University Biology II: Plant Biodiversity and Adaptation Project

This report provides a comprehensive analysis of plant biodiversity and adaptation, focusing on the evolutionary transition from aquatic to terrestrial habitats. It begins by highlighting the origins of land plants from aquatic algae and their subsequent diversification into subgroups like mosses, ferns, conifers, and flowering plants. The report then delves into the challenges plants faced during this transition, including body support, tissue differentiation, and fertilization methods. It examines the evolutionary adaptations that enabled plants to overcome these challenges, such as the development of supportive tissues, conducting vessels, and specialized reproductive strategies. Furthermore, the report discusses the role of natural selection in shaping plant evolution, particularly during the Paleozoic periods. It explores how environmental factors, such as competition for sunlight and periods of drying, drove the development of terrestrial features. The report also details the advantages of life on land, including increased sunlight and access to nutrients. Finally, it emphasizes the significance of plant evolution in shaping the environment and paving the way for the evolution of land animals. The report references several sources to support its findings and provide a well-rounded understanding of the topic.

Running head: Plant Biodiversity and Adaptation
Assignment
Biology II Week 1 Project
Plant Biodiversity and Adaptation
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Plant Biodiversity and Adaptation 2
Plant Biodiversity and Adaptation
There are significant evidences that earlier land plants have originated from the aquatic habitats
(Annenberg Foundation, 2017). The protists known as single celled freshwater green algae
(charophytes), evolved into a new form of terrestrial eukaryotic plants diversifying into four
subgroups namely mosses, ferns, conifers and flowering plants. These four subgroups are known
to exhibit a certain evolutionary pattern depicting the transition from water to land. The algae
still exhibit similarities with the plants like both have green pigment and both have cellulose in
cell walls.
Challenges faced by Plants during Transition
Body Support
The transition involved many challenges in their adaptations. For example, the body structure of
aquatic plants consisted of gas filled vesicles and kelps which provided them features to float on
the water. Under the water the plants had to face lower levels of gravitational forces. On the
other hand the land plants had to counter the force of gravity while getting taller. The adaptive
organelles like cell walls, and woody tissue provided support to the growing flowering plants and
conifers. Mosses do not possess any supportive woody tissues therefore exhibit only lower level
of growth on the land. The ferns have primitive tissue support confining their growth to just less
than a meter over the grounds.
Differentiation of Tissues

Plant Biodiversity and Adaptation 3
During the evolution of land adaptations in plants, tube like conducting vessels (xylem and
phloem) emerged to take the water and minerals up and down. The different parts of plants
exhibited differentiation where the leaves conducted the functions of making food, well
developed root system used to uptake nutrients from the soil, and the stem used to support the
plants structure (CK-12 Foundation, 2019). The aquatic plants used to take the nutrients directly
from the water through their surface. Such tissue differentiation was an evolutionary adaptation
in the plants to serve the diverse set of roles like making food, transporting it, and growing taller
on land habitat.
Earlier aquatic plants had a waxy layer named cuticle, to protect them under water and avoid te
loss of water from pant body. In land plants, the stomata evolved in the leaves to carry out the
gaseous exchange and water exchange.
Fertilization
In aquatic plants the transfer of pollen occurred through water. While in land adaptations, it
requires wind to transport the pollen and there is no need of water. In aquatic conditions, the
fertilized egg is always moist and never at risk of getting dehydrated while in land plants the
embryo are enclosed in seeds where it receives food for its development and growth. The
conifers and the flowering plants have seeds while the ferns and mosses rely on water for
dehydration of embryo and do not produce seeds.
The evolution of plants from aquatic to terrestrial habitats can be best represented by the plants
Mosses ( For example, Hygrohypnum styriacum)

Plant Biodiversity and Adaptation 4
, Ferns (Polypodiophyta polypodiidae), Conifers ( For example, Pinus longaeva) and Flowering
Plants respectively in sequence (Annenberg Foundation, 2017). The mosses require water for
fertilization; have no stiff support tissues, no true leaves, stems, roots, no seeds flowers and
fruits, and no conducting tissues. Ferns are next in evolution, having stiff tissue system,
conducting tissues, and true differentiation of plant parts. However they need water for
fertilization and have no seeds, flowers and fruits. The conifers are at next advance level. They
have no flowers and fruits and don’t need water for fertilization. The flowering plants have all
the advanced features with seeds enclosed inside fruits.
Role of Natural Selection
The Paleozoic periods are identified for the gradual development of reproductive mechanism and
the novel structures. In aquatic environment, the algae used to compete for receiving maximum
sunlight (Vries & Archibald, 2017). Transition to land habitats, eliminated the need of such
competition for sunlight. There were favorable conditions of decreased competition and
increased photosynthesis.
The areas where this transition took place had periods of drying out and saturation. Certain plants
developed terrestrial features which helped them evolve and survive during the dry season,
through natural selection.
Recovered fossil specimens show that Devonian periods saw an increase in ferns, and seed
plants which further took form of trees and the dense forests. It is identified that the plants had

Plant Biodiversity and Adaptation 5
developed before the animals on land. When the animals fed over the vast sources of greenery on
land, the plants gradually acquired the features to combat predation like thorns and spines.
The studies conducted on mosses Physcomitrella patens demonstrated that during the devonian
period, reduced concentration of carbon dioxide (90%) in atmosphere initiated the development
of leaves. The leaves enhanced the efficiency of Carbon Dioxide trapping for performing the
process of photosynthesis. The environment also needed elevation in density of stomata to
facilitate the high rate of photosynthesis in leaves. It led to development of different types of
phyllotaxy in the leaves structure. A number of transcription factors lead to genetic innovations
like retention of zygote, development of cuticle, stiff erect growth of stem, resulting into
transition of adaptations from water to land (Reski, 2018).
The mechanisms like Genome doubling also played an important role in the evolution of plants
leading to polyploidy and redundancy in functional roles.
Advantages of Life on Land
There is plenty of sunlight. The chlorophyll is available in adequate amount to foster the
production of high amounts of nutrients for the plants which would be helpful in addressing the
development needs of the tall plants. The earliest plants developed and propagated at the coastal
areas of the water bodies. It helped them deal with the water scarcity and satisfy their needs.
However the resistance to Desiccation allowed the plants to move towards distant locations away
from the water bodies. The plants developed thorns and spines like that in cactus, which prevents
the excessive water loss from the plant at highest temperatures. The land plants also developed
adaptations to sustain their prevalence and diversity in the terrestrial environments. Additionally

Plant Biodiversity and Adaptation 6
the main four adaptations also developed in the land plants like Apical Meristem tissue in the
shoot and root, a Gametangium giving rise to haploid cells, a Sporangium and alternation of
generations (Open University of Hong Kong, 2015). The most primitive plants like algae had
rhizoids in place of roots. The vascular plants had other adaptations like lignen, and variations in
the life cycle with a dominant diploid generation (sporophytic) to survive on harsh conditions of
land. It was advantageous as the diploid plants are susceptible to harmful impact due to
mutations and genetic variations.
With high numbers of vascular plants, the non vascular plants got extinct. We can say that the
plants were the earliest living beings which left the aquatic habitats in oceans and colonized on
land. The increase in land animals undoubtedly elevated the oxygen levels and manipulated the
carbon cycle (Reski, 2018). These conditions were favorable breeding grounds for the evolution
of land animals.

Plant Biodiversity and Adaptation 7
References
Annenberg Foundation (2017). The transition from water to land. Retrieved from
https://www.learner.org/courses/essential/life/session4/closer2.html
Candella,L.(n.d.). Early plant life. Retrieved from https://courses.lumenlearning.com/boundless-
biology/chapter/early-plant-life/
CK-12 Foundation (2019). Plant Evolution. Retrieved from https://www.ck12.org/biology/plant-
evolution/lesson/Plants-Adaptations-for-Life-on-Land-MS-LS/
Open University of Hong Kong (2015). Plant Adaptations to life on land. Retrieved from
http://www.opentextbooks.org.hk/ditatopic/34995
Reski,R.(2018). Enabling the water to land transition. Nature Plants. 4(2), 67-68. Retrieved from
DOI: 10.1038/s41477-018-0101-5
Vries,J. & Archibald, J.M.,(2017). Plant Evolution: Landmark on the path to terrestrial life.
Retrieved from https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.14975