Starting with your arrows, you are doing a good job having them turn in space. You are also doing a good job of having them go from larger to smaller as. they go back in space. The way you have tapered them towards the back helps to sell the illusion. Make sure to draw your lines confidently, for each line make one confident, smooth, and fluid mark. There are a few spots where your lines get a big wobly. Also, there are a few spots where you added line weight and it wasn't needed. Try to add line weight subtly and very intentionally, only on areas where you are trying to mark out which line is in front, so for this exercise that would be on all the spots where the ribbon crosses over itself, at the curves.

For the organic forms and contour elipses, you did a great job making confident marks on this one. In general you also did a good job angling your elipses, so that the edge of the elipse and the edge of the organic form hit at the right spot, or in other words, the elipse is centered well. One thing to work on would be the size of your elipses. There are a few spots where the size of the elipse is a bit off and it breaks the illusion of a 3D mass on the page. Like in the lesson, think about a coin in space and how it get bigger or smaller depending on your vantage point.

For the organic forms and contour lines you did a good job making confident marks and in placing the center line. You also did great at curving your contour lines at the ends. One thing to work on would be that your contour lines get flat in the middle, so the form doesn't look rounded in those areas but flat.

Your texture analysis looks good. For your textures on organic forms, you did a good job on most of them in leaving some areas lighter and implying the texture there. I would recommend when looking at the reference, look very closely and observe the shapes and details of the cast shadows. Don't draw more than a few seconds before you look back at the reference photo.

On your intersecting boxes and shapes, your boxes are looking good and believable, they appear as if the lines are aimed towards the same vanishing points. Your other 3D forms are also looking good. You did a good job placing the intersection lines within the area that the boxes and forms overlap each other, but within that area they seem to be placed randomly. Think about the different planes on the forms and how they intersect with each other.

Your intersecting organic forms look good. You seem to have gotten the idea down. Most of them look good as far as selling illusion that they are wrapped over the forms beneath them. One thing to work on would be the shadow placement. On a few of them, where the shadow lands would cross multiple different forms, but you have one straight shadow line, as if it were just one flat surface that the shadow is cast onto. Consider how the shadow would change as it landed on different forms that are at different angles to and distance from the form that is casting the shadow.