Summary WJEC (England) Eduqas A-Level Biology 3. Requirements for life - 3. Nutrition
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Course
3. Requirements for life
Institution
WJEC
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a. Autotrophic = complex organic molecules from simple inorganic + energy source
Photoautotrophic – photosynthesis: energy = sunlight
plants + some protoctista + some bacteria
Chemoautotrophic – chemosynthesis: energy = from exergonic chemical reactions
some bacteria
b. Heterotrophic (saprotrophic/holozoic/parasitic) = eat other organism for complex organic molecules
c. Saprotrophic = external digestion – fungi (hyphae grow over matter) + some bacteria
1. secrete enzymes onto dead organic matter
2. extracellularly digest food material
3. absorb digestion products – diffusion & active transport
d. Holozoic = internal digestion in gut – most animals
1. Ingestion: take in food
2. Digestion: break down molecules
- Mechanical: reduces size – increase SA for chemical digestion
- Chemical: enzymes hydrolyse large/insoluble/complex → small/soluble/simple molecules
3. Absorption into blood stream
4. Assimilation into cells
o synthesise other needed molecules (enzymes)
o respire (to release energy)
5. Egestion: eliminate undigested food
e. unicellular organisms
Amoeba – holozoic: nutrients through cell membrane
- endocytosis: engulf other unicellular organisms (bacteria/algae) into vacuole
- intracellular digestion: lysosomes fuse with vacuole – release digestive enzymes
- absorption of products into cytoplasm
- exocytosis: egest undigested material
f. multicellular organisms
Hydra: unspecialised sac-like gut + single opening
- tentacles paralyse fleas Daphnia: move through opening into gut cavity
- extracellular digestion: endodermis secretes protease & lipase
- intracellular digestion: phagocytosis moves partially digested food into endodermal cells
- egest undigested material via opening
Human alimentary canal: tube gut + different openings for ingestion & egestion
+ specialised regions for digestion of different food substances
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