The bacteria can chemically combine nitrogen with hydrogen to form ammonia (NH3). This combining process is called nitrogen fixation.

Which group of organisms chemically combines nitrogen with hydrogen in a process called nitrogen fixation?

bacteria

birds and reptiles

only aquatic plants

all mammals

Bacteria

Explanation:

Nitrification fixation takes place by nitrogen-fixing bacteria like Azotobacter, Klebsiella, Bacillus etc which convert atmospheric nitrogen gas into fixed-nitrogen compounds like nitrates or ammonium ions for the plants to readily absorb.

The nitrogen fixing bacteria can be free-living like cyanobacteria or live with symbiotic relationship with plants and fungi.

The chemical conversion of di-nitrogen to ammonia takes place with the help of enzymes like nitrogenase in combination with leghahemoglobin, a protein through a reduction reaction.

the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.