The Evolution of Plants Did you know that plants used to live only in water millions of years ago? In fact, they didn’t even look like plants… plants ancestors were simply algae! Eventually, they evolved to find their way onto land and make use of a completely new environment. Advantages for plants to live on land: Living on land offered new opportunities such as… o Unlimited sunlight o Abundant CO2 o Initially, there were very few pathogens and herbivores. Challenges for plants to live on land: Even though living on land had its perks… there were also several problems with it… Water beads on the waxy cuticle of kale leaves Plants had to figure out how to regulate water loss within the cells. The waxy covering on top of leaves, called a plant cuticle, evolved on the surface of leaves to reduce water loss. This is why leaves are shiny, waxy and water rolls off. Human epidermis (skin) is similar in its function because our skin serves as a defense against physical damage and infectious organisms and the oils on our skin help us retain water (and keep the epidermis flexible). Plants had to figure out how to obtain resources from soil and air. There were no vessels that could carry water throughout the plant… so eventually they developed vascular tissue to transport water/sugar within the plant. Plants had to figure out how to support their body up in the air because algae had no such structures. This gave way to the specialization of the root system and the shoot system. Plants had to figure out how to reproduce and disperse their offspring without water. This gave way to spores, seeds and fruits for dispersal and pollen for fertilization.
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The Evolution of Plants
Did you know that plants used to live only in water millions of years ago? In fact, they didn’t even look like plants… plants
ancestors were simply algae! Eventually, they evolved to find their way onto land and make use of a completely new
environment.
Advantages for plants to live on land:
Living on land offered new opportunities such as…
o Unlimited sunlight
o Abundant CO2
o Initially, there were very few pathogens and herbivores.
Challenges for plants to live on land:
Even though living on land had its perks… there were also several problems with it…
Water beads on the waxy cuticle of kale leaves
Plants had to figure out how to regulate water loss within the cells. The waxy covering on top of leaves, called a plant cuticle,
evolved on the surface of leaves to reduce water loss. This is why leaves are shiny, waxy and water rolls off. Human epidermis
(skin) is similar in its function because our skin serves as a defense against physical damage and infectious organisms and the
oils on our skin help us retain water (and keep the epidermis flexible).
Plants had to figure out how to obtain resources from soil and air. There were no vessels that could carry water throughout the
plant… so eventually they developed vascular tissue to transport water/sugar within the plant.
Plants had to figure out how to support their body up in the air because algae had no
such structures. This gave way to the specialization of the root system and the shoot system.
Plants had to figure out how to reproduce and disperse their offspring without water. This gave way to spores, seeds and fruits
for dispersal and pollen for fertilization.
In all plants, the zygote develops into an embryo while attached to and nourished by the parent plant. Plants are embryophytes,
with multicellular, dependent embryos.
From algae to moss to seedless, vascular plants to seed-bearing plants to finally… flowering-plants.
The first group of plants that made it on land are best known as BRYOPHYTES.
Bryophytes: the
first land plants. They need relatively moist/wet environments to survive.
Early land plants reproduced with spores that would swim (with little whipping tails called flagella) through moist soil and find the
female organs. This is why they needed to be in constantly damp environments and early plants only existed near shores and
streams.
Without a robust vascular system, plants couldn’t get taller than a couple feet max and most were very close to the
ground. Plants eventually evolved to have vessels and those were able to grow very tall and grab more sunlight for
photosynthesis (literally overshadowing the competitors) and their spores were able to be blown greater distances due to the
Plants adapted to the dehydrating land environment through the development of
new physical structures and reproductive mechanisms. LEARNING OBJECTIVES[ EDIT ]
Discuss how lack of water in the terrestrial environment led to significant adaptations in plants
Describe the life cycle of a haplodiplodontic species
KEY POINTS[ EDIT ]
While some plants remain dependent on a moist and humid environment, many have adapted to a more arid climate by developing tolerance or resistance to drought conditions.
Alternation of generations describes a life cycle in which an organism has both haploid (1n) and diploid (2n) multicellular stages, although in different species the haploid or diploid stage can be dominant.
The life on land presents significant challenges for plants, including the potential for desiccation, mutagenic radiation from the sun, and a lack of buoyancy from the water.
TERMS[ EDIT ]
desiccation tolerance the ability of an organism to withstand or endure extreme dryness, or drought-like condition
alternation of generation the life cycle of plants with a multicellular sporophyte, which is diploid, that alternates with a multicellular gametophyte, which is haploid
Plant Adaptations to Life on Land As organisms adapted to life on land, they had to contend with several challenges in the terrestrial environment.
The cell's interior is mostly water: in this medium, smallmolecules dissolve and diffuse and the majority of the
chemical reactions ofmetabolism take place. Desiccation, or drying out, is a constant danger for organisms
exposed to air. Even when parts of a plant are close to a source of water, the aerial structures are prone to
desiccation. Water also provides buoyancy to organisms. On land, plants need to develop structural support in
a medium that does not give the same lift as water. The organism is also subject to bombardment by mutagenic
radiation because air does not filter out the ultraviolet rays of sunlight. Additionally, the male gametes must
reach the female gametes using new strategies because swimming is no longer possible. As such, both gametes
and zygotes must be protected from desiccation. Successful land plants have developed strategies to face all of
these challenges. Not all adaptations appeared at once; some species never moved very far from the aquatic
environment, although others went on to conquer the driest environments on Earth.
Despite these survival challenges, life on land does offer several advantages. First, sunlight is abundant. Water
acts as a filter, altering the spectral quality of light absorbed by the photosynthetic pigment chlorophyll. Second,
carbon dioxide is more readily available in air than water since it diffuses faster in air. Third, land plants
evolved before land animals; therefore, until dry land was also colonized by animals, no predators threatened
plant life. This situation changed as animals emerged from the water and fed on the abundant sources