Chapter 8: Cell Diversity

Not all cells in the body are identical.
All different cells have different functions, they diversify their structure to suit their function.

Types of Cells:
Cheek cells, red blood cells, nerve cells, muscle cells, and plant cells are all examples of different types of cells. Many types of cells exist.

Tissue

A tissue is a group of similar cells that are modified (or adapted) to carry out the same function within a multicellular organism.

Plant tissue:

Dermal
Provides protection

Vascular
Provides transport

Ground
Provides storage and structure

Meristematic
Provides new growth

Dermal Tissue

The outside of all plants is covered with dermal tissue.

Location:
Dermal tissue is like the skin of the plant. It is found covering leaves, stems, and roots. The outside of a herbaceous plant (non-woody) is covered by a layer called the epidermis.
Woody plants have a periderm (bark).

Description:
Epidermis cells are living cells that are rectangular in shape. These cells are tightly packed together and often have a thickened cell wall. Aerial parts of the plant are often covered with wax (cuticle). This will reduce water loss.

Function:
The main function of dermal tissue is to protect the plant. The cuticle, if present has the function of preventing water loss.

Vascular Tissue

The vascular tissue of flowering plants consists of two mains types, xylem and phloem. This is an example of complex tissue.

Xylem

• Description:
  Xylem consists of two types of conducting cells, xylem tracheids and xylem vessels. Both tracheids and vessels are dead and hollow at maturity. These hollow tubes run continuously from the roots, through the stem and into the leaves.

• Function:
  Xylem transports water and dissolved minerals throughout the plant. Secondary function is to provide support in woody plants.

Phloem

• Description:
  Phloem also consists of tube-like structures. Phloem is found in the leaves, stems, and roots.

• Function:
  Food made in the leaves is transported all around the plant by the phloem.

In a vascular bundle, the xylem is orange and the phloem is pink.

Animal Tissue

Epithelial

Connective

Muscular

Nervous

Connective Tissue

• Description:
  Attaches things together, give support and make blood.
  3 main components: Cells, fibres, and extracellular matrix.

• Adaptation

• Cells are spread over a matrix

• Examples:
  Blood: Consists of red blood cells, white blood cells and platelets suspended in a matrix called plasma.
  Cartilage: A rubber matrix that is flexible yet strong. It separates cells. In the matrix, there are elastic or collagen fibres. e.g. nose and joints.

Muscle Tissue

Description:
Tissue composed of cells that have the special ability to shorten or contract in order to produce movement of the body parts

Function:
Produce movement and stabilise joints

Adaptation:
Many mitochondria, can contract and relax

Nervous Tissue

• Description:
  Nervous tissue is the main component of the nervous system (brain, spinal cord, nerves)
  It is composed of neurons.

• Function:
  Neurons carry messages to and from the brain via the spinal cord in the form of electrical impulses.

• Adaptation:
  Has myelin sheath to insulate impulses

Tissue Culture

Tissue culture is the growth of cells in or on a sterile nutrient medium outside an organism.

A sample of tissue is removed from a plant or animal. The tissue is grown in glassware (in vitro) or in a bioreactor under carefully controlled conditions such as:
- Temperature and gas concentrations.
- PH, glucose concentrations.
- Vitamins, minerals, salts, amino acids.
- Hormones.

A lot of time and money has been spent in the prevention of contamintation by microorganisms. Many microorganisms (e.g. bacteria, yeast) grow rapidly, producing wastes which contaminate the container and kill the desired cells.
- Sterile: No Microorganisms
- Aseptic: No Unwanted Microorganisms

Applications

Skin Graft

Skin grafts are used to treat patients who are badly burnt.
Previously, a piece of skin had to be taken from a healthy part of the body. But now, new skin is grown using stem cells.
Stem cells can develop into any body tissue. Stem cells are found in embryos, umbilical cords, and bone marrow. (Pluripotent cells are found in the embryo)
Stem cells are selected and nourished with liquid containing all the nutrients and elements needed for healthy growth.
The cells divide and grow to form skin on the bottom of the flask.
This sheet of cells are then transplanted onto the patients burn area.

Advantages:
Since these cells are genetically identical to the recipient, then there is little chance of rejection.

Micropropagation

Part of a desireable plant is cut into many small pieces and are cultured on a suitable medium under controlled conditions.
In time the cells form a callus. (clump of similar cells)
Growth conditions are changed.
Each callus forms a new plant.

Advantages:
- Large number of plants in short space of time.
- New plants are treated during culture so they are virus free (healthier plants).
- All plants are genetically identical.
- Inexpensive way to produce similar plants.

Organs

A structure composed of a number of tissues that work together to carry out one or more functions.

Plants have 6 main organs - roots, stem, leaves, flowers, seeds and fruit.

Animals have many organs - skin, heart, liver, lungs, etc.

The Leaf

Function:
Responsible for photosynthesis (Creates C₆H₁₂O₆ + O₂)

Leaves have 3 types of plant tissue:
- Dermal Tissue: Flattened cells making up the epidermis.
- Vascular Tissue: Xylem and phloem cells found in vascular bundles.
- Ground Tissue: Cells making up the body of the leaf.

The Heart

Function:
Pump blood all around the body.

Composed of 4 tissue types:
- Muscular Tissue: Walls of the heart are made of cardiac tissue.
- Epithelial Tissue: Heart is enclosed in a membrane called the pericardium (Protection: Shock absorber and stops friction).
- Connective Tissue: Blood and blood vessels.
- Nervous Tissue: Controls the tissue.

Organ Systems

A number of organs working together to carry out one or more functions.

Circulatory System:
Consists of the heart, blood, blood vessels, lymph and lymph vessels.
Functions to transport materials around the body to fight infection.

Digestive System:
Consists of the mouth, oesophagus, stomach, small intestine, large intestine (in association with the liver and pancreas).
It fuctions to take in food, digest it, and transfer the digested food into the circulatory system.