Cell death, Cancer cells and the Cell cycle

An insight into some of the reasons we age, and why we die.. And what can kill us

Necrosis is death due to unexpected and accidental cell damage.  A number of toxic chemical or physical events can cause necrosis: toxins, radiation, heat, trauma, lack of oxygen due the blockage of blood flow, etc.    - physical or chemical insults can lead to the lethal disruption of cell structure and activity -As necrotic cells begin to die, they swell – holes appear in the plasma membrane and intracellular materials spill out into the surrounding environment.

Apoptosis

Apoptosis is sometimes called programmed cell death. Apoptosis originally referred to the process by which leaves falls from trees in the autumn, but it has been adapted to describe this type of non-traumatic cell death. Apoptosis is a way to remove unwanted cells. During apoptosis, cellular contents are not released and inflammation does not occur. The apoptotic cells are rapidly engulfed by their neighbours and removed.

But outside the obvious reasons, why would cells still choose to die?

What are cancer cells, and where do they come from?

Cancer:

Cells with abnormal genetic material that are dividing uncontrollably and can spread to other body parts.

So, how do these cells manage to get out of hand?

Now, we start putting it all together

Plants: From Cells to Systems

As we have already discussed, each cell in the body has a specific task that it is programmed to carry out. Biologists call this “cell specialization.

Cell specialization:

The process by which cells develop from similar cells into cells that have specific functions within a multicellular organism.

Cell specialization

Cell differentiation:

A stage of development of a living organism during which specialized cells form.

In general, cells specialize as a result of the production of different proteins. Although all cells in an organisms body contain the same genes, not all genes produce the same proteins. Certain genes are activated in some cells, and suppressed in others. Which proteins are produced determines a cell’s specialization.

Cell differentiation

As we have already learned, plants are fundamental to the Earth’s biosphere. Although they are not the most complex organism that exists on planet Earth, they too are multicellular.

Assuming ideal conditions, plants are always growing and making new specialized cells. A plants (and an animals) structure can be subdivided as follows:

Specialized Cells and Tissues in Plants

Tissues:A cluster of similar cells that share the same specialized structure and function.Organs:A combination of several types of tissue working together to perform a specific function.In plants, meristematic cells are responsible for continued growth.Meristematic cell:An unspecialized plant cell that can form specialized cells.

Specialized Cells and Tissues in Plants cont’d

The first major tissue formed by meristem is dermal tissueDermal Tissue (epidermis):The outermost covering of the plants organs. This tissue, made up of epidermal cells, is a barrier between the plant and its external environment. The epidermis protects the delicate inner tissues from damage and controls the exchange of water and gases between the plant and its environment.

Three Major Tissues in a Plants body

The second and third major tissues formed by meristem is the ground tissue Ground TissueHas several functions. For example, some ground tissue is made of cells that perform photosynthesis, while other ground tissue is made of cells that provide support for the plants body. Vascular TissueHelps provide physical support for the plants body. It also performs the critical job of transporting sap throughout the plant

Tissues in Plants cont’d

Vascular tissue is made up of 2 types of cells:Xylem cells:Dead tubular cells, laid end to end, transport water and minerals from plant roots to other parts of the plant.Phloem cells:Living tubular cells, joined end to end, transport sugars from leaves to other parts of the plant.

Tissues in Plants cont’d

The Leaf

As we have just seen, the leaf is composed of multiple parts. The following is a breakdown of the leafs structure:-Upper leaf is made of dermal tissue, epidermis-Main function is protection; epidermis cells do not perform photosynthesis-Below the upper leafs epidermis is a layer of palisade tissue. -The palisade tissue is made up of specialized cells that perform photosynthesis. -The tops of these cells are arranged to meet the Sun’s rays head on, so that the rays pass through the length of the cell

-This ensures the Sun’s rays pass through as many chloroplasts as possible.-These cells are very active, so they are packed with mitochondria-Mesophyll tissue is below the dermal and palisades tissues. Cells are loosely packed to form a network with open spaces; spongy tissue.-Spaces contain the gases needed or used in photosynthesis.-The centre of the leaf contains the xylem and phloem tissue arranged into vascular bundles. These are the plants veins.-At their tips, the vessels meet the open spaces in the mesophyll tissue. There, the xylem delivers water vapour for the photosynthesizing cells, and phloem picks up sugars and delivers them to cells throughout the plant.

The lower leaf surface is made of an epidermis that is critical to the exchange of gases between the leaf and the outside environment. The surface is summarized as follows:-Gases are allowed to move in and out via the guard cells, scattered across the lower surface of the leaf.-Guard cells change their shape to control the opening and closing of pores in the leaf. These openings are called stomata. - Stoma are connected to the open spaces in the mesophyll.-Guard cells and stoma play an important role in transpiration

Transpiration: The evaporation of water from leaves

In every Chloroplast, photosynthesis occurs. Light energy from the Sun combines with carbon dioxide from the air and water from the soil to form glucose.

-Glucose is a carbohydrate used by both plants and animals. Animals acquire glucose through the foods they eat, and plants make their own. -Oxygen gas is a product of photosynthesis, and plays a major role in cellular respiration plants and animals. -The chemical formula of photosynthesis is 6CO2 + 6H2O + light energy -> C6H12O6 +

6O2-Chloroplasts change their shape and location to in a cell to increase the amount of light they capture. - Contain sacs called Thylakoids, which contain the light-trapping molecules called chlorophyll. This is the actual location of photosynthesis-Thylakoids are arranged in a stack called granum

A Plant Stem has two main functions: 1) physical support and 2) the transportation of sap.

Characteristics:-Stem’s contain most of the plants xylem tissue. As xylem cells grow, they form long straw-like tubes. The cells then die, but their thick cell walls remain behind, forming long fibrous pipes through which sap can flow.-The dead xylem cells are fortified with a hard substance called lignin, making the straw-like tubes strong-Xylem vessels are grouped with phloem vessels.-Phloem tissue is also made of vertically stacked tubes; porous so they can exchange materials with neighbouring cells.

Roots play a vital role in the life of a plant. In summary:-They anchor plants to the ground, and allow it to take up water and mineral salts from the soil.-They act as storage.-Made up of three main parts: 1) outer layer (epidermis), 2) a middle layer of ground tissue (cortex), and an 3) inner layer of tissue (pericycle).-Pericycle contains the xylem and the phloem.-Cells in the cortex have reinforced cell walls to provide support.-Many spaces between these cells to allow materials to flow easily to the pericycle.-Pericycle cells allow the movement of water into the pericycle, but not 0ut of it.

Plant galls (refer to the picture in your textbook on page 67) are similar to tumours found in animals. Like tumours, they are produced by the abnormal growth of groups of cells. Plant Galls:An abnormal growth of plant tissue caused by insects or micro-organisms

-Plants produce galls in response to attacks by other organisms such as insects, fungi, bacteria, and viruses. -Insects promote the growth of galls by injecting chemicals into the plants tissue, which alters the plants genes. -Unlike tumours found in animals, plant galls do not spread to the rest of the plant and they are seldom fatal.

The flower is the one plant organ which does not partake in the maintenance of the plant itself. Although the flower is not the only way a plant can reproduce, it is the most common way. -The leaves are specialized to perform special tasks.-One set of leaves specializes in pollen production, which manufactures sperm.-Another set produces eggs. -Pollination occurs with the help of wind, insects, and/or other animals. -Once the pollen of a plant reaches the female parts of another plant, fertilization can occur. Sometimes, pollen will be transferred to the female parts found on a flower of the same plant. -Fertilization produces seeds, which are sometimes embedded in fruits.