Equine biological systems

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1 Equine biological systems Pack 9 How animal cells work Pack Code: EBS9 This pack you will help you to: Identify the main components of an animal cell Describe the functions of the main cell components Explain the importance of homeostasis

2 About this pack Objectives When you have completed this pack you should able to describe the main components and functions of animal cells. The pack will help you to: Identify the main components of an animal cell Describe the functions of the main cell components Explain the importance of homeostasis The pack is also relevant to the level 3 unit Understand the Principles of Animal Biology, and in particular to: Outcome 1: Know the functions of the main animal cell organelles. Links to other packs This is one of a series of learning packs, each tackling an aspect of equine biology. They are: EBS1: The skeleton EBS2: Joints EBS3: Circulation EBS4: Respiration EBS5: The digestive system of the horse EBS6: The reproductive system EBS7: Oestrus and hormones EBS8: Gestation and birth EBS9: How animal cells work EBS10: How animal cells divide EBS11: Connective and epithelial tissue EBS12: Muscle and nervous tissue EBS13: The horse s sensory organs EBS14: Introduction to genetics EBS15: Meiosis EBS16: Inheritance EBS17: Selective breeding EBS18: Breeding technology EBS19: Managing breeding EBS20: The lymphatic system EBS21: The endocrine system EBS22: The nervous system Equine biological systems 2

3 Introduction to animal cells Cells are the building blocks of all living things a horse s skin, blood, muscles, and organs are all made of millions of cells. A complex animal like the horse has trillions of cells in its body! Cells are truly remarkable things. They carry the horse s individual genetic make up. They fight off disease. And all this despite the fact they are so small that we need a powerful microscope to see them. Components of a horse cell A typical animal cell has a number of components, also called organelles. The following diagram shows the main components. These organelles help the cell to carry out its many functions: to control what goes in and out to store and protect the horse s DNA to synthesise proteins to produce energy to clean up waste. We will look at these points in turn Equine biological systems 3

4 The cell membrane controlling what goes in and out Horse cells are surrounded by a cell membrane which regulates what can go into and out of the cell. Animal cells have much in common with plant cells similar organelles are found in both. However, the animal cell membrane is very different from the plant cell wall, and this has important implications for how the cell works. Whereas a plant cell wall is made from cellulose and is quite rigid, an animal cell membrane is made from fatty acids (lipids) and is more fluid. This means that: Larger molecules such as proteins can pass through the cell membrane using a process called active transport. Some proteins can be embedded in the membrane to carry out specialized tasks for example, some act as receptors to alert the cell to what is happening around it and antigens which alert the body to bacteria, The cell membrane is able to repair itself if damaged. These factors have allowed animal cells to develop into the wide variety of types that make animals like horses such remarkable creatures. Cilia and flagella Some cells have cilia or flagella sticking out from the membrane. These help with movement: They enable sperm cells to swim. In other cells such as those living air passages, they move liquid such as mucus over the surface of the cell. Equine biological systems 4

5 The nucleus storing the horse s genetic fingerprint The nucleus is the heart of a cell and is the most visible organelle under the microscope. The nucleus has several vital functions: It stores and protects the horse s genes and DNA (in the form of chromatin which condenses into chromosomes during cell division see pack EBS10). Every cell in the body contains similar DNA. However, individual genes may be switched on or off to give the cell its unique characteristics. This is why a blood cell is different from a muscle cell. The DNA controls the cell s activities. It also allows the cell to divide see the learning pack on How animal cells divide. In this way cells can be replaced as they get old and worn out. Part of the nucleus, called the nucleolus produces ribosomes that are used in protein synthesis (see later in the pack). The nucleus is surrounded by a nuclear membrane. Centrioles Other organelles, called centrioles, also play a crucial role in cell division they separate the chromosomes in the nucleus. Two centrioles are contained within a centrosome. Before a cell divides, it creates a second centrosome. Again, for more on this see the pack on How animal cells divide. Activity Match the following organelles to their functions: Cell membrane Cilia and flagella Nucleus Centrioles Help with movement Separate chromosomes Regulate what goes in and out of the cell Store genes and DNA Check your answers at the end of this pack Equine biological systems 5

6 Synthesising proteins A crucial part of a cell s work is to synthesise proteins either for use within the cell s own functions, or for sending off for use by other parts of the body. Several organelles are involved in the process: The endoplasmic reticulum (ER) There are two parts of the endoplasmic reticulum (ER): The rough ER receives ribosomes from the nucleus and uses these to synthesise proteins. The smooth ER helps to synthesise other substances such as hormones. In liver cells it breaks down toxins. The Golgi apparatus The Golgi apparatus sometimes called the Golgi complex takes the proteins synthesised by the ER and prepares them for use elsewhere in the cell and beyond. It adds sugars to the proteins. It then sends proteins to the: lysosome, to aid digestion cell membrane, for example, to act as receptors and antigens. Some proteins are secreted from the cell to meet the needs of other cells and tissues. Equine biological systems 6

7 Lysosomes cleaning the cell Lysosomes have the job of cleaning up the cell. They contain proteins called enzymes that digest: worn out cell components bacteria or viruses that the cell has engulfed food particles As the enzymes are acidic, the lysosome has a membrane to stop the enzymes damaging the rest of the cell. Waste products are expelled from the cell so that they can be disposed of. Mitochondria producing energy Another cell organelle the mitochondria produces the energy that the cell needs for all its activities for active transport, movement, division and so forth. They produce energy by combining oxygen with sugar. The energy produced is called ATP. Activity Match the following organelles to their functions: Mitochondria ER Golgi apparatus Lysosomes Synthesises proteins Clean up the cell Produce energy Sends proteins elsewhere Check your answers at the end of this pack. Equine biological systems 7

8 The cytoskeleton giving structure to the cell All the cell organelles outside the nucleus are contained within the cytoplasm. The cytoplasm contains the cytoskeleton a network of protein fibres that give the cell structure and support. The cytoskeleton includes: Microtubules: hollow rods that give support. Microfilaments: solid rods that are particularly important in muscle contraction. Intermediate filaments: help hold microtubules and filaments in place. Homeostasis keeping the horse s body in balance We have seen in this pack how complex cells are and how all the components or organelles of a cell help to keep us alive. Scientists use the term homeostasis to describe how the body of an animal such as a horse maintains a stable internal environment. In particular, this means regulating temperature, glucose levels and the amount of water and mineral salts in blood. Cells need the right levels of temperature, glucose, water and mineral salts to function properly. For more on homeostasis, see pack EBS22: The nervous system. Activity Label the organelles in the following diagram: Check your answers with the labelled diagram on page 3. Equine biological systems 8

9 Glossary Active transport Antigen Cilia Cytoplasm Cytoskeleton Endoplasmic reticulum Flagella Mechanism for using larger molecules such as protein through a membrane Protein embedded in cell membrane that warns of the presence of bacteria, viruses, etc. Organelle that aids movement Fluid within the cell that contains the cell organelles Network of protein fibres that give the cell structure and support Organelle which synthesises proteins Organelle that aids movement Golgi apparatus Organelle that prepares proteins for use elsewhere in the cell or beyond Homeostasis Intermediate filaments How the body maintains a stable internal environment Help hold microtubules and filaments in place Lysosomes Organelle that prepares proteins for use elsewhere Membrane Regulates what enters and leaves the cell Microfilaments Solid rods in the cytoskeleton that are particularly important in muscle contraction Microtubules Mitochondria Nucleolus Organelle Receptor Ribosomes Hollow rods in the cytoskeleton that give support Organelle that produces energy that the cell needs Organelle that contains the cell s genes and DNA. Component of a cell Protein embedded in the cell membrane Used by the ER to synthesise proteins. Equine biological systems 9

10 Answers to activities Answers to activity on page 5 Cell membrane Cilia and flagella Nucleus Centrioles Regulate what goes in and out of the cell Help with movement Store genes and DNA Separate chromosomes Answers to activity on page 7 Mitochondria ER Golgi apparatus Lysosomes Produce energy Synthesises proteins Sends proteins elsewhere Clean up the cell Other resources Relevant books include: Zoe Davies, Introduction to horse biology, Blackwell, 2005 which contains a chapter on cells and tissues Sarah Pilliner and Zoe Davies, Equine science, Blackwell, 2004 which contains a chapter on the cell D R Lane and B Cooper (eds), Veterinary Nursing, Elsevier Health Sciences, 2003 Some useful websites include: Cellupedia at tml Equine biological systems 10

11 Knowledge quiz Check your knowledge with the following questions. 1 Which cell organelle stores the horse s DNA? 2 Give one benefit for animal cells of having a cell membrane rather than a rigid cell wall: 3 What is the function of cilia and flagella? 4 What is the function of the mitochondria? 5 Place the following stages of protein processing in order: a) The Golgi apparatus prepares proteins for use elsewhere b) The nucleolus produces ribosomes c) the rough ER uses ribosomes to synthesise proteins 6 Name three important aspects of homeostasis: Equine biological systems 11

12 Acknowledgements This learning pack has been produced by the Land Based Colleges National Consortium Ltd. The LBCNC is a consortium of colleges working in the land-based sector which cooperate in the development and production of quality flexible learning materials which encourage independent learning. We would like to acknowledge the contributions made by the following individuals and colleges in the development of this learning pack. Cover photograph: Steve Watson, Riseholme College, University of Lincoln Developed and produced for LBCNC by Learners First Written by May Johnstone Illustrations: Shevanthi De-Silva Revised in July The Land Based Colleges National Consortium Ltd. All rights reserved. Permission to photocopy or adapt the material in this learning pack is granted to members of the Land Based Colleges National Consortium Ltd. only. For further information please contact the LBCNC project management team at 7 Tyne Road, Bishopston, Bristol BS7 8EE. Tel Equine biological systems 12