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TOPIC 2.1. Topic 2: Cells By the end of this lesson, you should be able to: Outline the Cell Theory Be able to compare relative sizes of cells and cellular.

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Presentation on theme: "TOPIC 2.1. Topic 2: Cells By the end of this lesson, you should be able to: Outline the Cell Theory Be able to compare relative sizes of cells and cellular."— Presentation transcript:

1 TOPIC 2.1

2 Topic 2: Cells

3 By the end of this lesson, you should be able to: Outline the Cell Theory Be able to compare relative sizes of cells and cellular components Be able to calculate linear magnification of drawings Understand gene selectivity Understand the importance of stem cells

4 What level of complexity is necessary for life? Aristotle (384 – 322BC)

5 History of the Cell Hooke, 1665 – Looked through compound microscope at cork samples and coined the term “cells ”

6 History of the Cell Leeuwenhoek, 1675 – Discovers unicellular organisms in pond water

7 History of the Cell Matthias Schleiden & Theodor Schwann, – Suggested that plants and animals; respectively, are composed of cells – “The cell is the basic unit of living tissue” Rudolf Virchow (1858) noted that: “all cells come from pre- existing cells”

8 Cell Theory Those early scientists did experiments on living things and developed CELL THEORY Main Ideas of Cell Theory All living things are made of one or more cells 1) Cells are the basic units of structure & function of living things; “The smallest unit of life” 2) All cells come from existing cells 3)

9 What is a theory?

10 Cell: “The smallest Unit of Life” Leeuwenhoek’s unicellular organisms show all the signs of life  Metabolism  Response to stimuli  Growth  Reproduction  Homeostasis  Nutrition

11 2.1 Cell Theory State that unicellular organisms carry out all the functions of life. (1) MOVEMENT – Intracellular and/or extracellular RESPIRATION – Gas exchange. Not always O 2 and CO 2 NUTRITION – Need raw materials, i.e.- food, water, minerals EXCRETION – Get rid of waste materials REPRODUCTION – Ability to produce like organisms IRRATIBILITY – Respond to external stimuli GROWTH – Cells grow larger... and don’t forget...

12 What level of complexity is necessary for life? Xavier Bichat ( ): An organ is composed of different tissues and several organs can be grouped together as an organ system (e.g. the digestive system) An idea of hierarchy of structure developed : Organism Organ-system Organ Tissue Cell

13 2.1 Cell Theory Discuss the theory that living organisms are composed of cells. (3) Skeletal muscle and some fungal hyphae are not divided into cells but have a multinucleate cytoplasm. Some biologists consider unicellular organisms to be acellular.

14 2.1 Cell Theory State that a virus is a non-cellular structure consisting of DNA or RNA surrounded by a protein coat. (1)

15 2.1 Cell Theory

16 2.1.3 State that all cells are formed from other cells. (1) x ref Mitosis, 8.1- Meiosis

17 2.1 Cell Theory Explain three advantages of using light microscopes. (3) Advantages include: colour images instead of monochrome, a larger field of view, easily prepared sample material, the possibility of examining living material and observing movement.

18 2.1 Cell Theory Outline the advantages of using electron microscopes.(2) Greater: Resolution – the ability to distinguish between two points on an image. Like pixels in a digital camera. Magnification – how much bigger a sample appears to be under the microscope than it is in real life.

19 3.1 Cell Theory Transmission electron microscopes pass a beam of electrons through the specimen. The electrons that pass through the specimen are detected on a fluorescent screen on which the image is displayed. Thin sections of specimen are needed for transmission electron microscopy as the electrons have to pass through the specimen for the image to be produced.

20 2.1 Cell Theory Scanning electron microscopes pass a beam of electrons over the surface of the specimen in the form of a ‘scanning’ beam. Electrons are reflected off the surface of the specimen as it has been previously coated in heavy metals. It is these reflected electron beams that are focused on the fluorescent screen in order to make up the image. Larger, thicker structures can thus be seen under the scanning electron microscope as the electrons do not have to pass through the sample in order to form the image. However the resolution of the scanning electron microscope is lower than that of the transmission electron microscope.

21 2.1 Cell TheoryLightElectron Cheap to purchase (£100 – 500) Expensive to buy (over £1,000,000) Cheap to operate Expensive to produce electron beams Small and portable Large and requires special rooms Simple and easy preparations Lengthy and complex preparations Material rarely distorted by preparation Preparation distorts material Vacuum is not required Vacuum is required Natural color maintained All images in black and white Magnifies objects only up to 2000 times Magnifies over 500,000 times

22 2.1 Cell Theory Define organelle. (1) Literally ‘little organ’ An organelle is a discrete structure within a cell, and has a specific function. i.e. – nucleus, cell membrane, mitochondria

23 2.1 Cell Theory Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using appropriate SI units Appreciation of relative size is required (2) molecules (1 nm), thickness of membranes (10 nm), xref. 1.4 viruses (100 nm), bacteria (1 µm), xref organelles (up to 10 µm), xref , 7.1.3, most cells (up to 100 µm). Don’t forget: all of these structures are in 3D space

24 2.1 Cell Theory

25 2.1.5 Calculate linear magnification of drawings. (2) Drawings should show cells and cell ultra- structure with scale bars Magnification could also be stated, eg x250.

26 How Big are Cells? Eukaryotic CellUp to 100 μm OrganellesUp to 10 μm Bacteria (prokaryote) 1 μm Large Virus (HIV)100 nm Cell Membrane10 nm Molecules1 nm Weem et al., 2007 Adenovirus E. coli 1 micrometer (μm) is 1 millionth of a meter (10 -6 ) 1 nanometer (nm) is 1billionth (1 thousand milllionth) of a meter (10 -9 )

27 Why so small? If cell was larger…. – Diffusion distance becomes too far to be energy efficient – Surface to volume ratio becomes too small to allow the necessary exchange

28 Why so small? The production rate of cellular heat/waste and consumption of resources is directly proportional to its volume Since everything goes via the cell membrane, the rate of uptake/removal is proportional to the cell surface area

29 2.1 Cell Theory Explain the importance of the surface area to volume ratio as a factor limiting cell size. (3) The rate of metabolism of a cell is a function of its mass:volume ratio, Whereas the rate of exchange of materials and energy (heat) is a function of its surface area. Simple mathematical models involving cubes and the changes in the ratio that occur as the sides increase by one unit could be compared.

30 Volume and surface to area ratios Length of side = 1 cm Surface area = 6 cm 2 (6 * 1 * 1) Volume = 1 cm 3 Surface area:Volume ratio = 6:1 This means every 1 cm 3 of cell has 6 cm 2 of surface area Length of side = 10 cm Surface area = 600 cm 2 (6 * 10 * 10) Volume = 1000 cm 3 Surface area:Volume ratio = 0.6:1 This means that every 1 cm 3 of cell has 0.6 cm 2 of surface area; 10 times less 10

31 Ratio of V:S.A. Cube Side Length Volume (x 3 ) S.A. (6x 2 ) Ratio (S.A./V) 1 1 cm 2 10 cm cm 1 cm cm cm 3 6 cm cm cm

32 Ways cells adapt to help this problem Protrusions Flattening cell

33 Multicellular organisms have same problem Lungs – Alveoli help to increase surface area to allow greater diffusion Intestines – Villi help to increase surface area to allow greater absorption Circulatory system – Reduces diffusion distance

34 2.1 Cell Theory Define: (1) Tissue – A group of cells working together to perform a common function Organ – A group of tissues working together to perform a common function Organ System – A group of organs working together to perform a common function

35 2.1.8 More is different! As a multicellular organism grows and develops it follows a structured plan The cells specialize (differentiate) A developing multicellular organism shows emergent properties The whole is more than the sum of its parts

36 2.1.7 Emergent properties Cells interact to acquire properties that, alone, they do not possess Example: The human brain – Individual neurons not capable of thought but the cooperation and communication among the individuals enables us to think

37 Specialized cells In multicellular organisms, cells differentiate to become specialized for their function Only a small portion of the genes are necessary – Each human cell has 40,000 potential genes – To avoid waste, cell activates only those genes necessary to carry out its function

38 Stem Cells Unspecialized, “immortal” cells Have not silenced their genes yet, therefore, can potentially become any cell Totipotent – Can become any type of cell – Embryonic cells Pluripotent – Partly differentiated, are restricted to certain cell types (ex. Blood cells) – Most of your stem cells in your bone marrow are pluripotent – Zygotic cells Multipotent – More differentiated but can still differentiate into a limited number of cell types

39 What can stem cells do for you? Cell therapy – The totipotent potential of stem cells permits their use to replenish damaged/missing cells of our own body

40 Cell Therapy Leukemia (cancer of the blood) – A bone marrow transplant can replenish blood cells lost to leukemia/chemotherapy Skin grafts – Stem cells can re-grow skin damaged by burns/accidents Corneal replacement – Re-grow cells of the eye for vision restoration Parkinson’s/Alzheimer’s – Stem cells possess the ability to re-grow brain cells Diabetes – Pancreas cells responsible for insulin production could be re-grown for type I diabetes

41 Where do stem cells come from? Umbilical cord Embryos – Unused from in-vitro fertilization – Aborted Your own bone marrow – Although not totipotent, investigation is determining whether they can be converted to be totipotent Requires embryonic investigation

42 TOPIC 2.2 and 2.3


44 2.2

45 Damon, et al Standard Level Biology, 2009 Escherichia coli Electron micrograph of E.coli

46 2.2.3 Prokaryotic Cells Cytoplasm Cytoplasm – contains enzymes that catalyse the chemical reactions of meabolism and DNA in a region call the nucleoid Pili (not in all cells) Pili (not in all cells) – Hairlike growth on the outside of cell membrane – Used for attachment – Main function is to join bacterial cells in preparation for DNA exchange Flagella (not in all cells) Flagella (not in all cells) – longer than pili – Used for motility Size 5-10µm

47 ribosomes 70s ribosomes 70s – synthesize proteins by translating messenger RNA. Some proteins stay in the cell and others are secreted Nucleoid (naked DNA) Nucleoid (naked DNA) – stores the genetic information that controls the cell and is passed on to daughter cells – Single, long, continuous (circular) – Bacteria may contain plasmids small, circular DNA fragments that replicate independently of the bacterial chromosome small, circular DNA fragments that replicate independently of the bacterial chromosome

48 2.2.4 Bacterial Replication Reproduce by binary fission No exchange of genetic material Takes 20 min in good conditions

49 Eukaryotic Cells Eukaryotic Cells Contains a nucleus and distinct organelles Contains a nucleus and distinct organelles DNA is enclosed in a nuclear envelope DNA is enclosed in a nuclear envelope Cell division by mitosis Cell division by mitosis Size µm

50 Weem et al., 2007

51 Eukaryotic Cells Eukaryotic Cells Ribosomes 80s – protein synthesis Rough endoplasmic reticulum (rER) – synthesis of proteins to be secreted Lysosome – holds digestive enzymes Golgi apparatus – for processing of proteins Mitochondrion – for aerobic respiration Nucleus – holds the chromosomes


53 2.3.5 State three differences between plant and animal cells. Carbohydrates stored as starch. Carbohydrates stored as glycogen. Stores large amounts of liquid (juice). Larger size of cell.  Central Vacuole XDoes not store large amounts of liquid. Smaller size of cell. Rigid, cannot easily change shape.  Cell Wall XFlexible, can easily change shape. Can produce its own food. ChloroplastXCannot produce its own food Plant Cells Structure Animal Cells


55 2.3.6 Extracellular components The plant cell wall The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity. Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement.

56 TOPIC 2.4

57 2.4 Membranes Go to the boardwork!!!! Draw a diagram to show the fluid mosaic model of a biological membrane. The diagram should show the phospholipid bilayer, cholesterol, glycoproteins and integral and peripheral proteins. Integral proteins are embedded in the phospholipid of the membrane whereas peripheral proteins are attached to its surface.

58 2.4 Membranes Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. (3) Hydrophobic – ‘afraid of water’ Hydrophilic – ‘loves water’





63 2.4.3 List the functions of membrane proteins including hormone binding sites enzymes electron carriers channels for passive transport pumps for active transport.



66 Passive Transport Diffusion Simple diffusion Facillitated diffusion Osmosis Requires no energy Moves from down the concentration gradient Some molecules pass through the membrane Some molecules use channels for facilitated diffusion

67 Diffusion Define diffusion Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient), until there is an equal distribution. Define osmosis Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration (high water concentration) to a region of higher solute concentration (low water concentration).

68 High Concentration Low Concentration Diffusion moves down the concentration gradient just like a ball rolling down a hill. It cannot roll uphill without energy. Do not mix diffusion with osmosis!!!

69 Simple diffusion Osmosis v Facillitated diffusion channel carrier EXAMPLES

70 Active Transport Transporters (proteins) Directly use of energy Indirectly use of energy Requires energy (ATP) or adenosine triphosphate Movement of molecules or ions against concentration gradient Pumps fit specific molecules The pump changes shape when ATP activates it, this moves the molecule across the membrane Use of the energy already stored in the gradient of a directly-pumped ion Bind ATP directly and use the energy of its hydrolysis to drive active transport Transport through vesicles Endocytosis Exocytosis

71 Chemiosmosis: Electron transport provides energy for the synthesis of ATP, but only indirectly. When electron transport chains pump H+ across the membrane, the protons become more concentrated on one side of the membrane than on the other. Such a concentration gradient stores potential energy. ATP is generated by a molecule called ATP synthase. ATP synthase is a combination of proteins that act as both an ion channel and an enzyme. As an ion channel in the membrane of the mitochondria or thylakoids, it allows H+ to diffuse through it (facilitated diffusion). This actionspins a component of the ATP synthase. This rotation activates the active sites in the enzyme that attach phosphate groups to ADP molecules to generate ATP. EXAMPLES Indirectly use of energy ATP Synthase Directly use of energy Na + /K + ATPase It uses the energy from the hydrolysis of ATP toactively transport 3 Na + ions out of the cellfor each 2 K + ions pumped into the cell. The picture is in Cell Resp ppt!!

72 Active Transport Ex: Sodium – Potassium pump


74 2.4.7 Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane Describe how the fluidity of the membrane allows it to change shape, break and reform during endocytosis and exocytosis. THIS ITEM IS IN MEMBRANE´S BOARDWORK!!!!! Transport through vesicles

75 2.4.7

76 2.4 Membranes Endocytosis – the mass movement INTO the cell by the membrane ‘pinching’ into a vacuole Exocytosis – the mass movement OUT of the cell by the fusion of a vacuole and the membrane This is possible because the of the fluid properties of the membrane (able to break and reform easily, phospholipids not attached just attracted) 2.4.8

77 Exocytosis

78 Endocytosis

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