A Level Biology Transition project Summer 2016 Taking a closer look at cells and cell structure.

Transcription

1 A Level Biology Transition project Summer 2016 Taking a closer look at cells and cell structure. Learning objectives To develop an understanding of the ultrastructure of cells to including identification and explanation of the role of cell organelles. To recognise the fundamental difference between pro and eukaryotic cell structure and their defining characteristics. To have an understanding of the importance of cell structure in providing indirect evidence for evolution. To recognise the relative size and scale of cells and organelles and to convert between the different units used in biological measurement. To explain the principles of magnification and resolution. To explain how light, transmission electron microscopes and scanning electron microscopes work and the key differences between them and their limitations. Name: Pass Borderline Fail What went well: To further develop your understanding:

2 Task one: GCSE Review You will have studied the humble cell at GCSE. To ensure you are confident with the subject matter review the following list to audit your knowledge. Where you feel less familiar, use the CGP revision guide or BBC Bitesize web site to re visit the topic before you develop your understanding in this transition unit. What you should know GCSE review. CGP pg. reference Subject knowledge reviewed. Most human and animal cells have a nucleus, cytoplasm, cell membrane, mitochondria and ribosomes. 44 & 46 Plant and algal cells also have a cell wall made of cellulose which strengthens the cells. Plant cells often have chloroplast sand 44 & 46 permanent vacuole filled with cell sap. A bacterial cell consists of cytoplasm and a membrane surrounded by a cell wall; the genes are not in a distinct nucleus. 44 Task two: Cell similarities and differences, an introduction to pro and eukaryotic cells. Your body's composed of trillions of cells; lots of different types of cells that make up different organs and other parts of your body. Your body is also where 10 times that number of bacteria call 'home sweet home.' But don't be afraid - these bacteria do more good than harm to you. And besides, just in case you wanted to strike up a conversation with your tenants, you and your bacteria do have a few things in common. All cells share some common characteristics that make them living things. All organisms whether they be bacteria, fungi, plant, protist or animal are composed of cells - the basic fundamental unit of life. All cells contain DNA as a heritable genetic material, and they can reproduce. They transcribe DNA into RNA and translate RNA into proteins on ribosomes. They can also regulate transport across a cell membrane and require chemical energy for some cellular processes. This provides in-direct evidence for the theory of evolution. The number one biggest difference between the bacteria in your body and the cells making up your body are these tiny cellular components called organelles. Organelles are simply membrane-bound compartments within a cell, such as the nucleus, mitochondria, chloroplasts, golgi, and endoplasmic reticulum. You are a eukaryote. Your cells are eukaryotic. Eukaryotic cells contain membrane-bound organelles, including a nucleus. Eukaryotes can be single-celled or multicelled, such as you, me, plants, fungi, and insects. Bacteria are an example of prokaryotes. Prokaryotic cells do not contain a nucleus or any other membrane-bound organelle. Prokaryotes include two groups: bacteria and another group called archaea. Having organelles is a big deal for a cell. A bacteria cell gets along just fine without organelles, but bacteria are tiny. That's why we're able to have so many of them on our body without really noticing them. Our cells, though - they're still small to the naked eye, but they're huge in comparison to bacteria. Our eukaryotic cells are bigger in size, with much more DNA. More DNA means more transcription, and more transcription means more translation, and more translation means more proteins. Bigger cells create the need for organelles. Organelles are an efficient way to organize everything that's going on in the cell - to compartmentalize cellular functions. That's exactly what a eukaryotic cell is doing - separating cellular processes and organizing its space. But don't be fooled by the 'simplicity' of prokaryotes. In this project you will learn about the ultrastructure of the cell types. This means examining the cells at a level of detail smaller than could be viewed with a light microscope. You will learn the importance of the structures in creating a fully functional cell and begin to recognise why certain structures may be more developed in certain groups of cells. To help you complete the actvities which follow you need to develop you subject knowledge. Go to the link below and take a Tour of the cell with Bozeman Science to build your knowledge. If it helps pause the video and make your own notes to help you with the learning the key facts. Take a look at the the notes section about eukaryotic and prokaryotic cells on the Biology mad site. You could print out these key notes and highlight them rather than copying notes down if you find it more useful or you could make a revsion flash card on each organelle. A tour of the cell Bozeman Science: Biology mad: Other useful resources for learning about cell structure:

3 Task three: Applying knowledge of cell ultrastructure Eukaryotic cells (i) Add labels to the following diagrams show the ultra-structure of a liver cell which demonstrates the typical features of a eukaryotic cell. The two different images show a 2D and 3D structure. Nucleus (with nucleolus) Smooth endoplasmic reticulum Golgi body Plasma Cell membrane Cytosol Rough Endoplasmic reticulum Peroxisome Rough Endoplasmic reticulum Centrioles Cytoskeleton Mitochondrion (singular) Lysosome Ribosomes 80S Pinocytotic vesicle (ii) Which additional features would you expect to see if you were to be shown a palisade cell from a plant cell? (iii) Use the internet to search for and print out a suitable image of a fully labelled eukaryotic cell from a plant, add this to your notes for this section.

4 Task four: Examining prokaryotic cell structure Your task is to produce a clearly labelled diagram of a typical prokaryotic cell in the space below. It is a very important skill to be able to reproduce diagrams and biological drawings regardless of your artistic ability. Please bare in mind the following guidelines when putting together your diagram, as this will help you in the future when you draw specimens that you examine in class. Diagrams must be drawn and labelled in pencil. They must be large and clear so that features can be easily distinguished. Distinct single lines should be used when drawing, do not sketch. Add a title and labels to your diagram. The title should be centred above the diagram and all the labels down either the left or right hand side of the diagram. Each label line should be straight and must not overlap with other label lines. Annotation can be added, next to or underneath the label. Add a scale bar to show relative sizes of the parts of the cell.

5 Task five: Developing knowledge of cell ultra structure. Using the knowledge you have gained in tasks two three and four, match up each organelle with the correct description of its structure and its function. You should then use the internet to research the sizes of each. Organelle Plasma membrane Approx size (Including units) Description of structure Found on surface of animals cells and beneath the cell wall of plant and prokaryotic cells. Also forms a membrane around organelles. Made of lipid and protein Description of function Provides strength. Stops the cell bursting under the pressure of water entering by osmosis. Allows water to pass through it contributing to the movement of water through a plant. Nucleus A round organelle with no clear structure, surrounded by a membrane. Formed from the vesicles produced by the Golgi. Contain enzymes such as protease, lipase and lysozymes Synthesis stores and transports lipids and carbohydrates Lysosome Ribosome Rough Endoplasmic Reticulum (RER) System of membranes enclosing a fluid filled spaces. Forms a tubular like structure. Surrounded by a double membrane called the nuclear envelope which contains many pores. The outer membrane is continuous with the ER. It contains the genetic material (DNA) and often a nucleolus, suspended in nucleoplasm. Nucleoplasm is a jelly like substance which makes up most of the structure System of membranes enclosing a fluid filled space, forms a tubular like structure. Covered in ribosomes. Provides a large surface area for the synthesis of proteins and glycoproteins. Folds and processes the proteins that have been made at the ribosomes. Provides a pathway for the transport of proteins throughout the cell. The site of protein synthesis. Reads mrna instruction, which determines the sequence of amino acids in a protein chain. Selectively permeable, regulating the movement of substances into and out of the cell. Also have receptors which allow it to respond to chemical like hormones. Forms the structure of some organelles. Smooth Endoplasmic reticulum Can float free in the cytoplasm or be attached to RER. There are two types 80S and 70S. Made of two subunits each of which contains ribosomal RNA and protein. Their enzymes are involved in digesting worn out organelles or bacteria which have been engulfed by phagocytes. Also release enzymes out of the cell by exocytosis to material around the cell can be digested. Golgi apparatus Cell wall Mitochondrion Chloroplast Found in plants, algae and fungi. In plants they are made of micro fibrils of cellulose, in algae from cellulose or glycoprotein and fungi it is made of a substance called chitin. Between the cells walls of two adjacent cells there is a middle lamellae cementing the cells together. Usually oval shaped, they have a double membrane forming their outer structure. The external membrane is smooth, the inner membrane is folded to form structures called cristae. This provides a large surface area on to which the enzymes involved in respiration can attach. Inside the organelle is a fluid filled matrix that contains the enzymes for part of respiration. A group of fluid filled, flattened sacs of membrane called cisternae with small, round hollow structures called vesicles. Organelle found in plants. Surrounded by a chloroplast envelope to control entry and exit. Inside there are stacks of thylakoids forming grana. Extensions between thylakoids join grana together. A fluid filled matrix surrounds these structures. This is called stroma. DNA (the genetic material of the cell.) is transcribed to mrna which exits the pores of the nucleus to the ribosomes where the mrna instruction will be translated to protein. DNA is retained in the nucleus in the form of chromosomes. The nucleolus makes the ribosomes. Modifies, processes (by adding new groups such as adding a carbohydrate to a protein) and packages new lipids and proteins which were made in the ER. It then sorts them and sends them to their correct destination. Also makes lysosomes. This organelle is the site of aerobic respiration. They are found in large numbers in cells that are very metabolically active. These are ones that require lots of energy. The reactions involved in photosynthesis occur here. (light absorption in the grana and synthesis of sugar in the stroma.) Vacuoles Fluid filled sac bound by a single membrane called a tonoplast. The solution inside contains mineral salts, amino acids, sugars and pigments Provide support to parts of plants by making the cell turgid. Provide a temporary food store. The pigment colours may help to attract insects.

6 i. Which of the organelles listed above are not bound by a membrane. ii. Which of the organelles contains nucleic acid? iii. Write down two or three sentences to describe the links between the functions of the nucleus, ribosomes and endoplasmic reticulum. iv. Complete the table below to describe the structure and function of some of the features found in a prokaryotic cell. You may wish to revisit the Biology mad website referred to in task two. Component of prokaryotic cell Structure Function Circular DNA Posses genetic information for the replication of cells Cell membrane Made of phospholipids and proteins. Cell wall Cytoplasm containing ribosomes A physical barrier which excludes certain substances and protects against mechanical damage and osmotic lysis. Site of protein synthesis DNA in the form of small circular strands. An outer mucilaginous layer. Posses the genes that may aid survival of bacteria in adverse conditions eg. produces enzymes that breakdown antibiotics. Protects the bacterium from other cells and helps groups of bacteria to stick together for further protection.

7 Task Six: Tackling A level exam style questions Using the knowledge that you have acquired answer the following questions. You may need to leave 2c until you have completed the work on the different types of microscope. 1. The diagram on the left shows two organelles found in eukaryotic cells. a. Name organelles A and B (2 marks) b. Explain how the inner membrane is adapted to its function in organelle A (2 marks) c. Give one feature of a prokaryotic cell that is not found in a eukaryotic cell. (1 mark) 2. The photograph on the left shows a eukaryotic cell. a. Organelle X is a mitochondrion. What is the function of this organelle? (1 mark) b. Name organelle Y. (1 mark) c. This photograph was taken using a transmission electron microscope. The structures present could not have been seen using an optical (light) microscope. Explain why. (2 marks)

8 Task seven: Developing maths skills in Biology Size and scale of cells and cellular structures. Thinking about cells and organelles can be tricky to get your head around. Follow through the slides in the presentation on the link below which will help you make relative comparisons of the sizes of each part. Remember here everything has been scaled up times. As you can appreciate from this presentation when we are studying scales we are thinking about very small structures so using units such and metres and centimetres is not going to be appropriate. Click on the link below and use the sliding bar on the animation to view the relative sizes of objects, cells, organelles, biological molecules and even atoms! You will notice that some units, that you were less familiar with, were used for viewing some structures. Look at resource 1 to help you get head around how these units relate to a metre and the terms used to describe the units. You need to be able to convert between the units used when measuring cells and parts of cells. eg mm to μm. This will be a very important skill when we do some practical microscopy and calculations on cell size and magnification so it is important to get your head around it now. Complete the gaps in the table to show the sizes of different organelles when expressed as different units. Structure metres millimetres micrometres nanometres Human egg cell 130 Amoba proteus 0.5 length of a sperm cell length of an E.Coli bacterium 3000 Diameter of a lysosome Width of a mitochondrion 0.8 Diameter of the measles virus 220 Diameter of the rhinovirus (cold virus) 30 Ribosome Antibody 12 Divide by 1000 for each step to convert in this direction nano micro milli whole kilo unit e.g nm e.g μm e.g mm e.g m eg km Multiply by 1000 for each step to convert in this direction When we convert between square or cube units we need to take a little more care. For example to convert 1m 2 to mm 2, you need to remember that it is x1000 x1000, so your conversion factor is x or m 2 = mm 2 To convert m 3 to mm 3 is x1000 x1000 x1000, so your conversion factor is x or m 3 = mm 3 Convert the following: 10m 2 to km 2 2m 2 to mm mm 3 to m m 3 to mm 3

9 Resource 1 Measurement of size in biology Unit prefixes and their standard form. Name Number Symbol Standard form Getting it in perspective deci 0.1m d 10-1 One tenth of a metre centi 0.01m c 10-2 One hundredth of a metre milli 0.001m m 10-3 Thousandth of a metre micro m μ 10-6 Millionth of a metre nano m n 10-9 Billionth of a metre pico m p Trillionth of a metre

10 Task eight: Examining cells, researching the use of microscopes. All living organisms are made up of cells that can only come from pre-existing like-cells. Therefore, to understand behaviour, genetics or disease we must study cells. Our knowledge of cell structure has come through a variety of approaches including biochemistry, physical analysis, computer analysis, and molecular genetics. However the traditional microscope has to have been the single most important tool in examining these all important work-houses. Your task is to produce an A4 information sheet about light and electron microscopy. You may use any of the following resources listed below or any other resources, however all resources must be appropriately referenced. It is vital that all work is in your own words, you will not demonstrate your understanding of a topic by simply cutting and pasting. It is very important that you get your head around ideas and then write about them. Your fact sheet must include the following points: Why we need to use microscopes to study cells. A brief summary of the types of microscope available and a simple description of how each one works (limited to optical, transmission electron microscopes and scanning electron microscopes) You may wish to use diagrams in this section. What we mean by the terms magnification and resolution and how and why these vary in the different types of microscope. Why increasing magnification does not always increase the detail you can view of a specimen or image. Reference to the different cellular components, tissues, organs, systems and organisms that can be viewed with each type of microscopy. The main limitations of each of the three types of microscope. You could also research the history how microscopes have developed and the importance of recent advance in staining techniques in developing our understanding. The key terminology which should appear in your information sheet is listed in the table below. For your own learning you may benefit from producing a glossary for each of the terms shown in bold. microscopy resolution magnification specimen image transmission electron scanning electron microscope Optical microscope wavelength of light wavelength of a beam of microscope (TEM) (SEM) electrons resolving power eye piece lens objective lens condenser lens photomicrograph electron gun artefacts 2D image 3D image scattered electrons. Resources: The LRC also has numerous A level textbooks that will help you with this section.