the nature and variety of organisms

• nutrition: to provide living organisms with energy and the raw materials for growth and repair. Nutrients like proteins, fats, carbohydrates, vitamins and minerals.
• respiration: organisms release energy from their food by a process called respiration
• excretion: waste products such as carbon dioxide and urine have to be removed
• Sensitivity: organisms can react to changes in their surroundings
• Movement: organisms move towards things like water and food and away from things like predators and poisons. even plants can move a bit.
• Control: they can control their internal conditions - temperature and water content
• reproduction: organisms have to produce offspring (children) in order for their species to survive
• growth: grow and develop into their full adult form
• cells can be eukaryotic or prokaryotic. eukaryotic cells are complex and includes all animal and plant cells. prokaryotic cells are smaller and simpler (like bacteria)
• organelles are tiny structures within cells, you can only see them using a microscope
• The nucleus is an organelle which contains the genetic material that controls the cell's activities and is surrounded by its own membrane.
• The cell membrane forms the outer surface of the cell and controls the substances that go in and out.
• Cytoplasm is a gel-like substance where most of the cell's chemical reactions happen and contains enzymes which control these reactions.
• Mitochondria are small organelles where most of the reactions for aerobic respiration take place, a process that transfers energy that the cell needs to work.
• Ribosomes are small organelles where proteins are made in the cell.
• plant cells usually have all the organelles that animal cells have and a few extra:

  1. chloroplasts: contains a green substance called chlorophyll that absorbs sunlight to help make food during photosynthesis
  2. cell wall: a rigid structure made of cellulose, which surrounds the cell membrane. it supports and strengthens the cell
  3. vacuole: a large organelle that contains cell sap (a weak solution of sugars and salts) and helps support the cell
• a tissue is a group of similar cells that work together to carry out a particular function

  example: plants have xylem tissue (for transporting water and mineral salts) and phloem tissue (for transporting sucrose and amino acids)

  • a tissue can contain more than one cell type
• tissues are organised into organs

  • an organ is a group of different tissues that work together to perform a function
  • lungs in mammals and leaves on plants are two examples of organs since they're both made up of several different tissue types
• organs make up organ systems

  1. organs work together to form organ systems.
  2. for example, in mammals, the digestive system is made up of organs including the stomach, intestines, pancreas and liver.
• plants, animal and fungi are eukaryotic organisms
• plants

  • multicellular
  • have chloroplasts which means they can photosynthesise
  • their cells have cell walls made of cellulose
  • plants store carbohydrates as sucrose or starch
  • examples: flowering plants like cereals (maize), herbaceous legumes (peas and beans)
• animals

  • animals are multicellular
  • no chloroplasts and cannot photosynthesis
  • no cell walls
  • most have some kind of nervous coordination = respond rapidly to changes in their environment
  • can usually move around from one place to another
  • store carbohydrate in the form of glycogen
  • example: mammals (humans), insects (houseflies and mosquitoes)
• fungi

  • some are single celled
  • others have a body called mycelium which is made up of hyphae (thread-like structures). the hyphae contains a lot of nuclei
  • they can't photosynthesise
  • cell walls made of chitin
  • most feed by saprotropic nutrition - they secrete extracellular enzymes into the area outside their body to dissolve their food so they can then absorb the nutrients
  • stores carbohydrates as glycogen
  • examples: yeast (single celled fungus), mucor (multicellular and has a mycelium and a hyphae)
• protoctists are eukaryotic organisms.
• protoctists

  • single-celled and microscopic (really tiny)
  • some have chloroplasts and are similar to plant cells
  • others are more like animal cells
  • examples: chlorella (plant-cell like), amoeba (animal-cell like) - lives in pond water
• bacteria

  • single-celled and microscopic
  • no nucleus
  • circular chromosome of dna
  • some can photosynthesise
  • most bacteria feed off other organisms - both living and dead
  • example: lactobacillus bulgaricus - can be used to make milk go sour and turn yoghurt. (rod shaped), pneumococcus - spherical in shape
• viruses

  • particles rather than cells
  • smaller than bacteria
  • only reproduces inside living cells.
  • like a parasite - depends on another organism to grow and reproduce
  • they infect all types of living organisms
  • they come in loads of different shapes and sizes
  • they don't have a cellular structure - they have a protein coat around some genetic material (DNA or rna)
  • example: influenza, tobacco mosiac virus, hiv