Cell Division

In this chapter you will learn:

  1. What is Cell division?

  2. Chromosomes and DNA

  3. Mitosis and the cell cycle

  4. Stem cells

  5. Cell differentiation

  6. Cloning in plants

  7. Using human stem cells

  8. Therapeutic cloning

  9. Risks and concerns

Cell division

Cell division is a basic process by which a parent cell is divided into two daughter cells. This involves separation of the genetic material into two or more daughter cells.

Chromosomes and DNA

Chromosomes carry genetic information in a molecule called DNA.

Human body cell has 23 pairs of chromosomes.

DNA is the molecule that carries the genetic information .

DNA is found in the nucleus of a cell.

Each section of DNA that codes for a specific protein is called a gene.

The majority of cells in your body have a nucleus containing your genetic information.

Every chromosome has a large number of genes.

Mitosis and the cell cycle

Mitosis is a type of cell division.

In mitosis, two daughter cells with the same genetic component as the parent cell are produced.

Cell division by mitosis is important in the growth and development of multicellular organisms.

Cell cycle is a sequence of stages that cells pass through to allow them to divide and produce new cells.

Stem cells

Undifferentiated cells are called stem cells.

Stem cells have the unique ability to develop into many different types of cells.

Differentiation is the process when a cell develops to do more specialised role.

Stem cells are found in early human embryos.

Adult stem cells can be fouund in different regions of the body including brain, bone marrow, blood vessels, skeletal muscle, skin, heart and liver.

Stem cells in plants

Cell division in plants is the process of mitosis.

The only cells that divide by mitosis are found in plant tissues, called meristems.

Meristem are found in the tip of the roots and shoots.

Cell differentiation

Cell differentiation is the process through which a young and immature cell becomes specialised for a particular function.

Cellular differentiation is the process by which a cell develops more specialised functions.

Cells differentiate to specialize for different functions.

Cell Specialisation - Animal

Cells have to perform different jobs. Cells display specialised features to perform these jobs more effectively.

The following are a few examples of specialised cells.

Sperm Cells

The head contains enzymes that helps penetrate the egg cell membrane to allow fertilisation.

The middle part is packed with mitochondria to release energy that is needed to swim.

The tail of the cell enables the sperm to swim to the ovum.

Sperm cells contain the genetic information.

Nerve Cells

Nerve cells are specialized to carry messages through electric signals.

The nerve cell is covered with a fatty sheath.

Nerve cells have a long axon to carry the impulse to the target organ.

Nerve cells have branched connections at each end.

Red blood cells

Red blood cell contain haemoglobin which transports oxygen to other cells.

Red blood cells carry oxygen around the body.

Red blood cells are a flat disc shape.

Red blood cells have a thin outer membrane.

Cell Specialisation - Plant

Xylem Cell

Xylem cells have a small tubes that carry water from the roots to the leaves.

Cells have no end walls between them Their walls become thickened and woody.

Xylem forms a continuous, hollow tube.

Root Hair Cell

The root hair cell has a large surface area to increase the rate of absorption.

Cells have thin walls that allow plants to absorb more water .

Palisade Cell

The function of cell is to enable photosynthesis to be carried out.

Cells contain about 70% of the chloroplasts.

Cloning in plants

Plant stem cells from meristems can be used to make clones.

Tissue culture is another technique that has been used for cloning plants.

Tissue culture involves growing cells in an artificial growth medium like an agar jelly.

New plants, or clones, will be genetically identical to the original plant that provided the meristem cells.

Cloning in Plants is done to produce identical plants quickly and economically.

Using cuttings from plants: A small piece of branch is cut from a larger plant and is perhaps dipped into an auxin rooting powder.

In a few weeks a new plant develops.

Using human stem cells

Stem cells have the potential to be converted into any type of cell found in the human body.

Stem cells have the potential to be transplanted into patients to treat certain medical conditions.

stem cells can be used to treat various medical conditions such as replacing damaged tissue e.g. paralysed by spinal injury, diabetes and alzheimer's disease.

Leukaemia is a cancer of the blood or bone marrow. It can be successfully treated using stem cell technology.

The stem cells in the bone marrow are important in replacing dead cells.

Cells from early human embryos and adult bone marrow can differentiate into many different types of cell.

Therapeutic cloning

Therapeutic cloning involves producing stem cells with the same genes as the patient.

They have same genetic makeup therefore they will not be rejected by the patient's immune system.

Therapeutic cloning involves the transfer of the nucleus from a patient's cell, to an egg cell from which the nucleus has been removed.

Risks and concerns

If the stem cells come from a donor there is a chance that patient's immune system will respond in a negative way, and trigger an immune response to attack and remove invasive cells..

Stem cells divide very quickly and if cell division cannot be controlled inside a patient a tumor may develop.

Cultured stem cells could be contaminated with viruses, which would be passed to the patient.

Currently it is difficult to find suitable stem cell donors.