Oxygen shows cooperative binding to hemoglobin. cooperative binding has the following effects on the binding and release of oxygen:
oxygen binding to hemoglobin: when one molecule of oxygen binds to one of hemoglobin's four subunits, the other subunits change shape slightly, increasing their affinity for oxygen.
oxygen release from hemoglobin: when four oxygen molecules are bound to hemoglobin's subunits and one subunit releases its oxygen, the other three subunits change shape again. this causes them to release their oxygen more readily.
these two graphs show how cooperative binding differs from a hypothetical situation where binding is not cooperative.
the x-axis shows the partial pressure of oxygen (po2). this is a measure of the amount of oxygen present in a tissue. the blue arrows on the x-axis show the partial pressure of oxygen in various tissues of the body.
the y-axis shows the oxygen saturation of hemoglobin (o2 saturation). this is the percentage of oxygen-binding sites on hemoglobin molecules that are actually bound to oxygen.

When four oxygen molecules are bound to hemoglobin's subunits and one subunit releases its oxygen, the other three subunits change shape again. This causes them to release their oxygen more readily.

Explanation:

Each hemoglobin molecule can bind up fou oxygen molecules, hemoglobin exhibits what it is call cooperative binding, as oxygen binding increases the affinity of hemoglobin for more oxygen. Incresed affinity is caused by a conformational change, or structural change in the hemoglobin molecule.

The cooperative binding of oxygen to hemoglobin is an important adaptation for gas exchange . Cooperativity allows hemoglobin to release much more oxygen to our body's tissues.

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

step 1: initiation

initiation is the beginning of transcription. it occurs when the enzyme rna polymerase binds to a region of a gene called the promoter. this signals the dna to unwind so the enzyme can ‘‘read’’ the bases in one of the dna strands. the enzyme is now ready to make a strand of mrna with a complementary sequence of bases.

step 2: elongation

elongation is the addition of nucleotides to the mrna strand. rna polymerase reads the unwound dna strand and builds the mrna molecule, using complementary base pairs. there is a brief time during this process when the newly formed rna is bound to the unwound dna. during this process, an adenine (a) in the dna binds to an uracil (u) in the rna.

step 3: termination

termination is the ending of transcription, and occurs when rna polymerase crosses a stop (termination) sequence in the gene. the mrna strand is complete, and it detaches from dna.