Cell Diversity
Tissues 
Huge diversity of cells exist which form different groups to carry out a specific function.
A tissue is a group of similar cells that carry out a particular function. 
Animal Tissues 
There are four main types of animal tissue; 
1.	Connective Tissue 
Connective Tissue consists of a number of cells that spread out in a liquid or solid matrix. 
Connective Tissue joins and supports other body structures. 
Examples of Connective Tissue are Adipose Tissue (which stores fat), cartilage (which surrounds the ends of bones), ligaments, tendons and blood. Connective Tissue is formed by Vitamin C. 
2.	Nervous Tissue
Nervous Tissue is composed of nerve cells called neurons 
Nervous Tissue is specialised to transmit electrical impulses 
3.	Epithelial Tissue 
Epithelial Tissue is made up of a layer of cells that cover the inner and outer surfaces 
Human skin, the inner lining of blood vessels and the respiratory system are examples of Epithelial Tissue. 
4.	Muscular Tissue
Muscular Tissue is made of long cells that can contract 
There are 3 distinct types of muscle tissue; skeletal, smooth and cardiac. 
•	Skeletal Muscle – voluntary muscle that allows bone to move. 
•	Smooth Muscle – involuntary muscle present in the arteries, veins, the stomach and oesophagus 
•	Cardiac Muscle – found in the heart and it never tires 
Plant Tissues 
Plant Tissues can be divided into four main types; 
1.	Dermal Tissue 
Dermal (or epidermal) Tissue covers and protects the surfaces of plants. 
This tissue covers stems, leaves and roots. 
Dermal Tissue have a slightly thickened cell wall (made of cellulose) to aid protection 
2.	Ground Tissue
Ground Tissue fills the inside of a plant. Its function depends on its location. 
It can carry out a range of functions such as photosynthesis, food storage and giving strength to the plant . 
3.	Vascular Tissue
The main function of vascular tissue is to transport materials around the plant. 
It is a complex tissue as it is made of two types of cells; xylem and phloem. 
Xylem cells work together to transport water and minerals. 
Phloem cells work together to transport food. 
4.	Meristematic Tissue 
This tissue is where cell production occurs. 
Meristematic tissue is located at the tips of roots and shoots. 

Tissue Culture
Tissue culture is the growth of cells in or on a sterile nutrient medium outside an organism 
Tissue culture is called in vitro growth – meaning outside the body
Tissue Culture is used in Plant Breeding, Cancer Research & Skin grafts 
1.	Plant Breeding 
Growing large numbers of plants from plant cells is called micropropagation. 
A plant is cut into small pieces. The cells are grown in the laboratory in a nutrient medium. In time they form a clump of cells called a Callus.
Growing conditions such as temperature, oxygen, moisture are kept changed so that the callus continues to grow. 
Benefits of Micropropagation; A large number of plants are produced in a short time, plants grown in this way are genetically identical & its inexpensive. 

2.	Skin Grafts 
Stem cells are used to grow tissue suitable as new skin for patients who have been badly burned. 
Stem cells are cells that can develop into any body tissue. 
Benefits of skin produced by tissue culture; no need to remove skin from another part of the body & the new skin is identical to the patient’s skin and is not rejected by the body’s immune system. 

Organs 
An organ is a group of tissues that work together to carry out a similar function 
Animal Organs include the Brain, Lungs, Heart, Stomach and Kidneys 
Plant Organs include the Roots, Stem, Leaf and Flower. 

Systems 
A system is a group of organs that work together to carry out a similar function. 
In flowering plants there are two systems; 
-	Shoot system – the organs above ground 
-	Root system – the organs below ground 
In humans, organs work together to form different systems such as the 
-	Circulatory system – heart, blood vessels and blood 
-	Digestive system – mouth, oesophagus, stomach, small intestine and large intestine.