeces and dead organisms. Hence, not enough ChPE available (as food) to organisms in the higher trophic level (→starvation).
	c)	ChPE in faeces and dead organisms is transferred (as food) to micro-organisms, which feed on them.
	d)	(i) Light strikes the molecule of chlorophyll. The energy levels of two of the electrons in the chlorophyll molecule are raised. These electrons leave the chlorophyll molecule and pass to an electron acceptor. (ii) DCMU blocks the flow of electrons through electron transport chain (ETCh), hence NADPH2 not produced. Therefore GP (glycerate 3-phosphate) cannot be converted/reduced to triose phosphate (in the Calvin cycle).
	e)	ATP is a molecule with a high-energy bond. It can release energy locked in this bond immediately by undergoing a one-step reaction: ATP → ADP + P + energy. A molecule of glucose needs to undergo a series of chemical changes before energy locked in its chemical bonds can be released. Energy can't be released from a molecule of glucose immediately.
	f)	(i) High demand for ATP means more ATP → ADP + P + energy, hence more ADP molecules in the cytoplasm. If more ATP is present, electrons are passed down the ETCh, so that: ADP + P + energy → ATP The opposite will happen if there is a low demand for ATP (ii) The electrons pass from one molecule to the next one along the ETCh. At each transfer, a small amount of energy is released. This energy is used to produce ATP DNP allows the transport of electrons down the ETCh without production of ATP In this situation, energy released from electrons as they move down the ETCh is not converted to ATP, but to heat.
P112/Q2	a)	Fractional ultracentrifugation. Cell fractionation → cells homogenised and suspended in isotonic solution → homogenate filtered to remove unbroken cells → filtrate centrifuged and pellet of organelles removed → if necessary, fluid supernatant can be spun again at higher speed. New pellet (containing heavier nuclei) removed.
	b)	(i) Pi is combined with ADP to form ATP (ii) light independent reaction takes place in stroma, because intact chloroplasts (stroma present in them) absorb a lot of CO₂, while chloroplast membranes (stroma absent) absorb little CO₂.
P112/Q3	a)	Cristae increase surface area available for electron carriers (Electron Transport/Carrier Chain) and synthesis of ATP
	b)	RQ = 57/80 = 0.71
	c)	(i) The main respiratory substrate is a carbohydrate. (ii) Various respiratory substrates (carbohydrates, triglycerides, amino acids and proteins) used over 24-hour period have different RQ values.