7.1. History of Microscopes and the Discovery of cells 7.14, TheCell Theory The cell theory states that albiiving:thinigs are made uproficelist_ ‘The smailestunit of life is a cell The cell theory has been tested for such a long time that scientists are sure it is true. We can be certain that, when we look at any animal or plant under a microscope, we will find that it is made up of cells. Cells cannot be seen unless . Nobody saw cells until microscopes7.2. Cytology - the study of cells. Cells are composed of complex living matter called PROTOPLASMI] Cells are the basic structural units of all living organisms. Celis differ in size, shape and struc order to carry out specialised functions. 7.2.4. Characteristics of Living Organisms (Basic Processes of Life) Life on earth is dynamic, with homeostasis maintaining the balance of every level of organisation. [7. REPRODUCTION: roducing of offspring to ensure survival of the species, 2. IRRITABILITY: The response of living organisms to external stimuli to maintain a relatively stable relationship with its environment. 3. METABOLISM: (Nutrition) This refers to all the building up or anabolic processes €.g., assimilation, photosynthesis, and all the breaking down or catabolic processes that occur in living organisms. e.g., digestion and respiration 4. EXCRETION: The getting rid of waste products formed during metabolic processes (urine, C02) 5. MOVEMENT: Usually, animals can move the whole body, whereas | movement in plants is restricted to certain parts. .9., the opening and closing of petals. 6. GROWTH: Associated with life, An anabolic process as a result of ‘nutrition (feeding) etc. Cells either produce their own food or obtain food from elsewhere. 7, RESPIRATION: Acatabolic process that uses glucose and oxygen to | produce energy. 8. DEATH: 7.2.2. Cell Organisation All plants and animals have one characteristic: they are made up of cells. An ORGANELLE is any part of a living cell that has a particular structure and function. A CELL is the basic unit of living organisms. All cells have a specific function and for this reason not all cells are the same, but they are differentiated for a specific function ATTISSUE is a group of cells performing essentially the same function and are of similar structure, e.g.: muscle tissue for movement, bone tissue for support in animals. ‘An ORGAN is a collection of different tissues grouped together for the same ‘special purpose, e.g.: the leaf is an organ for producing food for the plant, the heart is an organ for pumping blood. 4 SYSTEM is an arrangement of organs concerned with the same function/e.g.: the digestive system, the nervous system. 89An ORGANISM Is a living plant or animal, whether unicellular (one celled) or multicellular (many cells) voit cece “ » organism —~———— bone | = 0 = ‘skeletal system ‘bone call ‘bone tissue ASIMPLIFIED DIAGRAM OF AN ANIMAL CELL Seytoplasm 4 endoplasmic reticulum {emooth ER.) 15 endoplasmic reticulum (rough E.R.) ‘11 nucleolus 14 nucleus 902H Lon Microscopic Investigation of the Cell structure A The cell wall - only in plants: Cell wall is - thick and rigid - to give the cell its rigid shape = consists of cellulose (indigestible carbohydrate) - fully permeable - allows any substance to enter and leave the cell = non living TASK 28: Cell Wall Colour code and label the followings diagrams. an abate £e ‘ Secondary cell wall ea) Middle lametia, eran colar Mae ok tgs aes substance ts permeate 8S pengermeable During the development of a new cell wall, a layer called the middle lamella is laid down first. This layer cements the cell walls of adjacent cells, together. The middle lamella may rupture to create intercellular air spaces. The middle lamella is made up of pectin The primary cell wall is then laid down on the inside of the middle lamella. This primary wall is made up of long, tough, cellulose fibres. As the cell grows older all three layers may be filled with lignin (woody substances) for extra strength. The contents of the cell then dies and disintegrates and a hollow space (|umen) is formed, Functions of the Cell wall: - Gives shape, strength, and rigidity to cell, i.e., supports the cell Is fully permeable to most substances. Plasmodesmata allows neighbouring cells to connect and allows transport between cells. i coal oli ee yy membrane {op laerrodegmale Orde cokCell membrane (Plasma lemma) (Plasma membrane) Both plant and animal cells have a cell membrane. Lies under the cell wall in plants. - Outermost layer in animal cells. Can usually change shape. These molecules move around (like balls in water) but the arrangement always AB stays the same. head (hydroptiylic) phospholipid molecule { tall (hydrophobic) Structure of the cell membrane (Fluld Mosaic Model) Functions of the Cell Membrane: The cell membrane keeps the contents of the cell together, i.e. forms a boundary. Controls the exchange of substances that pass into the cell and out of the cell i.e. semi- permeable which means that it only allows certain substances to pass through. This is important in osmosis. Provide a large surface area for chemical reactions. Retains the shape and structure of different organelles Transport of substances: movement across / Key membranes) [] concentration H-high L- low Y - water potential Substances are transported through membranes by three major processes. Diffusion ») amos c) Active transport 2) Diffusion (gas or quia) The mavementof substances (gases o liquid) from an area of Difusion in a cup of tea ation to an area of (Wer Concentration. Example: lungs (alveoli) - gaseous exchange leaf (stomata) - gaseous exchange b) hee molecules only from a region | A RERSAERORMT to a m rion of IW Water pote oc 2 semipermeable membrane Example: kidneys in humans, root hairs in plantsc) _ Active Transport The eniergyrequired for transportof substances from an areaiofilower concentration te an area of higher concentration. H,O and small molecules move through the PORES, but large molecules can't (e.g. sugar). Cells need sugar for energy. Active transport eee to get sugar across. to a protein in the celtmembrane! the sugar across Using/ENERGYS across gellmembranes, from soil water (weak'solution) to cell \wacuolés (contain strong solutions), Plants needwater andc. prep Protoplasm consists of cytoplasm and nucleoplasm. = “CYTOPLASM | Occurs between the cellimembrane | | Occurs within thesmuctoar and nuclear membrane. ‘membrane: ‘The CYTOPLASM includes everything between the eeltamemibfaiie and the nucleus. It of callistructures and is the site;ofmosteeitactivity. Cytoplasm has 2 The cytoplasm may revert from one state to the other, depending on the circulation requirements of the cell r eyclosis is the f the cytoplasm. In some plant cells and protozoans, These cells are large and as suc will not be The cytoplasmic streaming S8AVES to cyclosis, suffici (OVEFEOMIS this problem. The composition of water and 10% dissolved Srganic and Function rcpane She D. TheiNucleus: Functions of the Nucleus - Controls all of the activities of the cell e.g., protein synthesis. - Chromatin network (chromosomes) controls the transmission of hereditary characteristics. Passes genetic information on to the daughter cells when cells divide. 96Mitochondria are Mitochondria rele Stores ATP ehetavearierinels) ae OeHIFoouGuosey —_-.. Eneray(ATP)SEICONEMIOT Mitochondria are more numerous in cells that use a lot of energy e.g. muscle cells and liver cells. The more active the cell the more mitochondria it has. The Mitochondria is structurally adapteditolits function: ~ The:smoothoutenmembrane allows'easymovement of the mitochondria’ through the eytoplasm. ~The folded cristae provide an inerease in surface’area for chemical reactiéns (like cellular respiration). : he ease SaRIATTBOEITE= and otter'chemiieals to control the prowess) of iTEAST Allend in the word ‘plast’ and are found only in plant cells eG gel Chloroplasts) _Chromoplasts Photosynthetic * Red & yellow « »= 7 * Starch-storage organelles colours organelles * Contain green * In cells of ripening * Occur mostly in pigment chlorophyll fruivautumn leaves roots. * Found in cells of = Colourless leaves and stems. - Qvalshaped - Parallel flattenedsacs#hiVlakOidS are stacked in places'toiformgrana - Grana are itergrana = Grana contain the pigmentichlorophyll” - Photosynthesis: Sunlight energy + CO, + H,O - CO¥and O; balances are maintained. cneroRI Oo, + Food (glucose) 98G. Vacuoles Structure Vacuoles are membranous structures filled with fluid. Unlike plastids they are enclosed by a single membrane. A plant cell has a large, centralised vacuole, compared to an animal cell that has smaller vacuoles. In plant cells, the membrane is called a tonoplast, and the fluid is called cell sap. Function Vacuoles in plants have the following functions: - Storage of water and minerals = Provides support (turgidity) for the cell / maintains turgor pressure = May contain pigments that give colour to plants Turgidity and support in plant cells =no pressure on cell wall (wilted) Vacuoles in animal cells have the following functions: VACUOLE CONTENT FUNCTION Lysosome Digestive enzyme (intracellular) Digestion Contractile vacuole Water ‘Osmoregulation Food vacuole Digestive food particles Distribution of nutrients, 100Organelle Function H. Endoplasmic Reticulum (E.R.) A network of membranes located within the cytoplasm. It is continuous with the nucleus and may extend to the cell membrane 2 Transport system - allows substances to move in or out of nucleus and cytoplasm |. Ribosomes Ribosomes are attached to the E.R. to transport the proteins to the Golgi Body. Location -attached to the E.R. tomake rough E.R. ~~ or found in cytoplasm Composition Protein synthesis J. Golgi Body Protein produced by the ribosome arrive at the Golgi Body and are then packaged into vesicles. These substances in the vesicles are either used by the cell or secreted L Made of protein and RNA Secretion of substance i.e., saliva in salivary glands. (The Golgi body in a plant cells called a dictyosome) K. Centrosome Only in animal cells. The centrosome is the area where the centrioles are found. Plays a role in cell division