B1 - Cells and organization

QUESTION 1 7 marks Criterion A

Medium

Comparing cell types

The diagram shows three cell types.

a. Identify cells A, B and C.

[3]

b. Give two features shared by all three.

[2]

c. Explain why C is prokaryotic.

[2]

Show complete worked solution

(a)

A is an animal cell, B is a plant cell and C is a bacterium.

(b)

All have a cell membrane, cytoplasm, ribosomes and genetic material; any two are valid.

(c)

Its DNA is not enclosed by a nucleus and it lacks membrane-bound organelles.

QUESTION 2 8 marks Criterion B

Hard

Testing membrane damage

Plan an investigation into how temperature affects membrane permeability in beetroot cells.

a. State a testable hypothesis.

[2]

b. Describe a controlled method.

[5]

c. State one safety precaution.

[1]

Show complete worked solution

(a)

Higher temperature will increase pigment leakage because membrane proteins and phospholipids become disrupted.

(b)

Cut equal beetroot cylinders, rinse until wash water is clear, place them in equal water volumes at several thermostatically controlled temperatures for the same time, remove tissue and measure solution absorbance. Control cylinder dimensions, tissue source, pH and mixing; repeat each temperature.

(c)

Use forceps and heatproof equipment when handling hot water and take care with the cork borer or blade.

QUESTION 3 6 marks Criterion C

Medium

Organelle-count evidence

Cell X has many mitochondria and membrane infoldings. Cell Y has many chloroplasts and a large vacuole.

a. Infer a likely function of X and justify.

[2]

b. Infer the tissue location of Y.

[2]

c. Explain why organelle abundance is evidence rather than proof.

[2]

Show complete worked solution

(a)

X is adapted for energy-demanding transport or movement; many mitochondria supply ATP and infoldings increase membrane area.

(b)

Y is likely a photosynthetic leaf cell, because chloroplasts absorb light and the vacuole supports turgor.

(c)

Different cells can share adaptations, and function also depends on location, gene expression and direct physiological measurements.

QUESTION 4 6 marks Criterion D

Medium

Cell models in education

A school can buy detailed plastic cell models or use low-cost interactive digital models.

a. State one scientific limitation common to both.

[2]

b. Recommend a combined approach.

[4]

Show complete worked solution

(a)

Both enlarge and simplify structures, often giving false fixed colors, proportions or positions and failing to show molecular movement.

(b)

Use physical models for spatial relationships and digital models for scale changes and processes. Pair both with real micrographs, scale bars and explicit model limitations. Choose using accessibility, durability, device availability and learning evidence.

QUESTION 1 5 marks Criterion A

Medium

Magnification and cell size

A cell image is 48 mm long at \( imes 600\) magnification.

a. Calculate the actual length in millimeters.

[2]

b. Convert to micrometers.

[2]

c. Explain why magnification must include units only for image and actual size.

[1]

Show complete worked solution

(a)

\[\text{actual size}=\frac{48}{600}=0.080\,\mathrm{mm}\]

(b)

\[0.080\,\mathrm{mm}\times1000=80\,\mathrm{\mu m}\]

(c)

Magnification is a ratio of two lengths in the same units, so the units cancel.

QUESTION 2 8 marks Criterion B

Hard

Calibrating a microscope

Plan to calibrate an eyepiece graticule at low and high objective powers using a stage micrometer.

a. Describe the calibration procedure.

[5]

b. Explain how measurement uncertainty is reduced.

[2]

c. State how a specimen is then measured.

[1]

Show complete worked solution

(a)

Align the two scales, find a long interval where lines coincide, divide the known stage-micrometer distance by the eyepiece divisions, and record micrometers per division. Repeat for each objective because changing magnification changes the calibration.

(b)

Use the longest clear overlap, repeat alignments and average, focus both scales sharply and avoid measuring a single division.

(c)

Count eyepiece divisions across it and multiply by the calibration for that objective.

QUESTION 3 7 marks Criterion C

Hard

Using a scale bar

In the diagram, the 100 µm scale bar measures 150 mm on screen. One cell measures 96 mm on screen.

a. Calculate actual cell length.

[3]

b. Calculate the image magnification.

[2]

c. Explain why a scale bar is useful if the image is resized.

[2]

Show complete worked solution

(a)

\[\text{cell length}=\frac{96}{150}(100)=64\,\mathrm{\mu m}\]

(b)

\[100\,\mathrm{\mu m}=0.100\,\mathrm{mm}\] \[M=\frac{150}{0.100}=1500\]

(c)

The bar resizes with the image, so its ratio to the specimen remains valid, while a printed magnification label becomes incorrect after resizing.

QUESTION 4 6 marks Criterion D

Medium

Microscope claims in advertising

A phone attachment is advertised as a “2000× scientific microscope”, but no resolution test or scale calibration is supplied.

a. Distinguish magnification from resolution.

[2]

b. Evaluate the claim.

[4]

Show complete worked solution

(a)

Magnification enlarges an image; resolution is the ability to distinguish close points as separate.

(b)

High digital enlargement may only magnify blur. Require images of a calibrated resolution target, field of view, numerical aperture, scale accuracy and performance across the frame. Compare with a standard microscope under the same specimen and lighting conditions.

QUESTION 1 6 marks Criterion A

Medium

Specialized-cell adaptations

Explain how each cell is adapted to its function.

a. Sperm cell.

[2]

b. Root-hair cell.

[2]

c. Red blood cell.

[2]

Show complete worked solution

(a)

A flagellum enables movement, many mitochondria supply ATP, an acrosome contains enzymes, and a haploid nucleus carries genetic information.

(b)

A long projection provides large surface area for water and mineral uptake; transport proteins and mitochondria support active transport.

(c)

A biconcave shape gives large surface area and short diffusion distance, while loss of nucleus leaves more room for hemoglobin.

QUESTION 2 8 marks Criterion B

Hard

Relating form to function

Plan a comparative microscopy study to test whether exercise-trained muscle contains a higher mitochondrial density than untrained muscle.

a. Define the dependent variable.

[2]

b. Describe sampling and controls.

[4]

c. State an ethical requirement.

[2]

Show complete worked solution

(a)

Measure mitochondrial number or mitochondrial area as a percentage of cell area in standardized micrograph fields.

(b)

Use equivalent muscle, age and imaging preparation, random blinded fields, equal magnification and calibration, multiple cells from multiple individuals, and the same counting rule.

(c)

Use existing anonymized images or informed consent and approved minimally invasive sampling; do not assign harmful exercise solely for the study.

QUESTION 3 6 marks Criterion C

Hard

Surface-area adaptation data

A root-hair cell has estimated membrane area \(9200\,\mathrm{\mu m^2}\); a similar cell without the projection has \(3600\,\mathrm{\mu m^2}\).

a. Calculate percentage increase.

[2]

b. Explain the biological advantage.

[2]

c. State why uptake may not rise by exactly 156%.

[2]

Show complete worked solution

(a)

\[\frac{9200-3600}{3600}\times100=156\%\]

(b)

More membrane area permits more water channels and mineral transport proteins, increasing potential uptake from soil.

(c)

Uptake can be limited by soil concentration, water potential, respiration, transporter number and flow away from the cell.

QUESTION 4 6 marks Criterion D

Hard

Stem-cell treatment decisions

A proposed stem-cell therapy improves movement in a small uncontrolled study but has uncertain tumor risk.

a. Explain the biological promise and risk.

[2]

b. Evaluate whether routine use is justified.

[4]

Show complete worked solution

(a)

Stem cells may differentiate into replacement cells, but uncontrolled division or incorrect differentiation can form tumors or damage tissue.

(b)

Not yet. Require controlled trials, long-term follow-up, dose and cell-line quality data, adverse-event reporting and independent replication. Consider consent, alternatives, equitable access and regulation before wider use.

QUESTION 1 6 marks Criterion A

Medium

Membrane transport mechanisms

Compare diffusion, osmosis and active transport.

a. Diffusion.

[2]

b. Osmosis.

[2]

c. Active transport.

[2]

Show complete worked solution

(a)

Net particle movement from higher to lower concentration down a concentration gradient, without direct ATP use.

(b)

Net water movement through a partially permeable membrane from higher water potential to lower water potential.

(c)

Movement against a concentration gradient using membrane proteins and energy from ATP.

QUESTION 2 8 marks Criterion B

Hard

Potato-osmosis investigation

Plan to estimate the internal solute concentration of potato tissue.

a. Describe the method.

[5]

b. Explain how internal concentration is estimated.

[2]

c. State one control.

[1]

Show complete worked solution

(a)

Cut equal potato cylinders, blot and record initial mass, place them in equal volumes of a range of sucrose concentrations for equal time and temperature, blot consistently and record final mass. Repeat each concentration and calculate percentage mass change.

(b)

Plot mean percentage mass change against sucrose concentration and find the x-intercept where net mass change is zero.

(c)

Use tissue from the same potato and control cylinder size, solution volume, duration and temperature.

QUESTION 3 6 marks Criterion C

Hard

Osmosis-data analysis

Potato mass changes are: 0.0 mol dm?³ +18%, 0.2 +9%, 0.4 +1%, 0.6 ?8%, 0.8 ?17%.

a. Estimate the isotonic concentration by linear interpolation between 0.4 and 0.6.

[3]

b. Explain the sign change.

[2]

c. Give one uncertainty in the estimate.

[1]

Show complete worked solution

(a)

The zero point is \(1/(1+8)\) of the 0.2 interval above 0.4: \[c=0.4+\frac{1}{9}(0.2)=0.422\,\mathrm{mol\,dm^{-3}}\]

(b)

Below the isotonic value water enters tissue; above it, the external solution has lower water potential and water leaves.

(c)

Only widely spaced concentrations were tested and biological cylinders vary; more values near the intercept are needed.

QUESTION 4 6 marks Criterion D

Hard

Saline concentration in medicine

A social-media post recommends using pure water rather than isotonic saline to rinse exposed living tissue.

a. Use osmosis to explain the risk.

[2]

b. Evaluate the advice.

[4]

Show complete worked solution

(a)

Pure water has much higher water potential than cell contents, so water can enter cells, causing swelling and possible lysis.

(b)

Do not use a generic post as medical guidance. Appropriate sterile isotonic solutions reduce osmotic stress, but the correct response depends on tissue, contamination and emergency protocol. Use approved instructions and clinical evidence.

QUESTION 1 6 marks Criterion A

Medium

Levels of organization

Arrange and connect the following: cardiac muscle cell, cardiac muscle tissue, heart, circulatory system, human.

a. Give the order from smallest to largest.

[2]

b. Explain why the heart is an organ rather than a tissue.

[2]

c. Explain one interdependence between two organ systems.

[2]

Show complete worked solution

(a)

Cell ? tissue ? organ ? organ system ? organism.

(b)

It contains several tissues, including muscle, nervous, connective and epithelial tissue, coordinated for pumping.

(c)

The respiratory system loads oxygen into blood, while the circulatory system transports it to respiring tissues and returns carbon dioxide.

QUESTION 2 8 marks Criterion B

Hard

Modeling organ-system response

Design a non-invasive study of how stepping exercise affects interaction between respiratory and circulatory systems.

a. State measurements and timing.

[3]

b. Describe controls and reliability.

[4]

c. State a testable prediction.

[1]

Show complete worked solution

(a)

Measure heart rate and breathing rate at rest, immediately after a standardized stepping period and at fixed recovery intervals; oxygen saturation may also be recorded.

(b)

Use the same step height, cadence, duration, posture, recovery position and device. Screen participants, obtain consent, stop for symptoms and repeat on separate days or use adequate participants.

(c)

Heart and breathing rates will rise after exercise and then approach resting values during recovery.

QUESTION 3 6 marks Criterion C

Hard

Recovery-data interpretation

After exercise, heart rate is 150 beats min?¹ and breathing rate 36 breaths min?¹. After 6 min they are 82 and 15; resting values are 74 and 13.

a. Calculate percentage recovery of heart-rate elevation.

[3]

b. Interpret both measurements.

[2]

c. State one reason a single person cannot define fitness standards.

[1]

Show complete worked solution

(a)

Initial elevation \(=150-74=76\). Remaining elevation \(=82-74=8\). \[\%\text{recovered}=\frac{76-8}{76}\times100=89.5\%\]

(b)

Both have moved close to resting levels, showing coordinated recovery of oxygen delivery and ventilation, but neither has fully returned.

(c)

Age, health, temperature, effort, stress and normal individual variation affect recovery.

QUESTION 4 6 marks Criterion D

Hard

Artificial-organ decisions

A hospital can expand dialysis capacity or invest in transplant services. Dialysis is repeatedly available; transplant can restore more kidney function but needs donors and immunosuppression.

a. Relate both treatments to kidney-system function.

[2]

b. Propose a balanced allocation approach.

[4]

Show complete worked solution

(a)

Both replace removal of wastes and regulation of water and ions; a transplant can perform more continuous endocrine and regulatory functions.

(b)

Maintain safe dialysis access while expanding ethical donation and transplantation. Use clinical benefit, waiting time and compatibility transparently; include long-term outcomes, immunosuppression risk, cost, travel burden and patient preference. Do not divert all resources to one pathway.

B1 - Cells and organization

B1.1 - Prokaryotic and eukaryotic cell structure 4 questions

B1.2 - Microscopy, magnification and scale 4 questions

B1.3 - Specialized cells and differentiation 4 questions

B1.4 - Diffusion, osmosis and active transport 4 questions

B1.5 - Tissues, organs and organ systems 4 questions