Sure, if you feel like you have more after this response feel free to let us know and we'll try to point you in the right direction.

Finding curved lines more difficult than straight lines is normal, a lot of this comes down to mileage and putting in your best effort. We don't expect perfection but we do expect your best attempt at the exercises, the more conscious you are about what you're doing and by putting in your best effort the faster you'll find yourself improving.

In the arrows exercise your lines are wobbly showing you're not drawing confidently. This isn't uniquely a problem with just your curved lines however; your straight lines that you use in your hatching are also wobbly and not planned out. Overall you're tackling exercises too quickly and not giving yourself enough time to plan your marks or think about what you're trying to achieve as well as what you learned in the previous exercises. On your second page of arrows, the top middle arrow is a good example of this, if you follow the lines from the center of the swirl, the inner line ends up on the opposite side of the arrow at the point. Try simpler "S" shaped arrows, if you find something difficult it's better to start simple rather than frustrate yourself with more complex tasks.

For the texture exercises, it is completely normal for students to struggle with these concepts - that holding an understanding of a single textural form (like a single chunk of cracked mud, or a single scale) in your mind, and to understand what kind of shadow it would cast on its surroundings, is inherently difficult, and we do not expect students to do it well in their first attempts. What we do want to see however are signs that the student is actually thinking about each individual textural form one at a time, and drawing those cast shadow shapes with one form in mind at a time. You can see demonstrations of this in the video for this exercise. Right now, looking at your work, you're definitely still trying to draw all the texture at once, thinking about it more in terms of patterns that can be replicated across the whole thing, rather than one little piece at a time.

This is a fairly normal misunderstanding that occurs largely because it's easier - and most importantly, faster - to focus on the lines you see and to draw them directly, rather than to study each individual textural form on their own. When we focus on completing the assignment within a set amount of time (maybe to get the whole page done in a single sitting), we opt for the quicker solution even when the approach described in the demonstrations is quite different. So, for now, just focus on investing as much time as you need to execute the instructions to the best of your current ability. If it takes multiple sittings, or multiple days, to complete a page - or even a single texture study - that's perfectly fine. There are no deadlines, no expectations for speed or efficiency. Take as much time as you require.

Your form intersections are actually the strongest part of your submission in my opinion, your line work is mostly ok here the issue once again is that you're going from form to form too quickly. Your convergences aren't always consistent, you don't always draw the intersections, this is a good exercise to experiment with hatching which is shown in this exercise's lesson section as well. So it's not a case of this is section is done poorly, it's a case of I know you're capable of better than this and as mentioned at the start of the course you're meant to submit your best attempts.

Your organic intersections lack solidity for a few reasons, wobbly lines is one of them as you mentioned. Some other reasons are that your contours are quite stiff and don't shift their degree along the form properly as well as your form suddenly shift from rounded forms to straight lines to hide behind another form as quickly as possible so they're out of your thought process. Our biggest goal in this course is to grow more comfortable thinking and working in 3D space, doing so allows our work to appear solid. People try to rush through the basics so they can learn style but style is built on knowing the rules and how to break them in intentional ways so it requires understanding of how to make things appear solid to begin with.

I do hope this helped, if you have more questions feel free to ask. I once again apologize if this came off as blunt, but genuinely the reason behind a lot of these issues is you didn't give the lesson reading/exercises the time you needed.