- all living organisms are made out of cells, which have the same basic features in common. - there are two main types of organism - eukaryotes and prokaryotes . prokaryotic organisms are prokaryotic cells (i.e. they're single celled organisms). eukaryotic organisms are made up of eukaryotic cells. both of these types of cells contain organelles - but eukaryotic cells are more complex than the smaller and simpler prokaryotic cells.
- organelles are parts of cells. each one has a specific function. if you examine a cell through an electron microscope you can see its organelles and the internal structures of most of them.
- eukaryotic cells are generally a bit more complicated than prokaryotic cells and have more organelles. animal, plant, algal and fungal cells are all eukaryotic.
- animal cells contain the following organelles ; cell-surface (plasma) membrane, rough endoplasmic reticulum, nucleolus, nucleus, smooth endoplasmic reticulum, lysosomes, ribosomes, nuclear envelope, golgi apparatus, cytoplasm and mitochondria.
- plant cells have the same organelles as animal cells, but with a few added extras : a cellulose wall with plasmodesmata ('channels' for exchanging substances between adjacent cells), a vacuole (fluid-filled compartment), and chloroplasts (the organelles involved in photosynthesis).
- algae carry out photosynthesis, like plants, but unlike plants they can be unicellular (e.g. chlorella ) or multicellular (e.g. seaweed). - algal cells are a lot like plant cells - they have all the same organelles, including a cellulose cell wall and chloroplasts. however, the chloroplasts in many algal cells are a very different shape and size to plant chloroplasts. for example, some algae have one large chloroplast rather than several smaller chloroplasts.
- fungi can also be multicellular (e.g. mushrooms) or unicellular (e.g. yeast). fungal cells are also a lot like plant cells, but with two key differences : their cell walls are made up of chitin rather than cellulose and they don't have chloroplasts (because they don't photosynthesise).
functions of organelles
i made flash cards on this instead :)
cell function and organelles
- in multicellular eukaryotic organisms, cells become specialised to carry out specific functions. - a cell's structure (i.e. its shape and the organelles it contains) helps it to carry out its function - so depending on what job it does, a specialised cell can look very different than in a regular cell diagram. - in the exam, you might get a question where you need to apply your knowledge of organelles to explain why a specialised cell is particularly suited to its function. you'll need to think about what organelles the cell needs to do its job - e.g. if the cell uses a lot of energy, it'll need lots of mitochondria. if it makes a lot of proteins it'll need a lot of ribosomes.
- epithelial cells in the small intestine are adapted to absorb food efficiently ; the walls of the small intestine have lots of finger-like projections called villi. these increase the surface area for absorption to take place. the epithelial cells on the surface of the villi have folds in their cell surface membranes, called microvilli. microvilli further increase the surface area. they also have lots of mitochondria - to provide energy for the transport of digested food molecules into the cell. - red blood cells are adapted to carry oxygen around the body. they have no nucleus to make room for the oxygen-carrying compound haemoglobin. - sperm cells contain a lot of mitochondria to provide the large amounts of energy they need to propel themselves towards an egg.
- in multicellular eukaryotic organisms, specialised cells are grouped together to form tissues. a tissue is a group of cells working together to perform a particular function. different tissues work together to form organs. different organs make up an organ system. - for example; epithelial cells make up epithelial tissue. epithelial tissue, muscular tissue and glandular tissue (which secretes chemicals) all work together to form the stomach - an organ. the stomach is part of the digestive system - this is an organ system made up of all the organs involved in the digestion and absorption of food (including the small intestine, large intestine and liver).