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Transcript
1.1 Cells – structure and function How are we made? � Key term Organelles – Small structures within cells. Each carries out a particular function. All living things on Earth are made of cells. Some consist of just one cell but some, like you, are made of many cells. Cells are the building blocks of organisms. Cells are very small but you can see them with a microscope. cell wall chloroplast outer cell membrane cytoplasm cytoplasm nucleus nucleus mitochondrion outer cell membrane ft large fluid-filled vacuole The structure of a typical animal cell. ra The structure of a typical plant cell. mitochondria Case study Plant and animal cells are called eukaryotic cells. Eukaryotic organisms have cells with their genetic material enclosed in a nucleus. Nearly all of the living things on Earth, except bacteria, are eukaryotes. Sue is a cytology screener. She works in a hospital laboratory and has to look at microscope slides of cells to see if any are abnormal. This could indicate that the person whose cells they are has early stage cancer. Sue has to know about cell structure so she can tell abnormal cells from normal ones. Cytology is the study of cell structure. D Did you know? Link Lesson 4.4 discusses how viruses are not made of cells. 12 BTEC First Principles of Applied Science A microscope slide showing abnormal (red) and normal cells from the cervix. Principles of Science UNIT 1 Plant and animal cells have many components, called organelles, such as chloroplasts and mitochondria. The table shows the different functions of the organelles found in plant and animal cells. Function In plant cells? In animal cells? Outer cell membrane Encloses the cell and keeps it separate from its environment. It controls how substances enter and leave the cell. 3 3 Nucleus Contains DNA (genetic information) arranged into chromosomes. It controls the activities of the cell. 3 3 Jelly-like substance in which the organelles are held. Many chemical reactions take place in the cytoplasm. 3 3 Mitochondrion (plural: mitochondria) The organelle where aerobic respiration – the release of energy from glucose or fat in the presence of oxygen – takes place. 3 Cell wall Made from cellulose. The cell wall is very strong and prevents the cell from bursting. It gives the cell shape. 3 7 Contains chlorophyll, which absorbs light energy for photosynthesis. 3 7 ra Cytoplasm D Chloroplast Vacuole ft Cell component Contains cell sap and provides extra support for the cell. The vacuole can store nutrients and waste products. 3 3 7 Activity A List the ways that animal and plant cells are (a) similar to each other and (b) different from each other. Common misconception Many people think that plants do not have genes. Their cells contain a nucleus, with DNA organised into chromosomes. Genes are lengths of DNA. So plants do have genes. Just checking For each of the following statements, say whether it is true or false. 1 All living things are made of many eukaryotic cells. 2 Plant cells do not contain mitochondria. 3 Animal cells do not have a large vacuole. 4 The cell membrane controls which substances enter and leave a cell. Lesson outcomes You should know about the basic structure and function of some eukaryotic cells and of some of their components. 13 1.2 Specialised cells You, like many other organisms including plants, started life as a single cell – a fertilised egg. This divides and forms an embryo. Cells become specialised to perform different functions. This is called differentiation (becoming different). Some examples of specialised cells are shown below. (a) to (f) are animal cells and (g) to (j) are plant cells. They all have the same basic components but each type has some differences in structure. These differences enable the cells to carry out their particular function (job). Each type of cell is adapted for its function. (a) (b) Egg cell – for sexual reproduction. outer cell membrane Sperm cell – for sexual reproduction. The sperm has a tail to help it move to find the egg. It also has a large number of mitochondria to supply the energy needed for the movement. nucleus very small amount mitochondria of cytoplasm large amount of cytoplasm nucleus mitochondria head ft tail (c) Red blood cells – small cells, packed with haemoglobin which carriesoxygen. They have no nucleus, no mitochondria and little cytoplasm in order to carry more oxygen. (d) White blood cells – for defence against infection. There are different types of white blood cell, but they all have a nucleus, cell membrane, cytoplasm and mitochondria. ra outer cell membrane (e) Sensory neurone – long fibres carry impulses from D sensory receptors to brain and spinal cord. cell membrane cell body nucleus receptor in skin fatty sheath (g) outer cell membrane vacuole BTEC First Principles of Applied Science cell body nucleus (h) cell wall 14 spinal cord to muscles or glands. dendrites Root hair cell – for absorption. Extension of cell increases surface area for absorption of water and minerals from soil. (f) Motor neurone – long fibres carry impulses from brain or long fibre direction of impulse nucleus fatty sheath long fibre direction of impulse muscle fibres Xylem – to carry water. There is no cytoplasm or organelles. cell wall with lignin to make it strong empty hollow vessel for carrying water from roots to rest of plant Principles of Science i) UNIT 1 (j) Guard cells in epidermis of leaf – to allow carbon dioxide Phloem – carries dissolved sugars from leaves to other parts of plant. to enter for photosynthesis. cytoplasm sieve tube companion cell with organelles cell wall chloroplasts nucleus sieve plate nucleus guard cells pore open epidermal cells Tissues � A tissue is a group of similar, specialised cells that work together to carry out a particular function in the body. Some examples of animal tissues are given in the table below. Where found in the body Functions Epithelial (covering tissues) Outside of skin. Make up the inside linings of heart, blood vessels, airways and gut. Some epithelial cells have tiny hairs, called cilia, on them. Protection, absorption, filtration and excretion. Glands are also made of epithelial cells. Production of useful substances, such as saliva, hormones and mucus. Bone Makes up skeleton – supports you and allows you to move. D Connective ra ft Type of tissue Blood Muscle Nervous Transport and defence against invading microorganisms. Smooth muscle in walls of blood vessels and gut Able to contract – arteries pulsate. Gut moves food through it. Heart muscle Heart beats to pump blood around body. Nerves, spinal cord and brain For sensing and responding in a coordinated way to the environment. Activity A 1 Draw large, clear diagrams of one specialised animal cell and one specialised plant cell. 2 Label and annotate (write notes next to the labels) the diagrams to show how each cell is adapted for its function. You should also research, using the Internet and textbooks, to find out more about how the cells you have chosen are adapted. Use a ruler to draw the label lines. Just checking For each of the following statements, say whether it is true or false. 1 Red blood cells cannot carry out aerobic respiration because they do not have mitochondria. 2 Neurones are the longest cells in your body. 3 Blood and bone are types of connective tissue. Lesson outcomes You should know how cells become adapted to carry out specific functions, and that cells form tissues. 15