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Question 1

(a) Complete the sentences to describe enzymes.
Use words or phrases from the list.
Each word or phrase may be used once, more than once or not at all.

Enzymes are proteins. All proteins are made up from a chain of smaller ………….. called …………… .
All proteins contain the chemical elements ……………., …………… and …………….. .

(b) Enzymes function as biological catalysts. Describe what is meant by the term catalyst.
(c) Fig. 1.1 shows a reaction catalysed by an enzyme.
Use Fig. 1.1 to describe enzyme action.
(d) Some bacteria are found living in very high temperatures.
Fig. 1.2 shows the effect of temperature on the activity of an enzyme in these bacteria.

Using the information in Fig. 1.2:
(i) Identify the optimum temperature for this enzyme.
(ii) Identify the temperature when the enzyme is completely denatured. Explain how you identified your choice.
(iii) Calculate the difference in enzyme activity between \(20~^\circ\text{C}\) and \(40~^\circ\text{C}\).
Space for working.
(iv) The mean body temperature for humans is \(37~^\circ\text{C}\). On Fig. 1.2, sketch the curve for the activity of an enzyme found in humans. [2]

Most-appropriate topic codes (Syllabus 0610):

• TOPIC 4.1: Biological molecules — part (a)
• TOPIC 5.1: Enzymes — parts (a), (b), (c), (d)
▶️ Answer/Explanation
Detailed solution

(a)
Enzymes are proteins. All proteins are made up from a chain of smaller molecules called amino acids.
All proteins contain the chemical elements carbon, hydrogen and nitrogen (or oxygen).
(Note: Proteins consist of Carbon, Hydrogen, Oxygen, and Nitrogen. Since there are three blanks, listing any three of these from the list is acceptable, but Nitrogen is the key element distinguishing proteins from carbohydrates and fats).

(b)
A catalyst is a substance that increases the rate of a chemical reaction and is not changed by the reaction (it can be used again).

(c)
Using the “lock and key” hypothesis shown in Fig 1.1:

  • The substrate has a specific shape that is complementary to the enzyme’s active site.
  • The substrate binds to the active site to form an enzyme-substrate complex.
  • The reaction occurs (breakdown or synthesis), and products are formed.
  • The products leave the active site, and the enzyme remains unchanged.

(d)(i)
Optimum temperature: \(50 \pm 1\) \(^\circ\text{C}\).
(This is the temperature corresponding to the peak of the curve on the graph).

(d)(ii)
Temperature: \(66\) \(^\circ\text{C}\).
Explanation: There is zero activity / no enzyme activity at this point.
(At this temperature, the enzyme has denatured, meaning the active site has lost its shape and can no longer bind to the substrate).

(d)(iii)
Calculation:
At \(40~^\circ\text{C}\), activity = \(10\) arbitrary units.
At \(20~^\circ\text{C}\), activity = \(2.8\) arbitrary units (each small square on the y-axis represents \(0.4\) units; the point is 2 squares above 2).
Difference: \(10 – 2.8 = \mathbf{7.2}\) arbitrary units.

(d)(iv)
Sketch:
The curve should have the same shape as the bacterial enzyme (gradual rise to a peak, then sharp decline). The optimum (peak) should be shifted to the left, centered around \(37~^\circ\text{C}\) \(\pm 2\).

Question 2

(a) Fig. 2.1 shows the human digestive system.

(i) The human digestive system is made up of the alimentary canal and the associated organs.
Food moves through the alimentary canal, but does not move through the associated organs.
The pancreas is one of the associated organs.

State the letter in Fig. 2.1 that identifies the pancreas and state the name of two enzymes secreted by the pancreas.

(ii) State one letter in Fig. 2.1 that identifies one other associated organ of the digestive system.
Name this organ.
(iii) In Fig. 2.1, structure J is the small intestine.
State two functions of the small intestine.
(b) Some antibiotics are taken into the body as tablets.
Fig. 2.2 shows the concentration of antibiotic in the blood after a tablet is taken.
(i) Using Fig. 2.2, describe how the concentration of antibiotic in the blood changes.

(ii) Circle the name of the process of taking substances into the body.

    assimilation        digestion        egestion        excretion        ingestion

(iii) Antibiotics are transported around the body by the blood.
State the name of the component of blood that transports substances such as nutrients, hormones and antibiotics.
(iv) State the type of organism killed by antibiotics.

Most-appropriate topic codes (Syllabus 0610):

• TOPIC 7.2: Digestive system — parts (a)(i), (a)(ii), (b)(ii)
• TOPIC 7.4: Chemical digestion — part (a)(i)
• TOPIC 7.5: Absorption — part (a)(iii)
• TOPIC 15.1: Drugs — parts (b)(i), (b)(iv)
• TOPIC 9.4: Blood — part (b)(iii)
▶️ Answer/Explanation
Detailed solution

(a)(i)
Letter: G
Enzymes: Amylase, Protease (or trypsin), Lipase (any two).
Explanation: In Fig. 2.1, G points to the pancreas, a leaf-shaped gland located just below the stomach (F). The pancreas acts as an accessory organ by secreting digestive enzymes into the duodenum (the first part of the small intestine). These enzymes include amylase (digests starch), protease/trypsin (digests proteins), and lipase (digests fats).

(a)(ii)
Letter: D Name: Liver
OR
Letter: E Name: Gall bladder
OR
Letter: B Name: Salivary glands
Explanation: Associated organs help in digestion but food does not pass through them. D is the liver (produces bile), E is the gall bladder (stores bile), and B represents the salivary glands near the mouth.

(a)(iii)
1. Chemical digestion (breakdown of large molecules into small molecules).
2. Absorption of nutrients (movement of digested food molecules into the blood).
Explanation: Structure J is the small intestine. It is the primary site where enzymatic digestion is completed (using enzymes from the pancreas and its own lining) and where digested nutrients are absorbed into the bloodstream through structures called villi.

(b)(i)
The concentration of antibiotic increases rapidly to a peak of $1.8$ arbitrary units at $2$ hours. After the peak, the concentration decreases gradually/slowly but remains in the blood (around $0.3$ units) after $10$ hours.
Explanation: The graph shows an initial absorption phase where the drug enters the blood, followed by a metabolism/excretion phase where the level drops.

(b)(ii)
Ingestion should be circled.
Explanation: Ingestion is defined as “the taking of substances, e.g., food and drink, into the body” (usually through the mouth). Digestion is the breakdown of food; egestion is the removal of undigested waste; excretion is the removal of metabolic waste.

(b)(iii)
Plasma
Explanation: Plasma is the liquid component of blood (mostly water) responsible for transporting dissolved substances, including glucose, amino acids, hormones, carbon dioxide, urea, and drugs like antibiotics.

(b)(iv)
Bacteria
Explanation: Antibiotics are chemical substances that kill or inhibit the growth of bacteria. They are ineffective against viruses because viruses lack the cell structures (like cell walls or ribosomes) that antibiotics target.

Question 3

(a) Fig. 3.1 shows blood flow through a human heart.
The arrows show the direction of blood flow.
(i) On Fig. 3.1, draw a label line and the letter X to identify the muscular wall of the left ventricle.
(ii) Describe the path taken by blood as it moves from A to B in Fig. 3.1.
(iii) State the name of blood vessel C shown in Fig. 3.1. 
(b) The activity of the heart can be monitored using an ECG.
Fig. 3.2 shows the results of an ECG for a person who has been resting for 15 minutes.

(i) Fig. 3.3 shows the results of ECGs for the same person:

  • resting
  • during vigorous physical activity
  • one minute after physical activity
  • one hour after physical activity.

Draw lines to link each activity with its ECG. Draw three lines.
One has been done for you.

(ii) State two other ways that the activity of the heart can be monitored.
(c) During vigorous physical activity humans respire anaerobically.
(i) Tick (✓) three statements that describe anaerobic respiration in humans.
(ii) State how vigorous exercise affects the rate and depth of breathing.

Most-appropriate topic codes (Syllabus 0610):

• TOPIC 9.2: Heart — parts (a), (b)
• TOPIC 12.3: Anaerobic respiration — part (c)(i)
• TOPIC 11.1: Gas exchange in humans — part (c)(ii)
▶️ Answer/Explanation
Detailed solution

(a) (i)
The label line X must point to the thick muscular wall of the left ventricle. (Note: The left ventricle is on the right side of the diagram, characterised by a thicker wall compared to the right ventricle).

(a) (ii)
The path of blood from A (Vena Cava) to B (Pulmonary Artery) is as follows:

  • Blood enters the right atrium from A.
  • It moves into the right ventricle.
  • It passes through a valve (specifically the tricuspid valve into the ventricle, or the semilunar valve out of the ventricle) to exit via B.

(a) (iii)
Pulmonary vein. (This vessel carries oxygenated blood from the lungs back to the left atrium).

(b) (i)


Matching the activity to the ECG trace:

  • Resting: Top graph (Normal/slow rhythm) — (Already matched in question).
  • During vigorous physical activity: 2nd graph down (The peaks are closest together, indicating the fastest heart rate).
  • One minute after physical activity: 3rd graph down (The heart rate is slowing down but is still faster than resting).
  • One hour after physical activity: Bottom graph (The heart rate has returned to the resting rate).

(b) (ii)
Any two of the following:

  • Counting the pulse rate.
  • Listening to the sound of the valves (using a stethoscope).
  • Measuring blood pressure (AVP).

(c) (i)
The correct statements for anaerobic respiration in humans are:

Note: Alcohol and carbon dioxide are produced during anaerobic respiration in yeast (fermentation), not humans.

(c) (ii)
Vigorous exercise causes an:

  • Increase in the rate of breathing.
  • Increase in the depth of breathing.

Question 4

Fig. 4.1 shows part of a leaf from a Mexican hat plant.

(a) The Mexican hat plant shown in Fig. 4.1 is reproducing.

Tick (✓) three statements that describe the reproduction shown in Fig. 4.1.

(b) Fig. 4.2 shows a section of a flower.

Identify structures L, M and N shown in Fig. 4.2.

(c) Fig. 4.3 shows a flower from a Crocus plant.

(i) Using the information in Fig. 4.3, predict the type of pollination used by the Crocus plant. Explain your prediction.

(ii) Describe the process of pollination.

(d) Fig. 4.4 is a photomicrograph of pollen grains.

(i) State one letter in Fig. 4.4 that identifies a pollen grain from a wind-pollinated flower.

(ii) Using the information in Fig. 4.4, estimate the maximum length of pollen grain V. Include the unit.

(iii) State two characteristics of pollen grains from insect-pollinated flowers.

Most-appropriate topic codes (Cambridge IGCSE Biology 0610):

• TOPIC 16.1: Asexual reproduction — part (a)
• TOPIC 16.3: Sexual reproduction in plants — parts (b), (c), (d)
▶️ Answer/Explanation
Detailed solution

(a)
The correct statements are:

Explanation: Fig. 4.1 shows plantlets growing directly from the leaf margin. This is vegetative propagation, a form of asexual reproduction. Asexual reproduction involves mitosis, requires only one parent, and produces clones (genetically identical offspring). It does not involve gametes, pollination, or implantation (which is an animal process).

(b)
L: Filament (The stalk that supports the anther).
M: Ovule (The structure inside the ovary that contains the female gamete/egg).
N: Sepal (The outer parts of the flower, often green, that protect the bud).

(c)(i)
Prediction: Insect pollination.
Explanation: The flower has large petals which serve to attract insects visually. Additionally, the anthers and stigma are enclosed by the petals (not hanging outside as in wind-pollinated flowers), meaning insects must enter the flower to contact them.

(c)(ii)
Pollination is the transfer of pollen from an anther to a stigma.

(d)(i)
Q or R.
Explanation: Pollen grains Q and R appear smooth and relatively small compared to the others. Wind-pollinated pollen needs to be light and smooth to float easily in the air without clumping.

(d)(ii)
\(0.08 \text{ mm}\) – \(0.10 \text{ mm}\)
Explanation: The scale bar represents \(0.03 \text{ mm}\). Pollen grain V is roughly \(2.5\) to \(3\) times the length of the scale bar.
Calculation: \(0.03 \times 3 \approx 0.09 \text{ mm}\).

(d)(iii)
Any two of the following characteristics:

  • Spiky / hooks / rough surface (to attach to the fur or body of insects).
  • Sticky (to adhere to insects).
  • Heavy / large (compared to wind-borne pollen).

Explanation: In Fig. 4.4, grains like W and S show distinct spikes, which are adaptations for hooking onto passing pollinators.

Question 5

(a) Fig. 5.1 shows a leaf insect on a leaf.
(i) State one feature visible in Fig. 5.1 that identifies this leaf insect as an insect.
(ii) State one feature visible in Fig. 5.1 that identifies this leaf insect as an arthropod.
(b) The leaf insect in Fig. 5.1 has adaptive features.
(i) Describe the adaptive features visible in the insect shown in Fig. 5.1, and explain the importance of these features.

(ii) Complete the sentences by writing a suitable word in each space.

In a population of leaf insects there are differences between the individuals. The term for the difference between individuals of the same species is ………………. .

Individuals that reproduce are able to pass on their ………………….. to the next generation. Over many generations the features of individuals that reproduce will be more common in the population. This process is called ……………………. selection.

(c) Some species of leaf insect are endangered.
State three ways that endangered species can be conserved.

Most-appropriate topic codes (Cambridge IGCSE Biology 0610):

• TOPIC 1.3: Features of organisms — parts (a)(i), (a)(ii)
• TOPIC 18.2: Adaptive features — part (b)(i)
• TOPIC 18.1 & 18.3: Variation and Selection — part (b)(ii) 
• TOPIC 20.4: Conservation — part (c) 
▶️ Answer/Explanation
Detailed solution

(a)(i)
Any one of the following features visible in the diagram identifies it as an insect:

  • 3 pairs of legs
  • Body divided into three parts (head, thorax, and abdomen)
  • One pair of antennae

(a)(ii)
Any one of the following features visible in the diagram identifies it as an arthropod:

  • Jointed legs (or jointed appendages)
  • Segmented body

Note: An exoskeleton is a feature of arthropods, but strictly speaking, one cannot simply “see” the exoskeleton in a photo in the same way one sees segmentation or joints, though “exoskeleton” is often accepted if implied by the structure. The most distinct visual features are jointed limbs and segments.

(b)(i)
Features: The body is wide and flat, and the leg joints are flattened/wide. The insect looks like a leaf (mimicry).
Importance: This provides camouflage, making it difficult for predators to see or detect the insect. Consequently, it is less likely to be eaten (predation is reduced), increasing its chances to survive and reproduce.

(b)(ii)
In a population of leaf insects there are differences between the individuals. The term for the difference between individuals of the same species is variation.
Individuals that reproduce are able to pass on their alleles (or genes) to the next generation. Over many generations the features of individuals that reproduce will be more common in the population. This process is called natural selection.

(c)
Any three of the following methods can conserve endangered species:

  • Monitoring or counting species populations
  • Protecting habitats (e.g., creating nature reserves)
  • Education (raising awareness)
  • Captive breeding programmes (breeding in zoos/labs to release later)
  • Seed banks (for plants, though less relevant to insects, it is a general conservation method)
  • Reducing hunting, predation, or poaching
  • Reducing pollution

Question 6

(a) Barley is a crop plant. Fig. 6.1 shows the yield of barley per unit area of crops grown between 1945 and 2020.
(i) Selective breeding of barley plants has increased the yield of barley. Identify the period, A, B or C, when the largest increase in yield occurred. Explain how you made your choice. 
(ii) Using the information in Fig. 6.1, calculate the yield of barley in the year 2000 in kilograms per unit area. One tonne = \(1000 \text{ kg}\).

(iii) The list contains statements that describe selective breeding of barley plants to increase yield.

  • A Humans select barley plants with a high yield.
  • B New barley plants are grown.
  • C Offspring with a high yield are selected and bred together.
  • D Pollination and fertilisation occurs.
  • E Seeds form.
  • F The process is repeated over many generations.

Arrange the statements in the correct order to describe the process of selective breeding in barley plants. Two have been done for you.

(iv) State three other ways that humans can increase the yield of barley.
(b) Barley can be grown as a monoculture.
(i) Describe what is meant by the term monoculture.
(ii) State one advantage and one disadvantage of growing crops as monocultures.

Most-appropriate topic codes (Cambridge IGCSE Biology 0610):

• TOPIC 18.3: Selection (Selective breeding) — parts (a)(i), (a)(ii), (a)(iii)
• TOPIC 20.1: Food supply (Monoculture, increasing food production) — parts (a)(iv), (b)(i), (b)(ii)
▶️ Answer/Explanation
Detailed solution

(a)(i)
Period: B
Explanation: This section of the graph has the steepest curve (gradient), indicating the fastest rate of yield increase over time.

(a)(ii)
Answer: \(6400 \text{ kg}\)
Calculation: Reading from the graph at the year 2000, the yield is \(6.4\) tonnes. Since \(1 \text{ tonne} = 1000 \text{ kg}\): $$6.4 \times 1000 = 6400 \text{ kg}$$

(a)(iii)
Order: A, D, E, B, C, F
The logical sequence of selective breeding is: 1. Humans select high yield plants (A). 2. These plants are bred/crossed via pollination/fertilisation (D). 3. Seeds result from this cross (E). 4. These seeds are grown into new plants (B). 5. The best offspring are selected (C). 6. The process is repeated (F).

(a)(iv)
Any three from the following:

  • Use fertilisers (to provide minerals/ions).
  • Use insecticides / pesticides (to kill pests).
  • Use herbicides (to kill weeds).
  • Use Genetically Modified (GM) seeds.
  • Use irrigation / improved drainage / watering systems.
  • Deter animals that eat barley.

(b)(i)
Monoculture: Growing only one type of plant / single crop species in a specific area (at the same time).

(b)(ii)
Advantage (any one):

  • Allows large area of land to be used efficiently.
  • Increases overall yield.
  • Allows specialized machinery to be used (easier harvesting).
  • Allows farmers to specialise.

Disadvantage (any one):

  • Increases population of insect pests (due to abundant food supply).
  • Increases risk of disease spread (rapid transmission between identical plants).
  • Risks total crop failure.
  • Reduces biodiversity.
  • Depletes specific soil nutrients.
Explanation

Graph Analysis (Part a): In biological graphs, the rate of a process is determined by the gradient (slope) of the line. Section B is the steepest part of the sigmoid curve, representing the period where agricultural technology (like the “Green Revolution”) likely had the most impact on yield. For part (ii), accurate graph reading is required. The y-axis is in “tonnes per unit area”. The line intersects the year 2000 exactly at the \(6.4\) mark. The question demands the answer in kilograms, necessitating the conversion \(6.4 \times 1000\).

Selective Breeding (Part a-iii): This question tests the understanding of artificial selection as a step-by-step process. It mirrors natural selection but is directed by human choice. The key is recognizing that “Pollination” (D) and “Seeds forming” (E) must happen before “New plants are grown” (B), and that selection of offspring (C) happens after the new generation has grown.

Food Supply & Monoculture (Part b): This relates directly to the impact of humans on ecosystems. While monoculture is economically efficient (high yield, standardized machinery), it is ecologically fragile. A single pest species can wipe out the entire crop because there are no physical barriers or genetic variations to stop it. Furthermore, growing the same crop repeatedly exhausts specific soil ions (like nitrates), requiring heavy fertiliser use.

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