Plants are autotrophic i.e. they do not rely on other organisms for food. Instead they build complex molecules from simple substances by the process of photosynthesis, using light energy. Light energy is absorbed by the green pigment chlorophyll found in the chloroplasts of most plant cells. This energy is required to combine carbon dioxide and water. They also have a cellulose cell wall.
The Plant kingdom
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Different challenges Plants faced when they moved onto land:
Solutions!
Presence of waxy cuticle and epidermis that absorb UV light
Presence of waxy cuticle and hair like structures to reduce loss of water
Specialised reproductive structures that do not require water for gamete transfer
Major milestones in plants evolution
1) Growth occurring at shoot and root tips allowing them to reach additional space and resources
2) Cells developed lignin that offered support enabling the plant to grow tall and upright exposing the leaves to the sun
3) Vascular (transport) tissues enabled plants to transport nutrients and water efficiently throughout the plant body
4) Leaves developed pigments that absorb UV radiation, a waterproof cuticle layer that reduces water loss and stomata (to allow gaseous exchange)
5) A main plant body that ensures that the new generation of plants can survive until conditions are favourable for growth.
UV radiation causes mutations
Angiosperms
Gymnosperms
Ferns
Moss
Spermatophytes
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They are non-vascular seedless plants
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They have a very simple structure called a thallus, which lacks proper roots, leaves, and stems
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They have hair-like structures called rhizoids on the lower surface absorb moisture.
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They are vascular seedless plants
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They have roots, stems, and leaves.
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They have a waxy layer that allows them to colonize drier areas
Vascular tissue allows ferns to attain considerable sizes. This led to their domination of land forming vast forests and providing food for the animals that were starting to move on land.
The absence of vascular tissue limits their size and spread and they are heavily dependent on water for reproduction.
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Reproduction still requires a damp environment and so ferns can’t live in very dry places like deserts.
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They are vascular seed plants.
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They are able to conserve water and reproduce through seeds.
These are plants whose seeds are formed in cones and are not enclosed in an ovary (fruit).
They have needle-like leaves and a waxy cuticle.
Examples include conifers.
These are flowering plants whose seeds are formed within the ovaries of flowers, which develop into fruits that aid seed dispersal.
They are the most diverse and successful group of land plants, making up approximately 90% of all living plant species.
They are divided into monocots and dicots.
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Plant Classification
Land plants can be characterized by:
➔ the presence or absence of vascular tissue (xylem and phloem)
➔ the way they reproduce, with or without seeds.
There are 3 main groups:
1) Non-vascular seedless plants: These are plants that lack vascular tissue and reproduce without seeds. Examples include mosses.
2) Vascular seedless plants: These are plants that have vascular tissue but reproduce without seeds. Examples include ferns.
3) Vascular seed plants: These are plants that have vascular tissue and reproduce through seeds. Examples include gymnosperms and angiosperms.
