B2: Cell Division

Topics Covered: White/Black - Cell Structure Yellow - Chromosomes Blue - Cell Cycle Red - Cell Division Purple - Stem Cells Green - Therapeutic Cloning

Cytoplasm

Site of chemical reactions

Nucleus

Contains genetic information and controls the cell

Cell Membrane

Controls what enters and exits the cell

Mitochondria

Site of aerobic respiration

Cell Wall

Maintains the shape of the cell

Vacuole

Contains cell sap and keeps the cell rigid

Chloroplasts

Where photosynthesis takes place

Cell

Basic building block of an organism

Chromosome

Thread-like structures holding genes

Gene

Section of DNA that controls the production of a protein

DNA

Chemical from which chromosomes are made (Deoxyribonucleic acid)

How many chromosomes do people have?

46, organised into 23 pairs.

Karyotype

A picture of a set of chromosomes from one person. Can be useful for spotting any abnormalities in the number or structure of the chromosomes.

When might Mitosis be useful?

Growth, Repair and Asexual Reproduction

3 Cell Cycle Stages

1 - Getting the cell ready for division

2 - Mitosis

3 - Cell Division

Stage 1

Before the cell divides, the DNA makes a genetically identical copy of itself. This is called DNA replication. Mitochondria is also produced, for respiration, and more ribosomes.

Stage 2

The chromosomes line up at the equator of the cell and then are pulled apart to opposite ends.

Stage 3

The cytoplasm and cell membrane are split in half so two new cells are formed. The daughter cell is an exact replica.

Stem Cell Examples

Root Hair Cell, Red Blood Cell, Sperm Cell

Stem Cell

An undifferentiated cell of an organism which is capable or giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.

Differentiation

When cells become specialised

Plant Stem Cells from Meristems

Plant stem cells are found in regions of active growth called meristems. In a plant these are found at the tips of growing shoots and roots and where branches bud. The cells within these regions can differentiate into any type of cell throughout the plant’s life. Unlike stem cells in animals, it is also possible for cells in a plant to re-differentiate into other plant cell types. We make use of this when taking cutting (a form of plant cloning.)

Embryonic Stem Cells

Obtained from the inner cell mass of human blastocysts (early stage of a developing embryo). They are pluripotent, so they can divide into more stem cells or can become any type of cell in the body. Embryonic stem cells are more useful for treatments than adult stem cells. Embryonic stem cell research holds greater promise for understanding debilitating diseases. Research is ethically and politically controversial as it involves the killing of human embryos.

Adult Stem Cells

Adult stem cells can be obtained from the skin, bone marrow, spinal chord, liver, skeletal muscle. etc. Adult Stem Cells are only multipotent - they can only develop into a limited number of cell types, not all. Using adult stem cells can cure incurable diseases, diabetes, eyesight for the blind, damaged bone and cartilage, and heart damage. No embryo is used. However, they can cause cancer if the cells divide too quickly, and cells could be infected with a virus. May trigger an immune response if cells from an unrelated person.

Therapeutic Cloning

Involves using the cells of an adult to produce a cloned early embryo of themselves. This would provide a source of embryonic stem cells (overcoming the limited use of adult stem cells) whilst also ensuring no rejection occurs due to the embryo created being genetically identical to the patient. This embryo can be created using adult cell cloning.

Four diseased therapeutic cloning can treat

Paralysis, Diabetes, Blindness and Damaged heart tissue.