Introduction to Cells

Transcription

1 Learning Outcomes 1 To revise the basic structure of plant and animal cells to discuss the similarities and differences between animal and plant cells. Identify variation in structure between cells within a tissue

2 Introduction to Cells Cell The basic unit of life Smallest structure able to lead independent life and show all characteristics of living things. There are seven characteristics Movement, Reproduction, Sensitivity, Growth, Respiration, Excretion and Nutrition (MRS GREN) Nucleus contains the genetic information, controls the cell.

3 Learning Outcome 2 To observe a variety of different tissues To recognize and account for the variation in structure of the following tissues Columnar, ciliated and glandular epithelia Palisade and spongy mesophyll Xylem and phloem

4 Cell Theory - Starter The cell is the fundamental unit of life. All organisms, whatever their type or size, are composed of cells. The modern theory of cellular organisation states:- All living things are composed of cells and cell products. New cells are formed only by the division of preexisting cells The cell contains inherited information (genes), which is used as instructions for growth, functioning and development. The cell is the functioning unit of life; the metabolic reactions of life take place within the cells.

5 Cell Theory - Question Before the development of cell theory, it was commonly believe that living organisms could arise by spontaneous generation. Explain what this term means and why it has been discredited as a theory.

6 Multi-cellular organisms Cells tissues organs organ systems organism Division of labour a tissue is a group of cells specialised to carry out a particular function.

7 Cell Variety Variation within one tissue e.g. blood contains red blood cells and white blood cells Variation between different tissues e.g. compare xylem and phloem

8 Structure in Relation to Function The structure of each cell is exactly tailored to suit its function. Advantage of specialisation Ability to function at a higher level

9 Ciliated Epithelium This tissue is found lining the ends of the bronchioles in the lungs.

10 Squamous Epithelium

11 Plan Diagrams dicotyledonous leaf

12 Plan Diagrams - dicotyledonous leaf

13 Tissues You should be able to discuss the structure and function of the tissue types, and discuss how their structure suits their function. e.g. describe how a xylem vessel is structurally suited to perform 2 functions. FOR THE ACTIVITY BELOW GIVE TISSUE, CELL TYPE, SPECIALISED STRUCTURAL FEATURES AND FUNCTION. Choose 3 of the human tissues try to relate structure to function. Choose 3 of the plant tissues try to relate structure to function.

14 Homework Questions (10 marks) By means of two examples, show how the differences between the structure of cells in different tissues are related to the different functions of these tissues.

15 Learning Outcome 3 To observe plant cells from fresh tissue, using a stain. To observe prepared slides of plant and animal cells and tissues.

16 Cell Biology and Microscopy When Scientists began to observe cells, they started with simple microscopes. Today two different types of microscope are in use, both microscopes use a form of radiation to create an image of the specimen: Light microscope uses light Electron microscope uses electrons

17 Using a light microscope Magnification Number of times larger an image is compared with the real size of the object Resolution The ability to distinguish between two separate points

18 Structure of a generalised animal cell as seen with a very high power quality light microscope (diameter ~ 20ųm)

19 Structure of a generalised plant cell as seen with a very high power quality light microscope (diameter ~ 40ųm)

20 Light Microscope For the microscope in front of you, work out The magnification of each lens The field of view for each lens Using a graticule / stage micrometer All diagrams should include title, labels, magnification

21 Learning Outcome 4 Identify an appropriate example of a unicellular organism To know the functions of each of its most obvious organelles

22 Unicellular Organisms (one cell) A unicellular organism must make all chemicals and perform all functions necessary for life. Pleurococcus is a unicellular plant Paramecium is a unicellular animal Euglena is a unicellular organism, which demonstrates characteristics of both plant and animal cells.

23 Summary Questions Why is the cell described as the basic unit of life? Explain the meaning of the terms unicellular and multicellular organism. Describe the roles played by a named unicellular plant s cell wall, nucleus and chloroplast. Describe the role played by a food vacuole and a contractile vacuole in a unicellular animal.

24 Extended Response Question Give an account of the differences between uni-cellular and multi-cellular organisms, including examples of each. Marks available = 10 Maximum of 8 marks for content Coherence 1 or 0 Relevance 1 or 0

25 Learning Outcome 5 To state the overall cellular function associated with a particular cell organelle To identify some organelles in an electron micrograph

26 Animal Cell

27 Plant cell

28 Animal cell - answers

29 Plant cell - answers

30 Questions 1. State three differences that exist between a typical plant and a typical animal cell. 2. Name three organelles common to both plant and animal cells. 3. State a structural difference between rough and smooth endoplasmic reticulum. 4. Explain briefly why a liver cell may contain as many as one thousand mitochondria. 5. Why do the cells in a frog tadpole s tail contain many lysosomes?

31 Learning Outcome 10 To describe the structure of the plasma membrane To describe the methods of absorption and secretion. To investigate the chemical nature of the Plasma membrane.

32 Absorption and Secretion Absorption The uptake of materials by a cell from its external environment Secretion The discharge of useful intracellular molecules into the surrounding medium by a cell

33 Methods of A and S Diffusion Osmosis Active transport Endocytosis Phagocytosis Pinocytosis Exocytosis (secretion)

34 Cell boundaries All living cells are surrounded by a plasma membrane. Plants cells are also surrounded by a cell wall.

35 Structure of the Plasma Membrane The plasma membrane is composed of phospholipids and proteins. The current theory is a fluid mosaic model Fluid layer of moving phospholipids Patchy mosaic of protein molecules

36 Investigating the chemical nature of the cell membrane The cell sap present in the central vacuole of a beetroot cell contains red pigment. Bleeding indicates that the cell s plasma and vacuolar membranes have been damaged. You are going to investigate the chemical nature of the plasma membrane using beetroot cylinders.

37 The results In which test tubes did bleeding occur and why? Think think think think think think think Structure of plasma membrane How would each of the conditions affect it? Which test tube was the control?

38 Explanation bleeding occurs in B, C, and D, it can be concluded that the cell membranes have been destroyed in each of these tubes. Acid and high temperature destroy the membrane by denaturing the protein molecules. Alcohol dissolves the phospholipid (fat) component of the membrane. These allow the red pigment to escape.

39 Learning Outcome 11 To discuss cell membrane structure with relation to the fluid mosaic model To explain the function of the plasma membrane in relation to active transport and the absorption and release of materials. To handle data concerning the solute concentration in aquatic organisms

40 Structure of the plasma membrane The plasma membrane is a fluid phospholipid bilayer, with a mosaic of protein molecules.

41 Diffusion Diffusion The net movement of molecules or ions from a region of high concentration to a region of low concentration. Diffusion occurs along a concentration gradient.

42 Diffusion across a membrane

43 Factors affecting the rate of diffusion Concentration gradient Greater the difference in concentration the greater the rate of diffusion Temperature At higher temperature kinetic energy particles increases Diffusion is faster Surface area Greater the surface area, more particles can cross Increases rate of diffusion Nature of molecules or ions Large molecules diffuse slower Non-polar molecules diffuse more easily

44 Active transport Active transport is the uptake of molecules or ions against a concentration gradient using energy from respiration Helps to build up a high concentration of molecules/ions inside the cell. Special carrier proteins in the membrane actively transport specific molecules and ions.

45 Active Transport Examples include: Muscle contraction Absorption of mineral ions by roots Excretion of urea by the kidney

46 Absorption and Secretion of Materials Unit 1 Cell Biology

47 Learning Outcomes To understand osmosis To understand the role of the cell wall To discuss the cell wall with reference to cellulose fibres and permeability. To understand bulk transport

48 Absorption and Secretion Revision Absorption Uptake of materials by a cell from it s external environment. Secretion Discharge of molecules into the surrounding medium by the cell This movement is normally by:- Osmosis, diffusion or active transport.

49 Diffusion and Osmosis Definitions Diffusion T he net movement of molecules or ions from a region of high concentration to a region of low concentration. Diffusion occurs along a concentration gradient. Osmosis The net movement of water from a region of high water concentration (HWC) to a region of low water concentration (LWC)through a selectively permeable membrane.

50 Osmosis All cell membranes are permeable to water to a small degree, because water molecules are able to diffuse through the phospholipid bi-layer. Some membranes are as much as a thousand times more permeable due to the presence of aquaporins (transmembrane proteins acting as water channels)

51 Example: Osmosis Two solutions are separated by a partially permeable membrane. Solute molecules are too large to pass through pores in the membrane, but water molecules are small enough.

52 What would happen if the membrane were not present? Net movement of solute molecules from B to A by diffusion Net movement of water molecules from A to B by diffusion Equilibrium concentrations of water molecules and solute molecules in A would equal that in B.

53 What will happen if the membrane is present?

54 What will happen if the membrane is present? Solute molecules too large to pass through membrane Water molecules pass easily from A to B Net movement of water from A to B until equilibrium is reached, i.e. solution A has the same concentration of water molecules as solution B. The level of liquid A will fall and the level of liquid B will rise. Equilibrium is brought about by the movement of water molecules alone.

55 Osmosis in red blood cells If a red blood cell is placed in a hypotonic solution it will burst If a red blood cell is placed in an isotonic solution there is no net movement of water and the cell remains unchanged If a red blood cell is placed in a hypertonic solution is will shrink (crenate)

56 Effect of osmosis on blood cells Surrounded with pure water Cell swells and bursts Surrounded by a solution containing 0.85% salt Normal red blood cell containing 0.85% dissolved solute Surrounded with a solution containing 1.7% dissolved solute No change shrinks

57 Plant cells If a plant cell is placed in a hypotonic solution it becomes turgid If a plant cell is placed in an isotonic solution there is no net movement of water and the cell remains unchanged If a plant cell is placed in a hypertonic solution it becomes plasmolysed

58 Effect of osmosis on plant cells Surrounded by pure water Turgi d Plant cell containing 3% dissolved solute Surrounded by solution containing 3% sugar Surrounded by a solution containing 10% sugar Plasmolyse

59 Osmoregulation in Paramecium lives in fresh water it continuously gains water by osmosis The cell is prevented from bursting by the presence of contractile vacuoles Paramecium

60 Contractile Vacuoles canals collect excess water when swollen the vacuole contracts and discharges it contents through a pore The two contractile vacuoles discharge their contents alternately

61 Bulk Transport Endocytosis - Absorption Engulfing of molecules into the cell Phagocytosis large molecules Pinocytosis liquids Exocytosis secretion The release of large molecules to the outside of the cell

62 Cell Wall cell wall is composed of cellulose fibres. Consists of two layers. primary wall is random arrangement of cellulose fibres. secondary wall consists of layers of closely packed fibres of cellulose laid down like a mesh spaces between the cellulose fibres are filled with water Water moves easily from cell to cell