AQA GCSE Biology Biology Paper 1 (Higher), November 2021: Question 6
17 marks · Standard Demand difficulty · Extended Answer
Identify leaf tissues, compare xylem and phloem, and calculate the rate of water loss using a tangent to a graph.
Practise this questionQuestion
Question text
06 Figure 9 shows a cross section of a leaf.
Figure 9
06.1 Which cell is most transparent?
[1 mark]
Tick ( ) one box.
A B C D
06.2 Which cell structure in a leaf mesophyll cell is not found in a root hair cell?
[1 mark]
Plants lose water through their leaves.
06.3 Name the cells in a leaf that control the rate of water loss.
[1 mark]
06.4 Water is taken in by the roots, transported up the plant and lost from the leaves.
*22* Which scientific term describes this movement of water?
[1 mark]
06.5 Which change would decrease the rate of water loss from a plant’s leaves?
[1 mark]
Tick ( ) one box.
Increased humidity
Increased light intensity
Increased density of stomata
Increased temperature 24
06.6 Compare the structure and function of xylem tissue and phloem tissue.
[6 marks]
Figure 10 shows the total volume of water lost from a plant over 6 hours.
Figure 10
06.7 Determine the rate of water loss at 12:00
Use the tangent on Figure 10.
Give your answer:
• in cm3 per minute
• in standard form.
[4 marks]
*26* Rate of water loss = cm3 per minute
06.8 The rate of water loss at midnight was much lower than at 12:00
Explain why.
[2 marks]
Mark scheme
Show the mark scheme
AO /
Question Answers Extra information Mark
Spec. Ref.
06.1 A 1 AO2
4.2.3.1
06.2 chloroplast(s) ignore chlorophyll 1 AO1
4.1.1.3
4.2.3.1
06.3 guard (cells) ignore stoma(ta) 1 AO1
4.2.3.1
4.2.3.2
06.4 transpiration stream ignore transpiration unqualified 1 AO1
4.2.3.2
06.5 increased humidity 1 AO2
4.2.3.2
06.6 Level 2: Scientifically relevant features are identified; the way(s) in 4‒6 AO1
which they are similar/different is made clear and (where 4.2.3.1
appropriate) the magnitude of the similarity/difference is noted. 4.2.3.2
Level 1: Relevant features are identified and differences noted. 1‒3
No relevant content. 0
Indicative content:
Structure
• xylem is made of dead cells
and
phloem is made of living cells
• phloem cells have pores in their end walls
and
xylem cells do not have pores in their end walls
• xylem is hollow or xylem does not contain cytoplasm
and
phloem contains cytoplasm
• xylem contains lignin
and
phloem does not (contain lignin)
• both made of cells
• both tubular
Function
• xylem transports water / mineral ions
and
phloem transports (dissolved) sugars
• xylem is involved in transpiration
and 17
phloem is involved in translocation
• xylem transports unidirectionally
and
phloem transports bidirectionally
• both transport liquids / substances throughout the stem / leaves /
roots / plant
For Level 2, students must refer to both structure and function of
xylem and phloem tissue.
06.7 allow correct answer from AO2
student’s readings throughout 4.2.3.2
(correct division)
40 ÷ 7 (in hours) 1
or
40 ÷ 420 (in minutes)
5.71 (in hours) allow correct division from 1
or incorrect reading(s) from the
18 0.0952…(in minutes) tangent
(correct conversion to minutes)
0.0952… allow correct conversion at any 1
point in the calculation
allow correct conversion of
calculated value to minutes
(answer in standard form)
9.5(238) x 10-2 allow correct conversion of 1
calculated value to standard
form
06.8 allow converse if clearly AO3
describing 12:00 4.2.3.2
(less water loss at night)
stomata are (almost completely) 1
closed
(because) it’s cooler / colder 1
or
(because) there’s less / no light ignore it’s dark at night
Total 17
How to answer it
Plant Tissues, Transport Systems, and Transpiration
This question assesses fundamental plant biology from AQA Topic 4.2 (Organisation in Plants):
- Leaf Structure & Adaptations: Identifying epidermal cells, palisade/spongy mesophyll, and guard cells.
- Specialised Cells: Differentiating cellular organelles between photosynthetic leaf cells and underground root hair cells.
- Transport Systems: Detailed structural and functional comparison of xylem and phloem tissues.
- Transpiration Factors: Factors governing water loss (humidity, light intensity, and temperature).
- Mathematical Skills: Calculating rate from a curved graph using a tangent line ( gradient = Δy / Δx ), converting hours to minutes, and expressing answers in standard form.
Parts 06.1 – 06.5: Leaf Structure & Plant Transport Concepts
Quick-fire recall and understanding of leaf anatomy and transpiration
✅ 06.1: Most Transparent Cell
Answer: A (Upper Epidermal cell)
Upper epidermal cells are transparent to allow maximum sunlight to penetrate down to the palisade mesophyll below.
✅ 06.2: Leaf Cell vs Root Hair Cell
Answer: Chloroplast(s)
Root hair cells are underground where there is no light, so they do not contain chloroplasts.
✅ 06.3: Cells Controlling Water Loss
Answer: Guard cells (or guard)
Guard cells change shape to open and close the stomatal pore, regulating transpiration.
✅ 06.4: Movement of Water
Answer: Transpiration stream
Water evaporation from leaves pulls water continuously upwards from the roots through xylem vessels.
✅ 06.5: Decreasing Water Loss
Answer: Increased humidity
Higher humidity reduces the water vapour concentration gradient between inside the leaf and outside air, slowing diffusion.
❌ Common Errors (06.1 – 06.5)
- 06.2: Writing chlorophyll instead of chloroplast. Chlorophyll is a chemical pigment; chloroplast is the cell structure (organelle).
- 06.3: Writing stoma / stomata. Stomata are pores/holes, not cells. The question specifically asks to name the cells.
- 06.4: Writing just transpiration. The mark scheme explicitly states: ignore transpiration unqualified . You must state transpiration stream.
Part 06.6: Extended Response — Compare Xylem and Phloem
Compare the structure and function of xylem tissue and phloem tissue [6 marks]
🧠 How to Secure Level 2 (5–6 Marks)
To reach Level 2, examiners require you to cover both structure AND function of both tissues, explicitly pointing out similarities and differences. Use clear comparative linking words like "whereas", "however", or "both".
| Feature | Xylem Tissue | Phloem Tissue |
|---|---|---|
| Cell Viability (Structure) | Made of dead cells. | Made of living cells. |
| Cell Wall & Support (Structure) | Thickened and strengthened with lignin. | Cellulose cell walls (no lignin). |
| Internal Contents (Structure) | Hollow tubes; no cytoplasm or internal organelles. | Contains cytoplasm; supported by companion cells. |
| End Walls (Structure) | No end walls between cells (continuous hollow tube). | End walls contain pores / perforations (sieve plates). |
| Substances Carried (Function) | Transports water and dissolved mineral ions. | Transports dissolved sugars (sucrose) and amino acids. |
| Direction of Transport (Function) | One direction only (unidirectional: roots to leaves). | Both directions (bidirectional: up and down the plant). |
| Process Name (Function) | Involved in transpiration (driven by evaporation). | Involved in translocation (energy-requiring process). |
| Similarities | Both are tubular vascular tissues made of cells that transport liquids throughout the plant stem, roots, and leaves. |
❌ Common Errors in 6-Mark Comparisons
- Only writing about function and forgetting structure (or vice versa), capping the answer at Level 1 (max 3 marks).
- Writing two separate paragraphs with no direct comparative links. Always compare side-by-side using connective words.
- Mixing up transpiration (water moving through xylem) with translocation (sugar moving through phloem).
Part 06.7: Tangent & Rate Calculation
Determine the rate of water loss at 12:00 using the tangent line [4 marks]
📐 Step-by-Step Calculation
- Find the gradient of the tangent line ( Δy ÷ Δx ):
At 08:00, y = 190 cm³
At 15:00, y = 230 cm³
Change in y (volume) = 230 − 190 = 40 cm³
Change in x (time) = 15:00 − 08:00 = 7 hours
Division: 40 ÷ 7 = 5.714 cm³ per hourMark 1: Correct division ( 40 ÷ 7 or 40 ÷ 420 ) - Calculate value in hours or minutes:
5.71 cm³ per hour OR 0.0952... cm³ per minuteMark 2: Correct calculated division value - Convert time to minutes:
There are 60 minutes in an hour: 5.714 ÷ 60 = 0.095238... cm³ per min
(Or initially doing: 7 × 60 = 420 mins , then 40 ÷ 420 = 0.0952... )Mark 3: Conversion to cm³ per minute - Convert to Standard Form:
0.0952 = 9.52 × 10⁻² cm³ per minute (accept 9.5 × 10⁻²)Mark 4: Final value correctly converted to standard form
❌ Common Traps on This Question
- Reading off the curve instead of the tangent: The question explicitly says "Use the tangent on Figure 10". You must use points along the straight tangent line, not the S-shaped curve!
- Missing the unit conversion: The x-axis is given in hours (08:00 to 15:00), but the question requires cm³ per minute . Always circle required units!
- Incorrect standard form exponent: Writing 9.5 × 10² or 9.5 × 10⁻¹ instead of 9.5 × 10⁻² . Remember: moving the decimal point two places to the right requires a 10⁻² factor.
Part 06.8: Explaining Rate of Water Loss at Night
The rate of water loss at midnight was much lower than at 12:00. Explain why. [2 marks]
✅ Model Answer
- Point 1: The stomata are (almost completely) closed.
- Point 2: Because it is cooler / colder OR because there is no light / less light.
🧠 Examiner Insight
Notice how the mark scheme treats vague descriptions:
- "Ignore: it's dark at night": Writing just "it's dark" does not receive credit as a biological reason. You must state no light / less light (explaining that photosynthesis stops, leading guard cells to close stomata) or that it is colder / cooler.
- Full converse statements explaining midday (e.g., "at 12:00 stomata are open because it is brighter and warmer") are fully accepted.
Topics
Biology · B1: Cell Biology · B2: Organisation
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 1 (Higher), November 2021. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.