hello and welcome to another complete Cambridge IGCSE biology lesson where you'll learn absolutely everything you need to know on topic 2.1 cell structure as always we'll be following the Cambridge syllabus exactly and we'll cover absolutely everything you need to know for your final exam the topic 2.1 you need to be able to describe the term cell tissue organ organ system and organism understand how new cells are produced describe the structure of a plant cell animal cell and bacterial cell and describe the functions of these structures and state the specific functions of certain specialized cells by taking an extremely thin section of plant or animal tissue applying a dial stain and viewing it under the microscope thousands of tiny box-like structures can be seen these are cells the building blocks of living things in plants and animals cells are extremely numerous for example it's estimated that humans have up to 40 trillion of them this means that any one cell on its own has essentially no impact on the functioning of the organism which is why cells are grouped and work together in vast numbers tissues are groups of cells with similar structures that work together to perform a shared function for example one kind of muscle cell forms a sheet of muscle tissue which is capable of Contracting while epithelial cells form an epithelium which is a thin layer that lines the surfaces of the body like the inside of the mouth windpipe and intestines organs are structures made up of groups of tissues that work together to perform a specific function for example the small intestine is a digestive organ that contains tissues made from gland cells muscle cells nerve cells and epithelial cells further examples of organs include the lungs and brain and animals and the root stem and leaves in plants next organ systems are groups of organs with related functions that work together to perform a specific body function for example the heart and blood vessels make up the circulatory system the brain spinal cord and nerves make up the nervous system and implants the stem leaves and reproductive parts make up the shoot system which will return to in chapter 8. finally an organism is a complete living thing made up of multiple organ systems or organisms can survive independently and exhibit the properties of Life Next you need to be able to describe the structure of animal cells and plant cells and the functions of these structures we'll begin with the structures that are common to both types of cells the cytoplasm is a jelly-like substance containing nutrient particles and organelles which are the components of cells that perform specific roles it's the site of chemical reactions and is enclosed by a cell membrane the cell membrane is a partially permeable layer that holds the contents of the cell in place and controls the movement of substances both into and out of the cell the nucleus contains most of the cell's genetic material in the form of DNA which is organized into structures called chromosomes the nucleus essentially controls the cell's activities which include cell development and division mitochondria are circular or oval-shaped organelles that release energy from nutrients like glucose via aerobic respiration and don't worry we'll return to respiration in chapter 12. ribosomes are small circular structure that are either attached to a membrane or found free within the cytoplasm they're responsible for protein synthesis or the production of new proteins now onto the features that make plant cells unique from animal cells plant cells have a cell wall which is a tough layer made of cellulose surrounding the cell membrane they prevent cells from bursting and allows water and salts to pass through freely chloroplasts contain chlorophyll which is a green pigment that plays a crucial role in photosynthesis or the conversion of light into energy finally a vacuole is a fluid-filled space surrounded by a membrane it contains cell sap a watery solution of sugars and salts and helps to give cells firmness and structure by pushing outwards against the cytoplasm and cell wall in addition to plant and animal cells you also need to know about bacterial cells so bacteria are single-celled organisms and like plants and animal cells they have a cytoplasm cell membrane and ribosomes they're also surrounded by a cell wall but unlike plants this wall is not made of cellulose bacterial cell cells have no nucleus instead each cell contains a single chromosome made of a coiled strand of DNA they also contain plasmids which are small circular structures that are also made of DNA they carry additional genetic information that helps the bacterium to survive and reproduce next you need to know a little bit about how new cells are produced although this will be covered in Greater detail in chapter 17. the process by which new cells are produced is known as mitosis or cell division and is controlled by the nucleus first the chromosomes are replicated and then the nucleus divides of the two cells that are formed one may keep the ability to divide while the other may become a specialized cell with a specific shape and function now multicellular organisms possess a wide variety of specialized cells and there are six specialized animal and plant cells that you need to know ciliated cells line the structures of the respiratory system and are covered with tiny hair-like filaments called cilia these cilia are covered with mucus which traps dust and bacteria and are capable of moving to create a continuous flow of mucus away from the lungs neurons or nerve cells are specialized to deliver information throughout the body in the form of electrical impulses these cells are often very long as they connect distant parts of the body like the feet to the brain and spinal cord next red blood cells are responsible for transporting oxygen to the body's tissues they contain a protein called hemoglobin which binds to oxygen forming oxyhemoglobin they also have a specialized shape called a biconcave disc that maximizes their surface area and allows gases to be absorbed more easily sperm and egg cells otherwise known as gametes are the sex cells whose sole purpose is reproduction sperm cells are composed of three sections the head has a nucleus which contains the cell's DNA and an acrosome that secretes enzymes that help the sperm cell penetrate the egg the midsection is densely packed with mitochondria to provide energy for movement and the tail allows the sperm cell to swim egg cells have a nuclear cell membrane and jelly coat as well as a large cytoplasm that can contains yolk droplets made of proteins and fats these droplets provide nutrition during the early stages of development following conception root hair cells in plants are specialized to absorb water and minerals from the soil the hair-like projection on each cell penetrates between the soil particles and provides a large surface area for absorption in addition the cell membrane is able to selectively control which substances enter the cell finally Palisade mesophyll cells are found just under the surface or upper epidermis of plant leaves and are densely packed with chloroplasts their role is to convert light energy into glucose via photosynthesis well done you've just covered absolutely everything you need to know on topic 2.1 cell structure if you enjoyed this video I'd really appreciate your subscription and I'll see you next time for topic 2.2 size of specimens