I85PREP
⌘ K
BGCSE Science Single Award 0568 study materials
BGCSE Science Single Award 0568 study resources

BGCSE Science Single Award 0568 practice questions

One question at a time. Build your BGCSE Science Single Award 0568 understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Scientific Investigation, Practical Skills and the Nature of Science

A student wants to find out how the temperature of water affects how quickly sugar dissolves. Which factor should the student change deliberately in the investigation?

  1. The volume of water used
  2. The time allowed for stirring
  3. The amount of sugar used
  4. The temperature of the water Correct answer.

Explanation

The independent variable is the one factor the investigator deliberately changes to see its effect. Here the question asks about the effect of temperature, so temperature is the independent variable. All other factors must be held constant so the comparison is fair.

Question 2Scientific Investigation, Practical Skills and the Nature of Science

In the sugar investigation, the time taken for the sugar to dissolve completely is recorded for each temperature. What name is given to this measured quantity?

  1. The random error
  2. The control variable
  3. The dependent variable Correct answer.
  4. The independent variable

Explanation

The dependent variable is what is measured in response to the change made by the investigator. Dissolving time depends on the temperature that was set, so it is the dependent variable. Control variables are the factors kept fixed, and the independent variable is the one deliberately changed.

Question 3Scientific Investigation, Practical Skills and the Nature of Science

A student repeats a measurement of the length of a leaf five times and obtains values that are all very close together. Which statement best describes these results?

  1. They are accurate but not precise
  2. They are precise but may still be inaccurate Correct answer.
  3. They are neither precise nor accurate
  4. They are both accurate and precise

Explanation

Precision refers to how close repeated measurements are to each other, while accuracy refers to how close they are to the true value. Repeated readings that agree closely are precise. Without knowing the true length, accuracy cannot be judged, so the results may still be inaccurate.

Question 4Scientific Investigation, Practical Skills and the Nature of Science

A measuring cylinder has a scale marked every 1 cm³. A student reads a volume as 42 cm³. What is the most appropriate way to record this reading with its uncertainty?

  1. 42 ± 0.01 cm³
  2. 42 ± 10 cm³
  3. 42 ± 0.5 cm³ Correct answer.
  4. 42 ± 5 cm³

Explanation

When the smallest scale division is 1 cm³, the uncertainty of a single reading is about half of that division, which is 0.5 cm³. The uncertainty should be recorded together with the value and the unit. Choosing a value far larger or far smaller than half a division misrepresents the instrument.

Question 5Scientific Investigation, Practical Skills and the Nature of Science

A group measures the boiling point of a liquid three times and gets 79 °C, 81 °C and 80 °C. The accepted value is 78 °C. Which conclusion is best supported?

  1. The results are precise and accurate
  2. The results are accurate but not precise
  3. The results are precise but not accurate Correct answer.
  4. The results are neither precise nor accurate

Explanation

The three readings lie within 1 °C of each other, so they are precise. However, all three are above the accepted value of 78 °C, so they are not accurate. Good precision does not guarantee accuracy because a systematic error may shift all readings.

Question 6Scientific Investigation, Practical Skills and the Nature of Science

Which piece of apparatus is most suitable for measuring out exactly 25.0 cm³ of dilute acid?

  1. A pipette Correct answer.
  2. A conical flask
  3. A measuring cylinder
  4. A beaker

Explanation

A pipette is designed to deliver one fixed, accurate volume, so it is the best choice for exactly 25.0 cm³. Measuring cylinders are less accurate, and beakers and flasks carry only approximate graduations. Accurate volume delivery matters when the result depends on the amount of acid used.

Question 7Scientific Investigation, Practical Skills and the Nature of Science

A test tube containing a liquid is being heated over a Bunsen burner. Which safety precaution is most important?

  1. Using a test-tube holder and pointing the tube away from people Correct answer.
  2. Pointing the tube towards a partner
  3. Filling the tube to the top
  4. Holding the tube with bare fingers

Explanation

Heating a liquid can cause it to spit or boil over, so the tube must be held with a holder and angled away from everyone. This protects the user and others from hot liquid. Filling the tube completely increases the risk of ejection.

Question 8Scientific Investigation, Practical Skills and the Nature of Science

A student draws a table of results but writes 'temperature' in the column heading without a unit. Why is this a problem?

  1. The column heading should be a symbol, not a word
  2. Units are only needed for mass measurements
  3. The table will be too wide to fit on the page
  4. The numbers cannot be interpreted because the scale of measurement is unknown Correct answer.

Explanation

A number without a unit has no defined meaning, since the same figure could be in degrees Celsius, kelvin or another scale. Including units in headings makes data unambiguous and lets others check or repeat the work. Units are required for all measured quantities, not just mass.

Question 9Scientific Investigation, Practical Skills and the Nature of Science

A student plots a graph of gas volume against time and obtains a straight line passing through the origin. What does this show?

  1. The experiment has failed
  2. Volume is unrelated to time
  3. Volume decreases as time increases
  4. Volume increases at a steady rate with time Correct answer.

Explanation

A straight line through the origin means the two quantities are directly proportional. As time increases by equal amounts, volume increases by equal amounts, so the rate is constant. A curve or a line not through the origin would indicate a different relationship.

Question 10Scientific Investigation, Practical Skills and the Nature of Science

On a graph, the line of best fit is drawn through the points. What is the main purpose of drawing such a line?

  1. To hide points that do not fit
  2. To make the graph look attractive
  3. To show the overall trend of the data Correct answer.
  4. To join every data point exactly

Explanation

A line of best fit summarises the overall trend and averages out small random variations in the points. It does not need to pass through every point, and points that scatter around it are still valid data. The line helps in reading values and identifying the relationship.

Question 11Scientific Investigation, Practical Skills and the Nature of Science

A student wants to test whether light is needed for a plant to produce starch. Which pair of conditions gives a valid comparison?

  1. One plant in the dark and one plant with extra fertiliser
  2. One plant in light and one plant given extra water
  3. One plant in light and one plant in the dark Correct answer.
  4. Two plants both in the dark

Explanation

A valid comparison changes only the factor being tested, which is light, and keeps everything else the same. Comparing a plant in light with one in the dark isolates light as the only difference. Changing water or fertiliser as well introduces extra variables.

Question 12Scientific Investigation, Practical Skills and the Nature of Science

Why is it important to repeat an experiment several times?

  1. To guarantee that no errors occur
  2. To make the results look longer
  3. To reduce the effect of random errors on the conclusion Correct answer.
  4. To use up the equipment

Explanation

Repeating measurements reduces the influence of random variation, so the mean is likely to be closer to the true value. Repeats also help identify anomalous readings that should be checked. They cannot remove systematic errors, which affect all readings in the same way.

Question 13Scientific Investigation, Practical Skills and the Nature of Science

During a neutralisation experiment a student spills some acid on the bench. What is the first appropriate action?

  1. Tell the teacher and follow the agreed spill procedure Correct answer.
  2. Neutralise it with more acid
  3. Ignore it because the acid is dilute
  4. Wipe it up with a paper towel and continue

Explanation

Spills must be reported to the teacher, who will direct the correct procedure, which usually involves diluting with plenty of water and cleaning up safely. Even dilute acids can damage skin, clothing and equipment. Improvising without guidance can spread the hazard.

Question 14Scientific Investigation, Practical Skills and the Nature of Science

A student reads the volume in a measuring cylinder while looking from above the meniscus. What effect does this have on the recorded volume?

  1. The reading is too low Correct answer.
  2. The reading becomes more accurate
  3. The reading is too high
  4. It makes no difference to the reading

Explanation

The meniscus should be viewed at eye level to avoid parallax error. Looking down from above makes the meniscus appear higher on the scale than it really is, so the recorded volume is too high. Viewing from below would make the reading too low.

Question 15Scientific Investigation, Practical Skills and the Nature of Science

A student claims that a plant food makes plants grow taller. She measures 20 plants given the food and 20 plants given water only. Which feature makes this a stronger investigation?

  1. Measuring the plants only once at the end
  2. Using a large number of plants in each group Correct answer.
  3. Using only one plant in each group
  4. Keeping all plants in the same pot

Explanation

A larger sample size reduces the chance that differences are due to natural variation between individual plants. This makes any conclusion about the plant food more reliable. A single plant per group would give very weak evidence.

Question 16Scientific Investigation, Practical Skills and the Nature of Science

A student records these readings for the time of a reaction: 34 s, 35 s, 33 s, 88 s, 34 s. What is the most appropriate next step?

  1. Change the 88 s reading to 34 s
  2. Ignore the 88 s reading and check whether it is an anomaly Correct answer.
  3. Discard the whole set of results
  4. Use all five readings to calculate the mean

Explanation

The value 88 s is far from the others and is likely to be an anomalous result caused by an error. It should be checked and, if a mistake is found, excluded before calculating a mean. Silently altering a reading to fit the pattern would be dishonest.

Question 17Scientific Investigation, Practical Skills and the Nature of Science

Which statement best describes a hypothesis in a scientific investigation?

  1. A list of the apparatus needed
  2. A final conclusion proved to be true
  3. A measurement taken during the experiment
  4. A testable prediction based on prior knowledge Correct answer.

Explanation

A hypothesis is a proposed explanation or prediction that can be tested by experiment. It is not a conclusion, since conclusions come after evidence has been gathered. A hypothesis that cannot be tested is of little use in an investigation.

Question 18Scientific Investigation, Practical Skills and the Nature of Science

A student measures the mass of a solid as 5.2 g on a balance reading to 0.1 g. She then measures it again as 5.3 g. What is the most likely explanation for the difference?

  1. The mass of an object is not fixed
  2. The solid changed chemically between weighings
  3. There is a small random error in reading the balance Correct answer.
  4. The balance is completely broken

Explanation

Small differences between repeated readings are expected because of random error, such as judging the last digit or slight fluctuations in the balance. The difference of 0.1 g is within the resolution of the instrument. A broken balance or a chemical change would produce larger or systematic effects.

Question 19Scientific Investigation, Practical Skills and the Nature of Science

A graph of temperature against time is plotted for a cooling liquid. The points fall on a smooth curve that flattens out. What does the flattening of the curve suggest?

  1. Time has stopped being recorded
  2. The liquid is cooling more quickly over time
  3. The temperature is approaching a steady value Correct answer.
  4. The thermometer has stopped working

Explanation

A curve that flattens means the temperature changes less and less as time goes on, so it is approaching a constant value. This often happens when the liquid nears room temperature. A steeper curve would indicate faster cooling.

Question 20Scientific Investigation, Practical Skills and the Nature of Science

Which of these is an example of a categorical variable?

  1. The time taken for a reaction in seconds
  2. The mass of a sample in grams
  3. The colour of a flower Correct answer.
  4. The height of a plant in centimetres

Explanation

A categorical variable places items into named groups rather than measuring a numerical amount. Flower colour is a label, such as red or white, and has no numerical scale. Height, time and mass are all continuous numerical variables.

Question 21Scientific Investigation, Practical Skills and the Nature of Science

Two students measure the same book with the same ruler and get 21.4 cm and 21.5 cm. A third student using a different ruler gets 23.0 cm. What is the most reasonable interpretation?

  1. The first two readings must be wrong
  2. The third reading is probably affected by a systematic error in that ruler Correct answer.
  3. All three readings are equally reliable
  4. The book changed length between measurements

Explanation

The first two readings agree closely, suggesting the book is about 21.5 cm long. A reading consistently higher with a different ruler suggests that ruler has a systematic error, such as a worn end or a zero error. Random error would not produce such a large, consistent shift.

Question 22Scientific Investigation, Practical Skills and the Nature of Science

A student writes a conclusion stating that 'the higher the temperature, the faster the reaction'. Which additional information would make this conclusion more convincing?

  1. A drawing of the reaction vessel
  2. A description of the apparatus used
  3. Quantitative data showing the trend at several temperatures Correct answer.
  4. The name of the student

Explanation

A conclusion is stronger when it is supported by numerical evidence across a range of values. Data at several temperatures show whether the trend is consistent and how large the effect is. Descriptions of apparatus or drawings support the method but do not themselves demonstrate the trend.

Question 23Scientific Investigation, Practical Skills and the Nature of Science

Why should a control be included in an investigation testing a new fertiliser on plant growth?

  1. To show what happens without the fertiliser, for comparison Correct answer.
  2. To replace the need for measurements
  3. To make the experiment take longer
  4. To increase the amount of fertiliser used

Explanation

A control is a group treated in the same way but without the factor being tested. It shows what would happen naturally, so any difference can be attributed to the fertiliser. Without a control, other influences could explain the results.

Question 24Scientific Investigation, Practical Skills and the Nature of Science

A student uses a stopwatch to time a reaction but starts it late each time. What type of error is this, and what is its effect?

  1. No error, because the stopwatch is accurate
  2. Systematic error, so all readings are too long
  3. Systematic error, so all readings are too short Correct answer.
  4. Random error, so readings scatter both above and below the true value

Explanation

Starting the stopwatch late every time shifts all readings in the same direction, which is a systematic error. Because the timer starts after the reaction begins, the recorded times are shorter than the true times. Human reaction time affects all trials consistently in this case.

Question 25Scientific Investigation, Practical Skills and the Nature of Science

Which action best improves the reliability of a set of measurements?

  1. Repeating the measurement and calculating a mean Correct answer.
  2. Taking each measurement once with great care
  3. Rounding all values to whole numbers
  4. Choosing the largest value obtained

Explanation

Reliability improves when measurements are repeated and the results averaged, because random variations tend to cancel out. A single careful reading may still be affected by random error. Selecting the largest value or rounding does not reduce variation.

Question 26Scientific Investigation, Practical Skills and the Nature of Science

A student wants to find out whether the temperature of water affects how quickly sugar dissolves. Which of these is the independent variable in this investigation?

  1. The volume of water used
  2. The time taken for the sugar to dissolve
  3. The mass of sugar used
  4. The temperature of the water Correct answer.

Explanation

The independent variable is the one the investigator deliberately changes, which here is the water temperature set at different values. The time taken is the dependent variable because it is measured as the outcome. All other conditions, such as sugar mass and water volume, must be kept constant as control variables.

Question 27Scientific Investigation, Practical Skills and the Nature of Science

A student measures the length of a metal rod five times and obtains 12.4 cm, 12.5 cm, 12.4 cm, 12.5 cm and 12.4 cm. Which statement best describes these measurements?

  1. They are both accurate and precise
  2. They are accurate but not precise
  3. They are precise but may not be accurate Correct answer.
  4. They are neither accurate nor precise

Explanation

Precision describes how closely repeated readings agree with each other, and these values cluster tightly within 0.1 cm, so they are precise. Accuracy describes how close a reading is to the true value, which cannot be judged without knowing the actual length of the rod. A systematic fault such as a worn ruler could make precise readings inaccurate.

Question 28Scientific Investigation, Practical Skills and the Nature of Science

A student investigates how the height of a ramp affects the distance a toy car travels along the floor. She keeps the same car, the same floor and the same starting point each time. Why is it important to keep these conditions the same?

  1. So that any change in distance can be attributed to the ramp height alone Correct answer.
  2. So that the car will always travel the same distance
  3. So that the experiment can be completed more quickly
  4. So that fewer measurements are needed

Explanation

A fair test requires that only the independent variable is changed while all other factors are held constant. If the car or surface changed between trials, the distance travelled could be affected by those factors rather than the ramp height. Controlling them makes the results valid and allows a causal link to be drawn.

Question 29Scientific Investigation, Practical Skills and the Nature of Science

A student tests a new paper towel by measuring how much water each brand absorbs. He tests one sheet of each brand once. Which change would most improve the validity of his conclusion?

  1. Test each brand using a larger sheet of paper
  2. Record the results to two decimal places
  3. Test several sheets of each brand and use the same size of sheet Correct answer.
  4. Use warmer water for the second brand

Explanation

Testing several sheets of each brand gives repeat readings, which reduces the effect of random variation and makes the comparison more reliable. Using the same size of sheet ensures the comparison is fair, since a larger sheet could absorb more water simply because of its area. Together these changes make the conclusion about brand performance more trustworthy.

Question 30Scientific Investigation, Practical Skills and the Nature of Science

Two students each measure the boiling point of the same liquid. Student A reports 78.2 °C using a thermometer with 1 °C divisions. Student B reports 78.24 °C using the same thermometer. Which statement is the best evaluation of the two reports?

  1. Both values are equally valid because the thermometer is the same
  2. Student B's extra digit is unjustified because the thermometer cannot resolve hundredths of a degree Correct answer.
  3. Student A's value must be wrong because it is less precise
  4. Student B's value is better because it contains more significant figures

Explanation

The precision of a reported measurement should not exceed the resolution of the instrument used to make it. A thermometer marked in 1 °C divisions can be read to about 0.1 °C at best, so quoting hundredths implies a precision the instrument does not have. Recording an unjustified extra digit misrepresents the uncertainty of the measurement.

Question 31Cells, Organisms and Life Processes

Which structure controls the activities of a typical animal cell and contains the genetic material?

  1. The mitochondrion
  2. The cytoplasm
  3. The cell membrane
  4. The nucleus Correct answer.

Explanation

The nucleus holds the chromosomes, which are made of DNA, and this DNA carries the instructions that direct the cell's activities, including growth and division. Other organelles carry out specific jobs but do not store the main genetic instructions.

Question 32Cells, Organisms and Life Processes

A student observes a cell with a thick rigid wall, a large permanent vacuole and green chloroplasts. Which type of cell is being described?

  1. A nerve cell
  2. A red blood cell
  3. A palisade mesophyll cell Correct answer.
  4. A root hair cell

Explanation

Palisade mesophyll cells sit in the upper part of a leaf, packed with chloroplasts to absorb light for photosynthesis, and like other plant cells they have a cellulose wall and a large vacuole. Root hair cells lack chloroplasts because they are underground.

Question 33Cells, Organisms and Life Processes

Which process allows oxygen to move from the air inside an alveolus into the blood?

  1. Osmosis
  2. Diffusion Correct answer.
  3. Active transport
  4. Transpiration

Explanation

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. Oxygen is more concentrated in the alveolar air than in the blood, so it diffuses across the thin alveolar wall into the capillaries.

Question 34Cells, Organisms and Life Processes

Which enzyme breaks down starch into simpler sugars?

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

Explanation

Enzymes are specific, so each type acts on one kind of substrate. Amylase catalyses the breakdown of starch into maltose and other sugars, and it is produced in the salivary glands and pancreas.

Question 35Cells, Organisms and Life Processes

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

  1. The pulmonary artery
  2. The pulmonary vein
  3. The vena cava
  4. The aorta Correct answer.

Explanation

The aorta is the large artery leaving the left ventricle, and it carries oxygenated blood at high pressure to the rest of the body. Arteries generally carry blood away from the heart, and the aorta is the main systemic artery.

Question 36Cells, Organisms and Life Processes

Which part of a flowering plant absorbs most of the water needed for photosynthesis?

  1. The guard cells
  2. The palisade cells
  3. The root hair cells Correct answer.
  4. The xylem vessels in the stem

Explanation

Root hair cells are long, thin extensions of root epidermal cells that greatly increase the surface area for absorbing water and mineral ions from the soil. Water then travels up the xylem to the leaves.

Question 37Cells, Organisms and Life Processes

Which gas is released by a green plant during photosynthesis?

  1. Nitrogen
  2. Water vapour
  3. Carbon dioxide
  4. Oxygen Correct answer.

Explanation

During photosynthesis, carbon dioxide and water are combined using light energy to make glucose, and oxygen is released as a by-product. The oxygen leaves the leaf through the stomata.

Question 38Cells, Organisms and Life Processes

Which feature of a sperm cell helps it to reach and fertilise an egg?

  1. A tail that allows it to swim Correct answer.
  2. Many chloroplasts
  3. A thick cellulose wall
  4. A large store of food

Explanation

A sperm cell has a tail, or flagellum, which beats to propel it through the female reproductive tract towards the egg. It also has many mitochondria to supply the energy for this movement.

Question 39Cells, Organisms and Life Processes

A plant is placed in a dark cupboard for three days. Which statement best explains why it will not produce new starch?

  1. It runs out of chlorophyll in the dark
  2. Light energy is needed to drive the reactions of photosynthesis Correct answer.
  3. It cannot absorb water without light
  4. Carbon dioxide cannot enter leaves at night

Explanation

Photosynthesis requires light energy, which is absorbed by chlorophyll and used to convert carbon dioxide and water into glucose. Without light the light-dependent stage stops, so no glucose is made and none can be stored as starch.

Question 40Cells, Organisms and Life Processes

Which statement correctly describes the movement of water during osmosis?

  1. Water moves only when the two solutions have equal concentrations on each side of a membrane
  2. Water moves from a region of lower water potential to a region of higher water potential using energy from respiration
  3. Water moves from a region of higher water potential to a region of lower water potential through a partially permeable membrane Correct answer.
  4. Water moves from a region of higher solute concentration to a region of lower solute concentration through any membrane

Explanation

Osmosis is the diffusion of water across a partially permeable membrane from a dilute solution, where water potential is high, to a more concentrated solution, where water potential is lower. It is a passive process and needs no energy from respiration.

Question 41Cells, Organisms and Life Processes

A piece of potato is placed in pure water. It becomes firm and increases in mass. Which explanation is correct?

  1. Salt enters the potato cells and draws water with it
  2. Water enters the potato cells by osmosis because the cells contain a more concentrated solution Correct answer.
  3. Water leaves the potato cells by osmosis, making them turgid
  4. The potato cells lose water by diffusion through the cell wall

Explanation

The cell contents contain dissolved sugars and salts, so the solution inside the cells is more concentrated than pure water outside. Water therefore moves into the cells by osmosis, the vacuole swells and pushes on the cell wall, making the tissue firm and heavier.

Question 42Cells, Organisms and Life Processes

Which change would most increase the rate of diffusion of a gas into a cell?

  1. Increasing the distance the gas must travel
  2. Lowering the temperature of the cell
  3. Reducing the surface area of the cell membrane
  4. Increasing the concentration difference across the membrane Correct answer.

Explanation

The rate of diffusion depends on the concentration gradient, surface area, distance and temperature. A steeper concentration difference means more particles cross the membrane each second, so the rate rises.

Question 43Cells, Organisms and Life Processes

Which statement best explains why an enzyme is described as having a specific shape?

  1. The enzyme is used up each time it catalyses a reaction
  2. The enzyme changes shape to fit any substrate it meets
  3. The enzyme provides energy to make the reaction happen
  4. The active site is complementary in shape to one particular substrate Correct answer.

Explanation

Only a substrate whose shape is complementary to the enzyme's active site can bind and form an enzyme-substrate complex. This lock-and-key fit explains why each enzyme catalyses only one type of reaction.

Question 44Cells, Organisms and Life Processes

A student tests the effect of pH on an enzyme and finds the highest activity at pH 7. What is the best explanation for the low activity at pH 2?

  1. The reaction needs more light energy at low pH
  2. The enzyme is denatured because its active site shape is altered Correct answer.
  3. The enzyme is used up faster in acidic conditions
  4. The substrate concentration becomes too low at pH 2

Explanation

Very acidic or alkaline conditions change the charges on the amino acids in the enzyme, which breaks the bonds holding its shape. The active site is distorted so the substrate no longer fits, and the enzyme is said to be denatured.

Question 45Cells, Organisms and Life Processes

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

  1. A thick, smooth inner lining
  2. A short length to speed up the flow of food
  3. A lining covered in a waterproof waxy layer
  4. Many finger-like villi with thin walls and a good blood supply Correct answer.

Explanation

Villi greatly increase the surface area available for absorption, their walls are only one cell thick so the diffusion distance is short, and a dense capillary network carries absorbed nutrients away to maintain a steep concentration gradient.

Question 46Cells, Organisms and Life Processes

Which statement correctly describes the role of the diaphragm during breathing?

  1. It contracts and moves upward, reducing the volume of the chest
  2. It relaxes and flattens, forcing air out of the lungs
  3. It contracts and flattens, increasing the volume of the chest so air is drawn in Correct answer.
  4. It produces mucus to trap dust particles

Explanation

When the diaphragm contracts it moves downward and flattens, and the intercostal muscles lift the ribs. The volume of the thorax increases, so pressure inside falls below atmospheric pressure and air flows into the lungs.

Question 47Cells, Organisms and Life Processes

Which sequence correctly describes the pathway of blood through the heart?

  1. Right atrium, right ventricle, lungs, left atrium, left ventricle, body Correct answer.
  2. Right ventricle, right atrium, lungs, left ventricle, left atrium, body
  3. Left atrium, left ventricle, lungs, right atrium, right ventricle, body
  4. Right atrium, left atrium, right ventricle, left ventricle, lungs, body

Explanation

Deoxygenated blood returns to the right atrium, passes into the right ventricle and is pumped to the lungs. Oxygenated blood then returns to the left atrium, enters the left ventricle and is pumped out through the aorta to the body.

Question 48Cells, Organisms and Life Processes

A plant stem is cut and its lower end placed in coloured water. After some hours, coloured water is seen in narrow tubes in the stem. Which tissue is being observed?

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

Explanation

Xylem vessels are dead, hollow tubes that transport water and dissolved mineral ions upward from the roots to the leaves. The coloured water is drawn up through these vessels by transpiration.

Question 49Cells, Organisms and Life Processes

Which statement best explains why leaves are broad and flat?

  1. To increase the surface area for absorbing light for photosynthesis Correct answer.
  2. To store the glucose made during respiration
  3. To allow gases to pass only through the stem
  4. To reduce water loss by transpiration

Explanation

A broad, flat leaf presents a large surface area to sunlight, so many chloroplasts can absorb light energy. It also allows carbon dioxide to diffuse in over a wide area.

Question 50Cells, Organisms and Life Processes

During exercise, a person's breathing rate and heart rate both increase. Which explanation is most complete?

  1. Muscles need more oxygen for respiration and produce more carbon dioxide to be removed Correct answer.
  2. Muscles need less oxygen and produce less carbon dioxide during exercise
  3. The lungs need to store extra oxygen for use when exercise stops
  4. The body needs to cool down, so the heart pumps more blood to the skin only

Explanation

Active muscles respire faster and so need more oxygen and glucose for aerobic respiration, while producing more carbon dioxide. The increased breathing rate supplies oxygen and removes carbon dioxide, and the faster heart rate delivers oxygen more quickly.