The wonderful world of cells!A fascinating insight into the world ofcells, who discovered them, thedifferent types and what they aremade up of.
Microscopes Light microscope Electron microscopeUses light rays Uses electron ‘beams’Magnification – x2000 Magnification – x500,000Resolving power – 200nm Resolving power – 1nmFocused by glass lenses Focused by electromagnetsSpecimens can be living or Specimens must be deaddeadSmall, portable and Large, static and veryrelatively inexpensive expensive
Microscopes Magnification – to make an image appear bigger To calculate the magnifying power of a microscope:eye piece lens magnification X objective lens Resolution – the minimum distance between 2 points at which they are still visible as 2 separate points
Robert HookeHe looked at corkcells under amicroscope andused the term‘cell’. The holesthat he observedwhere once filledwith living material(cytoplasm)
Robert Hooke’s cells
Cell theory with the cellSchwann and Schleiden came up theory.They proposed that all plants and animals were made up of cells and that cells were the basic units of lifeAnother scientist, Rudolf Virchow discovered that new cells can only arise from the division of pre-existing ones.
Prokaryotic and Eukaryotic cells No true nucleus Distinct nucleus Few organelles except for surrounded by a nuclear envelope small ribosomes Many membrane bound Single strand of genetic organelles material free in the cell Genetic material is stored Simple structure in the nucleus Small in size Highly organized to carry Include bacteria and out complex functions blue/green algae Large in size Include plants, animals and fungi
Animal cells: these are cheek cells asseen with a compound microscope,compare these cells to the next onesseen through an electron microscope.
Plant and animal cells Cellulose cell wall No cell wall Chloroplasts No chloroplasts Large permanent Small, temporary vacuole with cell sap vacuoles No centrioles Centrioles present Starch grains for Glycogen granules storage for storage
Cytoplasm Watery, jelly-like material Contains many substances for metabolism The other organelles are suspended in it
Cellulose cell wall Many cellulose fibers glued together Strong to resist expansion of the cell as water enters – this supports the cell Provides mechanical strength to the cell Freely permeable
Vacuole Large permanent vacuole in plant cells is called a central vacuole. It contains cell sap, a solution of sugar and minerals. They are food stores They accumulate waste products Some contain pigments to give color Vacuoles in animal cells are small and temporary
Nucleus Largest cell organelle Surrounded by a double membrane that allows materials to pass in and out Contains genetic material (DNA) which is used to make proteins Controls the metabolic activity of the cell
Nucleolus Found in the nucleus Dense, spherical structure Contains RNA for the production of ribosomes
Ribosomes Small, dense organelles Can be free in the cytoplasm or attached to rough endoplasmic reticulum They are made in the nucleolus They are the site of protein synthesis
Endoplasmic reticulum Complex system of double membranes with fluid-filled sacs in between called cisternae Connected with the nuclear membrane and the cell membrane It collects, stores and distributes materials Rough endoplasmic reticulum has ribosomes on it. It packages and transports proteins made by ribosomes Smooth endoplasmic reticulum is the site of lipid (fat) synthesis.
Golgi complex Also known as golgi body or apparatus Made from small pieces of rough ER pinched off at the end to form vesicles which fuse together Site of protein modification Vesicles pinch off at the ends to carry the new chemicals away (some vesicles become lysosomes)
Lysosomes Small vesicles formed when pieces of the golgi body pinch off Contain hydrolytic enzymes that can digest cell material They destroy worn out organelles They can destroy material brought into the cell (e.g. bacteria) They can release enzymes out of the cell to digest other cells They can cause the cell to self destruct
Mitochondria Has a double membrane. The outer one controls entry of materials and the inner one has many folds called cristae Has a matrix containing DNA, ribosomes and enzymes Site of aerobic respiration The more active the cell, the more mitochondria it has
Chloroplasts Found in plants cells that carry out photosynthesis They are the site of photosynthesis They have a double membrane filled with fluid (stroma) where the photosynthesis reactions take place The stroma contains piles of flattened scas (grana) where chlorophyll is found and light is absorbed
Cytoskeleton This is a network of fibrous proteins It allows movement and gives the cell shape and support It is made up of microtubules and microfilaments
Centrioles These are 2 short bundles of microtubules positioned at right angles to each other. They are found just outside the nucleus in animal cells During cell division, they move to opposite ends of the cell and produce the spindle
Flagella Also made up of microtubules Often used to help cells move (e.g. sperm)
Cell membrane Made up of a bilayer of phospholipids that allows some materials through but not others (semi-permeable) Contains proteins that can act as pores, carriers or be involved in cell recognition The main function is to regulate the movement of molecules and ions
Cell membrane structure Made up of a bilayer of phospholipids. They have a polar end (water liking) and a non-polar end (water hating) Protein carrier molecules are found embedded in the cell membrane; these molecules form specific bridges allowing specific molecules to pass through
Transport across membranes The cell membrane is thin and provides a large surface area for diffusion to occur Diffusion is the movement of molecules or ions from a region of high concentration to a region of low concentration until they are spread out evenly (down a concentration gradient) A big difference in concentration, an increase in temperature, small molecules and a short diffusion distance makes the rate of diffusion faster
Facilitated diffusion This allows faster movement It involves the use of proteins to assist (facilitate) diffusion Specific channel proteins form pores for specific molecules Carrier molecules bind to specific molecules, change shape and deliver the molecule to the other side of the membrane
Osmosis This is the diffusion of water molecules They move from where they are in a high concentration (a dilute solution) to where they are in a low concentration (a concentrated solution)
Osmosis in plant cells As water enters a plant cell, the cell starts to swell. The cell wall starts to resist the stretching which creates pressure When no more water can enter the cell, it is said to be TURGID. This provides strength and support to the cell If water leaves a cell, the membrane can pull away from the cell wall. This causes a plant to wilt
Different solutions Solution – a mixture of 2 or more substances Solvent – the liquid that a substance dissolves in Solute – the substance that dissolves in a solvent Hypotonic – a weak solution: weaker in solute concentration than cell Hypertonic – a strong solution: stronger in solute concentration than cell Isotonic – a solution with the same concentration as cell.
Active transport Moving molecules against a concentration gradient (from low to high concentration) It requires special carrier proteins called membrane pumps It uses energy in the form of ATP
Endocytosis and exocytosis For molecules too large to pass through the membrane Endocytosis – taking materials into the cell by closing the cell membrane around it to form a vesicle (There are 2 types, pincytosis and phagocytosis) Exocytosis – material in vesicles in the cell fuse with the cell membrane and are released