WAEC SSCE - Biology - 2020

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A semi-permeable membrane is a barrier that allows some substances to pass through, but not others. All living cells have semi-permeable membranes that regulate the exchange of substances between the cell and its environment. Out of the four options, the material that is not a living semi-permeable membrane is "sheet of cellophane". Cellophane is a synthetic, non-living material that is often used as a packaging material or for wrapping food. It does not have the ability to regulate the exchange of substances like a living semi-permeable membrane.

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The network of double membrane that conveys materials through the cytoplasm is called the Endoplasmic Reticulum (ER). The ER is an important organelle in the cell and is made up of a network of flattened, sac-like structures that are surrounded by two membranes. This double membrane system helps to transport materials, such as proteins and lipids, from one part of the cell to another. The ER also plays a role in maintaining the cell's shape and in controlling the levels of calcium ions in the cytoplasm. In summary, the ER is an important transport network in the cell that helps to maintain the cell's structure and regulate its functions.

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The theory of evolution by natural selection was proposed by Charles Darwin, an English naturalist, in his book "On the Origin of Species" published in 1859. Darwin's theory suggests that all species of organisms have descended over time from common ancestors through a process he called natural selection. In simple terms, Darwin's theory states that within a population, there is variation in traits that can be inherited. Some of these traits may give individuals an advantage in surviving and reproducing in their environment, while others may not. Individuals with advantageous traits are more likely to survive and pass those traits on to their offspring, while individuals with less advantageous traits are less likely to survive and reproduce. Over time, this process can lead to the evolution of new species as those with advantageous traits become more prevalent in the population. While other scientists, including Lamarck and Aristotle, had proposed ideas about how species could change over time, Darwin's theory of evolution by natural selection provided a comprehensive explanation supported by extensive evidence from his travels and observations of various species.

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The enzyme that catalyzes the replication of DNA molecules is called polymerase. DNA replication is the process by which a cell makes an exact copy of its DNA. Polymerase is responsible for attaching nucleotides (the building blocks of DNA) in the correct order to form a new strand of DNA. It reads the sequence of nucleotides on the template strand of DNA and adds complementary nucleotides to the new strand, following the base pairing rules (A pairs with T, and C pairs with G). This results in two identical copies of the original DNA molecule, each containing one original strand and one newly synthesized strand. Polymerase plays a crucial role in DNA replication, and without it, cells would not be able to divide and pass on their genetic information to their offspring.

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The position occupied by an organism in a food chain is called a trophic level. A food chain is a series of organisms that are connected by the transfer of energy and nutrients through eating and being eaten. Trophic levels refer to the different levels in the food chain where organisms get their energy from. For example, plants occupy the first trophic level because they are at the bottom of the food chain and produce their own energy through photosynthesis. Herbivores, which eat plants, occupy the second trophic level. Carnivores, which eat herbivores, occupy the third trophic level, and so on. Each trophic level is higher up the food chain and receives less energy from the previous level. In this way, the trophic level of an organism helps to describe its role in the food chain and the source of its energy.

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Measurements of height and weight of students in a class show continuous variation. Continuous variation refers to the variation in traits that can take any value within a range. In the case of height and weight, there is a wide range of values that students can have. Some students may be tall and thin, while others may be short and heavy. This continuous variation is due to the interaction of multiple genes and environmental factors that influence growth and development. The information provided in the question does not indicate whether shortness is more prevalent or if fatness is less prevalent. It only describes the type of variation observed in the measurements of height and weight of students. Therefore, we cannot conclude anything about the prevalence of shortness or fatness in the class based on the given information.

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The process that gave rise to the F1 generation in the diagram is cross-fertilization. This is because plant ! and plant B are different plants of the same species, and they were intentionally bred (crossed) by a human or other means to produce offspring with mixed characteristics, which are the F1 generation.

Cross-fertilization involves transferring pollen from one plant to another plant, which is different from self-fertilization where a plant can fertilize itself. Therefore, since the diagram shows two different plants being bred to produce the F1 generation, the process that gave rise to the F1 generation is cross-fertilization.

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Based on the information provided in the table, we can see that there are no antelopes in habitat W, but there are 51 antelopes in habitat Y. On the other hand, there are no lions in habitat Y, but there are 6 lions in habitat W. This suggests that lions are the predators in this ecosystem, while antelopes are the prey. In other words, lions hunt and eat antelopes to survive. Therefore, the correct answer is "is the predator while the antelope is the prey".

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The respiratory organ of a cockroach is the trachea. A trachea is a series of tubes that bring air into the body of an insect. The air enters the trachea and then travels to the tissues where it is used to provide oxygen to the cells. The trachea is a simple and efficient system that allows insects like the cockroach to breathe and get the oxygen they need to survive.

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The excretory product of some reptiles, birds and insects is uric acid. Uric acid is a waste product that is produced when the body breaks down food. Unlike mammals, which excrete waste products as urine, reptiles, birds and insects excrete waste products as uric acid. This is because they have a more efficient system for conserving water, which is important for species living in arid environments. The uric acid is solid and is excreted as white, crystalline deposits that can be seen in the feces of these animals. This type of excretion is also known as "dry excretion".

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Based on the provided diagram, the plant organ shown is a bulb. A bulb is a type of underground plant stem that stores food for the plant. It has a short stem with fleshy storage leaves or scales attached to it. The diagram shows a short stem with several fleshy storage leaves or scales arranged in a concentric manner, forming a bulb-like structure. This storage structure allows the plant to survive adverse environmental conditions by storing nutrients for future use. Therefore, the plant organ in the diagram is a bulb.

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Out of the given options, only sickle cell anemia can be inherited. Sickle cell anemia is a genetic disorder caused by a mutation in the gene that codes for hemoglobin, a protein found in red blood cells that carries oxygen. Individuals inherit two copies of this gene, one from each parent. When both copies of the gene are mutated, as in sickle cell anemia, the shape of the red blood cells changes, causing them to become stiff and curved instead of round and flexible. This can lead to a range of health problems, including anemia, organ damage, and increased risk of infection. In contrast, pneumonia, whooping cough, and malaria are infectious diseases caused by bacteria or parasites, and are not inherited. Pneumonia is an infection that inflames the air sacs in one or both lungs, while whooping cough is a highly contagious respiratory infection. Malaria is a disease caused by a parasite that is transmitted to humans through the bite of infected mosquitoes.

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The properties of the endocrine system are: 1. Secretion of hormones 2. Transportation by blood to target organs 3. Having a specific effect The property that is not included in the endocrine system is the release of secretion into ducts. Unlike exocrine glands that release their secretions into ducts, endocrine glands secrete hormones directly into the bloodstream. These hormones travel through the bloodstream to target organs where they bind to specific receptors and initiate a response. The endocrine system plays an important role in regulating various physiological processes in the body, such as metabolism, growth and development, and reproduction, among others.

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The reagent used in testing for carbon (IV) oxide is lime water. Lime water is a clear solution made by dissolving calcium hydroxide in water. When carbon (IV) oxide is bubbled through lime water, it turns milky white due to the formation of calcium carbonate. This reaction is a simple and easy way to detect the presence of carbon (IV) oxide in the air or in a gas sample.

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The function of the part labeled I is to receive the pollen grain. Part I, which is called the stigma, is the top part of the female reproductive structure of a flower called the pistil. The stigma is covered with a sticky substance that allows it to capture pollen grains that are transferred from the male reproductive structure, the anther, either by wind, insects or other means. Once the pollen grain has landed on the stigma, it can then germinate and produce a pollen tube that grows down through the style, which is the narrow part of the pistil connecting the stigma to the ovary. This allows the male gametes in the pollen to reach the ovules in the ovary, leading to double fertilization and the production of seeds. Therefore, the main function of the stigma is to receive the pollen grain and provide the site for germination and subsequent fertilization. It does not directly attract pollinators, although some flowers may have other structures, such as bright colors or strong scents, to help attract pollinators to the flower.

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Conservation of natural resources does not threaten the survival of species. In fact, it helps to protect and preserve different species and their habitats, ensuring their survival for future generations. Conservation efforts aim to maintain a balance between human use and protection of natural resources, so that both people and the environment can benefit. By preserving the beauty of nature, conservation also attracts tourists, adding to the local economy. Overall, conservation of natural resources is an important step towards a sustainable future for both people and the planet.

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Continuous variation is a type of variation that exhibits a wide range from one extreme to the other. This means that there is a smooth and gradual change in the characteristics of a particular trait from one individual to the next. For example, height in a population can be considered a continuous variation, as there is no clear cutoff between short and tall individuals, but rather a gradual change from one to the other.

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Parenchyma tissue does not provide support in flowering plants. Parenchyma cells are the most common type of plant cells, and they are involved in various functions such as photosynthesis, storage, and secretion. They are usually loosely packed with thin cell walls, which make them flexible and able to adapt to different shapes and sizes. Collenchyma tissue, on the other hand, is a type of plant tissue that provides mechanical support to the plant. Collenchyma cells have thickened cell walls that are capable of stretching and elongating as the plant grows, which helps to support the plant. Xylem and phloem are also plant tissues that provide support to the plant. Xylem is responsible for transporting water and minerals from the roots to the rest of the plant, while phloem is responsible for transporting sugars and other organic molecules from the leaves to other parts of the plant. Therefore, the correct answer is Parenchyma, which does not provide support in flowering plants. It is mainly involved in metabolic processes and does not have the necessary structural features to support the plant.

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The cell is the basic unit of life because it is the smallest unit of living matter that can carry out all the functions necessary for life. All living things are made up of cells, and each cell has certain components that allow it to carry out its functions. The two most important components of a cell are the nucleus and the cytoplasm. The nucleus contains the cell's genetic material, which controls the cell's functions and determines what the cell will become. The cytoplasm is the jelly-like substance that fills the cell and contains all the other components necessary for the cell's function, such as organelles like mitochondria and ribosomes. Some cells, such as plant cells, also have a cell wall that surrounds the cell membrane and gives the cell structure and protection. Additionally, plant cells may also have a large central vacuole that stores water, nutrients, and waste products. Therefore, the correct option is "cytoplasm and nucleus" as these two components are essential for a cell to function and carry out its basic processes.

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Based on the table, it appears that habitat W is a pond. This is because there are aquatic organisms such as plankton, water flea, and tilapia present in the habitat, but no antelope, lions, or grass, which would be more commonly found in a terrestrial environment like a desert or rainforest.

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The set-up can measure comparatively the rate of transpiration of a single shoot of a plant under different experimental conditions. Transpiration is the process of water movement through a plant and its evaporation from aerial parts, primarily from the leaves. In the illustration, the plant shoot is enclosed in a container, and the amount of water lost from the shoot is measured. By changing the experimental conditions, such as the temperature or humidity, and measuring the transpiration rate under each set of conditions, the set-up can be used to compare the rates of transpiration under different conditions for a single shoot of a plant.

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Oxygen comes out of the stomata during photosynthesis through the process known as diffusion. Diffusion is a natural process where molecules move from areas of high concentration to areas of low concentration until they are evenly spread out. In photosynthesis, oxygen is produced in the leaves by the plant cells during the light-dependent reactions. The oxygen diffuses out of the plant cell into the surrounding air through the stomata, which are small pores on the surface of the leaf. The stomata open and close to allow for gas exchange, and when they are open, the oxygen can easily diffuse out into the atmosphere. Diffusion does not require energy from the plant and occurs naturally due to the concentration gradient.

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The part of the central nervous system that controls unconscious actions in humans is the cerebellum. The cerebellum is located at the back of the brain and is responsible for coordinating and regulating unconscious movements and balance, such as walking, running, and standing upright. It receives information from the sensory systems in the body, as well as from other parts of the brain, and uses this information to fine-tune and adjust movements. While the cerebrum is responsible for conscious actions and decision-making, the cerebellum is in charge of many of our automatic, involuntary movements. For example, you don't have to consciously think about how to move your legs while walking, but your cerebellum is constantly working to make sure your movements are coordinated and balanced.

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The part of the mammalian kidney that stores urine is the bladder. The bladder is a muscular sac that is located in the lower part of the abdomen. It receives urine from the kidneys through two tubes called ureters and stores it until it is expelled from the body through another tube called the urethra during urination. The capsule is a thin layer that covers the kidney, the medulla is the innermost part of the kidney, and the pelvis is a funnel-shaped structure that collects urine from the kidney and connects it to the ureters.

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The prohibition on producing bags made from natural leopard skin is an attempt to conserve wildlife. Leopards are animals that live in the wild, and their population is threatened by hunting and poaching. By prohibiting the production of bags made from leopard skin, the government or authority is trying to prevent the killing of leopards and protect their population. This conservation effort is necessary to maintain the balance of the ecosystem and prevent the extinction of species.

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The first stable product of photosynthesis is glucose. Photosynthesis is the process by which plants use sunlight, carbon dioxide, and water to produce glucose, which is a type of sugar that plants use as a source of energy. During the process of photosynthesis, light energy is used to convert carbon dioxide and water into glucose and oxygen. Glucose is considered the first stable product of photosynthesis because it is the first molecule produced that is able to be stored and used by the plant for energy. Starch, fructose, and sucrose are all types of sugars that can be produced from glucose, but they are not the first stable product of photosynthesis. Glucose is the primary molecule produced during photosynthesis, and it is then converted into other forms of sugar for storage or transport within the plant.

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The statement that is correct is "The number present in a specie is constant." Chromosomes are structures made of DNA molecules that carry genetic information in living organisms. Each species has a specific number of chromosomes, which is constant and unique to that species. For example, humans have 23 pairs of chromosomes, while dogs have 39 pairs of chromosomes. Chromosomes come in different shapes and sizes, and their appearance can differ between species, so the statement that "All the chromosomes of a species are the same shape" is incorrect. Chromosomes are not neatly arranged in the cytoplasm, but instead, they are found in the nucleus of a cell. The nucleus is surrounded by a nuclear membrane that separates the chromosomes from the cytoplasm. Finally, chromosomes do not bear ribosomes on their outer membranes. Ribosomes are tiny structures in the cytoplasm that are responsible for synthesizing proteins. They are not located on the outer membranes of chromosomes.

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The insect that destroys grains is the weevil. Weevils are a type of beetle that lay their eggs inside grains such as rice, wheat, and corn. When the eggs hatch, the larvae feed on the inside of the grain, causing damage and reducing the quality of the grain. Weevils are common pests in grain storage facilities, and can also infest grains in households if they are not properly stored in airtight containers. So, if you see small holes in your stored grains, or notice a fine powder in the package, there is a chance that they have been infested by weevils.

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The depletion of the ozone layer can result in the earth's surface receiving more ultraviolet (UV) rays. Ozone is a gas that exists naturally in the Earth's upper atmosphere, and it helps to filter out harmful UV rays from the sun. When human-made chemicals like chlorofluorocarbons (CFCs) are released into the atmosphere, they can react with ozone molecules, causing the ozone layer to become thinner. As the ozone layer becomes thinner, more UV rays can reach the Earth's surface. UV rays are a type of radiation that can be harmful to living organisms. They can cause skin cancer, cataracts, and other health problems in humans, as well as damage to crops and other plants. In summary, the depletion of the ozone layer can result in the earth's surface receiving more harmful ultraviolet rays, which can have negative effects on human health and the environment.

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(a) How the human ear carries out its function of balancing

Balance is controlled by the inner ear, using the three semicircular canals together with the utricle and saccule.

• The three semicircular canals are set at right angles to one another, so they detect movement of the head in all three planes.
• Each canal is filled with fluid (endolymph) and has a swollen base, the ampulla, which contains sensory hair cells.
• When the head moves or turns in any direction, the endolymph moves and bends the sensory hair cells in the ampulla, setting up nerve impulses.
• The utricle and saccule contain tiny chalk grains (otoliths) that respond to the position of the head with respect to gravity.
• The impulses travel along the auditory (vestibular) nerve to the brain (cerebellum), which interprets them and relays impulses to the body muscles so that posture is adjusted and balance is maintained.

(b)(i) Drawing of the structure of the human ear (8 cm to 10 cm long, fully labelled)

(b)(ii) Structure of the middle ear in humans

The middle ear is an air-filled chamber in the skull.

• It is separated from the outer ear by the ear drum (tympanic membrane / tympanum).
• It contains three small bones, the ear ossicles: the malleus (hammer), the incus (anvil) and the stapes (stirrup), linked in a chain.
• The malleus is attached to the tympanic membrane, each bone is in direct contact with the next, and the stapes fits into the oval window (fenestra ovalis) of the inner ear. In this way the ossicles transmit and amplify the sound vibrations from the ear drum to the oval window.
• The Eustachian tube arises at the base of the middle ear and links it to the back of the throat (pharynx), equalising the air pressure on both sides of the ear drum.

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(a)(i) Independent assortment of genes

Independent assortment is the principle that during the formation of gametes (in meiosis), the two alleles of one gene separate into gametes independently of the alleles of another gene carried on a different pair of chromosomes. As a result, the members of one pair of contrasting characters are distributed to the gametes randomly and independently of the members of another pair, producing new combinations of characters.

(a)(ii) Why blood group O exists only in the homozygous form

Blood group O is produced by the allele i, which is recessive to both I^A and I^B. A recessive character can only be expressed when the allele is present in a double (homozygous) dose. Therefore group O can only appear as ii. Blood groups A and B, however, are produced by the dominant alleles I^A and I^B. A dominant allele shows its effect whether it is paired with an identical allele or with the recessive i. Hence group A can be I^AI^A (homozygous) or I^Ai (heterozygous), and group B can be I^BI^B (homozygous) or I^Bi (heterozygous).

(b) Classes of vertebrates in evolutionary order with examples

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(a) Types of fertilisation

• (i) External fertilisation: the fusion of the male and female gametes takes place outside the body of the female, usually in water. The female lays her eggs and the male sheds sperm over them in the surrounding water.
• (ii) Internal fertilisation: the fusion of the male and female gametes takes place inside the body of the female, the sperm being deposited into her reproductive tract during mating.

(b) Two groups of animals for each type

• External fertilisation: bony fishes and amphibians (frogs/toads).
• Internal fertilisation: mammals and birds (also reptiles).

(c)(i) Three effects on the foetus if the placenta detaches from the uterine wall

• The foetus is cut off from its supply of food and oxygen, so it may suffocate and die.
• Waste products (carbon dioxide, urea) cannot be removed from the foetus, so they accumulate and poison it.
• It causes bleeding (haemorrhage) and may lead to miscarriage or premature birth of the foetus.

(c)(ii) Three other features of the uterus useful for foetal development

• A thick, muscular wall that protects the foetus and contracts to expel it at birth.
• A rich supply of blood vessels in the uterine lining that supplies food and oxygen and removes wastes.
• The amnion containing amniotic fluid that surrounds and cushions the foetus against shock (and the umbilical cord linking foetus to placenta).

(d) How the activities of organisms bring about dynamic equilibrium in a habitat

In a stable habitat, producers, consumers and decomposers interact so that materials and numbers stay roughly balanced. Green plants make food and release oxygen while animals consume food and release carbon dioxide, so the gases are kept balanced through photosynthesis and respiration. Predators feed on prey and so control the number of prey, while the food supply controls the number of predators, keeping populations steady. Decomposers break down dead matter and return mineral nutrients to the soil for plants to reuse. These continuous, opposing activities balance one another, so the habitat stays in a steady state called dynamic equilibrium.

(e) Four problems of organisms in the intertidal zone of a marine habitat

• Danger of drying out (desiccation) when the tide goes out and they are exposed to air and sun.
• Strong wave action that can wash them away or break them off the rocks.
• Wide changes in temperature and salinity as pools warm up, cool down or are diluted by rain.
• Exposure to predators (birds at low tide, fish at high tide) and changing oxygen supply.

(f) Why the following are necessary for germination

• (i) Moisture (water): water is absorbed to soften the seed coat, activate the enzymes, and dissolve and transport the stored food to the growing embryo.
• (ii) Viable seeds: the seed must be alive with a healthy, living embryo; a dead (non-viable) embryo cannot divide and grow, so no germination can occur.

(g) Why light energy is a limiting factor in food production by autotrophs

Autotrophs (green plants) make food by photosynthesis, and light provides the energy for the process. When light is dim or absent, the rate of photosynthesis is low no matter how much carbon dioxide and water are available, so the amount of food made is restricted. Because a shortage of light holds back (limits) the rate of food production, light energy is described as a limiting factor.

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(a) Completed table

(b) Biological basis of food preservation

(i) Salting

Adding salt creates a very concentrated (hypertonic) medium around the food. Water is drawn out of the micro-organisms by osmosis, dehydrating them so they cannot grow, multiply or spoil the food. The dry, salty condition also removes the water that microbes need.

(ii) Irradiation

Food is exposed to ionising radiation (such as gamma rays). The radiation destroys or damages the cells and DNA of bacteria, fungi and other micro-organisms (and inactivates enzymes), killing them so they can no longer cause spoilage.

(iii) Smoking

Smoking dries the food by heat, removing water that micro-organisms need. In addition, the smoke deposits antimicrobial chemicals (such as phenols and creosote) on the food surface which inhibit the growth of bacteria and fungi.

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(a)(i) What is a deficiency disease?

A deficiency disease is a disease that results from the lack or inadequate supply of a particular nutrient (such as a vitamin or a mineral element) in the diet over a period of time.

(a)(ii) Five nutrient deficiency diseases and their remedies

(Night blindness from lack of vitamin A, corrected by eating carrots, red palm oil and green vegetables, is an acceptable alternative.)

(b) Chemical tests

(i) Test for starch in a tuber of yam

1. Place a small piece of the yam on a white tile.
2. Add two or three drops of iodine solution to it.
3. Observation: the yam turns blue-black.
4. Inference: starch is present.

(ii) Test for glucose in orange fruit

1. Put some orange juice into a test tube.
2. Add an equal volume of Benedict's (or Fehling's) solution.
3. Heat the mixture in a water bath (boil).
4. Observation: the blue colour changes through green and yellow to a brick-red precipitate.
5. Inference: a reducing sugar (glucose) is present.