Lessons 13–14 · 2 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology, Grade 10, 1st edition. “Sharq” publishing and printing joint-stock company, Tashkent, 2017
14
Types of organisms by mode of nutrition
Textbook: pp. 63–65
GoalDistinguish the types of nutrition of organisms (autotrophic, heterotrophic and their kinds) and explain their importance.
Nutrition is the taking in of matter and energy by an organism. By carbon source, autotrophs (make organic matter from inorganic) and heterotrophs (feed on ready-made organic matter) are distinguished. Autotrophs divide by energy source into phototrophs (green plants, cyanobacteria) and chemotrophs (nitrifying, iron, sulfur and hydrogen bacteria). Heterotrophs include animals, fungi, most bacteria and parasitic plants. In holozoic nutrition food is ingested, digested and absorbed (herbivorous and carnivorous animals). Saprotrophs (fungi, some bacteria) first release enzymes into the environment, break the food down outside and absorb the ready products. Parasites live at the expense of a host organism (the tetanus bacterium, rust fungi, dodder, the malaria Plasmodium, Ascaris). Some organisms feed in a mixed way (mixotrophs), for example Euglena. Plants absorb mineral salts dissolved in water (nitrates, phosphates, sulfates) from the soil; animals need elements such as Ca, P, Fe and F. Hygiene (washing hands, well-cooked food, clean water) protects against parasites.
Worked examples
A cap fungus growing on rotting wood releases enzymes outside: this is saprotrophic nutrition.
Dodder is a plant without green leaves that clings to another plant’s stem and draws ready substances from it: parasitic nutrition.
Class activity
“Food chain – type of nutrition”. 12 organism cards are sorted on the board into: phototroph, chemotroph, holozoic, saprotroph, parasite.
Practice
1
State the main difference between autotrophs and heterotrophs.
Autotrophs make organic matter from inorganic matter themselves; heterotrophs feed on ready organic matter.
2
Assign a nutrition type: cattle, yeast fungus, nitrifying bacterium, Ascaris.
How do the steps of saprotrophic and holozoic nutrition differ?
In holozoic nutrition food is ingested first, then digested inside and absorbed; in saprotrophic nutrition enzymes are released outside, digestion happens outside, and the products are then absorbed.
4
Why do plants need to get nitrogen, phosphorus and sulfur from the soil although they are autotrophs?
Photosynthesis makes carbohydrate only from C, H and O; proteins, nucleic acids, ATP and chlorophyll also need N, P, S and Mg, which are absorbed as mineral salts.