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NSSCO Biology 6116 study materials
NSSCO Biology 6116 study resources

NSSCO Biology 6116 practice questions

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Question 1Working scientifically: experimental design, measurement, data handling and evaluation

A student investigates how the distance of a lamp from pondweed affects the number of oxygen bubbles released per minute. Which is the dependent variable in this investigation?

  1. The distance of the lamp from the pondweed
  2. The mass of pondweed used in each trial
  3. The number of bubbles released per minute Correct answer.
  4. The temperature of the water in the beaker

Explanation

The dependent variable is the factor that is measured and that responds to the change being tested. Here the student alters the lamp distance and counts bubbles per minute, so the bubble count is the measured outcome. Lamp distance is the independent variable, while temperature and pondweed mass must be held constant.

Question 2Working scientifically: experimental design, measurement, data handling and evaluation

A student records the time taken for starch to disappear from five leaf discs and obtains five similar readings. Which action would best increase the reliability of the conclusion drawn from these readings?

  1. Round each reading to the nearest minute
  2. Ask a different student to read the stopwatch each time
  3. Repeat the whole investigation several times and compare the means Correct answer.
  4. Use a stopwatch that reads to 0.01 s

Explanation

Reliability is about how consistent results are when an investigation is repeated. Repeating the whole procedure and comparing means shows whether the pattern is repeatable rather than depending on one set of readings. Finer scales affect precision, and rounding only affects how data are presented.

Question 3Working scientifically: experimental design, measurement, data handling and evaluation

An enzyme-controlled reaction is followed by measuring the volume of gas collected every 30 seconds. Which unit correctly expresses the mean rate of gas production?

  1. minutes per cm³
  2. cm³ per minute Correct answer.
  3. seconds
  4. cm³

Explanation

A rate is a change in amount per unit time, so a rate of gas production must combine a volume unit with a time unit. Dividing the volume collected by the time taken gives cm³ per minute. A volume alone, a time alone, or time per volume does not describe how fast the gas is produced.

Question 4Working scientifically: experimental design, measurement, data handling and evaluation

A company claims that a new fertiliser increases maize growth. In a trial, 50 plants receive fertiliser and 50 plants receive the same volume of water only, and all plants are kept in the same greenhouse. Why is the second group of plants included?

  1. To show that maize plants can survive without any water
  2. To allow a comparison with plants grown without fertiliser Correct answer.
  3. To increase the total number of plants in the trial
  4. To make the results easier to plot on a graph

Explanation

A control group is treated in exactly the same way as the experimental group except that it does not receive the factor being tested. Without it there is nothing to compare against, so any extra growth cannot be credited to the fertiliser. The water-only plants therefore isolate the effect of the fertiliser from other conditions.

Question 5Working scientifically: experimental design, measurement, data handling and evaluation

A student's four repeated measurements of the pH of a buffer solution are 6.8, 6.9, 6.8 and 6.9, while the true pH of the solution is 4.0. Which description best fits these measurements?

  1. Precise but not accurate Correct answer.
  2. Accurate but not precise
  3. Both accurate and precise
  4. Neither accurate nor precise

Explanation

Precision describes how closely repeated readings agree with one another, and these four values are very close together. Accuracy describes how close readings are to the true value, and all four lie roughly 2.8 to 2.9 pH units away from 4.0. The readings are therefore consistent but systematically wrong.

Question 6Working scientifically: experimental design, measurement, data handling and evaluation

The mean mass of a seedling increases from 1.2 g to 1.8 g over 10 days. What is the percentage increase in mass?

  1. 150%
  2. 50% Correct answer.
  3. 33%
  4. 0.6%

Explanation

Percentage change compares the increase with the starting value, so the calculation is (0.6 ÷ 1.2) × 100 = 50%. The increase of 0.6 g must be divided by the original mass of 1.2 g, not by the final mass and not by the time period.

Question 7Working scientifically: experimental design, measurement, data handling and evaluation

A student investigates whether temperature affects the rate of yeast fermentation by counting bubbles per minute. Tubes are set up at 20, 30, 40 and 50 °C, but 5 g of yeast is used at 20 °C while 10 g is used at every other temperature. How does this affect the investigation?

  1. It has no effect because yeast mass does not influence bubble production
  2. It makes the investigation invalid, because yeast mass is not controlled Correct answer.
  3. It improves reliability because more yeast is used at higher temperatures
  4. It only affects the validity of the 50 °C results

Explanation

In a fair test only the independent variable, temperature, should differ between treatments. Using 5 g of yeast at one temperature and 10 g at the others means yeast quantity also varies, so any difference in bubble production could be due to yeast amount rather than temperature. The results therefore cannot be attributed to temperature and the investigation is not valid.

Question 8Working scientifically: experimental design, measurement, data handling and evaluation

To estimate the population of dandelions in a field, a student throws a 0.5 m × 0.5 m quadrat ten times at random. Which change would most improve the reliability of the estimate?

  1. Count the dandelions in one quadrat and multiply by the area of the field
  2. Count only the plants that touch the centre of each quadrat
  3. Take a larger number of random quadrats Correct answer.
  4. Place all the quadrats in the corner where dandelions are most common

Explanation

The reliability of an estimate improves when more independent samples are taken, because the mean density is then less affected by chance variation between quadrats. Random placement also keeps the sample representative of the whole field. Ten throws is a small sample, so increasing the number is the most direct improvement.

Question 9Working scientifically: experimental design, measurement, data handling and evaluation

In an investigation of oxygen release by pondweed, a student records the total volume of gas collected: 0 cm³ at 0 min, 2.4 cm³ at 2 min, 5.6 cm³ at 4 min and 8.0 cm³ at 6 min. In which time interval is the mean rate of gas production greatest?

  1. 4 to 6 minutes
  2. 0 to 2 minutes
  3. The mean rate is the same in all three intervals
  4. 2 to 4 minutes Correct answer.

Explanation

Rate is calculated by dividing the change in volume by the change in time for each interval. The increases are 2.4, 3.2 and 2.4 cm³, giving mean rates of 1.2, 1.6 and 1.2 cm³ per minute respectively. The middle interval therefore has the greatest mean rate of gas production.

Question 10Working scientifically: experimental design, measurement, data handling and evaluation

A student surveys 200 classmates and finds that those who eat breakfast report fewer headaches. Which conclusion is best supported by this evidence?

  1. Headaches cause students to skip breakfast
  2. Eating breakfast stops headaches from developing
  3. Breakfast and headaches are linked, but cause is not shown Correct answer.
  4. Breakfast has no effect on whether students get headaches

Explanation

The survey shows only that two variables were found together, which is a correlation. Other factors such as sleep, age or overall diet could influence both breakfast eating and headache frequency, and students were not assigned to treatments. A controlled experiment would be needed before claiming that breakfast prevents headaches.

Question 11Working scientifically: experimental design, measurement, data handling and evaluation

A student investigates how temperature affects the rate of germination of cress seeds. Which variable is the independent variable?

  1. The temperature at which the seeds are kept Correct answer.
  2. The type of soil used in each dish
  3. The number of seeds that germinate
  4. The volume of water given to each dish

Explanation

The independent variable is the factor deliberately changed by the investigator. In this investigation the student changes the temperature, so temperature is the independent variable. The number of seeds germinating is the dependent variable, while water volume and soil type should be controlled.

Question 12Working scientifically: experimental design, measurement, data handling and evaluation

Which piece of apparatus is most suitable for measuring 25 cm³ of water accurately in a school laboratory?

  1. A 25 cm³ measuring cylinder Correct answer.
  2. A test tube without markings
  3. A 100 cm³ beaker with volume markings
  4. A 10 cm³ syringe

Explanation

A measuring cylinder is graduated and is designed to measure a chosen volume accurately. A 25 cm³ cylinder can hold the required volume in one filling, close to its capacity. Beakers give only approximate volumes, a 10 cm³ syringe is too small, and an unmarked test tube cannot measure 25 cm³.

Question 13Working scientifically: experimental design, measurement, data handling and evaluation

A student records the number of each species of insect caught in four different habitats. Which type of graph is most suitable for displaying these data?

  1. A bar chart Correct answer.
  2. A line graph
  3. A histogram
  4. A scatter graph

Explanation

Species are categories, not continuous numerical values, so the data should be displayed as separate bars. A bar chart allows clear comparison of the number of insects in each species category. Line graphs, scatter graphs and histograms are used for continuous numerical data.

Question 14Working scientifically: experimental design, measurement, data handling and evaluation

A student measures the diameter of 20 onion epidermal cells and calculates a mean. Which action would most improve the reliability of this mean?

  1. Rounding each measurement to the nearest whole number
  2. Using a microscope with a much higher magnification
  3. Repeating measurements and recalculating the mean Correct answer.
  4. Measuring only the largest cells

Explanation

Reliability is improved by repeating measurements and using the mean of several sets of data. Repeating the whole procedure reduces the effect of random variation. Higher magnification may improve resolution but does not by itself test whether the result is repeatable.

Question 15Working scientifically: experimental design, measurement, data handling and evaluation

A student investigates the effect of temperature on the activity of amylase. Why is a buffer solution added to the reaction mixture?

  1. To stop the reaction at the end
  2. To provide the substrate for the enzyme
  3. To raise the temperature of the mixture
  4. To keep the pH constant Correct answer.

Explanation

A buffer resists changes in pH, so it keeps the pH constant during the investigation. This is important because pH affects enzyme activity and could otherwise act as a confounding variable. The substrate is starch, and stopping the reaction usually involves a different reagent.

Question 16Working scientifically: experimental design, measurement, data handling and evaluation

Two students each measure the boiling point of pure water four times. Student A obtains 99.8, 99.9, 99.8 and 99.9 °C. Student B obtains 97, 102, 98 and 103 °C. Which statement best compares the two sets of readings?

  1. Student A's readings are more precise than Student B's readings. Correct answer.
  2. Student A's readings are less accurate because they are close to 100 °C.
  3. Student B's readings are more precise because they cover a wider range.
  4. Both students have the same mean boiling point.

Explanation

Precision describes how close repeated measurements are to one another. Student A's readings differ by only 0.1 °C, whereas Student B's readings are spread over 6 °C, so A is more precise. Student A is also more accurate because the readings are close to the true boiling point of 100 °C.

Question 17Working scientifically: experimental design, measurement, data handling and evaluation

A student uses a line transect to study how plant species change from a pond edge to a drier area. Why are quadrats placed at regular intervals along the transect?

  1. To make sure only one species is recorded
  2. To increase the number of quadrats without any plan
  3. To show how the community changes gradually along the transect Correct answer.
  4. To ensure that the largest plants are counted

Explanation

A line transect is used to study how organisms are distributed along an environmental gradient. Placing quadrats at regular intervals gives a systematic sample that can reveal gradual changes in species composition. It is not intended to record only one species or to select the largest plants.

Question 18Working scientifically: experimental design, measurement, data handling and evaluation

A student records the volume of gas produced by an enzyme reaction each minute: 4, 8, 12, 30 and 20 cm³. The reading at 4 minutes is much higher than expected. What is the most appropriate action before calculating a mean rate?

  1. Add the 30 cm³ reading to the 20 cm³ reading
  2. Use the 30 cm³ reading without question because it is part of the data set
  3. Ignore all the readings and start a new experiment
  4. Repeat the measurement at 4 minutes to check whether it was an error Correct answer.

Explanation

A reading that is very different from the trend may be an anomalous result caused by a measurement or recording error. The best response is to repeat that measurement under the same conditions to see whether the high value is genuine. If it is confirmed, it can be included; if not, the repeat value can replace it.

Question 19Working scientifically: experimental design, measurement, data handling and evaluation

A student measures the rate of water uptake by a shoot at four wind speeds. The results are 2, 5, 8 and 8 mm³ per minute. Which conclusion is best supported by these data?

  1. Temperature must be the limiting factor at the lowest wind speed.
  2. Water uptake decreases as wind speed increases above 3 arbitrary units.
  3. Wind speed limits water uptake up to a point, after which another factor limits it. Correct answer.
  4. Water uptake is not affected by wind speed at any of the speeds tested.

Explanation

The rate rises from 2 to 8 mm³ per minute as wind speed increases, then stays at 8. This shows that wind speed is limiting at first but another factor becomes limiting at the higher speeds. The data do not show a decrease, and temperature was not measured.

Question 20Working scientifically: experimental design, measurement, data handling and evaluation

A student finds that seedlings grown in a new compost grow taller than seedlings grown in garden soil. The compost seedlings were also kept in a warmer greenhouse. Which statement is the best evaluation of the conclusion that the compost caused the extra growth?

  1. The conclusion is not valid because plant height cannot be measured.
  2. The conclusion is not valid because temperature was not controlled. Correct answer.
  3. The conclusion is valid because only one variable was changed.
  4. The conclusion is valid because the compost seedlings grew taller.

Explanation

The compost and the warmer greenhouse were changed at the same time, so the effect of temperature cannot be separated from the effect of compost. This makes temperature a confounding variable. To test the compost fairly, both groups should be kept at the same temperature.

Question 21Cell structure, cell division and movement of substances across membranes

Which organelle is the main site of aerobic respiration in a eukaryotic cell?

  1. Mitochondrion Correct answer.
  2. Nucleus
  3. Ribosome
  4. Chloroplast

Explanation

Aerobic respiration releases energy from glucose using oxygen. Most reactions of aerobic respiration, including the electron transport chain, occur on the inner membrane of the mitochondrion. Chloroplasts carry out photosynthesis, ribosomes make proteins and the nucleus stores genetic material.

Question 22Cell structure, cell division and movement of substances across membranes

Which feature is found in plant cells but is never found in animal cells?

  1. A cellulose cell wall Correct answer.
  2. A cell-surface membrane
  3. Ribosomes
  4. A nucleus

Explanation

Plant cells have a rigid cellulose cell wall outside the cell-surface membrane, which gives support and prevents bursting when water enters. Animal cells lack a cell wall and are bounded only by a flexible cell-surface membrane. Both plant and animal cells have ribosomes and a nucleus.

Question 23Cell structure, cell division and movement of substances across membranes

Which statement best describes diffusion?

  1. Movement of ions against a concentration gradient through carrier proteins
  2. Movement of particles from a low to a high concentration using energy from ATP
  3. Movement of water molecules across a partially permeable membrane
  4. Net movement of particles from a region of higher concentration to a region of lower concentration, without using energy from respiration Correct answer.

Explanation

Diffusion is the passive net movement of particles down a concentration gradient, from higher to lower concentration. It relies on the random motion of particles and does not require energy released by respiration. Osmosis is a special case of diffusion involving water, while active transport moves substances against a gradient using ATP.

Question 24Cell structure, cell division and movement of substances across membranes

A plant cell is placed in a dilute solution that has a higher water potential than the cell sap. What is the most likely result?

  1. Water enters the cell by osmosis, the vacuole expands and the cell becomes turgid Correct answer.
  2. Water leaves the cell by osmosis and the cell plasmolyses
  3. There is no net movement of water because the cell wall is impermeable
  4. Solutes are actively transported into the cell, causing it to swell

Explanation

Water moves by osmosis from a region of higher water potential to a region of lower water potential. The dilute solution outside has a higher water potential than the cell sap, so water enters the cell. The expanding vacuole pushes the cytoplasm against the cell wall, making the cell turgid.

Question 25Cell structure, cell division and movement of substances across membranes

Which feature distinguishes active transport from diffusion across a cell membrane?

  1. Active transport moves particles only from a high to a low concentration
  2. Active transport occurs only in non-living plant cells with a cellulose wall
  3. Active transport uses energy from respiration and can move a substance against its concentration gradient Correct answer.
  4. Active transport requires no membrane proteins and is entirely passive

Explanation

Active transport uses carrier proteins and energy released by respiration to move ions or molecules against a concentration gradient. Diffusion is passive and moves particles down a concentration gradient without ATP. Therefore, the ability to move a substance against its gradient and to use metabolic energy is the key distinguishing feature.

Question 26Cell structure, cell division and movement of substances across membranes

During mitosis, at which stage do the chromosomes line up along the equator of the cell before being pulled apart?

  1. Metaphase Correct answer.
  2. Prophase
  3. Telophase
  4. Anaphase

Explanation

In metaphase, spindle fibres attach to the centromeres of the chromosomes and arrange them along the cell equator. Prophase involves chromosome condensation, anaphase involves separation of chromatids to opposite poles, and telophase involves formation of two nuclei. Therefore, metaphase is the alignment stage.

Question 27Cell structure, cell division and movement of substances across membranes

What is the normal outcome of mitosis in a diploid body cell?

  1. Four daughter cells, each with half the chromosome number of the parent cell
  2. Two daughter cells, each with half the chromosome number of the parent cell
  3. Four genetically identical daughter cells, each with twice the chromosome number of the parent cell
  4. Two genetically identical daughter cells, each with the same chromosome number as the parent cell Correct answer.

Explanation

Before mitosis, DNA is replicated so each chromosome consists of two identical chromatids. Mitosis separates the chromatids into two daughter cells, each receiving the same diploid chromosome number as the parent cell. The daughter cells are genetically identical to each other and to the parent cell, which is important for growth and repair.

Question 28Cell structure, cell division and movement of substances across membranes

Which description best fits the fluid mosaic model of the cell-surface membrane?

  1. A single layer of protein molecules with lipid pores running through it
  2. A double layer of phospholipids with proteins scattered through it, some carrying carbohydrate chains Correct answer.
  3. A double layer of protein with lipid molecules embedded in it
  4. A rigid layer of cellulose with protein channels between the fibres

Explanation

The fluid mosaic model describes the membrane as a bilayer of phospholipid molecules in which proteins are embedded and can move laterally. Some proteins span the bilayer, some are on one side, and many have carbohydrate chains attached, forming glycoproteins. The phospholipid bilayer forms a barrier to water-soluble substances, while proteins help transport specific molecules.

Question 29Cell structure, cell division and movement of substances across membranes

Two spherical cells have the same shape but different sizes. Which cell will take up oxygen most rapidly by diffusion per unit of cell volume?

  1. Both cells will take up oxygen at the same rate per unit volume because they are the same shape
  2. The smaller cell, because it has a larger surface area to volume ratio Correct answer.
  3. The larger cell, because its thicker membrane allows more oxygen to diffuse through
  4. The larger cell, because it has a larger total surface area

Explanation

Diffusion occurs across the cell surface, so the rate of oxygen uptake depends on surface area, while the demand for oxygen depends on volume. As a cell becomes larger, its volume increases faster than its surface area, so the surface area to volume ratio falls. A small cell therefore has a relatively larger surface for exchange per unit volume and can supply its contents more rapidly by diffusion.

Question 30Cell structure, cell division and movement of substances across membranes

A plant cell is placed in a concentrated sugar solution. Which sequence describes the changes that lead to plasmolysis?

  1. Sugar molecules diffuse into the cytoplasm, increasing the solute concentration and causing the cell to become turgid
  2. The cell wall dissolves and the cell-surface membrane loses its partially permeable properties
  3. Water enters the vacuole by osmosis, the cell swells and the cell wall bursts
  4. Water leaves the vacuole by osmosis, the vacuole shrinks and the cytoplasm pulls away from the cell wall Correct answer.

Explanation

The concentrated sugar solution has a lower water potential than the cell sap, so water leaves the cell by osmosis. As the vacuole loses water it shrinks, and the cytoplasm and cell-surface membrane pull away from the rigid cell wall. This condition is called plasmolysis, and the cell is no longer turgid.

Question 31Cell structure, cell division and movement of substances across membranes

Which structure is present in a eukaryotic cell but is absent from a prokaryotic cell?

  1. Circular DNA molecules
  2. A nuclear envelope Correct answer.
  3. Ribosomes for protein synthesis
  4. A cell-surface membrane

Explanation

Prokaryotic cells have no membrane-bound organelles, so their genetic material lies free in the cytoplasm rather than inside a nucleus. A nuclear envelope therefore surrounds the chromosomes of eukaryotic cells and is never found in prokaryotes. Cell-surface membranes and ribosomes occur in both cell types.

Question 32Cell structure, cell division and movement of substances across membranes

What is the main function of ribosomes in a cell?

  1. Release of energy from glucose
  2. Synthesis of lipids
  3. Digestion of worn-out organelles
  4. Synthesis of proteins Correct answer.

Explanation

Ribosomes translate messenger RNA into polypeptide chains, so they are the site of protein synthesis. They occur free in the cytoplasm and attached to the rough endoplasmic reticulum. Lipid synthesis and organelle digestion are carried out by the smooth endoplasmic reticulum and lysosomes respectively.

Question 33Cell structure, cell division and movement of substances across membranes

A cell is 50 µm long. In a drawing its length is 5 mm. What is the magnification of the drawing?

  1. ×100 Correct answer.
  2. ×1000
  3. ×10
  4. ×0.01

Explanation

Both measurements must be converted to the same unit: 5 mm equals 5000 µm. Magnification is image length divided by actual length, so 5000 ÷ 50 gives ×100. Using the numbers without converting units would give an incorrect value.

Question 34Cell structure, cell division and movement of substances across membranes

In which phase of the cell cycle does DNA replication take place?

  1. Prophase
  2. G2 phase
  3. S phase Correct answer.
  4. G1 phase

Explanation

Interphase consists of G1, S and G2, and DNA replication occurs during S phase. After replication each chromosome consists of two sister chromatids. G1 and G2 are growth phases, while prophase is the first stage of mitosis.

Question 35Cell structure, cell division and movement of substances across membranes

What is the normal result of meiosis in a diploid cell?

  1. Two genetically identical haploid cells
  2. Four genetically different diploid cells
  3. Two genetically identical diploid cells
  4. Four genetically different haploid cells Correct answer.

Explanation

Meiosis involves two successive divisions after a single round of DNA replication. It produces four daughter cells, each with half the chromosome number of the parent, and crossing over and independent assortment make them genetically different. Mitosis, by contrast, produces two genetically identical diploid cells.

Question 36Cell structure, cell division and movement of substances across membranes

Glucose moves from a high concentration outside a red blood cell to a lower concentration inside it, passing through a membrane protein. Which process is this?

  1. Simple diffusion
  2. Facilitated diffusion Correct answer.
  3. Active transport
  4. Osmosis

Explanation

The movement is down a concentration gradient, so it is passive and does not require ATP. Glucose is large and polar, so it cannot cross the phospholipid bilayer freely and must use a carrier protein; this is facilitated diffusion. Active transport would move glucose against the gradient using energy.

Question 37Cell structure, cell division and movement of substances across membranes

A red blood cell is placed in distilled water. What is the most likely result?

  1. It stays the same size because water potentials are equal
  2. It becomes turgid because a cell wall prevents bursting
  3. It shrinks because water leaves the cell
  4. It swells and bursts because water enters the cell Correct answer.

Explanation

Distilled water has a higher water potential than the cytoplasm, so water enters the cell by osmosis. Animal cells lack a cell wall, so the cell-surface membrane cannot withstand the pressure and the cell bursts. A plant cell in the same solution would become turgid instead.

Question 38Cell structure, cell division and movement of substances across membranes

Why can an electron microscope resolve smaller details than a light microscope?

  1. Electron lenses magnify more strongly
  2. Specimens are always thinner
  3. Electrons carry a negative charge
  4. Electrons have a shorter wavelength Correct answer.

Explanation

Resolution is limited by the wavelength of the radiation used. Electrons have a much shorter wavelength than visible light, so they can distinguish objects that are closer together. Magnification alone does not improve resolution, which is why simply using stronger lenses in a light microscope does not reveal the same detail.

Question 39Cell structure, cell division and movement of substances across membranes

Beetroot tissue is placed in water at 60 °C and red pigment leaks out, but little pigment leaks out at 20 °C. Which explanation is most likely?

  1. The higher temperature denatures membrane proteins and increases the fluidity of the phospholipid bilayer Correct answer.
  2. The higher temperature makes the cellulose cell walls permeable to pigment
  3. The higher temperature increases the rate of diffusion of pigment through intact membranes
  4. The higher temperature increases the rate of active transport of pigment out of the cells

Explanation

At high temperature the phospholipid bilayer becomes more fluid and membrane proteins lose their tertiary structure, so the membrane loses its selective barrier function. The pigment, normally stored in the vacuole, can then leak into the surrounding water. Cellulose walls are already freely permeable to water and small molecules, so they cannot be the barrier that fails.

Question 40Cell structure, cell division and movement of substances across membranes

A mutation makes a cell-cycle checkpoint protein inactive, so the cell passes the checkpoint even when its DNA is damaged. What is the most likely consequence?

  1. The cell will divide repeatedly, forming a tumour Correct answer.
  2. The cell will stop dividing permanently
  3. The cell will undergo meiosis instead of mitosis
  4. The cell will repair the damaged DNA before dividing

Explanation

Checkpoints normally pause the cycle so that DNA damage can be repaired or the cell can be removed by apoptosis. If the checkpoint fails, cells with mutations continue through mitosis and can divide repeatedly, forming a tumour. Repair before division is precisely what the faulty checkpoint no longer ensures.

Question 41Cell structure, cell division and movement of substances across membranes

Which organelle modifies newly made proteins and packages them into vesicles for secretion from a eukaryotic cell?

  1. Smooth endoplasmic reticulum
  2. Golgi apparatus Correct answer.
  3. Lysosome
  4. Ribosome

Explanation

The Golgi apparatus receives proteins from the rough endoplasmic reticulum, modifies them, and packages them into vesicles for transport to the cell surface or other destinations. Lysosomes are enzyme-containing vesicles, ribosomes synthesise polypeptides, and smooth endoplasmic reticulum mainly makes lipids.

Question 42Cell structure, cell division and movement of substances across membranes

In a root tip squash, a dividing cell shows two separate groups of chromosomes at opposite poles and a cell plate forming across the middle of the cell. Which stage of mitosis is this?

  1. Metaphase
  2. Prophase
  3. Anaphase
  4. Telophase Correct answer.

Explanation

Telophase follows anaphase, when chromatids have reached the poles and begin to decondense; in plant cells, vesicles then gather at the equator to form a cell plate. Prophase, metaphase and anaphase occur earlier and do not show a cell plate forming between two chromosome groups.

Question 43Cell structure, cell division and movement of substances across membranes

Which statement best defines water potential?

  1. The pressure that water exerts on the inside of a plant cell wall
  2. The total volume of water contained in a cell or solution
  3. The speed at which water molecules cross a partially permeable membrane
  4. The potential energy of water per unit volume compared with pure water at atmospheric pressure Correct answer.

Explanation

Water potential is the potential energy of water per unit volume relative to pure water at atmospheric pressure, and it is measured in kPa. Pure water has a water potential of zero, and water moves from a region of higher water potential to a region of lower water potential.

Question 44Cell structure, cell division and movement of substances across membranes

A diploid organism has the genotype AaBb, and the genes A and B are located close together on the same chromosome. Which process during meiosis can produce gametes carrying the combination Ab or aB?

  1. Separation of homologous chromosomes in anaphase I
  2. Crossing over between non-sister chromatids in prophase I Correct answer.
  3. Replication of DNA during interphase
  4. Separation of sister chromatids in anaphase II

Explanation

When genes are linked on the same chromosome, crossing over between non-sister chromatids in prophase I can exchange corresponding sections and create new allele combinations such as Ab and aB. Separation of homologous chromosomes and sister chromatids redistributes existing combinations, while DNA replication copies them without creating new linkage arrangements.

Question 45Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

Which word equation summarises the process of photosynthesis?

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

Explanation

Photosynthesis combines carbon dioxide and water inside chloroplasts, using light energy trapped by chlorophyll, to produce glucose and oxygen. Oxygen leaves the leaf as a by-product, while glucose is used in respiration or stored as starch.

Question 46Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

A sailor on a long voyage without fresh fruit or vegetables develops bleeding gums, loose teeth and wounds that heal very slowly. Which nutrient is missing from the diet?

  1. vitamin D
  2. iron
  3. calcium
  4. vitamin C Correct answer.

Explanation

Vitamin C is needed to make collagen, the protein that gives strength to skin, gums and the walls of blood vessels. A shortage causes scurvy, with bleeding gums, loose teeth and slow-healing wounds, and it is prevented by fresh fruit and vegetables.

Question 47Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

Starch is broken down to maltose by amylase. In which part of the alimentary canal is amylase first added to the food?

  1. salivary glands in the mouth Correct answer.
  2. gastric glands in the stomach wall
  3. the gall bladder, which stores bile
  4. the lining of the large intestine

Explanation

Salivary glands secrete amylase into the mouth, where it begins the breakdown of starch into maltose while the food is chewed. The acid in the stomach stops amylase working, and starch digestion continues in the duodenum with amylase from the pancreas.

Question 48Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

What is the role of bile in the digestion of a fatty meal?

  1. It neutralises stomach acid and emulsifies fats into droplets. Correct answer.
  2. It supplies lipase, the enzyme that digests fat into fatty acids and glycerol.
  3. It absorbs the fatty acids and glycerol through the villi into the blood.
  4. It converts excess glucose into glycogen for storage in the liver.

Explanation

Bile is made in the liver and stored in the gall bladder before being released into the duodenum. It is alkaline, so it neutralises the acidic food arriving from the stomach, and bile salts break fat into tiny droplets, increasing the surface area for lipase, although bile itself contains no enzymes.

Question 49Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

Tomato plants grown in a nutrient solution that lacks magnesium develop yellow leaves and grow slowly. Why does this happen?

  1. Magnesium is part of the chlorophyll molecule, so less light energy is absorbed. Correct answer.
  2. Magnesium is needed to make cellulose for the cell walls, so the leaves collapse.
  3. Magnesium is required to split water molecules during the light-dependent stage.
  4. Magnesium is needed to build amino acids into proteins, so protein synthesis stops.

Explanation

Magnesium is the central atom of the chlorophyll molecule, so a shortage prevents chlorophyll from being made and the leaf looks yellow, a condition called chlorosis. Fewer chlorophyll molecules mean that less light energy is absorbed, so the rate of photosynthesis falls and growth is slow.

Question 50Nutrition: photosynthesis, plant mineral requirements, human diet and digestion

Which feature of the small intestine is an adaptation for the efficient absorption of digested food?

  1. The duodenum receives bile and pancreatic juice through a common duct.
  2. The lining is folded into many villi with thin walls and dense capillaries. Correct answer.
  3. Circular and longitudinal muscles move the contents along by peristalsis.
  4. The muscular walls churn the contents so that they mix thoroughly with digestive enzymes.

Explanation

The inner wall of the small intestine is folded and covered with villi, finger-like projections that greatly increase the surface area available for absorption. Each villus has a very thin epithelium, a dense network of blood capillaries and a central lacteal, so digested nutrients pass quickly into the blood or lymph.