For starters, plant cells have a tough Cell Wall made from cellulose, while animal cells only have the thin Cell Membrane. Also, plant cells have Plastids, while animal cells do not. The primary organelle which is present in plant cells but not in animal cells, however, are the Chloroplasts, which allow plant cells to carry on the natural process of photosynthesis, by which plants make their own food using sunlight, water, and nutrients from the soil. Hope that helped =)
If he studied a small sample it wouldn't be a representative sample. since he got such a large sample there is a chance most likely all organisms follow the rules of evolution.
