Lessons 31 · 1 lessons · A. G‘afurov, A. Abdukarimov, J. Tolipova, O. Ishankulov, M. Umaraliyeva, I. Abdurahmonova. Biology Grade 11, 1st edition. Sharq Publishing and Printing Joint-Stock Company, Tashkent, 2018
31
The biomass of the biosphere
Textbook: pp. 146–149
GoalCompare land, ocean and soil biomass; link biomass distribution to climate zones and productivity; assess human impact.
Biomass is the total mass of all living organisms in the biosphere. The textbook estimate is about 2400 billion tonnes of dry matter, while recent studies give about 550 billion tonnes of carbon; the numbers differ with the method, but the conclusion is the same: most living mass (about 80–99 %) is land plants. From the poles toward the equator, land biomass and species number rise: lowest in tundra (about 500 species), highest in humid tropical forest (over 8000 species). Although the world ocean covers about 70 % of the Earth’s surface, its biomass is small and mostly consists of animals and microorganisms, because phytoplankton multiplies very fast and is quickly eaten by zooplankton and fish. Soil is also a biocenosis: roots, bacteria, fungi, earthworms, insects and rodents raise soil fertility. Humans harm biomass by deforestation, overfishing, pesticides and oil spills.
Worked examples
If land has 2400 bn t of plants and 20 bn t of animals and microorganisms, plant biomass is 2400 : 20 = 120 times larger. In the ocean, animals and microorganisms (3.0 bn t) outweigh plants (0.2 bn t) – the biomass pyramid is «inverted».
Phytoplankton multiplies in days and is eaten as fast, so although the plant mass present at one time is small, the annual product is large; the textbook says about a third of photosynthesis is in the ocean, while modern estimates give nearly half.
Class activity
Take 1 spoon (10–20 g) of school soil, look at it on white paper with a hand lens and count the living things you can see; return the soil afterwards. Safety: wear gloves and wash hands with soap afterwards; keep soil away from the mouth.
Practice
1
Why does biomass increase from the poles toward the equator?
More heat, light and moisture make photosynthesis stronger.
2
70 % of the Earth’s 510 million km² is ocean. What is the ocean area in million km²?
357
3
Why can animal biomass in the ocean exceed plant biomass?
Phytoplankton multiplies and is eaten fast, so its mass at any moment is small.
4
Give two groups of organisms that make up soil biomass.