By Jeff Joniak–

(CBS) The Bears (5-6) host the 49ers (3-8) on Sunday at noon at Soldier Field. Here are my observations heading into the game.

READ MORE: SWAT Team Responds To Building In South Loop For Call Of Men With Guns Inside

First impression

What player whom the Bears acquired in the offseason by draft or free agency has made the biggest impact? I did a quick poll in the Halas Hall press room, and it confirms my answer: cornerback Tracy Porter.

An eight-year veteran, Porter has given the defense something it didn’t have a year ago at that spot — and with a bit of a swagger. Porter has permitted only a 40.4 completion percentage, according to Stats Inc., second only to Darrelle Revis of the Jets, while defending 10 passes and allowing only two touchdowns. You can argue outside linebacker Pernell McPhee is 1A on the biggest impact list or maybe safety Adrian Amos, but Porter has proved to be a steady and calming influence on the back end of a pass defense that leads the NFL with seven games of fewer than 200 passing yards allowed.

Second thought

It probably doesn’t shock you, but there are 19 first-round draft picks starting at left tackle in the NFL right now, including Joe Staley of the 49ers. There are two seventh-round NFL draft selections. One is Charles Leno Jr. of the Bears. Players don’t control where they’re drafted, but they do control what happens after they do.

Leno is a shining example of that right now after nabbing the starting spot ahead of big-money tackle Jermon Bushrod.

“I’m still growing,” Leno said. “I feel like I’m still young, still growing. This year I am starting to grow into my role. It’s just a blessing to be here.”

Leno believes everything starts in practice. He said he grinds every day, and tape study for him is addictive. He admittedly learned a lot about the move to left tackle in the preseason, but his preparation didn’t match his challenge. It was the turning point in his season and potentially in his career that he came to that realization.

READ MORE: AAA Estimates 1.7 Million Illinoisans Will Hit The Road For Memorial Day Weekend -- How Do They Come Up With Their Predictions?

You can hear more about Leno’s journey in Sunday’s second hour of WBBM’s “Countdown to Kickoff” Bears Radio pregame show when the Bears host the 49ers at Soldier Field.

Third degree

Stopping the run is clearly the headline coming out of the Bears’ locker room this week. From coach John Fox to defensive coordinator Vic Fangio to McPhee to Amos, all have mentioned that as the first order of business.

“We all got to get involved,” Amos said. “We have to hold our gaps, know when we’re filling, have good eyes so we know our run-pass reads.”

San Francisco’s missing lead back Carlos Hyde, but veteran Shaun Draughn has stepped in and has been productive. He’s averaging only 14 carries in the last three games, but he’s piled up 270 yards from scrimmage on 64 touches. It’s afforded quarterback Blane Gabbert the opportunity to set up the play-action pass and create some downfield opportunities for veteran Anquan Boldin and speedster Torrey Smith.

Eight times this season, the Bears have permitted more than 115 rushing yards. They’ve lost six of those games. In Week 12 at Green Bay, Chicago was gouged for a season-high 177 yards but managed to make enough big plays to derail the Packers offense.

Fourth-and-short

One of the most impressive aspects of the Bears defense is the ability to bend but not break — particularly in sudden-change situations. The defense has permitted only two touchdowns on drives of fewer than four plays and is tied for third in that category with 14 points allowed, trailing the impressive defenses of the Bengals, Seahawks and Panthers.

On the Bears’ last seven turnovers, the defense has given up only 10 total points, including one touchdown. They’ve given up no points on five of those situations over the last six games. In the first five games of the season, they gave up five touchdowns and 41 points.

MORE NEWS: Archer Heights Offering Food Giveaway Every Tuesday Night

Jeff Joniak is the play-by-play announcer for the Bears broadcasts on WBBM Newsradio 780. Follow him on Twitter @JeffJoniak.