Organisation of the organism

• Cell types


  • Animal cells
  • Plant cells
• Animal cells


  • Multicellular
  • Contain a nucleus with a distinct membrane
  • Do not have cellulose cell walls
  • Do not contain chloroplasts (so they are unable to carry out photosynthesis)
  • Feed on organic substances made by other living things
  • Often store carbohydrates as glycogen
  • Have nervous coordination
  • Able to move from place to place
• A typical animal cell has the following structures: cell membrane, nucleus, mitochondria, ribosomes, cytoplasm
• Plants


  • They are multicellular
  • Their cells contain a nucleus with a distinct membrane
  • Their cells have cell walls made out of cellulose
  • Their cells contain chloroplasts (so they can carry out photosynthesis)
  • They feed by photosynthesis
  • They store carbohydrates as starch or sucrose
  • They do not have nervous coordination
• Cell structures found in both animal and plant cells

  • Cell membrane
  • Nucleus
  • Cytoplasm
  • Mitochondria
  • Ribosomes
  • Endoplasmic reticulum
  • Golgi apparatus
• Plant cells have additional structures not found in animal cells, such as a cell wall made of cellulose and chloroplasts for photosynthesis
• Nucleus


  Contains the genetic material (DNA) which controls the activities of the cell
• Cytoplasm


  A gel-like substance composed of water and dissolved solutes that supports internal cell structures
• Cell membrane


  Holds the cell together, separating the inside of the cell from the outside; controls which substances can enter and leave the cell
• Ribosomes


  Found in the cytoplasm; site of protein synthesis
• Mitochondria


  Site of most of the reactions involved in aerobic respiration, where energy is released to fuel cellular processes; cells with high rates of metabolism have significantly higher numbers of mitochondria
• Bacteria


  • 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 that floats in the cytoplasm
  • Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes
  • Lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells
  • Some have a flagellum or several flagella that allow them to move
• Bacteria


  • Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk)
  • Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia)
• Mitochondria


  Organelles found throughout the cytoplasm
• Ribosomes


  Tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum
• Rough Endoplasmic Reticulum (R.E.R.)

  Endoplasmic reticulum studded with ribosomes
• Vesicles


  Small circular structures found moving throughout the cytoplasm
• Cell wall


  Made of cellulose (a polymer of glucose); gives the cell extra support, defining its shape
• Chloroplasts


  Contains green chlorophyll pigments (to absorb light energy) and the enzymes needed for photosynthesis
• Permanent vacuole


  Contains cell sap; a solution of sugars and salts dissolved in water; used for storage of certain materials; also helps support the shape of the cell
• Producing new cells


  1. Cells grow and divide over and over again

  2. New cells are produced by the division of existing cells
• Specialised cells in animals

  • 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
• Specialised cells in animals

  • Ciliated cell
  • Nerve cell
  • Red blood cell
  • Sperm cell
  • Egg cell
• Ciliated cell


  Extensions of the cytoplasm at the surface of the cell form hair-like structures called cilia which beat to move mucus and trapped particles up to the throat
• Nerve cell


  Long so that nerves can run to and from different parts of the body to the central nervous system; the axon (extension of cytoplasm away from the cell body) is covered with a fatty sheath, which insulates the nerve cell and speeds up the nerve impulse
• Red blood cell


  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


  The head contains the genetic material for fertilisation in a haploid nucleus; the acrosome in the head contains digestive enzymes so that a 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


  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
• Specialised cells in plants

  • Root hair cell: absorption of water and mineral ions from soil; walls are thin to ensure water moves through quickly
  • Xylem vessel: conduction of water through the plant; support of the plant; no top and bottom walls between xylem vessels, so there is a continuous column of water running through them; their walls become thickened with a substance called lignin which means they are able to help support the plant
  • Palisade mesophyll cell: photosynthesis; column shaped to maximize absorption of sunlight and fit as many in a layer under the upper epidermis of the leaf as possible
• Root hair cell


  • Increases surface area of cell to ensure maximum absorption of water and mineral ions from soil
  • Walls are thin to ensure water moves through quickly
  • No chloroplasts present
• Xylem vessel


  • No top and bottom walls between xylem vessels, so there is a continuous column of water running through them
  • Cells are dead without organelles or 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 mesophyll cell


  • Column shaped to maximize absorption of sunlight and fit as many in a layer under the upper epidermis of the leaf as possible
  • Contains many chloroplasts for maximum photosynthesis
• Levels of organisation in an organism

  • Cells
  • Tissues
  • Organs
  • Organ systems
  • Organism
• Organ systems in plants

  • Shoot system
  • Root system
  • Digestive system
  • Circulatory system
  • Immune system
  • Respiratory system
  • Excretory system
  • Nervous system
  • Reproductive system
• Magnification


  Magnification = Image size ÷ Actual size
• 1 mm = 1000 μm
• 1 cm = 10,000 μm