Lesson 1, Topic 1
In Progress

How cells form tissues

Figure: How cells from tissues
  1. Cells forming an epithelium A thin layer of tissue, e.g. the lining of the mouth cavity. Different types of epithelium form the internal lining of the windpipe, air passages food canal, etc., and protect these organs from physical or chemical damage.
  2. Cells forming a small tube e.g. a kidney tubule. Tubules such as this carry liquids from one part of an organ to another.
  3. One kind of muscle Forms a sheet of muscle tissue. Blood vessels, nerve fibres and connective tissues will also be present. Contractions of this kind of muscle help to move food along the food canal or close down small blood vessels.
  4. Cells forming part of a gland The cells make chemicals which are released into the central space and carried away by a tubule. Hundreds of cell groups like this would form a gland like the salivary gland.

Levels of organisation

Specialised cells combine to form tissues ….

Cells with similar structures and functions are massed together in tissues. Some plant and animal tissues are shown in the tables below.

Animal tissueMain Function
EpitheliumLines tubes such as the gut and covers
surfaces such as the skin
Connective tissueBinds and strengthens other tissues, such
as tendons
BloodTransports substances around the body,
and defends against disease
Skeletal tissueSupports and protects softer tissues, and
allows movement
Nervous tissueSets up nerve impulses and transmits them
around the body
Muscle tissueContracts to support and move the body
Plant tissueMain functions
EpidermisProtects against water loss, and may
be involved in absorption of water and ions
MesophyllPhotosynthesis
ParenchymaFills spaces between other plant
tissues and may be involved in
storage, as in the potato tuber
Vascular tissueTransports materials through the
plant body
Strenghtening tissueSupports the plant

…. tissues combine to form organs ….

Several tissues may be combined to form an organ, a complex structure with a particular function, such as the small intestine shown right.

…. organs combine to form organ systems

In complex organisms, several organs work together to perform a particular task. These organs form an organ system.

Each cell, tissue and organ in an organism has a specialised part to play (there is division of labour) but their activities must be coordinated.