National Cell structure Pupil notes. Cell Biology. Sub-topic (1.1) Cell Structure. On completion of this topic I will be able to state that:

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1 Cell Biology Sub-topic (1.1) Cell Structure On completion of this topic I will be able to state that: Cells differ in structure as to whether they are animal, plant, fungi or bacterial cells. The detail of the organelles inside living cells is known as the ultrastructure. Nucleus, cell membrane, cytoplasm, mitochondrion and ribosome are organelles found in both animal and plant cells. Nucleus contains genetic information and controls all cell activities. Cell membrane controls the entry and exit of materials from the cell. Cytoplasm is a jelly-like material in which chemical reactions take place. Mitochondrion is the site of aerobic respiration and is abundant in cells with high energy requirements. Ribosome is the site of protein synthesis. Ribosome can be found free in the cytoplasm or attached to tubular structures. Cell wall, vacuole and chloroplast are organelles found only in plant cells. Cell wall in plants is made of cellulose. Cell wall supports and gives structure to plant cells. Vacuole contains cell sap. Vacuole is important in maintaining the shape of a plant cell. Chloroplast is the site of photosynthesis. Chloroplast contains the green pigment, chlorophyll, which absorbs light energy. A bacterium and a fungus, such as yeast, are unicellular organisms. Plasmid is a ring-shaped structure found in a bacterium. Bacterium has a cell wall that is made of different materials to plant cell walls and the chromosomal material is not in a nucleus. Fungus has a cell wall made of different materials to plant cell walls and has a nucleus. In addition I will be able to: Use data provided to calculate cell length and breadth. Identify organelles in electron micrographs (or drawings made from them) and give a brief description of their functions. Duncanrig Secondary School MHC/LS 2017 Page 1 of 10

2 Cell Structure Cells are the basic units of life. All living things, whether plant, animal, fungus or bacteria, are made up of cells. The parts inside a cell are known as its organelles and different types of cell can have different organelles. REVISION In the S1 Science course, we found that all living organisms are made up of basic structural units called cells. Although cells can appear to be very different depending on their function, they may conveniently be divided into two groups, i.e. animal cells and plant cells. Activity 1: Label the diagrams below. TYPICAL ANIMAL CELL TYPICAL PLANT CELL Answer the following questions: 1. Name three structures found in both animal and plant cells. a) b) c) 2. Name two additional structures found in most plant cells. a) b) 3. Name one structure found only in green plant cells CELL ULTRASTRUCTURE Together, all the organelles in a cell are referred to as the cell s ultrastructure. Even the most powerful light microscope can only magnify objects by about 1500 times. At this magnification, we can see relatively large cell organelles such as the nucleus and chloroplasts. Most cell organelles, however, are too small to be seen with a light microscope and must be viewed using an electron microscope which can magnify up to 500,000 times. Duncanrig Secondary School MHC/LS 2017 Page 2 of 10

3 With the help of class resources, label the diagrams below, which are based on electron micrographs. Nuclear membrane Nuclear membrane Duncanrig Secondary School MHC/LS 2017 Page 3 of 10

4 FUNCTIONS OF CELL ORGANELLES Activity 2: Collect a laminated card which gives information about the parts of a cell. Use it to complete the table below by writing a summary of the function of each organelle. Organelle Function Nucleus Cytoplasm Cell Membrane Mitochondrion Ribosome Cell Wall Vacuole Chloroplast Multicellular organisms are made up of a large number of cells working together, but some cells exist on their own and are an entire organism. These cells are known as Unicellular Organisms and must perform all the functions necessary for life. Duncanrig Secondary School MHC/LS 2017 Page 4 of 10

5 UNICELLULAR ORGANISMS Like most multicellular organisms, some unicellular organisms can be classified as either plant or animal relatively easily. However, there are some unicellular organisms which possess some of the characteristics of both cell types and have structures that reflect this. It is, therefore, difficult to classify such organisms as either animal or plant. The following are some unicellular organisms which can be found in pond water. Activity 3: Look at the diagrams and the model of these organisms and answer the question below. Paramoecium Why is it difficult to tell whether Euglena is a plant or an animal? Two common types of unicellular organisms are bacteria and fungi. They have many of the cellular features you have studied so far, but can have organelles which are not found in typical plant and animal cells. Duncanrig Secondary School MHC/LS 2017 Page 5 of 10

6 BACTERIAL CELLS Although bacterial cells show some similarities to plant and animal cells, they differ in several ways. Although they have a cell wall, it is not made of cellulose. It has a different structure to the cell wall found in plants cells. They have no organelles such as a nucleus and their chromosomal material consists of one large loop with several very small rings known as plasmids. Activity 4: Study the two diagrams of bacterial cells and, using available resources, answer the questions below them. chromosomal material 1. What is the difference between a plant cell wall and a bacterial cell wall? 2. What is different about the location of DNA in a bacterium compared to a plant or animal cell? 3. What is a plasmid and why is it important to humans? Duncanrig Secondary School MHC/LS 2017 Page 6 of 10

7 FUNGAL CELLS Fungal cells also have similarities and differences when compared to plant and animal cells. They have organelles like plant and animal cells and have a cell wall like a plant cell. However, the cell wall is not made of cellulose. It has a different structure to the cell wall found in plants. Below are two diagrams of fungi. Together they show various parts which can be found in fungi. Food storage granule Nucleus Cell wall Vacuole Cell membrane Cytoplasm One of the most familiar fungal cells is yeast. Yeast is a single celled fungus that reproduces by growing a bud on its side. Although yeast has a cell wall like a plant cell, it is not made of cellulose. Yeast lacks chloroplasts and therefore does not carry out photosynthesis. It is important in the process of fermentation (a type of respiration). Activity 5: Complete the following table by placing a tick in the correct boxes to show where each of the organelles listed will be found. Type of cell Organelle Animal Plant Bacterium Fungus Nucleus Cytoplasm Cell membrane Vacuole Cell wall Chloroplast Mitochondrion Ribosome Plasmid Duncanrig Secondary School MHC/LS 2017 Page 7 of 10

8 CELL SIZES The size of cells is related to their function. An ovum (egg cell) is very large, often being the largest cell an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy that is available in the cells. Cells range in size enormously. Most commonly, cells are measured in unit of length called micrometres (µm) or nanometres (nm) µm = 1mm 1000 nm = 1 µm Activity 6: Complete the following table of conversions between these two measurements. Micrometres (µm) Nanometres (nm) 650 Measuring Cells The circle of light that is seen when using the microscope is called the field of view. By measuring the diameter of that circle, then counting the number of cells which fit into that diameter, the size of a cell can be estimated. A clear ruler can be placed on the stage and viewed at each of the magnifications to measure the diameter of the field of view. Duncanrig Secondary School MHC/LS 2017 Page 8 of 10

9 For example, in the diagrams below, the field of view is measured to be 2mm. When cells are viewed, 10 of them are seen across the same diameter. Therefore the calculation to find the size of 1 cell is 2 10 = 0 2mm Activity 7: Use the information given to calculate the average size of the cells shown in the diagrams below. Size of one cell = Size of one cell = Duncanrig Secondary School MHC/LS 2017 Page 9 of 10

10 Size of one cell = Size of one cell = Duncanrig Secondary School MHC/LS 2017 Page 10 of 10