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Higher Biology

Higher Biology. Unit 1 Cell Biology: Cell structure in relation to function. In a multicellular (many-celled) organism the cells are organised into tissues. A tissue is a group of similar cells which work together to carry out a specific function.

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Higher Biology

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  1. Higher Biology Unit 1 Cell Biology: Cell structure in relation to function

  2. In a multicellular (many-celled) organism the cells are organised into tissues. • A tissue is a group of similar cells which work together to carry out a specific function.

  3. Some tissues have only one type of cell (e.g. muscle). Other tissues have several types of cells (e.g. phloem contains sieve tubes and companion cells).

  4. The structure of a cell is related to its function (what the cell does). • In a unicellular (one-celled) organism (e.g. amoeba, paramecium, euglena or yeast) all the processes necessary for life are carried out in a single cell.

  5. Paramecium

  6. Euglena

  7. Root hair

  8. Leaf epidermis

  9. Phloem

  10. Xylem

  11. Leaf mesophyll

  12. Parenchyma

  13. Lining of kidney tubule

  14. Return Lining of trachea

  15. Lining of trachea

  16. Lining of mouth

  17. Bone cell

  18. Fat cell

  19. Red blood cell

  20. Muscle Cell

  21. Nerve cell

  22. Cell Ultrastructure

  23. Cell Boundries • Cell wall • Outer boundary of plant cells • Made of cellulose fibres in layers • Strong, slightly elastic • Absorbs water, providing a pathway for water movement through plant tissues.

  24. Plasma membrane • Forms the cell membrane and forms or surrounds all cell organelles.

  25. Made of a double layer of phospholipid molecules with protein molecules embedded. • Called “fluid-mosaic” model because • Molecules move around like fluid • Proteins form a pattern on surface (mosaic) • Some protein molecules enclose a pore through which small molecules can pass in/out of the cell.

  26. Functions of the plasma membrane Molecules can enter or leave a cell, across the membrane, in 5 ways: • Diffusion • Osmosis • Endocytosis • Exocytosis • Active Transport

  27. Diffusion • Movement of molecules of (gas or) liquid from an area of high concentration to an area of low concentration down a concentration gradient.

  28. The concentration gradient is the difference in concentration between two areas.

  29. Molecules cross the plasma membrane in two ways: • Through the phospholipid layer • Through pores in the protein molecules

  30. Osmosis • Diffusion of water molecules • Through a selectively permeable membrane (e.g. plasma membrane) • (S.P. Membrane is a membrane with pores which allows small molecules to pass but not large ones)

  31. Water moves from a high water concentration to low water concentration HWC LWC

  32. Effects of osmosis on cells

  33. Hypotonic – higher water concentration Hypertonic – lower water concentration Isotonic – same water concentration

  34. Turgid – cell swollen with water Flaccid – cell limp through loss of water Plasmolysed – in Plant cells, water loss causes cytoplasm to shrink away from the cell wall.

  35. Endo- and Exo-cytosis Cells sometimes take in, or expel, large quantities of material by forming a “pocket” in the membrane. This is called endocytosis (taking material into the cell) or exocytosis (materials leave the cell).

  36. An example of endocytosis is:

  37. Phagocytosis

  38. In this form of endocytosis the cell engulfs solid particles (e.g. amoeba) – like “eating” a bacterium.

  39. Active Transport Movement of ions across the plasma membrane against the concentration gradient i.e. Low concentration → High concentration

  40. Energy is needed. Protein molecules transport ions across the membrane.

  41. IN High conc. inside the cell Low conc. outside the cell Energy Low conc. inside the cell High conc. outside the cell OUT

  42. Essay question Discuss the role of the plasma membrane under the following headings: • The structure of the plasma membrane (4 marks) • The role of the plasma membrane in transport (6 marks)

  43. Discuss the role of the plasma membrane under the following headings: • The structure of the plasma membrane (4 marks) • The role of the plasma membrane in transport (6 marks) Plasma membrane: • Composed of phospholipid bilayer (two layers) • Contains proteins. • Some proteins form pores through the membrane. • Described as a “fluid mosaic” Role of plasma membrane: • Diffusion + movement of liquid/gas from area of high conc. to area of low conc. • Osmosis + movement of water from area of HWC to area of LWC. • Endocytosis + description of engulfing a large molecule. • Phagocytosis is an example of endocytosis (eating bacteria). • Active transport + movement from area of low conc. to area of high conc. • Active transport requires energy and a carrier protein. 1 mark for each bullet point. TOTAL 10 Marks

  44. Concentrations in mM per kg

  45. In the example above, the lobster actively transports sodium inwards (higher concentration in the body than the sea water), actively transports magnesium out (lower concentration in body than sea water), but does not regulate chloride (concentration equal).

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