How plants colonized the land

1. How Plants Colonized the Land
and Evolution of Seed Plants
Selected Topics in Biology
Ariane B. Sogo-an
MST Biology

2. Objectives
At the end of the lesson, the MST Biology
students are expected to conduct the following
with at least 80% level of accuracy:
– Relate Evolution and Biodiversity of Plant Kingdom
– Trace the evolutionary modification of plants
throughout time.
– Determine the different plant group per
evolutionary modification and characteristics.

3. Biodiversity and Evolution
• There are more than 290,000 recorded species
of plants known today to be inhibiting the
planet earth and most of them adapted
mechanisms to be able for them to inhabit
various corners of the world such as deserts,
grassland and forest.

4. Biodiversity and Evolution
• There are even terrestrial plants that
seemingly shares characteristics from aquatic
plants thus pushing the curiosity of mankind
to try to explain the origin of plants and how it
colonized the world since the beginning of
time.

5. Biodiversity and Evolution
• The great diversity of life is
the PRODUCT of evolution.
It represents the many
different ways in which the
common elements of life’s
organization have
combined to provide new
and successful ways to
survive and reproduce.
• Modification for survival to
certain environment
• Ability to bear seeds

6. An Overview of Land Plant Evolution

7. • For more than the first 3
billion years of Earth’s
history, the terrestrial
surface was lifeless and
plants first inhabited
bodies of water.

8. • The movement onto land carried many
benefits: including unfiltered sun, more
plentiful CO2, nutrient-rich soil, and few
herbivores or pathogens

9. Aquatic to Terrestrial plants
• Three (3) major obstacles.
– Water retention (not drying
out),
– Structural support (against
gravity), and
– Dependence on water for
reproduction (getting
gametes together).

10. Shared Traits of Algae and Plants
• Like brown, red, and some green algae, plants
are multicellular, eukaryotic, photosynthetic
autotrophs.
• Like green algae, plants have cellulose cell
walls.
• Like green algae, euglenids, and some
dinoflagellates, plants have chlorophylls a and
b.

13. Charophytes
• Many species of Charophyte algae live in
shallow water around the edges of lakes and
ponds. How do they withstand that kind of
situation?
– Sporopollenin - a layer of a durable polymer that
prevents exposed zygotes from drying out.
– It was traced scientists that a similar chemical
adaptation is found in the sporopollenin walls that
encase plant spores.

14. EVIDENCES THAT SUPPORT THE PHYLOGENETIC
CONNECTION BETWEEN LAND PLANTS AND GREEN ALGAE
• Homologous chloroplasts
• presence of chlorophyll b and beta-carotene and
thylakoids stacked as grana. DNA comparison with
terrestrial.
• Homologous cellulose walls
– cellulose comprises 20-26% of the cell wall.

15. EVIDENCES THAT SUPPORT THE PHYLOGENETIC
CONNECTION BETWEEN LAND PLANTS AND GREEN ALGAE
• Homologous peroxisomes
– Both land plants and charophycean algae package
enzymes that minimize the costs of photorespiration
in peroxisomes.
• Phagmoplasts
– These plate-like structures occur during cell division
only in land plants and charopyceans.
• Flagellated sperm
– Many plants have flagellated sperm, which match
charophycean sperm closely in ultrastructure.

16. EVIDENCES THAT SUPPORT THE PHYLOGENETIC
CONNECTION BETWEEN LAND PLANTS AND GREEN ALGAE
• Molecular systematics
– In addition to similarities derived from
comparisons of chloroplast genes, analyses of
several nuclear genes also provide evidence of a
Charophycean ancestry of plants.

17. Terrestrial Plant Adaptation
• Alternation of generations and multicellular,
dependent embryos
• Spores produced in sporangia
• Multicellular gametangia
• Apicalmeristem

18. Evolution of Roots, Stem and Leaves

19. Physiological modifications of plants
to survive above sea level:
• root system.
• shoot system
• Stems grew and branches extensively only after plants
developed a biochemical capacity to synthesize and
deposit lignin, an organic compound in cell wall.
• xylem (distributes water) and phloem (distributes
dissolved sugars and other photosynthetic products).
• Cuticle
• Stomata

20. Further adaptations of plants
• Cuticle
• Mycorrhizae – important to plants without
roots. Nitrogen fixing agent.
• Secondary compounds – ex. alkaloids,
terpenes, and tannins

21. From Haploid to Diploid Dominance
• In Algae, a haploid (n) phase in the form of
gametophytes (gamete producing bodies),
dominates their life cycles.
• The dipoid (2n) phase is the zygote, which
forms when gametes fuse at fertilization.

23. Evolution of Pollen and Seeds
• Like some seedless species, seed bearing
plants produce not one but two (2) types of
spores.
• This condition is called heterospory, an
opposed to homospory (only one type).
• pollen grains, which develop into a mature
sperm bearing male gametophytes.
– do not require free-standing water to reach the
egg

24. Pollen Grain
• The evolution of pollen
grains contributed to
the successful radiation
of seed bearing plants
into high and dry
habitats

25. Seeds
• It was no coincidence that
during the Permian time
when the climate was
extreme, seed plants rose
dominant.

26. Plant Diversity
• Bryophytes
• The Bryophytes lineage consists of about
18,600 species called mosses, liverworts and
hornworts.
• These nonvascular plants are mostly well
adapted to grow in fully or seasonally moist
habitats although there is also other rare
types of mosses thriving in deserts and
windswept plateaus of Antartica.

27. Examples of Bryophytes
Liverworts
(Phylum Hephaeophyta)
Hornworts
(Phylum Anthoceraphyta)

28. Mosses
Phylum Bryophyta

29. Physical Characteristics of Bryophytes
• All known Bryophytes are less
than twenty (20) centimeters
(eight inches tall). They have
leaflike, stemlike and rootlike
parts but these do not contain
xylem and phloem.
• Most have rhizoids, which are
elongated cells or threadlike
structures that attach
gametophytes to the soil and
serve as absorptive structures.

30. Evolution of Bryophytes
• Presence of Cuticle
• Cellular Jacket
• Large gametophytes

31. Mode of Reproduction of Bryophytes

32. SEEDLESS VASCULAR PLANTS
• Descendants of seedless plants lineage still
exist today such as whisk ferns, lycophytes,
horsetails and ferns.

33. How does Vascular plants differ from Bryophytes?
• Sporophytes does not remain attached to
gametophyte
• It has true vascular tissues
• Seedless Vascular plants is larger and have
longer lived phase life cycle

34. Characteristics of Seedless Vascular
plants
• Most seedless vascular plants live in wet,
humid places, and their gametophytes lack
vascular tissues. Water droplets clinging to the
plants are the only means by which flagellated
sperm can reach the eggs.

35. Life Cycle of Vascular Seedless plants

36. Examples of Seedless Vascular Plants
Whisk Ferns
(Psilophyta)
Lycophytes
(Lycophyta)

37. Examples of Seedless Vascular Plants
Horsetail
(Sphenophyta)
Ferns
(Pterophyta)

38. RISE OF THE SEED-BEARING PLANTS
• In terms of diversity, numbers and
distribution, they would become the most
successful groups of the plant kingdom.
• Seed Ferns, Gymnospserm and much later the
angiosperm were the dominant groups.

39. How do they differ from Seedless
Vascular Plants?
• Besides microspores, seed-bearing plants
also reproduce megaspores – these develop
within ovules the female reproductive
structures which at maturity are seeds.
• Each ovule consists of female gametophytes
(with its egg cell), nutrient-rich tissue, and a
jacket of cell layers which develops into seed
coats. A zygote will form inside the ovule.

40. • Compared with the seedless vascular plants,
gymnosperms had water conserving traits,
including thick cuticles and stomata recessed
below the surface of the leaf.

41. How do Pines Reproduce?
• Pine tress produces pine cones.
• The scales are parts of a mature female cone
which bears ovules in which megaspores formed
and developed into female gametophytes.
• Pine trees also produce male cones, in which
microspores forms and develop into pollen
grains.
• Pollination is completed when some land on
ovules of female cones.
• For pines, fertilization occurs months or a year
after pollination.

42. • Unlike the seeds of
flowering plant, which
are enclosed in a
reproductive chamber
(an ovary),
gymnosperm seeds
grows, in an exposed
location, on top of a
spore-producing
structure.

43. Gymnosperm Diversity
• Conifers

44. Gymnosperm Diversity
• Cycads

45. Gymnosperm Diversity
• Ginkgos

46. Angiosperms – The Flowering, Seed
Bearing plant
• Only the Angiosperm produce specialized
reproductive structures called Flowers.
• Angeion, which means vessel, refers to the
female reproductive parts at the center of the
flower. The enlarged base of the “vessel” is
the floral ovary, where ovules and seeds
develop.

48. Embryo Development of Angiosperms

49. Embryo Development in Angiosperm
• The first mitotic division of the zygote splits the
fertilized egg into a basal cell and a terminal cell
• The basal cell produces a multicellular suspensor,
which anchors the embryo to the parent plant
• The terminal cell gives rise to most of the embryo
• The cotyledons form and the embryo elongates

50. Structure of the Mature Seed
• The embryo and its food supply are
enclosed by a hard, protective seed
coat
• Below the cotyledons the
embryonic axis is called the
hypocotyl and terminates in the
radicle (embryonic root); above
the cotyledons it is called the
epicotyl
• The plumule comprises the
epicotyl, young leaves, and shoot
apical meristem

51. Derivation from seed to plant

52. • Seeds gives rise to mature plants when their
dormancy is disrupted in the presence of
water. Hypocotyl gives rise to shoot system of
the plant, Cotyledon diminishes once the
plant is already able to have stable transport
of nourishments.

53. • There are two (2) classes of flowering plants
called the dicots and monocots.
• The monocots are grass and "grass-like"
angiosperms (flowering plants). Particularly, the
embryos of monocots have only a single (mono-)
first leaf (a.k.a., seed leaves or cotyledon),
vascular bundles are arranged throughout the
stem’s ground tissue and leaf venation projects in
parallel unlike in Dicots which has netted
venation and their vascular bundles are arranged
in a ring.

54. Characteristics Monocot
Dicot
Number of
cotyledons
One Cotyledon Two Cotyledons
Number of floral
parts
Floral parts in three Floral parts in four
or five
Leaf venation Parallel Netted
Number of pores in
their pollen grain
Pollen grain has one
pore or furrow
Pollen grain has
three pore or
furrows
Arrangement of the
vascular bundles
Vascular bundles are
arranged
throughout stem’s
ground tissue
Vascular bundles
arranged in ring

57. END OF REPORT