A leaf is an organ: tissue layers have different tasks
הוצג| English | משמעות |
|---|---|
| palisade mesophyll/ˈpælɪseɪd ˈmesəfɪl/ | בלוטה מסודרת |
| stoma/ˈstəʊmə/ | נקבת אדים |
What would explain this observation?
- The upper leaf layer admits light while inner tissues exchange gases and photosynthesize. A leaf cross-section explains how several tissue types cooperate.
Build the model
- Epidermal tissue forms an outer covering.
- Palisade mesophyll 栅栏组织 has many chloroplasts and is suited to photosynthesis.
- Spongy mesophyll contains air spaces aiding gas movement.
- Xylem supplies water and mineral ions; phloem transports dissolved sugars.
- Guard cells surround stomata and change their opening.
- Meristems at growing shoot and root tips produce cells that can differentiate.
- palisade mesophyll: Leaf tissue with cells rich in chloroplasts.
- stoma 气孔: A leaf-surface opening bordered by guard cells.
Which tissue is especially associated with many chloroplasts?
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
Palisade mesophyll cells sit near the upper surface and are packed with chloroplasts for photosynthesis. Xylem vessels are hollow water pipes, and a stoma is an opening, not a photosynthetic tissue.
Match each technical term to its precise meaning.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- A tissue is defined by its cells and role, while the whole leaf is an organ.
- Light reaching palisade cells supports photosynthesis, and a short gas pathway through air spaces supports exchange.
- A vascular bundle contains distinct transport tissues; it is not one tube carrying every substance in the same way.
In the lab: Observe a prepared transverse leaf section or attributed micrograph. Draw visible layers with clear labels and a scale. Identify palisade versus spongy tissue from organization and spaces rather than colour alone. Include guard cells and stomata only where the actual section or supplied diagram shows them.
Which two habits make the investigation or model in this case more defensible?
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: a fictional microscope field covers 0.50 mm² and contains 12 stomata.
- Recorded density=12/0.50=24 stomata/mm².
- Compare several fields selected by a defined sampling rule, rather than choosing the field with the most stomata.
Your turn: A field of 0.25 mm² contains 10 stomata. Calculate stomatal density.
A field of 0.25 mm² contains 10 stomata. Calculate stomatal density.
רמת קושי 2/5 · 140 מטבעות + בונוס קטן בהשלמה הראשונה היום
The result is 40 per mm². Known: 10 stomata in 0.25 mm^2. Use density = count / area. Density = 10/0.25 = 40 stomata per mm^2. Several fields chosen by a fixed rule should be averaged.
Check the conclusion and its limits
- A stoma is the opening, while guard cells are the cells around it.
- Meristem is plant growth tissue, not a vessel moving sap.
- Every plant leaf need not have exactly the same arrangement as a standard schematic.
Not true: A stoma and its surrounding guard cells are the same structure. The stoma is the PORE; the guard cells are the pair of cells surrounding it that open and close it. They work together but are different structures.
- Epidermal tissue forms an outer covering.
- A tissue is defined by its cells and role, while the whole leaf is an organ.
- Watch for: A stoma is the opening, while guard cells are the cells around it.
The stoma is the PORE; the guard cells are the pair of cells surrounding it that open and close it.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
True. The stoma is the PORE; the guard cells are the pair of cells surrounding it that open and close it. They work together but are different structures.
Leaf tissue with cells rich in chloroplasts: write the technical term.
רמת קושי 1/5 · 100 מטבעות + בונוס קטן בהשלמה הראשונה היום
palisade mesophyll means Leaf tissue with cells rich in chloroplasts.