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Question 1

(a) Topic: 7.2 (digestive system)
(b) Topic: 7.4 (chemical digestion)
(c) Topic: 7.4 (chemical digestion)
(d) Topic: 7.4 (chemical digestion)
 

a) Fig. 1.1 is a diagram of the digestive system.

Each letter may be used once, more than once or not at all.
State the letter of the part shown in Fig. 1.1:

  • that produces bile
  • that produces gastric juice
  • that produces urea
  • where maltose is digested
  • where trypsin acts

(b) A student investigated the effect of bile on the digestion of fat in milk.
They set up three different test-tubes:
• test-tube A contained milk and bile
• test-tube B contained milk and lipase
• test-tube C contained milk, lipase and bile.
They used an indicator that is pink in alkaline solutions and colourless in acidic solutions.
They added the same volume of indicator to each test-tube.
The student observed and recorded the colour of the contents of each test-tube at 0 minutes, 20 minutes and 40 minutes.
Table 1.1 shows the results of the investigation

(i) Explain the results for test-tubes B and C in Table 1.1.

(ii) Explain the purpose of test-tube A in Table 1.1.

(c) The action of lipase is affected by temperature.
Fig. 1.2 shows the axes for a graph of the effect of temperature on the activity of lipase.
Complete the graph by:
• drawing a line to show the expected effect of temperature on the activity of lipase
• adding a label line and a label to show the point at which all the lipase has been denatured.

(d) Explain why lipase cannot be used to catalyse the breakdown of proteins.

▶️Answer/Explanation

(a)

  • that produces bile : K
  • that produces gastric juice: C
  • that produces urea: K
  • where maltose is digested : H
  • where trypsin acts: H

(b)(i) Any four from:
pH decreases / (solution) becomes acidic 
(pH changes because) fatty acids are produced 
lipase, digests / breaks down, fat 
fatty acids, produced , faster in test-tube C than B 
bile, emulsifies fats / converts large particles of fat to small particles 
bile increases the surface area (for lipase action) 

(b)(ii) compare with tubes B and C to assess effect of lipase and / or bile  shows that bile, does not (chemically) digest fats / does not make solution acidic , shows that, lipase / enzyme, is required (for breakdown of fats in milk) 

(c) line drawn showing that decrease after optimum is steeper than increase 
MP1 – line does not have to start at the origin or end at the x-axis label line to point where line meets the x-axis and label indicating that all the lipase is denatured 
MP2 – line must meet the x-axis

(d) Any three from:
ref to specificity 
(only) substrate for lipase is fat (molecules) 
shape of active site is, not complementary to protein / complementary to fat 
protein cannot, fit into / bind to, active site / lipase / enzyme 
enzyme-substrate complexes cannot be formed 

Question 2

(a) Topic: 3.2 (osmosis)
(b) Topic; 3.2 (osmosis)
(c) Topic: 3.3 (active transport)
(d) Topic: 6.1 (photosynthesis)
 

(a) A student investigated osmosis in potato plant cells.
He immersed cubes of potato tissue in water and different concentrations of sucrose solution for 30 minutes.
The masses of the potato cubes were measured before and after immersion.
The percentage changes in mass were calculated.
Table 2.1 shows the results

(i) Using the information in Table 2.1, calculate the percentage change in mass at 1.00mol\(dm^{–3}\).
Give your answer to two decimal places

(ii) Using the information in Table 2.1, explain the difference in the results between the 0.6mol\(dm^{–3} and the 0.8mol\(dm^{–3}\) sucrose solutions.
Use the term water potential in your answer.

(iii) Describe the expected appearance of a cell from a potato cube that has been immersed in distilled water for 30 minutes.

(b) Describe how the process of active transport differs from the process of osmosis

(c) State the type of plant cells that use active transport to absorb mineral ions from the
environment.

(d) Explain the effect of a lack of magnesium ions on the colour of plant leaves

▶️Answer/Explanation

(a)(i) –13.28 (%)

(a)(ii) Any five from:

potato (cube) in 0.8 (mol dm–3 solution) loses greater (percentage)
mass / ora 
movement of water out / loss of water, is cause of mass loss 
water moves from an area of high water potential to an area of low water potential
water potential of 0.8 (mol \(dm^{–3}\) solution) is lower than the water potential of the 0.6 (mol \(dm^{–3}\) solution) 
greater / steeper, water potential gradient in 0.8 (mol dm–3) than in 0.6 (mm \(dm^{–3}\)) 
(relatively) more water leaves the potato (cube) in 0.8 (mol \(dm^{–3}\) solution) 

(a)(iii) Any two from:

(cell is) swollen / large(r) / big(ger) / wide(r) 
(cell is) turgid 
vacuole is, swollen / large(r) / big(ger) / wide(r) 
cell wall bulges 
cell membrane / cytoplasm / cell contents, presses on cell wall 

(b) Any three from:
uses energy (from respiration / mitochondria) 
(transport / movement is) against a concentration gradient
involves movement of, sugars / ions / substance(s) other than water involves protein carriers 

(c) root hair (cells) 

Question 3

(a) Topic: 11.1 (gas exchange in humans)
(b) Topic: 11.1 (gas exchange in humans)
(c) Topic: 11.1 (gas exchange in humans)
(d) Topic: 11.1 (gas exchange in humans)
(e) Topic: 11.1 (gas exchange in humans)
 

(a) Fig. 3.1 is a photomicrograph of some cells lining the trachea

(i) Describe the role of goblet cells.

(ii) Explain how the cell labelled X in Fig. 3.1 is adapted for its function

(iii) State the name of one other part of the body where the type of cell labelled X in Fig. 3.1 is found

(b) Table 3.1 contains some features of the breathing system.
Complete Table 3.1 to show the actions of each feature of the breathing system that occur to cause inspiration

(c) State the name of the gas that is excreted by the breathing system.
(d) Good ventilation is one feature of gas exchange surfaces.
State two other features.
(e) State the name of the gas exchange surface in humans.

▶️Answer/Explanation

(a)(i) produce / secrete, mucus

traps / catches pathogens / bacteria / particulates
e.g., water in mucus moistens surface in, nose / airways

(a)(ii) Any two from:

ciliated / has cilia / has hair-like cilia
move / sweep / waft / AW, mucus (with pathogens)
(a)(iii) bronchi / bronchioles

(c) carbon dioxide / water vapour 

(d) Any two from:
large (surface) area 
thin (surface) / one cell thick / short diffusion distance 
good blood supply
e.g., moist / ref. to surfactant

(e) alveoli 

Question 4

(a) Topic: 6.1 (photosynthesis)
(b) Topic: 6.1 (photosynthesis)
(c) Topic: 6.1 (photosynthesis)
 

(a) Fig. 4.1 shows the effect of light intensity on the rate of photosynthesis at different temperatures and concentrations of carbon dioxide.

Describe and explain the reasons for the shape of lines B and C in Fig. 4.1.

(b) \(C_6H_{12}O_6\) is one of the products of photosynthesis.
State the chemical formula of the other product.
(c) Outline how the carbohydrates made during photosynthesis are used in plants.

▶️Answer/Explanation

(a) Any six from:
LIGHT
(B and C as light intensity increases) the rate (of photosynthesis) increases and remains constant
rates (of photosynthesis) are the same at low(est) light intensities
light provides energy (for photosynthesis) where the line rises / initially, light intensity is, limiting / the limiting factor 
line(s) / rate, levels off where light intensity is not limiting
in B light intensity becomes limiting at higher light intensity than C 

CARBON DIOXIDE
Idea that line C levels off, at a lower rate (of photosynthesis) / lower light intensity
carbon dioxide (concentration) is, lower for C / 0.04% vs 0.4% 
carbon dioxide is, reactant / substrate / raw material / needed, for photosynthesis 
in C carbon dioxide is a limiting factor at a lower light intensity 
in B carbon dioxide is a limiting factor at a higher light intensity 
TEMPERATURE
idea that temperature is limiting for B at high light intensities 

(b) \(O_2\)
(c) Any four from:
(glucose) used, in respiration / to provide energy / to release energy as an energy store 
(glucose) converted to / stored as, starch 
(glucose) converted to sucrose 
sucrose for, translocation / transport (in the phloem) / sent to sink(s) 
(glucose / fructose / sucrose) in nectar 
(nectar) to attract, insects / pollinators 
(glucose / fructose / sucrose) in fruits (to attract animals) 
(glucose) converted to cellulose 
cellulose to build cell walls 
lignin for cell walls 
used to make, amino acids / fatty acids 

Question 5

(a) Topic: 17.1 (chromosomes, genes and proteins)
(b) Topic: 17.1 (chromosomes, genes and proteins)
(c) Topic: 18.1 (variation)
(d) Topic: 18.3 (selection)
(e) Topic: 18.3 (selection)
 

(a) Fig. 5.1 shows the stages involved in protein synthesis.

(i) State the names of the parts labelled X, Y and Z in Fig. 5.1.
(ii) State what determines the sequence of the amino acids in the protein that is produced.
(iii) Explain why the sequence of amino acids is important in the production of receptor molecules for neurotransmitters.

(b) Explain why body cells can have different specialised functions even though they contain the
same genes.

c) Allele frequency in a population can be changed by natural selection and artificial selection.
State the meaning of the term allele

(d) Describe how artificial selection differs from natural selection.

(e) Mutation causes formation of new alleles which increases genetic variation.
State two other sources of genetic variation in populations.

▶️Answer/Explanation

(a)(i)

X – nucleus 
Y – mRNA 
Z – ribosome 

(a)(ii) sequence / order, of bases in, mRNA / DNA / gene

(a)(iii) (the sequence of amino acids) determines the shape of the, protein / receptor ,complementary / specific, shape is required for the receptor molecule to, bind / attach / fit, to neurotransmitter

(b) not all genes are, expressed / switched on / activated
cells only produce the (specific) proteins they need

(c) either
an alternative form of a gene 

(d) humans choose, specific feature(s) / desired features 
humans choose, individuals / offspring, to reproduce 
selection not influenced by environment / humans manipulate environment 
decreases (genetic) variation / decreases size of gene pool 
faster / shorter 
for economic / aesthetic, reasons 
no / less, evolution 
e.g. decrease in fitness

(e) Any two from:
meiosis 
random mating / cross pollination / crossbreeding , random fertilisation 

Question 6

(a) Topic: 12.3 (anaerobic respiration)
(b) Topic: 12.3 (anaerobic respiration)

(a) A scientist monitored the changes in the pH in muscles before, during and after two minutes of vigorous exercise.
The changes in pH are caused by the production of lactic acid

Complete the sentences to describe and explain the results in Fig. 6.1.
The pH decreases from ……………………………………….. to ……………………………………….. during vigorous exercise.
There is not enough ……………………………………….. supplied to the muscles.
The body respires anaerobically. The lactic acid produced builds up in the muscles causing an ……………………………………….. debt.
It takes ……………………………………….. minutes for the muscle pH to return to its initial level after exercise.
The pH value increases after vigorous exercise has ended, as lactic acid is transported in the ……………………………………….. to the ……………………………………….. .
During this time the breathing rate and ……………………………………….. rate remain high.

(b) Yeast can respire anaerobically.
(i) Complete the balanced chemical equation for anaerobic respiration in yeast.
\(C_6H_{12}O_6\)
(ii) Yeast belongs to the kingdom fungus.
State one cell component that is present in yeast cells but is absent in animal cells.

▶️Answer/Explanation

(a) The pH decreases from 7.07 to 6.55 during vigorous exercise.
There is not enough oxygen / oxygenated blood supplied to the muscles.
The body respires anaerobically. The lactic acid produced builds up in the muscles causing an oxygen. debt.
It takes any time between 31 and 32 (minutes) minutes for the muscle pH to return to its initial level after exercise.
The pH value increases after vigorous exercise has ended, as lactic acid is transported in the blood(stream) / (blood) plasma to the liver
During this time the breathing rate and .heart / pulse. rate remain high.

(b)(i) \((C_6H_{12} O_6) \rightarrow 2C_2H_5OH + 2CO_2\)

(b)(ii) cell wall / (large) vacuole / plasmid(s)

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