Key differences between plant and animal cells include:

1. Cell wall: Present in plant cells, absent in animal cells
2. Chloroplasts: Present in plant cells for photosynthesis, absent in animal cells
3. Vacuoles: Large central vacuole in plant cells, smaller in animal cells
4. Shape: Plant cells have a fixed shape due to the cell wall, animal cells have variable shapes
5. Energy storage: Plants store energy as starch, animals as glycogen
6. Centrioles: Present in animal cells, typically absent in plant cells

Main organelles in a eukaryotic cell:

1. Nucleus: Contains genetic material and controls cell activities
2. Mitochondria: Produce energy through cellular respiration
3. Endoplasmic reticulum: Synthesizes and transports proteins and lipids
4. Golgi apparatus: Modifies, packages, and distributes cellular products
5. Lysosomes: Break down cellular waste and foreign materials
6. Ribosomes: Synthesize proteins based on genetic instructions

Cell communication methods:

1. Chemical signaling: Release of molecules that bind to receptors on other cells
2. Gap junctions: Direct connections between adjacent cells for small molecule exchange
3. Plasmodesmata: Channels between plant cells for communication and transport
4. Synapses: Specialized junctions for neuron communication in the nervous system
5. Hormones: Long-distance chemical messengers that affect target cells
6. Cell adhesion molecules: Proteins that allow cells to recognize and bind to each other