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1. 3.1 Cells and Tissues (Page 199)

2. When a human embryo is only a few hours old, the fate of many cells has ____________________________________ Three factors influence specialization:

3. The effect of cytoplasm on cell specialization • Cells have identical chromosomes; however E.g. having more _____________allows a cell to release more energy as it grows thus affecting development The effect of environment on cell specialization • Temperature and presence of certain chemicals and nutrients • Environmental factors can also be responsible for developmental _____________________ • ___________________, pollution, parasites, diseases can trigger developmental abnormalities • In Siamese cats, skin cells that develop in cooler conditions (extremities) produce dark fur

4. The effect of neighbouring cells on specialization • one of the ____________________ on cell specialization • substances produced by neighbouring cells can ___________ across a cell’s membrane • substances can change how and when _________________ In chick embryos, neighbouring cells influence eye development (blue area)

5. Similar cell conditions form similar cells As a cell ages, genes are switched on and off by the influence of other cells and _______________________ therefore different situations can produce nerve cells or skeletal cells (for example) • Cells that experience similar influences usually become similarly specialized to do the same job Mature cells stop dividing and live out their lives as a specialized cell (____________________________________)

6. 4 Types of Tissues

7. Epithelial tissues • Line the • Made of cells with string connections between adjoining cell membranes so they Skin epithelial: • _______________ that act as a semi-permeable barrier between inside and outside the body Columnar epithelial: • columns of cells that line • may secrete ________, have cilia and absorb materials

8. Epithelial tissues

9. Muscle tissues • Change their shape by Skeletal Muscle: • cells line up; looks striated • attached to bone allowing body to move • in Smooth Muscle: • cells are tapered at both ends • found in • contracts slowly and can be sustained for long time Cardiac Muscle: • nuclei appear between cells, branched unevenly, striated • contracts as a unit & only found in

10. Muscle tissues

11. Connective tissues • Strengthens, supports, binds, connects cells and tissues Bone: • cells surrounded by calcium hardened tissue containing blood vessels Fat: • large tightly packed cells • found under skin and around organs Blood: • Red & white blood cells, platelets and plasma

12. Connective tissues

13. Nervous tissue • cells called • coordinates body actions • Varied in their action: • some relay signals from brain to muscles & glands • others detect info from their environment and trigger responses

15. Stem Cells An unspecialized cell that can produce various types of cells • Mammals can naturally only replace small amounts of tissues (bone & skin); not organs Totipotent: Pluripotent:

17. The Potential of Stem Cells • Huge potential in medicine: In 1968 Canadian researchers showed that healthy marrow can restore blood cells in an animal that had undergone radiation therapy Human embryonic stem cells (1 week old) can become over 300 different types of cells • these cells obtained from • egg cells fertilized in vitro (in glass) • egg cells come from fertility clinics • Harvesting stem cells destroys the embryo: