AQA GCSE (9-1) Biology: Plant Tissues, Organs, and Organ Systems

Key Takeaways: Plant Tissues, Organs, and Organ Systems

1. Plant Tissues

Key Tissues & Adaptations:

• Epidermis:
  • Function: Protects against water loss, regulates gas exchange (via stomata in leaves), absorbs water/minerals in roots.
  • Adaptation: Transparent to allow light penetration to palisade cells.
  • Example: Root hair cells (specialised epidermal cells) increase surface area for water absorption.
• Palisade Mesophyll:
  • Function: Main site of photosynthesis.
  • Adaptation: Tightly packed, columnar cells with many chloroplasts.
• Spongy Mesophyll:
  • Function: Facilitates gas exchange.
  • Adaptation: Irregularly shaped cells with air spaces for efficient diffusion of CO₂ and O₂.
• Xylem & Phloem (Vascular Bundles):
  • Xylem: Transports water/minerals upwards from roots (dead, hollow cells strengthened with lignin).
  • Phloem: Transports sucrose (from photosynthesis) bidirectionally (living sieve tube cells).

2. Transpiration & Translocation

• Transpiration:
  • Process: Water evaporates from spongy mesophyll → diffuses out via stomata → creates a transpiration stream (water pulled up xylem).
  • Factors Increasing Rate:
    • High temperature, low humidity, high wind speed, bright light (stomata open).
  • Equation: Water loss per cm² = Change in mass (g)Surface area (cm2)Surface area (cm2)Change in mass (g)​
    • Example: Leaf A loses 0.2g over 50 cm² → 0.2÷50=0.004 g/cm20.2÷50=0.004g/cm2.
• Translocation:
  • Movement of sucrose in phloem from sources (leaves) to sinks (roots, fruits).

Tip: Use “Xylem Up, Phloem Down” (but phloem is bidirectional!).

3. Plant Organs & Systems

• Roots:
  • Functions: Absorb water (osmosis) and minerals (active transport), anchor plant, store starch.
  • Adaptations: Root hairs (large surface area), no chloroplasts (white as no light underground).
• Leaves:
  • Adaptations:
    • Thin for short diffusion distance.
    • Stomata (mostly on lower surface to reduce water loss).
• Stems:
  • Contain vascular bundles (xylem/phloem).
  • Meristems at shoot tips for growth towards light.

4. Key Experiments

1. Stomata Density Investigation

• Method:
  1. Apply nail varnish to leaf surfaces.
  2. Peel off, mount on slide, and count stomata under a microscope.
• Calculation:
  • Stomatal density = Number of stomataArea (mm2)Area (mm2)Number of stomata​
  • Example: 50 stomata in 0.04 mm² → 50÷0.04=1250 stomata/mm250÷0.04=1250stomata/mm2.

2. Transpiration Rate Experiment

• Variables:
  • Independent: Leaf surface covered with petroleum jelly.
  • Dependent: Change in mass.
  • Control Variables: Light intensity, temperature.
• Result:
  • Leaf with lower surface covered (most stomata) loses least water.

5. Exam Tips

• Structure-Function Questions: Always link adaptations to their role (e.g., palisade cells have many chloroplasts → maximise photosynthesis).
• Data Analysis: Identify trends (e.g., higher stomatal density in plants from wet habitats).
• Common Errors:
  • Confusing xylem/phloem direction.
  • Forgetting that roots use active transport for minerals.

6. Key Definitions

• Osmosis: Movement of water from dilute → concentrated solution across a partially permeable membrane.
• Active Transport: Movement of substances against a concentration gradient (requires energy).
• Meristem: Region of undifferentiated cells (stem cells) in shoot/root tips for growth.

Practice Question
Q: Why do plants in dry habitats often have fewer stomata?
A: To reduce water loss via transpiration.

Visual Aid:

• Draw a leaf cross-section, labelling epidermis, palisade/spongy mesophyll, stomata, and vascular bundle.

Revision complete! Now test yourself with the chapter review questions. 🌱

50 GCSE Biology Questions on Plant Tissues, Organs, and Systems

Plant Tissues

1. What are the three main types of plant tissues?
2. Describe the function of the epidermis in leaves.
3. Why do palisade mesophyll cells contain many chloroplasts?
4. How does the structure of spongy mesophyll aid gas exchange?
5. State the difference between xylem and phloem in terms of structure.

Transpiration & Translocation

6. Define transpiration.
7. List four factors that increase the rate of transpiration.
8. Explain why stomata close at night.
9. What is the role of guard cells?
10. Calculate the water loss per cm² for a leaf that lost 0.3g over 60 cm².
11. How does wind speed affect transpiration?
12. What is translocation, and which tissue is responsible for it?
13. Why is sucrose transported in phloem instead of glucose?

Plant Organs & Systems

14. Name two functions of plant roots.
15. Why are roots usually white?
16. Describe how root hair cells are adapted for water absorption.
17. What is the role of the meristem in plants?
18. Explain why shoots grow towards light.
19. Name the organs that make up the plant transportation system.

Experiments

20. Describe how to use nail varnish to investigate stomatal density.
21. In a transpiration experiment, why is petroleum jelly applied to leaves?
22. A leaf covered on both surfaces with petroleum jelly lost 0.01g. Explain why.
23. Identify the independent variable in the transpiration experiment (Table 5.1).
24. Calculate stomatal density if 30 stomata are counted in a 0.06 mm² area.
25. What is the purpose of using a potometer?

Xylem & Phloem

26. Which tissue transports water from roots to leaves?
27. Explain how xylem vessels are adapted for their function.
28. Why does water form a continuous column in xylem?
29. What substance is transported in phloem?
30. How does translocation differ from transpiration?

Adaptations & Processes

31. Why do leaves have more stomata on their lower surface?
32. How are palisade mesophyll cells arranged to maximise photosynthesis?
33. What is the role of air spaces in spongy mesophyll?
34. Define osmosis.
35. How do plants absorb mineral ions from the soil?

Exam-Style Questions

36. Figure 5.8 shows a leaf cross-section. Label tissues A–D.
37. Figure 5.9: Species A has 200 stomata/mm²; Species B has 50 stomata/mm². Which is adapted to dry habitats?
38. Explain why a plant with wilted leaves has closed stomata.
39. Why does transpiration increase in bright light?
40. Describe two functions of the epidermis in roots.

Definitions

41. Define meristem.
42. What is active transport?
43. What does humid mean?
44. Define vascular bundle.
45. What is a sink in translocation?

Maths & Data Analysis

46. Convert 150 stomata in 0.03 mm² to stomata per 1 mm².
47. A potometer bubble moved 2.5 cm in 10 minutes. Calculate rate in cm/min.
48. In Table 5.3, why does Kelly’s data show large variations?
49. In Figure 5.10, why did flask A lose more mass than flask B?
50. Using Table 5.1, explain why leaf C lost less water than leaf A.

Detailed Answers

1. Epidermis, palisade mesophyll, spongy mesophyll.
2. Regulates gas exchange via stomata and reduces water loss.
3. To maximise light absorption for photosynthesis.
4. Air spaces allow efficient diffusion of CO₂ and O₂.
5. Xylem: dead, lignified cells; Phloem: living sieve tubes.
6. Loss of water vapour from leaves via stomata.
7. High temperature, low humidity, wind, bright light.
8. To reduce water loss when photosynthesis isn’t occurring.
9. Control stomatal opening/closing by changing shape.
10. 0.3÷60=0.005 g/cm20.3÷60=0.005g/cm2.
11. Wind removes humid air, steepening the concentration gradient.
12. Movement of sucrose in phloem from leaves (sources) to other parts (sinks).
13. Sucrose is less reactive and easier to transport.
14. Absorb water/minerals, anchor plant.
15. No chloroplasts (no light underground).
16. Long extensions increase surface area for osmosis.
17. Produces new cells for growth in shoot/root tips.
18. Phototropism: shoots grow towards light for photosynthesis.
19. Roots, stems, leaves.
20. Paint nail varnish on leaf, peel, mount on slide, count stomata under microscope.
21. To block stomata and test which surface loses more water.
22. Stomata blocked → no transpiration → minimal mass loss.
23. Surface covered with petroleum jelly.
24. 30÷0.06=500 stomata/mm230÷0.06=500stomata/mm2.
25. Measure rate of water uptake (indirectly measures transpiration).
26. Xylem.
27. Hollow, lignin-strengthened walls for upward water flow.
28. Cohesion-tension theory: water molecules stick together.
29. Sucrose (and amino acids).
30. Transpiration is passive water loss; translocation is active sugar transport.
31. Lower surface shaded → reduces water loss.
32. Tightly packed near upper epidermis for maximum light absorption.
33. Facilitate gas exchange between stomata and cells.
34. Water movement from dilute → concentrated solution across a membrane.
35. Active transport (against concentration gradient).
36. A: Epidermis, B: Palisade mesophyll, C: Spongy mesophyll, D: Vascular bundle.
37. Species B (fewer stomata reduce water loss).
38. To conserve water during drought.
39. Stomata open for photosynthesis → more water loss.
40. Protection and water/mineral absorption (via root hairs).
41. Region of stem cells for plant growth.
42. Movement of substances against gradient using energy.
43. High water vapour content in air.
44. Group of xylem and phloem in stems/roots.
45. Area where sucrose is used/stored (e.g., roots).
46. 150÷0.03=5000 stomata/mm2150÷0.03=5000stomata/mm2.
47. 2.5÷10=0.25 cm/min2.5÷10=0.25cm/min.
48. Parallax error: viewing bubble from different angles (systematic error).
49. Flask A has a plant losing water; flask B is a control.
50. Leaf C had lower surface blocked (most stomata there) → less transpiration.

Revise these answers and practice diagram labelling for exams! 🌿