TISSUES 

A tissue is a group or collection of similar cells performing a specific function. Tissues vary in size, shape and function.
Examples of tissues Animal tissues 

Animal tissues include; 
1. epithelial tissue, 
2. muscle tissue, 
3. nervous tissue, 
4. blood tissue and 
5. bony tissue. 


Epithelial tissue: 
Epithelial tissues cover the body lining cavities, hollow organs and tubes.

They are responsible for
(i) protection of the underlying structure from dehydration, and chemical and mechanical damages; 
(ii) secretion; and
(iii) absorption. 



Muscle tissue

Muscle tissue consists of cells specialized to contract and move the body. Muscle tissues can be: 
1.skeletal muscle tissue; 
2.smooth muscle tissue; or 
3.cardiac muscle tissue.

Skeletal muscle tissues form those muscles that move the bones 



Smooth muscle tissues 
These are found in the walls of hollow organs. They perform the following functions: 

  •  Regulate the diameter of blood vessels and parts of the respiratory tract. 
  •  Propel the contents of the ureters, ducts of glands and alimentary tract. 
  •  Expel contents of the urinary bladder and uterus. 


Cardiac muscle tissue 
This kind of muscle tissue is found only in the heart wall. It helps in contracting and relaxing of heart muscles thus pumping the blood to various body parts. 



Nervous tissues 
Nervous tissues have endings that detect changes in the environment. They transmit and conduct nerve impulses to the brain and spinal cord and to the effector organs.



Plant tissues 
Examples of plant tissues are collenchyma tissue, sclerenchyma tissue, epidermal tissue, conducting tissues e.g. phloem and xylem, palisade tissue and spongy tissue. 



ORGANS 

An organ is a collection of tissues working together to perform a certain function.


Animal organs
Other examples of animal organs include skin, testes, ears, noses and the brain. 



Plant organs 
Examples of plant organs include leaves, stems, roots, flowers and fruits. 



SYSTEM

Organ system 
A system refers to several interrelated organs performing a particular function. 

Digestive system 
The main organs that make up the digestive system are alimentary canal, liver and pancreas.The main function of this system is to digest and absorb food. 



Circulatory system 
This system consists of the heart, arteries and veins.The role of the circulatory system is to transport gases, food, hormones and distribute heat. 



Lymphatic system 
Lymphatic system has comprises of the lymph vessels and lymph nodes. The main function of the lymphatic system is to transport materials and protect against. 



Respiratory system 
The respiratory system consists of the trachea and the lungs. The role of the respiratory system is to take in oxygen and expel carbon dioxide gas. 



The urinary system 
The main organs of the urinary system are kidneys, ureter, bladder and urethra.The urinary system plays a role in removing metabolic waste products from the body and also it is responsible for osmoregulation. 



The nervous system 
This system consists of the brain, spinal cord and nerves.The role of the nervous system is to detect and respond to stimuli. 



The muscular system 
It consists of the organs muscles and tendons. The role of the muscular system is to bring about movement. 



The reproductive system 
It consists of the ovaries, testes and uterus. Its role is to produce offspring.

Male reproductive system 



Female reproductive system 



Endocrine system 
It consists of endocrine glands. Its role is to produce hormones.



Skeletal system 
It consists of a system of skeletons. Its function is to support the body, protect internal organs and produce blood cells. 




Examples of organ system in plants 

Root system –consists of roots.
 
Function: 
  • Holds the plant firmly into the soil 
  • Absorption of water and mineral salts from the soil 
  • Sometimes they act as storage organs in some plants 
  • Shoot system – consists of the organs flowers, fruits, stem and leaves Function.
  • Site of reproduction 
  • Transport of substances 
  • Photosynthesis occurs in the shoot 
  • Transpiration processes.