Feeding Flashcards
Why does life on earth require food?
All individuals, regardless of whether they are a single-celled or multi-cellular organism, require food (a resource) to maintain normal cellular function and replication, and, to reproduce.
The required food is either consumed directly or synthesised by the individual.
How food is acquired - Autotrophs
Are represented in all three Domains and four of the six Kingdoms of life (Bacteria, Archaea, Protista, Plantae)
Synthesise the food they require for life (but may need to source other nutrients such as Nitrogen, N, from the environment).
How food is acquired - Heterotrophs?
are unable to make their own food, and so must consume other sources
of organic carbon and other nutrients (i.e. by consuming other forms of life).
are found in all Domains and Kingdoms of life and is the exclusive mode of feeding for the Kingdoms Fungi and Animalia.
What are the types of autotrophs and their importance?
- Chemoautotrophs – these are bacteria that also synthesise their own organic molecules using the oxidation of inorganic compounds (hydrogen gas, hydrogen sulfide, methane, or ferrous ions) as a source of energy, rather than sunlight.
- Photoautotrophs – these green plants, some bacteria and algae manufacture all their required organic molecules from simple inorganic molecules, using sunlight as the energy source for photosynthesis.
What are the types of heterotrophs and their importance?
- Carnivores - eat animals
- Insectivores - eat insects
- Herbivores - eat plants
- Omnivores - eats meat, plants, fungi etc.
- Scavengers - eat remains of food left by carnivores and herbivores
- Detritivores - eat soil, leaf litter and other decaying organic matter
What was the ancestral state of heterotrophs?
Earliest life forms were likely single-celled primitive heterotrophs that would have resembled modern day bacteria
Fed by absorbing acid and base molecules in the early organic (C) oceans.
This chemical breakdown was a form of fermentation
What was the ancestral state of photoautotrophs?
The earliest photoautotrophs were likely photosynthetic bacteria
• These early forms were capable of anoxygenic photosynthesis – a
photosynthetic pathway that occurs in the absence of oxygen
• Over time we see the emergence of oxygenic photosynthesis – a photosynthetic pathway that occurs in the presence of oxygen
• Oxygenic photosynthesis evolved about 2.7 billion years ago in bacteria that were similar to modern cyanobacteria
• Then…. early eukaryotic cells engulfed photosynthetic bacteria (through endocytosis) resulting in the first plant cells – endosymbiotic theory.
Define the endosymbiotic theory
An endosymbiont is a cell which lives inside another cell with mutual benefit
Eukaryotic cells are believed to have evolved from early prokaryotes that were engulfed by phagocytosis
The engulfed prokaryotic cell remained undigested as it contributed new functionality to the engulfing cell (e.g. photosynthesis)
Over generations, the engulfed cell lost some of its independent utility and became a supplemental organelle
Support for the endosymbiotic theory
1.Phylogenetically related: Chloroplasts (related to cyanobacteria) and mitochondria (related to proteobacteria)
2. Genome reduced: As organelles, Mitochondria and Chloroplasts have their own DNA but the genome size is reduced compared to their prokaryote ancestors.
Autotroph adaptations to living on land
Roots to extract water and dissolved nutrients from soil
• Vascular tissue for transporting water and nutrients
• Water-resistant coating (cuticle) to minimise water loss to the atmosphere
• Tissue for structural support
• Diversity of leaf types and size for photosynthesis
Life’s Complexity
The importance of roots in autotroph adaptations
Are the underground organs of vascular plants
• Support nutrient (e.g. N, P, K and Ca, Mg, S) and water uptake from the soil
• Provide anchorage and support (important as plants increase in size)
• Synthesis of plant hormones and storage of nutritional reserves
• Can be modified (aerial roots for O2 uptake in salt marshes and swamps; clasping roots in climbing plants; prop roots that support and contractile roots to pull the plant firmly into its substrate).
The vascular system in autotroph adaptations
The vascular system consists of phloem for the transport of sugars and xylem for the transport of water and mineral ions
• In more advanced vascular plants the xylem is reinforced by a rigid layer of lignin
• Trees, have long stems and produce large amounts of wood through secondary growth
Two reasons the vascular system allowed for increased size:
• The conducting system allows transport of sugars and water to larger areas
• Lignin prevents xylem cells from collapsing under hydrostatic pressure.
The importance of leaves in autotroph adaptations
Land plants originally had their photosynthetic apparatus on the stems
• Leaves evolved multiple times in land plants and provided an increased SA for
photosynthesis and gas exchange
• Leaves are thought to have evolved from modified branches that overlapped and flattened
• Leaves are the most important organs of most vascular plants
• The structure and diversity of leaves is enormous and varies depending on the
type of environment and ecological niche
What are the ingenious adaptations of autotrophs to get food?
Parasitic plants (e.g. mistletoe)
• Derive all of their nutrients from other plants
• Have modified roots that penetrates the host plants walls connecting them to the vascular
system (either the xylem, phloem or both)
Carnivorous plants (e.g. Venus flytrap)
• Derives some nutrients from capturing prey (insects and arachnids)
• Have a trapping structure typically triggered by tiny “trigger” hairs on their inner surfaces.
Symbiotic legumes (e.g. pea plants)
• Many legumes house other symbiotic nitrogen-fixing bacteria (e.g. Rhizobium) in root structures called root nodules
• These bacteria are beneficial when soils have poor nutrients (e.g. N)
Symbiotic autotrophic algae (e.g. zooxanthellae)
• Zooxanthellae live in symbiosis within coral
• They provide nutrients to coral (sugars, glycerol, amino acids) and gain CO2, phosphates, and
nitrogen compounds in return.
What are the heterotroph feeding strategies?
Diffusion - movement of nutrients through the cell membrane (Domain/Kingdom: Bacteria)
Phagocytosis - engulfing items of food or prey (Kingdom Protista: Amoeba, Kingdom Animalia: Sponges) - Evolved specialised structures or cells to assist
Disadvantage of diffusion and Phagocytosis – unlikely to support larger or more complex species
