Nitrogen Cycle: In Depth: Dr A

Question 1

What is the FIRST STAGE of the NITROGEN CYCLE?
What occurs in this process?

Answer 1

• NITROGEN FIXIING
  -N2 GAS in ATMOSPHERE is ABSORBED by N-FIXING BACT.
• N-N is BROKEN which is then CONVERTED to NH4+
• Which is then ABSORBED into PLANT via ACTIVE TRANSPORT

Question 2

What is a RARE way in which NITROGEN can be FIXATED?

Answer 2

• By a LIGHTNING STRIKE
• Has enough energy to BREAK N-N
• And OXIDISE into NITRATES (NO3-)

Question 3

Why do PLANTS and N-FIXING BACTERIA have a SYMBIOTIC RELATIONSHIP?

Answer 3

• PLANTS provide N-FIXING BACT. with O2 so they can RESPIRE AEROBICALLY
• Whilst the N-FIXING BACT. provides the PLANT with NH4+

Question 4

Describe SAPROBIONT NUTRITION

Answer 4

SAPROBIONTS feeding on DEAD MATTER & WASTE

Question 5

Describe EXTRACELLULAR DIGESTION and WHAT IT ALLOWS

Answer 5

• SAPROBIONT secrete ENZYMES that allow the break down of ORGANIC MOLECULES
• Which they then ABSORB
  -This process allows SAPROBIONT NURTITION

Question 6

What is the SECOND STAGE of the NITROGEN CYCLE?
What occurs in this process?

Answer 6

• AMMONIFICATION
• SAPROBIONTS convert LARGER BIOLOGICAL MOLECULES in the SOIL into NH4+
• Via EXTRACELLULAR DIGESTION

Question 7

What is the THIRD STAGE of the NITROGEN CYCLE?
What occurs in this process?

Answer 7

• NITRIFICATION
• NITRIFYING BACT. convert NH4+ into NO2-, then into NO3-
• Which is EITHER:
  —> Returned into the ATMOSPHERE as N2 (g)
  —–> OR absorbed by plants to make LARGER BIOLOGICAL MOLECULES like PROTEINS & NUCLEIC ACIDS

Question 8

What is the FOURTH STAGE of the NITROGEN CYCLE?
What occurs in this process?

Answer 8

• DENITRIFICATION
• DENITRIFYING BACT. converts NO3- into N2 (g) which returns to the ATMOSPHERE
• OR the O3 in the NO3- is used by the DENITRIFYING BACT. to respire AEROBICALLY
• Which then leaves N2 (g) which can return to the ATMOSTPHERE OR be FIXATED into NH4+