Sieve cells are called this because the tubes act as one continuous cell and are a collection of sieve tube elements. They tend to look empty, have very prominent joints, are very long and don’t have a nucleus (like xylem, but are living cells). They don’t have a cytoskeleton, have very few organelles (probably no Golgi, plastids or lignin; some ER, few mitochondria, have plasma membrane). Companion cells, ordinary cells that feed sieve cells and keep them alive, are next to sieve cells. A ‘sieve plate’ is the wall in between each sieve cell. Sieve plates contain special clotting proteins and polysaccharides which should only be released when the phloem is damaged. They are like slime and are very prominent; these are phloem clots that stop the flow of nutrients if the phloem is damaged.
Comments
suggestion
This sentence might flow better with the rest of the paragraphs if you made some changes. The sentence is :"They don’t have a cytoskeleton, have very few organelles (probably no Golgi, plastids or lignin; some ER, few mitochondria, have plasma membrane)."
You can change it to, "They don't have a cystoskeleton and have very few organelles (probably no Golgi, plastids or lignin; some ER, few mitochondria, have plasma membrane.)"
suggestion
The wording of your first sentence sounds a little awkward. Instead of saying, "Sieve cells are called this because the tubes act as one continuous cell and are a collection of sieve tube elements." I would suggest something like, "Sieve cells are composed of tubes that act as one continuous cell and are a collection of sieve tube elements."
"called this"
Reword to sound more scientific:
"Sieve cells are named after..."
It will help the paragraph sound more professional