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Revision notes on cells, life processes and living organisms CHARACTERISTICS OF LIVING ORGANISMS 1.1 recall that living organisms share the following basic characteristics Movement Muscles in animals, directional growth in plants, flagella in bacteria Respiration Release energy from food Sensitivity Responding to changes in the environment Growth Increase in size and mass Reproduction Producing offspring (more of the same kind of organism) Excretion Getting rid of toxic waste Nutrition Taking in or producing their own food Control of internal conditions Keeping internal conditions constant, e.g body temperature VARIETY OF LIVING ORGANISMS 1.2 Describe common features shared by organisms within the groups: plants, animals, fungi, bacteria, protoctists and viruses, and describe examples and their features in each group Plants Plants are multicellular organisms Examples include flowering plants, such as a cereal (for example maize) and a herbaceous legume (for example peas or beans). Plants contain chloroplasts and are able to carry out photosynthesis Plants have cellulose cell walls. The cell wall and the vacuole together give the cell its shape and maintain turgor (stiffness) to support the plant (see point 2.14) Plants store carbohydrates as starch or sucrose. Starch is stored in the leaf and the root; sucrose is transported in the phloem (see point 2.51) Animals Animals are multicellular organisms Examples include mammals (e.g. humans) and insects (e.g. housefly and mosquito). Mammals keep a constant body temperature and are vertebrates (have a backbone) Insects are invertebrates Animals do not contain chloroplasts and are not able to carry out photosynthesis: animals are heterotrophic – they consume other organisms for their nutrition Animals usually have nervous coordination and are able to move from one place to another Animals have no cell walls and they often store carbohydrate as glycogen Revision notes on cells, life processes and living organisms Fungi Fungi are not able to carry out photosynthesis; many are multicellular; some, like yeast, are single-celled. Their body is usually organised into a mycelium of thread-like structures called hyphae, which contain many nuclei; the hyphae feed by excreting digestive enzymes onto food material and absorbing the organic products; this is known as saprotrophic nutrition Fungi have cell walls made of chitin; they may store carbohydrate as glycogen. Examples include mucor (green-blue mould) which reproduces using spores, and yeast, used to make bread or beer. Bacteria Bacteria are microscopic single-celled organisms with no nucleus (are prokaryotes). Examples: Lactobacillus bulgaricus, a rod-shaped bacterium used to make yoghurt from milk, and Pneumococcus, a spherical bacterium that causes pneumonia. Bacteria have a cell wall, cell membrane, cytoplasm and plasmids (rings of extra DNA: see points 5.12, 5.13). Bacteria DNA is in a large loop called the chromosome. Most bacteria feed off other living or dead organisms (saprotrophic nutrition). A few bacteria can carry out photosynthesis. Protoctists Protoctists are microscopic single-celled organisms. They are complex cells with a nucleus and other organelles. They are not animals or plants because each cell is an individual organism, not part of a multicellular organism. Some protoctists, like Amoeba, have features like an animal cell. Others, like Chlorella, have chloroplasts and are more like plants. A pathogenic protoctist, Plasmodium, is responsible for causing malaria (see point 1.30) Viruses Viruses are small particles, smaller than bacteria; they are parasites and can reproduce only inside living cells; they infect every type of living organism. Examples include the tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes Revision notes on cells, life processes and living organisms ‘flu’ and the HIV virus that causes AIDS (see point 1.30). 1.3 Viruses have a variety of shapes and sizes; they have no cellular structure but have a protein coat and contain genetic material - either DNA or RNA. Apart from reproduction, viruses do not perform any of the life processes (MRSGRENC) Recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or viruses. Pathogen: an organism that causes disese like a virus, fungus or bacterium. Viruses are responsible for AIDS and 'flu; bacteria can cause pneumonia; malaria is caused by a protoctist; Athlete's foot (Fusspilz) is a fungal infection (see point 1.2) NB white blood cells provide defence against pathogens: phagocytes are non-specific, lymphocytes are specific (see point 2.61) SECTION 2: STRUCTURES AND FUNCTIONS IN LIVING ORGANISMS A) LEVELS OF ORGANISATION 2.1 Describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems. ORGANISM < ORGAN SYSTEM < ORGAN < TISSUE < CELL < ORGANELLE < BIOLOGICAL MOLECULE Biological molecule – molecule made by organisms and used in life processes, e.g. respiration Examples: DNA, proteins, lipids, starch, glucose, amino acids, haemoglobin, enzymes Organelles - structures within a cell that carry out specific functions Examples: nucleus, chloroplast, mitochondria (see point 2.20, 2.30) Cells - the basic structural and functional unit from which all biological organisms are made Examples of specialized cells include nerve cells, sperm cells, root hair cells and palisade mesophyll cells Tissues - a group of specialized cells, which are adapted to carry out a specific function Examples include muscle tissue, nerve tissue, palisade mesophyll tissue (in leaves) Organs - a collection of two or more tissues, which carries out a specific function or functions Examples include the heart, brain, spinal cord, liver, kidneys, lungs, bladder, small intestine, pancreas and stomach; in a plant the leaf is an example of an organ. Organ Systems - a group of two or more Examples include the circulatory system, nervous system, endocrine system and digestive organs system. Revision notes on cells, life processes and living organisms B) CELL STRUCTURE 2.2 Recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole 2.3 Describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole 2.4 Nucleus structure: at the centre of the animal cell and between the vacuole and cell membrane in a plant cell. Contains DNA Nucleus function: Controls cell activities Cell membrane structure: selectively permeable boundary of the cell Cell membrane function: Controls what substances go in and out of cell Cytoplasm structure: a jelly-like substance that fills the cell and contains enzymes Cytoplasm function: site of most of the chemical reactions in the cell. Chloroplast structure: contain a green pigment called chlorophyll. (Only plant cells) Chloroplast function: Absorb light energy to make (food)glucose by photosynthesis Cell wall structure: made of cellulose or chitin which surrounds the cell membrane (Only plant cells) Cell wall function: rigid structure that gives the cell support and strengthens it. Vacuole structure: largest part of plant cell, in the centre; contains cell sap, a store of dissolved sugars and minerals. (Only in plants) Vacuole function: fills with water and maintains turgor to support the plant Describe the differences between plant and animal cells. Both contain a nucleus, cytoplasm and a cell membrane Animal cells do not have a cell wall, central vacuole or chloroplasts (see point 2.30)