▶️ Answer/Explanation
(a)(i)
Any two of the following features:
- They are multicellular.
- They are producers / contain chloroplasts (or chlorophyll) / carry out photosynthesis.
- They have a cell wall made of cellulose.
- They are non-motile (do not move from place to place).
(a)(ii)
Any two of the following kingdoms:
- Animal
- Fungi
- Protoctist
- Prokaryote
(b)
In a dicotyledonous stem, the vascular bundles are arranged in a ring (whereas they are scattered in the monocot).
(c)
To complete the diagram of the dicot root:
- Root hair: A label pointing to one of the extensions of the epidermal cells.
- Xylem: Drawn in the center, typically in a star or cross shape.
- Phloem: Drawn in the spaces between the arms of the xylem star.
(d)
Any two of the following functions:
- Transport of water.
- Transport of mineral ions (minerals).
- Physical support for the plant.
(e)
Description: The girdled trees produced a significantly greater mass of fruit ($1796$ g) compared to the ungirdled trees ($958$ g).
Explanation:
- The removal of the bark includes the removal of the phloem tissue.
- Phloem is responsible for translocation, the transport of sucrose (sugar) and amino acids.
- Sugars produced in the leaves (the source) via photosynthesis are usually transported downwards to the roots.
- Because of the girdle, these sugars cannot pass below the cut; they accumulate in the branch above the girdle.
- These excess sugars are then used for the growth of the fruit (the sink), leading to increased mass.
(f)
Pectinase.
Classification (Topic 1.3): All plants share specific features that distinguish them from other kingdoms. They are autotrophs (producers) that use sunlight to synthesize nutrients using chloroplasts, and their cells are structurally supported by cellulose cell walls. The other kingdoms of life include Animals, Fungi, Prokaryotes (bacteria), and Protoctists.
Plant Transport Anatomy (Topic 8.1): The arrangement of vascular tissue differs between monocots and dicots.
• Stems: Monocots have vascular bundles scattered throughout the stem (like chocolate chips in a cookie), while dicots have them arranged in a neat ring near the outside.
• Roots: In a dicot root, the vascular tissue is central to withstand pulling forces. The xylem forms a central “star” or “X” shape, and the phloem fills the pockets between the xylem arms.
Xylem Function (Topic 8.1): Xylem vessels are long, hollow tubes made of dead cells strengthened by lignin. Their primary roles are to conduct water and dissolved minerals from the roots to the leaves and to provide mechanical strength to keep the plant upright.
Translocation Experiment (Topic 8.4): The “girdling” or “ringing” experiment demonstrates the pathway of food transport. Phloem vessels are located in the inner bark, while xylem is deeper in the wood. Removing a ring of bark removes the phloem but leaves the xylem intact (so water still goes up). However, sugars made in the leaves cannot go down to the roots. They accumulate above the ring, forcing more resources into the fruit on that branch, making them larger.
Biotechnology (Topic 21.2): In fruit juice production, the enzyme pectinase is added to the crushed fruit. Pectin is a substance that holds plant cell walls together. Pectinase breaks this down, releasing more juice from the cells and making the juice clearer (less cloudy).