The first organisms were unicellular, however, they eventually formed colonies. The formation of colonies became more favorable. However, it required communication between cells. For example in bacteria colonies, bacterium will commit suicide if they have a particular signal from other cells in the event they develop a mutation. Eventually cells fused together and developed specialty functions forming multicellular organisms. Hence cells aggregate together to form tissue which can perform specialty functions to support the organism.
Animal tissue can be broken down into 4 different types, these include:
Epithelium tissue is the skin or any other cellular area which acts as a barrier between the inside of an organism and the gas or liquid surrounding it. Hence acting as an interface for exchange of material inside and outside of an organism.
The three types of muscular tissue include cardiac, skeletal and smooth. Cardiac muscle contains branching, it’s striated and contains intercalating disks – this is found in the heart. Skeletal muscle is voluntary muscles which contains multiple nuclei, striations and no branching. Smooth muscle contains no striations and is spindle shaped.
Nervous tissue allows for the coordination of voluntary and involuntary movement. Information is passed along cells as electrochemical signals.
Connective tissue is composed of living and non-living. The non-living component is referred to as the extracellular matrix composed of fibers (mainly collagen) and ground substances (mainly water). The living component is composed of cells.
Cells communicate using hormones and electrochemical signals. Different signals elicit different responses, these include survive, grow and divide, differentiate or die (through apoptosis).
In the event of a defective apoptosis signal, cancer cells emerge. Cancer cell’s will continually grow becoming a problem for the host.
In the event of stress the hypothalamus triggers the pituitary gland to secrete ACTH which activates the Adrenal cortex which releases cortisol reducing the CRH which the hypothalamus originally secreted. This results in an increase in blood glucose and the break down of fats and proteins.
The three different types of signals include:
Those from steroid hormones which can pass through the cell membrane and interact with the DNA of a cell. Neurotransmitters which join the cell and bind to a surface protein on the cell membrane opening a ion channel to mediate a cell response. As well as peptide hormones which converts ATP to cAMP to mediate a cell response.
A good way to remember the four types of tissue is (MENC)
Question 1. [4 marks]
Why was cellular communication important in the evolution from unicellular organisms to multicellular organisms?
Explain the function of the four types of animal tissue.
Outline the roles and types of cell signals.