A tissue is a group of similar cells working together to perform a common function.

An organ is a group of different tissues working together to perform a common function.

An organ system is a group of different organs working together to perform a common function.

cells ➔ tissues ➔ organs ➔ organ systems ➔ organisms

Epithelial tissue is made up of a layer of epithelial cells and forms a lining for many organs. 

Ciliated epithelium is a tissue made up of ciliated epithelial cells and goblet cells. It lines organs like the trachea where it sweeps away mucus. 

Cartilage is a type of connective tissue that acts as a cushion between bones and also provides support to organs. It is made up of chondrocyte cells fixed in an extracellular matrix. 

Muscle tissue is made up of muscle fibres that contract and relax to move different parts of the body. 

1. Smooth muscle tissue
2. Cardiac muscle tissue
3. Skeletal muscle tissue

The xylem transports water and minerals inside plants.

The xylem is made up of dead xylem vessel cells which have no end walls and no organelles to form a continuous column. The xylem walls are strengthened by lignin. 

The phloem transports organic materials like sugars in plants. 

The phloem is made up of columns of sieve tube cells and companion cells. Sieve tube cells are separated by sieve plates.