1.1.1 Cell Structure. Relevant Past Paper Questions. Condensed Notes By Specification Point January 5 e f i j June 2 e f g i

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1 1.1.1 Cell Structure Relevant Past Paper Questions Paper Question Specification point(s) tested 2013 January 5 e f i j 2012 June 2 e f g i 2012 January 4 a b d f 2011 June 1 part a only f 2011 January 5 part a only d h i 2010 June 1 except part c f i 2010 June 2 parts a and b a c 2010 January 1 parts a and b a b 2010 January 2 part c f h 2009 June 4 h i 2009 January 1 d e g Condensed Notes By Specification Point a) State the resolution and magnification that can be achieved by a light microscope, a transmission electron microscope and a scanning electron microscope. Light microscope TEM SEM Resolution 200nm 0.2nm 0.2nm Magnification up to 1500x up to x up to x SEM produces a 3D image with a high level of detail.tem produces a 2D image.

2 The following features of a eukaryotic cells would not be visible using the medium power of a light microscope: any membranes, ribosomes, golgi apparatus, ER, cytoskeleton, centrioles, vesicles, lysosomes and mitochondria. b) Explain the difference between magnification and resolution. Magnification is the number of times larger the image is than the object. Resolution is the ability to distinguish between two separate points. In other words, resolution is the ability to see detail, for example seeing that two close together objects are separate. c) Explain the need for staining samples for us in light microscopy and electron microscopy. Staining achieves the following: Makes the sample more visible and increases contrast. Makes it possible to see the ultrastructure (e.g. organelles). d) Calculate the linear magnification of an image. Image size = actual size x magnification e) Describe and interpret drawings and photographs of eukaryotic cells as seen under an electron microscope and be able to recognise the following structures: nucleus, nucleolus, nuclear envelope, rough and smooth endoplasmic reticulum (ER), Golgi apparatus, ribosomes, mitochondria, lysosomes, chloroplasts, plasma (cell surface) membrane, centrioles, flagella and cilia.

3 Ribosomes are very small organelles. Some of the cell s ribosomes are free in the cytoplasm and some are attached to the outer surface of the rough endoplasmic reticulum. f) Outline the functions of the structures listed in e). Nucleus: The nucleus contains the cell s DNA. Nucleolus: Makes rrna and ribosomes. Nuclear Envelope: Separates the DNA from the cytoplasm. Contains nuclear pores, which allow communication between the nucleus and the cytoplasm and allows molecules to enter and leave the nucleus. Rough endoplasmic reticulum (RER): Transports proteins that were made on the attached ribosomes. Smooth endoplasmic reticulum (SER): Synthesis of lipids. Golgi apparatus: Receives proteins from the ribosomes and then modifies them and packages them into vesicles, which it produces. One example of modification that is carried out in the golgi apparatus is the

4 addition of carbohydrate groups to a protein to form a glycoprotein. Another example is folding the protein into a new shape. The golgi apparatus also makes lysosomes, replenishes the plasma membrane and synthesises lipids. Ribosomes: The site of protein synthesis. Mitochondria: Produce ATP (the molecule which is the immediate source of energy for cellular processes) in aerobic respiration. Lysosomes: Contain digestive enzymes (lysins) that break down various things such as pathogens, toxins and old organelles. They also have a role in apoptosis (programmed cell death). Chloroplasts: The site of photosynthesis. Plasma membrane: Separates cell contents from the outside environment. Regulates the movement of materials into or out of cells. Cell recognition and cell signalling. Holds some enzymes in place. Centrioles: Organise the spindle fibres during mitosis. Flagella: Cell movement. Cilia: Movement of substances outside of the cell. g) Outline the interrelationship between the organelles involved in the production and secretion of proteins (no detail of protein synthesis is required). Some of the proteins produced by the cell are secreted out of the cell. This includes some enzymes, hormones and glycoproteins. One the proteins are made on ribosomes they are moved to the golgi apparatus where they are processed and then packaged into vesicles. The vesicles are then moved to the plasma membrane. They fuse with the plasma membrane, causing the proteins to be secreted by exocytosis. h) Explain the importance of the cytoskeleton in providing mechanical strength to cells, aiding transport within cells and enabling cell movement. They cytoskeleton has the following roles: Provides strength and stability to the cell. Determines the shape of the cell and moves the cell membrane. Moves organelles, chromosomes and proteins. Moves cilia in cells that have them. Holds organelles in place. Makes up the centrioles and the spindle fibers. i) Compare and contrast, with the aid of diagrams and electron micrographs, the structure of prokaryotic cells and eukaryotic cells.

5 Eukaryotic cells are much larger than prokaryotic cells. Eukaryotic cells usually have a diameter of about 20 40µm, whereas prokaryotic cells usually have a diameter of about 0.5 5µm. Eukaryotic cells contain many membrane bound organelles (nucleus, mitochondria, endoplasmic reticulum, golgi apparatus, chloroplasts, lysosomes), whereas prokaryotic cells do not contain any membrane bound organelles. In eukaryotic cells the DNA is associated with proteins to form a substance called chromatin and is in the nucleus, whereas in prokaryotic cells the DNA is naked and is free in the cytoplasm (prokaryotes do not have nuclei). Prokaryotic cells often contain loops of circular DNA called plasmids. Eukaryotic cells do not contain plasmids. Prokaryotic cells have smaller ribosomes then eukaryotic cells. Prokaryotic ribosomes have a diameter of 18nm. Eukaryotic ribosomes have a diameter of 22nm. Prokaryotes often have an infolding of the plasma membrane called the mesosome. Prokaryotic cells have cell walls made of peptidoglycan, whereas eukaryotic cells have cell walls made of cellulose (plants and algae) or chitin (fungi) or don t have cell walls at all (animals). Most eukaryotic cells, apart from plant cells, have centrioles, whereas prokaryotic cells do not have centrioles. j) Compare and contrast, with the aid of diagrams and electron micrographs, the structure and ultrastructure of plant cells and animal cells. There are some organelles that plant cells contain, but animals cells do not. These are chloroplasts, vacuole, cell wall. There are some organelles that animals cells contain but plant cells do not. These are centrioles. These are organelles that both plant cells and animals have. These are mitochondria, ribosomes. Detailed Notes