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CSEC Human and Social Biology study materials
CSEC Human and Social Biology study resources

CSEC Human and Social Biology practice questions

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Question 1Organisms and Metabolism

Which molecule is the main immediate source of energy for cellular processes in living organisms?

  1. DNA
  2. Starch
  3. ATP Correct answer.
  4. Glucose

Explanation

ATP is the universal energy currency of the cell; energy released from the breakdown of food molecules is transferred to ATP, which then supplies energy for processes such as active transport and muscle contraction. Starch and glucose are energy stores or fuels that must first be respired to release usable energy.

Question 2Organisms and Metabolism

A student breathes onto a cool glass slide and a mist forms. Which process explains the appearance of the mist?

  1. Condensation of water vapour in the exhaled air Correct answer.
  2. Osmosis of water into the glass
  3. Evaporation of water from the glass surface
  4. Diffusion of oxygen out of the air

Explanation

Exhaled air is saturated with water vapour, and when it meets the cooler glass the vapour loses energy and changes into tiny liquid droplets, forming a mist. This change of state from gas to liquid is condensation, not evaporation or osmosis.

Question 3Organisms and Metabolism

Which structure in a flowering plant is the main site of photosynthesis?

  1. Root hair cell
  2. Xylem vessel
  3. Palisade mesophyll cell Correct answer.
  4. Guard cell

Explanation

Palisade mesophyll cells lie near the upper surface of the leaf, contain many chloroplasts, and receive light and carbon dioxide, making them the principal photosynthetic cells. Root hair cells lack chloroplasts and xylem vessels are dead transport tubes.

Question 4Organisms and Metabolism

Which word equation summarises aerobic respiration?

  1. glucose → alcohol + carbon dioxide
  2. glucose → lactic acid
  3. carbon dioxide + water → glucose + oxygen
  4. glucose + oxygen → carbon dioxide + water Correct answer.

Explanation

Aerobic respiration uses oxygen to break down glucose completely, releasing carbon dioxide and water and transferring a large amount of energy to ATP. The reverse equation describes photosynthesis, while the others describe anaerobic pathways.

Question 5Organisms and Metabolism

Which type of tooth is adapted for tearing and cutting food?

  1. Incisor
  2. Molar
  3. Premolar
  4. Canine Correct answer.

Explanation

Canines are pointed teeth with a single cusp, adapted for gripping and tearing food such as meat. Incisors are chisel-shaped for biting, while premolars and molars have broad surfaces for crushing and grinding.

Question 6Organisms and Metabolism

Which blood vessel carries oxygenated blood away from the heart to the body tissues?

  1. Pulmonary vein
  2. Vena cava
  3. Aorta Correct answer.
  4. Pulmonary artery

Explanation

The aorta is the large artery leaving the left ventricle, carrying oxygenated blood at high pressure to the body. The pulmonary artery carries deoxygenated blood to the lungs, and the vena cava returns deoxygenated blood to the heart.

Question 7Organisms and Metabolism

Which component of blood is mainly responsible for transporting oxygen?

  1. Plasma
  2. White blood cells
  3. Platelets
  4. Red blood cells Correct answer.

Explanation

Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues where oxygen concentration is low. Plasma carries dissolved substances but only a small fraction of the oxygen.

Question 8Organisms and Metabolism

Which process allows a single-celled organism such as Amoeba to obtain oxygen directly from its surroundings?

  1. Active transport through gills
  2. Diffusion across the body surface Correct answer.
  3. Mass flow through tracheae
  4. Osmosis through a root hair

Explanation

Amoeba has a large surface area relative to its volume and a short diffusion distance, so oxygen diffuses directly across its cell membrane into the cytoplasm. Gills, tracheae and root hairs are structures of other organisms.

Question 9Organisms and Metabolism

Which enzyme digests starch into maltose?

  1. Lipase
  2. Protease
  3. Catalase
  4. Amylase Correct answer.

Explanation

Amylase breaks the glycosidic bonds in starch to produce maltose, and it acts in the mouth and small intestine. Lipase digests fats, protease digests proteins, and catalase breaks down hydrogen peroxide.

Question 10Organisms and Metabolism

An athlete runs a 400 m race and afterwards complains of cramp in the leg muscles. Which substance most likely accumulates in the muscles during the race?

  1. Carbon dioxide
  2. Urea
  3. Lactic acid Correct answer.
  4. Ethanol

Explanation

During vigorous exercise oxygen supply may be insufficient, so muscles respire glucose anaerobically, producing lactic acid, which builds up and contributes to cramp and fatigue. Ethanol is produced in yeast, and urea is formed in the liver from excess amino acids.

Question 11Organisms and Metabolism

A plant is kept in darkness for two days. Which change is most likely to occur in its leaves?

  1. The rate of photosynthesis will increase
  2. The rate of transpiration will increase sharply
  3. The starch stored in the leaves will decrease Correct answer.
  4. The amount of chlorophyll will double

Explanation

Without light, photosynthesis stops, so no new glucose is made and stored starch is broken down and used for respiration. Chlorophyll is not produced faster in darkness, and transpiration depends mainly on stomatal opening and environmental conditions.

Question 12Organisms and Metabolism

Which feature of the small intestine increases the absorption of digested food?

  1. Presence of hydrochloric acid in its lumen
  2. Presence of villi on its inner surface Correct answer.
  3. Presence of bile stored in its lining
  4. Presence of a thick, smooth muscular wall

Explanation

Villi are finger-like projections of the intestinal lining that greatly increase the surface area for absorption and contain a rich blood supply to carry away absorbed nutrients. The muscular wall aids movement, not absorption; hydrochloric acid acts in the stomach; bile is stored in the gall bladder.

Question 13Organisms and Metabolism

A person's diet lacks iron. Which symptom is most likely to develop?

  1. Rickets caused by weak bones
  2. Goitre caused by an enlarged thyroid
  3. Anaemia caused by reduced haemoglobin Correct answer.
  4. Scurvy caused by reduced collagen

Explanation

Iron is needed to make haemoglobin in red blood cells, so a deficiency reduces haemoglobin and causes anaemia, with tiredness and pallor. Scurvy results from vitamin C deficiency, rickets from vitamin D or calcium deficiency, and goitre from iodine deficiency.

Question 14Organisms and Metabolism

Which statement best explains why the rate of transpiration increases when the surrounding air is dry?

  1. Xylem vessels contract in dry conditions
  2. A steep water vapour gradient forms between the leaf and the air Correct answer.
  3. Water molecules become larger in dry air
  4. The stomata close to conserve water

Explanation

When the air is dry, the water vapour concentration outside the leaf is low, so a steep diffusion gradient exists between the moist air spaces inside the leaf and the external air, and water vapour diffuses out faster. Stomatal closure would reduce transpiration, and the other statements are physically incorrect.

Question 15Organisms and Metabolism

Which part of the nervous system controls involuntary activities such as heart rate and peristalsis?

  1. Autonomic nervous system Correct answer.
  2. Cerebrum
  3. Spinal cord
  4. Somatic nervous system

Explanation

The autonomic nervous system supplies smooth muscle, cardiac muscle and glands, regulating involuntary activities such as heartbeat, digestion and gland secretion. The somatic system controls voluntary skeletal muscle, while the cerebrum and spinal cord are parts of the central nervous system.

Question 16Organisms and Metabolism

A gardener applies a fertiliser containing nitrate ions to a plant. Which effect is expected?

  1. Increased uptake of oxygen through the roots
  2. Increased synthesis of amino acids and proteins Correct answer.
  3. Increased formation of chlorophyll only
  4. Increased absorption of water through root hairs

Explanation

Nitrate ions supply nitrogen, which is needed to make amino acids and hence proteins for growth. Magnesium rather than nitrate is the mineral central to chlorophyll, and water uptake is driven by osmosis, not by nitrate supply.

Question 17Organisms and Metabolism

Which sequence correctly describes the pathway of a nerve impulse in a simple reflex action?

  1. Receptor → sensory neurone → relay neurone → motor neurone → effector Correct answer.
  2. Effector → sensory neurone → relay neurone → motor neurone → receptor
  3. Receptor → motor neurone → relay neurone → sensory neurone → effector
  4. Receptor → relay neurone → sensory neurone → effector → motor neurone

Explanation

In a reflex arc the stimulus is detected by a receptor, and the impulse travels along a sensory neurone to a relay neurone in the spinal cord, then along a motor neurone to an effector such as a muscle, which responds. This pathway allows a rapid, automatic response.

Question 18Organisms and Metabolism

A person with a high fever sweats profusely. Which mechanism best explains why sweating cools the body?

  1. Sweat blocks the skin pores to reduce heat loss
  2. Evaporation of sweat removes latent heat from the skin Correct answer.
  3. Sweat carries excess salt out of the body
  4. Sweat increases blood flow to the skin surface

Explanation

As sweat evaporates from the skin surface it takes latent heat from the body, lowering body temperature. Sweating itself does not cool the body unless evaporation occurs, which is why high humidity reduces cooling.

Question 19Organisms and Metabolism

Which change would most directly increase the rate of diffusion of oxygen into a fish gill?

  1. Reducing the number of gill filaments
  2. Slowing the flow of water over the gills
  3. Maintaining a counter-current flow of water and blood Correct answer.
  4. Increasing the thickness of the gill epithelium

Explanation

In counter-current flow, water and blood move in opposite directions, so the concentration of oxygen in the water remains higher than in the blood along the whole length of the gill, maximising diffusion. Thicker epithelium and fewer filaments would reduce the rate.

Question 20Organisms and Metabolism

Which statement best explains why the walls of arteries are thicker and more elastic than those of veins?

  1. Arteries carry blood with a higher oxygen content than veins
  2. Arteries contain valves to prevent backflow of blood
  3. Arteries have a wider lumen to reduce resistance to flow
  4. Arteries carry blood at high pressure from the heart and must withstand and smooth the pressure surges Correct answer.

Explanation

Blood leaves the heart under high pressure, so artery walls contain more elastic and muscle tissue to stretch with each pulse and recoil to maintain pressure. Veins carry blood at low pressure, have thinner walls, wider lumens and valves to prevent backflow.

Question 21Organisms and Metabolism

A leaf is partially covered with an opaque strip and then exposed to light for several hours after being destarched. After decolourising and adding iodine solution, which result is expected?

  1. No part of the leaf changes colour
  2. Only the covered region turns blue-black
  3. The whole leaf turns blue-black
  4. Only the uncovered regions turn blue-black Correct answer.

Explanation

Starch is made only where light reaches the leaf, so the uncovered areas photosynthesise and stain blue-black with iodine, while the covered area cannot photosynthesise and remains brown. This shows that light is required for photosynthesis.

Question 22Organisms and Metabolism

A person's urine contains glucose even though blood glucose is only slightly above normal. Which explanation is most consistent with this finding?

  1. The ureter absorbs glucose from the urine
  2. The glomerulus filters proteins that are then converted to glucose
  3. The bladder secretes glucose into stored urine
  4. The kidney tubules fail to reabsorb all the glucose filtered at the glomerulus Correct answer.

Explanation

Glucose is normally filtered at the glomerulus and completely reabsorbed by the proximal tubule. If blood glucose exceeds the reabsorption capacity, or if tubular reabsorption is defective, glucose appears in the urine, a sign of diabetes mellitus.

Question 23Organisms and Metabolism

Which explanation best accounts for the higher energy yield of aerobic respiration compared with anaerobic respiration?

  1. Anaerobic respiration uses oxygen more efficiently than aerobic respiration
  2. Anaerobic respiration produces more ATP per glucose molecule
  3. Aerobic respiration completely oxidises glucose, releasing more energy for ATP synthesis Correct answer.
  4. Aerobic respiration occurs only in plants

Explanation

In aerobic respiration glucose is completely broken down to carbon dioxide and water, releasing a large amount of energy that is transferred to many ATP molecules. Anaerobic respiration breaks down glucose only partially, producing lactate or ethanol and far less ATP.

Question 24Organisms and Metabolism

A student compares two samples of the same enzyme at different temperatures. At 60 °C the reaction rate is much lower than at 40 °C. Which explanation is most likely?

  1. The enzyme has been denatured, so its active site no longer fits the substrate Correct answer.
  2. The enzyme is inhibited by its product
  3. The substrate molecules have all been used up
  4. The pH of the mixture has changed

Explanation

High temperatures break the bonds that maintain the enzyme's tertiary structure, altering the shape of the active site so the substrate can no longer bind; this denaturation is usually irreversible. The other options describe different factors that were not varied in the comparison.

Question 25Organisms and Metabolism

Which statement best explains why a mammal living in a hot desert produces small volumes of concentrated urine?

  1. Sweating is increased to lose more water
  2. Water is conserved by reabsorbing more water in the kidney tubules Correct answer.
  3. The bladder reabsorbs water from stored urine
  4. More water is filtered at the glomerulus and lost in urine

Explanation

In a hot, dry habitat water loss must be minimised, so more water is reabsorbed from the kidney tubules under the influence of antidiuretic hormone, producing small volumes of concentrated urine. The bladder does not reabsorb water, and increased sweating would increase water loss.

Question 26Organisms and Metabolism

Which food test uses Benedict's solution and gives a brick-red precipitate when heated with a positive sample?

  1. Test for lipid
  2. Test for reducing sugar Correct answer.
  3. Test for starch
  4. Test for protein

Explanation

Benedict's solution contains blue copper(II) sulfate, which is reduced to brick-red copper(I) oxide by reducing sugars such as glucose when the mixture is heated in a water bath. The colour change from blue through green and yellow to orange-red indicates a positive result.

Question 27Organisms and Metabolism

Which region of the alimentary canal is the main site where water is reabsorbed from undigested food material?

  1. The colon Correct answer.
  2. The oesophagus
  3. The duodenum
  4. The stomach

Explanation

The colon (large intestine) absorbs most of the remaining water, mineral salts and some vitamins from the semi-solid waste, converting it into faeces. This water conservation is essential for maintaining the body's water balance.

Question 28Organisms and Metabolism

Which type of tooth is adapted for tearing and gripping food in a carnivore such as a dog?

  1. Molar
  2. Incisor
  3. Premolar
  4. Canine Correct answer.

Explanation

Canines are pointed, cone-shaped teeth used for seizing prey and tearing flesh. Their shape concentrates force at a sharp tip, which is suited to gripping and ripping rather than grinding.

Question 29Organisms and Metabolism

Which structure prevents food from entering the trachea during swallowing?

  1. The soft palate
  2. The uvula
  3. The glottis
  4. The epiglottis Correct answer.

Explanation

During swallowing the larynx rises and the epiglottis folds back over the opening of the trachea, directing the bolus into the oesophagus. This reflex protects the airway from choking.

Question 30Organisms and Metabolism

Which chamber of the mammalian heart pumps oxygenated blood into the aorta?

  1. Right atrium
  2. Right ventricle
  3. Left ventricle Correct answer.
  4. Left atrium

Explanation

The left ventricle receives oxygenated blood from the left atrium and contracts powerfully to force it into the aorta for distribution around the body. Its thick muscular wall reflects the high pressure needed for systemic circulation.

Question 31Organisms and Metabolism

Which excretory organ removes urea, excess salts and water from the blood to form urine?

  1. The liver
  2. The lung
  3. The kidney Correct answer.
  4. The skin

Explanation

The kidneys filter blood in the nephrons, reabsorb useful substances and excrete urea, surplus salts and water as urine. This maintains the composition of body fluids within narrow limits.

Question 32Organisms and Metabolism

Which type of joint is found at the elbow, allowing movement in one plane only?

  1. Ball-and-socket joint
  2. Pivot joint
  3. Hinge joint Correct answer.
  4. Gliding joint

Explanation

A hinge joint permits movement in one plane, allowing the elbow to bend and straighten only. The matching surfaces of the bones and strong ligaments restrict other movements.

Question 33Organisms and Metabolism

Which type of microorganism causes malaria in humans?

  1. A fungus
  2. A protozoan Correct answer.
  3. A virus
  4. A bacterium

Explanation

Malaria is caused by Plasmodium, a protozoan parasite transmitted by the bite of an infected female Anopheles mosquito. The parasite multiplies inside red blood cells, causing fever and anaemia.

Question 34Organisms and Metabolism

A person eats a meal rich in protein. Which sequence best describes the fate of the amino acids absorbed into the blood?

  1. Amino acids are broken down to fatty acids in the small intestine
  2. Amino acids are stored unchanged in the liver until they are needed
  3. Excess amino acids are deaminated in the liver and the nitrogenous part is converted to urea Correct answer.
  4. Excess amino acids are converted directly to glucose in the kidneys

Explanation

Amino acids not required for growth or repair cannot be stored, so the liver removes the amino group (deamination). The nitrogenous part becomes urea, which is carried to the kidneys for excretion, while the remainder can be respired.

Question 35Organisms and Metabolism

A patient's gall bladder is removed, so bile cannot be stored. Which digestive process is most directly affected?

  1. Breakdown of proteins by pepsin
  2. Emulsification of fats into small droplets Correct answer.
  3. Absorption of glucose in the ileum
  4. Digestion of starch by amylase

Explanation

Bile salts emulsify large fat droplets into smaller ones, increasing the surface area for lipase action. Without gall bladder storage, fat digestion becomes less efficient, although bile still trickles continuously from the liver.

Question 36Organisms and Metabolism

During vigorous exercise, a person's breathing rate and depth increase. Which change in the blood most directly stimulates this response?

  1. A fall in oxygen concentration
  2. A fall in body temperature
  3. A rise in carbon dioxide concentration Correct answer.
  4. A rise in blood glucose concentration

Explanation

Chemoreceptors in the medulla and in the carotid bodies are especially sensitive to a rise in carbon dioxide, which lowers blood pH. This stimulates the breathing centre to increase ventilation rate and depth.

Question 37Organisms and Metabolism

A plant is given water containing a dissolved mineral that is taken up but not used in photosynthesis. In which tissue does this mineral travel upward to the leaves?

  1. Phloem
  2. Cambium
  3. Epidermis
  4. Xylem Correct answer.

Explanation

Water and dissolved mineral salts are absorbed by root hairs and transported upward through the xylem vessels. Transpiration pull and root pressure drive this movement to the leaves.

Question 38Organisms and Metabolism

A freshwater fish is placed in sea water. Which problem is it most likely to face?

  1. Its scales will prevent salt uptake
  2. Water will be lost from its body by osmosis Correct answer.
  3. Too much water will enter its body by osmosis
  4. Its gills will be unable to absorb oxygen

Explanation

Sea water is more concentrated than the fish's body fluids, so water leaves the body by osmosis across the gills and body surface. A freshwater fish is not adapted to conserve water and would quickly become dehydrated.

Question 39Organisms and Metabolism

Which feature of an insect's gas exchange system allows oxygen to reach cells deep inside the body without a circulatory carrier?

  1. The exoskeleton is thin and permeable to gases
  2. Tracheae branch into fine tracheoles that penetrate the tissues Correct answer.
  3. Blood is pumped at high pressure through open-ended vessels
  4. Gills have a large surface area for diffusion

Explanation

Air enters through spiracles and travels along tracheae that divide into tracheoles ending close to individual cells. Because the distance to the tissues is very short, diffusion alone supplies sufficient oxygen.

Question 40Organisms and Metabolism

A person suffers damage to the part of the brain that coordinates balance and muscle coordination. Which region is most likely affected?

  1. Hypothalamus
  2. Cerebrum
  3. Cerebellum Correct answer.
  4. Medulla oblongata

Explanation

The cerebellum coordinates voluntary movements, posture and balance using information from the ears and muscles. Damage produces unsteady movement and poor coordination.

Question 41Organisms and Metabolism

A woman's blood sample shows a high level of antibody against a pathogen she was vaccinated against years earlier. Which statement best explains this?

  1. Memory cells produced during the first exposure quickly form antibody-producing cells on re-exposure Correct answer.
  2. The pathogen mutated into a harmless form
  3. The vaccine permanently introduced antibodies into her blood
  4. Her red blood cells engulfed the pathogen and stored it

Explanation

Vaccination creates memory B and T cells that persist after the initial immune response. On later exposure, these cells divide rapidly and produce a large, fast secondary response, including antibodies.

Question 42Organisms and Metabolism

Two pea plants heterozygous for flower colour (purple dominant, white recessive) are crossed. What proportion of the offspring is expected to be white?

  1. None
  2. One quarter Correct answer.
  3. Three quarters
  4. One half

Explanation

A cross between two heterozygotes gives a 1:2:1 ratio of genotypes, so one quarter are homozygous recessive and show the white phenotype. This assumes simple dominance and independent assortment.

Question 43Organisms and Metabolism

Which change in a population of bacteria best explains the rapid spread of antibiotic resistance?

  1. Antibiotics cause mutations that make bacteria resistant
  2. Bacteria with resistance genes survive treatment and reproduce, passing the genes to offspring Correct answer.
  3. Bacteria learn to avoid antibiotics after repeated exposure
  4. All bacteria gradually become resistant because they need to survive

Explanation

Antibiotic treatment acts as a selection pressure: resistant variants survive and multiply while susceptible ones die. Resistance genes may also spread between bacteria by plasmid transfer.

Question 44Organisms and Metabolism

In a food chain, only about 10% of the energy at one trophic level is passed to the next. Which explanation best accounts for this?

  1. Energy is destroyed when organisms are eaten
  2. Most energy is lost as heat through respiration and in uneaten or undigested material Correct answer.
  3. Energy is converted entirely into body mass at each level
  4. Energy passes unchanged but is diluted in larger organisms

Explanation

Organisms use much of their energy in respiration, releasing heat, and some material is not eaten or not digested. Only the energy stored in biomass is available to the next trophic level.

Question 45Organisms and Metabolism

A potted plant is watered with a solution that blocks the action of abscisic acid. Which response is most likely when the plant is then exposed to dry air?

  1. The rate of photosynthesis falls immediately
  2. The stomata close faster and the plant conserves water
  3. The roots absorb more water from the dry soil
  4. The stomata remain open and the plant wilts more quickly Correct answer.

Explanation

Abscisic acid triggers stomatal closure when water is scarce, reducing transpiration. If its action is blocked, stomata stay open, so water loss continues and the plant loses turgor.

Question 46Organisms and Metabolism

A patient's kidneys fail to reabsorb glucose even though blood glucose is normal. Which part of the nephron is most likely damaged?

  1. The loop of Henle
  2. The collecting duct
  3. The glomerulus
  4. The proximal convoluted tubule Correct answer.

Explanation

Glucose is reabsorbed by active transport in the proximal convoluted tubule. If this region is damaged, glucose remains in the filtrate and appears in the urine despite normal blood levels.

Question 47Organisms and Metabolism

An enzyme is added to a substrate solution at a concentration far above the substrate concentration. Which graph shape best describes the effect of increasing substrate concentration on reaction rate?

  1. Rate increases steadily in a straight line with no limit
  2. Rate stays constant regardless of substrate concentration
  3. Rate falls as substrate concentration rises
  4. Rate rises steeply at first then levels off as enzyme active sites become saturated Correct answer.

Explanation

At low substrate concentration most active sites are free, so rate rises with substrate. Once all active sites are occupied, adding more substrate cannot increase the rate, giving a plateau.

Question 48Organisms and Metabolism

A person living at high altitude has a higher red blood cell count than someone at sea level. Which explanation is most complete?

  1. Reduced air pressure destroys white blood cells
  2. The heart beats faster so more red cells are made directly
  3. Low oxygen partial pressure stimulates erythropoietin release, increasing red cell production Correct answer.
  4. The cold air at altitude causes blood to thicken

Explanation

At altitude the partial pressure of oxygen is lower, so less oxygen binds to haemoglobin. The kidneys detect the reduced oxygen and release erythropoietin, which stimulates the bone marrow to produce more red blood cells.

Question 49Organisms and Metabolism

A homozygous tall pea plant is crossed with a short pea plant, and all offspring are tall. The F1 plants are then self-pollinated. Which ratio is expected in the F2 generation?

  1. All tall
  2. 1 tall : 3 short
  3. 1 tall : 1 short
  4. 3 tall : 1 short Correct answer.

Explanation

The F1 plants are all heterozygous (Tt) because tall is dominant. Self-pollination of Tt × Tt gives a genotypic ratio of 1 TT : 2 Tt : 1 tt, so three quarters are tall and one quarter short.

Question 50Organisms and Metabolism

Which molecule is the main product of photosynthesis that is stored as starch in a leaf?

  1. Oxygen
  2. Chlorophyll
  3. Carbon dioxide
  4. Glucose Correct answer.

Explanation

Photosynthesis uses light energy to combine carbon dioxide and water into glucose, which is a carbohydrate. Excess glucose is converted to starch for storage in the leaf. Carbon dioxide and water are raw materials, while oxygen is a by-product and chlorophyll is the pigment that absorbs light.