Cells: Size Does Matter in How They Function

1. Cells: Size Does Matter in How They Function HL Biology 1

2. 2.1.1 Cell Theory Review Living organisms are composed of cells. Cells are the smallest unit of life. Cells come from pre-existing cells.

3. Cell Theory • Robert Hooke discovered cells • The cell theory was proposed by Schleiden, Schwann and Virchow • Many other biologists contributed to Cell Theory • See Clegg p 3, Figure1.2

4. Additional Concepts of the Cell Theory • All cells pass along hereditary material to new cells during cell division • All cells are made of the same basic chemicals • All energy transformations of life take place in cells

5. 2.1.2 Evidence for Cell Theory Review Table 1.2, Clegg p4 Hooke-designed compound microscope; observed cork Pasteur-microbiologist; disproved spontaneous generation Watson and Crick-discovery of DNA has double helix Viruses? Data Hypothesis Theory (TOK emphasis)

6. One or Many? • Many living things consist of a single cell • Unicellular • Other living things consist of many cells • Multicellular; in such organisms the cells can become specialized for various functions

7. 2.1.3 Unicellular organisms carry out all the functions of life Obtaining energy Obtaining water Response Excretion of wastes Protection/Defense Reproduction Homeostasis—maintaining an internal environment within normal limits

8. 2.1.7Multicellular organisms show emergent properties • Emergent properties arise from the interaction of component parts; the whole is greater than the sum of its parts. • As multicellular organisms increase in complexity, component parts become highly specialized and more dependent upon one another for their division of labor.

9. Life is organized • Life has a hierarchy of organization • One level builds upon the next

10. Cell Types • Prokaryotes: do not contain membrane bound organelles, unorganized DNA • Eukaryotes: contain membrane bound organelles and organized DNA (in nucleus, wrapped around proteins)

11. Cell similarities Regardless of whether or not they are prokaryotic or eukaryotic, unicellular or multicellular, all cells have 4 things in common: • Cell membrane • DNA • Ribosomes • Cytoplasm

12. 2.1.6 The importance of the surface area to volume ratio as a factor limiting cell size. The rate of heat production/waste production/resource consumption of a cell is a function of its volume, whereas the rate of exchange of materials and energy (heat) is a function of its surface area.

13. Surface Area vs. Volume • Surface area represents how well the plasma membrane can allow for the exchange of materials between the interior and exterior of a cell • Volume represents how much the inside of the cell can hold; rate of heat and waste production and resource consumption is a function of volume • as the cell increases in size, the volume increases • Equations for surface area and volume of cube often used to illustrate inverse relationship that exist and explains why cells are small Formulas SA = L x W x number of sides (answer in units2) V = L x W x H (answer in units3)

14. Determine the Surface Area and Volume and Indicate the Relationship: 3 cm 3 cm 2 cm 2 cm 1 cm 1 cm 1 cm 3 cm 2 cm SA: 3 x 3 x 6 = 54cm2 SA: 2 x 2 x 6 = 24cm2 SA: 1 x 1 x 6 = 6cm2 V: 3 x 3 x 3 = 27cm3 V: 2 x 2 x 2 = 8cm3 V: 1 x 1 x 1 = 1cm3 SA:V = 54:27 = 2:1 SA:V = 24:8 = 3:1 SA:V = 6:1

15. Limits of Cell Size As the volume of a cell exceeds the surface area of the cell, the diffusion rate will increasingly slow down. If the diffusion rate of a cell is too slow, it will be difficult for the cell to take in nutrients and rid itself of wastes. The shapes of cells can also affect the amount of surface area that a cell has. Spherical cells have the least membrane per unit volume, while flat or long cells have the most. If cells get too big, they will die. As they become bigger they have less surface area per unit of volume of cytoplasm. This makes it much more difficult to exchange materials with the environment. If this condition is not changed, the cell will not be able to maintain its homeostasis (internal balance), and it could die. Cells must maintain a large surface area (SA) to volume (V) ratio to maintain good health.

16. 2.2 Prokaryotic Cells

17. 3 Domains of life

18. 2.2 Prokaryotic Cell Structure Figure 1.15, p16--Naked DNA in cytoplasm--Lack membrane-bound organelles--70S ribosomes--1 circular chromosome--divide by binary fission

19. 2.2.2 Functions of each Part Cell Wall--rigid covering Plasma Membrane--encloses cell contents;controls entry and exit of substances Cytoplasm--contains water and dissolved molecules Pili--Attachment structures Flagella--Locomotion organelles Ribosomes--Make proteins from RNA which is made from translating the DNA code Nucleoid--region-Contains the hereditary code (naked DNA) Capsule--a jelly-like covering provides protection and allows adhesion to surfaces

20. 3 Common Shapes of Bacteriacocci, bacilli, spirilla

21. 2.2.4 Prokaryotic cells divide by binary fissionprocess whereby a cell grows and then divides into 2 cells Image from http://science.nayland.school.nz/graemeb/images/2006pics/science2006/binaryfission.jpg

22. 2.3 Eukaryotic Cells

23. EukaryotesInclude the following Kingdoms: Protists Fungi Plants Animals

24. Many protists are unicellular like Euglena

25. Paramecium- unicellular protist

26. Other protists… Plasmodium Diatoms Giardia Trichomonas Trypanosoma

27. Protists Facts • Diatoms- photosynthetic; cell walls made of silica • Giardia- parasitic; causes Giardiasis, diarrheal illness • Plasmodium- causes malaria by infecting RBC; transmitted by Anopheles mosquitoes; flu-like symptoms, high fever, shaking chills, an anemia • Trichomonas- parasite lives in vagina, cervix or male lower genital tract; causes sexually transmitted infection • Trypanosoma- parasite transmitted by tsetse fly; causes sleeping sickness, by infecting the brain and meninges; can be fatal if left untreated

28. Eukaryotic cell structure; Page 15, Figure 1.13Hepatocyte-liver cells that make proteins, carbohydrates, cholesterol, bile salts and phospholipids Free ribosome80S Golgi Apparatus is the term used in IB Nuclear membrane Nucleus Eukaryotic-- Mitochondria and other membrane-bound organelles Internal membranes compartmentalize functions

29. Eukaryotic Animal Cell

30. Nucleus and its envelope Protects DNA Controls and directs cell activities Site of: DNA Replication Making of RNA Making of ribosomes

31. Ribosomes Make proteins from the mRNA code Some found free in cytoplasm, while some are on Rough ER

32. Endoplasmic Reticulum Smooth ER important in creation and storage of steroid and storage of ions; no ribosomes attached to surface of membrane. In liver cells, it produces enzymes used to detoxify certain compounds; Smooth ER is involved in carbohydrate and lipid synthesis, and assisting with muscle contractions Rough ER produces proteins for export to the plasma membrane and/or beyond; vesicle forms around protein and is used for protein transport. In leukocytes Rough ER produce antibodies, while in pancreatice cells it produces insulin

33. Golgi Apparatus Series of cup-shaped membranes that receive and modify cellular products, including those from the ER, and prepares them for external transport or transport to other locations inside the cell Vesicles carrying ER products bud from the ER and move through cytoplasm towards Golgi apparatus where they fuse;

34. Mitochondrion • Site of aerobic respiration and ATP production • Two membranes, with inner membrane consisting of many folds called cristae; they increase surface area Image from http://microbewiki.kenyon.edu/images/7/7b/Mito_pic_diagram.gif

35. Lysosome Phosopholipid bilayer membrane forms a barrier to maintain a separate, acidic internal environment which contains digestive enzymes and can digest macromolecules.

36. 2.3.4 Comparing Prokaryotic and Eukaryotic Cells

37. 2.3.5 Comparing Plant and Animal Cells

38. Plant vs. Animal Cells Image from intranet.canacad.ac.jp:3445/BiologyIBHL1/589

39. Extracellular components– substances that are secreted outside plasma membraneAnimal cells secrete glycoproteins which become part of an extracellular matrix; functions in support, adhesion and movement.

40. 2.3.6 Roles of Extracellular Components Many contents of the cell are contained within the plasma membrane. Cells also secrete material outside the plasma membrane, and these substances include plant cell walls and animal cell glycoproteins

41. Plant Cell

42. The Plant Cell Wall • The main component of plant cells walls is cellulose • Cellulose molecules are arranged in bundles called microfibrils • These give the cell wall great tensile strength and allow high pressures to develop inside the cell

43. THE CELL WALL • Maintains cell shape, • Prevents excessive water uptake • Holds the whole plant up against the force of gravity

44. Animal Cells • Rather than have a cell wall, animal cells have an extracellular matrix • Secreted by glycoproteins • Support the animal cell • Assist with adhesion and movement