00:00You know this guy, let's call him Bruce. He's insanely fast, and the way he moves might even
00:05break a major law of physics. This finding is actually huge. It could help fertility research,
00:11and even inspire the creation of tiny robots. But first, we've got to figure out how he's
00:16pulling off the impossible. So when Bruce's enter a woman's body, they've got one mission.
00:23Reach the egg and fertilize it. Tens of millions start the race, but in about 99% of cases,
00:30only one makes it. To do that, the fastest Bruce's travel a distance of roughly 3,000 times their
00:37body length in about half an hour. But here's the problem. If it gets there too late, the egg has
00:44already changed. Because once the egg is contacted by the first Bruce, it creates an electrical barrier
00:50that other Bruce's can't cross. No matter how strong or determined they are, they can't get in
00:56anymore. That's why it needs to be fast. But none of that is news. What's new is that scientists think
01:03the way the Bruce's move doesn't follow the third laws of motion. I mean the famous,
01:09for every action, there is an equal and opposite reaction.
01:15Here's an example. A swimmer just reached the end of the pool.
01:18He pushes off the wall and, at the same time, the wall pushes him back with an equal force
01:24in the opposite direction. This pushback is what makes him speed up. And that's Newton's third law.
01:31But Bruce's don't seem to follow this rule. At least, not in the usual way.
01:37Scientists figured this out after comparing male reproductive cells to tiny green algae,
01:42called clamidominus. Both swim in a surprisingly similar way, in a wave-like pattern. And they have
01:49to do it for a very strange reason. You see, the fluid around sperm cells and around these algae is
01:56really thick and sticky. It'd be like putting our swimmer in a pool of molasses. He could still move
02:02his arms and Newton's third law would still apply. Every time he pushes the molasses, it pushes back.
02:09But it's so thick that it resists every motion. So in the end, the whole cycle cancels out and he
02:15barely goes anywhere. The same thing should happen to Bruce's and to the green algae swimming in this
02:22jelly-like environment. They would push forward, then get pushed back. Zero progress. The thick
02:28fluid should soak up their energy, slow them down, and almost stop them right away. They shouldn't get
02:34far at all. But the opposite happens. They still move incredibly fast. But how?
02:41It all comes down to the special tail I mentioned earlier, known as flagellum. Since moving back and
02:48forth in a perfectly even way wouldn't work, they need a different motion. So this tail ripples in
02:54smooth waves. And those waves are what push the male reproductive cells forward. According to
03:01researchers at Utrecht University, for Bruce to swim forward, his head and tail have to move in sync.
03:07The motion starts in the tail, powered by tiny motor proteins that make it wiggle. But this movement
03:13has to be linked to the head too. And it has to be coordinated. Otherwise, Bruce won't be able to
03:20keep going. So, the tail and this coordinated movement with their heads is what helps them move
03:27in such a hard environment. But it's not what makes them all go in the same direction. I mean,
03:32they travel through the cervix, into the womb, and up the fallopian tubes, searching for the egg.
03:38But how do they all know that it's the right path?
03:42That happens because of a process called chemotaxis. The egg and the surrounding cells
03:48release chemicals that attract Bruce's. So basically, it's like the egg is calling out,
03:53hey, I'm over here. Bruce's have receptors that detect these chemicals, so they know which way to swim.
04:00And then, the male cells move forward, either in a straight line or in wide circles, until they reach the
04:07egg. What really propels the Bruce's forward, I mean, what gives them that extra push, is still kind of a
04:14mystery. But a 2025 study might have some answers. Researchers found that Bruce's don't just swim,
04:21they also spin as they move forward. As they swim, they create swirling loops in the fluid, a bit like
04:28corkscrews. Think of a straight rubber band. Twist it into a spiral, then twist it again so it becomes
04:35tighter and more coiled. A similar spiral shape forms around Bruce when it swims. Its tail movement
04:41creates tiny swirls in the fluid. But these swirls don't just drift away. They stay right next to the
04:48Bruce and spin along with it, almost like they're attached. As the Bruce and this spiral rotate together,
04:55the extra spin helps it move forward and stay on a straighter path through the fluid. And here's
05:01something curious. Bruce's tails always rotate to the left, so you'd think it would work like a car
05:07wheel. Turn left, and the car goes left. If Bruce's tails rotate to the left, they should always turn left,
05:15right? Well, no. When scientists watched them closely, they saw that Bruce's can still turn right.
05:22The reason is that they can steer by slightly tilting or bending their head and neck, kind of like
05:28leaning your body to change direction when something is pushing you the other way. But even with the help
05:34of those swirling loops, their tails would eventually get really tired from swimming through such thick
05:39fluid. That's where new research may finally solve the mystery. Scientists have found that the flagellum has
05:47a strange property. It's elastic, but not in the usual way. Its elasticity is odd. When the tail bends
05:54and snaps back, those male cells don't lose as much energy as they should. Here's what happens.
06:01Instead of pushing the fluid back and being pushed back equally, like Newton's third law suggests,
06:06the motion inside the tail itself does most of the work. Different parts of the tail interact with each
06:13other in a one-way pattern. The energy moves through the tail, not back and forth with the fluid. So
06:19it's
06:20not a simple push-and-push-back situation anymore. Because of this uneven internal behavior, the tail can
06:28create forward motion without triggering the reaction from the fluid. In simple terms, the tail seems to
06:34cheat the system. It's like it completely ignores its surroundings. But why does any of this matter, right?
06:42Two big reasons. First, it's just cool science. When something seems to break the laws of physics,
06:49it helps us understand the universe a little better. Second, it could be super practical.
06:55These discoveries might help engineers build tiny swimming robots or smart materials that can move
07:01on their own by using the same tricks living cells have been using forever.
07:06In the future, learning more about bruises could help scientists find better ways to treat fertility
07:12issues. According to a 2023 report by the World Health Organization, around one in six adults experience
07:20infertility issues, and research suggests male infertility contributes to roughly half of all cases.
07:27Since men produce close to a trillion reproductive cells over a lifetime, it's easy to think there's
07:34no problem. But research suggests bruise counts are dropping worldwide, and the decline seems to be
07:41speeding up. That's why it's important to understand things like the tiny swirls bruises leave behind.
07:47Those swirls could affect how they interact with each other, with nearby surfaces, or even with the egg itself.
07:54And it's not just for fertility issues. Studying bruises movements can also help scientists understand
08:01how other microscopic swimmers move too, like bacteria traveling through mucus, blood, or water.
08:07It may even help explain why some bacteria are so good at sticking to surfaces, like teeth, implants, or pipes.
08:16And that kind of insight could lead to better treatments and practical solutions.
08:20So yeah, understanding these tiny bruises could end up saving people from serious health problems
08:26down the road. And that's pretty impressive for something so tiny you can't even see.
08:36That's it for today. So hey, if you pacified your curiosity, then give the video a like and share
08:41it with your friends. Or if you want more, just click on these videos and stay on the Bright Side!
08:46A little bit harder.
08:46This is
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