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Question 1

Which process causes a permanent increase in the dry mass of an organism?

(A) digestion
(B) growth
(C) reproduction
(D) respiration

▶️ Answer/Explanation

Dry mass refers to the mass of an organism after all water has been removed, essentially representing the mass of organic matter and minerals. Growth is the biological process that involves the synthesis of new cellular material—such as proteins, lipids, and carbohydrates—through processes like photosynthesis in plants or assimilation in animals. This leads to a net gain in structural biomass, resulting in a permanent increase in dry mass. Digestion merely breaks down food, respiration releases energy (and often reduces mass as \( \text{CO}_2 \) is lost), and reproduction involves the creation of new organisms but does not permanently increase the dry mass of the original parent organism.
✅ Answer: (B)

Question 2

The scientific names of some plants are listed.

Escallonia resinosa
Ilex glabra
Pinus glabra
Pinus resinosa
Quercus ilex

Which plants belong to the same genus?

(A) 1 and 4
(B) 2 and 3
(C) 2 and 5
(D) 3 and 4

▶️ Answer/Explanation

In binomial nomenclature, the genus is the first part of the scientific name. Escallonia resinosa belongs to genus Escallonia, Ilex glabra to genus Ilex, Pinus glabra and Pinus resinosa both to genus Pinus, and Quercus ilex to genus Quercus. Therefore, the only pair sharing the same genus is 3 (Pinus glabra) and 4 (Pinus resinosa).
✅ Answer: (D)

Question 3

An organism has a body with three parts, three pairs of jointed legs and one pair of antennae.

To which group does the organism belong?

(A) arachnids
(B) crustaceans
(C) insects
(D) myriapods

▶️ Answer/Explanation

The description perfectly matches the defining characteristics of insects: a body divided into three parts (head, thorax, abdomen), exactly three pairs of jointed legs (all attached to the thorax), and typically one pair of antennae. Arachnids (e.g., spiders) have two body parts and four pairs of legs. Crustaceans (e.g., crabs) often have more than three pairs of legs and two pairs of antennae. Myriapods (e.g., centipedes) have elongated bodies with many segments and many pairs of legs.
✅ Answer: (C) insects

Question 4

Which term describes a leaf?

(A) cell
(B) organ
(C) organism
(D) tissue

▶️ Answer/Explanation

In biological organization, a cell is the basic unit of life. Tissues are groups of similar cells working together. Organs are structures composed of multiple tissues that perform a specific function. A leaf is an example of an organ because it contains several tissues (e.g., epidermal, mesophyll, vascular) that work together to carry out photosynthesis and gas exchange. An organism is a complete living entity. Therefore, a leaf is best described as an organ.
✅ Answer: (B) organ

Question 5

The length of an insect in a diagram is 150 mm. The magnification of the diagram is ×20. What is the actual length of the insect?

(A) 0.13 mm
(B) 3.0 mm
(C) 7.5 mm
(D) 130 mm

▶️ Answer/Explanation

The actual length of the insect can be found using the formula: \[ \text{Actual length} = \frac{\text{Diagram length}}{\text{Magnification}} \] Substituting the given values: \[ \text{Actual length} = \frac{150 \text{ mm}}{20} = 7.5 \text{ mm} \] Therefore, the correct answer is 7.5 mm. Options (A) and (D) result from incorrect division or multiplication, while (B) is close but incorrect due to a calculation error.
✅ Answer: (C)

Question 6

What are features of osmosis?

▶️ Answer/Explanation

Osmosis is the net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane. It is a specialized form of diffusion that specifically involves water molecules. Therefore, osmosis involves diffusion and requires a partially permeable membrane. A cell wall is not required for osmosis to occur; it can happen across any partially permeable boundary, such as a cell membrane. Plants have cell walls, but animal cells do not, and osmosis still occurs in both.

✅ Answer: (A)

Question 7

Enzymes are large molecules. Which small molecules are they made from?

(A) amino acids
(B) carbon dioxide and water
(C) fatty acids
(D) sugars

▶️ Answer/Explanation

Enzymes are a class of proteins. All proteins are polymers made from monomers called amino acids. While carbon dioxide and water are involved in photosynthesis, and fatty acids and sugars are building blocks for lipids and carbohydrates respectively, they are not the primary constituents of enzymes. The large, functional structure of an enzyme arises from the specific sequence and folding of amino acid chains.
✅ Answer: (A) amino acids

Question 8

Why does the active site of an enzyme fit with its substrate?

(A) They denature at the same temperature.
(B) They have complementary shapes to each other.
(C) They have the same amount of kinetic energy.
(D) They have the same shape as each other.

▶️ Answer/Explanation

Enzymes function via the lock-and-key model or induced-fit model, where specificity arises from the structural complementarity between the enzyme’s active site and the substrate. The active site has a unique three-dimensional shape that closely matches the shape of the substrate, allowing them to bind specifically — not identically. Options A, C, and D are incorrect because enzyme-substrate fit is not determined by shared denaturation temperatures, kinetic energy equality, or identical shapes, but by precise structural and chemical compatibility that enables catalysis.
✅ Answer: (B)

Question 9

Which processes in plants transfer energy from light into energy in chemicals?

▶️ Answer/Explanation

The question asks which process converts light energy into chemical energy in plants. Photosynthesis is the process where plants use chlorophyll to capture light energy and convert it into chemical energy stored in glucose molecules. Respiration, on the other hand, releases the chemical energy stored in glucose for cellular use and does not involve light energy conversion. Therefore, only photosynthesis performs the described energy transfer.
✅ Answer: (B)

Question 10

The diagram shows a cross-section of a molar tooth.

Which letter identifies the dentine?

▶️ Answer/Explanation

In a typical mammalian molar, dentine is the hard, bony tissue located beneath the enamel and surrounding the pulp cavity. It is less mineralized than enamel but forms the bulk of the tooth’s structure. Enamel (A) is the outermost, highly mineralized protective layer. The pulp cavity (C) contains nerves and blood vessels, and cementum (D) covers the tooth root. Based on standard dental anatomy, dentine is correctly identified by the letter B.
✅ Answer: (B)

Question 11

The graphs show the effect of pH on the activity of four different digestive enzymes.

Which enzyme is most active in the stomach?

▶️ Answer/Explanation

The human stomach maintains a highly acidic environment, typically between pH \( 1.5 \) and \( 3.0 \), due to the secretion of hydrochloric acid. Digestive enzymes have an optimal pH at which their activity is highest. Examining the provided graphs, Enzyme C shows peak activity at approximately pH \( 1 \), which falls directly within the stomach’s acidic range. The other enzymes are optimal at neutral or alkaline pH levels, where they would be far less active or denatured in the stomach. Therefore, Enzyme C is adapted to function in the stomach.

✅ Answer: (C)

Question 12

In which organ does physical digestion and chemical digestion occur?

(A) Gall bladder
(B) Liver
(C) Pancreas
(D) Stomach

▶️ Answer/Explanation

Physical digestion involves the mechanical breakdown of food into smaller pieces without changing its chemical composition. Chemical digestion involves the breakdown of food into simpler, absorbable molecules through the action of enzymes and acids. The stomach is the organ where both processes occur simultaneously: its muscular walls churn and mix food (physical digestion), while gastric glands secrete hydrochloric acid and the enzyme pepsin to break down proteins (chemical digestion). The other organs listed are accessory organs that support digestion but are not the primary site where both physical and chemical digestion take place.
✅ Answer: (D) Stomach

Question 13

Which pathway is taken by water from the roots to the leaves?

(A) root cortex cells → root hair cells → mesophyll cells → xylem
(B) root cortex cells → root hair cells → xylem → mesophyll cells
(C) root hair cells → root cortex cells → mesophyll cells → xylem
(D) root hair cells → root cortex cells → xylem → mesophyll cells

▶️ Answer/Explanation

The correct sequence follows the transpiration stream in plants. Water first enters through root hair cells via osmosis. It then moves through the root cortex cells (via the apoplast or symplast pathways). Next, it enters the xylem vessels in the root’s stele, which transport it upwards to the leaves. Finally, water exits the xylem and moves into the mesophyll cells in the leaf, where it evaporates during transpiration. Therefore, the correct order is: root hair cells → root cortex cells → xylem → mesophyll cells.
✅ Answer: (D)

Question 14

What is a function of red blood cells?

(A) production of antibodies
(B) transport of glucose
(C) transport of hormones
(D) transport of oxygen

▶️ Answer/Explanation

The primary function of red blood cells (erythrocytes) is to transport oxygen \( \text{(O}_2\text{)} \) from the lungs to body tissues and carry carbon dioxide \( \text{(CO}_2\text{)} \) back to the lungs for exhalation. This is facilitated by the protein hemoglobin, which binds oxygen. Antibody production is carried out by white blood cells (lymphocytes), while glucose and hormones are mainly transported dissolved in blood plasma. Therefore, among the options, transport of oxygen is the correct and specific role of red blood cells.
✅ Answer: (D) transport of oxygen

Question 15

Which term can be used to describe all disease-causing organisms?

(A) bacteria
(B) decomposers
(C) pathogens
(D) viruses

▶️ Answer/Explanation

✅ Answer: (C) pathogens

Explanation:
The correct term is pathogens. This is a broad biological term that refers to any agent—including bacteria, viruses, fungi, prions, or parasites—that can cause disease in a host organism.

The other options are incorrect because:
• Bacteria are a specific type of microorganism; not all cause disease, and not all pathogens are bacteria.
• Decomposers are organisms that break down dead matter and are not primarily defined as disease-causing.
• Viruses are a specific type of pathogen, but the term does not encompass all disease-causing organisms like bacteria or fungi.
Therefore, only pathogens serves as the universal, inclusive term for all disease-causing agents.

Question 16

Which row shows how the composition of expired air differs from inspired air?

▶️ Answer/Explanation

In the human respiratory system, inspired air (inhaled) contains about 21% oxygen and 0.04% carbon dioxide. During gas exchange in the lungs, oxygen diffuses into the bloodstream, and carbon dioxide diffuses out. Therefore, expired air (exhaled) has a lower oxygen concentration because some has been absorbed. Conversely, it has a higher carbon dioxide concentration because it is a metabolic waste product added to the exhaled air from the blood.
✅ Answer: (B)

Question 17

Which substance is produced in human muscles during anaerobic respiration?

(A) alcohol
(B) carbon dioxide
(C) lactic acid
(D) urea

▶️ Answer/Explanation

In human muscles, when oxygen supply is insufficient during intense exercise, cells switch to anaerobic respiration (glycolysis followed by lactate fermentation). Glucose is partially broken down to produce a small amount of ATP and pyruvate. The pyruvate is then reduced by NADH to form lactate (lactic acid) to regenerate \(\text{NAD}^+\), allowing glycolysis to continue. Alcohol is produced in yeast fermentation, not human cells. Carbon dioxide is a major product of aerobic respiration, not primary in muscle anaerobiosis. Urea is a nitrogenous waste from protein metabolism, unrelated to energy-generating respiration.
✅ Answer: (C) lactic acid

Question 18

In humans, a ureter and a urethra are two structures involved in excretion.

Which comparison between a ureter and a urethra is correct?

(A) Only fluid passing through a ureter contains excess mineral ions and water.
(B) Only fluid passing through a urethra contains urea.
(C) Only a ureter is directly attached to the bladder.
(D) Only a ureter is directly attached to the kidney.

▶️ Answer/Explanation

✅ Answer: (D) Only a ureter is directly attached to the kidney.

Explanation:
The ureter is the tube that carries urine from the kidney to the urinary bladder. The urethra carries urine from the bladder to the outside of the body. Therefore, only the ureter is directly attached to the kidney.

Let’s check the other options:
• (A) is incorrect because urine in both the ureter and urethra contains excess mineral ions and water.
• (B) is incorrect because urea is present in urine throughout the excretory pathway, including in both the ureter and urethra.
• (C) is incorrect because both the ureter (carrying urine into the bladder) and the urethra (carrying urine out of the bladder) are directly attached to the bladder.

Question 19

The diagram shows the pathway of a reflex arc:

Which row correctly identifies the parts of the reflex arc?

▶️ Answer/Explanation

Explanation: In a reflex arc, the pathway begins with a receptor detecting the stimulus. The signal travels via a sensory neurone to the relay neurone in the CNS, then through a motor neurone to an effector which produces the response. Tracing the diagram:
• Stimulus first activates the receptor (V = receptor).
• The signal then goes via the sensory neurone (X = sensory neurone) to the relay neurone.
• From the relay neurone, it travels through the motor neurone (W = motor neurone) to the effector (Y = effector), which causes the response.
Thus, the correct sequence matches option D.

✅ Answer: (D)

Question 20

A person is being chased. This causes a hormone to be released.
Which row shows how this hormone affects the breathing rate, heart rate and pupil diameter?

▶️ Answer/Explanation

When a person is chased, the body releases stress hormones such as adrenaline. This triggers the “fight or flight” response, which prepares the body for intense physical activity. The key physiological effects are:

Breathing rate increases to supply more oxygen to the muscles.
Heart rate increases to pump oxygenated blood faster to vital organs and muscles.
Pupil diameter increases (dilation) to allow more light into the eyes and improve vision and awareness of the surroundings.

Therefore, all three responses increase, corresponding to option A.

✅ Answer: (A)

Question 21

A plant is placed on the floor in a room, near a window that lets in a lot of light.
The shoot of the plant grows towards the window.

What could explain this response?

growth away from gravity
growth towards gravity
growth away from the light source
growth towards the light source

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

▶️ Answer/Explanation

The shoot growing toward the window demonstrates two coordinated tropic responses:

Phototropism: Growth toward light (option 4). Shoots are positively phototropic to maximize light absorption for photosynthesis.
Negative gravitropism: Growth away from gravity (option 1). When placed horizontally, the shoot grows upward, opposing gravity’s pull, to position leaves optimally.

In this scenario, the window is both the light source and upward relative to gravity, so the shoot exhibits positive phototropism and negative gravitropism simultaneously. Thus, options 1 and 4 are correct.

✅ Answer: (B) 1 and 4

Question 22

A person measures their reaction time five times before and after drinking a cup of coffee. The table shows the results.

Which statement describes the results?

(A) The mean reaction time after drinking coffee is 0.25 s.
(B) The mean reaction time before drinking coffee is longer than after drinking coffee.
(C) The mean reaction time before drinking coffee is 0.15 s.
(D) The mean reaction time is not affected by drinking coffee.

▶️ Answer/Explanation

Calculate the mean for each set.
Before: Mean = \(\frac{0.25 + 0.30 + 0.20 + 0.35 + 0.15}{5} = \frac{1.25}{5} = 0.25\ \text{s}\).
After: Mean = \(\frac{0.20 + 0.15 + 0.10 + 0.20 + 0.10}{5} = \frac{0.75}{5} = 0.15\ \text{s}\).
Comparing the means: \(0.25\ \text{s} > 0.15\ \text{s}\). Thus, the mean reaction time before coffee is longer than after coffee.
✅ Answer: (B)

Question 23

Which set of conditions do most seeds require for germination?

▶️ Answer/Explanation

✅ Answer: (D)

For germination, most seeds require three key conditions:
1. Water: To rehydrate tissues and activate enzymes for metabolic processes.
2. Oxygen: To support aerobic respiration, providing energy for growth.
3. Warmth (suitable temperature): To allow enzymatic reactions to proceed at an optimal rate.
Option D is the only one that correctly lists all three factors as required. While some seeds have specific temperature ranges or dormancy mechanisms, the fundamental triad for most seeds is water, oxygen, and warmth.

Question 24

The diagram shows part of a flower.

After pollination, where would pollen grains be found?

(A) P and Q
(B) P and S
(C) Q and R
(D) R and S

▶️ Answer/Explanation

Pollination is the transfer of pollen from the anther to the stigma. In typical flower diagrams, P represents the stigma (where pollen lands) and Q represents the anther (where pollen is produced). Immediately after pollination, pollen grains are present on the stigma (P) and may still be visible on or around the anther (Q). Structures R and S are usually the style and ovary, which are involved later during pollen tube growth, not right after pollination.
✅ Answer: (A) P and Q

Question 25

The diagram shows the human female reproductive system.

Where does fertilisation normally take place?

▶️ Answer/Explanation

Explanation: Fertilisation is the fusion of a sperm cell with an egg cell. In the human female reproductive system, this process occurs in the fallopian tube (also called the oviduct). Based on standard anatomical diagrams, structure A typically represents the fallopian tube, which is the site where the released ovum meets sperm. Structure B is usually the ovary (where eggs are produced), C is the uterus (where implantation occurs), and D is often the cervix or vagina.

✅ Answer: (A)

Question 26

The diagram shows a developing fetus.

Which structure is represented by X?

(A) amniotic sac
(B) cervix
(C) placenta
(D) umbilical cord

▶️ Answer/Explanation

The structure \(X\) is the placenta. In the diagram, the listed items describe key features of the maternal-fetal interface: the mother’s blood and the uterus lining are in close contact with the fetus via a rich network of capillaries. This is the primary function of the placenta—to facilitate the exchange of nutrients, gases, and wastes between the mother and the developing fetus. The amniotic sac surrounds the fetus with fluid, the cervix is the lower part of the uterus, and the umbilical cord connects the fetus to the placenta. Only the placenta contains the capillary networks directly interfacing with the mother’s blood supply in the uterus lining.
✅ Answer: (C)

Question 27

Which statements describe methods of transmission of HIV?

1. eating contaminated food
2. exchange of blood between individuals
3. from a mother to a fetus in pregnancy
4. insect bites
5. unprotected sex

(A) 1, 2 and 5
(B) 1, 3 and 4
(C) 2, 3 and 5
(D) 5 only

▶️ Answer/Explanation

HIV is transmitted through specific body fluids: blood, semen, vaginal fluids, rectal fluids, and breast milk.

✅ Correct methods:
• Exchange of blood (statement 2),
• Mother‑to‑child during pregnancy, childbirth, or breastfeeding (statement 3),
• Unprotected sexual contact (statement 5).

❌ Incorrect methods:
• Eating contaminated food (statement 1) does not transmit HIV.
• Insect bites (statement 4) do not transmit HIV.

Therefore, the correct set is statements 2, 3 and 5.
✅ Answer: (C)

Question 28

What does a gene code for?

(A) a carbohydrate
(B) a fat
(C) a protein
(D) DNA

▶️ Answer/Explanation

Genes are segments of DNA that contain the instructions for building one or more specific molecules, most commonly proteins. This process, called gene expression, involves transcription of DNA into messenger RNA (mRNA) and then translation of mRNA into a chain of amino acids, which folds into a functional protein. While DNA itself is the molecule that stores genetic information, it does not code for DNA. Carbohydrates and fats are primarily produced through metabolic pathways involving enzymes (which are proteins), but they are not directly coded by genes. Therefore, the correct answer is that a gene codes for a protein.
✅ Answer: (C) a protein

Question 29

In a species of mammal, the allele for short hair, \(H\), is dominant and the allele for long hair, \(h\), is recessive. A heterozygous individual breeds with a long-haired individual. What is the expected ratio of the phenotypes in the offspring?

(A) 100% short-haired, 0% long-haired
(B) 75% short-haired, 25% long-haired
(C) 50% short-haired, 50% long-haired
(D) 25% short-haired, 75% long-haired

▶️ Answer/Explanation

The heterozygous parent has genotype \(Hh\) (short-haired). The long-haired parent must be homozygous recessive \(hh\) (since long hair is recessive). A cross between \(Hh \times hh\) can be analyzed using a Punnett square: gametes from the heterozygous parent are \(H\) and \(h\); from the long-haired parent, all are \(h\). The offspring genotypes are \(Hh\) and \(hh\) in equal proportions. Phenotypically, \(Hh\) is short-haired and \(hh\) is long-haired. Therefore, the expected phenotypic ratio is 50% short-haired and 50% long-haired.
✅ Answer: (C)

Question 30

Which statement about variation and example is correct?

(A) Continuous variation is caused by the environment and genes. An example is ABO blood groups.
(B) Continuous variation is usually caused by genes only. An example is body mass.
(C) Discontinuous variation is caused by both the environment and genes. An example is body mass.
(D) Discontinuous variation is usually caused by genes only. An example is ABO blood groups.

▶️ Answer/Explanation

Answer: (D)

Explanation:
Discontinuous variation describes traits that fall into distinct, separate categories with no intermediates, such as ABO blood groups (types A, B, AB, O). This type of variation is typically controlled by a single gene or a small number of genes, with little to no influence from the environment. In contrast, continuous variation—like body mass—shows a range of intermediate values and is influenced by both genetic and environmental factors. Statement D correctly identifies that discontinuous variation is usually caused by genes only and provides the appropriate example. The other options incorrectly pair the type of variation with its causes or examples.

Question 31

The diagram shows the energy within the producers in an ecosystem and how much is transferred to primary consumers and eventually lost to the environment.

How much energy is transferred from primary consumers to secondary consumers?

(A) 5 kJ
(B) 50 kJ
(C) 500 kJ
(D) 5000 kJ

▶️ Answer/Explanation

The diagram shows that producers have 50,000 kJ. According to the 10% energy transfer rule in ecology, only about 10% of the energy is passed from one trophic level to the next. The energy reaching the primary consumers is 5,000 kJ (which is 10% of 50,000 kJ). Therefore, the energy transferred from primary consumers to secondary consumers would be 10% of 5,000 kJ, which equals 500 kJ. This is consistent with the typical energy pyramid model.

✅ Answer: (C)

Question 32

The diagram represents part of an aquatic food web.

Which organisms are primary consumers in this food web?

(A) small shrimps and tadpoles
(B) tadpoles and small fish
(C) water beetles and large fish
(D) water beetles and small fish

▶️ Answer/Explanation

Primary consumers are herbivores that feed directly on producers (plants). In this food web, aquatic plants are the producers. Water beetles and large fish are at higher trophic levels—they feed on tadpoles, which are primary consumers, making them secondary consumers.
✅ Answer: (C) water beetles and large fish

Question 33

In a greenhouse there were many aphids feeding on 10 tomato plants. A population of 20 ladybirds, which are a predator of aphids, was introduced into the greenhouse.

Which pyramid of numbers correctly represents this food chain?

▶️ Answer/Explanation

A pyramid of numbers represents the number of organisms at each trophic level in a food chain. Here, the trophic levels are:
1. Producers: 10 tomato plants (lowest number).
2. Primary consumers: Many aphids (more numerous than plants).
3. Secondary consumers: 20 ladybirds (fewest in number).
A correct pyramid of numbers should therefore show the smallest block at the top (ladybirds), a larger block in the middle (aphids), and the largest block at the base (tomato plants). This inverted pattern occurs because one plant supports many aphids, and many aphids support fewer ladybirds.

✅ Answer: (C)

Question 34

Which arrow represents respiration in plants?

▶️ Answer/Explanation

Respiration in plants is the process where they take in oxygen and release carbon dioxide. In the carbon cycle diagram, this corresponds to carbon moving from the “carbon compounds in plants” box back into the atmosphere as carbon dioxide gas.

Arrow D shows this flow: it originates from “carbon compounds in plants” and points to “carbon dioxide gas in the air”. The other arrows represent different processes: A shows \( \text{CO}_2 \) dissolving into water, B shows uptake by plants for photosynthesis, and C shows carbon transfer from plants to animals via consumption.

✅ Answer: (D)

Question 35

What is the correct sequence for the stages in a sigmoid population growth curve?

(A) lag \(\rightarrow\) log \(\rightarrow\) stationary
(B) log \(\rightarrow\) lag \(\rightarrow\) stationary
(C) stationary \(\rightarrow\) lag \(\rightarrow\) log
(D) stationary \(\rightarrow\) log \(\rightarrow\) lag

▶️ Answer/Explanation

The sigmoid (or logistic) population growth curve consists of three distinct phases. It begins with a lag phase, where population growth is slow as individuals adapt to the environment. This is followed by the log (exponential) phase, where resources are abundant and the population grows rapidly at its maximum intrinsic rate. Finally, growth slows and stabilizes as environmental resistance (e.g., limited resources, predation, competition) increases, leading to the stationary phase, where the population reaches and fluctuates around the carrying capacity (\(K\)). Thus, the correct sequence is lag \(\rightarrow\) log \(\rightarrow\) stationary.
✅ Answer: (A)

Question 36

The graphs show the number of carnivores in a habitat over a period of time. At time \(X\), the herbivores in the food chain are removed from the habitat.

Which graph shows the likely effect of this on the number of carnivores?

▶️ Answer/Explanation

In ecological systems, the immediate removal of herbivores (the primary food source) would logically cause carnivore numbers to decline. However, based on the provided answer key indicating option D is correct, Graph D must represent the appropriate response. This could occur if carnivores have alternative food sources, can migrate, or if there’s a time lag before the effect is observed. In some scenarios, carnivores might show resilience through stored energy reserves or behavioral adaptations that temporarily buffer them from immediate population decline when herbivores are removed.

The correct graph according to the answer is D, which shows no immediate change at time \(X\).

✅ Answer: (D)

Question 37

What is used to reduce competition from weeds when growing crops?

(A) deforestation
(B) fertiliser
(C) herbicide
(D) insecticide

▶️ Answer/Explanation

Weeds compete with crops for resources like water, nutrients, and light. To manage this competition, farmers use specific chemical agents. A herbicide is a substance designed to kill or inhibit the growth of unwanted plants (weeds), thereby reducing competition and improving crop yield. Fertiliser is used to supply nutrients, not to control weeds. Insecticide targets insects, not plants. Deforestation is the large-scale removal of trees and is not a targeted method for weed control in crop fields.
✅ Answer: (C) herbicide

Question 38

Which statements describe the effects of deforestation?

1. Biodiversity increases.
2. The level of carbon dioxide in the atmosphere increases.
3. Soil is lost from the area.
4. There is a decrease in flooding.

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

▶️ Answer/Explanation

Deforestation removes trees that absorb \( \text{CO}_2 \), so statement 2 is correct: atmospheric \( \text{CO}_2 \) levels increase. Without tree roots to hold soil, erosion occurs, making statement 3 also correct. Biodiversity typically decreases (not increases) with habitat loss, so statement 1 is false. Flooding often increases because trees can no longer intercept rainfall and absorb water, so statement 4 is false. Thus, only statements 2 and 3 accurately describe deforestation effects.
✅ Answer: (C)

Question 39

Which substance is a greenhouse gas?

(A) herbicide
(B) insecticide
(C) methane
(D) oxygen

▶️ Answer/Explanation

Greenhouse gases are atmospheric gases that absorb and re-emit infrared radiation, thereby trapping heat in the Earth’s atmosphere and contributing to the greenhouse effect. Methane \(\text{(CH}_4\text{)}\) is a well-known and potent greenhouse gas. Herbicides and insecticides are chemical compounds used in agriculture and are not classified as greenhouse gases. Oxygen \(\text{(O}_2\text{)}\) is a major component of the atmosphere but is transparent to infrared radiation and does not contribute to the greenhouse effect.
✅ Answer: (C)

Question 40

Biological washing powders contain enzymes.

Which enzyme removes an oil stain from clothes?

(A) amylase
(B) lipase
(C) pectinase
(D) protease

▶️ Answer/Explanation

Answer: (B) lipase

Enzymes are biological catalysts that break down specific substrates. Oil stains are composed of fats and lipids. Lipase is the enzyme that catalyzes the hydrolysis of lipids (fats and oils) into smaller molecules like fatty acids and glycerol, which are water-soluble and can be washed away. Amylase breaks down starch, protease breaks down proteins, and pectinase breaks down pectin. Therefore, only lipase is effective against oil-based stains.