Lesson 1: Unicellular, Colonial, and Multicellular Organisms PDF

Lesson 1: Unicellular, colonial and multicellular organisms All living organisms show seven basic characteristics of life. You may have learnt these to differentiate between living and non-living things. Let us look at these again. The seven characteristic functions of life are: Movement – Living...

Lesson 1: Unicellular, colonial and multicellular organisms All living organisms show seven basic characteristics of life. You may have learnt these to differentiate between living and non-living things. Let us look at these again. The seven characteristic functions of life are: Movement – Living things can move (it can be a change is position or movement of substances within the body) Respiration – Living things use energy from respiration Sensitivity – Living things are sensitive to internal and external stimuli Growth – Living things can grow in size Reproduction – Living things produce offspring, either sexually or asexually Excretion – Living things exhibit removal of waste products Nutrition – Living things take in nutrients (animals get it from their food sources and plants make their own nutrients from air and soil minerals) You can use the mnemonic MRS GREN to remember these seven characteristics. These seven characteristic features are the basis of life. This means that all living organisms show all of these features. In other words, for anything to be called living it has to show all of these basic characteristics of life otherwise it would not be considered as living. This includes all living organisms – plants, animals, fungi, protists, archaea and bacteria (refer to Module 1, Set 1 for further details). In Module 1, you also learnt about the prokaryotes and eukaryotes. Let us do a quick recap of the terms – prokaryotes and eukaryotes. Prokaryotes are unicellular organisms. Their cells do not have a nucleus or any other membrane-bound organelles in them. Eukaryotes can be either unicellular (single-celled) or multicellular organisms. The cells of eukaryotic organisms have a nucleus and membrane-bound organelles inside them. Organisation of Living Things 8 Set 1 – Organisation of Cells We are now going to look at another way of grouping living organisms, that is, unicellular, colonial and multicellular organisms. 1.1 Unicellular organisms A unicellular organism consists of just one cell and therefore it is also called as a single-celled organism. The single cell performs all the seven characteristic functions of life (discussed above). It is a complete living organism by itself and does not depends on other cells for its survival. Unicellular organisms can either be prokaryotic or eukaryotic. For example: 1. Prokaryotic organisms such as bacteria are all unicellular. Example: Escherichia.coli and Streptococcus sp E.coli Streptococcus In the above images each rod shaped (E.coli) and spherical (Streptococcus) structure is one bacterial cell. 2. Eukaryotic organisms can be unicellular. For example amoeba, paramecium, yeast and single celled algae such as chlorella and chlamydomonas. Amoeba Paramecium Organisation of Living Things 9 Set 1 – Organisation of Cells  Chlorella Each circular structure is an individual Chlorella. Notice the largest round structure within each cell. What do you think it is? Yes it is the nucleus. It is a membrane bound organelle that acts as the control centre of the cell. Why do you think each cell looks green? Yes, presence of many chloroplasts in each cell is the reason that the cells look all green. Chloroplasts are membrane bound organelles containing green coloured pigment called chlorophyll. Refer to Module 1, Set 1 for more details. Since Chlorella is a eukaryotic organism, it has a nucleus and other membrane bound organelles, such as chloroplasts. Organisation of Living Things 10 Set 1 – Organisation of Cells  Yeast The above image shows yeast cells as seen under a light microscope. Notice the small bud like structure on some of the cells. This is how yeast cells reproduce – by forming buds and the process is called budding. It is a type of asexual reproduction. Prokaryotic unicellular organisms such as bacteria do not have a distinct nucleus or other membrane-bound organelles in their cell. On the other hand, Eukaryotic unicellular organisms such as amoeba, chlorella and yeast have a nucleus and other membrane bound organelles in their cell. Organisation of Living Things 11 Set 1 – Organisation of Cells 1.2 Multicellular organisms A multicellular organism consists of millions of specialised cells that communicate with each other to perform different functions within the organism’s body. The organism as a whole carries out all the seven characteristic life functions with the help of specialised cells. If separated from the organism, the cells in a multicellular organism cannot survive on their own. In other words, the individual cells cannot survive without being a part of the organism. All multicellular organism are eukaryotic and therefore the cells of these organisms have nucleus and other membrane bound organelles. Examples of multicellular organisms include most plants, animals and fungi. Lady bug Mushrooms Deer Sunflower Human Being Examples of multicellular organisms Organisation of Living Things 12 Set 1 – Organisation of Cells 1.3 Colonial organisms Both unicellular and multicellular organisms can form colonies. When unicellular organisms form a colony, cells in that colony live as a connected group but do not depend on each other for their survival. Each individual cell of the colony can carry out its own life functions to survive. For example – each bacterial cell divides to reproduce and forms two new cells. Sometimes, the cell walls of some bacteria remain attached to one another after dividing and form a big group called as a bacterial colony. The image on the left shows many bacterial colonies growing on an agar plate under laboratory conditions. Each dot like structure is one colony containing millions of bacterial cells. All the cells in these colonies are prokaryotic and therefore do not contain nucleus or any other cell organelle. Each dot like structure is a bacterial colony Another example of a colonial organism formed from unicellular organisms is a type of green algae called Volvox. Volvox forms spherical or oval colonies that contain thousands of individual cells embedded in a gelatinous wall. Each individual cell in the colony is capable of surviving on its own in case it gets separated from the colony. The dark circles in the colonies are immature daughter colonies. The cells in volvox colonies are eukaryotic and therefore each cell contains nucleus and other membrane bound organelles A single volvox colony such as chloroplast and mitochondria. Organisation of Living Things 13 Set 1 – Organisation of Cells When multicellular organisms form a colony, the individuals in that colony depend on each other for their survival and reproduction. These individuals cannot survive if separated from the colony. Examples include Portuguese man-of-war (blue bottles) and corals. Portuguese man-of-war Corals Answer these questions, then self-mark using the answers provided. 1. Identify the following as unicellular, multicellular or colonial organisms. a. Amoeba - __________________________ b. Oak tree - __________________________ c. Beetle - __________________________ d. Volvox - __________________________ e. E.coli - __________________________ f. Corals - __________________________ g. Yeast - __________________________ h. Chlamydomonas - __________________________ i. Dog - __________________________ i. multicellular h. Unicellular g. Unicellular f. Colonial e. Unicellular d. Colonial c. Multicellular b. Multicellular a. Unicellular Answers: Organisation of Living Things 14 Set 1 – Organisation of Cells  Send-in exercises Lesson 1: Unicellular, colonial and multicellular organisms 1. Construct a table to show differences between unicellular and multicellular organisms. 2. Unicellular organisms do not contain nucleus and other membrane bound organelles. Do you agree or disagree. Justify your statement using examples. ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ________________________________________________________________ ACTIVITY SHEET 4.1 Hierarchy of structural organisation Name: ______________________________ Class: ______________________________ Read the following description of the hierarchical structural organisation of cells, tissues, organs and systems. Use the information to fill in the gaps on the concept map. All matter is composed of atoms, which can be organised into complex biological molecules. Cells are the basic unit of life. They are made up of many different types of molecules. There are two basic types of cells – prokaryote and eukaryote. The main difference between these two types of cells is the presence or absence of internal membranes. Bacteria are simple cells that do not contain internal membranes and are examples of prokaryotes. The more complex eukaryote cells contain internal membranes and can be found as single cells, as colonies of single cells working together or as specialised cells in multicellular organisms. An amoeba is an example of a unicellular eukaryote found in fresh water. Volvox colonies are examples of single cells working together. Specialised cells that perform a similar function in multicellular organisms are called a tissue. Skin (an organ) is made up of epithelial tissue. Different tissues that perform a particular function are grouped together in an organ, such as the heart. Blood vessels and the heart are two organs of the circulatory system. Add the following words and phrases to the boxes of the concept map showing the hierarchy of structural levels. Multicellular Completely functional single Example: circulatory system cell Eukaryote Collection of organs working Example: bacteria together, performing a particular function Organ Group of specialised cells Example: heart working together to perform a specialised function Molecule No internal membranes Example: Volvox Cengage Learning Australia Pty Ltd 2018 www.nelsonnet.com.au Page 1 of 2 Cengage Learning Australia Pty Ltd 2018 www.nelsonnet.com.au Page 2 of 2