How does Hansberry make the pages of 72 and 74 (act 1, scene 2) significant?

Act 1, scene 2, develops the conflicts in the Younger family established in the opening scene. It is Saturday, the day that the check for $10,000 arrives, a check that the Youngers have long waited for. The Youngers have dreams for the future, and all of them, whether they explicitly state it or not, hope that somehow this check will help improve their lives. They are tired of feeling trapped, as they live in their dark, cramped apartment. Walter is most explicit about his plans for the money; he wants to use the money to invest in a liquor store, so he can finally own his own business and be his own man.
However, his loud outspoken claim on the check creates tension that builds inside this small apartment until it explodes by the end of this scene (72-74 in the 2004 Vintage Edition), when Mama refuses to give Walter the money. Hansberry creates riveting dialogue between these two powerful figures; Mama is absolute in her belief that liquor stores end up hurting the community—so she cannot support them—whereas Walter, her son, is absolute in his beliefs that the world is choking him and that he must find a way to break free from the chokehold to follow his dream. They also love each other very much, and Hansberry shows the poignancy of their words when they beseech each other to listen to bridge the distance between them. Walter explains,

I want so many things that they are driving me kind of crazy . . . Mama—look at me.

He wants her to understand and needs to feel this connection to his mother. He needs her to support him. When Mama offers him soothing words, this calms him, and he continues. He is no longer explosive; he quietly explains to her his feelings about being trapped in a life where he must serve other people while “white boys are . . . sitting there turning deals worth millions of dollars.” When Mama wonders about why he is so focused on money, he explodes, “Because it is life, Mama!”
This outburst lays bare just how great the distance is that divides them. Mama, in quiet juxtaposition to her son, understands life very differently,

Once upon a time freedom used to be life—now it’s money. I guess the world really do change.

She sees that her experience of escaping from the brutality of the South is meaningless to her son, who cannot appreciate what she and her husband have provided for their family. The attempt of Mama and Walter to come closer to each other has ended up pushing them further apart. Walter retreats in defeat, realizing he cannot change Mama’s decision about the check, saying,

You just don’t understand, Mama, you just don’t understand.

Hansberry masterfully constructs this roller coaster of dialogue to show the quiet intimacies of love that bring them together but also the passionate frustrations that threaten to pull them apart.