Cell Structure PDF

Unit 2 - Organisation of the organism 2.1 Cell structure Animal & plant cells Animal cell structure The main features of animal cells: They contain a nucleus with a distinct membrane Cells do not have cellulose cell walls Their cells do not contain chloroplasts (so they are...

Unit 2 - Organisation of the organism 2.1 Cell structure Animal & plant cells Animal cell structure The main features of animal cells: They contain a nucleus with a distinct membrane Cells do not have cellulose cell walls Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis) They contain carbohydrates stored as glycogen Plant cell structure The main features of plant cells: They contain a nucleus with a distinct membrane Cells have cell walls made out of cellulose They contain chloroplasts (so they can carry out photosynthesis) Carbohydrates are stored as starch or sucrose Plant and animal cell structure and function Structure Function Nucleus Contains the DNA (genetic material) which controls the activities of the cell Cytoplasm A gel like substance composed of water and dissolved solutes Supports the internal structures of the cell Site of many chemical reactions  (including anaerobic respiration) Cell membrane Holds the cell together separating the inside of the cell from the outside Controls which substances enter or leave the cell Ribosomes Found in the cytoplasm The site of protein synthesis Mitochondria The site of aerobic respiration Plant cell structure and function Structure Function Cell wall Made of cellulose (a polymer of glucose) Gives the cell extra support, defining its shape Chloroplast Contains the green chlorophyll pigment that absorbs light energy for photosynthesis Permanent vacuole Contains cell sap: a solution of sugar and salt Used for storage of certain materials Helps to support the shape of the  cell Bacteria cells Bacteria cell structure Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics: They are microscopic single-celled organisms Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes Lack a nucleus but contain a circular chromosome of DNA A that floats in the cytoplasm Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move Examples of bacteria include: Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk) Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia) Identifying cell structures & function Within the cytoplasm, the following organelles are visible in almost all cells except prokaryotes when looking at higher magnification (ie using an electron microscope): Mitochondria (singular: mitochondrion) are organelles found throughout the cytoplasm Ribosomes are tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum  Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of Rough Endoplasmic Reticulum (often shortened to R.E.R.) Vesicles can also be seen using a higher magnification - these are small circular structures found moving throughout the cytoplasm 2.2 Organisation of Cells Producing New Cells The cells in your body need to be able to divide to help your body grow and repair itself Cells grow and divide over and over again New cells are produced by the division of existing cells Specialised Cells Specialised cells in animals Specialised cells are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus Cells specialise by undergoing differentiation: this is a process by which cells develop the structure and characteristics needed to be able to carry out their functions Cell Function Adaptations Ciliated cell Movement of mucus in Extensions of the cytoplasm at the surface of the trachea and the cell from hair - like structures called cilia bronchi which beat to move mucus and trapped particles up to the throat Nerve cell Conduction of Long so that nerves can run to and from impulses different parts of the body to the central nervous system The cell has extensions and branches, so that it can communicate with other nerve cells, muscles and glands The axon (extension of cytoplasm away from the cell body) is covered with a fatty stealth, which insulates the nerve cell and speeds up the nerve impulse Red blood cell Transport of oxygen Biconcave disc shape increases surface area for more efficient diffusion of oxygen Contains haemoglobin which joins with oxygen to transport it Contains no nucleus to increase amount of space available for haemoglobin inside cell Sperm cell Reproduction The head contains the genetic material for fertilisation in a haploid nucleus (containing half of the normal number of chromosomes) The acrosome in the head contains digestive enzymes so that sperm can penetrate an egg The mid-piece is packed with mitochondria to release energy needed to swim and fertilise the egg The tail enables the sperm to swim Egg cell (ovum) Reproduction Contains a lot of cytoplasm which has nutrients for the growth of the early embryo Haploid nucleus contains the genetic material for fertilisation Cell membrane changes after fertilisation by a single sperm so that no more sperm can enter Ciliated cell Nerve cell Red blood cell Sperm cell  Sperm cell Examples of specialised cells in plants: Root hair cell Absorption of water Root hair increases surface area of and mineral ions cell to ensure maximum absorption from soil of water and mineral ions Walls are thin to ensure water moves through quickly No chloroplasts present Xylem vessel Conduction of water No top and bottom walls between through the plant; xylem vessels, so there is a support of the plant continuous column of water running through them Cells are dead without organelles of cytoplasm to allow free passage of water Their walls become thickened with a substance called lignin which means they are able to help support the plant Palisade Photosynthesis Column shaped to maximise mesophyll cell absorption of sunlight and fit as many in a layer under the upper epidermis of the leaf as possible Contains many chloroplasts from maximum photosynthesis Root hair cell Xylem structure  Palisade mesophyll cell Levels of Organisation in an Organism Organ system Organs Tissue examples Shoot system Leaf, stem, flower, fruit Epidermis mesophyll Xylem Phloem Root system Root, tuber Xylem Phloem Ground tissue Digestive system Oesophagus, stomach, small Muscle  intestine, large intestine Connective Nerve Epithelial Circulatory system Heart, veins, arteries Muscle Connective Nerve Epithelial Immune system Thymus, spleen Bone marrow Respiratory system Trachea, bronchi, lungs Connective Muscle Epithelial Excretory system liver , kidney, skin, lungs Muscle Connective Epithelial Nerve Nervous system Brain, spinal cord Nerve Reproductive system Ovary, cervix, uterus, vagina, Muscle testes, penis Connective Nervous Erectile 2.3 Magnification formula Calculating magnification and specimen size using millimetres as units Magnification is calculated using the following equation: Magnification = Image size ÷ Actual size A better way to remember the equation is using an equation triangle: Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle - whatever you are trying to find, place your finger over it and whatever is left is what you do, so: Magnification = image size / actual size Actual size = image size / magnification  Image size = magnification x actual size Remember magnification does not have any units and is just written as ‘x 10’ or ‘x 5000’ To find the actual size of the cell: 2.4 Converting between units (extended) Using millimetres and micrometres as units The table below shows how millimetres are related to two other measures of length What this basically means is that 1mm = 1000µm and 1cm = 10,000µm This usually comes up in questions where you have two different units and you need to ensure that you convert them both into the same unit before proceeding with the calculation For example: