Unit 1: Human Cells: Chapter 1: Division & differentiation

Question 1

Differentiation

Answer 1

The process by which an unspecialized cell becomes altered and adapted to perform a specialized function as part of a permanent tissue.
Once a cell becomes differentiated it only expresses the genes that produce the proteins characteristic for that type of cell.

Question 2

Zygote

Answer 2

Egg cell (ovum) which has been fertilized by a sperm cell.

Question 3

Stem cells

Answer 3

Unspecialized cells that can

1. REPRODUCE - (‘self-renew’) themselves by repeated cell division (mitosis) while remaining undifferentiated.
2. DIFFERENTIATE - change into specialized cells with specific functions when required to do so by the multicellular organism.

Question 4

(Human) Blastocyst

Answer 4

Ball of approx 100 undifferentiated stem cells.

Question 5

Pluripotent

Answer 5

Having the potential for all genes within the cell to be switched on, so the cell is capable of differentiating into almost all of the cell types found within the human body.
(i.e. embryonic stem cell.)

Question 6

Tissue (adult) stem cells

Answer 6

Partially differentiated stem cells found in ‘stem cell niches’ - skin, bone marrow, teeth, brain, skeletal muscle, heart, gut, peripheral blood & liver. Narrower differentiation potential than embryonic stem cells because many of their genes are already switched off. Able to replenish continuously the supply of certain differentiated cells needed by the human body.

Question 7

Multipotent

Answer 7

Describes ability of tissue stem cells with potential to replenish all cell types found within a particular tissue type.

Question 8

Somatic cell

Answer 8

All differentiated cells (except reproductive cells) derived from stem cells.

Question 9

Epithelium

Answer 9

Composed of cells that unite to form membranes, either single (oesophagus, blood vessels) or multi layered (skin).

Question 10

Connective tissue

Answer 10

e.g. bone, cartilage & blood. Characterized by large quantity of material present in spaces between cells. Matrix may be solid (bone), fibrous or gelatinous (cartilage) or liquid (plasma in blood).

Question 11

Bone

Answer 11

Concentric layers of calcified material laid down around blood vessels. Live bone cells receive oxygen & nutrients via tiny canals in contact with blood vessels.

Question 12

Cartilage

Answer 12

Several forms differing in composition of extracellular material. Can be solid & smooth or slightly flexible with dense fibres embedded in a solid background.

Question 13

Blood

Answer 13

Classified as a connective tissue because approx 50% of its volume composed of plasma.

Question 14

Muscle

Answer 14

Cells capable of contraction.

1. SKELETAL - striped fibres.
2. SMOOTH - spindle shaped cells arranged in sheets e.g. alimentary canal & blood vessels.
3. CARDIAC - each cell has one or more branches in contact with adjacent cells.

Question 15

Nervous tissue

Answer 15

Composed of network of

1. NEURONS - to receive & transmit nerve impulses.
2. GLIAL - cells to support & maintain neurons

Question 16

Chromosome

Answer 16

An organized package, thread like structure of DNA found in the nucleus of a cell. Subdivided into genes, mostly in functional pairs.

Question 17

Diploid

Answer 17

Containing pairs of homologous chromosomes.

Question 18

Mitosis

Answer 18

Division of a cell nucleus, where genetic material is divided equally between 2 daughter nuclei. Each somatic cell receives an identical copy of full set of 23 paired homologous chromosomes.

Question 19

Germline cell

Answer 19

A cell that eventually leads to the formation of sex cells (gametes).
Germline cells are set aside from somatic cells early in the course of human development but, like a somatic cell, is diploid, i.e. contains 23 pairs of homologous chromosomes & can undergo mitosis to replicate to form more germline ‘mother’ diploid cells.

Question 20

Meiosis

Answer 20

Secondary nuclear division of germline cells. Genetic material doubled by replication but divided between 4 nuclei, each receiving single set of 23 chromosomes, and forming 4 haploid gametes.

Question 21

Mutation

Answer 21

Alteration of genetic material (genome) of a cell, which can be transmitted to descendants if in a germline cell. Mutations in somatic cells are not inheritable.

Question 22

Ethics

Answer 22

Moral values and rules that govern human conduct

Question 23

Induced pluripotent stem cells

Answer 23

Differentiated cells (e.g. from human skin) that have been genetically reprogrammed using transcription process to switch some of their turned-off genes back on again. They act as stem cells but can only be used for research, as the viruses used as transcription vectors have been shown to cause cancers in laboratory mice.

Question 24

Nuclear transfer technique

Answer 24

Introduction of a human cell nucleus into an enucleated animal cell to form a CYTOPLASMIC HYBRID CELL. Some of these cells will divide to produce undifferentiated stem cells. Can only be used for research because of mixed species origin not 100% human.

Question 25

Totipotent

Answer 25

Capable of differentiation into any cell type & giving rise to the complete organism.

Question 26

Cancer

Answer 26

Uncontrolled growth of cells. Cancer cells

1. Divide uncontrollably
2. Do not respond to body’s normal regulatory signals which instruct them to stop dividing or die. (Suppressor genes which code for proteins which restrict cell division at specific points in the cell cycle are often ‘switched off’ or disabled during formation of cancer cells.)
3. Lose their adherence molecules on the surface of their cells which causes them to detach to spread, becoming malignant.

Question 27

Tumour

Answer 27

Mass of abnormal cells. Can be

1. BENIGN - remains as a discrete group of abnormal cells in one place in otherwise normal tissue. Can usually be successfully removed.
2. MALIGNANT - some of cancer cells lose surface molecules that keep them attached to original cell group, enter circulatory system, invade other tissues & ‘seed’ new tumours elsewhere in body.

Question 28

Apoptosis

Answer 28

Programmed cell death.