13.3: Nutrient cycles

Question 1

N2

Answer 1

atmospheric nitrogen

Question 2

Extracellular digestion

Answer 2

A process carried out by saprobionts in which they secrete enzymes onto dead organic matter which break down large, insoluble molecules

Question 3

What are saprobionts

Answer 3

Microorganisms for example: fungi and bacteria

Question 4

Importance of extracellular digestion

Answer 4

vital so that continuously reusing nutrients

Question 5

What happens to the products of extracellular digestion?

Answer 5

they are small, soluble molecules which can be absorbed by the saprobiont and used in respiration or stored

Question 6

4 steps in nitrogen cycle

Answer 6

1: Nitrogen fixation
2: Ammonification
3: Nitrification
4: Denitrification

Question 7

Nitrogen fixation

step 1

Answer 7

N2 into NH3

by nitrogen fixing bacteria in the soil

Question 8

Nitrogen fixing bacteria (mutualistic)

Answer 8

Form a mutualistic relationship with leguminous plants by inhabiting their root nodules and provide a source of ammonium ions for the plants and the plants provide them with sugars

Question 9

Leguminous plants

Answer 9

eg: beans and peas

Question 10

Ammonification

step 2

Answer 10

Saprobionts decompose a dead organism by extracellular digestion they release inorganic ammonium ions into the soil

Question 11

Nitrification

step 3

Answer 11

NH4 + ions (that are released from step 2)

are converted into nitrates by nitrifying bacteria into nitries and then another bacteria convert them into nitrates

Question 12

Denitrification

step 4

Answer 12

Denitrifying bacteria convert nitrates back into N2

a process that occurs in anaerobic conditions when the soil is waterlogged

Question 13

2 types of nitrogen fixing bacteria

Answer 13

free-living nitrogen fixing bacteria

mutualistic nitrogen fixing bacteria

Question 14

Free-living nitrogen fixing bacteria

Answer 14

reduce gaseous nitrogen to ammonia then they manufacture amino acids

Question 15

The phosphorus cycle

Answer 15

Phosphorus exists mostly of PO4 3-
(phosphate ions) into sedimentary rock deposits in the sea but are often brought up to the surface by the geographical uplifting of rocks

Question 16

Mycohorrizae associations

Answer 16

Fungi form symbiotic relationships with the roots of plants and act like extensions of the plants roots

Question 17

Mycohorrizae role

3

Answer 17

vastly increase the SA of plants for the absorption of water and minerals and act like a sponge
enables plants resist droughts more easily
improves the uptake of quite scarce ions eg: phosphate ions