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Algae lack the various structures that characterize plants (which evolved from freshwater green algae), such as the phyllids (leaf-like structures) and rhizoids of bryophytes (non-vascular plants), and the roots, leaves and other xylemic/phloemic organs found in tracheophytes (vascular plants). Most algae are autotrophic, although some are ...
Streptophyte algae include all green algae, and are the only photosynthetic eukaryotes from which the macroscopic land flora evolved (red lines). That said, throughout the course of evolution, algae from various other lineages have colonized land (yellow lines) —but also streptophyte algae have continuously and independently made the wet to ...
Eukaryotic photoautotrophs include red algae, haptophytes, stramenopiles, cryptophytes, chlorophytes, and land plants. [6] These organisms perform photosynthesis through organelles called chloroplasts and are believed to have originated about 2 billion years ago. [1]
In plants, algae, and cyanobacteria, photosynthesis releases oxygen. This oxygenic photosynthesis is by far the most common type of photosynthesis used by living organisms. Some shade-loving plants (sciophytes) produce such low levels of oxygen during photosynthesis that they use all of it themselves instead of releasing it to the atmosphere. [12]
Photosynthesis is the main means by which plants, algae and many bacteria produce organic compounds and oxygen from carbon dioxide and water (green arrow). An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds , which can be used by other organisms .
[example needed] Most chlorophytes have one or more storage bodies called pyrenoids (central proteinaceous body covered with a starch sheath) that are localised around the chloroplast. Some algae may also store food in the form of oil droplets. The inner cell wall layer is made of cellulose and the outer layer of pectose.
The photosynthetic system of brown algae is made of a P700 complex containing chlorophyll a. Their plastids also contain chlorophyll c and carotenoids (the most widespread of those being fucoxanthin). [53] Brown algae produce a specific type of tannin called phlorotannins in higher amounts than red algae do.
Seaweed species such as kelps provide essential nursery habitat for fisheries and other marine species and thus protect food sources; other species, such as planktonic algae, play a vital role in capturing carbon and producing at least 50% of Earth's oxygen. [3] Natural seaweed ecosystems are sometimes under threat from human activity.