Plant tissues
Cut a slice of stem or hold a leaf up to the light: it is not a uniform mass of identical cells. Each zone has a different shape, a different wall and a different job. Learning to read that organisation into tissues means understanding how the whole plant works, from root to crown.
Meristems: the factories of new cells
Prune the tip of a plant's stem or place the base of an onion in water: after a few days, side branches or roots sprout exclusively from those ends, while the zones in between do not lengthen. Why do plants grow only at very specific points and not all over their body at once?
Unlike an animal, which stops growing in length once it reaches maturity, a plant can keep growing throughout its life because it keeps zones of active meristem at specific points.
Name the main plant tissues (meristems, parenchyma, supporting tissue, vascular tissue, and dermal tissue) and summarise the function of each in one sentence.
Name the main plant tissues (meristems, parenchyma, supporting tissue, vascular tissue, and dermal tissue) and summarise the function of each in one sentence.
Where are meristems located in a plant? Explain why, thanks to them, a plant can grow throughout its life, unlike an animal.
Where are meristems located in a plant? Explain why, thanks to them, a plant can grow throughout its life, unlike an animal.
Parenchyma and supporting tissues
From the meristems, adult tissues are formed; these no longer divide (with some exceptions) and are specialised in one function.
Distinguish between parenchymal tissue and supporting tissue: cellular appearance, cell wall thickness, and role in the plant, indicating where each is abundant.
Distinguish between parenchymal tissue and supporting tissue: cellular appearance, cell wall thickness, and role in the plant, indicating where each is abundant.
Collenchyma and sclerenchyma support the plant without lignifying its entire surface. Explain the difference between these two supporting tissues and relate it to the…
Collenchyma and sclerenchyma support the plant without lignifying its entire surface. Explain the difference between these two supporting tissues and relate it to the flexible habit of an herbaceous plant versus the rigidity of a tree.
Conducting tissues: xylem and phloem
Place a stalk of celery or a white carnation in a glass of water dyed blue: after a few hours, the dye climbs up fine visible lines to the edges of the leaves or petals. How does a plant manage to raise water tens of metres against gravity without a heart to push it?
Explain why the conducting cells of the xylem (tracheids and vessel elements) are dead and hollow at maturity, and why this, far from being a problem, improves their…
Explain why the conducting cells of the xylem (tracheids and vessel elements) are dead and hollow at maturity, and why this, far from being a problem, improves their function.
Xylem and phloem are the plant's vascular tissues. Compare their conducting cells (tracheids and vessel elements versus sieve tubes), the direction of transport, and the…
Xylem and phloem are the plant's vascular tissues. Compare their conducting cells (tracheids and vessel elements versus sieve tubes), the direction of transport, and the sap moved by each tissue.
The vascular bundles connect root, stem and leaf. Explain how they are arranged in the stem and in the vein of the leaf, how you would tell xylem and phloem apart in a…
The vascular bundles connect root, stem and leaf. Explain how they are arranged in the stem and in the vein of the leaf, how you would tell xylem and phloem apart in a section under the microscope (size and appearance of the cells, position) and what each one transports.
Epidermis, cuticle and stomata
If you peel an apple, its exposed flesh dries out and wrinkles within hours, whereas an intact apple keeps its moisture for weeks thanks to its waxy skin. How does a plant manage to protect itself from drying out without suffocating in the process?
Explain what a stoma is, which cells form it and which two vital processes its opening and closing regulate (gas exchange and water loss).
Explain what a stoma is, which cells form it and which two vital processes its opening and closing regulate (gas exchange and water loss).
Distinguish between epidermis and cuticle, and explain how together they protect the leaf against desiccation and against the entry of pathogens.
Distinguish between epidermis and cuticle, and explain how together they protect the leaf against desiccation and against the entry of pathogens.
Look at the leaf cross-section in the image. a) Identify the numbered structures and the tissue to which each belongs. b) Explain how each tissue relates to…
Look at the leaf cross-section in the image. a) Identify the numbered structures and the tissue to which each belongs. b) Explain how each tissue relates to photosynthesis or sap transport. c) State through which structure air enters and exits, and how this exchange is regulated.
The woody stem and secondary growth
What is the cambium and where is it located in a woody stem? Indicate which tissue it produces towards the inside and which towards the outside, and what happens to a…
What is the cambium and where is it located in a woody stem? Indicate which tissue it produces towards the inside and which towards the outside, and what happens to a tree if a complete ring of bark is removed from it.
Explain how an annual growth ring forms in the trunk (early wood and late wood), what dendrochronology is, and what is deduced from very narrow or very wide rings about…
Explain how an annual growth ring forms in the trunk (early wood and late wood), what dendrochronology is, and what is deduced from very narrow or very wide rings about the climate of each year.
Cork is obtained from the cork oak without felling it. Explain what the phellogen (cork cambium) is, what cork is and why the bark can be stripped periodically, as well…
Cork is obtained from the cork oak without felling it. Explain what the phellogen (cork cambium) is, what cork is and why the bark can be stripped periodically, as well as the ecological and economic value of the cork oak woodland.
Back to the beginning: When you look at that leaf against the light, the veins forming the network are vascular bundles of xylem and phloem wrapped in supporting fibres, the green filling is photosynthetic chlorophyll-containing parenchyma, and the translucent surface film is the epidermis with its stomata.