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Transcript
i-Science – interact, inquire, investigate P5&6 Background information Systems Ch 2 - Cells Cells – The building blocks of life Learning outcome: Show an understanding that a cell is a basic unit of life A cell is a basic unit of life. Every organism is made up of at least one cell. Organisms such as bacteria, amoebae, yeast and paramecia are made up of only one cell. They are called single-celled or unicellular organisms. Animals and plants are made up of many cells. They are called multicellular organisms. A human being, for example, is made up of trillions of cells. The study of cells began more than 300 years ago. In 1663, a scientist, named as Robert Hooke, examined thin slices of cork using a self-made microscope. He observed a network of tiny box-like compartments, which were similar to a honeycomb, and called these compartments ‘cellulae’ (little rooms). This is how the term ‘cell’ was derived. What Robert Hooke had observed were the cell walls of dead plant tissues. The work of two scientists, Schleiden (a botanist) and Schwann (a zoologist), later led to the cell theory, which proposed that the basic unit of structure and function in living organisms is the cell. The modern cell theory states the following: All living things are made up of cells. A cell is the structural and functional unit of all living things. All new cells arise from other pre-existing cells. All metabolic reactions of an organism take place in cells. Cells contain the hereditary information of the organisms of which they are part of, and this is passed on from the parent to the daughter cell. Plant and animal cells Learning outcomes: Identify the different parts of a typical plant cell and animal cell and relate the parts to the functions: - Parts of plant cell: cell wall, cell membrane, cytoplasm, nucleus and chloroplasts - Parts of animal cell: cell membrane, cytoplasm, nucleus Compare a typical plant and animal cell Pg 1 of 5 i-Science – interact, inquire, investigate P5&6 Background information Plants and animals are multicellular organisms made up of different types of cells. However, the cells share many similarities. A plant cell Nucleus Endoplasmic reticulum Golgi apparatus Vacuole Mitochondrion Cytoplasm Cell membrane Chloroplast Cell wall An animal cell Nucleus Endoplasmic reticulum Golgi apparatus Vacuole Mitochondrion Cell membrane Cytoplasm A cell is made up of many parts. Cell membrane It is a thin membrane separating a cell from its external environment. It allows only certain substances to pass through, hence, it is called a partially-permeable membrane. Transport across the cell membrane occurs to allow the cell to obtain nutrients, excrete waste materials or secrete useful substances. Pg 2 of 5 i-Science – interact, inquire, investigate P5&6 Background information Nucleus It controls the activities of a cell. It contains chromatin, which is the loosely coiled form of chromosomes. Chromosomes are made up of DNA (deoxyribonucleic acid) and proteins. Segments of DNA which contain instructions to make proteins are called genes. Genes control the activities of the cell and contain hereditary information which is passed on from one generation to the next. (Note: Human red blood cells do not contain nuclei.) Cytoplasm It is a jelly-like material which fills the cell between the nucleus and cell membrane. It is mostly made up of water with various chemicals, such as salt and proteins, dissolved or suspended in it. Many chemical reactions which are involved in life processes take place here. It contains organelles or cell parts such as mitochondria and Golgi apparatus. The cytoplasm almost fills a typical animal cell but is reduced to a thin lining in a plant cell. Chloroplasts They are present in plant cells but not in animal cells. It contains the green pigment, chlorophyll, and other pigments, such as carotenoids, which capture light energy for photosynthesis. Photosynthesis takes place in the chloroplasts of plant cells. Cell wall It is present in plant cells but not in animal cells. The cell wall of a plant cell is made of cellulose, a complex carbohydrate. The cell wall provides mechanical support and protection to the plant cell and keeps it in shape. It prevents the cell from bursting and it is also a pathway for the movement of water and mineral salts. Endoplasmic reticulum (ER) It is a continuation of the outer nuclear membrane. Some parts of the ER are smooth and are called smooth ER. Smooth ER is important for the synthesis of lipids and membrane proteins. Some parts of the ER are rough due to the presence of ribosomes on its surface. These parts are called rough ER and are important for the synthesis of proteins. Golgi apparatus It is composed of flattened sacs piled up in stacks. It packages macromolecules for transport to elsewhere in the cell, secretes carbohydrates involved in the production of new cell walls for plant cells, transports and stores lipids and processes the proteins made in the ER. Mitochondria They are the organelles where cellular respiration takes place. They provide the energy needs of the cell. Pg 3 of 5 i-Science – interact, inquire, investigate P5&6 Background information Vacuole It is a fluid-filled sac bound by a single membrane. It stores food and nutrients, such as mineral salts, sugars and amino acids. It stores wastes too. Mature plant cells usually have one large central vacuole. The vacuole of plant cells contains cell sap that keeps the cells turgid. Animal cells usually have numerous and much smaller vacuoles. A multicellular organism is made up of different types of cells. A human being, for example, is made up of different cells, such as nerve cells, blood cells, muscle cells and skin cells. These cells have different shapes and sizes to suit the functions they perform. A nerve cell, for example, is long so that it can transmit signals quickly. A red blood cell has a large surface area to volume ratio to absorb oxygen quickly. Red blood cells Nerve cells Using a microscope The following are some precautions to take when using a light microscope: Do not place fingers on the cover-slips. Hold the prepared slides at the ends or edges. Do not touch the objective lenses with your fingers. Place the specimen slide on the microscope stage such that the specimen is over the middle of the hole on the stage and light can be seen passing through it. Adjust the low power objective lens using the coarse focus knob until the low power objective lens is about 5 mm from the slide. Adjust the objective lens up (and not down) using the coarse adjustment until the specimen is in focus by looking through the eyepiece. If the objective lens is adjusted down, it may hit and damage the slide. Keep both eyes open and use each eye in turn. Internet links Micrographs and microscopes http://education.denniskunkel.com/index.php http://school.discoveryeducation.com/lessonplans/activities/electronmicroscope/ Pg 4 of 5 i-Science – interact, inquire, investigate P5&6 Background information http://www.biology.ualberta.ca/facilities/multimedia/index.php?Page=284 http://micro.magnet.fsu.edu/primer/virtual/magnifying/index.html http://www.bbc.co.uk/london/content/articles/2006/05/12/springwatch_microscope_featur e.shtml Cells http://www.cellsalive.com/index.htm http://www.sparknotes.com/testprep/books/sat2/biology/chapter4section1.rhtml http://nature.ca/genome/03/c/03c_e.cfm http://www.kathimitchell.com/cells.html http://science.howstuffworks.com/cell.htm Projects/Field trips Make a 3D model of a plant cell or an animal cell. Pupils may use a computer software to make a virtual 3D model of a cell. Label and describe the main parts of the cell. Design a scarf using the shapes of different types of cells or unicellular organisms. (Interdisciplinary project: art and science) Write and illustrate a story about the discovery of cells by Antonie van Leeuwenhoek (1632–1723) or Robert Hooke (1635–1703). Recommended reading The Usborne Internet-linked Complete Book of the Microscope (Publisher: Usborne) The Usborne Internet-linked Introduction to Genes and DNA (Publisher: Usborne) DK Megabites – Microlife (The Microscopic World of Tiny Creatures) (Publisher: DK) DK Eyewitness Guides – Life (Publisher: DK) Pg 5 of 5