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Question 1

When a herbivore sees a carnivore, which characteristic of living things is involved?

(A) excretion
(B) growth
(C) reproduction
(D) sensitivity

▶️ Answer/Explanation

Sensitivity (also known as irritability) is the ability of an organism to detect or sense stimuli in the internal or external environment and to make appropriate responses. In this scenario, the sight of the carnivore acts as a stimulus. The herbivore perceives this threat through its sensory organs and will typically respond by fleeing or hiding to ensure survival. Other options like excretion, growth, and reproduction describe internal biological maintenance or life cycle stages rather than immediate environmental interaction.
✅ Answer: (D)

Question 2

Which organism has been named using the binomial system?

(A) Brown seaweed
(B) Polar bear
(C) Red fox
(D) Vulpes vulpes

▶️ Answer/Explanation

The binomial system of nomenclature, developed by Carl Linnaeus, uses two Latin words to identify a species. The first word represents the genus (capitalized) and the second is the specific epithet (lowercase). While “Brown seaweed,” “Polar bear,” and “Red fox” are common names used in everyday language, they vary by region and language. Vulpes vulpes is the formal scientific name for the red fox, following the universal rules of biological classification. Scientific names are typically italicized to distinguish them from regular text.

✅ Answer: (D)

Question 3

Which list contains only arthropods?

(A) amphibians, insects, myriapods
(B) arachnids, crustaceans, myriapods
(C) crustaceans, insects, fish
(D) insects, myriapods, reptiles

▶️ Answer/Explanation

Arthropods are invertebrates characterized by having an exoskeleton, a segmented body, and paired jointed appendages. The phylum Arthropoda is primarily divided into four main groups: insects, arachnids, crustaceans, and myriapods.

Option (B) is correct because all three groups listed—arachnids (spiders, scorpions), crustaceans (crabs, lobsters), and myriapods (centipedes, millipedes)—are true arthropods. The other options are incorrect because they include vertebrates: amphibians (A), fish (C), and reptiles (D), which possess internal backbones and do not belong to the arthropod phylum.
✅ Answer: (B)

Question 4

The diagram shows a plant cell.

Which letter identifies where photosynthesis occurs in the cell?

▶️ Answer/Explanation

Photosynthesis is the process by which plants convert light energy into chemical energy, and it specifically takes place within the chloroplasts. In the provided diagram, Label $D$ points to these small, oval-shaped organelles containing chlorophyll. Label $A$ identifies the rigid cell wall, Label $B$ indicates the cell membrane, and Label $C$ represents the nucleus, which houses genetic material. Since chloroplasts are the exclusive site for light absorption and glucose production, Label $D$ is the correct identification. This organelle is essential for the survival of autotrophic organisms.
✅ Answer: (D)

Question 5

The table shows the magnifications and image lengths of three specimens when seen with a light microscope.

What is the order of increasing actual lengths of the specimens, from smallest to largest?

(A) $X \rightarrow Y \rightarrow Z$
(B) $X \rightarrow Z \rightarrow Y$
(C) $Y \rightarrow X \rightarrow Z$
(D) $Z \rightarrow Y \rightarrow X$

▶️ Answer/Explanation

To find the actual length, use the formula: $\text{Actual Length} = \frac{\text{Image Length}}{\text{Magnification}}$.
* For specimen $X$: $\frac{0.20}{50} = 0.0040$ $mm$.
* For specimen $Y$: $\frac{0.50}{150} \approx 0.0033$ $mm$.
* For specimen $Z$: $\frac{0.40}{250} = 0.0016$ $mm$.
Comparing these values, the smallest is $Z$ ($0.0016$ $mm$), followed by $Y$ ($0.0033$ $mm$), and the largest is $X$ ($0.0040$ $mm$).
Therefore, the order of increasing actual length is $Z \rightarrow Y \rightarrow X$.
✅ Answer: (D)

Question 6

The diagram represents two liquids separated by a partially permeable membrane.

Which statement describes how the molecules will move by osmosis?

(A) Molecules of the dissolved substance move from left to right.
(B) Molecules of the dissolved substance move from right to left.
(C) Overall, water molecules move from left to right.
(D) Overall, water molecules move from right to left.

▶️ Answer/Explanation

Osmosis is the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane. In the diagram, the left side has a higher concentration of water molecules and no dissolved substance, while the right side contains large solute molecules that cannot pass through the membrane pores. Consequently, there is a net flow of water from the left to the right to balance the concentration gradient. Options A and B are incorrect because the large “dissolved substance” molecules are too big to pass through the membrane. Therefore, the water molecules move “overall” to the right.
✅ Answer: (C)

Question 7

Small molecules are used to synthesise large food molecules.

Which statement is correct?

(A) Amino acids are the basic units of carbohydrates.
(B) Fatty acids are the basic units of glycogen.
(C) Glycerol is a basic unit of oils.
(D) Simple sugar is the basic unit of protein.

▶️ Answer/Explanation

Large biological molecules (polymers) are built from smaller subunits (monomers). Oils and fats belong to the lipid family, which are typically composed of glycerol and fatty acids. Statement (A) is incorrect because amino acids build proteins, not carbohydrates. Statement (B) is incorrect because glycogen is a polysaccharide made of glucose units. Statement (D) is incorrect because simple sugars (monosaccharides) build carbohydrates, while proteins are made of amino acids. Since glycerol is one of the two primary components required to synthesize a lipid like oil, statement (C) is the only accurate description of a building block relationship.

✅ Answer: (C)

Question 8

A student used biuret reagent to test milk for the presence of protein.

The milk tested positive for protein.

Which colour did the sample change to?

(A) blue
(B) blue-black
(C) brick red
(D) purple

▶️ Answer/Explanation

The Biuret test is used to detect the presence of peptide bonds in a substance. The reagent itself is naturally blue due to the presence of copper(II) sulfate. When proteins are present, the copper ions form a complex with the peptide bonds in an alkaline environment, resulting in a distinct color change to purple or violet. Other options represent different food tests: blue-black is the positive result for starch using iodine, while brick red is the positive result for reducing sugars using Benedict’s solution. Since milk contains proteins like casein and whey, the result is positive.
✅ Answer: (D)

Question 9

Which substances are used for photosynthesis?

(A) carbon dioxide and glucose
(B) carbon dioxide and water
(C) glucose and oxygen
(D) glucose and water

▶️ Answer/Explanation

Photosynthesis is the process by which green plants and certain other organisms transform light energy into chemical energy. During this process, plants take in carbon dioxide ($CO_{2}$) from the air and water ($H_{2}O$) from the soil. These serve as the raw materials (reactants) which, in the presence of sunlight and chlorophyll, are converted into glucose ($C_{6}H_{12}O_{6}$) and oxygen ($O_{2}$).

The balanced chemical equation for this process is:

$$6CO_{2} + 6H_{2}O \xrightarrow{\text{light}} C_{6}H_{12}O_{6} + 6O_{2}$$

Since the question asks for the substances used (the reactants), carbon dioxide and water are the correct choices. Glucose and oxygen are the products, not the starting materials.
✅ Answer: (B)

Question 10

What happens when a plant lacks magnesium ions?

▶️ Answer/Explanation

Magnesium ions are a fundamental component of the chlorophyll molecule, acting as the central atom in its structure. When a plant suffers from a magnesium deficiency, it cannot synthesize enough chlorophyll, leading to a decrease in production. Since chlorophyll is the pigment responsible for the green color of plants, its absence causes the leaves to lose their green pigment and turn yellow, a condition known as chlorosis. This usually starts between the veins of older leaves. Therefore, the correct observation is a decrease in chlorophyll and yellowing of leaves.

✅ Answer: (B)

Question 11

The diagram shows part of a cross-section of a leaf.

What are tissues $1$, $2$ and $3$?

▶️ Answer/Explanation

Tissue $1$ represents the upper epidermis, a thin, transparent outer layer of cells that protects the leaf. Tissue $2$ is the palisade mesophyll, characterized by tall, cylindrical cells packed with chloroplasts to maximize light absorption for photosynthesis. Tissue $3$ is the spongy mesophyll, which contains irregularly shaped cells with large air spaces between them to facilitate gas exchange. By identifying these layers from the top of the leaf downwards, we can see that they follow the sequence of epidermis, palisade, and then spongy tissue. This matches the arrangement shown in the cross-section diagram.
✅ Answer: (A)

Question 12

A diet contains a lot of plant material, but no meat.

Which dietary component is unlikely to be deficient in this diet?

(A) fat
(B) fibre
(C) protein
(D) vitamin D

▶️ Answer/Explanation

Dietary fibre (roughage) is composed of indigestible carbohydrates, primarily cellulose, which is found in the cell walls of plants. Since the diet is described as containing “a lot of plant material,” it will inherently be very high in fibre. In contrast, meat contains no fibre at all. While plants can provide fats and proteins, they are often found in lower concentrations compared to animal sources, and Vitamin D is notoriously difficult to obtain from a strictly plant-based diet without fortified foods or sunlight. Therefore, fibre is the component that is least likely to be lacking.
✅ Answer: (B)

Question 13

Which two parts of the mouth are teeth embedded in?

(A) cement and pulp
(B) enamel and dentine
(C) gums and bone
(D) pulp and bone

▶️ Answer/Explanation

Teeth are securely anchored in the mouth through a combination of soft and hard tissues. The root of the tooth is seated within sockets in the jawbone (maxilla or mandible), providing structural stability for chewing. Overlying this bone is the gingiva, commonly known as the gums, which provides a protective seal around the neck of the tooth. While structures like cementum help attach the tooth to the bone via ligaments, the “embedding” refers to the surrounding environment of the gums and bone. Options A, B, and D are incorrect because they include internal components of the tooth itself, such as enamel, dentine, or pulp.

✅ Answer: (C)

Question 14

The diagram shows part of the human digestive system.

Where does amylase act on food?

▶️ Answer/Explanation

Amylase is a digestive enzyme that breaks down starch into simpler sugars like maltose. While it is first secreted by salivary glands in the mouth, it also acts in the small intestine (specifically the duodenum). In the provided diagram, label C points to the duodenum, where pancreatic amylase (produced by the pancreas, label A) is secreted to continue the chemical digestion of carbohydrates. Label D is the stomach, which is too acidic for amylase to function, and label B is the anus, where no digestion occurs.
✅ Answer: (C)

Question 15

What is absorbed in the colon and the small intestine?

▶️ Answer/Explanation

The small intestine is the primary site for the absorption of nutrients (digested food) such as glucose and amino acids, but it also absorbs a significant volume of water via osmosis. The colon (large intestine) primarily functions to reabsorb water and mineral salts from the remaining undigested food material to form solid feces. While the colon does not absorb nutrients, both organs are involved in water transport. Therefore, the small intestine absorbs both digested food and water, while the colon focuses on water.
✅ Answer: (D)

Question 16

The diagram shows the movement of water molecules from a plant leaf to its environment. Two processes have been numbered.

Which row identifies the numbered processes?

▶️ Answer/Explanation

The diagram illustrates the pathway of water loss from a leaf, known as transpiration. Process $1$ occurs when liquid water on the damp surfaces of mesophyll cells turns into water vapor in the air spaces; this phase change is evaporation. Process $2$ shows the movement of that water vapor from the high concentration inside the leaf’s air spaces to the lower concentration in the external atmosphere through the stomata. This net movement of gas molecules down a concentration gradient is diffusion. Therefore, the sequence matches row B.
✅ Answer: (B)

Question 17

The diagram shows a simplified circulatory system in humans.

Which organ represents the pump in this circulatory system?

▶️ Answer/Explanation

In the human double circulatory system, the heart acts as the central pump that drives blood through two main circuits. In this schematic, Organ B represents the heart because it is the intersection point where blood is received from the lungs (Organ A) and pumped out to the rest of the body (Organs C and D).

Following the arrows, we see that blood flows from B to the lungs for oxygenation and then returns to B. From there, B pumps the oxygenated blood to the systemic organs (C and D) before it returns to B again to repeat the cycle. This central positioning and the direction of flow confirm that B is the muscular pump maintaining circulation.
✅ Answer: (B)

Question 18

Which blood vessel transports blood from the lungs to the heart?

(A) aorta
(B) pulmonary artery
(C) pulmonary vein
(D) vena cava

▶️ Answer/Explanation

In the circulatory system, “pulmonary” refers to the lungs. While most veins carry deoxygenated blood, the pulmonary vein is unique because it carries freshly oxygenated blood from the lungs back to the left atrium of the heart. Conversely, the pulmonary artery carries deoxygenated blood away from the heart to the lungs. The aorta and vena cava are part of the systemic circulation, dealing with the rest of the body rather than the gas exchange interface in the lungs. Therefore, the vessel returning to the heart from the lungs is the pulmonary vein.
✅ Answer: (C)

Question 19

How can the spread of disease be prevented?

(A) leaving food uncovered
(B) only washing hands after meals
(C) using the same equipment to prepare raw and cooked food
(D) washing hands before and after handling raw food

▶️ Answer/Explanation

Preventing the spread of disease requires breaking the chain of infection, particularly in food preparation. Raw foods, especially meats, often harbor pathogens like Salmonella or E. coli. Washing hands before handling food ensures you don’t introduce germs to the meal, while washing them after prevents the transfer of bacteria from the raw ingredients to other surfaces or your mouth. Options A, B, and C actually increase the risk of “cross-contamination,” which is a primary cause of foodborne illnesses. Regular hygiene and separating raw and cooked materials are the most effective preventative measures.
✅ Answer: (D)

Question 20

Which substance can be used to test for carbon dioxide?

(A) DCPIP
(B) ethanol
(C) iodine solution
(D) limewater

▶️ Answer/Explanation

Limewater, which is a solution of calcium hydroxide $Ca(OH)_2$, is the standard reagent used to detect the presence of carbon dioxide $CO_2$. When $CO_2$ is bubbled through limewater, it reacts to form calcium carbonate $CaCO_3$, an insoluble white precipitate that turns the solution “milky” or cloudy. In contrast, DCPIP is used to test for Vitamin C, ethanol is used in the emulsion test for lipids, and iodine solution is the specific indicator for starch. Therefore, only limewater provides a visible diagnostic result for carbon dioxide gas.

✅ Answer: (D)

Question 21

Which statement is a correct comparison of aerobic respiration and anaerobic respiration in yeast?

(A) Only aerobic respiration produces carbon dioxide.
(B) Only anaerobic respiration produces alcohol.
(C) They both produce water.
(D) They both use the reactants glucose and oxygen.

▶️ Answer/Explanation

To find the correct comparison, we must look at the products of both processes in yeast. Aerobic respiration completely breaks down glucose into $CO_{2}$ and $H_{2}O$, while anaerobic respiration (fermentation) in yeast produces ethanol (alcohol) and $CO_{2}$.

Statement A is incorrect because both types of respiration produce carbon dioxide ($CO_{2}$).
Statement B is correct; ethanol is a specific byproduct of anaerobic fermentation and is not produced during aerobic respiration.
Statement C is incorrect because anaerobic respiration in yeast does not produce water ($H_{2}O$).
Statement D is incorrect because anaerobic respiration occurs in the absence of oxygen ($O_{2}$).

✅ Answer: (B)

Question 22

The diagram shows some of the organs involved in excretion.

Which label is a ureter?

▶️ Answer/Explanation

In the human excretory system, the ureter is the muscular tube that transports urine from the kidney to the urinary bladder. Label D points specifically to one of these long tubes. Labels A and B represent the renal blood vessels (renal artery and renal vein) which supply and drain the kidneys. Label C points to the urethra, which is the final tube that carries urine out of the body from the bladder. Therefore, the tube connecting the kidney to the lower reservoir is the ureter.
✅ Answer: (D)

Question 23

A person touches a hot object which stimulates structure $P$ in the skin. This causes an electrical impulse to be sent through structure $Q$ to the central nervous system.

Which row identifies structures $P$ and $Q$?

▶️ Answer/Explanation

Structure $P$ is a receptor because its role is to detect a stimulus (the hot object) and convert it into an electrical signal. Structure $Q$ is a sensory neurone because it carries that electrical impulse away from the receptor toward the central nervous system (CNS). In a reflex arc, effectors and motor neurones only come into play after the CNS has processed the signal to coordinate a response, such as moving the hand away. Therefore, row D correctly identifies the roles of both structures based on the direction of the impulse.

✅ Answer: (D)

Question 24

The diagram shows the position of two glands in the body.

Which row states the hormones produced by these glands?

▶️ Answer/Explanation

To solve this, we must first identify the glands based on their anatomical positions. Gland $1$ is located on top of the kidneys, identifying it as the adrenal gland, which secretes the hormone adrenaline. Gland $2$ is situated in the curve of the duodenum, identifying it as the pancreas, which secretes the hormone insulin (as well as glucagon). While the pancreas also produces digestive enzymes like amylase and lipase, the question specifically asks for hormones. Amylase and lipase are enzymes, not hormones, which eliminates options B, C, and D.
✅ Answer: (A)

Question 25

A seedling was placed in a horizontal position.

Which diagram shows the expected gravitropic responses in the seedling?

▶️ Answer/Explanation

Gravitropism (or geotropism) is a growth response to gravity mediated by the distribution of auxins. When a seedling is horizontal, auxins accumulate on the lower side of both the root and the shoot. In the shoot, a high concentration of auxin stimulates cell elongation, causing the lower side to grow faster and the shoot to curve upward (negative gravitropism). Conversely, in the root, a high concentration of auxin inhibits cell elongation. This causes the upper side of the root to grow faster than the lower side, resulting in the root curving downward (positive gravitropism). Therefore, diagram C correctly illustrates the shoot growing away from gravity and the root growing toward it.
✅ Answer: (C)

Question 26

The diagram shows a sperm cell.

Which part contains digestive enzymes?

▶️ Answer/Explanation

The correct part is D, which represents the acrosome. The acrosome is a cap-like structure located at the very front of the sperm’s head. It contains specialized digestive enzymes, such as hyaluronidase and acrosin, which are essential for fertilization. These enzymes break down the protective outer layers of the egg cell (the corona radiata and zona pellucida), allowing the sperm to penetrate and deliver its genetic material.

For context: * A is the flagellum (tail) used for swimming. * B is the midpiece containing mitochondria for energy. * C is the nucleus containing the haploid set of chromosomes.
✅ Answer: (D)

Question 27

Which secondary sexual characteristic is associated with testosterone?

(A) breast development
(B) facial hair growth
(C) start of the menstrual cycle
(D) widening of hips

▶️ Answer/Explanation

Testosterone is the primary male sex hormone produced in the testes. During puberty, increased levels of testosterone trigger the development of secondary sexual characteristics in males. These include the deepening of the voice, increased muscle mass, and the stimulation of hair follicles leading to facial hair growth. In contrast, options (A), (C), and (D) are characteristics primarily driven by female sex hormones like estrogen and progesterone. Therefore, facial hair growth is the only characteristic listed that is directly associated with testosterone.

✅ Answer: (B)

Question 28

The diagram shows a human menstrual cycle.

What are represented by $X$, $Y$ and $Z$?

▶️ Answer/Explanation

The menstrual cycle begins on Day $0$ with menstruation, where the uterine lining breaks down and is shed; this corresponds to position $X$. Around the midpoint of a $28$-day cycle, typically Day $14$, ovulation occurs when an ovary releases a mature egg, matching position $Y$. Following ovulation, the hormone progesterone maintains a thick, vascularized uterine lining to prepare for potential implantation. This maintenance phase is occurring at Day $21$, represented by position $Z$. Comparing these events to the table, option A correctly aligns each label with its biological process.
✅ Answer: (A)

Question 29

What is an alternative form of a gene called?

(A) allele
(B) chromosome
(C) genotype
(D) protein

▶️ Answer/Explanation

An allele is one of two or more versions of a DNA sequence at a given genomic location. While a gene determines a specific trait (like eye color), the alleles are the variations of that gene (like blue vs. brown). Organisms inherit one allele from each parent for every gene, and the combination of these alleles determines the specific phenotype.

Other options like “chromosome” refer to the structure that carries the genes, while “genotype” describes the entire genetic makeup. Since “allele” specifically refers to the alternative versions of a single gene, it is the correct term.
✅ Answer: (A)

Question 30

Cystic fibrosis is an inherited condition that occurs when an individual is homozygous for the recessive allele.

If both parents are heterozygous for this characteristic, what is the probability that their first child will have cystic fibrosis?

(A) $0\%$
(B) $25\%$
(C) $50\%$
(D) $100\%$

▶️ Answer/Explanation

Cystic fibrosis is an autosomal recessive disorder. Let $F$ represent the dominant normal allele and $f$ represent the recessive cystic fibrosis allele. Since both parents are heterozygous, their genotypes are both $Ff$. When we cross $Ff \times Ff$ using a Punnett square, the resulting offspring genotypes are $FF$ (normal), $Ff$ (carrier), $Ff$ (carrier), and $ff$ (affected). Only the homozygous recessive genotype ($ff$) results in the condition. This occurs in $1$ out of $4$ possible combinations, which equates to a probability of $25\%$.
✅ Answer: (B)

Question 31

Which characteristic is an example of continuous variation?

(A) $ABO$ blood groups in humans
(B) body mass in cats
(C) seed colour in pea plants
(D) seed shape in pea plants

▶️ Answer/Explanation

Continuous variation refers to characteristics that show a complete range of values without distinct categories, often influenced by both multiple genes and environmental factors. Body mass in cats is a prime example because weight can be any value within a range and is affected by diet and exercise. In contrast, the other options represent discontinuous variation, where traits fall into distinct, separate categories. For instance, blood groups are strictly $A$, $B$, $AB$, or $O$, and pea seeds are either specific colors or shapes defined by clear genetic inheritance. Since body mass lacks these “steps” or fixed categories, it is classified as continuous.
✅ Answer: (B)

Question 32

The photograph shows the butterfly Caligo martia.

Which feature is an adaptation to prevent predation?

(A) large wings to fly slowly
(B) long antennae to detect flower nectar
(C) spots on the wings that look like large eyes
(D) the pattern on the wings that makes the butterfly easier to see

▶️ Answer/Explanation

The correct feature is the presence of large eye-like spots on the wings, a biological phenomenon known as mimicry. These “eyespots” serve as a startle defense mechanism by imitating the appearance of a much larger animal, such as an owl. When a predator approaches, the sudden flash of these spots can cause the predator to hesitate or flee out of fear of being attacked themselves. This morphological adaptation significantly increases the butterfly’s chances of survival. Other options, like flying slowly or being easier to see, would actually increase the risk of predation rather than prevent it.
✅ Answer: (C)

Question 33

What is the principal source of energy input to biological systems?

(A) kinetic
(B) photosynthesis
(C) respiration
(D) the Sun

▶️ Answer/Explanation

The primary source of energy for almost all life on Earth is the Sun. Through the process of photosynthesis, producers (like plants and algae) capture solar energy and convert it into chemical energy stored in glucose. This energy then flows through the food chain as consumers eat the plants or other animals. While photosynthesis and respiration are vital biological processes, they are mechanisms of energy conversion and release rather than the original input source. Without the continuous stream of light energy from the Sun, biological systems would eventually run out of the fuel needed to sustain life.

✅ Correct Answer: (D) the Sun

Question 34

The diagram shows the flow of energy in a food chain.

Which organism is the producer in the food chain?

▶️ Answer/Explanation

In a food chain diagram, the arrows represent the flow of energy. A producer is the starting point of energy flow, usually capturing energy from the sun. In this diagram, energy flows from organism C to organism B, and then to organism A, identifying C as the producer. Additionally, the arrows pointing from A, B, and C toward D indicate that D is likely a decomposer, receiving energy from all other levels when they die or produce waste. Since C is the only organism that provides energy to the consumers without receiving it from another organism in the chain, it must be the producer.
✅ Answer: (C)

Question 35

The diagram shows part of the carbon cycle.

Which two numbered arrows represent respiration?

(A) $1$ and $2$
(B) $1$ and $3$
(C) $2$ and $4$
(D) $3$ and $4$

▶️ Answer/Explanation

Respiration is the process by which living organisms release energy from food, resulting in the release of $CO_2$ back into the atmosphere. In the diagram, arrow $2$ shows carbon moving from plants to the atmosphere, while arrow $4$ shows carbon moving from animals to the atmosphere. Both represent the release of $CO_2$ via respiration. Conversely, arrow $1$ represents photosynthesis (taking $CO_2$ in), and arrow $3$ represents feeding (transferring carbon through the food chain). Therefore, the arrows pointing toward the atmospheric carbon dioxide from living organisms identify the respiratory phase.
✅ Answer: (C)

Question 36

The diagram shows a population curve.

Which letter identifies the lag phase in this sigmoid curve?

▶️ Answer/Explanation

The lag phase is the initial period of a sigmoid growth curve where the population size is small and the rate of increase is very slow as organisms adapt to their new environment. In the provided diagram, this corresponds to point A. Following this is the log (exponential) phase at B, the stationary phase at C where birth and death rates equalize, and finally the decline phase at D. Because the population is just beginning to establish itself at the start of the timeline, point A is the only correct identification of the lag phase.
✅ Answer: (A)

Question 37

The graph shows the percentage of species lost, in three different animal groups, due to different human activities during the last ten years.

Which activity has caused the highest percentage of species loss overall?

(A) habitat loss
(B) exploitation
(C) pollution
(D) other factors

▶️ Answer/Explanation

To determine the overall cause of the highest species loss, we must compare the bars across all three animal groups: mammals, reptiles and amphibians, and birds. In each group, the bar representing habitat loss (the darkest shaded bar) is significantly taller than the bars for exploitation, pollution, or other factors. For mammals and reptiles/amphibians, habitat loss accounts for approximately $48\%$ to $50\%$ of species lost, while for birds, it reaches nearly $50\%$. Since this category remains the dominant cause across every single group presented, it is the primary driver of species loss overall.
✅ Answer: (A)

Question 38

Why are bacteria useful in biotechnology and genetic modification?

1 They can make complex molecules.
2 They have a rapid reproduction rate.
3 They have cell walls.

(A) $1$, $2$ and $3$
(B) $1$ and $2$ only
(C) $1$ and $3$ only
(D) $2$ and $3$ only

▶️ Answer/Explanation

Bacteria are highly valued in biotechnology because they can be genetically engineered to synthesize complex molecules, such as human insulin, which would be difficult to produce chemically. Their rapid reproduction rate allows for the quick scaling of production, as populations can double in as little as $20$ minutes. While bacteria do possess cell walls, this structural feature is common to many organisms (like plants and fungi) and is not a specific reason why they are uniquely useful for genetic modification tasks. In fact, cell walls can sometimes act as a barrier that must be overcome to insert foreign DNA. Therefore, only statements $1$ and $2$ are correct justifications.
✅ Answer: (B)

Question 39

The graph shows how changing the temperature affects the rate of stain removal from clothes, using a biological washing powder.

What does the graph suggest about biological washing powders?

(A) Biological washing powders contain enzymes.
(B) Biological washing powders work best at all temperatures above $40$ °C.
(C) The optimum temperature for the reaction is between $10$ °C and $30$ °C.
(D) There is a directly proportional relationship between the temperature used and the rate at which stains are removed.

▶️ Answer/Explanation

The graph shows a characteristic bell-shaped curve typical of enzyme-controlled reactions. As temperature increases, the rate of reaction rises until it reaches an optimum temperature (around $40$ °C). Beyond this point, the rate drops sharply because the high temperatures cause the enzymes to denature, losing their functional shape. This specific pattern is a hallmark of biological catalysts, which confirms that the washing powder contains enzymes. Other options are incorrect because the rate decreases after $40$ °C, and the relationship is non-linear rather than directly proportional.
✅ Answer: (A)

Question 40

The flow chart shows some of the processes involved in making biofuel.

What are represented by $K$, $L$ and $M$ in the diagram?

▶️ Answer/Explanation

The process described is the production of bioethanol. First, plant biomass is processed to extract glucose ($K$), which serves as the substrate. Next, yeast ($L$) is added to perform anaerobic respiration (fermentation). During this biological process, the yeast breaks down the glucose to produce ethanol ($M$) and carbon dioxide. Since the goal is to create biofuel, ethanol is the specific product extracted at the end of the sequence.
✅ Answer: (B)