Grade 11 ยท Diversity, Change & Continuity ยท Lesson 2

Biodiversity of Plants

Plants are grouped into four divisions that reveal a clear evolutionary trend: decreasing dependence on water for reproduction. Explore bryophytes, pteridophytes, gymnosperms, and angiosperms.

Four divisions of the plant kingdom

Plants (Kingdom Plantae) are grouped into four major divisions. Moving from bryophytes through to angiosperms, there's a clear evolutionary trend: decreasing dependence on water for reproduction, alongside increasing structural complexity.

DivisionKey featuresReproduces via
BryophytesSimple moss plants; no vascular tissue, no true leaves or rootsSpores โ€” needs water for reproduction
PteridophytesRhizome and fronds (leaves) bearing sori (spore clusters); has vascular tissueSpores โ€” still needs water
GymnospermsTrue leaves (often needles) and roots; vascular tissue; conesSeeds โ€” not enclosed in fruit
AngiospermsTrue leaves and roots; vascular tissue; flowersSeeds โ€” enclosed in fruit

The big structural leap: vascular tissue

Bryophytes lack vascular tissue (xylem and phloem), which limits their size and ties them to damp habitats. Pteridophytes, gymnosperms, and angiosperms all have vascular tissue, allowing water and nutrient transport over longer distances โ€” enabling larger plants that can grow further from water sources.

Seeds versus spores

Gymnosperms and angiosperms produce seeds rather than spores. A seed contains a protected embryo with a food store, giving it a major survival advantage over a spore. The key difference between the two seed-producing groups is that angiosperm seeds are enclosed in a fruit, while gymnosperm seeds (e.g. in a pine cone) are not.

Try the Plant Division Explorer in the Explore tab to see how water-dependence decreases across the four divisions.

Plant Division Explorer

Click each division to compare structure, reproduction, and dependence on water.

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Answer in your exercise book.
Question 1 ยท (4 marks)
Name the four plant divisions in order of increasing structural complexity.
Question 2 ยท (2 marks)
Describe the evolutionary trend seen from bryophytes to angiosperms in terms of water dependence.
Question 3 ยท (3 marks)
Explain why the presence of vascular tissue allows plants to grow larger and further from water.
Question 4 ยท (2 marks)
Distinguish between how gymnosperms and angiosperms protect their seeds.
Question 5 ยท (3 marks)
Name the reproductive structures used to identify bryophytes, pteridophytes, and gymnosperms respectively.
Question 6 ยท (6 marks)
The table below shows the relative dependence on external water for reproduction (fertilisation) in each of the four plant divisions studied:

DivisionWater dependence for reproduction (%)
Bryophytes95
Pteridophytes70
Gymnosperms30
Angiosperms10

(a) Calculate the decrease in water dependence (in percentage points) between each successive pair of divisions: Bryophytes→Pteridophytes, Pteridophytes→Gymnosperms, and Gymnosperms→Angiosperms. (3 marks)
(b) Between which two divisions is this decrease the largest? (1 mark)
(c) Explain, referring to the reproductive structures involved and how the male gamete reaches the egg, why the decrease is largest at that point. (1 mark)
(d) Calculate the OVERALL decrease in water dependence from Bryophytes to Angiosperms. (1 mark)